So, welcome back. Today I would be talking on this microsystems fabrication by advanced manufacturing processes in the section that I would be dealing today is what is silicon and how do you process silicon using advanced manufacturing techniques. So, let us look at some of these amenable materials, sorry review of the previous lecture briefly. So, in the previous lecture we really tried to get a historical perspective of machining and this was followed by the description of some of the conventional and non-traditional domains of manufacturing wherein you know the machining processes or metal cutting processes, machining processes were classified as metal cutting processes or mechanical abrasion processes on one hand and the non-traditional or the non-conventional machining processes were classified on the basis of material removal mechanisms based on either mechanical removal, thermal removal or chemical electrochemical removal on another hand. And we also saw that the course's basic intention is a synergism between the microsystems technology and the way to fabricated and the advanced manufacturing processes and the integration between the two. So, let us now see of some of the materials which are very amenable to the use you know in developing in to their use of developing microsystems. So, silicon of course is one of the principle materials which are used for microsystem fabrication because as I mentioned earlier that the traditional processes really are the sorry the non-traditional processes on silicon are nothing but borrowed from the micro-electronic industry and therefore being a micro-electronic material the fallout processes which really comprise of MEMS processes are amenable to fabrication of silicon. Then of course quartz and glass because in most of the cases of microsystems you sometime need optical transparency and therefore glasses and quartz are the next line of materials amenable to the you know or can be classified as MEMS materials or microsystems materials. Then another whole lot of class of materials which are nowadays increasingly used for microsystems fabrication of polymers and then polymers particularly in this PDMS or polydiamethylsiloxane which is considered to be a very very bio-friendly material is most used particularly in biomedical MEMS or biomedical micro devices and then of course PMMA polymethyl methacrylate which is also an e-beam resist and it is used increasingly for e-beam lithography and other applications. Then this material of Teflon where Teflon is actually a commercial name of a material available from Dupont and this Teflon is a very very hydrophobic and it has excellent applications again in the biological world and so therefore Teflon is another very amenable material MEMS material which is used mostly for fabrication of microsystems and then of course there is this whole new domain of microsystems which is using biological entities like cells, proteins or DNA and these are also some of the very very frontier research areas in the bio MEMS as to how to micromanipulate or nano manipulate sometimes the biological entities for fabrication or advanced manufacturing of MEMS at this particular scale. So, let us begin with silicon so silicon of course is the most popular MEMS material obtained so far and silicon and its compounds a variety of compounds like oxides, nitrides, polysilicon etc. can be very amenably used for microsystems fabrication and not only that you can categorize these whole class of materials based on the amount of you know their range of order into crystalline polycrystalline or amorphous materials where the definition of these terms are kind of parallel to whatever you know conventional definitions are single crystalline means that there is one particular kind of crystal with the reputation of unit cells and there is no break of this crystal whatsoever. Polycrystalline is that the crystal growth takes place at several centers and it formulates into grains of different crystals with grain boundaries in between and amorphous is where the range of order is rather longer where the shorter where there is no orderliness at all and it is very randomly deposited and so these class of silicon oxide, nitride and silicon as such or polysilicon can be categorized into these various forms and domains. So, material like silicon dioxide for example are amorphous which means that did not possess any long range order. So, that is what is basically the categorization of silicon and let us look or delve into a little bit of crystallography and crystal structures when we talk about especially single crystalline silicon crystals are described by their most basic structural element the unit cells as most of us know and it is a regular array of such units repeated in three dimensions in a very regular manner which comprises of a crystal and the unit cell of interest have it is a cubic symmetry and each edge of this unit cell has the same length. So, you can divide these into different classes of crystals like simple cubic where you can see there are about 8 atoms on the 8 corners of this particular cube body centered cubic where you have atoms on the corners as well as one in the center of the whole cubic lattice and this is what one unit cell would comprise of a look like and a deputation of all these unit cells in the three dimensions would typically result in what you call a single crystalline material and then you have face centered where these faces also has some atoms apart from the corners and there is no atom in the center of this particular unit cell. So, these are some of the classifications of how cubic crystals can be divided as and just to reiterate or just to you know memorize some of the fundamentals which you probably may have obtained earlier these the crystals are really represented by directions and they are identified using Cartesian coordinate system and the square bracket here as you are seeing is indicative of the direction in which so the crystal would grow you know so it is the direction of growth of the particular crystal. So, if I say that it is a 1 0 0 growth that means it is growing the crystal is growing in the x direction if it is 0 1 0 it is growing in the y direction similarly it is a 0 0 1 it is growing in the z direction and not only that if you know you can change the planes if the growth is along a certain plane then it can be a 1 1 0 or it can be let us say you know 1 0 1 or a 0 1 1 which corresponds to different planes of the growth and then there can be a very interesting growth along the 1 1 1 direction which means that it is something like a triangle here as you can see. So, the 1 1 1 direction typically is perpendicular to this particular triangle so the direction of growth is perpendicular to this particular direction. So, whatever it is the directions are represented by these square brackets and it is a sort of sign convention to do that and you know if you want to represent the plane a particular plane that is perpendicular to the vector square bracket x y z you represent that by this round bracket x y z which comprises of the plane of which x y z was a direction of. So, this is the plane ground bracket and this is the direction square bracket and then of course a set of such planes are represented by these third bracket and the set of planes would be meaning all planes of type round bracket x y z represented by the third bracket x y z. So, that is a sort of nomenclature which you use for you know systems or for identifying silicon as such. So, let us now look into a little bit different aspect of how you can actually make single crystalline silicon and in context of that the most important method that is illustrated in literature very often is this Zock-Ralke's growth method in which silicon can be obtained from polycrystalline silicon and 99.99 percent pure polycrystalline silicon which is fused and this fused this fusion process is by thermal means there is a crucible which is indicated here in this figure which comprises of a central cavity and this cavity as I am illustrating by this border here contains the silicon material the silicon material the polycrystalline silicon fused material and this crucible so called is basically capable of rotation. So, you can rotate the whole crucible and also it is inertly filled. So, the chamber here is evacuated using pumping mechanisms as illustrated here and here and then you can fill the whole environment or atmosphere of this fused silicon container with argon or an inert gas. So, that it ensures the non inclusion of material like oxygen or nitrogen into the silicon lattice. So, it is extremely pure process and there are certain foundries in the world like one example is Mem-C which is based in St. Louis Missouri which actually manufactures some of these silicon wafers high purity single crystalline silicon wafers. So, the way the processing goes is that when this crucible is rotated and then there is something called a seed crystal which has been obtained from an earlier process and the seed can be probably a very small crystal of certain direction or grown in a certain direction let us say the 1 0 0 direction. So, the seed has been grown from an earlier process it is a pure crystal and the seed is inserted into this melt somewhere here as can be illustrated and as illustrated here. And so therefore, the rotation the relative rotation between the seed and the crucible and you know can be varied by varying the relative rpm and what is important here is that as the seed goes and dips into the material and the seed is slowly pulled out it tries to drag along with it a part of the silicon melt and the moment the silicon melt comes out into the open atmosphere it is no longer you know a part of the crucible and therefore, it can as well solidify. So, only advantage here is that the solidification the rates of this pulling can be balanced with the rate at which the relative rotation happens between the crucible and the seed and many other parameters are in a control manner. So, the rate at which the solidification front sort of cools off you know you can really tailor it or fine tailor it in a manner. So, that the growth takes place in the same direction as the direction of the seed crystal. So, this is the Zockeralki's crucible process. So, the seed is the mother crystal which would eventually result in formulation of a bowl of material as can be indicated by this outline that I am drawing here and this all material in this bowl is grown in the direction of the seed crystal and the parent direction is kind of grown into this particular bowl. So, once this bowl is extracted you can actually cut this bowl into pieces and you can fine polish them and there are a lot of methodologies like CNC wire cut EDM or some other instruments which are used for fine sizing or maybe even band saw which are used for fine sizing these wafers typically these wafers can vary between 400 microns thickness to about 900 microns thickness. So, some other an integrity of this process is that the chamber is actually filled with you know it is back filled with inert gas and the crucible is heated up till 1500 degree Celsius and the seed crystal is really small chemically etched crystal and lowered into the contact with the melt. So, that the melt can grow in that direction it has to be carefully oriented because this sort of serves as a template for growth of the much larger crystals later on. So, that is how the Zocrelki's growth method or growth process is actually executed. Now, let us do some mathematical modeling for this process which can give us an idea of how you know the liquid to solid conversion can take place in terms of latent heat of solidification and we can just do a simple one dimensional heat flow analogy to understand the situations. Let us say you have a crucible here in this particular example and we are considering this particular zone here as you can see which is also called the zone of fusion. The zone of fusion because sort of you know this is the zone where there is a presence of both the states the liquid state which is into the crucible and then the solid state which is a part of the seed which is getting withdrawn and so it is a sort of semi solid semi liquid kind of zone that we are considering. So, if we apply the Fourier's law of heat conduction. So, q dot x or the rate of flow of heat as a function of x or in the direction of x is really proportional to the interfacial area across which the heat is flowing. So, the interfacial area in this case can be thought of as going into the plane of this slide. So, this is the area across which the heat is flowing. So, this is also known as the heat phase and then it is also proportional to the temperature gradient which exists in the material in the direction of flow of heat. So, in this case for example, if the temperature here is T 1 the temperature here is T 2. So, temperature here is T 1 temperature here is T 2 and of course, in this particular case T 2 is more than T 1 which enables the heat to flow from the direction of T 2 to T 1. So, let us say in this particular zone of fusion that is in question we have a temperature T 1 which is actually higher than T 2 in this particular case which is that of the liquid part of the zone of fusion. So, the temperature of the liquid part is T 1 and the temperature of the solid part of the withdrawn seed and the bowel formulated on the seed is a template is basically T 2 as illustrated here and T 1 of course is greater than T 2 which enables the direction of heat flow in the positive y direction as you can see here. So, the heat flows from T 1 towards T 2 and we need to just investigate how the rate of heat flow here into the zone of fusion from the liquid side and the rate of flow out of the zone of fusion to the solid side would be balanced with each other and this heat loss which is happening is also a cause of the formation of the solid which means that in a solid state as you know the bond energy is always higher and therefore, there is a heat of formation of the solid which is lost it is called the latent heat of formation of the solid. So, the difference between the rate of heat flow into the zone of fusion and out of the zone of fusion is really the quantity of heat which is lost in formulating the solid from the liquid state. So, if you model it in that manner let us say for example, if we assume completely one dimensional heat flow in this particular case we can write the heat equation as minus k l a d t by d x in the liquid side the minus shows that the heat is always from the higher you know the towards the lower temperature from the higher temperature side which is also defined by the law of thermodynamics. So, k l is the conductivity the thermal conductivity of the liquid melt a is of course, the interfacial area of the zone of fusion and d t by d x is the temperature gradient available across that interface between the liquid on to the crucible and the zone of fusion and of course, this heat goes into the zone and the heat which is lost from the zone of fusion into the solid can be defined as minus of minus k a where k s sorry where k s is basically the thermal conductivity of the solid material times of interfacial area between the zone of fusion and the solid a we assume the area to be same in both the cases for simplicity of the model here times of d t by d x temperature gradient in the solid while the heat flows from the zone of fusion into the solid. So, that is the difference of heat flow into the zone of fusion and outside the zone of fusion and this net heat loss here is somewhere recorded as the solid formation at or the you know the heat of formation of the particular solid. So, if you assume that the rate at which the solid material gets formulated is d m by d t as you can see in this particular illustration here and l being the latent heat of formation which is in terms of how much mass per kg how much heat is the lost in order to formulate the solid. So, l d m by d t is really nothing but the amount of heat the rate of heat or the rate of heat loss in terms of formation of the solid bonds rate of heat loss can be equated in terms of heat going per unit time into the zone of fusion minus heat going away from the zone of fusion per unit time. So, you can really equate both these equations and that formulates a basis of the Zock-Ralke's growth process because you know heat flowing in here represented by the first term heat flowing out here represented by the second term and in between whatever is happening in resulting in this formation of the solid phase the l d m by d t. So, that is really what this Zock-Ralke's process is about d t by d x of course is the thermal gradient in the x direction from the either from liquid to the zone solid zone of fusion or from the zone of fusion to the solid and k l and k s are respectively the thermal conductivities of the liquid state and the solid state of the silicon. So, let us refine this equation a little more by assuming that you have draw as the density of the solid in this particular case and of course, a the area of the zone of fusion defined by a constant a is the interfacial area and if we assume that d x length of solid material is formulated because of this heat transfer process. So, d m really the differential amount of mass is nothing but density times of the volume a d x which is created by virtue of pull out from the zone of fusion into the solid state. So, if we equate the new term obtained for d m into the earlier equation we have l times of rho times of a times of d x by d t which is nothing but the pull rate the pull rate of the seed crystal in terms of the rate of displacement of the seed with respect to the crucible. So, this is the pull rate.  So, therefore, that is why the equation is change sign. So, if we were to assume that our pull rate is maximum for the purpose of high yield production we should have a situation where this negative component should go to 0. So, therefore typically whatever is coming as heat into the zone of fusion is really the amount of heat going away from the heat of fusion zone of fusion. So, that is typically a case in one dimensional heat transfer. So, this whole equation is a maximum on the left side only if this liquid heat transfer from liquid into the zone of fusion is 0 or the latent heat really in the zone of fusion is the only heat that is diffusing through the solid and. So, therefore, this is a one dimensional case where you have the maximum pull rate V max represented by k a by l times of d t by d m or k divided by rho l we are just putting the value of d m here rho a d x times of d t by d x. And this d t by d x mind you is in the solid domain as the heat emanates from the zone of fusion into the solid. So, the maximum pull rate is really proportional to d t by d x. So, the temperature gradient from the zone of fusion on to the d t by d x or the temperature gradient from the zone of fusion on to the solid material. And so, therefore, one may argue that if you have a very large d t by d x it would result in maximum yield or maximum pull rate which is actually not the case cut already. So, normally the maximum pull rate is never used and that is because if you give it very less time to formulate then there is always a tendency of a lot of point defects particularly in the zone of fusion nearer to the melt. And therefore, the point defect density would go up very high if the d t by d x increases. So, quick cooling would help to sort of on one hand create a lot of defects into the next formulating zone from the liquid although the defects may not be going into the solid crystal because you have very less time given for the cooling process to take place or the solidification to take place. However, another aspect of this huge too much thermal gradient is also creation of large thermal stresses within the solid which would rather create dislocations and particularly this is true for larger diameter wafers that the dislocations are very prominent because of that. So, it is really a trade off between the pull rate on the way that the defects would go into formulating the crystals or the amount of thermal stresses that the crystals can handle. And this together would define how much pull rate is really needed and it is really not a yield decision sometimes yield based decision sometimes it is basing itself on the purity of the material particularly when because we are growing single crystalline silicon here, the purity of the material in terms of point defects, high the density and also thermal stress created dislocations etcetera. So, it is a it is a function of a lot of other quality parameters for the wafer apart from the yield. So, that is how the Kralge's growth process works. So, the other method which is of some prominence is basically the single you know it is called the float zone method which is again another very important method realizing single crystalline silicon. So, in this particular method also called the float zone method you know it is a it is basically used for extremely high purity silicon growth although down the side of this particular process is that you cannot really go above a certain diameter of production of wafer like in Zocralchis you could go up to any extent including 8 inches or you know 5 inches bigger size wafer are also possible. In this particular case it is only limited to smaller size wafer and the process for production really is similar you have the concept of a seed crystal in this method as well as we had in Zocralchis. However, in this particular case as you can see there is a polycrystalline rod which is being pushed into the small orifice here and by means of non-contact mediated heating like an RF mechanism may be you heat this particular surface of the wafer to the almost melting temperature while pushing the polycrystalline rod all the way into the orifice. And on the other side you lower the seed crystal into the into the this orifice here and the seed crystal is actually used as a template for formation of growth of this polycrystalline material being pushed through the orifice on to the other side. So, from the naked region really in this particular region the seed crystal grows and makes you know a single crystalline silicon of the type of seed crystal from the polycrystalline melt which you are pushing through this particular orifice. The both the rod as well as the feeding rod as well as the wafer are moving at certain omega velocities and one good advantage here is the uniform heating. So, there are very less thermal stresses and as such no thermal stress related dislocations which is otherwise the case in Zocralchis method where there is a huge thermal gradient available because it is essentially a contact mode heating. Here most of the heating means are RF based so that this non-contact mediated and there are no thermal dislocations whatsoever in the particular crystal. So, that is another method of formulation of single crystalline silicon known as float zone method. So, the other material of importance of you know for to the microsystems fabrication has been indicated as glass and glass is actually chemically silicon oxide and the content of silicon oxide however varies from different glasses. For example, sodalime glass would contain about 68 percent of silicon oxide borosilicate another variety of glass would contain about 81 percent and the highest and the purest form of glass is the quartz really it is few silica which is actually 100 percent silicon oxide and basically there are certain other metal oxides along with silicon oxide which are present which would determine the optical transparency or clarity of the glass to you know the whole UV visible region of the spectrum and so therefore certain characteristic metal oxides and metal ions would emit their own signatures making glass unclean and absorb at certain frequencies whereas quartz being the purest or the highest form of glass will not absorb any of these wavelengths and would have a clean background as such. So, glass itself as a variety of desirable properties for example, it has a high mechanical strength it has high electrical insulation, transparency, high chemical resistance which are all amenable to microsystems. So, therefore glass sometimes can be used for packaging microsystems typically and commercially available glasses are now available freely like you know which can be photo pattern, photo run is one of one such glass can be directly photo pattern on to the substrates and therefore you know with glass also you can actually use photochemical machining or PCM to you know result in a variety of features and structures at the microscopic lens scale. So, for etching glasses for creating crevices cavities features structures of the micro scale within such glasses you normally use buffer HF solution which is actually the solution of HF along with the ammonium hydroxide and water. So, that is what glasses are that is how glasses are important for the microstructure domains. Let us also look little bit into the wafers specifications of silicon wafers and so essentially how they are prepared from the bowl which are being obtained either by Zocrelki's method or by the float zone method. So, the bowl is first characterized for resistivity and crystal perfection and these are done by various electrical tests on the bowl then the seed and tail are cut off the bowl and they are mechanically trimmed to proper diameter and then of course, then finally there is a finish trimming operation on to the final wafer diameter since additional etching will still need to be done on those bowels. So, for wafers 150 mm or less flats are ground through the entire length of the the bowl to denote crystal orientation. So, if you have 100 direction you will have that flat pointing out as a plane towards the plane perpendicular to indicate the perpendicular direction as the direction of growth of the particular crystal. So, most of the silicon wafers that you get from industry would have one or two cuts indicative of certain specifications particularly growth related specifications of the silicon wafer. So, the thing that has to be remembered is the largest flat which is also known as the primary flat in such a circular wafer is oriented always perpendicular to the 100 direction. So, therefore it is actually the x direction in a right handed coordinate system Cartesian coordinate system and the flat is always perpendicular to the x direction and that indicates the direction the other directions of the crystal. So, in comparison to that flat you can record what is the 111 direction or 110 direction or 101 direction or any other direction with respect to this x direction. So, one thing has to be very carefully seen or observed in any silicon wafer which comes from such a foundry you will have to first see what is the largest flat and that is called the primary flat and it is always oriented perpendicular to the 100 direction. Apart from that there are several other specifications of relative importance for example, you can actually have cleanliness in terms of particles per centimeter square on the surface area. You can have indication of oxygen concentration per centimeter cube that means this per unit volume, carbon concentration per unit volume, metal contaminants in terms of parts per billion within the crystal lattice and then also you can have per unit area what are the grown in dislocations. Sometimes these are very well measured using sophisticated non-contact mediated optical characterization tools like interferometry etc. Then you can also have an idea of oxidation induced stacking faults and that can be in the bulk of the wafer so that can be per unit volume. Apart from that some normal specifications like diameter and thickness of the wafer or the bow which is nothing but the way that the wafer is warped or bent sometimes and then aspects like flatness and cost. So, these are all indicated in a wafer box which comes from such a manufacturer or a foundry of silicon. So, these are some of the specifications which normally the manufacturer supplies and then with this specification on and the direction of the flat one can characterize the wafer very well. So, now once we have had a good introduction to silicon and gloss let us look at some of the MEMS fabrication techniques which are really available. So, it is really all about fabrication of micro nanostructures inside silicon or glass or some of the materials amenable for MEMS fabrication that we are concerned with. So, it is formation of structures which could be actually used for sensing or actuation purposes at the micro scale. So, that is the purpose of this kind of fabrication. And the idea is that these micro structures so formulated should be able to process some signals. It can be electrical signals or it can be non electrical like mechanical signals which can be somehow processed by means of transduction of these features or you know micro structured elements. And for production of these you have to use some conventional and some new semiconductor manufacturing techniques for in the MEMS region. And some of these manufacturing techniques could be something like chemical machining like etching. It could be gas based or based on some chemicals. It could be deposition where you can deposit a metal film or a resist film on the top of some of these wafers. And then of course, photo lithography where you can use the power of optical signals or light to actually carve and find out different features sizes and structures on to these films. And then you can use a variety of other processes like oxidation, epitaxy etc. which are planned like for example, epitaxy would be used for growth of single crystal silicon. Or oxidation as a matter of fact is thermal process whereby you can actually entrap oxygen in silicon and at the cost of silicon you can get a layer of silicon oxide or silicon dioxide. So, these are sort of conventional semiconductor manufacturing processes which have been merged into the MEMS domain or microsystems fabrication domain. Apart from that there are deep RIE or deep reactive ion etching which is a very new technique in the microsystems domain. And then of course, thick plating which is also used this is electroplating which is a sort of electrochemical machining operation where you can actually deposit films of certain size. And so therefore, these are the two other domains which are very commonly used for MEMS systems or microelectromechanical systems. Apart from that of course, there are these non-traditional processes like USM, AJM, EDM and ECM which have been very recently incorporated for doing activity in fabrication of the microsystem or micro manufactured components or devices. So, if you look at all these machining processes in bunch they can be categorized either as bulk micro machining processes or surface micro machining processes. And the bulk processes really are about the subtractive removal of material or subtractive processing of material from a wafer surface. For example, in this particular illustration here or cartoon here you can see this right here is a section across section of the silicon wafer. And you are trying to selectively etch off the material from this wafer. So, there can be for example, a protective layer here which you have etched out and created a small crevice or a cavity. So, another example is this particular etch pit here which is a high aspect ratio structure. And this can be obtained by a process called deep reactive ion etching where the power of plasma can be used for driving atoms in a particular direction so that they can knock off the surface atoms here. And then based on that high aspect ratio structures can be formulated. The third example as illustrated here is again a very interesting example where there is a P double plus layer which has been impregnated here using an implantation or some doping technique. And then as an anisotropic etch which actually goes on from the backside here and the material is selective to only silicon and so to P double plus. So, therefore, whenever the etch end actually comes and hits this area it actually leaves a membrane here a thin membrane here because it is not able to etch this part it is selective to P double plus as I already mentioned and the remaining silicon is etched away. So, this is another way of getting what you can say thin film pressure sensors and this is also known as bulk micromachined pressure sensors. So, why it is bulk is because you are subtractively removing material from the volume of this particular wafer and that is why bulk micromachining is an subtractive process it is a material removal mechanism. On the other hand surface micromachining is an additive process where you do not really remove the material from the bulk of the wafer but you keep on adding different layers of materials on to the top of the wafer because of which you can create these features and structures. To exemplify some let us look at this illustration here as can be represented. So, here for example, this is a polysilicon layer which has been put in a manner so that you had a sacrificial layer in this particular region given by the dots it could be a resist layer and then you have deposited the polysilicon layer on the top of this resist layer and then later on you can remove the resist layer away because polysilicon is a high strength material so that you can have a channel on the surface on one side and buried within this polysilicon layer on another side. So, you can remove away this resist later on it just goes off thus resulting in this channel into the plane of the paper or plane of the this transparency slide. So, this is an example of surface micromachining or additive micromachining. Other examples could be deposition of this pillars and pores by using either metals or photo resist where the structure so realize can be of some significance for example, all the metallic interconnects in in electronic microelectronic circuitry is actually made using such metal imprints it is called printed electronics and it is again a additive micromachining process or a surface micromachining process. So, in a nutshell machining can be divided into bulk where you are subtracting from the volume and surface micromachining where you are adding material on the surface to do microstructures and features. So, these are the two broad categories of all machining processes that can be assembled to realize micro systems or micro fabricated architectures. For example, is a slide which has been borrowed from Dr. Mark Madous book on micro fabrication. So, here it is showing how you can formulate a P double plus membrane and this has already been illustrated. So, you can actually formulate a small cavity here using resist and so this can be used as a H window as and there can be a an H n which can be selected to P double plus which is actually highly doped positive silicon on the other side and so the material starts etching away an anisotropic manner that is formulating a 54 degree angle and based on this it just goes up to the selective layer here which is the P double plus layer and stops etching process thus creating a membrane. The other hand this side is showing how a micro cantilever can be generated by additive micromachining where you have let us say a sacrificial layer over which you have put let us say a poly silicon layer like this and then you are removing the sacrificial layer away so that you can have a small cantilever which you have illustrated here in this particular example. So, these are some of the process flow charts or logic diagrams for formulating some of these micro features and micro structures in different illustrations. So, if you look at the bulk micromachining technique the first process that comes into existence is the etching and particularly wet etching where there is a chemical which is used for etching of the material. So, it is a subtractive technique again the etchant is a highly highly corroding or eroding agent which engraves its wherever it comes in contacts contact with the wafer and removes the material so that you can have these features etcetera imprinted and the etching solution is basically very often used in all the micro electronic processing and also in MEMS processing. So, etching can be divided into two classes one can be isotropic or homogeneous etching where the material removal is uniform as a function of the volume and there can be an isotropic etching where etching can be in a particular direction and the differences are in terms of etch chemistries as I will illustrate in detail in the following slides. So, let us look at isotropic etching and isotropic etching really as I mentioned before the etchant is able to remove or erode away material at uniform or homogeneous rate in all the directions. This for example, is an illustration where there is a etch protective layer which is now emboldened by the red pen here and so this window here of the etch protective layer is able to give an access to the fluid to go into and start etching away the material which is underneath this protective layer and in the process because it is a homogeneous process the material actually goes into the into this etch cavity and it starts etching in all directions resulting in this undercut. So, this layer here which has been formulated it say if this distance is x this is also known as the undercut because this was not really intended for it was not planned and because of the homogeneity of the etching the etching would happen in the lateral as well as the vertical direction which would always result in this kind of an undercut. So, when you design micro systems and the masks for the micro systems this undercut allowance has to be taken into account for the designing to happen. If the etching was not homogeneous for example, as illustrated here the etching may be a little more directional. So, in this case for example, you can see the etch rates are more towards the side. So, lateral etching is more in the vertical etching it would result in different shapes based on what is the directionality of the etching. And so typically if you had a very well stirred solution where whatever is coming out is going away from this etch window it would result in a homogeneous profile like this. If you do not have a stirred very well stirred solution it would rather result in this because the amount of atoms which are coming out of this material would have a higher concentration here and thus diffusional restrictions would prevent further etchant to move away and so the rate in the vertical direction would be reduced in comparison to the horizontal direction. Let us look at some of these materials and the etchants which are used for the materials and what it is selective to. So, etch selectivity again is a term which is used in reference to the fact that you know the there are certain materials which may not be able to get etched away by the etchant solution. And in that kind of a case this material which is not affected by the etchant solution can be used as a protective layer to stop the etching process very accurately. And therefore, an etch stop layer or an etch selective layer is always preferred as the layer which would prevent the etching from happening any further. So, let us look at this table back again here. So, the material illustrated can be silicon silicon dioxide, silicon nitride, aluminum so on so forth. And then there are these etchants which are amenable to removal of these materials. For example, H F or H N O 3 or C H 3 C O H or for example, K O H they can remove silicon very easily. But as soon as the etchant meets surface of Si O 2 it is selective to Si O 2. So, it will not etch Si O 2 anymore or it will not etch Si anymore in this particular illustration where N H 4 and H F combinations are used. So, therefore, there are certain materials certain etchants which are etching away this material and it is selective to silicon or it is etching away the silicon and it is selective to Si O 2. So, the combination of these can be used for a variety of etching architectures that can be realized accordingly. Thank you.


So I became interested in computer science in high school when I studied algorithms and data structures, which really were one of my biggest passions. Yeah, I've been into computing since I've been pretty young to be honest. Yeah, I had like one of the like brick phones and I like kind of took it apart. I just kind of saw these bits and I had no idea what they really did. I just became quite interested in like electronics and stuff. So I chose the University of Manchester because it's one of the best universities in the country for computer science. There is a lot going on here and research is done in many areas of computer science. The baby computer was invented here, so that was one of the reasons why I wanted to come here as well, because it was such a centre for technology. The university provides the opportunity for all the students to develop in the field that they are looking for, rather than one choice that they've made after finishing college. First year is compulsory and it gives you a grounding in everything, which is really nice because it means as soon as you hit second year you have optionals to pick between. So it means I can trial and test everything without just going straight down one path. When I first arrived on campus I was really excited. I like exploring, I like finding new things. I was nervous but I was really excited. I really wanted to know how it's living in the UK, how is the culture, the weather, the people. I think that the fact that Manchester is a cosmopolitan city has helped me a lot. Everyone is studying and focusing on the same things. There is always a point of discussion, a sort of discussion that is available for students to become friends and interact more. Everyone will just chat to each other even between years, which is the thing I never thought would happen.  They want you to come and ask questions, they want to push you with learning. They're there to aid you and so just get you to pass a grade. You can always just go up to a lecture and just ask them a question and they're really friendly. You mail them or we can arrange a meeting when we don't understand a topic or we want to discuss something about any specific subject. One really good thing that they do here is they have a personal tutor who you meet with one hour a week during first year, which means you have a really close bond with someone to go to if you have any problems. The School for Computer Science specifically has the hardware library for students from Kilburn to rent out some equipment. Rones and Oculus Rifts and Xboxes. We have labs which are just for computer science students, which means we will always have a computer when we need one, which is virtually all the time. And you can also use Linux and Windows, which is really handy to get used to two different operating systems. Personally, I have worked on projects with Maya robots or Sphere robots, which allowed me to get a better grasp of robotics. Industrial Year is a year between your second and final year, where you spend nine to twelve months out in industry getting paid to work but going to use experience in a computer science field. During my studies, I did two internships with Google, but I learned so much, not only new tools and technologies, but also I improved on the ones that I already knew. My Industrial Year was at the HUD Group, which is a technical company focusing on retail. I have worked as a software engineer on most of my times, but as the company is still learning how to develop, I had the chance to grow my soft skills as well. Being a good computer scientist doesn't mean just knowing how to code. It means knowing how to work in a team. It means knowing how to deliver something, rather than just staying in front of a computer. This degree gives you so many opportunities and it will get you to places that you've only been dreaming of before. If you're really interested in the technology sector, going to the University of Manchester is the best option.


All right, good morning, Saber Traders. Welcome on back here this Friday, December 9th, to wrap up our week here live inside the cyber group room. Great to see Ray and Warren, Michael and Grant, and Alex and Lee, John, Skip, Norman, Ray, Jeff, and all of us otherwise. Just great to see all of us here this morning. Great to have all of us back on Social Media Facebook Live or YouTube. You can tell, of course, this is Josh Levitin speaking, tagging in for Fausto this morning. He's actually, if not in the air, he's en route to Florida. I know he has a couple of meetings down there. If not even today, then even for Monday of next week, I'll tag in for him. So with that, there's a lot to talk about. There always is a lot to talk about, even with the market pretty choppy heading into the afternoon like we had. But there were a bunch of trades that we ended up doing well on from yesterday that I wanna talk about. A couple of stocks that did all right for us early this morning in pre-market, but to be honest, for a Friday morning, you're not expecting really much of anything. So had a little bit of a drop early within the market after 8.30, but outside of that, not a whole lot of traction on a few different trades. So we'll go over what worked for us, what did not, and then we'll scan through. But at least to start with what's on the screen here for right now, the CLRO, one that at least for right now has started to work out off the support from a dollar, a dollar 10, it broke out from just there and tried to make a nice squeeze, but as you could see, now beginning to make that pullback. This is like a stock that was below a dollar before this morning. We normally don't trade these like real cheapy stocks like this and we'll get to one in a moment that will actually ran really well, but CLRO at least here for the meantime, I don't know if there's news that came out on this company, either way that the thing that I look at is the fact that this thing ran up so much just over the last like month straight from 50 cents all the way up to 85, just from yesterday, now a pop-up much higher to a buck 23. This thing's moved up too much too fast I think. So I'm gonna come back to this at the end, could be a good stock to put on our watch list if there's still strength by the end of the meeting, but I wanna see if there's anything looking a lot better, anything that's just a better opportunity in my eye. All right, so again, we'll start with putting this on our side list. Now, what I wanna do though is just jump back to yesterday because well, there we go. I had no idea this was popping folks.  I didn't look at this for the last 20 minutes. So perfect timing. PHVS making another big move up once again today, albeit still down five to 6% from yesterday's close. This thing blew the roof off early in the morning and ended up just making this huge parabolic run. I was not expecting to see this just continue the way it did after 12 o'clock. Now, there was some news that came out on this company that was like in relation to phase two trial studies meeting their primary and secondary end points.  Again, we'll get to a stock this morning that did not work out for us, right? And off of news, but when they meet their primary and secondary end points and it's phase two and then certainly one more phase three, that's like just the most significant phase within their trials test studies to go through before FDA approval. Phase two is pretty good still though. So it led to a nice pop early in the morning, but man, as soon as this ended up breaking above resistance off of 450, 460, ended up just exploding, got halted and the more it gets halted going up, you'd wonder when is it going to begin to pull back, crash back down and yeah, it shook back down a bit but this just kept giving. I mean, higher lows, higher lows built up this beautiful Fausto flag. You could probably see it even better on like a five or 15 minute chart there but nevertheless led to the next pop, topped off just right around 12 bucks, a little bit above and then eventually kind of just drifted off into the close but yeah, now another big move up again this morning. So it's hard to not put this on our watch list at least for right now that PHVS, especially with this move here. So for right now we'll do that, just be wary of it though, like, you know, hey, just before in the other ones, the CLRO, you can say the same on this thing. This thing moved up way too much, way too fast from yesterday. So I wasn't expecting this pop but for right now we'll at least put this on our main list. All right, actually for Friday I'm on the stick for a long time today. So I got to take a nice little water break there. Now with that, there was a couple of other trades that we ended up doing well on from yesterday too. The EXPR stock expressed like a meme stock back in the day, back from early last year in 2021. It had a nice squeeze up early in pre-market then from there just kind of dumped off after the open, didn't it? And ended up just kind of making lower highs but where we caught this trade. We ended up looking for support roughly off 161, 162 and for the most part it ended up holding that pretty nicely but based off C2 strategy, based off what we teach in class, especially you know, phase one, phase two when it breaks through the big level on the way up, right? So a couple of false opportunities there but you know, right before noon it re-broke through that level and it was smooth sailing since. Honestly to the point where I was calling out my home run target on this trade was roughly off 191 to 195. I can't copy and paste that in the chat but that's from yesterday's log. I would need to do a little digging for that but I was looking for that and nailed it perfectly. Doesn't always, you know cut out that way, right? But this was on a smooth steady trend and at that topped off perfectly at our target and then from there just kind of pulled back again. So if it was shortable, if this was easy to borrow then we'd flip the script and short it on the way down but it was hard to borrow on trade station at least the run was over from there. You know, down 6% this morning so it's not looking too good here for the open express. I put it on my side list but you know, I have no real interest in this trade now at this point. All right, we have two more from yesterday and then we'll just jump right through the percent gainers and losers list. So SMMT and we talked about this even just on another stock that we'll go through next but you know, like I just pushed up the last three days in a row so even if you think, oh, it's moved up too much it should dump off if it's volatile enough if it's trading good volume in pre-market technically there is still an opportunity, right? So with saying that SMMT and no other huge move yesterday morning ended up popping shortly after 9.30 ended up getting halted a couple of times on the way up similar to the other one ended up topping off just around that 450 level just man, what a move from just Wednesday this or from Tuesday this week from basically a dollar all the way up towards 450 and above so you know, hey, we tend to catch these runners on a day to day basis here but to have it literally the same stock for three days in a row you don't get that too often honestly so you know, this is a really nice gift to have personally I did pretty well on the stock back from Wednesday into Thursday yesterday so I missed out on it initially Tuesday but it was a nice stock in our phase three classes I was trading for Fausto then and then just yesterday morning caught a good chunk of it again for the open, you know it's trading some good volume order book will fill in a lot more after 9.30 it's not, it hasn't completely tanked, right? It's actually up 0.83% from yesterday's close so it's a lot better of a sideless stock at least this compared to that EXPR so I'm not gonna put this on the main list just yet but you know, maybe after 9.30 we'll reconsider all right, last one tour so another one just from the last few days the last week and a half I'd say really has made a non-stop push up on the daily chart up and above a dollar yesterday topped off at 2.39 as you could see breaking above that this morning just broke above 2.50 a moment ago and that's where you ask like hey this stock has moved up so much the last few days when is it gonna pull back? All right well if it breaks through the level and there's some good buying coming in and if it holds above the level at least then you know there's a chance so for right now it's doing just that but for anyone that was in this trade just earlier as we had called it out you would wanna see this make a bigger pop very soon you know normally we're out of trades in pre-market around 9.15 Eastern, 9.10, 9.15 so you know it's pushing up it's doing its job got a 15K iceberg on the bid at 2.50 that also helps but you know you don't necessarily wanna hold this one going into the open that's where you gotta wonder you know are we gonna see the sell off right away right? Is this gonna tank right away? And that's it like instantly so for right now hey I'll put this on our main list with that PHVS stock just be a little careful though going into the open on it all right so with that let's go from top to bottom now some good buying just came in on that towards the trade just there the AMAM this is the cheapie I was referring to that just non-stop is pushing up just a moment ago it broke below the trend line and then from that point just held pretty nicely off of like a dollar or a 105 maybe you could say from that point pushing back up here it's hard to not put this stock on our watch list just given how it looks right? You know I wouldn't be doing my job if I didn't put this on our watch list it's got a liquid order book you know I harp on that more than anything Fausto does as well of course but you know it's pretty inexpensive so it's right within everyone's price range just don't get caught slipping the stock is up already 183% for a stock that's up that much going into the open just like I said on tour you're gonna expect to see a little sell off prior to 9.30 so you know if you're in this trade already be very careful you cannot set stops like real stops in pre-market so just make sure that if this ends up pulling back a little bit here coming up get out ahead of time you could always look to get back in on the trade later on all right so with that AMAM well at least tag on our list all right so one that did not work out for us this morning at least yet BXRX some news that came out with like phase two they didn't meet primary end points or secondary end points like the other one did the news that came out on it was that they just initiated coverage on it or initiated their study so they started it so a little pop to begin right early in pre-market just didn't really make that squeeze up so if there's one thing in relation to news at least I can think about it's like hey if they meet their primary secondary end points or even just leader on go up to phase three that's a lot better than like just beginning a study so could it pump up higher of course but you know hey it ended up making lower highs going into eight o'clock lower highs often you're gonna see a break of support lower low so it ended up snapping these local lows and pulled back a lot so that's where you gotta be careful on it so yeah BXRX I'll still put this on our list just given you know hey it ended up trading a lot of volume this morning you know hopefully it could build up some support later on after the open the trend off the highs is clearly downward so you know don't try and catch the falling knife on this maybe it drops as low as five bucks another like 92 cents from here tests five and then could bounce you know that's just a loose thought but yeah I mean for right now I'll still put this on our radar on our watch list alright CLRO I'm gonna come back to at the very end I don't know how it looks right now since we last looked at it but I wanna just keep going through the MRIN stock marrying we are pretty familiar with this trade we did really well on this stock back in July of last year and this was a real run day over day over day and you know a couple in between you know pullbacks but it ended up making a huge squeeze for us back then so we're very familiar with this stock and for right now is kind of returned back to being like a stagnant level one trade you know it's not really making that big move just yet so hey that there's time hopefully this can make a bit better pop after the open I think some news came out between Marin software and Walmart with their Walmart connect partners program but with that at least you know there was news out on Marin with Amazon I think last year that may have led to that pop if not mistaken so you know hey this could lead to another similar squeeze I'm not expecting 25 let alone 10 let alone five you know but if this can make a fraction of the type of run it made for us back last year I'll take it and it's already up 35% but you know what I mean there's always a chance it can break higher later on holding over 150 and perhaps making a higher low off the VWAP afterwards but yeah the Marin trade I'll put back on our list here it was on our pre-market watch list all right what else we got here folks what else we got ACLX this thing doesn't not really the best looker there we'll keep going I mean I guess you could say the same on NRBO this stock was also on our list early but you know it was trending down even going into eight o'clock that's where even I just putting this on our list I assume that this isn't ready to make its big push yet with it trending down into eight o'clock and we teach that throughout class so here now it's building a better support off the two level off 190 at least you could see there but you know look for that off of two at least going into the open similar with the Marin I'll put this back on our list just you know overall activity in pre-market I didn't even check if there's news on the stock let me just actually double check on that really quick just jumping on Benzinga pro great you know software platform I should say otherwise so some news came out like in relation to just coverage on it just a firm initiated coverage on it back from earlier this week on Wednesday but that's all I got so for right now hey it's making a nice squeeze back up definitely could bounce off two now and hopefully off the VWAP here at 205 and tour already on our watch list and then we keep going so doc you sign little expensive but I'll still take a look at it if it was trending the other way at this point I'd be more inclined to put it on our watch list but for right now we'll pass ZH Chinese stock I think a lot of the China stocks gapped up again overnight but all kind of flat so this one definitely free sideways for right now forage not much of an order book showing there and that leads me to Chuck's Poyle trade Chuck got in and out on Boyle in pre-market from 32 59 got like a dollar 50 cents on his trade basically loosely speaking he got out at 33 33 96 so the loose math on that very nice trade from Chuck but with that in mind hey now a natural gas ETF this moves inversely to cold which we're really familiar with we're a lot more familiar with cold but hey if you do familiar if you do well on the natural gas ETFs all together or if you have book map level four then I'd really suggest for you to follow them if anything at least I'll be more inclined to put although we'll likely call that Boyle to Chuck the UNG moves the same way as Boyle it's just cheaper that's all so UNG and cold I'll put both on our watch list and I'm referring to Boyle with that in mind all right we don't really trade the ETFs so often so as a new student here please take our advice and I know that I'm not Fausto but Fausto would be the first one to say it here do not trade an ETF unless if you have level four because otherwise it makes it really difficult to trade trying to follow level three you're gonna do much better looking for iceberg orders on a publicly traded stock you know that could be Marin it could be Tor it could be the PHVS even that crazy thing but you know otherwise if you got level four then consider it if you do well on them obviously you'll put them on your main list but yeah just otherwise that's my thoughts on them Billy another Chinese stock that we're really familiar with this one's done us really well over the last week and a half I personally have become pretty familiar with this thing I wish I traded it back on Wednesday this week or Thursday Wednesday this week when it ended up making this big pop from 20 sub 20 I didn't print my chart then Billy right now at least heading into the open dropping off after the gap up so you know for right now just I'll keep it on our side list you could say the same thing on the XPEV you could say the same thing on the Neo trade and I even charted Neo prior to the market opening up even prior to 830 I ended up charting Neo early so you know that's my personal decision but that doesn't mean that this is gonna make a great move I just wanted to follow something just for my personal side list so all together the China stocks will pass on them for right now if they end up making a strong move just shortly after the open then I'll cycle through my book map we'll call them out appropriately all right all right and that even includes IQ which IQ we put on our pre-market watch list look at it now so this one was actually up six or five or 6% something like that early it was trending up well prior to eight o'clock I thought this had great ability to squeeze up higher you know ran up pretty nicely here just from the end of November into this month but had a big sharp pullback so it built that a little local support popped up yesterday I was hoping to see more this morning but obviously didn't get it so you know this one as well we'll pass on this we'll put this on our side list at least after the open all right current time 919 right now I wanna make sure all of our students have enough time to prep up make sure they get their last looks of prepping before the market opens so I see a bunch of crap that's hard to borrow on the loser's side except well we got a couple but except at least for my platform trade station Carvana CV&A I regret not following this as much as I should have yesterday I thought it was gonna be a lot slower of a trade yesterday just because the day before it was all over the map and that's not normal for you know a stock that is like $4 Carvana you know take a look at SoFi take a look at Neo back when it was a three, four, five dollar stock AMD they just become a lot more liquid a lot more slower moving so off of Wednesday's move I didn't think it was gonna move as well it did it ended up dropping off at first but then made a really sharp dead cap bounce so this morning I also prepped up Carvana Neo and Carvana those are my main two going into the open for Matt for Roger as well that private chatted me early this morning asking what I'm looking at you didn't know I was doing the meeting of course right but you know there you go Neo and Carvana those two mainly I'm watching Carvana though I'm gonna put on our main watch list this one definitely looks a lot more active it's down over 7% so far you know perhaps it could be another short day if it ends up breaking back below that 450 level that's what I was typing in the chat board earlier so yeah Carvana I just think that's a better trade for a lot of us here all together going into the open and then if it ends up holding 450 higher lows off the VWOT there and there's a chance maybe it did kept bounces again right Lee LI this one's actually that's not down over 5% but downtrend this morning this one's easy to borrow at least could be a good short good sideless stock I know a few of us like following Lee Coinbase dropping back down again not really doing a whole lot though for a $41 stock very rugged staticky moves so yeah not too particular about that folks we're also below 5% so if there's anything else that you see just type it in the chat board just let me know for Deb asking just what's the link for level 4 the program at least Rich will send you a private message as he just wrote you there you know we'll just give you the link we'll talk to you more about that at least just in a private chat alright so for all of us on social media Facebook Live YouTube once more I'm tagging in for Fausto this morning at least of course and I think perhaps for Monday as well so hey if you have any other questions just feel more than free to send over a quick email Josh at C2Trading.com I always like to post my email here at the streams especially in the afternoon when I always host them but otherwise if you're not joining us this afternoon coming up later on today enjoy the weekend with that in mind folks opening bell coming up just in about 8 or 7 minutes so I look forward to it I'll type and tweet out the list here in just a second folks so for Deb and Brian Grant Sid and all of us just here otherwise I look forward to speaking to you coming up take care come a cyber group member today just click the link below and receive all these amazing products and a world of knowledge for just $9 do it today


You know, fans of Alley 300 Davis Street, it's an anticipated weight to where people are waiting on and they ready, and that's a good thing too. You know what I mean? As long as it deliver. You gotta deliver, but that right there, you know, I don't feel pressure from that as far as quality of music and all of that. Vita Bland and Feta Means and that cane, yeah. Masked up, we strapped up like Ukraine. We built to do that, you know. Yeah, we on boss talk one-on-one. I see you be recognized by Trio Talk. Don't Pio talk a lot of times too. Like you, like he be posting, he gonna always post something with ALD. Just shout out to that boy. I always rock with him. Just what does it mean for the bloggers, for the podcasters, for the people to keep your name in their mouth just basically shouting up. Well, I'm gonna say this. This is very important.    Man, you gonna, so I'm just, I'm really hoping to communicate that over to people how much support that I need for this project. This ain't no, this is not no game, it's not a joke. I have to put an album into this culture that's gonna resonate with these people and be around. You know, this is Texas, so if you do it well, we're gonna remember it forever.  So I'm looking at this as my opportunity to put that level of project into the game, and we'll see, we'll see, but this shit is very important. No, no, you can tell. It's not no motherfucking joke, it's very important. The one thing you stated earlier when you were talking to Mrs. Jamaica was the fact of, and she brought it up, how you was always, and even a little kiki when I interviewed him, just how you was bringing those albums, those see, those crowns right after each other, bam, bam, bam, bam, just layering them out and then all of a sudden there's a quiet. There's a place of quietness now, before this next project. And I think it gets to the ones who really, fans of Aldi 300, David Street, it's an anticipated weight to where people are waiting on and they ready, and that's a good thing too. You know what I mean? As long as it deliver. You gotta deliver that right there. I don't feel pressure from that as far as quality of music and all of that. By the blend and feather means in that cane, yeah. Nasty up, we scrapped up like Ukraine. We built to do that, you know. What it is, is all of these other ancillary parts that have to go right in order for this to get past the level where I'm at to the bigger level, to take a right to step into the game for real, you know. I look at all of this as like, damn, like, you know, where we at in this process is beautiful, but I have to really kill with it and I need everybody to see it as it's not just me taking this step, this is us taking this step.  And we at a point right now where it's time to, you know, get everybody on the same page, you know.  Yeah, this is the whole, you know. Lee is on there, Buddha bless this B out of ATL, real big in the Migos catalog, Greg Street, you know, X-File who did the first single, Silver and Goldy got some more tracks on there. J-Stars, you know, of course, the Power Wilds, the Keys, all of them, you know, just, it's a collective effort.  So you say Power Wilds on there, is this your first time working with Power? Yeah, Power. Yeah. How was that? If you can just, I mean, he came in there over delivered. He came in there and got down to eat. He was only supposed to do, y'all gonna see what he did. Like he came in there and like he was supposed to do like something and he ended up doing something totally.   I have, man. At some point I just got to just say it.  So I feel like I got, I have no excuse. Like I have, there's nothing I can blame it on. Yeah, we on boss talk one on one.