25-nm n-MOSFFET

mcdeviceex02.in : 25-nm n-MOSFFET

Requires: MC Device
Minimum Versions: Atlas 5.24.1.R

This example demonstrates 2D Monte Carlo device modeling of a silicon n-MOSFET without quantum correction.

The first part of the input file specifies the algorithmic parameters of the Monte Carlo model. Many of the same parameters specified in the input file for the bulk example (mcdeviceex01) are used again here. In this case, the number of computational carriers (electrons) is set to 40,000 with the N parameter on the PARTICLE statement. N = 40000 is large enough to adequately sample the spatial distribution of mobile charge in the device. To better sample the tail of the distribution function, use a higher value of N or statistical enhancement.

On the ALGO statement, DT = 0.1e-15 s = 0.1 fs is ten times smaller than in the bulk example since the electrons must sense small variations in the 2D doping and field profiles. To get even closer to the steady-state solution, change from ITER = 2500 to ITER = 25000. With this change, MCDEVICE will take about 10 times longer to run the example, but the averages will be closer to the steady-state solution. As in the bulk case, you may want to change from TRANS = 0 to TRANS = 1000 to obtain a more accurate solution before TIME = 0 when MCDEVICE begins collecting data for its averages. We have kept this example short by using ITER = 2500 and TRANS = 0 so you can experience running a complete simulation in just a couple of minutes.

In this case, TSTEP = 5 on the POISSON statement indicates that Poisson's equation will be solved every 5 iterations (or every 5 * DT = 0.5 fs). This time must remain short in order for the electrons to properly sample spatial and temporal variations of the electric fields.

The second part of the input file specifies a rectangular tensor product mesh used to represent the physical structure of the device, to solve Poisson's equation, and to help enforce the MC carrier boundary conditions. A finer mesh captures more carrier-carrier interaction. A courser mesh captures less carrier-carrier interaction. In this example, we use a typical size of the 2D mesh for a 25-nm n-MOSFET. This 2D mesh is finer than what is typically used when solving for the steady-state solution of the drift diffusion or energy balance equations for the same device.

The third part of the input file specifies rectangular regions on the mesh. The REGION statements indicate both the material (MAT parameter) and type of region (TYPE parameter). When you specify the regions in your input file, always include regions with the TYPE of OUT, MC, BLOCK, and CONTACT. Please see the MCDEVICE chapter of the Atlas User's Manual for a complete description of the region types and how they control the Monte Carlo solution.

The fourth part of the input file specifies the rectangular current regions used to estimate the current in the device. In this case, the x-directed estimates of the current (dim=1 values in the mcdeviceex02_current.log file) from the first and third regions represent the terminal currents at the source and drain, respectively.

The fifth part of the input file specifies the doping profiles.

The last part of the input file includes a SOLVE statement. The SOLVE statement performs the Monte Carlo solve at the voltage biases provided by the V<NAME> parameters on the SOLVE statement. Additional commented SOLVE statements may be used to do perform voltage ramps or obtained solutions at other bias points.
