This page updated 30 November 2008

The purpose of the **MOSCALC** extension module is to provide prototype
MOSFET simulation compatible with the fast execution time and ease of use of BIPOLE3. It should be
noted that Bipole3 was developed for BJT and HBT simulation and has been extensively tested and calibrated in industry
and universities on these bipolar semiconductor devices.
This has not yet been done with **MOSCALC** for MOSFET structures.
The simulation is for a self aligned gate MOSFET structure and is based on vertical numerical
integration of Poisson's equation including free carrier charge and threshold
adjustment implants coupled to horizontal numerical integration of the majority
carrier drift equation in the conducting channel. Poisson's equation in polar
coordinate solution is used for the drain-substrate space charge region. Mobility
dependence on both vertical and horizontal electric fields in included.

The output consists of tables for a given V_{ds} including I_{ds},
g_{m}, source-drain transit time t_{ds} and figure of merit
C_{ox}/g_{m}.

BIPOLE3 graphs are provided for the following quantities:

- band, electric field and inversion layer charge versus depth diagrams for given surface potential
- inversion layer charge, surface potential, gate capacitance (high and low frequency) versus gate potential
- graphs of horizontal electric field and velocity versus 'y' for given V
_{gs}and I_{ds} - graphs of I
_{ds}vs V_{ds}for different V_{gs}values, and of I_{ds}vs V_{gs}at a specified V_{ds}.

Poisson's equation is solved numerically in the plane and sidewall regions for the diffused source and drain junctions neglecting free carriers in order to determine the zero bias junction capacitances.

For a specified source-drain current I_{DS}, the equation for horizontal (y direction)
charge-current potential is solved numerically for Q_{e}(y):

I_{DS} = µ_{e}(E_{x},E_{y}) Z E_{y}(y) Q_{e}(y)

The mobility is a function of doping level, horizontal and vertical electric
fields. The limit condition on Q_{e}(y) as the drain space charge region is
approached is given by the saturated velocity condition.
Beyond this point Poisson's equation is solved numerically using the drain
doping profile.

The surface charge is related to surface potential by solving Poisson's equation numerically at each value of horizontal distance ‘x' integrating from the surface to the substrate:

dE_{x}/dx = [(qN(x)/e ][1 + exp([V - 2f_{ F}]/V_{t})]

where:

Q_{s} = - e_{ox}E_{ox}

Q_{s} = -(Q_{i} + Q_{B})

and where Q_{B} is obtained from vertical numerical integration.

The above equations are solved numerically for a given I_{DS} and V_{GS}, with V_{DS}
being the resultant potential.

** 3. Physical models used in MOSFET simulation**

The physical models for bulk properties are those used for devices simulated for BJT structures and all the model parameter values are user accessible.
In addition, physical models for inversion layer mobility due to surface scattering, and field dependent mobility in the inversion layer are special to **MOSCALC**.

** 4. MOSCALC output examples**

The **Bipole3 Tutorial Guide**
available from this web site contain many examples of MOSFET simulation results.
These include graphs for both internal results (electric field and velocity, carrier concentration, band diagrams, inversion layer charge versus bias)
and terminal characteristics (Ids versus Vgs, Ids versus Vds for various Vgs, hf and lf capacitance versus bias).