from the model-simulator for a 130nm technology
| What : The
tutorial shows, in a design example, how to estimate device parameters
for hand calculations from the device models supplied by the IC vendor,
in this case a commercial 130nm. (for very basic
knowledge on how to enter a schematic and on how to simulate it, see this first) Background : The BSIM model is a device-physics based model with lots of physical parameters. It has become an industry standard for MOS transistor modeling. The model accounts for threshold voltage reduction, channel length modulation, sub-threshold conduction, velocity saturation, mobility degradation, parasitic drain/source resistance, hot-electron effects, etc. Motivation : While the model is very useful for accurate simulations, it is not useful for simple estimates through hand calculations. In this tutor, we will simulate n & p devices to extract the approximate values for K and/or µCox, Vth, and lambda, from simulation results, for hand calculations. |
How
: Remember the simplified
saturation region Id expression. Assuming that Vth is constant for two
different current levels, we can make the below calculation for two
current levels Id1 and Id2 to have an expression for K (we have already
ignored the channel-lenght modulation effect, that is, lambda; this
would not effect the final result too much).
 So, if one sweeps Idc and plot it vs
Vgs for A diode-connected nMOS or pMOS device, almost a straight line
could be achieved. Selecting two points on this line and substituting
the values into the above formula must give a good approximation for
the values of K (and also of µCox).
One also can use the first formulae (by substituting the Id1 and Vgs1 or Id2 and Vgs2 values from the plot that we will produce) to extract Vth which is assumed to be the same for both the current-levels/formulae. |
Ok, here we go !..
