5.5 Investigated Parameters
The fitting procedure described in this Chapter demonstrates the capabilities and limits of the simulation. Based on the presented example it is shown that the models described in Chapter 4 are flexible enough to simulate the transfer characteristics extremely well for VDS < 2 V and VGS < 0.8 V. Simultaneously the simulated CG(VGS) characteristics agree very well with data extracted from Sparameter measurements. This offers the capability of predictive simulations in the following technically important aspects.
A HEMT can be basically divided up into the epitaxial layers and the geometry including contacts defined by the process technology. Regarding the epitaxial layers the limits in indium content are given in Section 2.1. The doping, which depends extremely on the MBE growth, is optimized experimentally by Hall samples. Thus, for pseudomorphic GaAs-based HEMTs the optimization of the channel thickness as well as the indium and aluminum content is not in the focus of interest.
This is different for the geometry defined by process technology. Many trade-offs have to be made between the technological effort and device characteristics such as RF performance versus the cost of defining small gate structures. Many important characteristics can be optimized by considering gm max and the corresponding CG. The capabilities of predictive simulation of these and other related parameters will be demonstrated in the following Chapter.
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Helmut Brech 1998-03-11