In the course of this work the requirements for a both effective and efficient small-signal simulation mode have been identified. The respective features have been implemented in the general-purpose device/circuit simulator MINIMOS-NT, which provides now various small-signal capabilities for two- and three-dimensional device/circuit simulations. Among them are not only basic features like complex-valued excitations of the devices, but also extended ones which can be used to extract various figures of merit. Besides the correct and efficient implementation, the usability of the new features was an important issue.
Since the small-signal mode is based on the
approach, one
complex-valued linear equation system has to be assembled and solved for each
frequency step. The respective modules have been equipped with all necessary
features to handle both real-valued and complex-valued systems. They have been
extended to be generally applicable for all kind of simulations. The solving of
linear equation systems accounts for a large share of the simulation time. For
that reason, alternative solver systems with external modules among them, have
been integrated or coupled to the solver module. These modules, which take all
identified numerical requirements of semiconductor simulations into account,
are employed also by other simulators. In order to efficiently use new
available hardware architectures, parallelization strategies have been
discussed. Future developments in this area should focus on further
parallelization of the solver algorithms itself, but also of suitable parts of
the simulator code.
Basically, the implemented small-signal capabilities can be employed for a wide set of semiconductor device structures. Thus, the simulation of advanced RF CMOS transistors or devices with compound semiconductors is now possible in a straightforward way. In addition, higher-order transport models are directly applicable for small-signal simulations. The new simulation mode was used to describe the properties of different device structures and circuits. In the course of this work, two different heterojunction bipolar transistors based on the InGaP/GaAs and SiGe material system were analyzed. In addition, two amplification circuits and a Colpitts oscillator have been simulated by means of mixed-mode device/circuit simulation. Furthermore, an advanced RF silicon carbide MESFET was investigated and higher-order transport models were compared for several double-gate MOSFETs.
From the engineer's perspective, additional features of the simulator might be useful, for example the extraction of noise and linearity parameters. In addition, the large-signal simulation capabilities, which are now possible by means of transient simulations, could be extended by introducing a harmonic balance simulation mode. With respect to performance the on-going parallelization efforts of the various solvers are particularly interesting. In addition, platform-specific optimizations can be utilized. Due to the availability of drastically increased memory resources, also modules based on full matrix storages become more and more interesting. For that reason, the integration of the external LAPACK and BLAS routines might be useful. In order to make the solver module even more attractive for alternative simulators, the integration of solvers, including in-house codes, for symmetric matrices might be interesting.