Impact ionization and thermionic tunnelling as two possible breakdown mechanisms in scaled pseudomorphic high electron mobility transistors (PHEMTs) are investigated by Monte Carlo (MC) device simulations. Impact ionization is included in MC simulation as an additional scattering mechanism whereas thermionic tunnelling is treated in the WKB approximation during each time step in self-consistent MC simulation. Thermionic tunnelling starts at very low drain voltages but then quickly saturates. Therefore, it should not drastically affect the performance of scaled devices. Impact ionization threshold occurs at greater drain voltages which should assure a reasonable operation voltage scale for all scaled PHEMTs.

The full-band Monte Carlo technique is currently the most accurate device simulation method, but its usefulness is limited because it is very CPU intensive. This work describes efficient algorithms in detail, which raise the efficiency of the full-band Monte Carlo method to a level where it becomes applicable in the device design process beyond exemplary simulations. The k-space is discretized with a nonuniform tetrahedral grid, which minimizes the discretization error of the linear energy interpolation and memory requirements. A consistent discretization of the inverse mass tensor is utilized to formulate efficient transport parameter estimators. Particle scattering is modeled in such a way that a very fast rejection technique can be used for the generation of the final state eliminating the main cause of the inefficiency of full-band Monte Carlo simulations. The developed full-band Monte Carlo simulator is highly efficient. For example, in conjunction with the nonself-consistent simulation technique CPU times of a few CPU minutes per bias point are achieved for substrate current calculations. Self-consistent calculations of the drain current of a 60nm-NMOSFET take about a few CPU hours demonstrating the feasibility of full-band Monte Carlo simulations.

MOSFETs with sub-0.1 µm gate length were fabricated, and their low temperature operation was investigated. The drain current for drain voltage of 2 V increased monotonously as temperature was lowered to 15 K without an influence of the freeze-out effect. Moreover, the increase in the drain current was enhanced by the gate length reduction. The hot-carrier effect at low temperature was also investigated. Impact-ionization decreased as temperature was lowered under the condition of drain voltage 2 V. The decreasing ratio was enhanced as gate length became shorter. We consider this phenomenon is attributed to the non-steady-stationary effect. As a result, device degradation by DC stressing was reduced at 77 K in comparison with room temperature. In the case of 0.1 µm MOSFET, drain current was not degraded in condition of DC stress with gate- and drain-voltage was 1.5 V.

We propose a nonlocal impact ionization model applicable for the drain region where electric field increases exponentially. It is expressed as a function of an electric field and a characteristic length which is determined by a thickness of gate oxide and a source/drain junction depth. An analytical substrate current model for n-MOSFET is also derived from the new nonlocal impact ionization model. The model well explains the reason why the theoretical characteristic length differs from empirical expressions used in a pseudo two-dimensional model for MOSFET's. The nonlocal impact ionization model implemented in a device simulator demonstrates that the new model can predict substrate current correctly in the framework of drift-diffusion model.

Optical and electrical measurements of thin film n-channel SOI-MOSFETs reveal that the exponential tail in photon emission spectra originates from electron-hole recombination. Bremsstrahlung radiation model as a physical mechanism of photon emission was experimentally negated. Negative threshold voltage shift at the initial stage of high field stress is found to be caused by hole trapping in buried oxide. Subsequent turnover characteristics is explained by a competing process between electron trapping in the front gate oxide and hole trapping in the buried oxide. As to the degradation of transconductance, generated surface state as well as trapped holes in the buried oxide which reduce vertical electric field in SOI film are involved in the complicate degradation of transconductance.

Impact ionization () in two n+-n--n+ device structures is investigated. Data obtained from self-consistent Monte-Carlo (SCMC) simulations of the devices is used to show that the average energy () of only those high energy electrons contributing to is an appropriate variable for the modeling of . A transport model allowing one to calculate is derived from the Boltzmann transport equation (BTE) and calibrated by the SCMC simulation results. The values of and the coefficient, αii, predicted by the proposed model are in good agreement with the Monte-Carlo data.

This study is concerned with modeling and analyzing a nonlinear elastomer impact phenomenon when a mass experiences a collision with the contact pad mounted on the underlying linear dynamic structure. The contact pad which consists of the viscoelastic elastomer is modeled here by a nonlinear contact stiffness and nonlinear contact damper. The underlying dynamic structure is measured by a Fourier spectral analyzer and its analytical form is utilized in modeling and analyzing the whole dynamic impact problem. The impact force profiles are predicted and analyzed in terms of pulse duration, time-to-peak force, and peak force. Finally, the damping mechanism and its hysteresis phenomena are also discussed.