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We describe a new analytical model of a Heterostructure Field Effect Transistors (HFETs) that accounts for electron trapping in the gate-drain spacing of the device and for related non-ideal device behavior. Under conditions of a very strong trapping, the electron velocity saturates outside the gate, in the trapping region, and the negative trapped charge leads to relatively large differential output conductance at the drain voltages exceeding the knee voltage. Also under the conditions of severe trapping, the negative trapped charge leads to the positive offset of the output current-voltage (I-V) characteristic. The model describes quite well numerous experimental data for passivated and unpassivated AlGaN/GaN HFETs with and without field plates (FP) under different bias conditions.

A quantum-mechanical model, by combining the quantum mechanical carrier distribution and short channel effects (SCEs) with the classical carrier transport is used to predict the I–V characteristics at sub-90 nm technology nodes. I–V characteristics of 90, 65, and 45 nm for developed model are benchmarked. The analysis of SCEs, namely, velocity saturation, mobility degradation, and threshold voltage shift, has been carried out in this paper for these technology nodes. The detailed physical view of the variation of these effects with channel length (L) and drain voltage (V_ds) has been presented. Also, the impact of including these effects in I–V equations of nanoscale MOSFETs is included in the paper. The observations presented in this paper will help in developing a clear understanding of physical behavior of nanoscale MOSFETs.

The primary focus of a structural shake table system is the accurate reproduction of acceleration records for testing. However, many systems deliver variable and less than optimal performance, particularly when reproducing large near-field seismic events that require extreme table performance. Improved identification and control methods are developed for large hydraulic servo-actuated shake table systems that can exhibit unacceptable tracking response for large, near-field seismic testing. The research is presented in the context of a 5-tonne shake table facility at the University of Canterbury that is of typical design. The system is identified using a frequency response approach that accounts for the actual magnitudes and frequencies of motion encountered in seismic testing. The models and methods developed are experimentally verified and the impact of different feedback variables such as acceleration, velocity and displacement are examined.

The methods show that shake table control in testing large near-field seismic events is often a trade off between accurate tracking and nonlinear velocity saturation of the hydraulic valves that can result in severe acceleration spikes. Control methods are developed to improve performance and include both acceleration and displacement feedback to reduce the acceleration spikes, and record modification, where the reference signal is modified to conform to the shake table's operational parameters. Results show record modification gives exact tracking for near-field ground motions, and optimal system response for reference signals with velocity components greater then the system capabilities. Overall, the research presents a methodology for simple effective identification, modelling, diagnosis and control of structural shake table systems that can be readily generalised and applied to any similar facility.

RC and transit-time delays in a nanocircuit, where the resistor is a few nanometers in length, are evaluated taking into account the velocity and current saturation and applied to RC switching delay in InGaAs heterojunction field effect transistor (HFET). Transit time delay is the dominant factor in the ohmic regime where the applied voltage V is less than the critical voltage V_c for the onset of nonlinear nonohmic behavior. However, RC time constant is predominant in the nonohmic regime and increases linearly with the applied step voltage. The power in the nanocircuit is smaller and rises linearly in the nonohmic regime as compared to the quadratic behavior in the ohmic regime.

We describe a new analytical model of a Heterostructure Field Effect Transistors (HFETs) that accounts for electron trapping in the gate-drain spacing of the device and for related non-ideal device behavior. Under conditions of a very strong trapping, the electron velocity saturates outside the gate, in the trapping region, and the negative trapped charge leads to relatively large differential output conductance at the drain voltages exceeding the knee voltage. Also under the conditions of severe trapping, the negative trapped charge leads to the positive offset of the output current-voltage (I-V) characteristic. The model describes quite well numerous experimental data for passivated and unpassivated AlGaN/GaN HFETs with and without field plates (FP) under different bias conditions.