A new 4H silicon carbide metal semiconductor field-effect transistor (4H-SiC MESFET) structure with a buffer layer between the gate and the channel layer is proposed in this paper for high power microwave applications. The physics-based analytical models for calculating the performance of the proposed device are obtained by solving one- and two-dimensional Poisson's equations. In the models, we take into account not only two regions under the gate but also a third high field region between the gate and the drain which is usually omitted. The direct-current and the alternating-current performances for the proposed 4H-SiC MESFET with a buffer layer of 0.2 μm are calculated. The calculated results are in good agreement with the experimental data. The current is larger than that of the conventional structure. The cutoff frequency (fT) and the maximum oscillation frequency (fmax) are 20.4 GHz and 101.6 GHz, respectively, which are higher than 7.8 GHz and 45.3 GHz of the conventional structure. Therefore, the proposed 4H-SiC MESFET structure has better power and microwave performances than the conventional structure.

With the integrated circuits processing stepping into nanometer scale, the interconnect Joule heat becomes significantly large. Based on the RLC π equivalent circuit, this paper proposes a novel accurate model to evaluate Joule heat power of interconnected line in VLSI. The shielding effect of the inductor and the non-ideal step stimulation are considered in the proposed model. The power consumption of a typical interconnected topology in 90 nm complementary metal-oxide semiconductor process is computed. The error between results of this proposed method and Hspice simulation is within 3% when the input signal’s delay time is within 1 ns. The proposed model can be used to estimate Joule heat consumption where rough heat control is needed, such as route structure in the network on chip.

Interconnect power and repeater area are important in the interconnect optimization of nanometer scale integrated circuits. Based on the RLC interconnect delay model, by wire sizing, wire spacing and adopting low-swing interconnect technology, this paper proposed a power-area optimization model considering delay and bandwidth constraints simultaneously. The optimized model is verified based on 65-nm and 90-nm complementary metal-oxide semiconductor (CMOS) interconnect parameters. The verified results show that averages of 36% of interconnect power and 26% of repeater area can be saved under 65-nm CMOS process. The proposed model is especially suitable for the computer-aided design of nanometer scale systems-on-chip.

The Raman shifts of Si—Si， Ge—Ge and Si—Ge in Si（1-x）Gex alloys are calculated by Keating model. The calculated Raman shifts are 40275，41339 and 38815 cm-1 when the concentrations of Ge are 01， 05 and 09 respectively. These results are consistent with the reported experimental results， which indicates the validity of the Keating model for obtaining the Raman frequency of strained materials by changing the elastic coefficients of stretching and compression and bond-bending interaction. The single-phonon scattering peak at 477029 cm-1 in amorphous silicon is obtained for the first time by Keating model, which is in agreement with the result of 4800 cm-1 from the literature, indicating that the atoms of amorphous silicon as a whole are stretched compared with that of crystalline silicon.

In this paper, experimental results are reported about the new Al0.25Ga0.75N/GaN high electron mobility transistor (HEMT) with a step AlGaN layer. The rule of 2DEG concentration variation with the thickness of AlGaN epitaxial layer has been applied to the new AlGaN/GaN HEMTs: The step AlGaN layer is formed at the gate edge by inductively coupled plasma etching, the 2DEG concentration in the etched region is much lower than the other parts of the device. A new electric field peak appears at the corner of the step AlGaN layer. The high electric field at the gate edge is decreased effectively due to the emergence of the new electric field peak, and this optimizes the surface electric field of the new AlGaN/GaN HEMTs. The new devices have the same threshold voltage and transconductance as the conventional structure, -1.5 V and 150 mS/mm. That means, the step AlGaN layer does not affect the forward characteristics of the AlGaN/GaN HEMTs. As the more uniform surface electric field distribution usually leads to a higher breakdown voltage (BV), with the same gate to drain length LGD=4 m, the BV can be improved by 58% for the proposed Al0.25Ga0.75N/GaN HEMTs as compared with the conventional structure. At VGS=1 V, the saturation currents (Isat) is 230 mA/mm for the conventional Al0.25Ga0.75N/GaN HEMT and 220 mA/mm for the partially etched Al0.25Ga0.75N/GaN HEMT (LEtch=4 m, LGD=4 m). The decrease of Isat is at most 10 mA/mm. However, as the BV has a significant enhancement of almost 40 V, these drawbacks are small enough to be acceptable. During the pulse I-V test, the current collapse quantity of the conventional structure is almost 40% of the maximum IDS(DC), but this quantity in the new devices is only about 10%, thus the current collapse effect in Al0.25Ga0.75N/GaN HEMTs has a significant remission for a step AlGaN layer. And as the high electric field peak at the gate edge is decreased, the effect of the gate electrode on electron injection caused by this electric field peak is also included. The injected electrons may increase the leakage current during the off-state, and these injected electrons would form the surface trapped charge as to decrease the 2DEG density at the gate. As a result, the output current and the transconductance would decrease due to the decreased electron density during the on-state. That means, with the region partially etched, the electron injection effect of the gate electrode would be remissed and the stability of Schottky gate electrode would be improved. In addition, due to the decrease of the high electric field at the gate edge, the degradation of the device, which is caused by the high electric field converse piezoelectric effect, will be restrained. The stability of the partially etched AlGaN/GaN HEMT will become better.