Zhao Zhengping

Adaptive contact for improving the behavior of silicon MEMS switches

In this paper, the concept of adaptive contacts is proposed to reduce the tilting effect of MEMS switches resulting from the tolerance of the fabricating process. Using finite element analysis, two types of MEMS switches with adaptive contacts, including free-clamped and clamped-clamped structures, are designed and tested. The results are compared with the characteristics of a typical solid contact switch, which show that the pull-in voltage decreases from 40–60 volts to 15–25 volts after several initial collisions in the case of the free-clamped structure. The properties of the fabricated device show good agreement with the results obtained from finite element analysis.

Analytical Model and Simulation for AlGaN/GaN High Electron Mobility Transistor

Based on the charge control theory, a accurate analytical model of I-V characteristics for AlGaN/GaN high electron mobility transistor (HEMT) is presented considering the relationship between self-heating effect and polarization, electron mobility, velocity saturation, conduction band discontinuity, doping concentration, channel temperature. The comparison between simulations and physical calculation shows a good agreement. The model is simple in calculations, suitable for design of microwave device and circuit.

SOI-based radial-contour-mode micromechanical disk resonator

This paper reports a radial-contour-mode micromechanical disk resonator for radio frequency applications. This disk resonator with a gold plated layer as the electrodes, was prepared on a silicon-on-insulator wafer, which is supported by an anchor on another silicon wafer through Au-Au thermo-compression bonding. The gap between the disk and the surrounding gold electrodes is 100 nm. The radius of the disk is 20 μm and the thickness is 4.5 μm. In results, the resonator shows a resonant frequency of 143 MHz and a quality factor of 5600 in vacuum.

Ti/Al Based Ohmic Contact to As-Grown N-Polar GaN*

Ti/Al based Ohmic contacts to as-grown N-polar GaN are investigated by cross-section transmission electron microscopy and energy dispersive x-ray spectroscopy. Due to the higher oxygen background doping in the N-polar GaN, the Al metal in Ohmic stacks is found to react with background oxygen more easily, resulting in more AlOx. In addition, the formation of AlOx is affected by the Al layer thickness greatly. The AlOx combined with the presence of AlN is detrimental to the Ohmic contacts for N-polar GaN compared with Ga-polar GaN. With the reduction of the Al layer thickness to some extent, less AlOx and AlN are formed, and lower Ohmic contact resistance is obtained. The lowest contact resistivity ρ of 1.97 × 10−6 Ωcm2 is achieved with the Al layer thickness of 80 nm.

Large Signal Model of AlGaN/GaN High Electron Mobility Transistor

A accurate nonlinear large signal model was extracted in this paper. The model is capable of correctly modeling the DC characteristics of AlGaN/GaN HEMT. The parameters of model are obtained from a series of pulsed I-V characteristics and S parameters adopting the on-wafer testing technique and narrow pulse testing technology. The model is implemented in ADS software, simulations and measurements data show its availability and can be used for GaN MMIC’s designing.

Broadband MMIC Power Amplifier for X Band Applications

The large signal model of a PHEMT with total gate width 850μm is achieved by microwave on-wafer test and IC-CAP software, then the design and optimization of circuit are implemented by ADS software. A three-stage broadband power amplifier is designed with above model. At operation frequency from 6 to 18 GHz, the output power is over 33dBm, the power gain is higher than 19dB and the PAE is more than 25%. Otherwise, the power amplifier has better power gain flatness.

A compact serial RF MEMS switch for S-band application

This paper reviews the recent progress in MEMS for radio frequency (RF) switches. Several structures were designed, fabricated and tested in the background of S-band application. Among these structures a compact serial switch was presented in detail. The performance of 21.0 dB isolation and 0.5 dB insertion loss was demonstrated in a HP 85 10A vector Network Analyzer while mounted on a rf carrier.

As interstitials diffusion and its effects on native defects and electrical properties of undoped LECGaAs during annealing

Annealing has been carried out at 950/spl deg/C under various As pressure for undoped(ND) semi-insulating(SI) LECGaAs. The effects of the annealing on native defects and the electrical properties were investigated. The experimental results indicate that after a annealing at 950/spl deg/C for 14h under low As pressure, the Hall mobility decreases and the resistivity increases dramatically for the samples. These changes in electrical properties are due to the generation of intrinsic acceptor defects, and the generation of the intrinsic acceptor defects originates from the outdiffusion of As interstitial at high temperature. The generation of the intrinsic acceptor defects and these changes in electrical properties can be suppressed by increasing the applied As pressure during annealing.

Testing and analysis of lifetime of a vertical bulk MEMS switch

A single crystal silicon cantilever, bulk MEMS vertical switch is presented. Multi-way switches based on the above structure were fabricated for application in the area of computer aided testing. As the sticking point of MEMS switches, operating lifetime must be first considered. Dynamic testing was imposed on such a switch until its failure. Then analysis of the failure mechanism is given. As the conclusion, heat accumulation is demonstrated as the reason for failure.