Guoying Wu

The compatibility of ZnO piezoelectric film with micromachining process

Abstract This paper presents the compatibility of ZnO piezoelectric films with the process of micromachining. As a reactive material, ZnO films are sensitive to temperature, acids, bases, and even water. These films may easily be damaged in the subsequent process steps. Therefore, different from most of the present investigations that focus on how to fabricate ZnO films with good performance, this paper discusses how to protect ZnO films against degradation in subsequent micromachining processes. The main micromachining processes related to ZnO films, including cleaning, photolithography, etching, photoresist stripping, metal layer patterning, passivation and dielectric layer deposition, and reaction ion etching (RIE), are investigated. How these subsequent micromachining processes change ZnO films performance and how to minimize or avoid such performance changes is presented. Some suggestions about the subsequent micromachining process steps are given.

A bulk micromachined vibratory lateral gyroscope fabricated with wafer bonding and deep trench etching

Abstract A bulk micromachined vibratory lateral gyroscope, which is fabricated with Silicon-glass wafer bonding and deep trench etching, has been developed. By using entirely symmetric springs, drive mode and sense mode frequencies of the gyroscope are matched precisely, which is important to improve sensitivity. The gyroscope has a large mass and capacitance, and its thermal–mechanical noise floor is estimated to be about 0.05°/h/Hz1/2.

Bulk micromachined relay with lateral contact

A bulk micromachined relay has been developed with silicon-glass wafer bonding and deep reactive ion etch technologies. The microrelay has a lateral contact structure, and it is laterally driven by electrostatic actuators. The processing is very simple, and only two masks are used. To fulfill different demands, we designed various structures of the microrelay including sizes, contact structures and actuating structures. The mechanical structures are made by single-crystal silicon, which has perfect mechanical performance. Using sputtered gold as contact materials, the measured contact is below 1 Ω.

Design and fabrication of a highly symmetrical capacitive triaxial accelerometer

A monolithic capacitive triaxial accelerometer using a highly symmetric quad-beam structure with a single seismic mass is developed. The structure of the accelerometer is analysed in detail theoretically and numerically. Static and modal simulations with a finite element method simulator are done to analyse the mechanical response at accelerations of different directions. The simulated results show that the accelerometer can sense triaxial acceleration separately and synchronously. It has sensitivities of about 7.66, 6.08 and 6.08 fF g-1 in the z-axis, x-axis and y-axis, respectively, and has nearly zero cross-axis sensitivity theoretically. Moreover, some design optimizations are made to improve its performance. Finally, the fabrication and the basic performance of the device are presented.

Silicon–glass wafer bonding with silicon hydrophilic fusion bonding technology

Abstract Silicon–glass wafer bonding is realized with silicon hydrophilic fusion bonding technology. Tensile strength testing shows that the bonding strength is large enough for most applications of integrated circuits and transducers. The bonding strengths of 4 in. 525 μm thick #7740 glass–4 in. 525 μm thick silicon and of 1.5 in. 1000 μm thick #7740 glass–2 in. 380 μm thick silicon are larger than 9 MPa both with an annealing temperature of 450°C.

Silicon micro-accelerometer with mg resolution, high linearity and large frequency bandwidth fabricated with two mask bulk process

Abstract This paper presents a new kind of laterally capacity sensed accelerometer fabricated with silicon/glass anodic bonding and the inductively coupled plasma (ICP) high aspect ratio etching. The fabrication technology only needs two masks and it does not need aligning bonding technology. The process yield can be higher than 90% even after package. The accelerometer fabricated with this technology shows a sensitivity of 1.85 V/g (0.6 V p–p ), a linear coefficient of 99.9954% (−1× g to +1× g ), a linear frequency bandwidth of 800 Hz and a −3 dB frequency bandwidth of 1.45 KHz for open-loop application. The accelerometer has a noise floor of 0.33 mg at 1.6 Hz. The accelerometer can also at least afford 4500 g shock acceleration of 0.2 ms duration. The micro-accelerometer fabricated with this technology may be suitable for batch fabrication.

Numerical calculation of electromigration under pulse current with Joule heating

Electromigration behavior under pulsed directional current (PDC) was investigated theoretically and experimentally. A vacancy diffusion equation under current stress was derived, and the relationship between vacancy concentration and time to failure was calculated numerically. The results show that if Joule heating is considered, the ratio of lifetime under PDC to that under DC is less than what was reported by other authors. In addition, the dependence of the lifetime on duty ratios and frequencies of PDC is not the same in different regimes of PDC frequencies. The analytical equation describing the relation between MTF/sub PDC/ and MTF/sub DC/ in the entire regime of frequencies, including Joule heating, is given. All calculated results are compared to experimental results.

An SOI–MEMS technology using substrate layer and bonded glass as wafer-level package

Abstract We have developed a novel (silicon-on-insulator (SOI), microelectromechanical systems (MEMS)) SOI–MEMS technology combined with anodic bonding process. A metal layer on the glass substrate can provide out-of-plane electrodes and interconnects. More importantly, a wafer-level package of mechanical structures constructed by the top layer of the SOI wafer can be formed by the glass substrate and the substrate layer of the SOI wafer simultaneously. The package can protect fragile mechanical structures during post-release processes, such as dicing, mounting and wire bonding as an ordinary IC wafer. In addition, the wafer-level package can directly provide a specialized package, such as a vacuum package for gyroscopes. No special process other than micromachining is needed.

A novel isolation technology in bulk micromachining using deep reactive ion etching and a polysilicon refill

Isolation and interconnection of microstructures are important for microelectrical-mechanical system technology, because a microstructure generally acts as both a mechanical unit and an electric unit. In this work, we have developed a novel isolation technology for a bulk micromachining process using DRIE (deep reactive ion etching) and wafer bonding technology, which has gained importance in recent years. The technology combines DRIE and polysilicon refill technologies. A series of polysilicon bars covered by thermal oxide serves as the isolation structure. The structure can be used for flexible or rigid connection between two moveable microstructures or between a fixed structure and a moveable microstructure. The measured isolation and mechanical performance is good enough to realize its function.

Silicon/glass wafer-to-wafer bonding with Ti/Ni intermediate bonding

Abstract This paper presents silicon/glass wafer-to-wafer bonding with Ti/Ni intermediate at annealing temperature 440°C. Good adhesion between the wafers has been achieved as measured by tensile strength testing. The reason is that silicon reacts with nickel and forms nickel silicide at 440°C and Ti has good adhesion on SiO 2 even at room temperature. The annealing at 440°C enhances the adhesive quality of Ti on glass. The formed nickel silicide at the interface is NiSi from the analyses of X-ray diffractometer spectra and Auger electron spectrum surveys. Because the Ti/Ni film has a low resistivity, the bonding area can also be used as the electric interconnection.