Yilong Hao

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.

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.

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.

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.

Study on the application of silicide in surface micromachining

In this paper, we have applied silicide in surface micromachining technology to reduce the series resistance in devices, thus improving the dynamic performance of MEMS devices, especially for RF MEMS components. The compatibility with silicide for micromachining technology, improvement in resistance by using silicide and the issue of residue stress is studied. The experimental results show that CoSi2 and PtSi are good candidates for the grounded polysilicon layer and structural polysilicon layer respectively. After silicide is applied, the sheet resistivity becomes less than 2.0 from 200 Ω/ for the grounded polysilicon layer, and 2.5 from 60 Ω/ for the structural polysilicon layer respectively.

Low Temperature Silicon Wafer‐to‐Wafer Bonding with Nickel Silicide

A new low temperature silicon wafter-to-wafer bonding with nickel silicide at an annealing temperature of 440°C is presented. Good adhesion between the wafers has been achieved as measured by tensile strength testing, and observed by scanning electron microscopy. The bonding area percentage, measured by ultrasonic testing, is larger than 90%. The nickel silicide formed at the interface is NiSi, as observed by X-ray diffraction and Auger electron spectroscopy. The bonded pairs show good contact characteristics.

Fabrication and characterization of torsion-mirror actuators for optical networking applications

Abstract Novel torsion-mirror actuators with monolithically integrated new fiber holding structures, which can feature self-fixing and self-aligning of optical fibers, are fabricated in regular silicon wafers as well as in SOI wafers by using the mixed micromachining based on the surface and bulk silicon microelectronics. The electromechanical performances of the actuators and the optical properties of their micro-mirrors are investigated experimentally and theoretically. The electrostatic yielding voltages for driving the micro-mirrors of the actuators to tilt from 0° to 90° spontaneously are in the range of 270–290xa0V and the minimum holding voltages for keeping the tilting angle of the mirrors to be in 90° are found 55xa0V or so when the thickness of the torsion-beams suspending the mirrors is about 1xa0μm. Theoretical analysis manifests that the yielding voltage is most sensitive to the beam thickness among the series of design parameters about the torsion-mirror actuator structures. The micro-mirrors of the actuators can cyclically vibrate 10 8 times at least between 0° and 90°, and their shortest actuating time can reach an estimated less than 2xa0ms. The surface roughness and its distribution of the micro-mirrors of the actuators are small and smooth, respectively, which is acceptable for wavelength division multiplexing applications basically.