Pei-Zen Chang

Piezoelectric MEMS generators fabricated with an aerosol deposition PZT thin film

In this paper, we present the development of two piezoelectric MEMS generators, {3–1} mode and {3–3} mode, which have the ability to scavenge mechanical energy of ambient vibrations and transform it into useful electrical power. These two piezoelectric MEMS generators are of cantilever type made by a silicon process and which can transform mechanical energy into electrical energy through its piezoelectric PZT layers. We developed a PZT deposition machine which uses an aerosol deposition method to fabricate the high-quality PZT thin film efficiently. Our experimental results show that our {3–1} mode device possesses a maximum open circuit output voltage of 2.675 VP-P and a maximum output power of 2.765 µW with 1.792 VP-P output voltage excited at a resonant frequency of 255.9 Hz under a 2.5 g acceleration level. The {3–3} mode device possessed a maximum open circuit output voltage of 4.127 VP-P and a maximum output power of 1.288 µW with 2.292 VP-P output voltage at its resonant frequency of 214 Hz at a 2g acceleration. We also compared the output characteristics of both the {3–1} mode and the {3–3} mode piezoelectric MEMS generators which were both excited at a 2g acceleration level.

A low actuation voltage electrostatic actuator for RF MEMS switch applications

This paper presents the design, fabrication and characterization of an RF MEMS switch. Low actuation voltage and high isolation of the switch were achieved by exploiting buckling and bending effects induced by well-controlled residual stress. The effects of residual stress on improving the switch performance have been investigated using both analytical and numerical methods. The proposed RF switch has been fabricated by surface micromachining. The minimum actuation voltage of the fabricated switch was measured to be 10.2 V. At a 5 GHz signal frequency, the measured insertion loss and isolation are 0.21 dB and −44 dB, respectively. These results demonstrate that low voltage and high isolation of RF MEMS switches can be achieved with proper utilization of residual stresses.

Fabrication of a micromachined optical modulator using the CMOS process

This paper presents a new micromachined optical modulator design with electrostatic actuation fabricated by the conventional complementary metal-oxide semiconductor (CMOS) process. The modulator is operated by the interaction of the fixed part, stationary gratings and the movable part, sliding gratings. The period of the gratings varies with the slide of the movable part, thereby allowing different diffraction patterns of the reflected light. In addition, 100% modulation in the first order can serve as an optical switch. All procedures following the CMOS process merely require a simple post-process with maskless etching. With different profiles of the shape and sacrificial layer, two types of modulator are developed to obtain a high-aspect ratio and high efficiency of modulation, respectively.

A CMOS surface micromachined pressure sensor

Abstract A capacitive pressure sensor has been implemented by the industrial standard 0.8μm CMOS (Complementary metal oxide semiconductor) process. The device layout follows the entire set of CMOS IC (Integrated circuit) design rules. The sensing capacitor of the capacitive pressure sensor is composed of the upper metal (metal 2) and the polysilicon layer. The lower metal layer (metal 1) serves as the sacrificial layer. After completing the standard CMOS process, three CMOS‐compatible post‐processing steps were applied. First, phosphoric acid was used to etch the sacrificial layer to release the membrane of the capacitive pressure sensor. Second, PECVD (Plasma enhanced chemical vapor deposition) nitride was utilized to seal all access holes. Finally, RIE (Reaction ion etching) was used to remove nitride on the membrane. The dimensions of the capacitive pressure sensor are 1.0mm×0.9mm. This pressure sensor operates linearly in the range of 0 ∼ 200kPa, and the sensitivity is 0.07mV/kPa.

The method for integrating FBAR with circuitry on CMOS chip

A method is described to integrate a 3/spl times/2 ladder type film bulk acoustic wave (FBAR) filter on a CMOS chip. The modified Mason equivalent circuit model is used to simulate the FBAR characteristics. The filter is designed by the insertion loss method to meet the requirements. A low noise amplifier (LNA) has been designed and manufactured by the UMC 0.18 /spl mu/m process. By the use of a post CMOS process, the FBAR filter structure can be realized on a CMOS chip. Finally, the mass loading frequency trimming method can adjust the center frequency of the FBAR. The feasibility of integration can be proved by this method.

Inverse Determination of Coupling of Modes Parameters of Surface Acoustic Wave Resonators

Extraction of coupling of modes (COM) parameters from the manufacturing process of a surface acoustic wave device (SAW) is important in practice. In this study, we employed an inverse algorithm to recover the COM parameters from the measured admittance of a one-port SAW resonator. For completeness, the COM equations, the P-matrix representation and the related COM parameters have been summarized. The admittance of a one-port resonator was derived based on the P-matrix representation. One-port and two-port SAW resonator filters were fabricated and the related responses were measured. The simplex method was then used to determine the COM parameters inversely. The recovered COM parameters of the one-port SAW resonator have been demonstrated to be applicable to simulate not only the frequency response of the one-port SAW resonator but also that of the two-port one.

The fabrication of silicon-based PZT microstructures using an aerosol deposition method

This paper presents a series of processes for fabricating lead-zirconate-titanate (PZT) microstructures on a silicon substrate. An aerosol deposition method was used to deposit PZT thick film at room temperature. The low temperature deposition enabled a special lift-off process for patterning thick PZT films using a THB-151N photoresist. The milling rate of THB-151N by PZT particles was found to be the same as the PZT deposition rate of 5 μm h−1. Using this patterning technique, complex configurations of PZT microstructures have been demonstrated. Suspended multi-layer PZT microstructures have also been realized in this work.

Applied electrostatic parallelogram actuators for microwave switches using the standard CMOS process

This paper presents the fabrication of a laminated-suspension microwave switch using a conventional 0.6 µm single polysilicon three metals complementary metal-oxide semiconductor process. The post-processing is completed with maskless dry etching. The micromachined microwave switch consists of two electrostatic parallelogram actuators, two T-type connectors and one coplanar waveguide on a p-type silicon substrate. The switch only requires a low dc voltage of around 18 V for electrostatic traction. The testing results of the microwave switch show that the insertion loss is 6.8 dB and isolation is -7.8 dB in the range 10-20 GHz. In addition to demonstrating the design and fabrication of the microwave switch, this paper summarizes the experimental results.

CMOS microelectromechanical bandpass filters

This work fabricates a laminated-suspension microelectromechanical filter, respectively, by a fully compatible CMOS 0.6 μm single poly triple metal (SPTM) process and CMOS 0.35 μm single poly quadri-metal (SPQM) process. Experimentally, due to the top metal layer being used as the etch-resistant mask during the subsequent dry etching. Therefore, this study performs maskless etching with plasma and obtains excellent results including high selectivity and full release of the structure. Additionally, the microelectromechanical filter can be driven by applying low-voltage of around 5 V and a measured center frequency of around 13.1 kHz and a quality factor of around 1871 were obtained for a single-comb resonator operated in air. The filter successful proposed herein has a monolithic integration capability with the relative electric circuits in the standard CMOS 0.35 μm process.

An approximate analytical solution to the pull-in voltage of a micro bridge with an elastic boundary

This paper derives an approximate analytical solution to the pull-in voltage of a micro bridge with elastic boundaries. The analytical model considers the elastic boundary effect, fringing field capacitance, residual stresses and the distributed flexibility of the bridge. The accuracy of the present approximate analytical solution is verified by comparison with the simulation results of commercial FEM packages and other published closed-form solutions as well as experimental measured data. The deviation of the present approximate analytical solution is within 5% for a wide beam and a narrow beam in a small deflection regime. The present approximate analytical solution has explicit physical meaning and is highly accurate for device design.