Shih Jui Chen

Microelectromagnetic energy harvester with integrated magnets

This paper presents a microelectromagnetic power generator with integrated magnets that can be fabricated on silicon wafers in a batch process. The generator is fabricated by MEMS technologies and characterized at different vibration frequencies, amplitudes and load resistances. This compact generator occupies a volume of 15×13×0.4mm3, as no external permanent magnets are needed. Experimental results show that with a 20-turn spiral coil, the device can generate an induced electromotive force (EMF) of 0.27mV at a vibration frequency and amplitude of 350Hz and 10µm, respectively.

Multi-Cantilever-Driven Rotational Micrograting for MOEMS Spectrometer

For the purpose of detecting biological fluorescence, a rotational actuator with integrated diffraction grating is designed as the central part of a MOEMS spectrometer. In order to produce scanning with a lithographically defined micrograting, angular displacement is produced with multiple balanced beams placed in opposition around a semi-floating pivot point. Piezoelectrically driven, the beams rotate a suspended micro grating linearly with voltage, directly tuning the angularly spread spectral outputs. The design advantages, optimizations and fabrication are discussed. The fabricated actuator is used in a fluorescence scanning of paper cellulose fibers and Rhodamine B dye, and shown to be effective in rotating a diffraction grating for fluorescence spectroscopy.

Surface micromachined GHz tunable capacitor with 14:1 continuous tuning range

This paper reports a new simply-supported bridge structure and its use for GHz tunable capacitor application. Unlike traditional MEMS bridges with fully-clamped boundary condition (B.C.) at the anchors, the new bridge structure has simply-supported B.C. Through the implementation of a simply-supported bridge driven by two 100-mum-long ZnO-actuated cantilevers, a compact surface-micromachined tunable capacitor has been fabricated on a single chip without any warping, and shown to be capable of a 1,400% continuous tuning from 0.13 pF to 1.82 pF.

Surface micromachined, complementary-metal-oxide-semiconductor compatible tunable capacitor with 14:1 continuous tuning range

This letter reports a surface micromachined, complementary-metal-oxide-semiconductor compatible tunable capacitor utilizing a simply supported bridge structure, unlike traditional microelectromechanical-system bridges that use fully clamped boundary condition at the anchors. Through the implementation of a simply supported bridge driven by two 100-μm-long ZnO-actuated cantilevers, a compact tunable capacitor has been fabricated on silicon without any warping and shown to be capable of a 1400% continuous tuning from 0.13to1.82pF.

The fabrication of 3D aspherical silicon microlenses using a shadow mask

This work explores a new technique for 3D aspherical Si microlens fabrication using a shadow mask. With the shadow mask, a convex aspherical SiO2 layer is sputter deposited on a Si wafer due to the anisotropy of deposition. The shape of the SiO2 is transferred to Si by DRIE to form the aspherical microlens. Microlenses with controllable apertures (0.4mm – 2mm in diameter) and focal lengths (1mm – 12mm) can be fabricated using this simple, mass-production compatible and cost-effective method. The optical simulation verified the focal effect of the lens, which can be applied to infrared optics. Furthermore, a self-focusing acoustic transducer is fabricated using the Si microlens as a mold, providing potential good self-focusing effect for actuations and sensing.

The sensitivity enhancement for the radiation sensor based on Film Bulk Acoustic-Wave Resonator

This paper describes the new design and material selection used to improve the sensitivity of ionizing radiation sensing with a zinc oxide based Film Bulk Acoustic-Wave Resonator (FBAR). Prior results [1] demonstrated that the parallel resonant frequency of the FBAR decreased after irradiation due to radiation-induced charge trapping in the SiN. Here, by employing Plasma Enhanced Chemical Vapor Deposited (PECVD) silicon nitride (SiN) within a two layer SiN configuration, we were able to increase the sensitivity by over two orders of magnitude. The maximum sensitivity of 2300 kHz/krad was demonstrated and is the highest radiation sensitivity of resonant sensors known to the authors.

Frequency-multiplexed combinatory mass sensing with single data line from multiple integrated film bulk acoustic resonators

This paper presents a novel array of four film bulk acoustic resonators (FBAR) having four distinct fundamental resonant frequencies that offers parallel and/or combinatory mass sensing of multiple chembio species, such as various proteins. To achieve the multiple resonant frequencies, we connect multiple FBARs (having slightly different resonant frequencies, thus each representing a unique sensor) in parallel, and form one FBAR (out of the multiple) on a chip. This way, when we measure the frequency shifts of the arrayed FBAR through a network analyzer, we have multiple resonant frequencies, each of which will change as a function of added mass (of chembio species), independent of the others.

Directional acoustic underwater thruster

This study describes a tested prototype for a controllable directional underwater thruster with no moving parts. During operation, a high-intensity acoustic wave creates directional water jets and the device moves itself in the opposite direction. When the underwater thruster moves along a non-vertical angle, it can produce straight backward thrust of 2.3 mN and lateral thrust of 0.6 mN in parallel with the device surface, with a total thrust-to-weight ratio of 2:1. To enhance the acoustic streaming effect, a self-focusing acoustic transducer (SFAT) with air reflectors is used to focus the acoustic wave.

Multilayered MOEMS Tunable Spectrometer for Fluorescence Lifetime Detection

Spectral and time-domain fluorescence from biological samples are powerful diagnostic tools. For applications requiring a compact integrated spectrometer, the microoptoelectromechanical system (MOEMS) is an enabling technology. To improve upon previous microspectrometers, a multilayered, folded design is taken here to improve theoretical resolution and throughput. This sub-cm3 prototype, based on MOEMS piezoelectric diffractive micrograting, demonstrates over 100-nm tuning in the visible range. Moreover, it integrates a microlens with f = 2.2 mm within a microoptics package that is fabricated at wafer-level. The microspectrometer capably records both spectral and lifetime information for fluorescence standards fluorescein isothiocyanate (FITC, 2.5 ns) and Rhodamine B (2.9 ns), and also Collagen Type II (2.4 ns).