Chih-Hsiou Lin

Nitride-based light-emitting diodes with p-AlInGaN surface layers

We have prepared bulk p-AlInGaN layers and light-emitting diodes (LEDs) with p-AlInGaN surface layers by metal-organic chemical vapor deposition. By properly control the TMAl and TMIn flow rates, we could match the lattice constant of p-AlInGaN to that of GaN. It was found that surface of the LED with p-AlInGaN layer was rough with a high density of hexagonal pits. Although the forward voltage of the LED with p-AlInGaN layer was slightly larger, it was found that we can enhance the output power by 54% by using p-AlInGaN surface layer.

Nitride-based blue LEDs with GaN/SiN double buffer layers

GaN epitaxial layers and nitride-based multiquantum well light emitting diode (LED) structures with conventional single GaN buffer and GaN/SiN double buffers were prepared by metalorganic chemical vapor deposition. It was found that we could reduce defect density and thus improve crystal quality of the GaN epitaxial layers by using GaN/SiN double buffers. It was also found that we could use such a GaN/SiN double buffer to achieve more reliable nitride-based LEDs.

An Integrated Thermal Compensation System for MEMS Inertial Sensors

An active thermal compensation system for a low temperature-bias-drift (TBD) MEMS-based gyroscope is proposed in this study. First, a micro-gyroscope is fabricated by a high-aspect-ratio silicon-on-glass (SOG) process and vacuum packaged by glass frit bonding. Moreover, a drive/readout ASIC, implemented by the 0.25 μm 1P5M standard CMOS process, is designed and integrated with the gyroscope by directly wire bonding. Then, since the temperature effect is one of the critical issues in the high performance gyroscope applications, the temperature-dependent characteristics of the micro-gyroscope are discussed. Furthermore, to compensate the TBD of the micro-gyroscope, a thermal compensation system is proposed and integrated in the aforementioned ASIC to actively tune the parameters in the digital trimming mechanism, which is designed in the readout ASIC. Finally, some experimental results demonstrate that the TBD of the micro-gyroscope can be compensated effectively by the proposed compensation system.

Design, fabrication and performance characterizations of an integrated dual-axis tuning fork gyroscope

This paper deals with the design, fabrication and preliminary experimental characterizations of a novel integrated dual-axis tuning fork gyroscope (DTFG). The DTFG is fabricated by high-aspect-ratio silicon-on-glass (SOG) process and vacuum packaged by glass frit bonding. Furthermore, a CMOS drive/readout ASIC chip, which is fabricated by a 0.25 μm 1P5M standard CMOS process, is integrated with the fabricated DTFG by directly wire-bonding. The experimental results of DTFG demonstrate that the rate sensitivities of Z-axis and X-axis sense modes are 1.47 mV/DPS and 0.18 mV/DPS respectively and the associated R2-linearity are 0.9995 and 0.9996. The noise-floors are 0.030 DPS/ Hz1/2 and 0.247 DPS/Hz1/2 for Z-axis and X-axis sense modes respectively.

Active thermal compensation of MEMS based gyroscope

This paper presents a new thermal compensation system for low temperature-bias-drift (TBD) MEMS based gyroscope. The temperature-dependent characteristics of proposed micro-gyroscope are firstly investigated and discussed in this work. The absolute temperature of the gyroscope is obtained by the frequency synthesizer, which is implemented by field programmable gate array (FPGA), in the thermal compensation system. Besides, the digital trimming mechanism, which implemented in CMOS readout ASIC, is actively tuned by the frequency synthesizer such that the temperature-bias-drift of gyrosocpe can be compensated. The experimental results shows that the temperature resolution of thermal compensation system is about 0.2° and the TBD of the uncompensated and compensated gyroscope is about 0.47 DPS/° and ±0.02 DPS/°.

Design and experimental analysis for innovative wide bandwidth vibration sensor

An innovative design for capacitive wide bandwidth vibration sensor is proposed and verified by experiments in this work. Three-dimensional and high-g vibration motions can be individually detected by the proposed vibration sensor such that the other-axis effect can be reduced and the sensitivity can be enhanced. The shock absorb mechanisms, i.e., fixed-fixed beam stopper and cantilever beam stopper, are employed against the external shock acceleration so that the damage and stiction can be prevented. In addition, the readout circuit calibrated the gain and offset of the output signal which can improve the signal to noise ratio. By a series of experiments, the width and height of fabricated element are 2.45mm and 2.55mm, respectively. The bandwidths are about 15kHz/15kHz/ 10kHz with respect to X-/Y-/Z-axis, respectively. The element sensitivities of the sensor are about 0.113fF/g, 0.113fF/g and 0.095fF/g, respectively. Furthermore, the 10kG shock acceleration can be successfully absorbed by the proposed shock absorb mechanisms.

A miniature triaxial tactile sensor with calibratatele readout circuit

Industrial robot needed touch sensor to enhance the accuracy of the assembly and fabrication. In this paper, we designed and fabricated a novel tri-axial capacitive tactile sensor which can detect normal force and shear forces, simultaneously. The sensor consisted of a polymer bump, MEMS membrane, and readout circuit. The element of the sensor had individual sensing electrodes and polymer bump which can reduce the other-axis effect and enhance the sensitivity. The readout circuit calibrated the gain and offset of the output signal which can improve the error by the manufacture. The width and height of fabricated element are 950μm and 760μm, respectively. The measured sensitivities of the sensor with the calibratable readout circuit are 159 and 135mV/mN for the normal and shear force, respectively. The maximum other axis effect is 8.6% in the detection of normal force.

Electrowetting optical beam refractor

This paper systematically studies and demonstrates how to lower the operating voltage for an electrowetting optical beam refractor (EOBR). The results indicate that a low operating voltage can be achieved by decreasing the thickness of the dielectric layer and employing a higher dielectric constant, together with reducing the interfacial surface tension between the electrolyte and the surrounding ambient phase. The goal of this study was to explore various approaches to achieving a low operating voltage. First, two kinds of fluoropolymers (Teflon®AF1601 and Cytop®CTL-809M) were utilized to confirm the wettability. Second, Si3N4 dielectric layer with different thickness were tested to confirm the thickness and dielectric constant effect. Finally, three different surfactants (sodium dodecyl sulfate (SDS), Triton X100 and Triton X15) were used to confirm the interfacial surface tension effect. In this article, We demonstrate that the contact angle of water can change as much as 80° in a dodecane/water/Cytop®/Si3N4 system (containing 1% SDS) with an applied voltage as low as 14 V; furthermore, switchable apex angles of ≃± 20° and deflection of a beam passing through the meniscus of EOBR are presented.