This paper presents the first 3-axis MEMS gyroscope that employs intermittent free vibration realized by a "Catch-and-Release (CR)" method. While CR enables drive power reduction and instant start-up, its application to multi-axis tuning-fork (TF) gyroscope is not straightforward, since the increased degrees-of-freedom is likely to induce hazardous beat during the free vibration. To prevent this, a pantograph structure is introduced, in which drive motion is constrained by fixed-length joints, thereby eliminating the spurious beat. The fabricated gyroscope shows 3-axis sensitivities of 0.3-0.6 aF/dps and <2% cross-axis sensitivities. The consecutive CR operation with a release DC voltage at 25 V and a high Q factor of 440k at 20 kHz of pantograph mode are confirmed.

In this study, we investigated PdCuSi metallic glass (MG) as a sensing material for capacitive MEMS hydrogen sensors. We first confirmed by film analysis that the fabricated PdCuSi film was MG and that it had a trigonal prism cluster. The measured pressure-composition-temperature curve of PdCuSi MG exhibited no hysteresis during hydrogen absorption and desorption. The response time was found to become faster by two orders of magnitudes compared with that of Pd polycrystal. These properties were attributed to the trigonal prism clusters. Strain was evaluated in the low hydrogen concentration regime of 0.05 vol% to 4.0 vol%, and the strain of PdCuSi MG was found to follow Sieverts' law well, indicating that hydrogen is present in the MG in a diffuse state. The hydrogen-concentration dependence of a capacitive MEMS hydrogen sensor was measured and hysteresis-free characteristics were obtained, implying advantages in hydrogen leak detection applications.

We present two new techniques effective in realizing high precision MEMS Rate Integrating Gyroscope (RIG). First one is the application of the Catch-and-Release (CR) scheme, reported previously, to the RIG. We show that continuous angle measurement can be attained by catching and releasing a pair of CR-RIGs in a complementary manner. Direct angle measurement is also demonstrated by adopting a doughnut-shaped CR-RIG. Second one is a resistive tunable damper that can compensate the damping asymmetry, a major cause of the angle drift. In this tunable damper, the mechanical damping factor can be tuned by resistance and voltage. We show that the theoretical model fits well with the experimental results.

This paper addresses a capacitive MEMS hydrogen sensor using Pd based metallic glass for future hydrogen society. Firstly, we investigate PdCuSi as Pd based metallic glass (MG) and show this material is promising for capacitive MEMS hydrogen sensor. Secondly, we apply the Pd based MG to a hydrogen sensor having inverted T-shaped electrode. The sensor was fabricated by a surface micromachining process. We show that the fabricated hydrogen sensor exhibits hysteresis free and fast response property at room temperature.

To compare Si and poly-SiGe as MEMS structural materials having 20 pm-thick, we fabricated a capacitive accelerometer on an 8-inch Si substrate using CMOS standard process and measured capacitance sensitivities of an identical sensor design. As a result, we found that the sensitivity of the SiGe sensor is 2.1 times larger than that of the Si sensor. We also confirmed that the SiGe sensor can attain lower noise level as well as lower power consumption, thanks to the higher mass density of SiGe and availability of CMOS-embedded SiGe MEMS structure. The results indicate that the poly-SiGe film is promising candidates for future CMOS-embedded sensor technology applications.

We show that PdCuSi metallic glass (MG) is a promising material for Pd-based capacitive MEMS hydrogen sensors, reducing both hysteresis and response time of the sensing operation. Firstly, we demonstrate that the fabricated PdCuSi MG film exhibits no hysteresis during hydrogen absorption and desorption. Drastic reduction of the response time is also shown. We also show that, to eliminate the hysteresis and to reduce the response time, PuCuSi needs to be MG, not microcrystal. Secondly, based on the measured strain property, we show that the capacitive sensing scheme has advantage in sensing low concentration hydrogens.

This paper presents the first intermittent free-vibration MEMS gyroscope enabled by a "Catch-and-Release (CR)" drive mechanism, which realizes substantial power reduction and fast startup compared to existing stationary gyroscopes. In this architecture, the proof mass is captured at the maximum displacement position (catch-state), and then released to free vibration during which the Coriolis detection is performed (release-state). Thanks to the high quality factor (Q) of 72000, the released mass can be re-captured before attenuation. This CR mechanism enables instant startup and low power. The functionality and sensitivity (21.2 mu V/dps) of a prototype CR gyroscope (CR-G) are confirmed by experiments.

This paper presents a novel MEMS gyroscope that employs intermittent free vibration and mode matching. An intermittent operation is realized by a "Catch-and-Release (CR)" technique, which enables significant reduction of the drive power. Sensitivities of the mode-matching and mode-split conditions are investigated by electrostatically tuning the sense-mode frequency. A sensitivity as high as 2.14 mV/dps, 52 times higher than the mode-split case, is obtained when the drive and sense frequency difference Delta f is reduced to 50 Hz. Optimization for mode matching and quadrature nulling is also demonstrated.

We present a practical method to evaluate gas permeability for thin polymer films using an encapsulated micro-electro-mechanical-system (MEMS) oscillator. Previously, we have developed a hermetic thin-film dome structure for RF-MEMS tunable capacitor, using conventional back-end-of-the-line (BEOL) processes. The dome is made of multiple layers including a polymer film, whose gas permeability is an important factor with respect to productivity and reliability. So far, it had been difficult to evaluate the gas permeability for such small and thin polymer films with sub-millimeter diameter and micron-scale thickness. In this evaluation method, the pressure dependence of air-damping oscillation is used to measure the permeability. As a demonstration, we carried out a permeability measurement of a 0.5-mm-diameter dome sealed with a thin (1 mu m) polymer film. The resulting permeability coefficient is found to be 1X10(-16) mol/m/Pa/s, at room temperature.

A high creep-immunity MEMS actuator is proposed for RF-MEMS tunable capacitor. The creep-immunity is attained using silicon nitride, SiN, for the spring portions, where the stress is concentrated. Compared with an aluminum spring, the creep-induced deformation is reduced by a factor of 23 at 100 degrees C. We also confirmed by a billion cycle test that the SiN spring does not develop a brittle fracture. (C), 2011 Elsevier B.V. All rights reserved.

Actuators used in RF-MEMS tunable capacitors have an issue of creep-induced deformation. The creep is caused by a ductile-metal beam which is indispensable to attain the low loss. To avoid this issue, we previously reported an actuator structure that uses a brittle material, silicon nitride (SiN), at the stress-concentrated spring portions [1]. The present paper aims to clarify a long-term creep immunity of the actuator. We first determined parameters of Norton's law by measurements and then carried out Finite Element Method (FEM) simulations. As a result, we found that the shift of the up-state capacitance is 2.2% after keeping the actuator in down-state position for 3 years at 85°C. © 2011 IEEE.

In this paper, we show an RF-MEMS tunable capacitor that achieves excellent creep immunity and high power-handling capability. The tunable capacitor has a quadruple series capacitor (QSC) structure. The measured result demonstrates +36dBm hot-switching at 85°C with 21V pull-in voltage. The creep immunity is attained by employing SiN spring at the stress concentrations. Compared with aluminum springs, the creep deformation is reduced by a factor of 23 at 100°C.

This paper presents an RF MEMS tunable capacitor that achieves an excellent power-handling property with relatively low actuation voltage. The tunable capacitor consists of two fixed MIM (Metal-Insulator-Metal) capacitors and two MEMS capacitor elements, all connected in series. This quadruple series capacitor (QSC) structure enables reduction of the actuation voltage without sacrificing the power-handling capability, since the MIM capacitor reduces the RF voltage amplitude applied to the MEMS capacitors. The measured result demonstrates +36dBm hot-switching at 85 degrees C with 21V pull-in voltage.

This paper presents the theoretical formulation of a lithographical bending control (LBC) method that uses lithographical degrees of freedom to control the bending of a multilayered beam. LBC is applied to a piezoelectric actuator that uses PZT as the piezoelectric material. The theoretical model is compared with measurements using a weakly fixed bridge structure suited for curvature measurement.

This paper reports a wafer-level package (WLP) encapsulation and a stacked multi-chip package (MCP) for electrostatically actuated MEMS variable capacitor and control IC chips. Since the MEMS capacitor needs to be operated in dry atmosphere, we developed the WLP encapsulation structure with four thin-film layers fabricated by conventional back-end-of-the-line (BEOL) LSI technologies. Furthermore, since a MEMS chip is actuated by a control IC chip that provides high voltage, we developed the stacked MCP to integrate the MEMS chip and the control IC chip. In order to handle relatively fragile WLP encapsulation, the stacked MCP process was optimized. The stacked MCP has 4.5×4.5mm size and 0.8mm thickness, which is the thinnest package for stacked MEMS and IC chips. Normal operation of the MEMS variable capacitor in the stacked MCP confirmed up to 85%RH after reliability tests, i.e. temperature cycling, accelerated moisture resistance, and moisture/reflow sensitivity.

In this paper, we report a thin-film encapsulation technology for wafer-level micro-electro-mechanical systems (MEMS) variable capacitor package. The electrical characteristics of MEMS are adversely affected by moisture. In order to prevent moisture from permeating into a package, the top surface was protected with a plasma-enhanced chemical vapor deposition (PE-CVD) SiN layer. The developed packages become a hybrid thin-film hermetic encapsulation consisting of an internal shell using PE-CVD SiO, a seal layer coating with resin, and an external protective layer formed by PE-CVD SiN. The process is fully compatible with standard low-cost back-end-of-the-line (BEOL) technologies for LSIs as a wafer-level package (WLP). This hybrid structure was very effective for protecting the MEMS device from external moisture. Moreover, the electrode surface area has to be wide, because a wide range of capacities is necessary in MEMS variable capacitors. We have developed a large (1480 × 1080 μm) hermetic thin-film encapsulation as WLP. ©2009 IEEE.

It is difficult to realize the built-in antenna for wideband systems, because a frequency bandwidth of the low profile antenna is narrow. A frequency tunable antenna is a technique for wideband characteristics. In this paper a low profile double resonance frequency tunable antenna using MEMS variable capacitors is presented. It has high efficiency over a wide frequency band. Through both resonant portions from 465 to 665 MHz, the efficiency of more than -4 dB and the VSWR of less than 3 are observed in the measurement using the variable capacitor of 0.4-0.9 pF.

An RF MEMS variable capacitor module with intelligent bipolar actuation (IBA) is implemented in a driver IC to prevent stiction in electrostatic actuators. The IBA eliminates the dielectric charging of the electrostatic actuator by detecting the charge trapped in the dielectric film and reversing the electric field orientation if it exceeds a set threshold. No failure is observed up to 108 cycles at 85°C. ©2008 IEEE.

We propose an intelligent bipolar actuation (IBA) method for electrostatic actuators, which can suppress stiction induced by dielectric charging. The high stiction immunity is achieved by flipping the bias voltage polarity depending on the pull-out voltage, thereby restricting the amount of charge stored in the dielectric film. (c) 2007 Elsevier B.V. All rights reserved.