Yoshiteru Omura

New resonant accelerometer based on rigidity change

We propose a new resonant accelerometer based on the principle of a resonator rigidity change caused by the applied acceleration. The rigidity change of the resonator consisting of parallel beams is induced by a change in its cross-sectional shape. The feasibility of this sensing principle was confirmed by FEM analysis. A frequency change rate of 10%/g was calculated, and the sensor was fabricated by surface micromachining technology using an SOI wafer. Furthermore, we confirmed that the double resonator structure which was designed based on the same principle had a lower cross-axis sensitivity.

An SOI 3-axis accelerometer with a zigzag-shaped Z-electrode for differential detection

We have developed a fully-differential 3-axis accelerometer with a novel zigzag-shaped Z-electrode, which is used for motion controls of automobiles and robots.

An SOI tactile sensor with a quad seesaw electrode for 3-axis complete differential detection

This paper presents a novel SOI capacitive tactile sensor with a quad-seesaw electrode for 3-axis complete differential detection, which enables integration with a CMOS. For differentially detecting 3-axis forces, the tactile sensor is composed of four rotating plates individually suspended by torsion beams. In this study, to demonstrate the working principle, we fabricated a test device that integrates an SOI substrate with the quad-seesaw electrode and an anodically bondable LTCC substrate with fixed electrodes as an alternative to the CMOS. The experimental results of the test device successfully demonstrated the working principle as well as 3-axis differential detection with a matrix operation.

Fully-integrated, fully-differential 3-axis tactile sensor on platform LSI with TSV-based surface-mountable structure

The present paper reports a 2.8-mm-square surface-mountable MEMS-on-LSI integrated 3-axis tactile sensor for robot applications, which incorporates sensing and signal processing in a single chip. The MEMS part has a quad-seesaw-electrode structure for fully-differential capacitive 3-axis force sensing. The LSI is an original sensor platform LSI equipped with deep annular-type through silicon vias (TSVs). A multi-project LSI wafer was processed after fabrication in an LSI foundry. The MEMS part and the LSI part were integrated by Au-Au thermocompression bonding. The output is a digital packet and is transferred through the TSV and a bus line. A working test successfully demonstrated the fully-differential capacitive 3-axis force sensing of the fully-integrated tactile sensor.

SOI 3-axis accelerometer with a stress reduction structure

We developed a novel stress reduction structure (SRS) for a capacitive SOI 3-axis accelerometer for the advanced motion control of automobiles and robots. To improve the stability of the sensor output against temperature change, an FEM thermal stress analysis was carried out on a model with a sensor chip, a circuit board, and a package. The FEM results showed that the thermal stress caused by the different coefficients of thermal expansion bent the sensor chip and produced a change in the z-electrode gap. The zero output drift especially in the Z-axis direction by sensor chip bending should be minimized. The SRS was composed of grooves in both the lower and upper Si layers around the detection part of the sensor. Two types of low-stiffness suspensions for stress reduction and for wiring were formed in either the upper or the lower Si layer to connect both sides of the grooves. The experimental results showed that the ratio of zero output drift decreased by a factor of 8.9 by using the proposed SRS.

A 2-axis gyroscope with a synchronously-driven dual mass

We report a detuned 2-axis yaw-and-roll gyroscope with a single sensor element. We designed and fabricated a novel structure composed of a synchronously driven dual mass and three types of supporting beams to limit the movable direction of each mass. The designed resonant frequencies agreed well with the measured values, which resulted in 2-axis detuning ratios of -0.7 and -2.2%. The fabricated gyroscope showed a cross-axis sensitivity of +/-2.7%. The test results demonstrated that the gyroscope simultaneously detects yaw and roll rates with low cross-axis sensitivity.

A DRIE compensation mask pattern for fabricating an extremely thick comb electrode

This paper reports a novel DRIE compensation mask pattern for fabricating an extremely thick sense-comb structure. When we attempted to fabricate a 300-μm-thick sense-comb structure to improve the sensitivity of a capacitive sensor, we found that a bridge-shaped silicon residue (bridge) prevented its formation. We first investigated the detailed property and where the bridge appeared by the DRIE. Based on these investigations, we propose a DRIE compensation pattern to remove the bridge. We successfully formed a 300-μm-thick sense-comb structure by adding the compensation pattern to a tip of the comb structure. Experimental results demonstrated the effectiveness of the proposed compensation pattern.

Quartz angular rate sensor for automotive control

A new quartz angular rate sensor has been developed for automotive controls. The principle of the sensor is detection of the Coriolis force with a vibrator An H shape vibrator supported with a stein at the center was used The vibrator supported at the center was good for the isolation of a small motion detecting angular rate from an extremely large excitation motion. A new mechanical coupling model and the FEM analysis were used to reduce output offset of the sensor. The detection range of the sensor is from -100 deg/s to 100 deg/s. The sensor output offset is small within /spl plusmn/ l deg/s. The developed quartz sensor satisfied required specifications and had wide temperature reliability. Further, the sensor has been successfully used onboard passenger cars.

Long-term hermetic vacuum wafer-level packaging with copper-tin thin films

Long-term hermetic vacuum wafer-level packaging (WLP) by bonding with copper-tin (CuSn) thin films is presented. By improving the pretreatment of bonding, the shear strength reached 74 MPa on average with a CuSn 150-μm-wide seal frame. Furthermore, the cavity fabricated by WLP under the optimized conditions maintained its vacuum for 1.8 years. The cavity pressure was directly measured without an extra vibratory element by an ultra-low outgassing residual gas analyzer (RGA) system. The RGA system revealed that the cavity pressure after 1.8 years was 407 Pa. The measured cavity pressure demonstrates that WLP with CuSn films can achieve remarkable vacuum hermeticity.

Silicon Angular Rate Sensor for Automotive Control with Open Beam Structure

An angular rate sensor of SOI (silicon on insulator) has been developed for automotive control. The sensor detects yaw rate of automobiles. The concept of the sensor design is the open beam structure (OBS). In the OBS, excitation and detection electrodes are open toward exterior bonding pads in a plane. The OBS has high independency between excitation and detection modes. The FEM analysis was carried out and the results showed the OBS was highly independent compared to other structures. This good feature contributed to the stability of vibration mode for the sensor. The OBS also made it possible to wire from the electrodes besides the mass to the exterior bonding electrodes with mono-layer silicon of the SOI. By means of the easy wirings the process and the packaging became simple. The sensor was fabricated by surface micro machining process to miniaturize the size. The measured characteristics show the OBS is suitable for angular rate sensor to be small, highly precise, and low cost