Masahide Hayashi

Wafer-level two-step bonding process for combined sensor with two different pressure chambers

We developed a wafer-level two-step anodic bonding process for a combined sensor with two different pressure chambers: ambient and low vacuum pressure. This two-step bonding process features: a bonding and non-bonding area controlled with a glass bump array, an anodic bonding process with plastic deformation of the glass bumps at high temperature and high loading, and two different pressure chambers formed with a sequence of bonding processes.

Three-axis MEMS inertial sensor for automobile applications

A three-axis microelectromechanical systems (MEMS) inertial sensor measuring two-axis acceleration and angular rate (rotation) has been developed for an electronic stability control (ESC) system for automobiles. We combined the angular rate detection part with the two-axis acceleration detection parts on a single MEMS chip to miniaturize the sensor. The two detection parts were designed to work under different environmental pressures through a two-step wafer level package (WLP) process to achieve the required sensitivity for the gyroscope with excellent vibration immunity for the accelerometers. We report on the design concept and test results of the three-axis MEMS inertial combined sensor and the manufacturing processes of the two-step WLP and through-silicon vias (TSVs).

Deformation-robust gyroscope with 2.0-Hz frequency split variation over temperature range of −50 to 150°c

A micromachined deformation-robust gyroscope with only a 2.0-Hz frequency split variation over the temperature range for automobile applications was developed. Our design, which is a triangularly supported one-sided open frame with three sets of symmetrically arranged folded beams, dissipates and cancels the internal stress of springs caused by deformation. This suppresses the frequency variation between drive mode and sense mode (frequency split) over a wide range of temperatures. Experimental results showed that the proposed gyroscope has only a 2.0-Hz frequency split variation, which brings less than a 1% scale-factor change and an offset change that is 1.5% of the quadrature error.

MEMS Gyroscope With Less Than 1-deg/h Bias Instability Variation in Temperature Range From −40 °C to 125 °C

We developed a gyroscope with less than 1-deg/h bias instability variation in a temperature range from −40 °C to 125 °C while performing around 4-deg/h bias instability. This stability was achieved by using the stable frequency separation between the drive and sense modes of a Coriolis vibratory gyroscope. To achieve this stability, the mechanical part was designed with a one-sided open frame to mitigate the variation of resonant frequencies caused by thermal stress. At the circuit level, we implemented a self-clocking architecture with a bandpass

Development of wafer-level-packaging technology for simultaneous sealing of accelerometer and gyroscope under different pressures

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Combined sensor and its fabrication method

analog-to-digital converter to maintain low quantization noise level over the operational temperature range. The fabricated gyroscope demonstrated a 2-Hz variation of frequency separation for an operational frequency of 18.5 kHz in the operational temperature range. At a system level, a bias instability variation of 0.9 deg/h in the temperature range while performing bias instability less than 4.21 deg/h was demonstrated. This low-noise variation is potentially beneficial for applications requiring a Kalman filter, such as GPS-denied navigation systems, that demands a precise and predetermined noise property.

Airbag system using three-dimensional acceleration sensor

This research demonstrates a newly developed anodic bonding-based wafer-level-packaging technique to simultaneously seal an accelerometer in the atmosphere and a gyroscope in a vacuum with a glass cap for micro-electromechanical systems sensors. It is necessary for the accelerometer, with a damping oscillator, to be sealed in the atmosphere to achieve a high-speed response. As the gyroscope can achieve high sensitivity with a large displacement at the resonant frequency without air-damping, the gyroscope must be sealed in a vacuum. The technique consists of three processing steps: the first bonding step in the atmosphere for the accelerometer, the pressure control step and the second bonding step in a vacuum for the gyroscope. The process conditions were experimentally determined to achieve higher shear strength at the interface of the packaging. The packaging performance of the accelerometer and gyroscope after wafer-level packaging was also investigated using a laser Doppler velocimeter at room temperature. The amplitude at the resonant frequency of the accelerometer was reduced by air damping, and the quality factor of the gyroscope showed a value higher than 1000. The reliability of the gyroscope was also confirmed by a thermal cyclic test and an endurance test at high humidity and high temperature.