Fusao Kohsaka

Development of Highly Integrated Quartz Micro-Electro-Mechanical System Tilt Sensor

In this paper, we report the research progress of a recently developed quartz micro-electro-mechanical system (MEMS)-based capacitive tilt sensor using bulk micromachining technology. The sensor, which is composed of a sensitive cantilever, proof mass and high-aspect-ratio vertical comb electrodes in wafer thickness, was fabricated using an anisotropic wet etching process on a 100-µm-thick z-cut quartz wafer. A ceramic package was designed for mounting the sensor and integrating the capacitance to a digital AD7746 circuit (Analog Devices). The sensor was mounted on the package using a flip chip method via a AuSn alloy solder. The dimensions of the integrated sensing system are 12 ×12 ×3.2 mm3 and the weight of the system is below 1 g. The measured typical sensor sensitivity is 632 fF/° when the applied voltage is 0.625 V. The peak-to-peak output signal drift is limited to 1 fF in 2 h. Good linearity was achieved in the range of ±1°. High-precision detection at 0.001°, which corresponds to micro-g acceleration, was also demonstrated.

A novel lift off process and its application for capacitive tilt sensor

This paper presents a novel bi-layer (top image resist Shipley S1808 and bottom liftoff resist LOL2000) lift off process for patterning 3D devices. Resists are coated and patterned with an overhang profile on substrate before it is etched and before the film deposition. The key feature of the new lift off process is to create a resist undercut profile, which should be deep enough to reduce step coverage and durable to aggressive substrate etchant. Two-step development method was demonstrated effective. The resist profile is optimized by development time in the two step development process. Proposed lift off process was successively used for fabricating quartz based capacitive tilt sensor.

Characterization of a quarts MEMS tilt sensor with 0.001º precision

This paper presents the performance of recently developed MEMS capacitive tilt sensor. The capacitive sensor, which can be considered as a static accelerometer, is fabricated using bulk micromachining technique on a 100-μm-thick z-cut quartz wafer. High-sensitivity and low-noise are achieved with stable output performance in the range of ±1º. The performance evaluation was performed at the 0.625 V excitation voltage and 9.1 Hz data update rate. The typical sensitivity with good linearity is 403.5 fF/º, which corresponds to 23.1 pF/g and the typical RMS noise is 74 aF, which corresponds to 25 aF/vHz (0.9 μg/vHz) noise floor. High-precision measurement of 0.001º has been demonstrated.

Development of optimal electroplated platinum-black catalyst for quartz hydrogen sensors

A catalytic combustion type hydrogen sensor using quartz resonator with electroplated platinum-black catalysts was developed to provide high sensitivity and high reliability. In the previous work, because of catalysts pasted on the electrodes, Q-factor of the quartz resonator was decreased seriously. This paper is discussed about the fabrication method of platinum-black catalysts, which is able to realized excellent hydrogen sensitivity, and high Q-factor of resonator. As an experimental result, the highest Q-factor and the highest sensitivity were obtained by the platinum-black catalyst with thickness of around 100 nm.