MICRO ACCELEROMETER AND MAGNETORESISTIVE (MR) SENSOR DIRECTLY FABRICATED ON A CERAMIC SUBSTRATE

The concept of micro-electro-mechanical systems (MEMS) sensors directly fabricated on a ceramic substrate, which can be used for a package of end product, was proposed. As demonstrations of the sensors directly fabricated on a ceramic package, an accelerometer and a magnetoresistive (MR) sensor are focused on, and their fabrications on a ceramic substrate is investigated. The accelerometer utilizes a fringe capacitance formed in a ferroelectric material. For this sensor, in stead of a previously used bulk PZT plate, a screen-printed BaTiO3 (BTO) film on a ceramic alumina substrate was herein employed. An accelerometer using a BTO film was practically fabricated. The sensitivity of it was estimated as 0.1 pF/g, which is degraded a little compare with the previously developed accelerometer using a PZT plate; however, the order is the same. The magnetoresistive (MR) sensor can detect not only x- and y-axes magnetic field intensities but also z-axis one, where all fields are based on the sensor coordinate system. Namely, not only azimuth but also angle of elevation of the sensor can be detected from triaxis components of geomagnetic field. The principle is as follows: a permalloy (FeNi) plate is stood aside MR element. The plate distorts magnetic field and generates x- (or y-) component from originally z-directional field. So, the resistance of MR element changes in proportional to z-axis field intensity, provided that other axes intensities are kept constant.