Surface micromachined accelerometer using ferroelectric substrate

In this paper we describe a new accelerometer using ferroelectric material having a large dielectric constant, such as bulk PZT (ɛr = 2600). The measuring principle is detection of the capacitance change caused by the dielectric mass movement in the fringe electrical field. Considering practical fabrication, ferroelectric material is used for the substrate instead of the suspended proof mass. Since capacitance is increased electrically, and not mechanically, it is expected that the sensitivity will be considerably increased while retaining mechanical stiffness. This has the advantage of preventing touch down of the proof mass, and increasing the allowable measuring range of acceleration. The basic principle and the effectiveness of the proposed sensor are confirmed by both the theoretical calculation using an approximate model, and the finite element method (FEM) simulation. A practical sensor device was fabricated with basically only surface micromachining. A preliminary characterization was carried out under atmospheric pressure, confirming linearity between the sensor output and the input acceleration. The sensitivity is increased considerably (∼1000) compared to our previous sensor using polymer Parylene material having a comparatively low dielectric constant (ɛr = 3.15).