A Novel Z-Axis Accelerometer With Perfectly-Aligned, Fully-Offset Vertical Combs Fabricated Using The Extended Sacrificial Bulk Micromachining Process

Abstract

This paper presents a novel z-axis accelerometer with perfectly aligned vertical combs fabricated using the Extended Sacrificial Bulk Micromachining (ESBM) process. The z-axis accelerometer is fabricated using only one (111) SOI wafer and two photo masks without wafer bonding or CMP processes as used by other research efforts that involve vertical combs. In our process, there is no misalignment in lateral gap between the upper and lower comb electrodes, because all critical dimensions including lateral gaps are defined using only one masks. The fabricated accelerometer has the structure thickness of 40 μm, the vertical offset of 15 μm, and lateral gap between electrodes of 4 μm. Torsional springs and asymmetric proof mass produce a vertical displacement when an external z-axis acceleration is applied, and capacitance change due to the vertical displacement of the comb is detected by charge-to-voltage converter. The signal-to-noise ratio of the modulated and demodulated output signal is 80 dB and 76.5 dB, respectively. The noise equivalent input acceleration resolution of the modulated and demodulated output signal is calculated to be 500 μg and 748 μg. The scale factor and linearity of the accelerometer are measured to be 1.1 mV/g and 1.18 % FSO, respectively. The measured bandwidth is more than 100 Hz.