Accelerometers

In this section, various acceleration sensing mechanisms are discussed. Among them, piezoresistive sensing needs standard IC processing and materials only, can be batch fabricated using inexpensive bulk micromachining, and does not require small gaps or precise gap control. Its major limitation is the large temperature sensitivity. Capacitive sensing has good temperature stability, high resolution, and low fabrication cost, but its performance is greatly affected by parasitic capacitance and it is also susceptible to EMI. Optical sensing is immune to EMI and no connecting wires are needed especially in an electrically noisy environment. Optical sensing also inherently has the capabilities of remote access and multiplexing. The challenge is the packaging as discrete optical components are involved. Piezoelectric sensing has large bandwidth and high resolution. It is also suitable for building resonant accelerometers because of its dual nature of actuation and force sensing. Its main limitation is poor DC response due to leakage. The use of non-IC materials also increases the fabrication cost. Tunneling accelerometers have the potential to obtain ultrahigh nano-g resolution, but the fabrication process is complicated and the tunneling tip height control is still challenging. Thermal sensing has very simple structures with no moving parts. It is also very inexpensive and completely foundry CMOS compatible, but its resolution and bandwidth are limited. Accelerometers can be fabricated in many different ways. The basic process modules include bulk micromachining, surface micromachining, wafer bonding, and DRIE. In most cases, the fabrication involves a combination of two modules or more. The majority of....