ABSTRACT
Micromachining mechanical sensors such as accelerometers, gyroscopes, tactile, angle, and force sensors are other types of devices where the technology of microporous and macroporous silicon formation can be applied (Howe 1988; Anderson et al. 1994; Bell et al. 1996; Kaienburg and Schellin 1999; Gardner et al. 2001; Yang et al. 2002; Ádám et al. 2004, 2008; French and Sarro 2012). As a rule, all these devices are based on the membrane and cantilever principles (see Figure 7.1), and technology of their fabrication involves a deep etch to produce viable devices. As it was shown before in Porous Silicon: Formation and Properties (Chapter 12) and in the Chapter 11 of this book, silicon porosification is efficient technology for such applications. In particular, technology based on silicon porosification eliminates the need of bulk micromachining (Bean 1978), which sometimes causes low yield and high cost. In addition, the use of silicon porosification allows increasing the sensitivity of mechanical sensors in comparison with sensors fabricated using conventional surface micromachining (Howe 1988). The resulting large separation between the beams and the substrate on porous silicon (PSi) removal helps also to minimize parasitic capacitance in the devices. This large separation distance, as well as the roughness of the surface after PSi removal, helps to reduce sticking between beams and the substrate (Bell et al. 1996). For example, Mohammad et al. (2011) have found that with the 10-μm cavity, even 1-mm long and slender structures never get stuck to the substrate.
