Understanding Smart Sensors - Nomads.usp

Micromachining 37 orSiO 2(a)Damaged zoneSiSiO 2(b)35°{111}SiO 2SiSiO 2(c)55°{111}SiO 2SiSiO 2Figure 2.12 Combined effect of laser micromachining and anisotropic etching. (After: [27].)2.5.5 Chemical Etching and IC TechnologyWhile many of the processes used to manufacture a MEMS structure are similarto processes used to fabricate ICs, there are significant differences that makecombining ICs and microstructures a nontrivial task. Table 2.5 shows the differencebetween IC and micromachining processes in five different areas [28].One of the main concerns in integrating circuitry with micromachined structuresis the effect that the etching and the resulting temperatures can have onother semiconductor processes and the circuit elements. The combined surfaceand bulk micromachining process shown Figure 2.8 also included NMOS circuitryto process the signal for the capacitive sensor. Other examples will be discussedto show the different approaches that are being pursued.The process for an integrated sensor is more complex because it involvesthe joining of unique sensor processes with traditional IC processes. For example,bipolar operational amplifiers (op amps) typically are fabricated on silicon substrates, while pressure sensors typically are fabricated on