Implementing MEMS resonators in 90 nm CMOS

In the ubiquitous information age of today there is an increased interest in combining actuating and sensing technology with the advanced signal processing of the well established CMOS technology. With that in mind, this work investigates the possibility of making MEMS resonators in fine-pitch CMOS in contrast to making MEMS in more coarse-grain CMOS processes. This is done by using the metal layers in the CMOS process both as structural layers and as a mask, using only a few post-CMOS etch steps. A modern and mature 90 nm CMOS process from ST Microelectronics is used and test structures are analyzed. A set of design rules have been derived and a general design guideline is described. As a practical example, implemented MEMS frequency tunable resonators are shown that are intended to be used as VCOs in an FDSM system to show the feasibility of the work.