This work presents the first hybrid RF MEMS-CMOS resonators demonstrated in silicon at the transistor level of IBM\u2019s 32-nm SOI CMOS process, without the need for any post-processing or packaging. The unreleased, Si bulk acoustic resonators are driven capacitively and sensed using a field effect transistor (FET). MEMS-CMOS Si resonators with acoustic Bragg reflectors (ABRs) are demonstrated at 11.1 GHz with Q<\/em>~18 and a footprint of 5\u00b5m \u00d7 3\u00b5m.<\/p>\n

The majority of electromechanical devices require a release step to freely suspend moving structures, which necessitate costly complex encapsulation methods and back-end-of-line (BEOL) processing of large-scale devices ^{[1<\/a>] <\/sup>. Development of unreleased Si-based MEMS resonators in CMOS allows integration into front-end-of-line (FEOL) processing with no post-processing or packaging. We have previously demonstrated the Resonant Body Transistor (RBT), which employs active FET sensing of acoustic vibrations [2<\/a>] <\/sup> [3<\/a>] <\/sup>, which amplifies the mechanical signal before parasitics. Realization of the RBT in CMOS technology leverages high f_{T<\/sub><\/em>, high-performance transistors, enabling RF-MEMS resonators at frequencies orders of magnitude higher than possible with passive devices.<\/p>\n}}

The hybrid MEMS-CMOS RBT presented in this work is a Si bulk-acoustic resonator with electrostatic drive formed using the gate dielectric and a body-contacted nFET sense transducer (see Figure 1). Acoustic vibrations in the unreleased resonator are confined using 7 pairs of 1D ABRs surrounding the device, which are patterned using shallow trench isolation (STI). The DC characteristics of the sense transistor are similar to standard body-contacted nFETs of the 32-nm SOI process and show no direct effect of the capacitor drive voltage on the FET behavior. The frequency response of an 11.1-GHz resonator is shown in Figure 2 for multiple bias conditions, verifying the mechanical nature of the resonance.<\/p>\n

This first demonstration of an unreleased hybrid MEMS-CMOS resonator paves the way for monolithically integrated RF MEMS frequency sources and signal processors.<\/p>\n\n\t\t