CMOS-MEMS Resonant Gate Transistor-Based Devices

Abstract

The development of the semiconductor industry in general and IC (Integrated Circuits) fabrication technologies in particular enabled the miniaturization of moving electro-mechanical structures down to micrometer size. This significantly reduced the cost and power consumption, and improved the performance of modern Micro-Electro-Mechanical Systems (MEMS). Electrostatically-driven MEMS-based resonators are used in a vast range of applications, including sensors, high frequency filters, time reference signal generations, etc. However, with the resonance frequency continuously increasing and the physical dimensions of the resonators shrinking, the sensitivity of capacitive detection is becoming a major problem due to decreased output signals. The Resonating Suspended Gate Field Effect Transistor (RSG-FET) is seen as a perfect solution to overcome this problem. It replaces conventional capacitive detection with FET detection when the vibrating gate modulates the channel current. This thesis presents an RSG-FET-based resonator fabricated using conventional CMOS technology with additional post-processing. The concept of RSG-FET combines the advantages of both a high mechanical quality factor and an intrinsic gain of a transistor. The physical mechanisms behind the operation principle along with its advantages and disadvantages are thoroughly investigated using distributed and lumped analysis as well as Finite Element Analysis (FEA) methods. Various approaches for tuning the resonance frequency are studied analytically and verified experimentally. The fabrication of the device is carried out through a post-processing of a conventional CMOS process (TSMC CMOSP35). Possible applications for RSG-FET-based devices in high frequency filters and atomic force microscopy are also investigated.