Design, fabrication, and characterization of a submicroelectromechanical resonator with monolithically integrated CMOS readout circuit

In this paper, we report on the main aspects of the design, fabrication, and performance of a microelectromechanical system constituted by a mechanical submicrometer scale resonator (cantilever) and the readout circuitry used for monitoring its oscillation through the detection of the capacitive current. The CMOS circuitry is monolithically integrated with the mechanical resonator by a technology that allows the combination of standard CMOS processes and novel nanofabrication methods. The integrated system constitutes an example of a submicroelectromechanical system to be used as a cantilever-based mass sensor with both a high sensitivity and a high spatial resolution (on the order of 10/sup -18/ g and 300 nm, respectively). Experimental results on the electrical characterization of the resonance curve of the cantilever through the integrated CMOS readout circuit are shown.

I. Introduction

Examples of microelectromechanical systems include sensors for detecting different kinds of physical or chemical properties [1]. A reduction of the dimensions of the mechanical transducer leads to a new generation of systems called nanoelectromechanical systems (NEMS) [2]– [5] that represent an improvement on sensitivity, spatial resolution, energy efficiency and response time. As an example of NEMS, we present the design of a mass sensor based on a laterally oscillating cantilever with nanometer-scale dimensions, which has both a high sensitivity and a high spatial resolution (down to the range of and 300 nm, respectively). Mass detection is based on monitoring the resonant frequency shift of the cantilever when nanometer-sized particles or molecules are deposited on the cantilever [6], [7].