Evaluation of a Single-Crystal-Silicon Microelectromechanical Systems Resonator Utilizing a Narrow Gap Process

Abstract

To investigate a higher frequency microelectromechanical systems (MEMS) resonator, mechanical behaviors and electrical characteristics on a single-crystal-silicon MEMS resonator, utilizing a narrow gap process, have been evaluated. The size reduction for the resonators leads to a decrease in output signal. To overcome this problem, an increase in electromechanical coupling coefficient is required. To investigate the effect of the reduction of the gap between a beam and a driving electrode, two types of 100 kHz MEMS resonator with different gaps have been fabricated and compared. It has been observed that the resonator with a narrow gap (1 µm) has a larger displacement amplitude, as well as a larger phase transition, than that with a 4 µm gap, which suggests that the gap reduction is effective. Then, a 10 MHz MEMS resonator has been fabricated by using the narrow gap process with a focused-ion beam (FIB). The resonant vibration for the fabricated device has been observed at 11.262 MHz. To further improve the resonators, it is suggested that the substrate vibration near the beam resonant frequency should be suppressed and that a smooth surface of the gap should be fabricated.

Variable Resonance Frequency Selection for Fishbone-Shaped Microelectromechanical System Resonator Based on Multi-Physics Simulation

“…As an alternative to these devices, microelectromechanical system (MEMS) resonators have recently attracted much attention owing to their excellent features including higher direct vibration frequency, 1,2) smaller size, frequency tuning, 3) and peripheral integration capabilities. 4) Until now, various MEMS resonators with different vibration modes have been reported including the bending [5][6][7][8][9] and torsional modes [10][11][12][13] in beam resonators, Lame and higher-order extensional modes in square and octagonal resonators, [14][15][16][17] and the wine-glass modes in ring and disk resonators. [18][19][20][21] There exist several tradeoffs among the resonant frequencies, output signals, fabrication technology, and so forth.…”

MEMS resonator with wide frequency tuning range and linear response to control voltages for use in voltage control oscillators

“…Δε res is strongly dependent on packaging method. Equation (2) shows that RFC in beam resonators is caused by three factors, the temperature changes of Young's modulus, beam shape (thermal expansion), and residual stress.…”

“…Conventionally, the performance of electrostatic resonators has been improved by creating a narrow gap between two electrodes because the electromechanical transduction efficiency is inversely proportional to the square of the gap. To date, fine-pattern fabrication [2], moving driving electrodes (DEs) after processing [3][4][5], and a solid gap structure [6] have been reported. Since a solid gap structure is constructed using a buried isolation layer instead of an air gap, resonators having submicron gaps can be fairly easily fabricated.…”

Lamé-Mode Octagonal Microelectromechanical System Resonator Utilizing Slanting Shape of Sliding Driving Electrodes

“…In an electrostatic MEMS resonator, the force converting parameter between the electrical domain and the mechanical domain is an electromechanical coupling coefficient given by 20) e…”

“…To overcome this problem, the electromechanical coupling coefficient should be largely increased by narrowing the gap between the driving electrode and the resonant element. 20) Until now, many narrow-gap formations have been reported. 21,22) Although it easily provides a narrow gap, surface micromachining requires strict process control, e.g., residual stress control.…”