Charge control of micro-electromechanical device

Abstract

A charge control circuit for controlling a micro-electromechanical system (MEMS) device having variable capacitor formed by first conductive plate and a second conductive plate separated by a variable gap distance. The charge control circuit comprises a switch circuit configured to receive a reference voltage having a selected voltage level and configured to respond to an enable signal having a duration at least as long as an electrical time constant constant of the MEMS device, but shorter than a mechanical time constant of the MEMS device, to apply the selected voltage level across the first and second plates for the duration to thereby cause a stored charge having a desired magnitude to accumulate on the variable capacitor, wherein the variable gap distance is a function of the magnitude of the stored charge.

Description

THE FIELD OF THE INVENTION The present invention relates to the field of micro-electromechanical devices. More particularly, the present invention relates to charge control of a micro-electromechanical device. BACKGROUND OF THE INVENTION Micro-electromechanical systems (MEMS) are systems which are developed using thin film technology and which include both electrical and micro-mechanical components. MEMS devices are used in a variety of applications such as optical display systems, pressure sensors, flow sensors and charge control actuators. MEMS devices use electrostatic force or energy to move or monitor the movement of micro-mechanical electrodes which can store charge. In one type of MEMS device, to achieve a desired result, a gap distance between the electrodes is controlled by balancing an electrostatic force and a mechanical restoring force. Digital MEMS devices use two gap distances, while analog MEMS devices use multiple gap distances. MEMS devices have been developed us...

AI Technical Summary

Benefits of technology

One aspect of the present invention provides a charge control circuit for controlling a micro-electromechanical system (MEMS) device having variable capacitor formed by a first conductive plate and a second conductive plate separated by a variable gap distance. The charge control circuit comprises a switch circuit configured to receive a reference voltage having a selected voltage level and configured to respond to an enable signal having a duration at least as long as an electrical time constant constant of the MEMS device, but shorter than a mechanical time constant of the MEMS device, to apply the selected voltage level across the first and second plates for the duration to thereby cause a stored charge having a desired magnitude to accumulate on the variable capacitor, wherein the variable gap distance is a function of the magnitude of the stored charge.

Problems solved by technology

However, this approach suffers from electrostatic instability that greatly reduces a useable operating range over which the gap distance can be effectively controlled.

This non-linear relationship between the control voltage and the gap distance limits the controllable range of electrode movement to only about one-third of the initial gap distance, and thus limits the potential utility of the MEMS device.

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