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Method for electrostatic MEMS actuators

IP.com Disclosure Number: IPCOM000008674D
Publication Date: 2002-Jul-02
Document File: 5 page(s) / 436K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for electrostatic micro electro-mechanical systems (MEMS) actuators. Benefits include improved performance and improved functionality.

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Method for electrostatic MEMS actuators

Disclosed is a method for electrostatic micro electro-mechanical systems (MEMS) actuators. Benefits include improved performance and improved functionality.

Background

              MEMS actuators have been demonstrated for their advantages in various applications. In most cases, MEMS actuators are designed to be stiff for fast response. Very high AC voltages are required for device actuation, such as 60V for MEMS RF switches (see Figure 1). However, high AC driving circuit chips are more difficult and expensive to produce and consume more power using standard CMOS fabrication. No effective solutions for these problems exist, and no commercial RF MEMS products are on the market. A new actuation method for MEMS actuators is required.

              A cantilever beam switch is illustrated as a typical MEMS actuator. To achieve high switching speed, the beam designed to be very stiff for fast pull-up/release. The stiff beam requires high actuation voltage to achieve a speed of 5ms. Actuation voltage ~50-100V is too high for mobile devices. As a result, high AC drive voltages of ~40V-60V are  designed to achieve the device switch-down (ON-state) actuation. However, large AC excitation leads to greater power consumption and noise induction into the switch RF path and is, therefore, not acceptable. High-switched voltages also require special high voltage tolerant fabrication processes and circuits that are expensive and not easily integrated with low-cost MEMS fabrication processes.

General description

              The disclosed method is electrostatic MEMS actuators. The method eliminates the requirement for high-voltage AC driving circuits by using a combination of high-voltage DC bias and low voltage AC actuation. The high-voltage DC bias is achieved by using very simple devices, such as a charge pump or battery. The more complicated low-voltage AC actuation circuit can be easily fabricated using standard CMOS techniques. As result, the disclosed actuation method can be produced at much lower cost than the conventional process.

      The key elements of the method are:

·        Dynamic low AC actuation voltage superimposed on a high DC bias method to operate MEMS actuators

·        DC bias that sets the device movable part near the threshold pull-in voltage

·        Low AC voltage that is added to trigger the pull-in, achieving large displacement

·        Modified MEMS switch design configuration

 


Advantages

      The disclosed method provides technical advantages, including:

·        Improved effective MEMS device actuation at lower cost

·        Improved functionality due to a combination of static high-voltage bias and a dynamic low-voltage drive to actuate MEMS devices

·        Elimination of the requirement for a dynamic high-voltag...