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Fabrication of a MEMS Switch Device with a Mechanical Self Limiting Interelectrode Gap Area

IP.com Disclosure Number: IPCOM000127306D
Original Publication Date: 2005-Aug-22
Included in the Prior Art Database: 2005-Aug-22
Document File: 2 page(s) / 51K

Publishing Venue

IBM

Abstract

Fabrication of a MEMS Switch Device with a Mechanical Self Limiting Interelectrode Gap Area

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Fabrication of a MEMS Switch Device with a Mechanical Self Limiting Interelectrode Gap Area

Described here is a MEMS switch structure with well defined and readily controlled critical dimensions. The performance of MEMS switch devices is dependant on a number of factors including design, material properties and control of critical dimensions. One type of switch utilizes a free standing beam or membrane (shown below) which is electrostatically actuated by applying a bias between electrodes located on the beam and substrate. One of the key characteristics of MEMS switch devices targeted for use in portable applications is low actuation voltage. The actuation voltage is the voltage needed to move the switch beam or membrane between on and off states. This voltage is influenced by the material properties, size and shape of the beam, electrode overlap area as well as the insulation between the actuation electrodes. The two components that define the insulation are the dielectric layers over the electrode surfaces and the physical separation of the electrodes. In general the thinner the dielectric thickness and smaller the interelectrode gap, the lower the actuation voltage. During fabrication the switch beam is released by removal of a sacrificial layer resulting in a free standing structure, ideally with an interelectrode gap defined by the thickness of the initial sacrificial layer. A common problem encountered with membrane type devices is deflection or distortion resulting from film stresses and or stress gradients in the membrane. Depending on net membrane tensile stress and the position of the actuation electrodes, distortion can increase the interelectrode gap resulting in a significant increase in switch actuation voltage. The switch beams are typically made from multiple material layers of various thickness' and stress characteristics. By carefully tailoring and controlling individual film stress and layer thickness a net zero stress beam is possible but difficult to fabricate in a manufacturing environment.

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