Metallic Membrane MEMS Switch with Elliptical Cavity
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Solution Overview
Problem
Existing MEMS switches face challenges in achieving a balance between small size, high reliability, low contact resistance, and preventing sticking and arcing, particularly in electrostatically actuated galvanic (RF) MEMS switches, where the requirement for a large moving structure and small separation gap poses fabrication difficulties and leads to plastic deformations.
Innovation Solution
A compact galvanic (RF) MEMS switch with a metallic membrane, featuring a corrugated design and higher bending stiffness along the RF line than perpendicular to it, is fabricated using a method involving a sealed cavity with a metallic membrane and a top electrode, allowing for improved restoring force and reduced contact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the moving structure is made relatively large and the separation gap is made relatively small to achieve sufficient restoring force, then the restoring force is improved, but fabrication difficulty increases
Solution Approach 1:
The patent changes the material parameter from conventional non-metallic membranes to metallic membrane, which fundamentally alters the mechanical properties and enables new fabrication approaches. The metallic membrane's inherent properties allow for different structural designs that reduce fabrication complexity while maintaining sufficient restoring force
Solution Approach 2:
The patent introduces an elliptical geometry with different bending stiffness along different axes (RF line vs perpendicular direction). This dimensional differentiation allows the membrane to achieve the required restoring force in specific directions without requiring a uniformly large area, thereby simplifying fabrication
2Reliability
If the moving structure area is increased to reduce contact resistance, then contact resistance is reduced, but the device size increases
Solution Approach 1:
The patent changes the material composition to metallic membrane, which inherently provides lower contact resistance compared to conventional non-metallic materials. This material parameter change allows for reduced contact resistance without requiring a larger membrane area, thus maintaining compact device size
Solution Approach 2:
The patent employs a metallic membrane that combines both structural and electrical functions. The metallic material provides both the mechanical restoring force and the low contact resistance properties, eliminating the need to increase area for electrical performance alone
3Force
If the separation gap is reduced to improve restoring force, then restoring force is improved, but the risk of sticking and arcing increases
Solution Approach 1:
The patent changes the material parameter to metallic membrane with specific mechanical and electrical properties. The metallic material's conductivity and mechanical strength allow for optimized gap dimensions that provide sufficient restoring force while maintaining safe operating margins against sticking and arcing
Solution Approach 2:
The patent employs an elliptical membrane geometry with different bending stiffness along the RF line versus the perpendicular direction. This asymmetric design allows for optimized gap control in the critical RF direction while maintaining adequate restoring force, reducing the risk of sticking and arcing
4Ease of manufacture
If conventional materials are used for the membrane, then fabrication is easier, but contact resistance is higher and restoring force is insufficient
Solution Approach 1:
The patent fundamentally changes the material parameter from conventional non-metallic membranes to metallic membrane. This material substitution provides both low contact resistance and high restoring force while remaining compatible with standard MEMS fabrication processes, achieving improved reliability without sacrificing manufacturability
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides a reliable, compact MEMS switch with reduced contact resistance and enhanced reliability, preventing plastic deformations and improving the trade-off between switch size and reliability, while maintaining low electrical resistance and high mechanical restoring force.
Implementation Method 1
an electrostatic force is applied across the switch to actuate it by deflecting a moving structure or membrane
Implementation Method 2
the actuating mechanism has sufficient restoring force to return the switch to its unactuated state
Data Source
AI summary
A MEMS switch (1, 81), and methods of fabricating thereof, the switch comprising: a sealed cavity (24); and a membrane (26); wherein the sealed cavity (24) is defined in part by the membrane (26); and the membrane is a 5 metallic membrane (26), for example consisting of a single type of metal or metal alloy. The MEMS switch (1, 81) may comprise a top electrode (30), for example extending into the cavity (24), located in a hole (32) in the metallic membrane (26). Fabrication may include providing a sacrificial layer (22) in a partly defined cavity (24). The bending stiffness of the membrane (26) may be 10 higher along an RF line (102) than along a line (104) perpendicular to the RF line (102), for example by virtue of the cavity (24) being elliptical.