MEMS RF-switch contact stoppers for controlled landing
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Solution Overview
Problem
MEMS switches face challenges in maintaining controlled contact resistance and force over a wide voltage range due to process variations and the risk of dielectric charging, leading to variations in actuation voltage and contact force.
Innovation Solution
The MEMS device incorporates a substrate with anchor, RF, and pull-down electrodes, a switching element, and a dielectric layer with contact stoppers on islands, allowing controlled landing and reduced electric field exposure to prevent dielectric charging, while maintaining a high contact force through strategically designed contact heights and materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high voltage is applied to pull the MEMS plate intimate with the contact electrode to achieve good ohmic contact resistance, then contact resistance is improved, but the plate may secondary land on the dielectric layer causing reliability issues and dielectric charging
Solution Approach 1:
A contact stopper structure is introduced as an intermediary element between the MEMS plate and the dielectric layer. The contact stopper provides a controlled landing surface that enables sufficient contact force for low contact resistance while preventing the plate from making direct contact with the dielectric layer, thus avoiding dielectric charging and maintaining device reliability
Solution Approach 2:
The contact stopper creates a localized contact region with specific mechanical and electrical properties. By designing the contact stopper with appropriate material composition and geometry, the local contact quality is optimized to achieve low contact resistance without requiring excessive voltage that would cause dielectric breakdown
2Productivity
If operating voltage is increased above maximum expected variation in MEMS actuation voltage to ensure high yield, then manufacturing yield is improved, but contact force variations increase causing contact resistance variations
Solution Approach 1:
The contact stopper structure changes the mechanical parameter of contact force by providing a compliant or rigid stopping surface depending on design. This parameter change decouples the contact force from the actuation voltage variations, allowing consistent contact resistance across devices with different actuation voltages while maintaining high operating margins for yield
Solution Approach 2:
The contact stopper performs the preliminary action of limiting plate displacement before the plate can make uncontrolled contact with the dielectric layer. This preliminary mechanical constraint ensures that even with voltage overdrive, the contact force remains within acceptable ranges, preventing excessive contact force variations
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
This configuration ensures reliable and repeatable contact resistance across a large operating voltage window, minimizing variations in contact force and reducing the risk of dielectric charging, thereby stabilizing the actuation voltage and maintaining a consistent contact resistance.
Implementation Method 1
a movable plate that moves by applying a voltage to an actuation electrode... due to the higher electrostatic forces when the plate is close to the actuation electrode
Implementation Method 2
contact stoppers disposed on the dielectric layer at locations corresponding to the islands... controlled contact landing which results in a reliable repeatable contact resistance
Data Source
AI summary
A MEMS switch contains an RF electrode 102, pull-down electrodes 104 and anchor electrodes 108 located on a substrate 101. A plurality of islands 226 are provided in the pull-down electrode and electrically isolated therefrom. On top of the RF electrode is the RF contact 206 to which the MEMS-bridge 212, 214 forms an ohmic contact in the pulled-down state. The pull-down electrodes 104 are covered with a dielectric layer 202 to avoid a short-circuit between the bridge and the pull-down electrode. Contact stoppers 224 are disposed on the dielectric layer 202 at locations corresponding to the islands 226, and the resulting gap between the bridge and the dielectric layer in the pulled-down state reduces dielectric charging. In alternative embodiments, the contact stoppers are provide within the dielectric layer 202 or disposed on the islands themselves and under the dielectric layer. The switch provides good controllability of the contact resistance of MEMS switches over a wide voltage operating range.