MEMS Motion Limiter Structure for Reduced Stiction Impact

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Solution Overview

Problem

Existing MEMS devices face issues of stiction and structural damage due to direct contact between the rotor and stator, which can disrupt device operation and cause electrical faults.

Innovation Solution

A microelectromechanical element with two stopper bumps that contact the rotor at different times, reducing the contact area and dividing the impact force, utilizing a configuration where the first stopper bump contacts the stator before the second, and incorporating a twisting or tilting motion to minimize stiction and structural damage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a single bump is used as a motion limiter, then direct contact between rotor and stator is prevented, but stiction occurs and structural damage may still happen from strong impacts

Engineering Contradiction:

Improvedevice operation reliabilityVSAvoidstiction and impact damage

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The motion limiter is segmented into multiple bumps (at least two) instead of using a single bump. This segmentation distributes the impact force across multiple contact points and reduces stiction by ensuring that not all bumps contact the rotor simultaneously, thereby resolving the contradiction between preventing direct contact and avoiding stiction/impact damage.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The bumps are designed with varying heights or positions so that only some bumps contact the rotor at any given time during motion limitation. This partial action approach ensures that the rotor is restrained without complete contact, reducing stiction while still preventing direct rotor-stator contact and distributing impact forces.

Inventive Principle:

Principle #16Partial or excessive action

2Ease of operation

If the rotor is allowed to move freely, then device operation is maintained, but direct contact with the stator causes structural damage and electrical short-circuits

Engineering Contradiction:

Improverotor movement freedomVSAvoidstructural integrity

Core Design Contradiction:

Ease of operationVSStrength

Solution Approach 1:

The bumps are positioned and dimensioned to contact the rotor before it can reach the stator, providing beforehand cushioning that prevents direct contact between the rotor and stator. This cushioning effect protects the structural integrity of both components while allowing the rotor to move freely within the safe range defined by the bump positions.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Data Source

PatentUS12528693B2Motion limiter with reduced stiction

Publication Date: 2026.01.20 MURATA MFG CO LTD

AI summary

A microelectromechanical element is provided that includes a first device part and a second device part, and a motion-limiting structure having a first stopper bump and a second stopper bump. The first and second stopper bumps extend from the first device part toward the second device part. When one of the device parts moves toward the other device part in the out-of-plane direction and crosses a displacement threshold, the first stopper bump comes into contact with the second device part before the second stopper bump contacts the second device part, and the second stopper bump comes into contact with the second device part before the first device part contacts with the second device part.