MEMS Comb Structure to Prevent Etch Undercutting

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Solution Overview

Problem

Existing MEMS elements on silicon on insulator substrates face issues with reduced strength of bonding due to undercutting during etching, leading to potential breakage and loss of electrical insulation.

Innovation Solution

The MEMS element design includes protruding portions on lead portions and fixed-comb-teeth connecting portions, which are fixed to the insulation layer, preventing undercutting and maintaining structural integrity while allowing for efficient electrical insulation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If slits are formed by etching to separate fixed portions and moveable portion, then electrical insulation is achieved, but undercutting occurs reducing bonding strength

Engineering Contradiction:

Improveelectrical insulationVSAvoidbonding strength of insulation layer

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

Protruding portions are formed on the fixed portions before the etching process to prevent undercutting. These protruding portions extend into the slit regions and serve as preliminary structural reinforcements that prevent the insulation layer from being undercut during subsequent etching operations, thereby maintaining bonding strength while achieving electrical insulation.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The protruding portions are strategically positioned only at specific locations where undercutting would occur during etching. This localized structural modification provides targeted reinforcement to the insulation layer at critical bonding points without affecting other regions, thereby maintaining electrical insulation while preventing strength degradation at vulnerable locations.

Inventive Principle:

Principle #3Local quality

2Strength

If protective films are formed on lateral surfaces to prevent undercutting, then bonding strength is maintained, but processing complexity increases

Engineering Contradiction:

Improvebonding strength of insulation layerVSAvoidprocessing process complexity

Core Design Contradiction:

StrengthVSDevice complexity

Solution Approach 1:

The invention extracts the protective function from the photoresist material and transfers it to the protruding portions formed from the fixed portions themselves. Instead of using external protective films that require application and removal steps, the structural elements of the device itself provide the protective function, eliminating the need for additional processing steps.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The fixed portions serve their dual function: they provide structural support and simultaneously protect the insulation layer from undercutting through their protruding portions. The device structure serves itself by incorporating protective features as integral parts of the fixed portions, eliminating the need for external protective films and complex processing steps.

Inventive Principle:

Principle #25Self-service

Data Source

PatentUS12398032B2MEMS element and vibration-driven energy harvesting device

Publication Date: 2025.08.26 SAGINOMIYA SEISAKUSHO INC

AI summary

A MEMS element according to the present invention is provided with a base, an insulation layer fixed to one surface of the base, a first upper layer at least portions of which are fixed to the insulation layer, and a second upper layer provided surrounding the first upper layer and disposed being separated from the first upper layer by slits, wherein the first upper layer includes, at predetermined portions, protruding portions protruding toward the second upper layer, and the protruding portions are fixed to the insulation layer.