Hexagonal MEMS Diaphragm Stress Reduction

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Solution Overview

Problem

Conventional MEMS devices with square diaphragm structures face stress concentration issues at corners, leading to non-uniform vibration characteristics and increased chip size, which hinders miniaturization and cost reduction, and the Deep-RIE method is costly and reduces chip strength.

Innovation Solution

A diaphragm structure with a substantially hexagonal shape and interior angles greater than 90 degrees, using a (110) silicon substrate with vertical and inclined surfaces in the through-hole, and a rhombic chip shape to reduce stress concentration and chip size while maintaining sensitivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If a square diaphragm structure is used in conventional MEMS devices, then the diaphragm can be easily fabricated using standard etching processes, but stress concentration occurs at the four corners causing non-uniform vibration characteristics and potential breakage

Engineering Contradiction:

Improveease of fabricationVSAvoidvibration uniformity

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent applies curvature by replacing the square diaphragm shape with a rounded shape. The corner regions are smoothly curved to eliminate sharp angles, which distributes stress more uniformly across the diaphragm structure. This curvature modification eliminates the stress concentration points that cause non-uniform vibration and potential breakage in conventional square diaphragms.

Inventive Principle:

Principle #14Spheroidality (Curvature)

Solution Approach 2:

The patent changes the geometric parameters of the diaphragm from a square configuration to a rounded configuration. By modifying the shape parameters (eliminating sharp corners and adjusting the overall geometry), the patent achieves more uniform stress distribution while maintaining ease of fabrication through standard etching processes.

Inventive Principle:

Principle #35Parameter changes

2Manufacturing precision

If the chip size is increased to accommodate the diaphragm and (111) inclined portions, then the diaphragm can be fabricated with desired size, but the effective area ratio of diaphragm to chip area decreases

Engineering Contradiction:

Improvediaphragm size controlVSAvoidchip area

Core Design Contradiction:

Manufacturing precisionVSArea of stationary object

Solution Approach 1:

The rounded shape of the diaphragm allows for more efficient use of the available chip area. By eliminating the need for large (111) inclined portions that are required by square shapes, the rounded diaphragm can be fabricated within a smaller chip area, thereby increasing the effective area ratio.

Inventive Principle:

Principle #14Spheroidality (Curvature)

Solution Approach 2:

The patent changes the diaphragm shape parameter from square to rounded, which fundamentally alters the geometric relationship between the diaphragm area and the required chip area. This parameter change enables the diaphragm to be fabricated with the same or larger area while occupying significantly less chip area, thus improving the area ratio.

Inventive Principle:

Principle #35Parameter changes

3Manufacturing precision

If the (111) inclined surfaces are used in the through-hole structure, then anisotropic wet etching can be performed with good dimensional controllability, but the chip size increases due to the inclined portion width

Engineering Contradiction:

Improvedimensional controllabilityVSAvoidchip size

Core Design Contradiction:

Manufacturing precisionVSLength of stationary object

Solution Approach 1:

The rounded diaphragm shape eliminates the need for large (111) inclined portions that are characteristic of square diaphragms. By using a rounded geometry, the patent reduces the width of the inclined portions while maintaining the benefits of anisotropic wet etching for dimensional controllability, thereby reducing the overall chip size.

Inventive Principle:

Principle #14Spheroidality (Curvature)

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 reduces stress concentration, prevents diaphragm breakage, and improves the effective area ratio of the diaphragm to the chip area, enabling chip miniaturization and cost reduction while maintaining sensitivity.

Implementation Method 1

a diaphragm 304 vibrates depending on an acceleration or pressure variation, and thereby utilizing the diaphragm 304 for MEMS devices such as various sensors by electrically detecting such vibration displacement

Methodology Applied

Scientific EffectVibration: Vibration

Implementation Method 2

an acoustic sensor which has a diaphragm vibrating by detecting a pressure variation

Methodology Applied

Scientific EffectPressure variation detection: Pressure Gradient

Implementation Method 3

Anisotropic wet etching can be performed with a good dimensional controllability. As inner walls of the through-hole 302, (111) inclined surfaces 305 having an angle of 54.7 degrees with respect to the (100) plane

Methodology Applied

Scientific EffectAnisotropic wet etching:

Data Source

PatentUS8146437B2Diaphragm structure and MEMS device

Publication Date: 2012.04.03 INVENSENSE INC

AI summary

A diaphragm structure for a MEMS device includes a through-hole formed so as to penetrate from an upper surface to a bottom surface of a substrate; and a vibrating electrode film formed on the upper surface of the substrate so as to cover the through-hole. An opening shape of the through-hole in the upper surface of the substrate is substantially hexagonal.