Rocking Structure Differential Microphone for Atmospheric Pressure Resistance

Solution Overview

Problem

Miniature microphones face challenges in resisting deflection under atmospheric pressure while maintaining sensitivity to small sound pressures, and existing MEMS processing methods are not compatible with CMOS processes, limiting manufacturing options and fidelity.

Innovation Solution

A differential microphone design with sealed backside cavities and a rocking structure that rotates on a pivot, providing resistance to deflection and directional response, fabricated using MEMS surface micromachining without deep reactive ion etch, allowing for CMOS compatibility and vacuum sealing.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a compliant membrane is used to detect small sound pressures, then sensitivity to sound pressure is improved, but the membrane collapses under atmospheric pressure

Engineering Contradiction:

Core Design Contradiction:

Measurement precisionVSStrength

Solution Approach 1:

The microphone is divided into two separate backside sealed cavities instead of one large cavity, with each cavity supporting one diaphragm. This segmentation allows the atmospheric pressure to be distributed and managed independently in each cavity, preventing membrane collapse while maintaining sensitivity to small sound pressure variations.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces a rocking structure that acts as a counterbalancing element. The rocking structure provides mechanical support and counteracts the atmospheric pressure force acting on the diaphragms, allowing the compliant membranes to maintain their shape and sensitivity without collapsing under external pressure.

Inventive Principle:

Principle #8Anti-weight (Counterweight)

2Ease of manufacture

If deep reactive ion etch is used in MEMS processing, then through-wafer cavity formation is achieved, but CMOS compatibility is lost

Engineering Contradiction:

Core Design Contradiction:

Ease of manufactureVSAdaptability or versatility

Solution Approach 1:

Instead of using a single deep reactive ion etch step through the entire wafer, the patent segments the cavity formation process into multiple shallower etching steps performed on opposite sides of the wafer. This approach achieves the same through-wafer cavity formation capability while using etch processes that are compatible with CMOS manufacturing, eliminating the need for non-compatible deep etching.

Inventive Principle:

Principle #1Segmentation

3Stability of the object's composition

If a stiff diaphragm is used to resist atmospheric pressure, then structural stability is improved, but sensitivity to small sound pressures deteriorates

Engineering Contradiction:

Core Design Contradiction:

Stability of the object's compositionVSMeasurement precision

Solution Approach 1:

The rocking structure serves as a mechanical counterweight that provides the necessary structural stability to resist atmospheric pressure. This allows the diaphragms to remain compliant and sensitive to small sound pressures without requiring the diaphragms themselves to be stiff, as the rocking structure bears the mechanical load of atmospheric pressure.

Inventive Principle:

Principle #8Anti-weight (Counterweight)

Solution Approach 2:

The rocking structure acts as an intermediary element between the atmospheric pressure and the diaphragms. It mediates the force transmission, allowing the diaphragms to remain compliant for sound detection while the rocking structure handles the mechanical stress of atmospheric pressure, thus resolving the contradiction between stiffness and sensitivity.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 design effectively resists collapse under atmospheric pressure and provides directional sensitivity to small sound pressures, enabling higher fidelity and cost-effective manufacturing through CMOS-compatible processes.

Implementation Method 1

a rocking structure coupled to the first and second diaphragms, where the rocking structure rotates on a pivot

Methodology Applied

Scientific EffectRotation:

Implementation Method 2

sealed backside cavities... providing resistance to deflection under external atmospheric pressure

Methodology Applied

Scientific EffectPressure differential:

Data Source

PatentUS8989411B2Differential microphone with sealed backside cavities and diaphragms coupled to a rocking structure thereby providing resistance to deflection under atmospheric pressure and providing a directional response to sound pressure

Publication Date: 2015.03.24

AI summary

A vacuum sealed directional microphone and methods for fabricating said vacuum sealed directional microphone. A vacuum sealed directional microphone includes a rocking structure coupled to two vacuum sealed diaphragms which are responsible for collecting incoming sound and deforming under sound pressure. The rocking structure's resistance to bending aids in reducing the deflection of each diaphragm under large atmospheric pressure. Furthermore, the rocking structure exhibits little resistance about its pivot thereby enabling it to freely rotate in response to small pressure gradients characteristic of sound. The backside cavities of such a device can be fabricated without the use of the deep reactive ion etch step thereby allowing such a microphone to be fabricated with a CMOS compatible process.