Corrugated MEMS Capacitive Membrane Without a Back-Plate

Solution Overview

Problem

MEMS transducers, such as capacitive microphones, face issues with acoustic noise and non-linearity due to the back-plate structure, which affects the accuracy of sound wave detection.

Innovation Solution

A non-planar flexible membrane with conductive elements on both sides is used, allowing displacement of these elements relative to each other as the membrane deflects, eliminating the need for a separate back-plate and reducing acoustic noise by integrating the electrodes on the membrane itself.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If a back-plate structure is used in MEMS transducers, then structural support and electrode positioning are provided, but acoustic noise and non-linearity in displacement response increase

Engineering Contradiction:

Improvestructural supportVSAvoidacoustic noise

Core Design Contradiction:

StrengthVSObject-affected harmful factors

Solution Approach 1:

The patent removes the back-plate structure entirely from the MEMS transducer design. Instead of using a separate back-plate for structural support and electrode positioning, the invention integrates these functions into the diaphragm itself, which is formed as a non-planar structure with conductive elements directly on its surfaces. This extraction of the back-plate eliminates the source of acoustic noise while maintaining the necessary structural functions through the diaphragm's own geometry and material properties.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent merges the functions of the back-plate and diaphragm into a single integrated structure. The diaphragm is formed with non-planar geometry that provides both structural support and electrode positioning capabilities that were previously separated into distinct back-plate and diaphragm components. This merging reduces the number of parts and eliminates acoustic noise from the back-plate while maintaining all necessary structural functions.

Inventive Principle:

Principle #5Merging (Combining)

2Strength

If a back-plate structure is used in MEMS transducers, then structural support is provided, but device complexity and number of parts increase

Engineering Contradiction:

Improvestructural supportVSAvoidnumber of parts

Core Design Contradiction:

StrengthVSDevice complexity

Solution Approach 1:

The patent merges the functions of the back-plate and diaphragm into a single integrated structure. The diaphragm is formed with non-planar geometry that provides both structural support and electrode positioning capabilities that were previously separated into distinct back-plate and diaphragm components. This merging reduces the number of parts and eliminates acoustic noise from the back-plate while maintaining all necessary structural functions.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent removes the back-plate structure entirely from the MEMS transducer design. Instead of using a separate back-plate for structural support and electrode positioning, the invention integrates these functions into the diaphragm itself, which is formed as a non-planar structure with conductive elements directly on its surfaces. This extraction of the back-plate eliminates the source of acoustic noise while maintaining the necessary structural functions through the diaphragm's own geometry and material properties.

Inventive Principle:

Principle #2Taking out (Extraction)

3Ease of manufacture

If conventional planar membrane design is used, then manufacturing is simpler, but signal-to-noise ratio is reduced

Engineering Contradiction:

Improvemanufacturing simplicityVSAvoidsignal-to-noise ratio

Core Design Contradiction:

Ease of manufactureVSMeasurement precision

Solution Approach 1:

The patent employs a non-planar diaphragm structure with controlled curvature and non-uniform thickness distribution. The diaphragm features a convex portion with greater thickness and concave portions with lesser thickness, creating a three-dimensional geometry that enhances acoustic sensitivity and signal-to-noise ratio. This curved, non-planar design improves acoustic coupling and displacement response while remaining compatible with standard semiconductor fabrication processes through selective etching and deposition techniques.

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

This design reduces acoustic noise and non-linearity, enabling more accurate capacitance measurement and potentially lowering the transducer's height and part count, while allowing for common mode rejection to filter electrical noise.

Implementation Method 1

the flexible membrane is shaped such that the first and second conductive elements are displaced relative to each other when the flexible membrane deflects in response to a pressure differential across the membrane

Methodology Applied

Scientific EffectPressure differential: Pressure Gradient

Implementation Method 2

the first electrode and the second electrode form a capacitive sensor which is arranged to measure a change in capacitance between the first electrode and the second electrode

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentUS10111021B2MEMS device and process

Publication Date: 2018.10.23 CIRRUS LOGIC INC

AI summary

The application describes a MEMS transducer in which first and second conductive elements of a capacitor are both provided on the membrane. The membrane is shaped that the first and second conductive elements are displaced relative to each other when the flexible membrane deflects in response to a pressure differential across the membrane. For example the membrane may be corrugated.