MEMS Resonator Pressure Sensing With Gap-Modulated Electrodes

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Solution Overview

Problem

Conventional MEMS pressure sensors face challenges in detecting pressure with high accuracy due to difficulties in controlling the thickness of thin diaphragms and the deterioration of Q factor, which affects the resolution of pressure detection.

Innovation Solution

A MEMS pressure sensor design that utilizes a resonator with a mechanically vibrating part, a fixed part, and an electrode system where external pressure displaces the electrode to change the gap between the vibrator and the electrode, allowing for detection of pressure based on the transmission characteristics of AC signals, thereby utilizing high Q factor resonance for precise pressure measurement.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the diaphragm is designed to be extremely thin to improve pressure sensitivity, then the sensitivity to pressure is improved, but the manufacturing precision of the diaphragm thickness deteriorates

Engineering Contradiction:

Improvepressure detection resolutionVSAvoiddiaphragm thickness control

Core Design Contradiction:

Measurement precisionVSManufacturing precision

Solution Approach 1:

Instead of making the vibrator thin to improve sensitivity, the patent inverts the approach by keeping the vibrator thick (substrate side) and making the electrode thin and flexible. This allows the electrode to deflect under pressure while maintaining easy manufacturing control, resolving the contradiction between sensitivity and manufacturing precision.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent uses a thin flexible electrode film that can deflect under pressure to change the capacitance gap. This flexible thin film approach achieves high pressure sensitivity while maintaining manufacturing precision, as the flexibility is achieved through material selection rather than extreme thinning of structural components.

Inventive Principle:

Principle #30Flexible shells and thin films

2Measurement precision

If the vibrator is made extremely thin to improve pressure sensitivity, then the sensitivity to pressure is improved, but the Q factor of the resonator deteriorates

Engineering Contradiction:

Improvepressure detection resolutionVSAvoidQ factor

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent inverts the traditional design by making the vibrator (substrate side) thick and rigid to maintain high Q factor, while making the pressure-sensitive electrode thin and flexible. This inversion allows the system to achieve high pressure sensitivity through electrode deflection rather than vibrator thinning, thus preserving the Q factor.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent changes the parameters of the electrode (making it thin and flexible with specific material properties) rather than changing the vibrator parameters. This allows the system to achieve pressure sensitivity through electrode mechanical property changes while maintaining the vibrator's high Q factor characteristics.

Inventive Principle:

Principle #35Parameter changes

3Ease of manufacture

If a thin film process is used to form the vibrator and shell, then the manufacturing complexity is reduced, but the control over diaphragm thickness precision deteriorates

Engineering Contradiction:

Improveproduction process simplicityVSAvoiddiaphragm thickness control

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The patent inverts the design approach by making the substrate-side vibrator thick and the electrode-side pressure sensing element thin. This allows the use of standard thick substrate manufacturing while achieving precise thickness control for the pressure-sensitive electrode through separate fabrication processes, thus maintaining both ease of manufacture and thickness precision.

Inventive Principle:

Principle #13The other way round (Inversion)

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 enables high-resolution pressure detection by maintaining a high Q factor and simplifying the production process, allowing for accurate measurement of pressure changes without relying on stress changes in the vibrator, thus improving the sensitivity and accuracy of pressure sensing.

Implementation Method 1

at least one electrode that is disposed close to the vibrator and has an area overlapping with the vibrator across a gap

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

a resonator with a mechanically vibrating part... utilizing high Q factor resonance for precise pressure measurement

Methodology Applied

Scientific EffectResonance: Resonance

Data Source

PatentUS8516905B2MEMS pressure sensor

Publication Date: 2013.08.27 EXO IMAGING INC

AI summary

A MEMS resonator 100 including a substrate 112; an vibrator 102 including an mechanically vibrating part and a fixed part; at least one electrode 108 that is close to the vibrator and has an area overlapping with the vibrator across a gap 109 in a direction perpendicular to a surface of the substrate; and a pressure transferring mechanism to displace the at least one electrode according to an externally applied pressure so as to change the gap; is connected to a detection circuit that detects transmission characteristics of an AC signal from an input electrode to an output electrode, the input and output electrodes being one and the other of the vibrator 102 and the at least one electrode 108, and the pressure is detected based on the transmission characteristics of the AC signal that is detected by the detection circuit.