MEMS Pressure Sensor Thermo-Mechanical Stress Compensation

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Solution Overview

Problem

Thermo-mechanical stress during manufacturing, packaging, and aging leads to performance degradation in MEMS pressure sensors due to substrate deformation, causing sensitivity drift and accuracy issues, which existing solutions like trench isolation fail to adequately address.

Innovation Solution

The use of an array of pressure sensing membranes with suspended sensing electrodes and dielectric anchors reduces the impact of substrate deformation by decoupling the sensing electrodes from the substrate, enhancing pressure insensitivity to thermo-mechanical stress.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If traditional capacitive pressure sensor structure is used, then device complexity is reduced, but sensitivity drift occurs due to thermo-mechanical stress

Engineering Contradiction:

Improvesensor accuracyVSAvoidsensor structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The sensing electrode is divided into multiple segments (first sensing electrode segment and second sensing electrode segment) that are positioned on opposite sides of the membrane. This segmentation allows the sensor to measure differential capacitance changes, compensating for thermo-mechanical stress effects while maintaining a relatively simple overall structure.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A dummy membrane is introduced as an intermediary element that experiences the same thermo-mechanical stress as the sensing membrane but does not participate in pressure sensing. This dummy membrane serves as a reference to compensate for stress-induced capacitance changes, improving sensor accuracy without significantly increasing structural complexity.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Measurement precision

If membrane deformation is used for pressure sensing, then pressure measurement capability is achieved, but thermo-mechanical stress causes offset and sensitivity drift

Engineering Contradiction:

Improvepressure measurement accuracyVSAvoidthermo-mechanical stress

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The sensor measures capacitance changes from both the sensing membrane and the dummy membrane. By comparing these measurements, the system can identify and compensate for thermo-mechanical stress effects, maintaining accurate pressure measurements despite the presence of harmful stress factors.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The invention changes the measurement parameter from single-ended capacitance to differential capacitance. By measuring the difference in capacitance changes between the sensing electrode and the dummy membrane, the system eliminates offset and sensitivity drift caused by thermo-mechanical stress while maintaining pressure measurement capability.

Inventive Principle:

Principle #35Parameter changes

3Device complexity

If fixed sensing electrode is used, then device structure is simplified, but substrate deformation affects sensing output

Engineering Contradiction:

Improveelectrode configurationVSAvoidsensing output accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The fixed sensing electrode is segmented into multiple parts positioned on opposite sides of the membrane, with corresponding segments on the dummy membrane. This segmentation enables differential measurement that cancels out substrate deformation effects while maintaining a relatively simple electrode configuration.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The sensing electrode segments are positioned asymmetrically relative to the membrane center, with specific geometric relationships defined between the segments. This asymmetric positioning optimizes the differential measurement capability while compensating for substrate deformation effects.

Inventive Principle:

Principle #4Asymmetry

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 approach significantly reduces sensitivity drift by a factor of 25 compared to prior art, maintaining accurate pressure readings even under substrate deformation, and allows for easier integration with other inertial sensors, while being compatible with standard CMOS processes.

Implementation Method 1

The pressure sensor measures pressure by measuring the deflection of a membrane using a capacitive read-out. The pressure sensor comprises a moveable electrode and a fixed sensing electrode, spaced by a defined gap wherein the movable electrode deforms in response to the pressure difference

Methodology Applied

Scientific EffectCapacitive sensing: Capacitance

Implementation Method 2

The fixed sensing electrode is suspended over the sealed cavity by an elastic support structure. The elastic support structure reduces the impact of substrate deformation on the sensing output

Methodology Applied

Scientific EffectElastic support: Elasticity

Data Source

PatentUS9352955B2MEMS pressure sensor with improved insensitivity to thermo-mechanical stress

Publication Date: 2016.05.31 HANKING ELECTRONICS HONGKONG CO LTD

AI summary

This invention relates generally to semiconductor manufacturing and packaging and more specifically to semiconductor manufacturing in MEMS (Microelectromechanical systems) inertial sensing products. Embodiments of the present invention improve pressure sensor performance (e.g., absolute and relative accuracy) by increasing pressure insensitivity to changes in thermo-mechanical stress. The pressure insensitivity can be achieved by using the array of pressure sensing membranes, suspended sensing electrodes, and dielectric anchors.