Capacitive Pressure Sensor Bimetal Effect Reduction

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Solution Overview

Problem

Conventional capacitive pressure sensors face challenges with the global bimetal effect due to external stress, requiring multiple small elements that increase size and reduce sensitivity, and suffer from undesirable local bimetal effects from material differences in sealing regions, leading to compromised performance.

Innovation Solution

A capacitive pressure sensor device with a movable sensing membrane spring-mounted via micromechanical spring elements, reducing the global bimetal effect by using a structured counterelectrode and sacrificial layers to enhance stiffness and minimize edge regions, while maintaining sensitivity and robustness.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If many small pressure sensor elements are combined to counter the global bimetal effect, then the sensitivity to external stress is improved, but the device size increases and the stroke of sensing membranes is reduced

Engineering Contradiction:

Improvesensitivity to external stressVSAvoiddevice size

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The sensing membrane is divided into multiple independently supported sensing regions, each with its own support structure. This segmentation allows each region to respond independently to pressure while the overall structure maintains resistance to global bimetal effects, achieving both small size and stress sensitivity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the sensing membrane have different support characteristics - central regions are fully supported while edge regions have reduced support. This local differentiation optimizes the stroke capability in supported areas while maintaining sensitivity to external stress through the unsupported edge regions.

Inventive Principle:

Principle #3Local quality

2Area of stationary object

If the base distances and working distances are reduced to compensate for large edge regions, then the device size is reduced, but the sensitivity to mechanical bending increases

Engineering Contradiction:

Improvedevice sizeVSAvoidsensitivity to mechanical bending

Core Design Contradiction:

Area of stationary objectVSReliability

Solution Approach 1:

The support structures provide localized stiffness exactly where needed - under the sensing membrane regions that require stability. This allows the use of larger base distances without increasing sensitivity to mechanical bending, as the support structures counteract bending forces locally rather than requiring overall dimensional reduction.

Inventive Principle:

Principle #3Local quality

3Reliability

If different materials are used in the sealing regions of the sensing membranes, then the sealing function is improved, but undesirable local bimetal effects arise

Engineering Contradiction:

Improvesealing functionVSAvoidlocal bimetal effects

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The sealing function is extracted from the sensing membrane structure itself and implemented through separate sealing structures or techniques. This allows the sensing membrane to be made of a single material composition, eliminating local bimetal effects while maintaining effective sealing through dedicated sealing mechanisms.

Inventive Principle:

Principle #2Taking out (Extraction)

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 results in a smaller, more sensitive, and cost-effective pressure sensor with reduced mechanical bending sensitivity and improved resilience to external stress, achieving higher resonance frequencies and lower temperature offsets.

Implementation Method 1

the sensing membrane being directly or indirectly spring-mounted, in particular spring-mounted in two-dimensional fashion, in the (reference) pressure chamber relative to the counterelectrode by at least one micromechanical spring element

Methodology Applied

Scientific EffectElasticity: Elasticity

Implementation Method 2

Via a sacrificial layer etching method, a sacrificial layer between the sensing membrane and the counterelectrode is removed through an etching access that passes through the sensing membrane

Methodology Applied

Scientific EffectChemical etching:

Implementation Method 3

a bending of a movable sensing membrane as electrode, or an electrode, can be determined based on a fluid pressure difference that has arisen, via a change of an electrical capacitance of the movable electrode relative to a counterelectrode situated opposite the sensing membrane

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentUS11585710B2Capacitive pressure sensor with reduced bimetal effect

Publication Date: 2023.02.21 ROBERT BOSCH GMBH

AI summary

A pressure sensor device for a pressure sensor, in particular a capacitive pressure sensor, having a pressure chamber bounded by a movable sensing membrane and a stationary counterelectrode of the pressure sensor device. The sensing membrane and the counterelectrode each run in the longitudinal direction and the transverse direction of the pressure sensor device. The sensing membrane is directly or indirectly spring-mounted, in particular spring-mounted in two-dimensional fashion, in the pressure chamber relative to the counterelectrode by at least one micromechanical spring element, in particular a plurality of micromechanical spring elements.