Electrostatic Acceleration Sensor Shielding Film

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Solution Overview

Problem

Existing electrostatic-capacitance-type acceleration sensors face issues with flexibility in wiring design, sealing integrity, and movable electrode sticking due to static charge during anodic bonding, leading to variations in electrical characteristics and potential water penetration.

Innovation Solution

An electrostatic-capacitance-type acceleration sensor design featuring a conductive shielding film on the cap's central region, electrically connected to the movable part, which prevents electrode sticking and maintains sealing by equalizing potential and smoothing surface irregularities, ensuring reliable operation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If polycrystalline silicon and insulating film are stacked to form bonding frame and wiring, then flexibility in wiring design is improved, but surface irregularities become larger causing insufficient sealing

Engineering Contradiction:

Improvewiring design flexibilityVSAvoidsurface flatness

Core Design Contradiction:

Adaptability or versatilityVSManufacturing precision

Solution Approach 1:

A planarization layer is introduced as an intermediary between the stacked polycrystalline silicon and insulating film structure and the glass cap. This planarization layer smooths out surface irregularities while allowing the underlying multi-layer wiring structure to maintain its design flexibility, thus resolving the contradiction between wiring flexibility and surface flatness for sealing.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If anodic bonding is performed to seal the glass cap, then sealing integrity is improved, but static charge causes movable electrode to stick-bond

Engineering Contradiction:

Improvesealing integrityVSAvoidstatic charge

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent applies a conductive coating layer on the glass cap surface that normally serves as a shielding layer for ESD protection. During anodic bonding, this conductive layer acts as a charge dissipation path, converting the potentially harmful static charge into a beneficial charge dissipation mechanism that prevents movable electrode sticking while maintaining sealing integrity.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The surface properties of the glass cap are modified by applying a conductive coating layer, changing the electrical parameters of the bonding interface. This parameter change allows the bonding process to proceed with improved charge management, preventing static charge accumulation that would cause electrode sticking.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If single-crystalline silicon layer is used for bonding frame, then sealing is achieved, but wiring design flexibility is limited

Engineering Contradiction:

ImprovesealingVSAvoidwiring design flexibility

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The bonding frame structure is segmented into multiple functional layers: polycrystalline silicon layers for wiring implementation, insulating film layers for electrical isolation and structural support, and a planarization layer for surface smoothing. This segmentation allows different portions of the bonding frame to fulfill different functions, achieving both sealing capability and wiring design flexibility.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The bonding frame is constructed as a composite structure combining polycrystalline silicon, insulating films, and planarization layer. This composite material approach allows the bonding frame to simultaneously provide mechanical sealing (from the rigid structure), electrical functionality (from the polycrystalline silicon wiring), and surface quality (from the planarization layer).

Inventive Principle:

Principle #40Composite materials

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 enhances flexibility in wiring design, maintains sealing integrity, and prevents movable electrode sticking, resulting in stable and reliable acceleration sensor performance with improved sealing and reduced electrical characteristic variations over time.

Implementation Method 1

a conductive shielding film formed at least on the entire surface of the central region of the cap, wherein the shielding film is electrically connected to the movable part

Methodology Applied

Scientific EffectElectrostatic shielding: Faraday Cage

Implementation Method 2

the glass cap and the bonding frame are bonded by the anodic bonding

Methodology Applied

Scientific EffectAnodic bonding:

Data Source

PatentUS7533570B2Electrostatic-capacitance-type acceleration sensor

Publication Date: 2009.05.19 MITSUBISHI ELECTRIC CORP

AI summary

In an electrostatic-capacitance-type acceleration sensor, water, etc. penetrating into a sealed space incorporating an acceleration detector having a movable electrode 6, and sticking of the movable electrode 6 to a cap 8 due to static charge accumulated on the cap 8 during the anodic bonding being performed are prevented. A conductive shielding film 9 that can be extendedly transformed on the entire inner face of the cap 8 constituting the sealed space is provided, which is not only extendedly arranged so as to be sandwiched between a bonding frame 7 and the cap 8, but also electrically connected to the movable electrode 6; thereby, even if unevenness exists on the surface of the bonding frame 7, not only sufficient anodic bonding between the bonding frame 7 and the cap 8 becomes possible, but also the electric field due to the static charge accumulated in the cap 8 can be shielded.