MEMS Stiction Detection via Electrostatic Stress Testing

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Solution Overview

Problem

MEMS devices are vulnerable to stiction failures due to adhesion forces during manufacturing and usage, which affect device performance and reliability, and existing solutions either increase device size, cost, or compromise performance.

Innovation Solution

A high voltage smart circuit is used to perform a stress test on MEMS devices, applying an electrostatic force to detect and characterize stiction by measuring capacitance changes between movable and stationary parts, allowing for the identification and screening out of devices prone to stiction failures.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If material stiffness is increased to improve stiction robustness, then the mechanical restoring force increases, but device performance is reduced

Engineering Contradiction:

Improvestiction robustnessVSAvoiddevice performance

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent applies a preliminary stress test during manufacturing that simulates stiction conditions by applying electrostatic forces to deflect the proof-mass toward the substrate. This allows stiction-prone devices to be identified and screened out before deployment, resolving the contradiction by maintaining original material properties for performance while eliminating reliability issues through pre-screening

Inventive Principle:

Principle #10Preliminary action

2Reliability

If surface conditions are improved during fabrication to minimize stiction, then stiction effects are reduced, but manufacturing cost increases

Engineering Contradiction:

Improvestiction resistanceVSAvoidmanufacturing cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

Instead of implementing costly surface treatment processes during fabrication, the patent introduces a preliminary electrostatic stress test that identifies stiction-prone devices based on their electrical characteristics. This approach resolves the contradiction by maintaining simple, low-cost manufacturing processes while achieving reliable stiction resistance through electrical screening of defective devices

Inventive Principle:

Principle #10Preliminary action

3Reliability

If a stress test is implemented to detect stiction failures, then device reliability is improved, but device complexity increases

Engineering Contradiction:

Improvestiction failure detectionVSAvoidtesting circuit complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent implements a stress test that utilizes the MEMS device's own capacitive structure and electrostatic characteristics to perform self-diagnosis. By applying electrostatic forces and measuring the device's electrical response, the system resolves the contradiction by achieving reliable stiction detection without requiring external complex testing equipment or additional sensing components

Inventive Principle:

Principle #25Self-service

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 method enhances the reliability of MEMS devices by effectively detecting and preventing stiction failures during manufacturing, without increasing device size or sacrificing performance, thereby ensuring accurate operation and extended device lifespan.

Implementation Method 1

selectively apply a voltage to a fixed electrode to generate an electrostatic force that attracts a movable proof-mass within the MEMS device

Methodology Applied

Scientific EffectElectrostatic force: Electrostatics

Implementation Method 2

The stress test comprises directly or indirectly determining a capacitance value between the movable part and a fixed electrode

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 3

Stiction effects typically occur between two surfaces when an external force deflects a movable part in a manner so as to cause its surface to come in physical contact and adhere to the surface of an adjacent stationary part

Methodology Applied

Scientific EffectAdhesion: Adhesive

Implementation Method 4

Stiction adversely affects device performance and may be caused by a variety of forces including capillary forces caused by the presence of moisture

Methodology Applied

Scientific EffectCapillary forces: Capillary Action

Implementation Method 5

Stiction adversely affects device performance and may be caused by a variety of forces including van der Waals forces caused by surface contamination

Methodology Applied

Scientific EffectVan der Waals forces: Van der Waals Force

Data Source

PatentUS9733268B2Systems and methods to determine stiction failures in MEMS devices

Publication Date: 2017.08.15 HANKING ELECTRONICS HONGKONG CO LTD

AI summary

Various embodiments of the invention provide for stiction testing in MEMS devices, such as accelerometers. In certain embodiments, testing is accomplished by a high voltage smart circuit that enables an analog front-end circuit to accurately read the position of a movable proof-mass relative to a biased electrode in order to allow the detection of both contact and release conditions. Testing allows to detect actual or potential stiction failures and to reject defective parts in a Final Test stage of a manufacturing process where no other contributors to stiction issue can occur, thereby, minimizing stiction failure risks and extending the reliability of MEMS devices.