Out-of-Plane MEMS Resonator Using Stress Gradient Deflection

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Solution Overview

Problem

Conventional MEMS resonators operating in an in-plane mode face limitations due to nonlinear electrostatic forces, squeeze-film damping, and the need for costly or thermally taxing fabrication techniques to maintain flatness, which restrict their quality factor and transduction efficiency.

Innovation Solution

The development of MEMS devices with a structural layer having a residual film stress gradient that statically deflects a resonator out-of-plane, allowing for out-of-plane transduction without yield and reliability issues, and enabling better transduction efficiency and frequency adjustment through thickness modification.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional in-plane MEMS resonators are used with parallel-plate capacitor drive, then the resonator can be fabricated using standard techniques, but the electrostatic force becomes nonlinear and the quality factor is limited by squeeze-film dampening

Engineering Contradiction:

Improvequality factorVSAvoidnonlinear electrostatic force and squeeze-film dampening

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent transitions from in-plane lateral motion to out-of-plane motion. The resonator is designed to deflect vertically above and below the electrode plane rather than moving laterally within the plane. This dimensional change eliminates squeeze-film dampening between the resonator and electrode surfaces, and the electrostatic force becomes linear with respect to deflection distance, thereby improving quality factor and eliminating nonlinear effects.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Manufacturing precision

If fabrication techniques are used to ensure the resonator remains perfectly flat and in the plane of the electrode, then the resonator maintains proper alignment, but the fabrication becomes thermally taxing or requires prohibitively expensive methods

Engineering Contradiction:

Improveresonator flatness and alignmentVSAvoidfabrication cost and thermal processing

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

Instead of trying to fabricate a perfectly flat resonator that stays in the electrode plane, the patent inverts the approach by intentionally designing the resonator to be non-planar with a curved or bowed shape that enables out-of-plane motion. This inversion eliminates the need for expensive or thermally taxing flatness control techniques, as the resonator is designed to be out-of-plane from the start.

Inventive Principle:

Principle #13The other way round (Inversion)

3Reliability

If the resonator is designed for out-of-plane motion, then transduction efficiency improves and motional resistance decreases, but the resonator requires static out-of-plane deflection which needs to be controlled

Engineering Contradiction:

Improvetransduction efficiencyVSAvoidstatic deflection control

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent controls static out-of-plane deflection by adjusting physical parameters of the resonator structure, specifically the thickness and material composition of the structural layer. By changing these parameters, the resonator's natural curvature and static deflection are controlled, enabling reliable out-of-plane motion without adding device complexity. The structural layer thickness is optimized to provide the desired static deflection for maximum transduction efficiency.

Inventive Principle:

Principle #35Parameter changes

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 enhances transduction efficiency, reduces motional resistance, and allows for frequency trimming, independent of deflection distance and bias voltage, while eliminating the need for stress-reducing processing steps, thereby improving the performance of MEMS resonators.

Implementation Method 1

The structural layer is disposed about a perimeter of the electrode and has a residual film stress gradient. The residual film stress gradient deflects a first portion of the resonator out of a plane defined by a surface of the electrode.

Methodology Applied

Scientific EffectResidual film stress gradient: Stress Relaxation

Implementation Method 2

Forming the structural layer may include at least one of laser recrystallization or metal-induced crystallization to vary the crystallinity over the thickness of the structural element.

Methodology Applied

Scientific EffectMetal-induced crystallization: Crystallisation

Data Source

PatentUS8629739B2Out-of plane MEMS resonator with static out-of-plane deflection

Publication Date: 2014.01.14 SEMICON MFG INT (SHANGHAI) CORP

AI summary

A method of forming a microelectromechanical systems (MEMS) device includes forming an electrode on a substrate. The method includes forming a structural layer on the substrate. The structural layer is disposed about a perimeter of the electrode and has a residual film stress gradient. The method includes releasing the structural layer to form a resonator coupled to the substrate. The residual film stress gradient deflects a first portion of the resonator out of a plane defined by a surface of the electrode.