CMOS MEMS Resonator With Differential Piezoresistive Sensing

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Solution Overview

Problem

Conventional MEMS resonators face challenges in achieving high quality factor and signal-to-feedthrough ratio, leading to bulky size and high cost in RF systems, which impedes miniaturization and integration in wireless communication and sensor applications.

Innovation Solution

A MEMS resonator design featuring a substrate with an oscillator and a piezoresistor, where the piezoresistor has two output ends with a phase difference, allowing for improved motional signal extraction and reduced noise, utilizing CMOS fabrication processes for miniaturization and material efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If conventional MEMS resonator designs are used, then the quality factor can be maintained, but the signal-to-feedthrough ratio is insufficient and the device size remains bulky

Engineering Contradiction:

Improvesignal-to-feedthrough ratioVSAvoiddevice size

Core Design Contradiction:

Measurement precisionVSArea of stationary object

Solution Approach 1:

The resonator is segmented into distinct functional regions: a drive region with drive electrodes for generating oscillation, and a sense region with sense electrodes for detecting motion. This segmentation allows independent optimization of each region, improving signal-to-feedthrough ratio while reducing overall device area through focused functionality.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent transitions from planar electrode arrangements to a three-dimensional configuration where sense electrodes are positioned above the resonator structure at a controlled distance. This vertical dimensionality change enables enhanced coupling between the resonator and sense electrodes, improving signal detection without increasing the planar footprint.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Area of stationary object

If passive components are shrunk and integrated with transistor circuits, then miniaturization is achieved, but the quality factor decreases

Engineering Contradiction:

Improveintegration areaVSAvoidquality factor

Core Design Contradiction:

Area of stationary objectVSReliability

Solution Approach 1:

The patent replaces traditional mechanical coupling structures with electrostatic coupling fields. The resonator elements are coupled through electric fields generated by electrodes, eliminating the need for bulky mechanical connections and allowing direct integration with transistor circuits while preserving high quality factor through non-contact coupling.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent optimizes the electrostatic coupling parameters including electrode spacing, electrode area, and applied voltage to achieve strong coupling for miniaturization while maintaining the resonator's high quality factor. By carefully controlling these parameters, the system achieves both compact size and high performance.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If electrostatic MEMS resonators are used, then high quality factor is achieved, but the structure becomes complex and manufacturing difficulty increases

Engineering Contradiction:

Improvequality factorVSAvoidstructural complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The resonator structure serves multiple functions simultaneously: the same resonator elements that provide high quality factor oscillation also serve as the sensing elements for detecting motion. The electrodes function both as drive elements and as sense elements, eliminating the need for separate dedicated sense structures and simplifying the overall device architecture.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The patent merges the drive and sense functions into a unified resonator structure. The resonator elements are directly coupled to both drive and sense electrodes, combining what would traditionally be separate components into an integrated structure that reduces manufacturing complexity while maintaining high quality factor performance.

Inventive Principle:

Principle #5Merging (Combining)

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 design achieves a higher quality factor and signal-to-feedthrough ratio, enabling miniaturization and cost reduction while providing high added value through enhanced signal processing capabilities.

Implementation Method 1

the piezoresistor includes a first output end for outputting a first output signal and a second output end for outputting a second output signal, wherein a phase of the second output signal is different from a phase of the first output signal

Methodology Applied

Scientific EffectPiezoresistive effect: Piezoresistive Effect

Implementation Method 2

an oscillator and a piezoresistor, wherein the oscillator is located on the substrate

Methodology Applied

Scientific EffectMechanical vibration: Vibration

Data Source

PatentUS8854149B2MEMS resonator, manufacturing method thereof, and signal processing method using MEMS resonator

Publication Date: 2014.10.07 NATIONAL TSING HUA UNIVERSITY

AI summary

A capacitively-driven Micro-Electro-Mechanical System (MEMS) resonator is provided, in which a piezoresistively differential measurement is used to enable the MEMS resonator to transfer a signal. The MEMS resonator uses a Complementary Metal-Oxide-Semiconductor (CMOS) manufacturing process to make its oscillator and piezoresistor to achieve electrical insulation, thereby lowering the level of feedthrough signal.