Bulk-Substrate Proof Mass for Low-Noise MEMS Inertial Sensors

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Solution Overview

Problem

Existing MEMS inertial sensors face challenges with stiction risk, tether stiffness, and Brownian noise, which affect their performance and reliability.

Innovation Solution

Inertial sensors with a bulk substrate proof mass are developed, where a portion of the bulk substrate forms the proof mass, and a sensing structure detects relative motion between the bulk substrate and the proof mass, decoupling electrical and mechanical elements on different layers to reduce stiction risk and Brownian noise.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a proof mass is suspended by spring tethers over a substrate, then the proof mass can move in response to inertial forces, but stiction risk increases and tether stiffness decreases

Engineering Contradiction:

Improvestiction riskVSAvoidtether stiffness

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The proof mass is segmented from the bulk substrate through partial etching, creating a separate movable component that reduces stiction risk while maintaining mechanical connection through remaining tether structures

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent replaces traditional spring tethers with direct bulk substrate mechanical connections, eliminating the need for flexible spring elements and reducing stiction while maintaining stiffness through rigid substrate material properties

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Measurement precision

If traditional proof mass structures are used, then the sensor can detect inertial forces, but Brownian noise increases

Engineering Contradiction:

ImproveBrownian noiseVSAvoidsensor performance

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The proof mass is formed from bulk substrate material with increased mass and modified geometric parameters through partial etching, reducing Brownian noise through increased inertia while maintaining detectable motion range

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent utilizes composite structural approaches combining bulk substrate material with sensing structure materials to optimize both mechanical properties (reducing Brownian noise) and sensing capabilities

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 provides lower stiction risk, stiffer tethering, and reduced Brownian noise, enhancing the long-term stability and performance of MEMS inertial sensors.

Implementation Method 1

forming a sensing structure coupled to the bulk substrate, the capacitance sensing structure detecting a relative motion between the bulk substrate and the bulk substrate proof mass

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentUS20260063662A1Inertial sensors with bulk substrate proof mass

Publication Date: 2026.03.05 ANALOG DEVICES INC

AI summary

Inertial sensors with a bulk substrate proof mass are disclosed herein. In certain embodiments, an inertial sensor includes a bulk substrate and a bulk substrate proof mass formed from the bulk substrate. Additionally, the inertial sensor further includes a sensing structure that detects a relative motion between the bulk substrate and the bulk substrate proof mass. Accordingly, a portion of the bulk substrate is used to form the proof mass, which moves in a cavity relative to another portion of the bulk substrate that is fixed. Such an inertial sensor can provide a number of benefits including, for example, lower stiction risk, stiffer tethering, and/or lower Brownian noise.