MEMS RMS Sensor Thermal Isolation via Segmentation

Solution Overview

Problem

Existing root mean square (RMS) sensors face challenges in providing accurate and high-performance measurements due to mechanical and thermal stress from packaging, as well as limitations in linearity and frequency range, especially when operating from DC to high frequencies.

Innovation Solution

A sensor device incorporating micro-electro-mechanical (MEM) structures with thermal converters, featuring a heating element and temperature sensing element separated by insulating layers for galvanic isolation, and a support structure for mechanical and thermal isolation, allowing for high linearity and precision across a wide frequency range.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a thermal converter is used to convert AC signal to RMS value, then the heating effect measurement is achieved, but mechanical and thermal stress from packaging degrades measurement accuracy

Engineering Contradiction:

ImproveRMS measurement accuracyVSAvoidmechanical and thermal stress

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The device is divided into two separate MEMS structures: one dedicated to heating (heating element) and the other to sensing (temperature sensing element). This segmentation isolates the harmful thermal effects from the measurement function, allowing the sensing element to remain unaffected by the heating stress while still measuring the thermal effect needed for RMS calculation.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A thermal coupling structure acts as an intermediary between the heating element and the temperature sensing element. This mediator transfers the thermal energy from the heating element to the sensing element while isolating them mechanically and thermally, allowing accurate temperature measurement without direct stress transfer.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If conventional RMS sensors are used, then basic RMS measurement is achieved, but linearity and frequency range are limited especially from DC to high frequencies

Engineering Contradiction:

Improvefrequency rangeVSAvoidlinearity

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The patent replaces conventional mechanical RMS sensing mechanisms with a thermal-based MEMS system. The thermal conversion process naturally handles DC to high-frequency signals with superior linearity, as the thermal mass acts as an inherent integrator that maintains measurement accuracy across the entire frequency range without mechanical resonance limitations.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Volume of moving object

If heating element and temperature sensing element are placed close together for compact design, then device size is reduced, but thermal stress and mechanical stress from packaging affect measurement accuracy

Engineering Contradiction:

Improvedevice sizeVSAvoidmeasurement accuracy

Core Design Contradiction:

Volume of moving objectVSMeasurement precision

Solution Approach 1:

The device is divided into two separate MEMS structures: one dedicated to heating (heating element) and the other to sensing (temperature sensing element). This segmentation isolates the harmful thermal effects from the measurement function, allowing the sensing element to remain unaffected by the heating stress while still measuring the thermal effect needed for RMS calculation.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A thermal coupling structure acts as an intermediary between the heating element and the temperature sensing element. This mediator transfers the thermal energy from the heating element to the sensing element while isolating them mechanically and thermally, allowing accurate temperature measurement without direct stress transfer.

Inventive Principle:

Principle #24Intermediary (Mediator)

4Ease of manufacture

If thermal converter circuit is integrated directly with surrounding substrate, then manufacturing is simplified, but mechanical stress and thermal interference degrade performance

Engineering Contradiction:

Improveintegration simplicityVSAvoidperformance stability

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The device is divided into two separate MEMS structures: one dedicated to heating (heating element) and the other to sensing (temperature sensing element). This segmentation isolates the harmful thermal effects from the measurement function, allowing the sensing element to remain unaffected by the heating stress while still measuring the thermal effect needed for RMS calculation.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A thermal coupling structure acts as an intermediary between the heating element and the temperature sensing element. This mediator transfers the thermal energy from the heating element to the sensing element while isolating them mechanically and thermally, allowing accurate temperature measurement without direct stress transfer.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 MEM-based sensor device achieves high linearity and precision in RMS value representation, maintaining performance independent of mechanical stress and environmental conditions, with the ability to operate from DC to high frequencies without loading the signal being measured.

Implementation Method 1

a thermal converter circuit that is configured to heat the core region in response to a signal at an input thereof

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Implementation Method 2

a temperature sensing element on a second layer of the first MEM structure... the first layer being separated from the second layer by at least one insulating layer

Methodology Applied

Scientific EffectTemperature sensing: Thermistor

Implementation Method 3

The first MEM structure also includes a first temperature sensing element on a second layer of the first MEM structure, the first layer being separated from the second layer by at least one insulating layer

Methodology Applied

Scientific EffectThermal insulation: Thermal Insulation

Implementation Method 4

The support structure is configured to support the central core region to be thermally and mechanically isolated with respect to the surrounding substrate

Methodology Applied

Scientific EffectThermal isolation: Thermal Insulation

Data Source

PatentUS11884538B2Root mean square sensor device

Publication Date: 2024.01.30 TEXAS INSTRUMENTS INC

AI summary

A sensor device includes a first and second Micro-Electro-Mechanical (MEM) structures. The first MEM structure includes a first heating element on a first layer of the first MEM structure. The first heating element includes an input adapted to receive an input signal. The first MEM structure also includes a first temperature sensing element on a second layer of the first MEM structure. The second MEM structure includes a second heating element on a first layer of the second MEM structure and a second temperature sensing element on a second layer of the second MEM structure. An output circuit has a first input coupled to the first temperature sensing element and a second input coupled to the second temperature sensing element.