MEMS Airflow Sensor Die Integrating Signal Processing Circuitry

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Solution Overview

Problem

Existing flow sensors with external differential instrumentation and offset correction circuitry increase product costs, reduce reliability, and result in larger form factors due to added components, noise, and leakage issues, particularly when measuring small fluid flows.

Innovation Solution

Integration of a differential instrumentation amplifier and offset correction circuitry directly on the MEMS airflow die using bulk and surface micromachining techniques, leveraging unused silicon space without enlarging the die, along with heater control and temperature compensation circuitry.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If external differential instrumentation amplifier and offset correction circuitry are used, then the sensor can perform basic flow measurement functions, but the product cost increases

Engineering Contradiction:

Improveflow measurement capabilityVSAvoidproduct cost

Core Design Contradiction:

Measurement precisionVSEase of manufacture

Solution Approach 1:

The patent combines the transducer element, differential instrumentation amplifier, offset correction circuitry, temperature compensation, and heater control into a single integrated MEMS device. This merging eliminates the need for separate external components, reducing assembly costs and improving manufacturing efficiency while maintaining flow measurement functionality.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The MEMS die is designed to perform multiple functions: flow sensing, signal amplification, offset correction, temperature compensation, and heater control. This multi-functionality is achieved by integrating all necessary circuitry on the same die, reducing the overall system complexity and cost.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Measurement precision

If external differential instrumentation amplifier and offset correction circuitry are used, then the sensor can perform basic flow measurement functions, but the reliability decreases

Engineering Contradiction:

Improveflow measurement capabilityVSAvoidproduct reliability

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent incorporates temperature compensation circuitry and offset correction mechanisms within the integrated device to preemptively compensate for environmental variations and drift. This beforehand cushioning approach maintains measurement reliability without requiring additional external components that could introduce failure points.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

3Measurement precision

If external differential instrumentation amplifier and offset correction circuitry are used, then the sensor can perform basic flow measurement functions, but the form factor increases

Engineering Contradiction:

Improveflow measurement capabilityVSAvoidform factor

Core Design Contradiction:

Measurement precisionVSArea of stationary object

Solution Approach 1:

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent transitions from a planar arrangement of separate components to a three-dimensional integrated structure where multiple functional layers are stacked vertically on the MEMS die. This dimensional change allows all circuitry to be contained within a compact footprint, maintaining small form factor while providing complete flow measurement functionality.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

4Measurement precision

If external components are added, then the sensor can perform basic flow measurement functions, but the noise increases

Engineering Contradiction:

Improveflow measurement capabilityVSAvoidnoise

Core Design Contradiction:

Measurement precisionVSObject-generated harmful factors

Solution Approach 1:

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The integrated MEMS structure acts as an intermediary that directly couples the transducer element with the signal processing circuitry, eliminating the need for external connections and interfaces that would introduce noise. This direct integration maintains signal integrity while reducing electromagnetic interference and thermal noise.

Inventive Principle:

Principle #24Intermediary (Mediator)

5Measurement precision

If external components are added, then the sensor can perform basic flow measurement functions, but the leakage current increases

Engineering Contradiction:

Improveflow measurement capabilityVSAvoidleakage current

Core Design Contradiction:

Measurement precisionVSObject-generated harmful factors

Solution Approach 1:

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

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

This approach reduces product costs, size, noise, and leakage current, enhancing sensor reliability and accuracy while maintaining a compact form factor, making it more cost-effective and suitable for industrial and HVAC applications.

Implementation Method 1

heater control circuitry

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Implementation Method 2

temperature compensation circuitry

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentUS8640552B2MEMS airflow sensor die incorporating additional circuitry on the die

Publication Date: 2014.02.04 HONEYWELL INTERNATIONAL INC

AI summary

A MEMS airflow sensor die having a heater control circuit, differential instrumentation amplifier, temperature compensation, and/or offset correction circuitry integrated with an airflow sensor on the MEMS die. The added circuitry may be placed on space available on the basic airflow die with MEMS fabrication techniques without enlarging the sensor die. The die with the added circuitry may result in a device having a reduced form factor, improved reliability and lower cost.