Strain Measuring Device Sheet Resistance Variability

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Solution Overview

Problem

Existing strain measuring devices using semiconductor single crystalline substrors with impurity diffused resistors face accuracy issues due to variability in sheet resistance and sensitivity offset, particularly with p-type impurity diffused resistors, leading to decreased measurement precision and increased power consumption.

Innovation Solution

The solution involves configuring p-type impurity diffused resistors with higher sheet resistance and fewer strip lines compared to n-type resistors, ensuring they are adjacent in bridged circuits with uniform strip line intervals, which reduces variability and offset, and optimizing impurity concentrations to minimize temperature dependence and strain sensitivity fluctuations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If p-type impurity diffused resistors are used in bridged circuits, then measurement capability is provided, but variability of sheet resistance increases leading to decreased measurement accuracy

Engineering Contradiction:

Improvestrain measurement accuracyVSAvoidsheet resistance variability

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent changes the sheet resistance parameter of p-type impurity diffused resistors to be equal to or higher than that of n-type impurity diffused resistors. This parameter change reduces the variability of sheet resistance in p-type resistors, thereby improving measurement accuracy while maintaining the measurement capability provided by p-type resistors

Inventive Principle:

Principle #35Parameter changes

2Use of energy by moving object

If multiple strip lines are connected to form meander shaped resistors, then power consumption is reduced, but the number of contacts and wirings increases leading to increased device complexity

Engineering Contradiction:

Improvepower consumptionVSAvoidnumber of contacts and wirings

Core Design Contradiction:

Use of energy by moving objectVSDevice complexity

Solution Approach 1:

The patent merges adjacent impurity diffused resistors by making them overlap in the thickness direction of the substrate. This combining approach allows the resistors to function as meander shaped structures for reduced power consumption while eliminating the need for separate contacts and wirings, thereby reducing device complexity

Inventive Principle:

Principle #5Merging (Combining)

3Use of energy by moving object

If impurity diffused resistors are configured as meander shaped strip lines, then power consumption decreases, but offset and sensitivity fluctuation increase due to variability

Engineering Contradiction:

Improvepower consumptionVSAvoidsensitivity offset and fluctuation

Core Design Contradiction:

Use of energy by moving objectVSMeasurement precision

Solution Approach 1:

The patent equalizes the sheet resistance parameter of p-type and n-type impurity diffused resistors, with p-type resistors having equal or higher sheet resistance. This parameter standardization reduces variability in the meander shaped resistor configuration, minimizing offset and sensitivity fluctuation while maintaining low power consumption

Inventive Principle:

Principle #35Parameter changes

4Ease of operation

If p-type and n-type impurity diffused resistors are used with different sheet resistance characteristics, then measurement functionality is achieved, but offset of bridged circuit increases

Engineering Contradiction:

Improvemeasurement functionalityVSAvoidbridged circuit offset

Core Design Contradiction:

Ease of operationVSMeasurement precision

Solution Approach 1:

The patent modifies the sheet resistance parameter of p-type impurity diffused resistors to be equal to or higher than that of n-type resistors. This parameter adjustment balances the characteristics of both resistor types in the bridged circuit, reducing circuit offset while preserving measurement functionality

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

By equalizing the sheet resistance of p-type and n-type impurity diffused resistors, the patent creates equipotential conditions in the bridged circuit. This balance eliminates potential differences that cause offset, thereby improving measurement precision while maintaining full measurement functionality

Inventive Principle:

Principle #12Equipotentiality

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 configuration results in a strain measuring device with reduced variability in sheet resistance and sensitivity fluctuations, enabling highly accurate strain measurements, including biaxial strain, while maintaining low power consumption and minimizing measurement errors due to temperature changes.

Implementation Method 1

there is a method to measure strain of an object by attaching this mechanical quantity measuring device to the object, based on change of the resistance of the impurity diffused resistors caused by the strain

Methodology Applied

Scientific EffectPiezoresistive effect: Piezoresistive Effect

Data Source

PatentUS8186228B2Strain measuring device

Publication Date: 2012.05.29 HITACHI LTD

AI summary

A strain measuring device includes a bridge circuit comprising a p-type impurity diffused resistor as a strain detecting portion and a bridge circuit comprising an n-type impurity diffused resistor as a strain detecting portion in a semiconductor single crystalline substrate, Sheet resistance of the p-type impurity diffused resistor is 1.67 to 5 times higher than that of the n-type impurity diffused resistor. Furthermore, the impurity diffused resistor is configured to be a meander shape including strip lines and connecting portions.