pH Sensor Bonding Agent Strip Pattern for Deep-Sea Accuracy
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Solution Overview
Problem
Conventional pH sensors face accuracy limitations due to mechanical stresses induced by wide pressure and temperature variations in deep-sea environments, leading to measurement errors in ocean pH level monitoring.
Innovation Solution
A pH sensor design featuring an ion-sensitive field effect transistor (ISFET) die bonded to a substrate with a bonding agent material, utilizing a CTE mismatch effect to counteract pressure and temperature-induced mechanical stresses, achieved through anisotropic materials and strategic strip patterns of bonding agent materials with different thermal expansion coefficients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional pH sensors are used in deep-sea environments, then they can measure pH levels, but measurement accuracy deteriorates due to mechanical stresses from pressure and temperature variations
Solution Approach 1:
The patent changes the physical parameters of the bonding agent material by selecting materials with specific coefficients of thermal expansion (CTE) that differ from the ISFET die. This CTE mismatch creates thermal stress that compensates for piezoresistive effects, maintaining measurement accuracy across varying temperature and pressure conditions
Solution Approach 2:
The patent employs composite material structure consisting of the ISFET die bonded to a substrate through a bonding agent layer. This multi-material construction allows exploitation of differential thermal expansion properties between materials to generate compensating stresses that counteract pressure-induced measurement errors
2Measurement precision
If uniform bonding agent material is used between ISFET die and substrate, then bonding is simple, but piezoresistive errors are not reduced effectively
Solution Approach 1:
The patent applies local quality by using bonding agent material with non-uniform distribution or composition across the bonding interface. Specifically, the bonding agent may have varying CTE properties or be applied in specific patterns (e.g., strips, regions) to create localized stress fields that compensate for piezoresistive effects in different areas of the ISFET die
Solution Approach 2:
The bonding agent structure is segmented into different regions or layers with distinct material properties. This segmentation allows each region to contribute differently to the overall stress compensation, with some regions providing stronger CTE mismatch effects than others, thereby reducing piezoresistive errors more effectively
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 significantly reduces piezoresistive errors, maintaining the ISFET's resistance within 0.1-0.2% change over a pressure and temperature range, enhancing the accuracy of pH measurements in deep-sea conditions.
Implementation Method 1
utilizing a CTE mismatch effect to counteract pressure and temperature-induced mechanical stresses
Implementation Method 2
an ion sensing part that is configured to be exposed to a medium such that it outputs a signal related to the pH level of the medium
Data Source
AI summary
Embodiments described herein provide for a pH sensor that comprises a substrate and an ion sensitive field effect transistor (ISFET) die. The ISFET die includes an ion sensing part that is configured to be exposed to a medium such that it outputs a signal related to the pH level of the medium. The ISFET die is bonded to the substrate with at least one composition of bonding agent material disposed between the ISFET die and the substrate. One or more strips of the at least one composition of bonding agent material is disposed between the substrate and the ISFET die in a first pattern.