Ion Sensitive Sensor Multilayer Construction Alkaline Stability
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Solution Overview
Problem
Ion sensitive sensors with EIS structures, such as ISFETs, face instability in alkaline media, leading to potential damage and shifting of the working point due to media diffusion through the ion sensitive layer, which affects their precision and longevity.
Innovation Solution
A multilayer structure is implemented with a chemically stable intermediate insulator and an ion sensitive sensor layer, where the adapting or matching layer has electrical conductivity greater than the intermediate insulator, and an electrically conductive connection between the layers, using materials like tantalum oxide or tantalum oxynitride, to enhance media resistance and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Ta2O5 ion sensitive layer is used to achieve favorable sensitivity and linearity, then measurement precision is improved, but reliability deteriorates due to instability in alkaline media with pH>10
Solution Approach 1:
The sensor is divided into multiple functional layers: a Ta2O5 ion-sensitive layer for measurement precision and an underlying chemically stable insulator layer (e.g., SiO2, Si3N4, or polymer) for reliability in alkaline media. This segmentation allows each layer to perform its specialized function without compromising the other.
Solution Approach 2:
The sensor employs a composite structure combining Ta2O5 (for ion sensitivity) with chemically stable materials such as silicon oxide, silicon nitride, or fluorinated polymers. This composite approach leverages the advantageous properties of each material while mitigating their individual weaknesses, particularly the instability of Ta2O5 in high pH environments.
2Reliability
If multilayer construction with intermediate insulator is implemented to achieve media resistance, then reliability is improved, but device complexity increases
Solution Approach 1:
The sensor structure is segmented into distinct functional layers with clear interfaces: the ion-sensitive Ta2O5 layer, the chemically stable intermediate insulator layer, and the substrate oxide layer. This segmentation simplifies the design logic while achieving enhanced media resistance.
Solution Approach 2:
The intermediate insulator layer serves multiple functions simultaneously: it provides chemical stability in alkaline media, acts as a diffusion barrier, maintains electrical insulation, and supports the Ta2O5 layer. This multi-functionality reduces the need for additional specialized layers, thereby limiting complexity increase.
3Manufacturing precision
If ion sensitive layer and adapting layer form capacitor electrodes with intermediate insulator as dielectric, then manufacturing precision is achieved, but harmful factors increase due to charging and potential differences affecting working point stability
Solution Approach 1:
The chemically stable insulator layer acts as an intermediary barrier between the ion-sensitive Ta2O5 layer and the alkaline media. This intermediary prevents harmful interactions and stabilizes the electrical potential by blocking charge accumulation and potential differences that would otherwise destabilize the working point.
Solution Approach 2:
The patent converts the potential harmful effect of the capacitor structure (charging and potential differences) into a benefit by using the chemically stable insulator to control and stabilize these electrical characteristics. The insulator's low conductivity prevents charge leakage while maintaining stable potential, turning a potential problem into a stabilizing feature.
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 a media-resistant ion sensitive sensor with improved chemical stability, reduced hysteresis, and prolonged sensor lifetime, maintaining precise pH sensitivity even in extreme pH values and high temperatures.
Implementation Method 1
The adapting or matching layer and the ion sensitive, sensor layer each have an electrical conductivity greater than that of the intermediate insulator, wherein, according to the invention, there is an electrically conductive connection between the adapting or matching layer and the ion sensitive, sensor layer
Implementation Method 2
Ta2O5 ion sensitive layers, which have favorable properties as regards sensitivity and linearity, are especially unstable in the presence of alkaline media with a pH>10, which leads to such media diffusing through the ion sensitive layer; such media can damage or destroy deeper lying layers
Data Source
AI summary
An ion sensitive sensor having an EIS structure, including: a semiconductor substrate, on which a layer of a substrate oxides is produced; an adapting or matching layer, which is prepared on the substrate oxide; a chemically stable, intermediate insulator, which is deposited on the adapting or matching layer; and an ion sensitive, sensor layer, which is applied on the intermediate insulator. The adapting or matching layer differs from the intermediate insulator and the substrate oxide in its chemical composition and/or structure. The adapting or matching layer and the ion sensitive, sensor layer each have an electrical conductivity greater than that of the intermediate insulator. There is an electrically conductive connection between the adapting or matching layer and the ion sensitive, sensor layer.