Differential ISFET pH Sensor with Noble Metal Reference Electrode
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Solution Overview
Problem
Existing pH-change sensors face limitations in commercialization due to the size and complexity of reference electrodes, requiring specialized post-processing steps that increase costs and hinder mass production, especially when integrated with CMOS processes.
Innovation Solution
A differential ISFET configuration using a noble metal electrode as a pseudo or quasi-reference electrode, with two ion-sensitive transistor-operational-transconductance-amplifiers (IOTAs) having different drain-to-source resistances, allowing for pH change detection without additional processing steps, and incorporating a gold wire reference electrode for cost-effective integration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional Ag/AgCl reference electrode is used, then proper electrode-electrolyte potential is provided, but the size and complexity severely limit applicability and mass production capability
Solution Approach 1:
The patent extracts the reference electrode function from the complex Ag/AgCl structure and integrates it directly into the ISFET device as a simple gold wire or noble metal electrode. This eliminates the need for separate reference electrode components and their associated complexity, while maintaining the essential function of providing stable electrode-electrolyte potential.
Solution Approach 2:
The patent merges the reference electrode function with the ISFET structure by integrating the gold wire reference electrode directly into the transistor device. This combination eliminates the need for separate reference electrode components and their associated complexity, while maintaining the essential function of providing stable electrode-electrolyte potential.
2Manufacturing precision
If specialized post-processing steps are added for ISFET fabrication, then pH-sensitive layer deposition is achieved, but manufacturing cost increases and mass production capability is hindered
Solution Approach 1:
The patent makes the standard CMOS fabrication process universal by designing the ISFET structure to be compatible with existing CMOS manufacturing steps. The pH-sensitive layer is deposited as part of the standard process sequence, eliminating the need for specialized post-processing and enabling mass production using conventional CMOS facilities.
Solution Approach 2:
The patent incorporates the pH-sensitive layer deposition into the standard CMOS fabrication sequence as a preliminary step. By integrating this step into the existing manufacturing flow rather than adding it as a separate post-processing operation, the patent maintains manufacturing precision while enabling mass production.
3Ease of manufacture
If differential ISFET configuration with noble metal electrode is used, then pH change detection is enabled without additional processing, but device complexity increases
Solution Approach 1:
The patent uses a differential configuration where two ISFETs are used - one as the sensing device and the other as a reference device with identical structure. This copying approach allows pH change detection without additional processing, as both devices follow the same standard CMOS fabrication process, while the complexity is managed through the use of identical, well-understood device structures.
4Ease of manufacture
If CMOS fabricating techniques are used, then low cost and mass production are enabled, but power consumption may be higher
Solution Approach 1:
The patent employs operational transconductance amplifiers that automatically adjust their operation based on the input signal conditions. The differential configuration allows the circuit to self-regulate power consumption by only activating necessary components when pH changes occur, reducing overall power consumption while maintaining the benefits of CMOS fabrication for low cost and mass production.
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
Enables the production of low-cost, low-power, disposable pH-change sensors that can be mass-produced without specialized post-fabrication processing, with improved manufacturing efficiency and the ability to detect pH changes accurately, reducing variations from temperature and ambient light.
Implementation Method 1
a pH-sensitive layer (43) over the gate (41)
Implementation Method 2
using a noble metal electrode (either gold or platinum) as the pseudo or quasi reference electrode
Data Source
AI summary
pH-change sensors and related methods are disclosed. One such sensor may have a first ion-sensitive transistor-operational-transconductance-amplifier (the “first IOTA”) and a second ion-sensitive transistor-operational-transconductance-amplifier (the “second IOTA”). Each IOTA may have an ion-sensitive transistor, a load transistor, and an output. In each IOTA, the drain region of the ion-sensitive transistor may be connected to the drain region of the load transistor. A differential sensor may be connected to the IOTAs, and an output from the differential sensor may indicate a voltage difference between the IOTA outputs. The output from the differential sensor may be used to provide an indication of a change in pH.