Inorganic ISFET Reference Electrode Stability via CMOS Integration
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Solution Overview
Problem
The microminiaturization of reference electrodes in Ion Sensitive Field Effect Transistor (ISFET) systems is hindered by stability and service life issues, which restricts their application in biomedical fields due to the limitations of conventional glass reference electrodes and organic membranes.
Innovation Solution
The integration of inorganic Ion Sensitive Field Effect Transistor and Reference Field Effect Transistor on a semiconductor substrate using a P-type silicon chip with N-well and P-well structures, single-layer silicon nitride, and platinum, allowing for the formation of an inorganic membrane with adjustable sensitivity and high deformation stress, and the use of a differential amplifier to reduce non-ideal effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional glass reference electrode is used in ISFET system, then stable potential can be provided, but the electrode stability and service life are reduced due to microminiaturization
Solution Approach 1:
The patent merges the reference electrode function directly into the semiconductor substrate by forming a reference well (P-well or N-well) within the substrate itself. This integration eliminates the need for separate glass reference electrodes and internal ion exchange solutions, thereby maintaining electrode stability while enabling microminiaturization and extending service life through solid-state construction.
Solution Approach 2:
The patent replaces the mechanical/chemical system of glass reference electrodes with internal ion exchange solutions with a solid-state semiconductor-based reference well. This substitution eliminates the depletion of internal ion exchange solutions that limits service life in miniaturized glass electrodes, while maintaining stable potential through the semiconductor's inherent properties.
2Measurement precision
If organic membrane is employed to form ion-blocking or ion-unblocking layer, then sensitivity can be adjusted, but the transconductance of element is decayed and process complexity increases
Solution Approach 1:
The patent changes the material parameter from organic membrane to inorganic semiconductor material (P-type or N-type doped silicon). This parameter change allows sensitivity adjustment through doping concentration control while maintaining high transconductance and enabling complete CMOS process compatibility, thereby reducing overall device complexity.
Solution Approach 2:
The patent uses homogeneous semiconductor material (P-type or N-type doped silicon) for both the sensing element and reference electrode, eliminating the need for heterogeneous organic membrane layers. This homogeneity simplifies the manufacturing process to standard CMOS steps while maintaining adjustable sensitivity through doping variations.
3Ease of manufacture
If inorganic membrane is used to form Reference Field Effect Transistor, then the process can be simplified and compatible with CMOS process, but the sensitivity adjustment capability is reduced
Solution Approach 1:
The patent uses parameter changes in the semiconductor doping concentration to achieve sensitivity adjustment. By varying the doping level in the P-well or N-well, the sensitivity of the reference electrode can be precisely controlled while maintaining full CMOS process compatibility and using only inorganic materials throughout the structure.
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 enhances the stability and service life of reference electrodes, improves transconductance, and simplifies the manufacturing process, enabling more efficient and accurate ion concentration sensing while reducing operational costs and environmental impact.
Implementation Method 1
the first single-layer silicon nitride (Si3N4) (108A) is formed on the surface of N-well (102) to form the first hydrogen ion sensitive membrane, because the first silicon nitride (108A) will not influence the sensitivity of hydrogen ion
Implementation Method 2
the second single-layer silicon nitride (108B) is formed on the surface of P-well (104) to form the second hydrogen ion sensitive membrane, it can reduce the sensitivity of hydrogen ion effectively
Data Source
AI summary
The invention discloses a sensitive field effect transistor apparatus, which uses an inorganic membrane to sense hydrogen ions. The invention adopts the membrane with high deformation stress. The sensitivity of the sensitive membrane to hydrogen ions is adjusted through altering the membrane thickness and changing the substrate type and doped concentration. A differential amplifier is used to read a signal to form the inorganic Ion Sensitive Field Effect Transistor/Reference Field Effect Transistor apparatus.