Dual FET Sensor Eliminates Immersed Electrode for Biomolecule Detection
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Solution Overview
Problem
Existing FET-based sensors for biomolecules and charged ions face challenges such as cumbersome setup due to immersed electrodes, reliability issues, high sensitivity requirements, and complex fabrication processes for thin silicon nanowires and buried oxide layers, which limit miniaturization and automation.
Innovation Solution
A dual FET sensor structure comprising a control FET and a sense FET with a shared node, where the electrolyte acts as the gate of the sense FET, eliminating the need for an immersed electrode, and the gate dielectric surface is functionalized to bind biomolecules, allowing detection based on changes in drain current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an electrode is immersed in the electrolyte to apply voltage to the FET gate, then the sensor can detect biomolecules, but the setup becomes cumbersome and reliability deteriorates due to chemical changes in the electrode material
Solution Approach 1:
The patent extracts and removes the electrode component from the sensing system. Instead of using an immersed electrode to apply voltage to the FET gate, the system uses a reference electrode in a separate reference electrolyte chamber, eliminating the problematic immersed electrode from the main sensing electrolyte and thereby improving reliability while simplifying the setup.
Solution Approach 2:
The patent introduces a reference electrolyte chamber as an intermediary system. This separate chamber with its own reference electrode mediates the voltage application function, allowing the main sensing electrolyte to remain free of immersed electrodes while still enabling proper FET gate control through the shared membrane interface.
2Use of energy by moving object
If the buried oxide layer thickness is reduced to lower sensing voltage, then sensing voltage decreases, but fabrication complexity and cost increase
Solution Approach 1:
The patent changes the electrical parameters of the buried oxide layer by introducing fixed positive charges through specific fabrication processes. This parameter change allows the oxide layer to function as a back-gate that provides the necessary electric field for low-sensing-voltage operation while maintaining a thicker, easier-to-fabricate oxide layer structure.
3Measurement precision
If silicon nanowire diameter is reduced to improve sensitivity, then sensitivity increases, but fabrication yield deteriorates
Solution Approach 1:
The patent changes the electrical parameters of the silicon nanowire FET by introducing fixed charges in the buried oxide layer, which modifies the threshold voltage and electric field distribution. This allows the use of thicker, easier-to-fabricate nanowires while maintaining high sensitivity through the enhanced electric field effect from the charged oxide layer.
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 detection of biomolecules and charged ions without an immersed electrode, improving sensitivity and simplifying fabrication while reducing complexity and cost, thus enhancing sensor reliability and miniaturization potential.
Implementation Method 1
the gate dielectric surface is functionalized to bind biomolecules
Implementation Method 2
A field effect transistor (FET), comprising a source, a drain, and a gate, may be used as a sensor for various types of biomolecules
Data Source
AI summary
A method for operating a sensor for biomolecules or charged ions, the sensor comprising a first field effect transistor (FET) and a second FET, wherein the first FET and the second FET comprise a shared node includes placing an electrolyte containing the biomolecules or charged ions on a sensing surface of the sensor, the electrolyte comprising a gate of the second FET; applying an inversion voltage to a gate of the first FET; making a first electrical connection to an unshared node of the first FET; making a second electrical connection to unshared node of the second FET; determining a change in a drain current flowing between the unshared node of the first FET and the unshared node of the second FET; and determining an amount of biomolecules or charged ions contained in the electrolyte based on the determined change in the drain current.