TiN Sensing Layer for ISFET Microwell Capacitance Reduction
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Solution Overview
Problem
In electrochemical detection systems with microwell arrays, high capacitance between microwells and chemFETs affects the quality of output signals, making highly-sensitive measurements challenging.
Innovation Solution
A titanium nitride (TiN) layer is disposed on the gate structure of field effect transistors in the array structure, forming the bottom surface of microwells and acting as a barrier between the sample and the chemFET, improving impedance characteristics by forming an ohmic contact with the gate structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional microwell structures are used with chemFETs, then the basic sensing function is achieved, but high capacitance between microwell and chemFET degrades signal quality
Solution Approach 1:
A titanium nitride (TiN) layer is introduced as an intermediary between the microwell and the chemFET gate structure. This TiN layer forms an ohmic contact that acts as a mediator to improve electrical coupling and reduce capacitance effects, thereby enhancing signal quality without compromising the basic sensing function.
Solution Approach 2:
The invention changes the electrical parameters at the interface between microwell and chemFET by depositing a TiN layer. This material modification alters the capacitance and contact resistance parameters, creating an ohmic contact that optimizes the electrical characteristics for high-quality signal transfer.
2Measurement precision
If a TiN layer is deposited on the gate structure, then impedance characteristics are improved and signal quality increases, but the device structure becomes more complex
Solution Approach 1:
The gate structure is segmented into multiple functional layers, with the TiN layer deposited specifically on the gate structure to form the micrawell bottom. This segmentation allows the TiN layer to perform its specialized function of improving impedance characteristics while maintaining the overall chemFET structure.
Solution Approach 2:
The TiN layer serves multiple functions simultaneously: it forms the bottom surface of the micrawell, provides ohmic contact to reduce capacitance, and improves impedance characteristics. This multi-functionality achieves signal quality improvement without requiring additional separate components, thereby limiting the increase in device complexity.
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 TiN layer enhances the quality of output signals from chemFETs by reducing capacitance, allowing for higher sensitivity measurements by ensuring a higher fraction of the voltage signal is transferred to the floating gate, thereby improving detection capabilities.
Implementation Method 1
improving impedance characteristics by forming an ohmic contact with the gate structure
Data Source
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AI summary
A method of fabricating a microwell in an array structure is disclosed herein. The array structure includes a plurality of field effect transistors (FETs), where each FET has a gate structure. The method includes disposing a titanium nitride (TiN) layer on at least one conductive layer coupled to the gate structure of at least one FET. A insulation layer is disposed on the array structure, where the insulation layer lies above the TiN layer. Further, an opening above the gate structure of the at least one FET is etched to remove the insulation layer above the gate structure and to expose the TiN layer. A microwell with at least one sidewall formed from the insulation layer and with a bottom surface formed from the TiN layer is a result of the etching process. The gate structure is specified as a floating gate structure and the FET is an ISFET.