Multi-Gate ISFET Sensor with Asymmetric Source Resistance
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Solution Overview
Problem
Conventional ion-sensitive field-effect transistors (ISFETs) have limited sensitivity, which is inadequate for applications such as human genome sequencing, and scaling up sensor dimensions to improve sensitivity leads to undesirable increases in sensor size.
Innovation Solution
A sensor device with a multi-gate design, featuring a first semiconductor structure and a second semiconductor structure with different source and drain resistances, where the second source resistance is higher than the first, allowing for compensation of pH changes in the solution to maintain a constant current flow, thereby enhancing sensitivity without increasing sensor size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional ISFET design is used, then manufacturing simplicity is maintained, but sensitivity is limited to the Nernst limit of 59 mV/pH
Solution Approach 1:
The patent merges two transistor structures into a single integrated device where the first transistor's gate structure serves dual purposes: as the sensing element for pH detection and as part of the overall transistor operation. This integration allows the device to achieve enhanced sensitivity through the combined operation of both transistors while maintaining a compact, manufacturable structure using standard CMOS processes.
Solution Approach 2:
The gate oxide layer and gate structure serve as an intermediary between the pH-sensitive solution and the transistor channel. This intermediary structure transduces the chemical pH signal into an electrical signal that modulates the current flow, enabling sensitive detection while maintaining clear separation between the chemical sensing function and the electrical signal processing function.
2Measurement precision
If sensor dimensions are scaled up to improve sensitivity, then sensitivity increases, but sensor size increases undesirably
Solution Approach 1:
The patent moves from a single-transistor design to a two-transistor integrated structure, adding a dimensional aspect to the sensing mechanism. By incorporating a second transistor with different source resistance that operates in conjunction with the first transistor, the device achieves enhanced sensitivity through the interaction of multiple current paths without requiring proportional increases in the physical footprint of individual components.
Solution Approach 2:
The patent changes the electrical parameters of the transistor structure by introducing a second transistor with specifically engineered source resistance that differs from the first transistor. This parameter differentiation allows the device to operate in a regime where small changes in gate voltage (caused by pH changes) produce amplified changes in current, thereby increasing sensitivity without scaling up the physical dimensions.
3Measurement precision
If dual gate ISFET with back gate is used, then sensitivity is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The gate structure in the patent serves multiple functions: it acts as the pH-sensitive sensing element, provides gate control for the first transistor, and its voltage influences the overall device operation through the coupled transistor configuration. This multi-functionality eliminates the need for separate back-gate structures while achieving similar or enhanced sensitivity improvements.
Solution Approach 2:
The patent achieves sensitivity enhancement by changing the operational parameters of standard CMOS transistors rather than introducing entirely new device structures. By carefully selecting and engineering the source resistance values of the two transistors and operating them in a coupled configuration, the device achieves improved sensitivity using existing manufacturing processes and device types.
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 multi-gate sensor device achieves improved sensitivity by compensating for pH changes with a higher second source resistance, allowing for more precise detection of biochemical reactions without the need for larger sensor dimensions.
Implementation Method 1
The first gate structure may be configured to receive a voltage VG,1 based on a pH of the solution 110 and is further configured to control the first current flow through the first transistor 102 based on the voltage VG,1
Implementation Method 2
The second current flow through the second transistor 104 changes to compensate for the change in the first current flow through the first transistor 102. This in turn changes the voltage VG,2 at the gate electrode 114 of the second transistor 104
Data Source
AI summary
A sensor device may include a substrate, first and second source regions, first and second drain regions, first and second channel regions, and first and second gate structures disposed over the first and second channel regions, respectively. The source regions and drain regions may be at least partially disposed within the substrate. The first and second source regions may have first and second source resistances, respectively, and the second source resistance may be higher than the first source resistance. The first gate structure may receive a solution, and a change in pH in the solution may cause a change in a first current flow through the first channel region. In turn, the second current flow through the second channel region may change to compensate for the change in the first current flow to maintain a constant current flow through the sensor device.