CMOS Sensor Array for Microscale Electrochemical Measurements
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Solution Overview
Problem
Capacitive sensing and electrochemical impedance spectroscopy (EIS) biosensors face challenges with low dynamic range and chemical specificity due to ion screening effects, and ion-sensitive field effect transistors (ISFETs) experience drift and flicker noise, limiting their effectiveness in long-duration applications such as cell culture monitoring.
Innovation Solution
A CMOS sensor array with a 64×64 pixel design using high-frequency impedance spectroscopy and code-division multiplexing, along with an in-pixel chopping circuit for ISFETs, to overcome ion screening and reduce noise, enabling extended integration times and improved sensing modalities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If EIS biosensors are used for miniaturized biochemical measurements, then low cost and simple instrumentation are achieved, but low dynamic range and low chemical specificity occur
Solution Approach 1:
The patent segments the sensing function into multiple frequency domains by applying impedance spectroscopy across a broad frequency range (e.g., 1 Hz to 10 MHz). Each frequency provides complementary information about different electrochemical processes, effectively segmenting the measurement to overcome the limited dynamic range of single-frequency EIS while maintaining the simplicity of the basic sensor structure.
Solution Approach 2:
The patent adds the frequency dimension to the traditional single-point EIS measurement. By measuring impedance across multiple frequencies simultaneously, the system transforms a one-dimensional measurement (single impedance value) into a multi-dimensional spectral signature that provides both enhanced dynamic range and chemical specificity without increasing physical sensor complexity.
2Productivity
If ISFETs are used for cell culture monitoring, then integrated circuit technology and scaling are achieved, but drift and flicker noise increase
Solution Approach 1:
The patent applies periodic modulation of the ISFET gate voltage at high frequencies (e.g., AC coupling or chopper stabilization techniques). This periodic action shifts the operating point away from the low-frequency region where flicker noise dominates, effectively reducing 1/f noise while maintaining the ability to perform long-duration cell culture monitoring with high throughput arrays.
Solution Approach 2:
The patent replaces direct DC measurement of ISFET output with high-frequency AC impedance spectroscopy. By substituting the measurement mechanism from direct voltage reading to frequency-domain impedance analysis, the system eliminates low-frequency drift and flicker noise while preserving the scalability and integration benefits of ISFET arrays.
3Area of moving object
If ion screening effects are present in EIS measurements, then miniaturized sensing is enabled, but chemical specificity is reduced
Solution Approach 1:
The patent compensates for ion screening effects by adding the frequency dimension to the measurement. Different frequencies probe different depths and ranges of the electric field, allowing the system to overcome the limited penetration depth caused by ion screening in miniaturized sensors. The frequency-resolved impedance spectrum provides chemical specificity that would be lost in single-frequency measurements at the microscale.
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 solution enhances the dynamic range and chemical specificity of EIS biosensors and reduces drift and flicker noise in ISFETs, allowing for more accurate and stable measurements in cell culture monitoring and other applications.
Implementation Method 1
non-overlapping clocks configured to rapidly charge and discharge the exposed surface electrode
Implementation Method 2
the ion-sensitive field effect transistor (ISFET) has cemented an important commercial role
Data Source
AI summary
A complementary metal-oxide-semiconductor sensor array includes an active sensing area of pixels arranged in an array with a pitch, each pixel including an exposed surface electrode alongside switches and logic gates, and non-overlapping clocks configured to rapidly charge and discharge the exposed surface electrode, wherein control signals steer a switched output current between shared column outputs.