Ion-Sensing Charge Accumulation Circuit for ISFET Readout
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Solution Overview
Problem
Ion-sensing systems, particularly those using ISFETs, face challenges in accurately measuring ion concentration due to small changes in voltage or current at the source or drain, non-linear threshold voltage functions, and requirements for complex readout circuits, which limit speed, accuracy, and performance metrics.
Innovation Solution
An ion-sensitive circuit with a charge accumulation device and control/readout transistors is employed, accumulating charge packets based on ion concentration and generating output signals, enhancing signal-to-noise ratio and performance through controlled charge packet accumulation and readout processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional ISFET measurement methods are used, then ion concentration can be detected, but measurement precision deteriorates due to small voltage/current changes and non-linear threshold voltage functions
Solution Approach 1:
The patent segments the continuous ion concentration measurement into discrete charge packet accumulations. Each charge packet represents a quantized unit of ion concentration measurement, allowing for more precise and reliable detection by breaking down the measurement into manageable, countable units that can be accumulated over time to improve signal-to-noise ratio.
Solution Approach 2:
The patent implements preliminary charge accumulation before final measurement. Charge packets are accumulated in the floating gate over a predetermined period before being transferred to the readout transistor, allowing the signal to build up to a measurable level and improving both precision and reliability by integrating multiple measurement units.
2Measurement precision
If conventional ISFET readout circuits are used, then ion concentration can be measured, but device complexity increases due to requirements for complex readout circuits
Solution Approach 1:
The patent merges the charge accumulation function and charge storage function into a single floating gate structure. This eliminates the need for separate accumulation and storage circuits, reducing device complexity while maintaining the ability to perform precise ion concentration measurements through charge packet accumulation.
Solution Approach 2:
The floating gate structure serves multiple functions: it acts as the charge accumulation node, the charge storage element, and the interface to the readout transistor. This multi-functionality reduces the overall circuit complexity while enabling precise measurement capabilities through charge packet accumulation and controlled transfer.
3Measurement precision
If conventional ISFET operation is used, then ion concentration can be detected, but productivity decreases due to limited measurement speed
Solution Approach 1:
The patent implements periodic charge packet transfer from the floating gate to the readout transistor at controlled intervals. This periodic operation allows for rapid sequential measurements while maintaining precision through accumulated charge packets, thereby increasing measurement speed and productivity without sacrificing accuracy.
Solution Approach 2:
The patent enables dynamic control of the charge transfer timing and rate from the floating gate to the readout transistor. By dynamically adjusting the transfer frequency and accumulation period, the system can optimize between measurement precision and measurement speed, improving productivity while maintaining required accuracy levels.
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 improves the accuracy and linearity of ion concentration measurements, reducing noise and increasing signal-to-noise ratio, thereby enhancing the performance of ion-sensing systems while maintaining compatibility with CMOS processing.
Implementation Method 1
an ion-sensitive surface 204 of the passivation layer 196
Implementation Method 2
a gate semiconductor region 224, to accumulate a plurality of charge packets 216 as a function of an ion concentration
Data Source
AI summary
An ion-sensitive circuit can include a charge accumulation device, to accumulate a plurality of charge packets as a function of an ion concentration of a fluid, and at least one control and readout transistor, to generate an output signal as a function of the accumulated plurality of charge packets, the output signal representing the ion concentration of the solution. The charge accumulation device can include a first charge control electrode above a first electrode semiconductor region, an electrically floating gate structure above a gate semiconductor region and below an ion-sensitive passivation surface, a second charge control electrode above a second electrode semiconductor region, and a drain diffusion region. The first control electrode can control entry of charge into a gate semiconductor region in response to a first control signal. The ion-sensitive passivation surface can be configured to receive the fluid. The second charge control electrode can control transmission of the plurality of charge packets out of the gate semiconductor region and into the drain diffusion region in response to a second control signal. The drain diffusion region can receive the plurality of charge packets from the gate semiconductor region via the second electrode semiconductor region.