AM-EWOD Array Element Circuit with Integrated Impedance Sensing
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Solution Overview
Problem
Existing active matrix electrowetting-on-dielectric (EWOD) devices face limitations in efficiently sensing the location, size, and constitution of ionic droplets due to the need for external sensor electronics and limited connectivity, which restricts the number of array elements that can be sensed and increases costs.
Innovation Solution
Integration of an AC coupled impedance sensor capability into the AM-EWOD device, allowing for simultaneous measurement of impedance at multiple array elements with reduced circuit components and connections, enabling efficient droplet positioning, sizing, and constitution analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Difficulty of detecting and measuring
If external sensor electronics are used for sensing droplets in AM-EWOD devices, then droplet sensing capability is achieved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent combines the EWOD drive circuit and impedance sensing circuit into a single integrated array element circuit. The sense transistor shares the hydrophobic cell with the drive transistor, eliminating the need for separate external sensor electronics. This integration directly reduces device complexity while maintaining full droplet sensing capability through impedance measurement at the array element level.
2Difficulty of detecting and measuring
If external sensor electronics are used for sensing droplets, then droplet sensing is enabled, but the number of array elements that can be sensed is limited
Solution Approach 1:
The patent divides the sensing function into individual array element circuits, with each element containing its own sense transistor and impedance sensing capability. This segmentation allows each array element to be sensed independently and simultaneously, enabling the full array to be monitored without the limitations of external sensor electronics that would require multiplexing or sequential scanning.
3Difficulty of detecting and measuring
If external sensor electronics are used, then droplet sensing is achieved, but manufacturing cost increases
Solution Approach 1:
The hydrophobic cell is designed to serve dual functions: as the active element for electrowetting-driven droplet manipulation and as the sensing element for impedance-based droplet detection. The same physical structure and electrode configuration used for driving droplets also enables impedance sensing, eliminating the need for separate sensing components and reducing manufacturing cost.
4Productivity
If AC coupled impedance sensing is integrated into AM-EWOD devices, then simultaneous measurement at multiple array elements is enabled, but circuit design complexity increases
Solution Approach 1:
The patent employs AC coupling for impedance sensing, where an AC test signal is applied to the array element during sensing periods. The AC coupling capacitor blocks DC components while allowing AC signals to pass, enabling impedance measurement without interfering with the DC electrowetting drive voltage. This periodic AC sensing approach allows simultaneous multi-element measurement while managing circuit complexity through standardized AC coupling design.
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 precise monitoring of droplet positions, sizes, and chemical reactions across a large number of array elements with reduced manufacturing costs and improved reliability, enhancing the reliability and efficiency of droplet operations.
Implementation Method 1
an AC coupled impedance sensor capability into the AM-EWOD device, allowing for simultaneous measurement of impedance at multiple array elements
Implementation Method 2
Active Matrix EWOD (AM-EWOD) refers to implementation of EWOD in an active matrix array, for example by using thin film transistors (TFTs)
Data Source
AI summary
A static random-access memory (SRAM) cell which includes: a sampling switch and a feedback switch; and a first inverter and a second inverter connected in series whereby an output of the first inverter is connected to an input of the second inverter. An input of the first inverter is connected to a data input of the SRAM cell via the sampling switch, and to a data output of the SRAM cell independent of the feedback switch, an output of the second inverter is connected to the input of the first inverter via the feedback switch, and first and second clock inputs of the SRAM cell are configured to control the sampling switch and the feedback switch, respectively.