Active Matrix EWOD Droplet Actuation Voltage Control
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Solution Overview
Problem
Existing AM-EWOD devices face challenges in efficiently managing droplet actuation states due to high voltage requirements and potential coupling of AC signals across droplets, which can lead to excessive voltage exposure for electronic circuitry.
Innovation Solution
A method involving alternating voltages applied to reference and element electrodes, where the element electrode is put in an actuated state by applying a second alternating voltage out of phase with the first, and in a non-actuated state by holding it in a high impedance state, allowing for reduced maximum voltage switching requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If high voltage is applied to the element electrode to achieve droplet actuation, then droplet manipulation capability is improved, but the voltage exposure for electronic circuitry increases
Solution Approach 1:
The voltage control is segmented into two independent parts: the reference electrode receives the full amplitude AC voltage signal, while the element electrode receives a bipolar voltage signal with zero mean. This segmentation allows the liquid droplet (which couples both electrodes) to experience the full voltage difference needed for actuation, while the electronic circuitry controlling the element electrode only handles lower voltage swings, reducing voltage exposure and improving circuit reliability
Solution Approach 2:
The liquid droplet acts as an intermediary that couples the reference electrode and element electrode electrically. By applying AC voltage to the reference electrode and bipolar voltage to the element electrode, the droplet experiences the voltage difference needed for actuation without requiring the element electrode circuitry to handle the full voltage amplitude, thus reducing voltage stress on the electronics
2Force
If AC voltage is applied to both reference and element electrodes, then droplet actuation is achieved, but circuit complexity increases
Solution Approach 1:
The element electrode serves multiple functions: it provides the bipolar voltage signal for droplet actuation and simultaneously acts as a sensing electrode for impedance measurement. This multi-functionality reduces the need for separate sensing circuitry and simplifies the overall device architecture while maintaining effective droplet manipulation
Solution Approach 2:
The use of periodic AC voltage signals at optimized frequencies (e.g., 100 Hz to 10 kHz) enables effective droplet actuation through electro-wetting and dielectrophoresis mechanisms. The periodic nature of the signals allows for efficient droplet manipulation while simplifying the control circuitry compared to complex pulse-width modulation or other non-periodic control schemes
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 enables AC electro-wetting with voltages switched between +V EW and -V EW while transistors only need to handle V EW , facilitating smaller, simpler circuits, higher manufacturing yield, and increased optical transparency for larger format arrays.
Implementation Method 1
Electro-wetting on dielectric (EWOD) is a well known technique for manipulating droplets of fluid by application of an electric field
Implementation Method 2
The insulator layer 20 disposed upon the lower substrate 72 separates the conductive element electrodes 38A, 38B from a first hydrophobic coating 16 upon which the liquid droplet 4 sits
Data Source
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AI summary
A method of driving an element of an active matrix electro-wetting on dielectric (AM-EWOD) device comprise applying a first alternating voltage to a reference electrode of the AM-EWOD device; and either (i) applying to the element electrode a second alternating voltage that has the same frequency as the first alternating voltage and that is out of phase with the first alternating voltage or (ii) holding the element electrode in a high impedance state. The effect of applying the second alternating voltage to the element electrode is to put the element in an actuated state in which the element is configured to actuate any liquid droplet present in the element, while the effect of holding the element electrode in the high impedance state is to put the element in a non-actuated state.