US-12623219-B2 - Driving circuit for electrowetting-on-dielectric (EWOD) pixel and EWOD system using the same

Abstract

A driving circuit for an electrowetting on dielectric (EWOD) pixel. The driving circuit includes a latch circuit for transmitting a source data pulse to a storage capacitor in response to an activation gate signal applied to the gate of the switch transistor and generating a latch voltage and an inversion circuit for outputting a driving voltage at either a first power voltage or a second power voltage based on the latch voltage generated by the latch circuit.

Inventors

• Tung-Yu WU
• Chung-Yi Wang
• Tang-Hung Po

Assignees

• CYTESI, INC.

Dates

Publication Date

20260512

Application Date

20230103

Claims (3)

1. 1 . A driving circuit for an electrowetting on dielectric (EWOD) pixel, comprising: a latch circuit comprising a switch transistor that has a source connected to a matrix source line and a gate connected to a matrix gate line and a storage capacitor connected between a drain of the switch transistor and ground and configured to transmit a source data pulse from the matrix source line to the storage capacitor in response to an activation gate signal that is applied to the gate of the switch transistor and write a latch voltage at a latch output node; and an inversion circuit supplied with a first power voltage and a second power voltage and connected to the latch output node for outputting a driving voltage at either the first power voltage or the second power voltage based on the latch voltage at the latch output node; wherein the inversion circuit includes a CMOS inverter formed of a first NMOS transistor and a first PMOS transistor connected in series between the first power voltage and the second power voltage for outputting the driving voltage between the first NMOS transistor and the first PMOS transistor with the gates of the first NMOS transistor and the first PMOS transistor connected to the latch output node of the latch circuit.
2. 2 . A circuit arrangement for an active matrix electrowetting on dielectric system, comprising: an M×N array of pixels arranged in M rows and N columns, each of the pixels including a driving circuit as recited in any of claim 1 ; a shift register circuit including serially connected N flip-flops, each of the N flip-flops connected for sequentially outputting the source data pulses to the sources of the M switch transistors in the same column; and M matrix gate lines connected to the gates of the N switch transistors in the same rows; wherein each of the pixels further comprises: a thermal bias portion formed of two serially connected NMOS transistors, one of the two serially connected NMOS transistors being a sensor transistor with a gate connected to a bias signal and a drain connected to ground and the other of the two serially connected NMOS transistors being a selection transistor with a gate connected to the gate of the switch transistor and a drain connected to the source of the sensor transistor, and the circuit arrangement further comprising a selection unit having (M×N) input terminals connected to source of each selection transistor of the thermal bias portions in the pixels and a column selection terminal.
3. 3 . A driving circuit for an electrowetting on dielectric (EWOD) pixel, comprising: a latch circuit comprising a switch transistor that has a source connected to a matrix source line and a gate connected to a matrix gate line and a storage capacitor connected between a drain of the switch transistor and ground and configured to transmit a source data pulse from the matrix source line to the storage capacitor in response to an activation gate signal that is applied to the gate of the switch transistor and write a latch voltage at a latch output node; an inversion circuit supplied with a first power voltage and a second power voltage and connected to the latch output node for outputting a driving voltage at either the first power voltage or the second power voltage based on the latch voltage at the latch output node, and a shifter circuit comprising a cross-coupled pull-up formed by a second PMOS transistor and a third PMOS transistor and a differential pair formed by a second NMOS transistor and a third NMOS transistor, wherein the source of said second and third PMOS transistors are coupled to an operative voltage higher than the driving voltage outputted from the inversion circuit, wherein the gate of the second PMOS transistor and the drain of the third PMOS transistor are coupled to the drain of the third NMOS transistor to form a level-shifted output, wherein the gate of the third PMOS transistor and the drain of the second PMOS transistor are coupled to the drain of the second NMOS transistor, and wherein the sources of the second NMOS transistor and the third NMOS transistor are grounded and the gate of the second NMOS transistor is coupled to receive the driving voltage outputted from the inversion circuit and the gate of the third NMOS transistor is coupled to the latch output node of the latch circuit.

Description

CROSS-REFERENCE This application claims the benefit of U.S. Provisional Patent Application No. 63/299,244, filed Jan. 13, 2022, which application is incorporated by reference in its entirety. TECHNICAL FIELD The present disclosure relates to a driving circuit that drives a data line and an Electrowetting-On-Dielectric (EWOD) system having the driving circuit. BACKGROUND Electrowetting-On-Dielectric (EWOD) is a known technique for manipulating droplets of fluid on an array. The motion of the droplets is initiated and controlled by electrowetting through an application of an electric field between a droplet and a drive electrode electrically insulated from the droplet by a dielectric layer. Accordingly, the electric field therebetween should be sufficiently great as to move the droplet. However, when a constant voltage is applied, the dielectric layer is susceptible to polarization, ultimately the electrowetting effect completely vanishes. Accordingly, an approach of applying an alternative current (AC) pulse of greater than 30 volts (V) to the drive electrode is proposed as to move the droplet and prevent the dielectric layer from polarization. FIG. 1 shows a diagrammatic cross-section of a portion of an example traditional EWOD device 100. The EWOD device 100 includes first and second substrates 102, 104 spaced apart to form a cavity 106 in which a droplet 10 is constrained. The first and second substrates 102, 104 may take the form of glass plates. An array of drive electrodes 108 (e.g., VP1, VP2, VP3) is formed on the first substrate 102. The drive electrodes 108 may be transparent, for example being formed of transparent Indium Tin Oxide (ITO). A dielectric layer 110 is formed over the drive electrodes 108 to provide appropriate dielectric capacitance between the drive electrodes 108 and droplet 10. A ground electrode 112 (e.g., Vcom) is formed on the lower surface of the second substrate 104. The ground electrode 112 may be transparent, for example, being formed of transparent ITO. This allows visual inspection of microfluidic operation. One ground electrode 112 may be associated with one corresponding drive electrode VP1, VP2, or VP3 as to form a respective EWOD pixel C1, C2, or C3 as illustrated in FIG. 1. To move droplet 10 in a direction indicated by the arrow in FIG. 1, drive electrode VP2 is energized at 30V to attract droplet 10 and cause droplet 10 to move and become centered on drive electrode VP2. Subsequent activation of drive electrode VP3, followed by removal of the voltage potential at drive electrode VP2, cause droplet 10 to move onto drive electrode VP3. This sequencing of biasing these electrodes can be repeated to cause droplet 10 to continue to move in any direction as desired. In the above scheme, shown in FIG. 1, there are 0V and 30V for drive electrodes 108, however, as dielectric layer 110 always suffers a fixed direction of electric field, dielectric layer 110 is rapidly deteriorated by polarization. Though another approach of biasing ground electrode 112 to 15V has been proposed such that a voltage difference in pixel C1 is Vcom−VP1, i.e., 15V; a voltage difference in pixel C2 is −15V; and a voltage difference in Pixel C3 is 15V. However, in such a scenario, droplet 10 would not be moved, since an absolute value of the voltage differences between any two adjacent EWOD pixels C1, C2 and C3 are the same. FIG. 2 shows a known circuit 20 of 1 transistor and 1 capacitor (1T1C) for an EWOD pixel which can be used in controlling each individual EWOD pixel in FIG. 1. The circuit 20 consists of a switch transistor SW, and a storage capacitor CST. The switch transistor SW (a TFT) is connected between a matrix source line 24 and a drive electrode 26. A matrix gate line 28 is connected to a gate of transistor SW. The storage capacitor CST is connected between the drive electrode 26 and ground. Ideally, by applying of voltage pulses to the matrix source line 24 and the matrix gate line 28, a voltage VE can be written to the drive electrode 26 and stored in the storage capacitor CST. By appropriate design and operation, different voltages VE may be applied to different electrodes (e.g., drive electrodes VP1, VP2, VP3 and ground electrode 112, respectively). However, in practice, the drive voltage VE across the storage capacitor CST varies when droplet is moved and renders controlling to the pixel unreliable. SUMMARY OF THE INVENTION According to one aspect of the invention, a method for driving EWOD device with frame times to diminish the damage caused by polarization of the dielectric layer is provided. According to another aspect of the invention, the ground electrode is grounded at zero volts. Accordingly, the voltage difference across each pixel is the voltage on the active pixel so that the droplet is attracted to the active pixel. According to a further aspect of the invention, the ground electrode is supplied with a AC pulse out of phase with the active electrode as to double the volta