HIGH VOLTAGE DRIVING USING TOP PLANE SWITCHING
Improved methods for driving an active matrix of pixel electrodes controlled with thin film transistors when the voltage on a top electrode is being altered between driving frames. The method is useful for electrowetting devices. In particular, the methods can provide for more consistent droplet movement when used with a digital microfluidic device based upon an active matrix of pixel electrodes.
1 . An electrowetting device, comprising:
a top electrode;
a plurality of thin film transistors (TFTs) each of the plurality of TFTs include a source, a gate, and a drain;
a plurality of storage capacitors;
a backplane comprising a plurality of addressable pixel electrodes, each of the addressable pixel electrodes electrically coupled to the drain of a respective one of the plurality of TFTs and one of the plurality of storage capacitors;
a microfluidic workspace between the top electrode and the backplane;
a plurality of gate lines, the gate of each of the plurality of TFTs electrically coupled to a respective one of the plurality of gate lines,
a plurality of scan lines, the source of each of the plurality of TFTs electrically coupled to a respective one of the plurality of scan lines; and
a controller electrically coupled to the plurality of gate lines, the plurality of scan lines, the top electrode, and the plurality of storage capacitors to provide time-dependent voltages thereto, the controller further configured or programmed to perform top plane switching to drive the electrowetting device by:
driving the top electrode with a first voltage;
driving the plurality of gate lines with a pulsed waveform to open the plurality of TFTs;
driving the plurality of storage capacitors and the plurality of scan lines with a low level voltage for at least one period of the pulsed waveform; and
driving the top electrode with a second voltage.
2 . The electrowetting device of claim 1 , wherein driving the plurality of storage capacitors and the plurality of scan lines with a low level voltage for one period of the pulsed waveform returns a voltage level at the plurality of storage capacitors to zero volts and returns a voltage level at the plurality of scan lines to zero volts.
3 . The electrowetting device of claim 1 , wherein driving the plurality of gate lines with the pulsed waveform to open the plurality of TFTs includes sequentially driving the plurality of gate lines in a first scan direction with the first pulsed waveform and sequentially driving the plurality of gate lines in a reversed scan direction with a second pulsed waveform.
4 . The electrowetting device of claim 1 , wherein the controller is configured to drive the electrowetting device by
a) providing a first high voltage to the plurality of scan lines and a first low voltage to the top electrode and a second side of the plurality of storage capacitors;
b) providing a first gate pulse sufficient to open the plurality of TFTs;
c) after the first gate pulse, providing a zero voltage to the plurality of scan lines, the top electrode and the second side of the plurality of storage capacitors;
d) providing a second gate pulse sufficient to open the plurality of TFTs;
e) after the second gate pulse, providing a second low voltage to the plurality of scan lines and a second high voltage to the top electrode and a second side of the plurality of storage capacitors; and
f) providing a third gate pulse sufficient to open the plurality of TFTs.
5 . The electrowetting device of claim 1 , wherein the controller is configured to drive the electrowetting device by
a) providing a first high voltage to the plurality of scan lines and a first low voltage to the top electrode and a second side of the plurality of storage capacitors;
b) providing a first gate pulse sufficient to open the plurality of TFTs;
c) after the first gate pulse, providing a second low voltage to the plurality of scan lines;
d) providing a second gate pulse sufficient to open the plurality of TFTs;
e) after a second gate pulse, providing a second high voltage to the top electrode and the second side of the plurality of storage capacitors; and
f) providing a third gate pulse sufficient to open the TFTs.
6 . The electrowetting device of claim 1 , wherein the controller is configured to drive the electrowetting device by
a) providing a first high voltage to the plurality of scan lines and a first low voltage to the top electrode and a second side of the plurality of storage capacitors;
b) providing a first gate pulse sufficient to open the TFTs;
c) after the first gate pulse, providing a second high voltage to the top electrode and a second side of the storage capacitors;
d) providing a second gate pulse sufficient to open the TFTs;
e) after the second gate pulse, providing a second low voltage to the scan lines; and
f) providing a third gate pulse sufficient to open the TFTs.
7 . The electrowetting device of claim 1 , wherein the controller is configured to drive the electrowetting device by
(a) providing a first voltage to the top electrode;
(b) providing a specific voltage to each electrode of the plurality of addressable pixel electrodes in a first sequential order;
(c) providing a specific voltage to each electrode of the plurality of addressable pixel electrodes in a second sequential order, wherein the order of providing specific voltages to plurality of addressable pixel electrodes in the second sequential order is a reverse order of the first sequential order, and wherein each pixel of the plurality of addressable pixel electrodes receives the same specific voltage in both the first sequential order and the second sequential order; and
(d) providing a second voltage different from the first voltage to the top electrode.
8 . The device of claim 1 , wherein the top electrode is light-transmissive.
9 . The device of claim 1 , wherein the top electrode and a second side of the storage capacitor are electrically coupled to a common node.
10 . The device of claim 1 , wherein the plurality of TFTs are fabricated from amorphous silicon.
11 . (canceled)
12 . (canceled)
13 . The device of claim 1 , wherein the backplane and the top electrode are coated with a hydrophobic material, wherein the hydrophobic material is adjacent the microfluidic workspace.
14 . The device of claim 1 , wherein the backplane additionally comprises a dielectric layer between the plurality of addressable pixel electrodes and the hydrophobic material.
15 . (canceled)
16 . A method of driving an electrowetting device comprising:
a top electrode;
a plurality of thin film transistors (TFTs) each of the plurality of TFTs include a source, a gate, and a drain;
a plurality of storage capacitors;
a backplane comprising a plurality of addressable pixel electrodes, each of the addressable pixel electrodes electrically coupled to the drain of a respective one of the plurality of TFTs and one of the storage capacitors;
a microfluidic workspace between the top electrode and the backplane;
a plurality of gate lines, the gate of each of the plurality of TFTs electrically coupled to a respective one of the plurality of gate lines,
a plurality of scan lines, the source of each of the plurality of TFTs electrically coupled to a respective one of the plurality of scan lines; and
a controller electrically coupled to the plurality of gate lines, the plurality of scan lines, the top electrode, and the plurality of storage capacitors to provide time-dependent voltages thereto, the method comprising:
driving the top electrode with a first voltage;
driving the plurality of gate lines with a pulsed waveform to open the plurality of TFTs;
driving the plurality of storage capacitors and the plurality of scan lines with a low level voltage for at least one period of the pulsed waveform; and
driving the top electrode with a second voltage.
17 . The method of claim 16 further comprising a method of driving (in order):
a) providing a first high voltage to the plurality of scan lines and a first low voltage to the top electrode and a second side of the plurality of storage capacitors;
b) providing a first gate pulse sufficient to open the plurality of TFTs;
c) after the first gate pulse, providing a zero voltage to the plurality of scan lines, the top electrode and a second side of the plurality of storage capacitors;
d) providing a second gate pulse sufficient to open the plurality of TFTs;
e) after the second gate pulse, providing a second low voltage to the plurality of scan lines and a second high voltage to the top electrode and the second side of the plurality of storage capacitors; and
f) providing a third gate pulse sufficient to open the plurality of TFTs.
18 . The method of claim 16 further comprising a method of driving (in order):
a) providing a first high voltage to the plurality of scan lines and a first low voltage to the top electrode and a second side of the plurality of storage capacitors;
b) providing a first gate pulse sufficient to open the plurality of TFTs;
c) after the first gate pulse, providing a second low voltage to the plurality of scan lines;
d) providing a second gate pulse sufficient to open the plurality of TFTs;
e) after the second gate pulse, providing a second high voltage to the top electrode and the second side of the plurality of storage capacitors; and
f) providing a third gate pulse sufficient to open the plurality of TFTs.
19 . The method of claim 16 further comprising a method of driving (in order):
a) providing a first high voltage to the plurality of scan lines and a first low voltage to the top electrode and a second side of the plurality of storage capacitors;
b) providing a first gate pulse sufficient to open the plurality of TFTs;
c) after the first gate pulse, providing a second high voltage to the top electrode and the second side of the storage capacitors;
d) providing a second gate pulse sufficient to open the plurality of TFTs;
e) after the second gate pulse, providing a second low voltage to the plurality of scan lines; and
f) providing a third gate pulse sufficient to open the plurality of TFTs.
20 . The method of claim 16 further comprising a method of driving (in order):
(a) providing a first voltage to the top electrode;
(b) providing a specific voltage to each electrode of the addressable pixel electrodes in a first sequential order;
(c) providing a specific voltage to each electrode of the addressable pixel electrodes in a second sequential order, wherein the order of providing specific voltages to the addressable pixel electrodes in the second sequential order is a reverse order of the first sequential order, and wherein each of the addressable pixel electrodes receives the same specific voltage in both the first sequential order and the second sequential order; and
(d) providing a second voltage different from the first voltage to the top electrode.
21 . (canceled)
22 . The method of claim 17 , wherein the first and second high voltage are +15V.
23 . The method of claim 17 , wherein the first and second low voltages are −15V.
24 . The method of claim 19 wherein at least 100 pixels of the addressable pixel electrodes have specific voltages different from the majority of the addressable pixel electrodes.