Spatially variable hydrophobic layers for digital microfluidics

1. An active matrix electrowetting on dielectric (AM-EWoD) device, comprising:

a substrate comprising a plurality of driving electrodes coupled to a set of thin-film-transistors, and including a dielectric layer covering both the plurality of driving electrodes and the set of thin-film-transistors;

a controller operatively coupled to the set of thin-film-transistors and configured to provide a driving voltage to at least a portion of the plurality of driving electrodes, and

a spatially variable wettability layer covering the dielectric layer, wherein the spatially variable wettability layer has portions which are hydrophobic, and portions which are superhydrophobic, and

a top hydrophobic layer covering a singular top electrode, wherein the top hydrophobic layer includes a second spatially variable wettability layer.

2. The active matrix electrowetting on dielectric (AM-EWoD) device of claim 1 , wherein the spatially variable wettability layer comprises a first portion having a first contact angle between 90° and 160°, and a second portion having a second contact angle which is greater than 160°.

3. The active matrix electrowetting on dielectric (AM-EWoD) device of claim 2 , wherein a difference between the first contact angle and the second contact angle is at least 20°.

4. The active matrix electrowetting on dielectric (AM-EWoD) device of claim 2 , wherein a difference between the first contact angle and the second contact angle is at least 50°.

5. The active matrix electrowetting on dielectric (AM-EWoD) device of claim 1 , wherein the spatially variable wettability layer comprises at least a portion having a contact angle gradient.

6. The active matrix electrowetting on dielectric (AM-EWoD) device of claim 5 , wherein a difference in contact angle between a first end of the gradient and a second end of the gradient is at least 20°.

7. The active matrix electrowetting on dielectric (AM-EWoD) device of claim 5 , wherein a difference in contact angle between a first end of the gradient and a second end of the gradient is at least 50°.

8. The active matrix electrowetting on dielectric (AM-EWoD) device of claim 5 , wherein the contact angle gradient is located at an inlet or reservoir entry point for introducing liquids from an external source into the digital microfluidic device.

9. The active matrix electrowetting on dielectric (AM-EWoD) device of claim 1 , further comprising a spacer separating the spatially variable wettability layer and the top hydrophobic layer and creating a microfluidic region between the spatially variable wettability layer and top hydrophobic layers.

10. The active matrix electrowetting on dielectric (AM-EWoD) device of claim 1 , wherein the second spatially variable wettability layer covering the singular top electrode comprises a first portion having a first contact angle, and a second portion having a second contact angle.

11. The active matrix electrowetting on dielectric (AM-EWoD) device of claim 10 , wherein the contact angles of the spatially variable wettability layer and the second spatially variable wettability layers are the same along an axis perpendicular to the plane of the substrate comprising a plurality of driving electrodes.

12. The active matrix electrowetting on dielectric (AM-EWoD) device of claim 10 , wherein the contact angles of the spatially variable wettability layer and the second spatially variable wettability layers are not the same along an axis perpendicular to the plane of the substrate comprising a plurality of driving electrodes.

13. The active matrix electrowetting on dielectric (AM-EWoD) device of claim 12 , wherein a difference between the contact angles of the first and second variable wettability layers along an axis perpendicular to the plane of the substrate comprising a plurality of driving electrodes is at least 20° 1 .

14. The active matrix electrowetting on dielectric (AM-EWoD) device of claim 1 , wherein the second spatially variable wettability layer covering the singular top electrode comprises at least a portion having a contact angle gradient.

15. The active matrix electrowetting on dielectric (AM-EWoD) device of claim 9 , wherein the singular top electrode includes at least one light-transmissive region.

16. The active matrix electrowetting on dielectric (AM-EWoD) device of claim 15 , wherein the light-transmissive region is at least 10 mm 2 in area.

17. A method of manufacturing an active matrix electrowetting on dielectric (AM-EWoD) device, the method comprising:

coupling a substrate comprising a plurality of driving electrodes to a set of thin-film-transistors;

operatively coupling a controller to the set of thin-film-transistors, wherein the controller is configured to provide a driving voltage to at least a portion of the plurality of driving electrodes;

forming a dielectric layer covering the plurality of driving electrodes and the set of thin-film-transistors;

forming a spatially variable wettability layer covering the dielectric layer, wherein the spatially variable wettability layer has a hydrophobic region and a superhydrophobic region, and

a top hydrophobic layer covering a singular top electrode, wherein the top hydrophobic layer includes a second spatially variable wettability layer.

18. The method of manufacturing the active matrix electrowetting on dielectric (AM-EWoD) device of claim 17 , wherein forming the spatially variable wettability layer comprises:

depositing a first material having a first contact angle to form a first zone of the spatially variable wettability layer, and

depositing a second material having a second contact angle to form a second zone of the spatially variable wettability layer.

19. The method of manufacturing the active matrix electrowetting on dielectric (AM-EWoD) device of claim 18 , wherein forming the spatially variable wettability layer comprises depositing each material on its respective zone while the other zones are masked off, thereby generating one or more differences in relative hydrophobicity along the surface.