Layered structure with high dielectric constant for use with active matrix backplanes
Layered dielectric materials for use in controlling dielectric strength in microelectronic devices, especially as they relate to electrophoretic and electrowetting applications. Specifically, a combination of a first atomic layer deposition (ALD) step, a sputtering step, and a second ALD step result in a layer that is chemically robust and nearly pinhole free. The dielectric layer may be disposed on the transparent common electrode of an electrophoretic display or covering the pixelated backplane electrodes, or both.
1. An electrowetting on dielectric (EWoD) device having electrodes disposed in an array where each electrode is associated with a thin film transistor (TFT), the device comprising:
a layered dielectric comprising:
a first layer of an aluminum oxide or a hafnium oxide, the first layer having a thickness between 20 nm and 40 nm;
a second layer of a tantalum oxide or a hafnium oxide, the second layer having a thickness between 40 nm and 250 nm; and
a third layer of a tantalum oxide or a hafnium oxide, the third layer having a thickness between 10 nm and 35 nm, wherein the second layer is disposed between the first and third layers; and
a hydrophobic layer deposited on the layered dielectric.
2. The device of claim 1 , wherein the first layer comprises Al 2 O 3 , the second layer comprises HfO 2 , and the third layer comprises Ta 2 O 5 .
3. The device of claim 1 , wherein the first layer comprises Al 2 O 3 , the second layer comprises Ta 2 O 5 , and the third layer comprises HfO 2 .
4. The device of claim 1 , wherein the second layer is 100 to 150 nm thick.
5. The device of claim 1 , comprising a plurality of active matrix electrodes covered by the layered dielectric.
6. The device of claim 1 , wherein the hydrophobic layer comprises a fluoropolymer.
7. The device of claim 1 , wherein the hydrophobic layer is between 10 and 50 nm thick.
8. The device of claim 1 , wherein the dielectric strength of the layered dielectric is greater than 6 MV/cm.
9. A method of creating an electrowetting on dielectric (EWoD) device having a layered structure, the method comprising:
providing a substrate;
depositing a layered dielectric on the substrate by:
depositing a first layer of aluminum oxide or hafnium oxide using atomic layer deposition, the first layer having a thickness between 20 nm and 40 nm;
depositing a second layer of tantalum oxide or hafnium oxide using sputtering, the second layer having a thickness between 40 nm and 250 nm; and
depositing a third layer of tantalum oxide or hafnium oxide using atomic layer deposition, the third layer having a thickness between 10 nm and 35 nm; and
depositing a hydrophobic layer on the layered dielectric.
10. The method of claim 9 , wherein the hydrophobic layer is coated onto the layered dielectric by spin coating.