Dielectric layers for digital microfluidic devices

1. An electrowetting system for performing droplet operations, the system including:

a plurality of electrodes configured to manipulate droplets of fluid in a microfluidic space, wherein each electrode is coupled to circuitry operative to selectively apply a driving voltage to the electrode; and

a dielectric stack comprising:

a first dielectric pair comprising a first layer having a first dielectric constant and a second layer having a second dielectric constant, wherein the second dielectric constant is larger than the first dielectric constant, and

a second dielectric pair comprising a third layer having a third dielectric constant and a fourth layer having a fourth dielectric constant, wherein:

the fourth dielectric constant is larger than the third dielectric constant;

a ratio T 4 : T 3 is in the range from about 2:1 to about 8:1, wherein T 3 is a thickness of the third layer and T 4 is a thickness of the fourth layer; and

the total thickness of the second dielectric pair is thinner than the total thickness of the first dielectric pair.

2. The electrowetting system according to claim 1 , wherein the ratio T 4 :T 3 is in the range from about 4.5:1 to about 5.5:1.

3. The electrowetting system according to claim 1 , wherein the first layer and the third layer each comprise a material independently selected from the group consisting of alumina (Al 2 O 3 ), silica (SiO 2 ), and silicon nitride (Si 3 N 4 ).

4. The electrowetting system according to claim 1 , wherein the second layer and the fourth layer each comprise a material independently selected from the group consisting of hafnium oxide (HfO 2 ), tantalum oxide (Ta 2 O 5 ), titanium oxide (TiO 2 ), zirconium oxide (ZrO 2 ), yttrium oxide (Y 2 O 3 ), and lanthanum oxide (La 2 O 5 ).

5. The electrowetting system according to claim 1 , wherein first, second, third, and fourth layers are formed by atomic layer deposition (ALD).

6. The electrowetting system according to claim 1 , further comprising a third dielectric pair comprising a fifth layer having a fifth dielectric constant and a sixth layer having a sixth dielectric constant and a fourth dielectric pair comprising a seventh layer having a seventh dielectric constant and an eighth layer having an eighth dielectric constant,

the sixth dielectric constant is larger than the fifth dielectric constant;

a ratio T 6 :T 5 is in the range from about 3:1 to about 8:1, wherein T 5 is a thickness of the fifth layer and T 4 is a thickness of the fourth layer;

the third dielectric pair is thinner than the first dielectric pair;

the eighth dielectric constant that is larger than the seventh dielectric constant;

a ratio T 8 :T 7 is in the range from about 3:1 to about 8:1, wherein T 7 is a thickness of the seventh layer and T 8 is a thickness of the eighth layer; and

the fourth dielectric pair is thinner than the first dielectric pair.

7. The electrowetting system according to claim 1 , further comprising 1 to 10 further dielectric pairs, wherein:

each further dielectric pair is thinner than the first electric pair; and

each further dielectric pair comprises two layers, wherein one of the two layers has a higher dielectric constant than the other of the two layers.

8. The electrowetting system according to claim 7 , wherein each layer of each thin dielectric pair is formed by atomic layer deposition (ALD).

9. An electrowetting system for performing droplet operations, the system including:

a plurality of electrodes configured to manipulate droplets of fluid in a microfluidic space, wherein each electrode is coupled to circuitry operative to selectively apply a driving voltage to the electrode; and

a dielectric stack comprising:

a first dielectric layer having a first dielectric constant, and

a thin dielectric pair comprising a second dielectric layer having a second dielectric constant and a third dielectric layer having a third dielectric constant:

the third dielectric constant greater than the second dielectric constant;

a ratio T H :T L is in the range from about 3:1 to about 8:1, wherein TH is a thickness of the third dielectric layer and TL is a thickness of the second dielectric layer; and

the dielectric pair is thinner than the first dielectric layer.

10. The electrowetting system according to claim 9 , wherein the third dielectric layer has a dielectric constant that is greater than the dielectric constant of the first dielectric layer.

11. The electrowetting system according to claim 9 , wherein the first dielectric layer comprises silicon nitride alumina (Al 2 O 3 ), silica (SiO 2 ), or silicon nitride (Si 3 N 4 ).

12. The electrowetting system according to claim 9 , wherein the first dielectric layer is formed by plasma enhanced chemical vapor deposition (PECVD).

13. The electrowetting system according to claim 9 , wherein the second dielectric layer comprises a material selected from the group consisting of alumina (Al 2 O 3 ) and silica (SiO 2 ).

14. The electrowetting system according to claim 9 , wherein the third dielectric layer comprises a material selected from the group consisting of hafnium oxide (HfO 2 ), tantalum oxide (Ta 2 O 5 ), titanium oxide (TiO 2 ), zirconium oxide (ZrO 2 ), yttrium oxide (Y 2 O 3 ), and lanthanum oxide (La 2 O 5 ).

15. The electrowetting system according to claim 9 , wherein the second dielectric layer and the third dielectric layer are formed by atomic layer deposition (ALD).