Semiconductor devices with guard rings

1. A semiconductor transistor, comprising:

a semiconductor material layer;

a conductive channel in the semiconductor material layer;

a source electrode and a drain electrode contacting the conductive channel;

a gate between the source electrode and the drain electrode;

an insulating layer on a surface of the semiconductor material layer; and

a guard ring above the semiconductor material layer and between the gate and the drain electrode, the guard ring comprising an electrically conductive material which is electrically isolated from the source electrode, the drain electrode, and the gate; wherein

a portion of the insulating layer is between at least a portion of the guard ring and the semiconductor material layer, and the guard ring comprises a field mitigating portion.

2. The semiconductor transistor of claim 1 , wherein the field mitigating portion comprises electrically conductive material extending from the guard ring towards the drain electrode.

3. The semiconductor transistor of claim 1 , wherein the guard ring comprises a first portion extending from a top of the insulating layer towards a bottom of the insulating layer, and wherein the field mitigation portion is substantially perpendicular to the first portion and extends from the first portion towards the drain electrode.

4. The semiconductor transistor of claim 1 , wherein the field mitigating portion is formed on top of first and second separating portions of the insulating layer, and wherein the first separating portion is narrower than the second separating portion.

5. The semiconductor transistor of claim 1 , wherein the field mitigating portion is slanted, being formed around a via in the insulating layer that is narrower towards the bottom of the insulating layer and wider towards the top of the insulating layer.

6. The semiconductor transistor of claim 1 , wherein the guard ring is not electrically connected to any DC and AC voltage sources.

7. The semiconductor transistor of claim 1 , wherein the guard ring extends from a top of the insulating layer towards a bottom of the insulating layer without contacting the semiconductor material layer.

8. The guard ring of claim 7 , wherein a minimum separation between the guard ring and the semiconductor material layer is at least 20 nanometers.

9. The semiconductor transistor of claim 1 , wherein the guard ring is at a distance from the gate where a depletion region in the semiconductor material layer extends prior to or at breakdown of the transistor in a similar transistor which lacks the guard ring.

10. The semiconductor transistor of claim 1 , further comprising a field plate.

11. The semiconductor transistor of claim 10 , wherein the field plate is electrically connected to the gate.

12. The semiconductor transistor of claim 10 , wherein the field plate comprises electrically conducting material contacting the gate and extending from the gate towards the drain electrode.

13. The semiconductor transistor of claim 10 , wherein the field plate is slanted, being formed around a via in the insulating layer that is narrower towards a bottom of the insulating layer and wider towards a top of the insulating layer.

14. The semiconductor transistor of claim 1 , wherein the transistor is a III-N device.

15. The semiconductor transistor of claim 1 , wherein the semiconductor material layer comprises a III-N channel layer and a III-N barrier layer above the III-N channel layer.

16. The semiconductor transistor of claim 15 , wherein the conductive channel is a two-dimensional electron gas (2DEG) channel induced in the III-N channel layer near the interface between the III-N channel layer and the III-N barrier layer.

17. The semiconductor transistor of claim 15 , wherein the III-N channel layer comprises a layer of GaN.

18. The semiconductor transistor of claim 15 , wherein the III-N barrier layer comprises a layer of Al x Ga 1-x N.

19. The semiconductor transistor of claim 1 , wherein the transistor is a high-voltage device.

20. A semiconductor transistor, comprising:

a semiconductor material layer;

a conductive channel in the semiconductor material layer;

a source electrode and a drain electrode contacting the conductive channel;

a gate between the source electrode and the drain electrode;

an insulating layer on a surface of the semiconductor material laver; and

a guard ring above the semiconductor material layer and between the gate and the drain electrode, the guard ring comprising an electrically conductive material which is electrically isolated from the source electrode, the drain electrode, and the gate; wherein the guard ring extends from a top of the insulating layer towards a bottom of the insulating layer and contacts the semiconductor material layer.

21. The semiconductor transistor of claim 20 , wherein the transistor is a III-N device.

22. The semiconductor transistor of claim 20 , wherein the semiconductor material layer comprises a III-N channel layer and a III-N barrier layer above the III-N channel layer.

23. The semiconductor transistor of claim 22 , wherein the conductive channel is a two-dimensional electron gas (2DEG) channel induced in the III-N channel layer near the interface between the III-N channel layer and the III-N barrier layer.

24. The semiconductor transistor of claim 22 , wherein the III-N channel layer comprises a layer of GaN.

25. The semiconductor transistor of claim 22 , wherein the III-N barrier layer comprises a layer of Al x Ga 1-x N.

26. A method of manufacturing a semiconductor transistor, the method comprising:

forming a semiconductor material layer on a substrate;

forming an insulating layer on a surface of the semiconductor material layer;

adding source and drain electrodes contacting a conductive channel in the semiconductor material layer;

etching the insulating layer to receive a deposition of conductive material; and

depositing conductive material to form a gate between the source electrode and the drain electrode and a guard ring between the gate and the drain electrode, wherein the guard ring comprises a field mitigating portion and is electrically isolated from the source electrode, the drain electrode, and the gate, and wherein a portion of the insulating layer is between at least a portion of the guard ring and the semiconductor material layer.

27. The method of claim 26 , wherein etching the insulating layer comprises etching the insulating layer so that the guard ring is at a distance from the gate where a depletion region in the semiconductor material layer extends prior to or at breakdown of the transistor in a similar transistor which lacks the guard ring.

28. The method of claim 26 , wherein etching the insulating layer comprises etching the insulating layer to define a guard ring including a field mitigating portion extending from the guard ring towards the drain electrode.

29. The method of claim 28 , wherein the field mitigating portion comprises a plurality of perpendicular field mitigating portions between the top of the insulating layer and the bottom of the insulating layer, each perpendicular field mitigating portion extending perpendicularly from the main portion towards the drain electrode.

30. The method of claim 28 , wherein the field mitigating portion is slanted, being formed around a via in the insulating layer that is narrower towards the bottom of the insulating layer and wider towards the top of the insulating layer.

31. The method of claim 26 , wherein etching the insulating layer comprises etching the insulating layer to define a field plate.

32. The method of claim 31 , further comprising depositing conductive material so that the field plate is electrically connected to the gate.

33. The method of claim 26 , wherein forming the semiconductor material layer comprises forming a III-N channel layer and a III-N barrier layer above the III-N channel layer.

34. A method of manufacturing a semiconductor transistor, the method comprising:

forming a semiconductor material layer on a substrate;

forming an insulating layer on a surface of the semiconductor material layer;

adding source and drain electrodes contacting a conductive channel in the semiconductor material layer;

etching the insulating layer to receive a deposition of conductive material; and

depositing conductive material to form a gate between the source electrode and the drain electrode and a guard ring between the gate and the drain electrode, wherein the guard ring is electrically isolated from the source electrode, the drain electrode, and the gate, and wherein the guard ring extends from a top of the insulating layer towards a bottom of the insulating layer and contacts the semiconductor material layer.

35. The method of claim 34 , wherein etching the insulating layer comprises etching the insulating layer so that the guard ring is at a distance from the gate where a depletion region in the semiconductor material layer extends prior to or at breakdown of the transistor in a similar transistor which lacks the guard ring.

36. The method of claim 34 , wherein etching the insulating layer comprises etching the insulating layer to define a guard ring including a field mitigating portion extending from the guard ring towards the drain electrode.

37. The method of claim 36 , wherein the field mitigating portion comprises a plurality of perpendicular field mitigating portions between the top of the insulating layer and the bottom of the insulating layer, each perpendicular field mitigating portion extending perpendicularly from the main portion towards the drain electrode.

38. The method of claim 36 , wherein the field mitigating portion is slanted, being formed around a via in the insulating layer that is narrower towards the bottom of the insulating layer and wider towards the top of the insulating layer.

39. The method of claim 34 , wherein etching the insulating layer comprises etching the insulating layer to define a field plate.

40. The method of claim 39 , further comprising depositing conductive material so that the field plate is electrically connected to the gate.

41. The method of claim 34 , wherein forming the semiconductor material layer comprises forming a III-N channel layer and a III-N barrier layer above the III-N channel layer.