High electron mobility transistors having improved drain current drift and/or leakage current performance
A high electron mobility transistor includes a channel layer, a barrier layer on the channel layer, source and drain contacts on the barrier layer, a gate contact between the source and drain contacts, and a multi-layer passivation structure on the upper surface of the barrier layer between the source contact and the drain contact. The multi-layer passivation structure includes a first passivation layer that comprises a charge dissipation material directly contacts the upper surface of the barrier layer and a second passivation layer comprising a different material than the first passivation layer that also directly contacts the upper surface of the barrier layer. In some embodiments, at least one recess may be formed in the upper surface of the barrier layer and the second passivation layer may be formed within the recesses.
1. A high electron mobility transistor, comprising:
a channel layer;
a barrier layer on the channel layer, the barrier layer having a lower surface that is adjacent the channel layer and an upper surface that is opposite the lower surface;
a source contact on the upper surface of the barrier layer;
a drain contact on the upper surface of the barrier layer;
a gate contact on the upper surface of the barrier layer between the source contact and the drain contact; and
a passivation layer on the upper surface of the barrier layer between the source contact and the drain contact,
wherein the passivation layer is within a first recess that is provided in the upper surface of the barrier layer adjacent a sidewall of one of the source contact and the drain contact that faces the gate contact, the first recess extending further into the barrier layer than at least one of the source contact and the drain contact,
wherein a longitudinal axis of the first recess extends in parallel to a longitudinal axis of the drain contact.
2. The high electron mobility transistor of claim 1 , wherein the passivation layer comprises a second passivation layer, the high electron mobility transistor further comprising a first passivation layer on the upper surface of the barrier layer between the source contact and the drain contact, wherein both the first passivation layer and the second passivation layer directly contact the barrier layer, and wherein the first passivation layer comprises a first material and the second passivation layer comprises a second material that is different than the first material.
3. The high electron mobility transistor of claim 2 , wherein the first material is a first silicon nitride material having a first ratio of silicon to nitrogen and the second material is a second silicon nitride material having a second ratio of silicon to nitrogen, wherein the first ratio of silicon to nitrogen is at least ten percentage points greater than the second ratio of silicon to nitrogen.
4. The high electron mobility transistor of claim 1 , wherein the passivation layer comprises a second passivation layer, the high electron mobility transistor further comprising a first passivation layer on the upper surface of the barrier layer between the source contact and the drain contact, wherein the first passivation layer comprises a first material that is a charge dissipation material and the second passivation layer comprises a second material that is different than the first material.
5. The high electron mobility transistor of claim 4 , wherein the second passivation layer is not a charge dissipation material.
6. The high electron mobility transistor of claim 5 , wherein the charge dissipation material is silicon-rich silicon nitride or alumina.
7. The high electron mobility transistor of claim 1 , wherein the first recess only extends partially through the barrier layer.
8. The high electron mobility transistor of claim 1 , wherein the first recess is adjacent the drain contact and the barrier layer, the high electron mobility transistor further comprising a second recess in the upper surface of the barrier layer adjacent the source contact, the second recess only extending partially through the barrier layer, the passivation layer also being within the second recess.
9. The high electron mobility transistor of claim 8 , further comprising a third recess in the upper surface of the barrier layer, wherein the second passivation layer is within the third recess, wherein the third recess is underneath the gate contact.
10. A high electron mobility transistor, comprising:
a channel layer;
a barrier layer on the channel layer, the barrier layer having a lower surface that is adjacent the channel layer and an upper surface that is opposite the lower surface;
a source contact on the upper surface of the barrier layer;
a drain contact on the upper surface of the barrier layer;
a gate contact on the upper surface of the barrier layer between the source contact and the drain contact; and
a passivation layer on the upper surface of the barrier layer between the source contact and the drain contact,
wherein the passivation layer is within a first recess in the upper surface of the barrier layer that only extends partially through the barrier layer, the first recess being adjacent one of the source contact and the drain contact.
11. The high electron mobility transistor of claim 10 , wherein the first recess is adjacent the drain contact and the barrier layer, the high electron mobility transistor further comprising a second recess in the upper surface of the barrier layer adjacent the source contact, the second recess only extending partially through the barrier layer, the passivation layer also being within the second recess.
12. The high electron mobility transistor of claim 11 , further comprising a third recess in the upper surface of the barrier layer, wherein the second passivation layer is within the third recess, wherein the third recess is underneath the gate contact.
13. The high electron mobility transistor of claim 10 , wherein the passivation layer comprises a second passivation layer, the high electron mobility transistor further comprising a first passivation layer on the upper surface of the barrier layer between the source contact and the drain contact, wherein both the first passivation layer and the second passivation layer directly contact the barrier layer, and wherein the first passivation layer comprises a first material that is a charge dissipation material and the second passivation layer comprises a second material that is different than the first material.
14. A high electron mobility transistor, comprising:
a channel layer;
a barrier layer on the channel layer, the barrier layer having a lower surface that is adjacent the channel layer and an upper surface that is opposite the lower surface;
a source contact on the upper surface of the barrier layer;
a drain contact on the upper surface of the barrier layer;
a gate contact on the upper surface of the barrier layer between the source contact and the drain contact; and
a passivation layer on the upper surface of the barrier layer between the source contact and the drain contact,
wherein the passivation layer is within a first recess in the barrier layer,
wherein a sidewall of the first recess is aligned with a sidewall of one of the source contact and the drain contact, and
wherein a bottom of the first recess is closer to the channel layer than is a bottom surface of at least one of the source contact and the drain contact.
15. The high electron mobility transistor of claim 14 , wherein the passivation layer comprises a second passivation layer, the high electron mobility transistor further comprising a first passivation layer on the upper surface of the barrier layer between the source contact and the drain contact, wherein both the first passivation layer and the second passivation layer directly contact the barrier layer, and wherein the first passivation layer comprises a first material and the second passivation layer comprises a second material that is different than the first material.
16. The high electron mobility transistor of claim 15 , wherein a portion of the first passivation layer that directly contacts the upper surface of the barrier layer is positioned between the gate contact and a portion of the second passivation layer that directly contacts the upper surface of the barrier layer.
17. The high electron mobility transistor of claim 15 , wherein the first material is silicon-rich silicon nitride or alumina.
18. The high electron mobility transistor of claim 14 , wherein the first recess only extends partially through the barrier layer.
19. The high electron mobility transistor of claim 14 , wherein the first recess is adjacent the drain contact and the barrier layer further comprises a second recess that only extends partially through the barrier layer adjacent the source contact, the passivation layer also being within the second recess.
20. The high electron mobility transistor of claim 19 , further comprising a third recess in the upper surface of the barrier layer, wherein the passivation layer is within the third recess, wherein the third recess is underneath the gate contact.