Semiconductor devices with back surface isolation
Circuits, structures and techniques for independently connecting a surrounding material in a part of a semiconductor device to a contact of its respective device. To achieve this, a combination of one or more conductive wells that are electrically isolated in at least one bias polarity are provided.
1. A transistor device comprising:
a substrate;
at least one buffer layer comprising a compound semiconductor material and formed over the substrate;
a device layer including a current conducting region formed over the at least one buffer layer;
a source contact and a drain contact formed on a top surface of the device layer;
a conductive well formed in the substrate and disposed underneath both the source and drain contacts, wherein the conductive well is electrically isolated in at least one bias polarity from the substrate such that a potential under the source and drain contacts is independent from a potential of the substrate; and
a conductive via extending from the top surface of the device layer through the device layer and through the buffer layer to penetrate and terminate within the conductive well to electrically connect the source contact to the conductive well,
wherein the substrate has a backside opposite a side adjacent the buffer layer and the drain contact is independent in potential from the backside of the substrate; and
wherein the conductive well has a doping and the substrate is substantially undoped.
2. The transistor device of claim 1 , wherein the compound semiconductor material of the at least one buffer layer comprises:
aluminum nitride;
aluminum gallium nitride; and gallium nitride.
3. The transistor device of claim 1 , wherein said substrate comprises at least one of:
silicon;
silicon carbide;
sapphire;
aluminum nitride;
gallium-nitride; and
gallium-arsenide.
4. The transistor device of claim 1 , further comprising an insulating layer formed on the substrate and a doped conductive material formed on the insulating layer.
5. The transistor device of claim 1 , wherein the conductive well comprises conductive material implanted within the substrate.
6. The transistor device of claim 1 , wherein the conductive via comprises TiN and Al, and wherein an outer portion of the via comprises TiN and an inner portion of the via comprises Al.
7. The transistor device of claim 6 , further comprising a plurality of conductive wells.
8. The transistor device of claim 7 , further comprising:
a gate structure formed between the source contact and the drain contact on the device layer;
wherein the plurality of conductive wells form a pin diode, and wherein respective conductive wells are electrically connected to the source and drain contacts.
9. The transistor device of claim 7 , further comprising:
a gate structure formed between the source contact and the drain contact on the device layer;
wherein the plurality of conductive wells form a series of P—N diodes, and wherein respective conductive wells are electrically connected to one of the source and drain contacts and the gate structure.
10. The transistor device of claim 7 , wherein at least one of the plurality of conductive wells has a Schottky connection to the conductive via.
11. The transistor device of claim 7 , wherein at least one of the plurality of conductive wells comprises an ohmic region at a connection to the conductive via.
12. The transistor device of claim 9 , wherein alternating P-N diodes in the series of P-N diodes include a tunnel junction.
13. The transistor device of claim 1 , wherein the conductive via comprises tungsten or copper.
14. The transistor device of claim 1 , wherein the conductive via comprises aluminum, silicon, or gold.
15. The transistor device of claim 1 , further comprising a plurality of conductive layers formed between the substrate and the conductive well, wherein the plurality of conductive layers have alternating doped polarities.
16. The transistor device of claim 1 , further comprising:
a first current conducting region in the device layer; and
a second current conducting region in the conductive well.
17. The transistor device of claim 16 , further comprising a channel connection extending through the buffer layer and connecting the first and second current conducting regions.
18. The transistor device of claim 17 , wherein the channel connection comprises at least one of tungsten, aluminum with titanium nitride, or silicon.
19. The transistor device of claim 1 , wherein the transistor device is part of an integrated circuit comprising a plurality of transistor devices.
20. The transistor device of claim 19 , wherein respective substrates below the transistor devices are electrically isolated in at least one polarity.
21. The transistor device of claim 19 , wherein the integrated circuit comprises a plurality of respective current conducting regions for each transistor device, wherein the plurality of respective current conducting regions are isolated from one another by isolation structures.
22. The transistor device of claim 19 , wherein the plurality of transistor devices includes a second transistor device comprising:
a contact formed on the device layer electrically connected to another respective current conducting region; and
a second conductive well electrically connected to the contact of the second transistor device through the buffer layer.
23. The transistor device of claim 19 , wherein at least two of the plurality of transistor devices share a common contact.
24. The transistor device of claim 21 , wherein the isolation structures comprise diodes formed within a current conducting layer to separate the respective current conducting regions.
25. The transistor device of claim 24 , wherein the diodes comprise implanted conductive regions having a first doping polarity and tunnel regions having a second doping polarity.
26. The transistor device of claim 1 , further comprising a metal oxide semiconductor gate structure, and wherein the metal oxide semiconductor gate structure is positioned over a back channel region for accumulating electrons.
27. The transistor device of claim 1 , further comprising:
the source contact, wherein the source contact is electrically connected to the conductive well through the buffer layer;
the drain contact electrically connected to a second conductive well through the buffer layer;
an etched opening in the device layer between the source and drain contacts;
a gate structure formed at least partially within the etched opening; and
a back channel depletion region for accumulating electrons formed between the conductive well and the second conductive well.
28. The transistor device of claim 27 , further comprising a depletion region formed between one of the conductive well and the second conductive well and the back channel region, wherein the depletion region has a lower dopant level than the conductive well.
29. The transistor device of claim 28 , further comprising a dielectric material lining the etched opening, wherein the dielectric material has a higher dielectric constant than the gate structure.
30. The transistor device of claim 1 , wherein the transistor device is part of an integrated circuit comprising a plurality of transistor devices, and wherein the respective conductive wells of the plurality of transistor devices are electrically isolated from one another.
31. A transistor device, comprising:
a substrate;
at least one buffer layer comprising a compound semiconductor material and formed over the substrate;
a device layer including a current conducting region formed over the at least one buffer layer;
a source contact and a drain contact formed on a top surface of the device layer;
a conductive well formed in the substrate and disposed underneath both the source and drain contacts, wherein the conductive well is electrically isolated in at least one bias polarity from the substrate such that a potential under the source and drain contacts is independent from a potential of the substrate; and
a conductive via extending from the top surface of the device layer through the device layer and through the buffer layer to penetrate and terminate within the conductive well to electrically connect the source contact to the conductive well,
wherein the substrate has a backside opposite a side adjacent the buffer layer and the drain contact is independent in potential from the backside of the substrate; and
wherein the substrate is substantially non-conductive, and the conductive well comprises a conductive material.