US6686616B1
Expired / Lapsed
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Silicon carbide metal-semiconductor field effect transistors
Assignee: Wolfspeed Inc
•
Filing: 2000-05-10
•
Granted: 2004-02-03
•
Expires: 2020-05-10
Abstract
Abstract SiC MESFETs are disclosed which utilize a semi-insulating SiC substrate which substantially free of deep-level dopants. Utilization of the semi-insulating substrate may reduce back-gating effects in the MESFETs. Also provided are SiC MESFETs with a two recess gate structure. MESFETS with a selectively doped p-type buffer layer are also provided. Utilization of such a buffer layer may reduce output conductance by a factor of 3 and produce a 3 db increase in power gain over SiC MESFETs with conventional p-type buffer layers. A ground contact may also be provided to the p-type buffer layer and the p-type buffer layer may be made of two p-type layers with the layer formed on the substrate having a higher dopant concentration. SiC MESFETs according to embodiments of the present invention may also utilize chromium as a Schottky gate material. Furthermore, an oxide-nitride-oxide (ONO) passivation layer may be utilized to reduce surface effects in SiC MESFETs. Also, source and drain ohmic contacts may be formed directly on the n-type channel layer, thus, the n + regions need not be fabricated and the steps associated with such fabrication may be eliminated from the fabrication process. Methods of fabricating such SiC MESFETs and gate structures for SiC FETs as well as passivation layers are also disclosed.
Inventors
- 👤 Scott T. Allen
- 👤 John W. Palmour
- 👤 Terrence S. Alcorn
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-24 22:39
CPC Classifications
H; H10; H10D; H10D30/00; H10D30/80; H10D30/87; H10D30/877; H10D12/00; H10D12/01; H10D12/031; H10D30/01; H10D30/061; H10D62/00; H10D62/80; H10D62/83; H10D62/832; H10D62/8325; H10D64/00; H10D64/60; H10D64/64; H10W; H10W10/00; H10W10/01
Claims Analysis
Total Claims: 132
Claim 1
Independent Claim
153 words
A metal-semiconductor field-effect transistor comprising: a semi-insulating silicon carbide substrate which is substantially free of deep level dopants; an n-type epitaxial layer of n-type conductivity silicon carbide on the substrate, ohmic contacts on the n-type epitaxial layer that respectively define a source and a drain; a cap layer of n-type silicon carbide on the n-type epitaxial layer; a first recess in the cap layer; a second recess in the n-type epitaxial layer, wherein the recess in the n-type epitaxial layer is within the first recess in the cap layer; and a Schottky metal contact on the n-type epitaxial layer that is between the ohmic contacts and thereby between the source and the drain to form an active channel in the n-type epitaxial layer between the source and the drain when a bias is applied to the Schottky metal contact wherein the Schottky metal contact is within the recess in the n-type epitaxial layer.
Claim 2
Dependent Claim
153 words
A metal-semiconductor field-effect transistor comprising: a semi-insulating silicon carbide substrate which is substantially free of deep level dopants; an n-type epitaxial layer of n-type conductivity silicon carbide on the substrate, ohmic contacts on the n-type epitaxial layer that respectively define a source and a drain; a cap layer of n-type silicon carbide on the n-type epitaxial layer; a first recess in the cap layer; a second recess in the n-type epitaxial layer, wherein the recess in the n-type epitaxial layer is within the first recess in the cap layer; and a Schottky metal contact on the n-type epitaxial layer that is between the ohmic contacts and thereby between the source and the drain to form an active channel in the n-type epitaxial layer between the source and the drain when a bias is applied to the Schottky metal contact wherein the Schottky metal contact is within the recess in the n-type epitaxial layer.
Claim 3
Dependent Claim
32 words
A metal-semiconductor field-effect transistor according to claim 1 , wherein the semi-insulating substrate has a level of deep level dopants which is below a level which dominates the resistivity of the substrate.
Claim 4
Dependent Claim
33 words
A metal-semiconductor field-effect transistor according to claim 1 , wherein the semi-insulating silicon carbide substrate has less than about 1×10 16 cm −3 of heavy metals, transition elements and deep level trapping elements.
Claim 5
Dependent Claim
33 words
A metal-semiconductor field-effect transistor according to claim 1 , wherein the semi-insulating silicon carbide substrate has less than about 1×10 14 cm −3 of heavy metals, transition elements and deep level trapping elements.
Claim 6
Dependent Claim
26 words
A metal-semiconductor field-effect transistor according to claim 1 , wherein the n-type epitaxial layer and the cap layer have carrier concentrations which are substantially the same.
Claim 7
Dependent Claim
28 words
A transistor according to claim 1 , wherein the recess in the n-type epitaxial layer extends to a depth of from about 20 nm to about 120 nm.
Claim 8
Dependent Claim
28 words
A transistor according to claim 1 , wherein the cap layer has a dopant level from about 1×10 15 cm −3 to about 5×10 17 cm −3 .
Claim 9
Dependent Claim
23 words
A transistor according to claim 1 , wherein the cap layer has a thickness of from about 50 nm to about 300 nm.
Claim 10
Dependent Claim
18 words
A transistor according to claim 1 , wherein the ohmic contacts are directly on the n-type epitaxial layer.
Claim 11
Dependent Claim
24 words
A transistor according to claim 1 , further comprising regions of n + silicon carbide between the n-type epitaxial layer and the ohmic contacts.
Claim 12
Dependent Claim
20 words
A transistor according to claim 1 , wherein the ohmic contacts comprise nickel contacts directly on the n-type epitaxial layer.
Claim 13
Dependent Claim
19 words
A transistor according to claim 1 further comprising an overlayer on the ohmic contacts and the Schottky metal contact.
Claim 14
Dependent Claim
24 words
A transistor according to claim 12 , wherein the ohmic contacts comprise nickel and wherein the overlayer comprises layers of titanium, platinum and gold.
Claim 15
Dependent Claim
28 words
A transistor according to claim 1 , wherein the n-type epitaxial forms a mesa having sidewalls extending through the n-type layer which define the periphery of the transistor.
Claim 16
Dependent Claim
16 words
A transistor according to claim 14 wherein the sidewalls of the mesa extend into the substrate.
Claim 17
Dependent Claim
26 words
A transistor according to claim 14 , further comprising a passivation layer on the sidewalls of the mesa and exposed portions of the n-type epitaxial layer.
Claim 18
Dependent Claim
16 words
A transistor according to claim 16 , wherein the passivation layer is an ONO passivation layer.
Claim 19
Dependent Claim
24 words
A transistor according to claim 1 wherein the Schottky metal contact comprises a first gate layer of chromium directly on the n-type epitaxial layer.
Claim 20
Dependent Claim
30 words
A transistor according to claim 18 , wherein the Schottky metal contact further comprises an overlayer on the first gate layer, wherein the overlayer comprises layers of platinum and gold.
Claim 21
Dependent Claim
16 words
A transistor according to claim 19 , wherein the Schottky metal contact is a mushroom gate.
Claim 22
Dependent Claim
32 words
A transistor according to claim 20 , further comprising a recess in the n-type epitaxial layer and wherein the first gate layer is formed in the recess in the n-type epitaxial layer.
Claim 23
Dependent Claim
19 words
A transistor according to claim 20 , wherein the mushroom gate is self aligned with respect to the recess.
Claim 24
Dependent Claim
24 words
A transistor according to claim 1 , further comprising an undoped silicon carbide buffer layer formed between the substrate and the n-type epitaxial layer.
Claim 25
Dependent Claim
25 words
A transistor according to claim 1 , further comprising an n-type conductivity silicon carbide buffer layer formed between the substrate and the n-type epitaxial layer.
Claim 26
Dependent Claim
24 words
A transistor according to claim 1 , further comprising a p-type silicon carbide buffer layer formed between the substrate and the n-type epitaxial layer.
Claim 27
Dependent Claim
17 words
A transistor according to claim 25 , further comprising an ohmic contact to the p-type buffer layer.
Claim 28
Dependent Claim
36 words
A transistor according to claim 26 , further comprising a well region of p + silicon carbide formed in the p-type buffer layer and wherein the ohmic contact is formed on the p + well region.
Claim 29
Dependent Claim
41 words
A transistor according to claim 26 , wherein the p-type buffer layer comprises: a first p-type layer; and a second p-type layer, wherein the first p-type layer has a doping concentration higher than a doping concentration of the second p-type layer.
Claim 30
Dependent Claim
114 words
A metal-semiconductor field-effect transistor comprising: a silicon carbide substrate; an n-type epitaxial layer of n-type conductivity silicon carbide on the substrate; ohmic contacts on the n-type epitaxial layer that respectively define a source and a drain; a Schottky metal contact on the n-type epitaxial layer that is between the ohmic contacts and thereby between the source and the drain to form an active channel in the n-type epitaxial layer between the source and the drain when a bias is applied to the Schottky metal contact; metallization formed on the substrate opposite the n-type layer; and wherein the metallization comprises layers of titanium, platinum and gold coated with an overlayer of eutectic alloy of AuGe.
Claim 31
Dependent Claim
114 words
A metal-semiconductor field-effect transistor comprising: a silicon carbide substrate; an n-type epitaxial layer of n-type conductivity silicon carbide on the substrate; ohmic contacts on the n-type epitaxial layer that respectively define a source and a drain; a Schottky metal contact on the n-type epitaxial layer that is between the ohmic contacts and thereby between the source and the drain to form an active channel in the n-type epitaxial layer between the source and the drain when a bias is applied to the Schottky metal contact; metallization formed on the substrate opposite the n-type layer; and wherein the metallization comprises layers of titanium, platinum and gold coated with an overlayer of eutectic alloy of AuGe.
Claim 32
Dependent Claim
19 words
A transistor according to claim 29 , wherein the substrate has a thickness of about 100 μm or less.
Claim 33
Dependent Claim
144 words
A metal-semiconductor field-effect transistor comprising: a silicon carbide substrate; an n-type epitaxial layer of n-type conductivity silicon carbide on the substrate; ohmic contacts on the n-type epitaxial layer that respectively define a source and a drain; a cap layer of n-type silicon carbide on the n-type epitaxial layer; a first recess in the cap layer; a second recess in the n-type epitaxial layer, wherein the recess in the n-type epitaxial layer is within the first recess in the cap layer; and a Schottky metal contact on the n-type epitaxial layer that is between the ohmic contacts and thereby between the source and the drain to form an active channel in the n-type epitaxial layer between the source and the drain when a bias is applied to the Schottky metal contact wherein the Schottky metal contact is within the recess in the n-type epitaxial layer.
Claim 34
Dependent Claim
144 words
A metal-semiconductor field-effect transistor comprising: a silicon carbide substrate; an n-type epitaxial layer of n-type conductivity silicon carbide on the substrate; ohmic contacts on the n-type epitaxial layer that respectively define a source and a drain; a cap layer of n-type silicon carbide on the n-type epitaxial layer; a first recess in the cap layer; a second recess in the n-type epitaxial layer, wherein the recess in the n-type epitaxial layer is within the first recess in the cap layer; and a Schottky metal contact on the n-type epitaxial layer that is between the ohmic contacts and thereby between the source and the drain to form an active channel in the n-type epitaxial layer between the source and the drain when a bias is applied to the Schottky metal contact wherein the Schottky metal contact is within the recess in the n-type epitaxial layer.
Claim 35
Dependent Claim
26 words
A metal-semiconductor field-effect transistor according to claim 31 , wherein the n-type epitaxial layer and the cap layer have carrier concentrations which are substantially the same.
Claim 36
Dependent Claim
28 words
A transistor according to claim 31 , wherein the recess in the n-type epitaxial layer extends to a depth of from about 20 nm to about 120 nm.
Claim 37
Dependent Claim
28 words
A transistor according to claim 31 , wherein the cap layer has a dopant level from about 1×10 15 cm −3 to about 5×10 17 cm −3 .
Claim 38
Dependent Claim
23 words
A transistor according to claim 31 , wherein the cap layer has a thickness of from about 50 nm to about 300 nm.
Claim 39
Dependent Claim
18 words
A transistor according to claim 31 , wherein the ohmic contacts are directly on the n-type epitaxial layer.
Claim 40
Dependent Claim
24 words
A transistor according to claim 31 , further comprising regions of n + silicon carbide between the n-type epitaxial layer and the ohmic contacts.
Claim 41
Dependent Claim
20 words
A transistor according to claim 31 , wherein the ohmic contacts comprise nickel contacts directly on the n-type epitaxial layer.
Claim 42
Dependent Claim
19 words
A transistor according to claim 31 further comprising an overlayer on the ohmic contacts and the Schottky metal contact.
Claim 43
Dependent Claim
24 words
A transistor according to claim 39 , wherein the ohmic contacts comprise nickel and wherein the overlayer comprises layers of titanium, platinum and gold.
Claim 44
Dependent Claim
28 words
A transistor according to claim 31 , wherein the n-type epitaxial forms a mesa having sidewalls extending through the n-type layer which define the periphery of the transistor.
Claim 45
Dependent Claim
16 words
A transistor according to claim 41 wherein the sidewalls of the mesa extend into the substrate.
Claim 46
Dependent Claim
26 words
A transistor according to claim 41 , further comprising a passivation layer on the sidewalls of the mesa and exposed portions of the n-type epitaxial layer.
Claim 47
Dependent Claim
16 words
A transistor according to claim 43 , wherein the passivation layer is an ONO passivation layer.
Claim 48
Dependent Claim
18 words
A transistor according to claim 31 , further comprising metallization formed on the substrate opposite the n-type layer.
Claim 49
Dependent Claim
19 words
A transistor according to claim 45 , wherein the substrate has a thickness of about 100 μm or less.
Claim 50
Dependent Claim
26 words
A transistor according to claim 45 , wherein the metallization comprises layers of titanium, platinum and gold coated with an overlayer of eutectic alloy of AuGe.
Claim 51
Dependent Claim
24 words
A transistor according to claim 31 wherein the Schottky metal contact comprises a first gate layer of chromium directly on the n-type epitaxial layer.
Claim 52
Dependent Claim
30 words
A transistor according to claim 48 , wherein the Schottky metal contact further comprises an overlayer on the first gate layer, wherein the overlayer comprises layers of platinum and gold.
Claim 53
Dependent Claim
16 words
A transistor according to claim 49 , wherein the Schottky metal contact is a mushroom gate.
Claim 54
Dependent Claim
20 words
A transistor according to claim 50 , wherein the mushroom gate is self aligned with respect to the second recess.
Claim 55
Dependent Claim
24 words
A transistor according to claim 31 , further comprising an undoped silicon carbide buffer layer formed between the substrate and the n-type epitaxial layer.
Claim 56
Dependent Claim
25 words
A transistor according to claim 31 , further comprising an n-type conductivity silicon carbide buffer layer formed between the substrate and the n-type epitaxial layer.
Claim 57
Dependent Claim
24 words
A transistor according to claim 31 , further comprising a p-type silicon carbide buffer layer formed between the substrate and the n-type epitaxial layer.
Claim 58
Dependent Claim
17 words
A transistor according to claim 54 , further comprising an ohmic contact to the p-type buffer layer.
Claim 59
Dependent Claim
36 words
A transistor according to claim 55 , further comprising a well region of p + silicon carbide formed in the p-type buffer layer and wherein the ohmic contact is formed on the p + well region.
Claim 60
Dependent Claim
41 words
A transistor according to claim 55 , wherein the p-type buffer layer comprises: a first p-type layer; and a second p-type layer, wherein the first p-type layer has a doping concentration higher than a doping concentration of the second p-type layer.
Claim 61
Dependent Claim
158 words
A metal-semiconductor field-effect transistor comprising: a bulk single crystal semi-insulating silicon carbide substrate; an n-type epitaxial layer of n-type conductivity silicon carbide on the substrate; a p-type epitaxial layer of selectively doped p-type conductivity silicon carbide between the substrate and the n-type epitaxial layer; ohmic contacts on the n-type epitaxial layer that respectively define a source and a drain; a Schottky metal contact on the n-type epitaxial layer that is between the ohmic contacts and thereby between the source and the drain to form an active channel in the n-type epitaxial layer between the source and the drain when a bias is applied to the Schottky metal contact; and wherein the p-type epitaxial layer comprises: a first p-type conductivity silicon carbide layer formed on the substrate; and a second p-type conductivity silicon carbide layer formed on the substrate, wherein the first p-type conductivity silicon carbide layer is more heavily doped than the second p-type conductivity silicon carbide layer.
Claim 62
Dependent Claim
158 words
A metal-semiconductor field-effect transistor comprising: a bulk single crystal semi-insulating silicon carbide substrate; an n-type epitaxial layer of n-type conductivity silicon carbide on the substrate; a p-type epitaxial layer of selectively doped p-type conductivity silicon carbide between the substrate and the n-type epitaxial layer; ohmic contacts on the n-type epitaxial layer that respectively define a source and a drain; a Schottky metal contact on the n-type epitaxial layer that is between the ohmic contacts and thereby between the source and the drain to form an active channel in the n-type epitaxial layer between the source and the drain when a bias is applied to the Schottky metal contact; and wherein the p-type epitaxial layer comprises: a first p-type conductivity silicon carbide layer formed on the substrate; and a second p-type conductivity silicon carbide layer formed on the substrate, wherein the first p-type conductivity silicon carbide layer is more heavily doped than the second p-type conductivity silicon carbide layer.
Claim 63
Dependent Claim
18 words
A transistor according to claim 58 , wherein the ohmic contacts are directly on the n-type epitaxial layer.
Claim 64
Dependent Claim
24 words
A transistor according to claim 58 , further comprising regions of n + silicon carbide between the n-type epitaxial layer and the ohmic contacts.
Claim 65
Dependent Claim
20 words
A transistor according to claim 58 , wherein the ohmic contacts comprise nickel contacts directly on the n-type epitaxial layer.
Claim 66
Dependent Claim
19 words
A transistor according to claim 58 further comprising an overlayer on the ohmic contacts and the Schottky metal contact.
Claim 67
Dependent Claim
24 words
A transistor according to claim 62 , wherein the ohmic contacts comprise nickel and wherein the overlayer comprises layers of titanium, platinum and gold.
Claim 68
Dependent Claim
36 words
A transistor according to claim 58 , wherein the n-type epitaxial and p-type epitaxial layers form a mesa having sidewalls extending from the n-type layer into the p-type layer which define the periphery of the transistor.
Claim 69
Dependent Claim
16 words
A transistor according to claim 64 wherein the sidewalls of the mesa extend into the substrate.
Claim 70
Dependent Claim
26 words
A transistor according to claim 64 , further comprising a passivation layer on the sidewalls of the mesa and exposed portions of the n-type epitaxial layer.
Claim 71
Dependent Claim
16 words
A transistor according to claim 66 , wherein the passivation layer is an ONO passivation layer.
Claim 72
Dependent Claim
18 words
A transistor according to claim 58 , further comprising metallization formed on the substrate opposite the n-type layer.
Claim 73
Dependent Claim
19 words
A transistor according to claim 68 , wherein the substrate has a thickness of about 100 μm or less.
Claim 74
Dependent Claim
26 words
A transistor according to claim 68 , wherein the metallization comprises layers of titanium, platinum and gold coated with an overlayer of eutectic alloy of AuGe.
Claim 75
Dependent Claim
24 words
A transistor according to claim 58 wherein the Schottky metal contact comprises a first gate layer of chromium directly on the n-type epitaxial layer.
Claim 76
Dependent Claim
30 words
A transistor according to claim 71 , wherein the Schottky metal contact further comprises an overlayer on the first gate layer, wherein the overlayer comprises layers of platinum and gold.
Claim 77
Dependent Claim
16 words
A transistor according to claim 72 , wherein the Schottky metal contact is a mushroom gate.
Claim 78
Dependent Claim
32 words
A transistor according to claim 73 , further comprising a recess in the n-type epitaxial layer and wherein the first gate layer is formed in the recess in the n-type epitaxial layer.
Claim 79
Dependent Claim
19 words
A transistor according to claim 73 , wherein the mushroom gate is self aligned with respect to the recess.
Claim 80
Dependent Claim
65 words
A transistor according to claim 58 , further comprising: a cap layer of n-type silicon carbide on the n-type epitaxial layer; a recess in the cap layer; a recess in the n-type epitaxial layer, wherein the recess in the n-type epitaxial layer is within the recess in the cap layer; and wherein the Schottky metal contact is within the recess in the n-type epitaxial layer.
Claim 81
Dependent Claim
28 words
A transistor according to claim 76 , wherein the recess in the n-type epitaxial layer extends to a depth of from about 20 nm to about 120 nm.
Claim 82
Dependent Claim
22 words
A transistor according to claim 76 , wherein the cap layer is doped at the same level as the n-type epitaxial layer.
Claim 83
Dependent Claim
28 words
A transistor according to claim 76 , wherein the cap layer has a dopant level from about 1×10 15 cm −3 to about 5×10 17 cm −3 .
Claim 84
Dependent Claim
23 words
A transistor according to claim 76 , wherein the cap layer has a thickness of from about 50 nm to about 300 nm.
Claim 85
Dependent Claim
19 words
A transistor according to claim 58 , wherein the semi-insulating silicon carbide is substantially free of deep level dopants.
Claim 86
Dependent Claim
165 words
A metal-semiconductor field-effect transistor comprising: a bulk single crystal semi-insulating silicon carbide substrate; an n-type epitaxial layer of n-type conductivity silicon carbide on the substrate; a p-type epitaxial layer of selectively doped p-type conductivity silicon carbide between the substrate and the n-type epitaxial layer; ohmic contacts on the n-type epitaxial layer that respectively define a source and a drain; a Schottky metal contact on the n-type epitaxial layer that is between the ohmic contacts and thereby between the source and the drain to form an active channel in the n-type epitaxial layer between the source and the drain when a bias is applied to the Schottky metal contact; a contact to the p-type epitaxial layer; and wherein the p-type epitaxial layer comprises: a first p-type conductivity silicon carbide layer formed on the substrate; and a second p-type conductivity silicon carbide layer formed on the substrate, wherein the first p-type conductivity silicon carbide layer is more heavily doped than the second p-type conductivity silicon carbide layer.
Claim 87
Dependent Claim
165 words
A metal-semiconductor field-effect transistor comprising: a bulk single crystal semi-insulating silicon carbide substrate; an n-type epitaxial layer of n-type conductivity silicon carbide on the substrate; a p-type epitaxial layer of selectively doped p-type conductivity silicon carbide between the substrate and the n-type epitaxial layer; ohmic contacts on the n-type epitaxial layer that respectively define a source and a drain; a Schottky metal contact on the n-type epitaxial layer that is between the ohmic contacts and thereby between the source and the drain to form an active channel in the n-type epitaxial layer between the source and the drain when a bias is applied to the Schottky metal contact; a contact to the p-type epitaxial layer; and wherein the p-type epitaxial layer comprises: a first p-type conductivity silicon carbide layer formed on the substrate; and a second p-type conductivity silicon carbide layer formed on the substrate, wherein the first p-type conductivity silicon carbide layer is more heavily doped than the second p-type conductivity silicon carbide layer.
Claim 88
Dependent Claim
37 words
A transistor according to claim 82 , further comprising: a p + well region formed in the p-type epitaxial layer; and wherein the contact to the p-type epitaxial layer is formed on the p + well region.
Claim 89
Dependent Claim
118 words
A metal-semiconductor field-effect transistor comprising: an n-type layer of n-type conductivity silicon carbide on a silicon carbide substrate; ohmic contacts on the n-type layer and spaced apart that respectively define a source and a drain; a region of chromium on the n-type layer that is between the ohmic contacts and thereby between the source and the drain so as to provide a Schottky metal contact to form an active channel in the n-type layer between the source and the drain when a bias is applied to the Schottky metal contact; and metallization on the substrate opposite the n-type layer, wherein the metallization comprises layers of titanium, platinum and gold coated with an overlayer of eutectic alloy of AuGe.
Claim 90
Dependent Claim
118 words
A metal-semiconductor field-effect transistor comprising: an n-type layer of n-type conductivity silicon carbide on a silicon carbide substrate; ohmic contacts on the n-type layer and spaced apart that respectively define a source and a drain; a region of chromium on the n-type layer that is between the ohmic contacts and thereby between the source and the drain so as to provide a Schottky metal contact to form an active channel in the n-type layer between the source and the drain when a bias is applied to the Schottky metal contact; and metallization on the substrate opposite the n-type layer, wherein the metallization comprises layers of titanium, platinum and gold coated with an overlayer of eutectic alloy of AuGe.
Claim 91
Dependent Claim
24 words
A transistor according to claim 84 , further comprising a p-type layer of p-type conductivity silicon carbide between the substrate and the n-type layer.
Claim 92
Dependent Claim
17 words
A transistor according to claim 85 , further comprising an ohmic contact to the p-type buffer layer.
Claim 93
Dependent Claim
36 words
A transistor according to claim 86 , further comprising a well region of p + silicon carbide formed in the p-type buffer layer and wherein the ohmic contact is formed on the p + well region.
Claim 94
Dependent Claim
41 words
A transistor according to claim 86 , wherein the p-type buffer layer comprises: a first p-type layer; and a second p-type layer, wherein the first p-type layer has a doping concentration higher than a doping concentration of the second p-type layer.
Claim 95
Dependent Claim
34 words
A transistor according to claim 85 , wherein the n-type and p-type layers forms a mesa having sidewalls extending from the n-type layer into the p-type layer which define the periphery of the transistor.
Claim 96
Dependent Claim
17 words
A transistor according to claim 89 , wherein the sidewalls of the mesa extend into the substrate.
Claim 97
Dependent Claim
26 words
A transistor according to claim 89 , further comprising a passivation layer on the sidewalls of the mesa and exposed portions of the n-type epitaxial layer.
Claim 98
Dependent Claim
16 words
A transistor according to claim 91 , wherein the passivation layer is an ONO passivation layer.
Claim 99
Dependent Claim
29 words
A transistor according to claim 87 , wherein the Schottky metal contact further comprises an overlayer on the chromium region, wherein the overlay comprises layers of platinum and gold.
Claim 100
Dependent Claim
23 words
A transistor according to claim 84 , further comprising regions of n + silicon carbide between the n-type layer and the ohmic contacts.
Claim 101
Dependent Claim
19 words
A transistor according to claim 84 further comprising an overlayer on the ohmic contacts and the Schottky metal contact.
Claim 102
Dependent Claim
24 words
A transistor according to claim 95 , wherein the ohmic contacts comprise nickel and wherein the overlayer comprises layers of titanium, platinum and gold.
Claim 103
Dependent Claim
18 words
A transistor according to claim 84 , wherein the substrate has a thickness of 100 μm or less.
Claim 104
Dependent Claim
16 words
A transistor according to claim 84 , wherein the Schottky metal contact is a mushroom gate.
Claim 105
Dependent Claim
28 words
A transistor according to claim 84 , further comprising a recess in the n-type layer and wherein the chromium region is in the recess in the n-type layer.
Claim 106
Dependent Claim
14 words
A transistor according to claim 99 , wherein the chromium region is self aligned.
Claim 107
Dependent Claim
17 words
A transistor according to claim 84 , wherein the ohmic contacts are directly on the n-type layer.
Claim 108
Dependent Claim
113 words
A metal-semiconductor field-effect transistor comprising: a bulk single crystal semi-insulating silicon carbide substrate; an n-type epitaxial layer of n-type conductivity silicon carbide on the substrate; ohmic contacts on the n-type epitaxial layer that respectively define a source and a drain; a Schottky metal contact on the n-type epitaxial layer that is between the ohmic contacts and thereby between the source and the drain to form an active channel in the n-type epitaxial layer between the source and the drain when a bias is applied to the Schottky metal contact; a p-type layer of p-type conductivity silicon carbide between the substrate and the n-type epitaxial layer; and an ohmic contact to the p-type layer.
Claim 109
Dependent Claim
113 words
A metal-semiconductor field-effect transistor comprising: a bulk single crystal semi-insulating silicon carbide substrate; an n-type epitaxial layer of n-type conductivity silicon carbide on the substrate; ohmic contacts on the n-type epitaxial layer that respectively define a source and a drain; a Schottky metal contact on the n-type epitaxial layer that is between the ohmic contacts and thereby between the source and the drain to form an active channel in the n-type epitaxial layer between the source and the drain when a bias is applied to the Schottky metal contact; a p-type layer of p-type conductivity silicon carbide between the substrate and the n-type epitaxial layer; and an ohmic contact to the p-type layer.
Claim 110
Dependent Claim
45 words
A transistor according to claim 102 , wherein the n-type epitaxial layer forms a mesa having sidewalls extending into the n-type layer which define the periphery of the transistor; and wherein the sidewalls of the mesa extends from the n-type layer into the p-type layer.
Claim 111
Dependent Claim
16 words
A transistor according to claim 103 wherein the sidewalls of the mesa extend into the substrate.
Claim 112
Dependent Claim
21 words
A transistor according to claim 103 , wherein the ohmic contact on the p-type layer is directly on the p-type layer.
Claim 113
Dependent Claim
28 words
A transistor according to claim 103 , further comprising an ONO passivation layer on the sidewalls of the mesa and on exposed portions of the n-type epitaxial layer.
Claim 114
Dependent Claim
18 words
A transistor according to claim 102 , wherein the ohmic contacts are directly on the n-type epitaxial layer.
Claim 115
Dependent Claim
24 words
A transistor according to claim 102 , further comprising regions of n + silicon carbide between the n-type epitaxial layer and the ohmic contacts.
Claim 116
Dependent Claim
20 words
A transistor according to claim 102 , wherein the ohmic contacts comprise nickel contacts directly on the n-type epitaxial layer.
Claim 117
Dependent Claim
19 words
A transistor according to claim 102 further comprising an overlayer on the ohmic contacts and the Schottky metal contact.
Claim 118
Dependent Claim
24 words
A transistor according to claim 110 , wherein the ohmic contacts comprise nickel and wherein the overlayer comprises layers of titanium, platinum and gold.
Claim 119
Dependent Claim
18 words
A transistor according to claim 102 , further comprising metallization formed on the substrate opposite the n-type layer.
Claim 120
Dependent Claim
19 words
A transistor according to claim 112 , wherein the substrate has a thickness of about 100 μm or less.
Claim 121
Dependent Claim
26 words
A transistor according to claim 112 , wherein the metallization comprises layers of titanium, platinum and gold coated with an overlayer of eutectic alloy of AuGe.
Claim 122
Dependent Claim
16 words
A transistor according to claim 102 , wherein the Schottky metal contact is a mushroom gate.
Claim 123
Dependent Claim
31 words
A transistor according to claim 102 , further comprising a recess in the n-type epitaxial layer and wherein the gate contact is formed in the recess in the n-type epitaxial layer.
Claim 124
Dependent Claim
17 words
A transistor according to claim 116 , wherein the gate contact is a self aligned gate contact.
Claim 125
Dependent Claim
139 words
A metal-semiconductor field-effect transistor comprising: a bulk single crystal silicon carbide substrate; an n-type epitaxial layer of n-type conductivity silicon carbide on the substrate; ohmic contacts on the n-type epitaxial layer that respectively define a source and a drain; a Schottky metal contact on the n-type epitaxial layer that is between the ohmic contacts and thereby between the source and the drain to form an active channel in the n-type epitaxial layer between the source and the drain when a bias is applied to the Schottky metal contact; a p-type layer of p-type conductivity silicon carbide between the substrate and the n-type epitaxial layer; an ohmic contact to the p-type layer; and a well region of p + silicon carbide formed in the p-type epitaxial layer and wherein the ohmic contact is formed on the p + well region.
Claim 126
Dependent Claim
139 words
A metal-semiconductor field-effect transistor comprising: a bulk single crystal silicon carbide substrate; an n-type epitaxial layer of n-type conductivity silicon carbide on the substrate; ohmic contacts on the n-type epitaxial layer that respectively define a source and a drain; a Schottky metal contact on the n-type epitaxial layer that is between the ohmic contacts and thereby between the source and the drain to form an active channel in the n-type epitaxial layer between the source and the drain when a bias is applied to the Schottky metal contact; a p-type layer of p-type conductivity silicon carbide between the substrate and the n-type epitaxial layer; an ohmic contact to the p-type layer; and a well region of p + silicon carbide formed in the p-type epitaxial layer and wherein the ohmic contact is formed on the p + well region.
Claim 127
Dependent Claim
145 words
A metal-semiconductor field-effect transistor comprising: a bulk single crystal silicon carbide substrate; an n-type epitaxial layer of n-type conductivity silicon carbide on the substrate; ohmic contacts on the n-type epitaxial layer that respectively define a source and a drain; a Schottky metal contact on the n-type epitaxial layer that is between the ohmic contacts and thereby between the source and the drain to form an active channel in the n-type epitaxial layer between the source and the drain when a bias is applied to the Schottky metal contact; a p-type layer of p-type conductivity silicon carbide between the substrate and the n-type epitaxial layer; an ohmic contact to the p-type layer; and wherein the p-type layer comprises: a first p-type layer; and a second p-type layer, wherein the first p-type layer has a doping concentration higher than a doping concentration of the second p-type layer.
Claim 128
Dependent Claim
145 words
A metal-semiconductor field-effect transistor comprising: a bulk single crystal silicon carbide substrate; an n-type epitaxial layer of n-type conductivity silicon carbide on the substrate; ohmic contacts on the n-type epitaxial layer that respectively define a source and a drain; a Schottky metal contact on the n-type epitaxial layer that is between the ohmic contacts and thereby between the source and the drain to form an active channel in the n-type epitaxial layer between the source and the drain when a bias is applied to the Schottky metal contact; a p-type layer of p-type conductivity silicon carbide between the substrate and the n-type epitaxial layer; an ohmic contact to the p-type layer; and wherein the p-type layer comprises: a first p-type layer; and a second p-type layer, wherein the first p-type layer has a doping concentration higher than a doping concentration of the second p-type layer.
Claim 129
Dependent Claim
195 words
A metal-semiconductor field-effect transistor comprising: a semi-insulating silicon carbide substrate which is substantially free of deep level dopants; a buffer layer of silicon carbide on the semi-insulating silicon carbide substrate; an n-type epitaxial layer on the buffer layer; a cap layer on the n-type epitaxial layer; ohmic contacts on the n-type epitaxial layer that respectively define a source and a drain; a first recess in the cap layer between the source and drain contacts; a second recess in the n-type epitaxial layer within the first recess; a Schottky metal contact on the n-type epitaxial layer that is between the ohmic contacts and thereby between the source and the drain to form an active channel in the n-type epitaxial layer between the source and the drain when a bias is applied to the Schottky metal contact, wherein the Schottky metal contact includes a layer of chromium on the n-type epitaxial layer in the second recess; wherein the n-type epitaxial layer forms a mesa having sidewalls extending into the n-type layer which define the periphery of the transistor; and an ONO passivation layer on the sidewalls of the mesa and exposed portions of the n-type epitaxial layer.
Claim 130
Dependent Claim
195 words
A metal-semiconductor field-effect transistor comprising: a semi-insulating silicon carbide substrate which is substantially free of deep level dopants; a buffer layer of silicon carbide on the semi-insulating silicon carbide substrate; an n-type epitaxial layer on the buffer layer; a cap layer on the n-type epitaxial layer; ohmic contacts on the n-type epitaxial layer that respectively define a source and a drain; a first recess in the cap layer between the source and drain contacts; a second recess in the n-type epitaxial layer within the first recess; a Schottky metal contact on the n-type epitaxial layer that is between the ohmic contacts and thereby between the source and the drain to form an active channel in the n-type epitaxial layer between the source and the drain when a bias is applied to the Schottky metal contact, wherein the Schottky metal contact includes a layer of chromium on the n-type epitaxial layer in the second recess; wherein the n-type epitaxial layer forms a mesa having sidewalls extending into the n-type layer which define the periphery of the transistor; and an ONO passivation layer on the sidewalls of the mesa and exposed portions of the n-type epitaxial layer.
Claim 131
Dependent Claim
53 words
A transistor according to claim 120 , wherein the buffer layer comprises a p-type epitaxial layer of selectively doped p-type conductivity silicon carbide between the substrate and the n-type epitaxial layer, wherein the p-type conductivity silicon carbide has a carrier concentration of from about 1×10 16 to about 1×10 17 cm −3 .
Claim 132
Dependent Claim
15 words
A transistor according to claim 120 , wherein the buffer layer comprises undoped silicon carbide.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
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| 3.5 Years (Year 4) | 2007-02-02 | 2007-08-04 | 2008-02-03 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2011-02-02 | 2011-08-04 | 2012-02-03 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2015-02-02 | 2015-08-04 | 2016-02-03 | $7700.00 | Window Closed / Lapsed |