Patent EP0520560A2 successfully refreshed from Google Patents.
EP0520560A2
Expired / Lapsed
EP
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Thin-film transistors and their manufacture
Assignee: Philips Electronics UK Ltd
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Filing: 1992-06-19
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Granted: —
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Expires: 2012-06-19
Abstract
Abstract The off-state leakage current, threshold voltage and on-state current of a thin-film transistor (TFT) can be degraded by operation at high drain bias voltages, e.g. above 15 volts. Such degradation is significantly reduced in accordance with the invention by forming the drain (6) as a highly-doped semiconductor electrode layer (56) on part of an intermediate lower-doped layer (55) on the semiconductor film (2) forming the TFT channel. The drain electrode layer (56) is laterally separated from the transistor channel. An area (A) of the intermediate layer (55) not overlapped by the electrode layer (56) nor modulated by the gate (4) extends from the drain electrode layer (56) towards the gate (4) so as to provide along the intermediate layer (55) a low-doped field-relief region in at least part of the area of lateral separation. The TFTs may be, for example, of the coplanar type or even of the inverted staggered type.
Inventors
- 👤 Nigel David Young
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-02 17:48
CPC Classifications
H; H10; H10D; H10D30/00; H10D30/60; H10D30/67; H10D30/6704; H10D30/6713; H10D30/6715; H10D30/01; H10D30/021; H10D30/031; H10D30/0312; H10D30/0314; H10D30/6717
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
158 words
A thin-film transistor comprising a semiconductor film which provides a transistor channel coupled to a gate of the transistor, the transistor having a drain disposed at a face of the semiconductor film, the drain comprising a semiconductor electrode layer and an intermediate semiconductor layer, which intermediate layer lies between the semiconductor film and the semiconductor drain electrode layer, has a lower conductivity-determining doping concentration than the drain electrode layer and serves to reduce the electric field intensity in the region between the gate and the drain electrode layer, characterised in that, viewed perpendicular to the face of the film, the drain electrode layer is separated laterally from the transistor channel, and there is present an area of the intermediate layer which is not overlapped by the drain electrode layer and not modulated by the gate and which extends from the drain electrode layer towards the gate so as to provide along the intermediate layer a low-doped field-relief region.
Claim 2
Dependent Claim
42 words
A thin-film transistor as claimed in claim 1, further characterised in that the area of the intermediate layer providing the low-doped field-relief region extends along substantially the whole area of the lateral separation, from the transistor channel to the drain electrode layer.
Claim 3
Dependent Claim
53 words
A thin-film transistor as claimed in claim 2, further characterised in that the gate is present on an insulating layer at the same face of the semiconductor film as the drain, and in that both the insulating layer and gate overlap the intermediate layer adjacent to the area providing the low-doped field-relief region.
Claim 4
Dependent Claim
39 words
A thin-film transistor as claimed in claim 1, further characterised in that, viewed perpendicular to the face of the film, a gap is present between the gate and the area of the intermediate layer providing the low-doped field-relief region.
Claim 5
Dependent Claim
54 words
A thin-film transistor as claimed in any one of the preceding claims, further characterised in that the electrode layer and intermediate layer are parts of a single deposited layer having a doping concentration which varies gradually from a high level in the electrode layer part to the lower level in the intermediate layer part.
Claim 6
Dependent Claim
41 words
A thin-film transistor as claimed in any one of the preceding claims, further characterised in that the area of the intermediate layer providing the low-doped field-relief region extends a distance of at least one micrometre (1µm) from the drain electrode layer.
Claim 7
Independent Claim
187 words
A method of manufacturing a thin-film transistor comprising a semiconductor film which provides a transistor channel coupled to a gate of the transistor, the transistor having a drain disposed at a face of the semiconductor film, the drain being formed by depositing a semiconductor electrode layer on an intermediate semiconductor layer on the face of the semiconductor film, wherein the intermediate layer is doped with a lower conductivity-determining doping concentration than the electrode layer and serves to reduce the electric field intensity in the region between the gate and the drain electrode layer, which method is characterised by the steps of (a) removing from the intermediate layer a part of the drain electrode layer so as to separate the drain electrode layer laterally from the transistor channel, and to form an area of the intermediate layer which is not overlapped by the drain electrode layer, and (b) providing the gate so as not to overlap and modulate at least a part of the said area of the intermediate layer, which part thereby provides along the intermediate layer a low-doped field-relief region in the area of lateral separation.
Claim 8
Dependent Claim
41 words
A method as claimed in claim 7, further characterised in that the step (b) is carried out after the step (a), and the gate is provided on an insulating layer at the same face of the semiconductor film as the drain.
Claim 9
Dependent Claim
22 words
A method as claimed in claim 7, further characterised by providing the gate in step (b) before carrying out the step (a).
Claim 10
Dependent Claim
63 words
A method as claimed in claim 9, further characterised in that, after providing the gate in step (b), a photolithographic step is carried out using the gate as a photomask to define a window in a photoresist layer on the drain electrode layer, and the drain electrode layer exposed at the window is etched away from the intermediate layer in the step (a).
Claim 11
Dependent Claim
30 words
A method as claimed in claim 10, further characterised in that the gate is provided in the step (b) at the same face of the semiconductor film as the drain.
References Cited (Backward Citations)
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