EP0520561A2
Expired / Lapsed
EP
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Thin-film ROM devices 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 A thin-film ROM devise comprises an array of open-circuit and closed-circuit cells (5 to 8) formed from a stack of thin films (12,21,22,23,11) on a glass or other substrate (10). The semiconductor films (21,22,23) may be of hydrogenated amorphous silicon. In accordance with the present invention, at least one of the semiconductor films (21,22,23) is removed from some of the closed-circuit cell areas (5,7,8) before depositing the next film. In this way, at least a second type of thin-film diode (MIM, MIN, MIP) is formed having a different conduction characteristic to that of a first type (NIP), so increasing the information content of the ROM array. A lower semiconductor film (23) can be readily etched away from the lower electrode film (11) by a selective etching treatment in which the electrode film (11) acts as an etch stop. By monitoring emissions during plasma etching, an upper semiconductor film (21 or 22) can be removed from a lower semiconductor film (22 or 23). PN diodes and back-to-back PNP or NPN or PINIP or NIPIN diodes may be formed for some of the closed-circuit cells.
Inventors
- 👤 Ian Douglas French
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-01 05:00
CPC Classifications
H; H10; H10B; H10B20/00
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
126 words
A thin-film ROM device comprising an array of open-circuit and closed-circuit cells formed on a substrate, each closed-circuit cell comprising a thin-film diode, the array being formed from a stack of thin films carried on the substrate and including at least lower and upper semiconductor films of different conductivity type and/or conductivity between lower and upper electrode films, characterised in that only some of the closed-circuit cells comprise areas of both the upper and lower semiconductor films to form a first type of thin-film diode, and in that in others of the closed-circuit cells at least one of the semiconductor films is absent to form at least a second type of thin-film diode having a different conduction characteristic to that of the first type of diode.
Claim 2
Dependent Claim
44 words
A device as claimed in claim 1, further characterised in that the lower semiconductor film is absent in one second type of diode, the lower electrode film of which forms a Schottky barrier with an area of the upper semiconductor film in this diode.
Claim 3
Dependent Claim
60 words
A device as claimed in claim 2, further characterised in that a further semiconductor film is present between the upper semiconductor film and the upper electrode in at least some of the closed-circuit cells, and in that both the further semiconductor film and the lower semiconductor film have a high conductivity-determining doping concentration as compared with the upper semiconductor film.
Claim 4
Dependent Claim
64 words
A device as claimed in claim 3, further characterised in that the lower and further semiconductor films are of opposite conductivity type and the upper semiconductor film is substantially intrinsic so that some closed-circuit cells comprise PIN diodes and other closed-circuit cells comprise PIM or NIM diodes where M represents a metal-based electrode film forming a Schottky barrier with the substantially intrinsic semiconductor film.
Claim 5
Independent Claim
73 words
A device as claimed in any one of the preceding claims, further characterised in that the upper semiconductor film is an alloy of a semiconductor element with another element which provides the film with semi-insulating conductive properties, and in that the lower semiconductor film is absent in one second type of diode which has a MIM structure comprising the semi-insulating upper semiconductor film (represented by I) between metal-based upper and lower electrode films.
Claim 6
Independent Claim
31 words
A device as claimed in any one of the preceding claims, further characterised in that the open-circuit cells comprise an insulating layer between the upper electrode film and the semiconductor films.
Claim 7
Independent Claim
178 words
A method of manufacturing a thin-film ROM device, comprising (a) successively depositing a plurality of thin films as a stack on a substrate, the films comprising a lower semiconductor film on a lower electrode film on the substrate, at least one upper semiconductor film on the lower semiconductor film, and an upper electrode film, the semiconductor films being of different conductivity type and/or conductivity, and (b) etching locally through the semiconductor films to define separate cell areas in the stack for an array of open-circuit and closed-circuit cells, each closed-circuit cell comprising a thin-film diode formed from the stack of semiconductor and electrode films, characterised in that, at least one of the deposited semiconductor films is retained in areas where closed-circuit cells comprising a first type of thin-film diode are to be formed and is removed from other closed-circuit cell areas before depositing the next film of the stack so as to provide in these other cell areas at least a second type of thin-film diode which has a different conduction characteristic to that of the first type.
Claim 8
Dependent Claim
58 words
A method as claimed in claim 7, further characterised in that, before depositing an upper semiconductor film, the lower semiconductor film is removed from the lower electrode film in areas where a second type of thin-film diode is to be formed, which second type comprises an area of the upper semiconductor film directly on the lower electrode film.
Claim 9
Dependent Claim
41 words
A method as claimed in claim 7 or claim 8, further characterised in that an upper semiconductor film in some closed-circuit areas is removed from a lower semiconductor film by plasma etching before depositing a further upper film of the stack.
Claim 10
Dependent Claim
46 words
A method as claimed in claim 9, further characterised in that during the plasma etching the optical emission of the plasma is monitored to determine when the lower semiconductor film is exposed to the etching by the removal of the upper semiconductor film in these areas.
Claim 11
Independent Claim
36 words
A device as claimed in any one of claims 1 to 6 or a method as claimed in any one of claims 7 to 10, further characterised in that the semiconductor films are hydrogenated amorphous silicon.
References Cited (Backward Citations)
No citation records indexed.
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