Thin-film ROM devices and their manufacture
First Claim
1. A thin-film ROM device comprising an array of laterally separated 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 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, but not both, of the semiconductor films is absent to form at least a second type thin-film diode having a different conduction characteristic than that of the first type of diode.
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Accused Products
Abstract
A thin-film ROM device includes 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. 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.
92 Citations
7 Claims
- 1. A thin-film ROM device comprising an array of laterally separated 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 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, but not both, of the semiconductor films is absent to form at least a second type thin-film diode having a different conduction characteristic than that of the first type of diode.
Specification