The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Aug. 24, 2004
Filed:
Aug. 29, 2002
Noboru Egawa, Tokyo, JP;
Hitoshi Kokubun, Tokyo, JP;
Oki Electric Industry Co., Ltd., Tokyo, JP;
Abstract
A method of manufacturing a mask ROM for storing quaternary data enables short turn around time, makes refining cell sizes simple, and enables stable reading of data. Gaps are formed between word lines in the memory cell transistors and two diffusion areas. Impurities are doped into these gaps in accordance with quaternary write data when data is written. A current runs between these diffusion areas only when one of these two areas into which impurities have been doped is used as a drain. Accordingly, quaternary data can be read by a first reading when the first diffusion area is a source and the other diffusion area is a drain, and by reading a second reading when the first diffusion area is used as a drain and the other diffusion area as a source.