PURPOSE: To manufacture a finished product in a short time by writing informations by writing informations by using the change of the threshold voltage of a plural floating gate type field-effect transistors by the projection of ultraviolet rays or X-rays.
CONSTITUTION: MOS FETs 43, 44, 45 are each constituted by n+ layers 28, 30, 32 (source regions), n+ layers 29, 31, 33 (drain regions) and floating gates 34, 35, 36, and these FETs are mutually isolated electrically by p+ layers 26, 27 as channel-stoppers. Predetermined informations are written to an ROM by projecting ultraviolet rays 47 for a fixed time through a passivation film 42 consisting of films 39, 40, 41 applied and formed on an Al electrode 38 by using a photo- mask 46 prepared in response to informations to be written to the ROM, thus completing the ROM. Accordingly, threshold voltage VT viewed from the Al electrode 38 of the MOS FETs is controlled by the projection of ultraviolet rays 47, and the predetermined informations are written to the ROM by the value of VT.
KIDO NOBUYUKI
WATANABE TOSHIO
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