Ultraviolet erasable semiconductor memory device

Details Ultraviolet erasable semiconductor memory device Ultraviolet erasable semiconductor memory device

2007-07-10

2007-07-10

Mai, Son L. (Department: 2827)

Static information storage and retrieval

Floating gate

C365S104000, C365S184000, C365S186000

Reexamination Certificate

active

11053851

ABSTRACT:
Each memory cell of an EPROM contains two MOSFETs and a data of each memory cell is read out by detecting a current difference between the two MOSFETs by using a differential amplifier. In such constitution as described above, even when the data is erased by irradiating an ultraviolet ray, a stable output of the differential amplifier can be obtained and, therefore, confirmation of an initialized state can be facilitated. Specifically, a channel width WAof one of the two MOSFETs constituting the memory cell is formed narrower than a channel width WBof the other. By such arrangement as described above, in an initialized state in which the ultraviolet ray is irradiated, a data signal current value IHAof the MOSFET having the channel width WAbecomes smaller than a data signal current value IHBflowing in the MOSFET having the channel width WB. Accordingly, the output of the differential amplifier is fixed in accordance with a current magnitude relation of IHA<IHB, to thereby define a data “0”. On the other hand, in writing a data “1”, charges are injected in a floating gate electrode of the MOSFET having the channel width WBto raise a threshold voltage Vt and, then, the MOSFET is set in an “off” state.

REFERENCES:
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patent: 5677867 (1997-10-01), Hazani
patent: 5930180 (1999-07-01), Callahan
patent: 6618282 (2003-09-01), Poplevine et al.

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