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Method and apparatus for erasing an array of electrically erasable EPROM cells

  • US 5,138,576 A
  • Filed: 11/06/1991
  • Issued: 08/11/1992
  • Est. Priority Date: 11/06/1991
  • Status: Expired due to Term
First Claim
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1. Apparatus for erasing an array of Flash cells and for stopping erasure of each cell in said array of cells on onset of conduction by said cell, each of said cells having a gate, a source, a drain, a floating gate from which charge must be removed by placing a high potential difference thereacross to erase the cell, and an erase node for applying said high potential across said floating gate, said cells connected in parallel columns, the sources of all cells in each said column being connected in common to a respective source line for said column and the drains of all cells in each said column being connected in common to a respective drain line for said column, said cells also arranged in parallel rows orthogonal to said columns, said gates of said cells in each one of said rows being connected to a respective gate line for said one of said rows, said apparatus comprising:

  • a supply of ground potential;

    means for applying ground potential to each of said source lines;

    means for applying ground potential to each of said gates;

    a supply of high positive potential;

    a plurality of column erase lines, each associated with a respective column, for connecting the erase node of each cell in said respective column to said supply of high positive potential;

    a plurality of sense amplifier means, each associated with a respective column for sensing conduction between the drain line and the source line of said respective column;

    a plurality of switching means, each associated with a respective column, for switchably connecting each respective column erase line to said supply of high positive potential responsive to output of a respective one of said sense amplifier means, said respective column erase line being connected to said supply of high positive potential in absence of conduction and being disconnected from said supply of high positive potential when there is conduction;

    a plurality of selecting means, each associated with one of said cells for selectively connecting the erase node of said one of said cells to said respective column erase line; and

    a plurality of select lines, each associated with a respective row for actuating said selecting means of all cells in said respective row;

    wherein;

    when a row is selected by assertion of its respective select line, said high positive potential causes electrons to flow off said floating gates of each of said cells in said selected row whose respective switching means is switched to connect its respective column erase line to said supply of high positive potential, such that as enough electrons have been removed from said floating gate of each one of said cells in said selected row;

    said one of said cells begins to conduct,said output of said sense amplifier associated with the column of said one of said cells changes, andsaid switching means disconnects the respective column erase line associated with said one of said cells from said supply of high positive potential, insufficient potential remaining across said floating gate to remove additional electrons, whereby erasure of each cell in said selected row is stopped at onset of conduction by said cell.

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