Method of erasing a high density contactless flash EPROM array

Claim 1

A method of erasing selected rows in a contactless flash EPROM array formed in a P-type well that is formed in an N-type silicon substrate, and wherein the flash EPROM array includes a layer of tunnel oxide about 100-120Å thick formed on a surface of the P-type well, a plurality of rows and columns of polysilicon floating gates formed on the tunnel oxide layer, each polysilicon floating gate having a layer of dielectric material formed thereon, an N-type bit line formed in the P-type well between each two adjacent columns of polysilicon floating gates to define a plurality of spaced-apart N-type bit lines in the P-type well, alternating of said bit lines being contacted to define drain bit lines of said array, bit lines between adjacent drain bit lines being non-contacted to define source bit lines of said array such that each source bit line has first and second adjacent drain bit lines associated therewith, each source bit line being electrically connectable to the associated first adjacent drain bit line via a first MOS select transistor having its gate connected to a polysilicon first select line and to the associated second adjacent drain bit line via a second MOS select transistor having its gate connected to a polysilicon second select line, the array further including a plurality of spaced-apart parallel polysilicon word lines formed perpendicular to the columns of floating gates, each word line overlying the floating gates in a row of said array such that the floating gates in said row are separated from said word line by the dielectric material formed on each said floating gate in said row of said array, the erase method comprising: while maintaining the P-type well at a positive supply voltage, applying a negative erase voltage to the polysilicon word line of each row of said array selected for erasure; maintaining the source bit lines and the drain bit lines of said array floating; and applying the supply voltage to the polysilicon word line of each row of said array not selected for erasure.

Claim 2

A method of erasing selected rows in a contactless flash EPROM array formed in a P-type well that is formed in an N-type silicon substrate, and wherein the flash EPROM array includes a layer of tunnel oxide about 100-120Å thick formed on a surface of the P-type well, a plurality of rows and columns of polysilicon floating gates formed on the tunnel oxide layer, each polysilicon floating gate having a layer of dielectric material formed thereon, an N-type bit line formed in the P-type well between each two adjacent columns of polysilicon floating gates to define a plurality of spaced-apart N-type bit lines in the P-type well, alternating of said bit lines being contacted to define drain bit lines of said array, bit lines between adjacent drain bit lines being non-contacted to define source bit lines of said array such that each source bit line has first and second adjacent drain bit lines associated therewith, each source bit line being electrically connectable to the associated first adjacent drain bit line via a first MOS select transistor having its gate connected to a polysilicon first select line and to the associated second adjacent drain bit line via a second MOS select transistor having its gate connected to a polysilicon second select line, the array further including a plurality of spaced-apart parallel polysilicon word lines formed perpendicular to the columns of floating gates, each word line overlying the floating gates in a row of said array such that the floating gates in said row are separated from said word line by the dielectric material formed on each said floating gate in said row of said array, the erase method comprising: while maintaining the P-type well at a positive supply voltage, applying a negative erase voltage to the polysilicon word line of each row of said array selected for erasure; maintaining the source bit lines and the drain bit lines of said array floating; and applying the supply voltage to the polysilicon word line of each row of said array not selected for erasure.