Method of programming a continuous-channel flash memory device
View Patent ↗A split gate NAND flash memory structure is formed on a semiconductor substrate of a first conductivity type. The NAND structure comprises a first region of a second conductivity type in the substrate with a second region of the second conductivity type in the substrate, spaced apart from the first region. A continuous first channel region is defined between the first region and the second region. A plurality of floating gates are spaced apart from one another with each positioned over a separate portion of the channel region. A plurality of control gates are provided with each associated with and adjacent to a floating gate. Each control gate has two portions: a first portion over a portion of the channel region and a second portion over the associated floating gate and capacitively coupled thereto.
1. A method of operating a certain flash memory cell in a plurality of flash memory cells in a flash memory structure formed on a semiconductor substrate of a first conductivity type wherein said structure has a first region of a second conductivity type in said substrate; a second region of the second conductivity type in said substrate, spaced apart from said first region, thereby defining a continuous first channel region therebetween; a plurality of floating gates, spaced apart from one another, each of the plurality of floating gates is positioned physically over and controlling a conductivity of a separate portion of the continuous channel region, wherein each floating gate defines a flash memory cell; a plurality of control gates, each of the plurality of control gates is associated with and adjacent to one of the floating gates, each control gate having two portions: a first portion physically over and controlling a conductivity of a portion of the continuous channel region with no portion of the associated floating gate disposed between the control gate first portion and the substrate, and a second portion physically over and capacitively coupled to the associated floating gate; wherein said method comprising:
erasing all of the floating gates in said flash memory structure;
applying a first voltage to said first region;
applying a second voltage, more positive than said first voltage to said second region;
sequentially programming each floating gate from said second region to said first region, commencing with one of the floating gates which is closest to said second region by:
applying a third voltage to one or more of the control gates associated with one or more of the floating gates closest to said second region which have either been programmed or is to be programmed, said third voltage sufficient to turn on the portion of the continuous channel region which the associated floating gate controls, and to turn on the portion of the continuous channel region which the associated control gate controls;
applying a fourth voltage to one of the control gates closest to one of the floating gates to be programmed but wherein said one control gate is not associated with said one floating gate to be programmed; said fourth voltage sufficient to turn on the portion of the continuous channel region which the one control gate controls, and to turn on the portion of the continuous channel region which the associated floating gate controls; and
applying a fifth voltage to all the other control gates sufficient to turn on the portions of the continuous channel regions which said all other control gates control and the portions of the continuous channel regions which the associated floating gates control.
2. The method of claim 1 wherein the difference between said fourth voltage and said third voltage causes hot electrons to be injected from the continuous channel region onto the floating gate.
3. The method of claim 2 wherein said fifth voltage is substantially the same as said third voltage.