Virtual ground non-volatile memory array
A memory device with memory cell pairs each having a single continuous channel region, first and second floating gates over first and second portions of the channel region, an erase gate over a third portion of the channel region between the first and second channel region portions, and first and second control gates over the first and second floating gates. For each of the pairs of memory cells, the first region is electrically connected to the second region of an adjacent pair of memory cells in the same active region, and the second region is electrically connected to the first region of an adjacent pair of the memory cells in the same active region.
1. A memory device comprising:
a substrate of semiconductor material of a first conductivity type;
spaced apart isolation regions formed on the substrate which are substantially parallel to one another and have lengths that extend in a first direction, with an active region between each pair of adjacent isolation regions, wherein each of the active regions has a length extending in the first direction;
each of the active regions including a plurality of pairs of memory cells, each of the memory cell pairs includes:
first and second regions spaced apart in the substrate and having a second conductivity type different than the first conductivity type, with a continuous channel region in the substrate extending entirely between the first and second regions,
a first floating gate disposed vertically over and insulated from a first portion of the channel region adjacent to the first region,
a second floating gate disposed vertically over and insulated from a second portion of the channel region adjacent to the second region,
an erase gate disposed vertically over and insulated from a third portion of the channel region between the first and second channel region portions,
a first control gate disposed vertically over and insulated from the first floating gate, and
a second control gate disposed vertically over and insulated from the second floating gate;
wherein the pairs of memory cells are configured in an array such that for each of the pairs of memory cells, the channel region extends entirely from the first region to the second region in the first direction, the first region is electrically connected to the second region of an adjacent pair of memory cells in the same active region, and the second region is electrically connected to the first region of an adjacent pair of the memory cells in the same active region;
a plurality of first control gate lines having lengths extending in a second direction orthogonal to the first direction and each electrically connected to one of the first control gates in each of the active regions;
a plurality of second control gate lines having lengths extending in the second direction and each electrically connected to one of the second control gates in each of the active regions;
a plurality of bit lines having lengths extending in the second direction and each electrically connected to one of the first regions and one of the second regions in each of the active regions;
a plurality of erase gate lines having lengths extending in the first direction and each electrically connected to the erase gates in one of the active regions.
2. The memory device of claim 1 , further comprising:
control circuitry configured to, during a read operation for a selected one of the memory cells, apply:
a positive voltage to the bit line electrically connected to the selected memory cell;
a positive voltage to the erase gate line electrically connected to the erase gate of the selected memory cell;
a positive voltage to the control gate line electrically connected to the control gate of the selected memory cell;
a positive voltage to the control gate line electrically connected to the control gate of the memory cell paired with the selected memory cell;
a zero voltage to the control gate lines electrically connected to the control gates of the pairs of memory cells not containing the selected memory cell; and
a zero voltage to the bit lines electrically connected to the memory cells that are not the selected memory cell.
3. The memory device of claim 1 , further comprising:
control circuitry configured to, during a program operation for a selected one of the memory cells, apply:
a positive voltage to the bit line electrically connected to the selected memory cell;
a positive voltage to the erase gate line electrically connected to the erase gate of the selected memory cell;
a positive voltage to the control gate line electrically connected to the control gate of the selected memory cell;
an electrical current to the bit line electrically connected to the memory cell paired with the selected memory cell; and
a positive voltage to the control gate line electrically connected to the control gate of the memory cell paired with the selected memory cell.
4. The memory device of claim 3 , wherein the control circuitry is configured further to apply:
a negative voltage to the control gate lines electrically connected to the control gates of a memory cell pair adjacent to the memory cell pair containing the selected memory cell; and
a zero voltage to the control gate lines electrically connected to the control gates of pairs of the memory cells not containing the selected memory cell and not adjacent to the pair of memory cells containing the selected memory cell.
5. The memory device of claim 1 , further comprising:
control circuitry configured to, during an erase operation for a selected one of the memory cells, apply:
a positive voltage to the erase gate line electrically connected to the erase gate of the selected memory cell; and
a negative voltage to the control gate line electrically connected to the control gate of the selected memory cell.