Reference circuits and methods for resistive memories
A memory device can include a plurality of memory cells formed in a substrate, each having a resistive element programmable between at least two different resistance states, including memory cells configured to store data received by the memory device, and reference cells; a reference circuit formed in the substrate configured to generate at least a first reference resistance from resistances of a plurality of reference cells; a sense circuit formed in the substrate coupled to the memory cells and at least the first reference resistance and configured to compare a resistance of a selected memory cell to at least the first reference resistance to determine the data stored by the selected memory cell.
1. A memory device, comprising:
a plurality of cells formed as part of an integrated circuit (IC), each having a resistive element programmable between at least two different resistance states, the plurality of cells including
memory cells configured to store data received by the memory device, and
reference cells;
a reference circuit formed as part of the IC configured to generate at least a first reference resistance by
averaging the resistances of a plurality of the reference cells programmed to a first resistance state to generate a first resistance portion, and
adding an offset resistance to the first resistance portion; and
a sense circuit formed as part of the IC coupled to the memory cells and at least the first reference resistance and configured to compare a resistance of a selected memory cell to at least the first reference resistance to determine the data stored by the selected memory cell.
2. The memory device of claim 1 , wherein:
each memory cell resistive element is programmable between a program state and an erase state, the program state having a resistance lower than the erase state; and
the first resistance state is the program state.
3. The memory device of claim 1 , wherein the offset resistance varies according to any selected from: at least one determined temperature of the memory device and number of times a group of memory cells has been programmed.
4. The memory device of claim 1 , wherein:
the reference circuit is configured to generate
a second reference resistance from at least one reference cell having the resistive element programmed to a second resistance state different than the first resistance state; and
the sense circuit is configured to compare the resistance of the selected memory cell to both the first reference resistance and the second reference resistance to determine the data stored by the selected memory cell.
5. The memory device of claim 4 , wherein:
the reference circuit is configured to generate
the second reference resistance from a plurality of reference cells having resistive elements programmed to the second resistance state.
6. The memory device of claim 1 , wherein:
each resistive element is programmable between the at least two different resistance states in response to an application of electric fields between first and second electrodes, the programming including any selected from the group of:
an oxidation-reduction reaction, and
solid ion conduction.
7. A method, comprising:
in a memory device, storing data in a plurality of memory cells by programming a resistive element in the memory cells between at least two different resistance states;
programming reference cells to at least one of the resistance states;
by operation of a reference circuit of the memory device, generating at least a first reference resistance from resistances of a plurality of reference cells; and
by operation of a sense circuit of the memory device, comparing a resistance of a selected memory cell to at least the first reference resistance to determine the data stored by the selected memory cell; wherein
generating at least the first reference resistance includes
generating a first resistance portion by averaging the resistances of the plurality of reference cells that are programmed to a first resistance state, and
adding an offset resistance to the first resistance portion.
8. The method of claim 7 , wherein generating at least a first reference resistance includes generating a second reference resistance from resistances of a plurality of reference cells programmed to a second resistance state different from the first resistance state.
9. The method of claim 8 , wherein:
comparing the resistance of the selected memory cell to at least the first reference resistance includes comparing the resistance of the selected memory cell to both the first reference resistance and the second reference resistance.
10. The memory device of claim 7 , wherein:
the offset resistance varies according to any selected from: at least one determined temperature of the memory device and a number of times a group of memory cells has been programmed.
11. The method of claim 7 , wherein:
programming the resistive element in the memory cells includes
applying electric fields between first and second electrodes of each resistive element to induce any selected from the group of:
an oxidation-reduction reaction, and
solid ion conduction.