Method of programming a nonvolatile memory device containing a carbon storage material

1. A method of programming a nonvolatile memory cell comprising a steering element located in series with a storage element, wherein the storage element comprises a carbon material, the method comprising:

applying a reset pulse to change a resistivity state of the carbon material from a first state to a second state which is higher than the first state; and

applying a set pulse to change a resistivity state of the carbon material from the second state to a third state which is lower than the second state,

wherein a fall time of the reset pulse is shorter than a fall time of the set pulse, and

wherein the steering element comprises a diode or a transistor and the carbon material comprises a carbon flake resistivity switching material.

2. The method of claim 1 , wherein the fall time of the reset pulse is at least ten times shorter than the fall time of the set pulse.

3. The method of claim 2 , further comprising:

applying a second reset pulse to change a resistivity state of the carbon material; and

applying a second set pulse to change a resistivity state of the carbon material.

4. The method of claim 1 , wherein the fall time of the reset pulse is less than 10 nanoseconds long and the fall time of the set pulse is between 1 and 200 microseconds long.

5. The method of claim 1 , wherein the fall time of the reset pulse is 3 to 5 nanoseconds long and the fall time of the set pulse is between 10 and 100 microseconds long.

6. The method of claim 1 , wherein:

the reset pulse and set pulse comprise forward bias pulses; and

the reset pulse has a larger amplitude than the set pulse.

7. The method of claim 6 , wherein a duration of the reset pulse is at least ten times shorter than a duration of the set pulse.

8. The method of claim 7 , wherein reset pulse has a duration of 20 to 300 nanoseconds and the set pulse has a duration of 2 to 500 microseconds.

9. The method of claim 1 , wherein memory cell comprises a portion of a monolithic three dimensional array of nonvolatile memory cells.

10. The method of claim 1 , wherein the steering element comprises the diode and the carbon material comprises sheets or pieces of polycrystalline carbon comprising a hexagonal unit cell structure but lacking well defined and orderly A-B graphene sheet stacking of hexagonal graphite.

11. The method of claim 10 , wherein the carbon material comprises the polycrystalline carbon having a first Raman spectrum peak between 1300 and 1350 cm −1 and a second Raman spectrum peak between 1600 and 1650 cm −1 .

12. A method of programming a nonvolatile memory cell comprising a steering element located in series with a storage element, wherein the storage element comprises a carbon material, the method comprising:

applying a reset pulse to the carbon material in a lower resistivity polycrystalline state to at least partially convert the carbon material to a higher resistivity amorphous state and to quench the carbon material into the higher resistivity amorphous state; and

applying a set pulse to the carbon material to at least partially convert the carbon material from the higher resistivity amorphous state to the lower resistivity polycrystalline state,

wherein a fall time of the reset pulse is shorter than a fall time of the set pulse, and

wherein:

the fall time of the reset pulse is 3 to 5 nanoseconds long;

the fall time of the set pulse is between 10 and 100 microseconds long;

the reset pulse and set pulse comprise forward bias pulses;

the reset pulse has a larger amplitude than the set pulse;

a duration of the reset pulse is at least ten times shorter than a duration of the set pulse;

the steering element comprises a diode; and

the polycrystalline carbon material comprises a carbon flake resistivity switching material.

13. The method of claim 12 , wherein:

the carbon material is at least partially melted during the reset pulse and the carbon material is cooled to the amorphous state during a fall time of the reset pulse; and

the carbon material is at least partially melted during the set pulse and is cooled to the polycrystalline state at a slower rate than during the reset pulse.

14. A method of programming a nonvolatile memory cell comprising a steering element located in series with a storage element, wherein the storage element comprises a carbon flake material, the method comprising:

applying a reset pulse to the carbon flake material such that carbon flakes separate from each other to increase a resistivity of the carbon flake material from a first state to a second state; and

applying a set pulse to the carbon material such that the carbon flakes contact each other more than in the second state to decrease a resistivity of the carbon flake material from the second state to a third state.

15. The method of claim 14 , wherein:

a fall time of the reset pulse is shorter than a fall time of the set pulse;

during the shorter reset pulse fall time, the carbon flakes are not in a potential energy minimum state as a function of interflake distance and are locked into the second resistivity state;

during the longer set pulse fall time, the carbon flakes are in a potential energy minimum state as a function of interflake distance and are locked into the third resistivity state.

16. The method of claim 15 , wherein the carbon flakes are bound to each other after the set pulse.

17. The method of claim 14 , wherein:

the fall time of the reset pulse is 3 to 5 nanoseconds long;

the fall time of the set pulse is between 10 and 100 microseconds long;

the reset pulse and set pulse comprise forward bias pulses;

the reset pulse has a larger amplitude than the set pulse;

a duration of the reset pulse is at least ten times shorter than a duration of the set pulse;

the steering element comprises a diode; and

the polycrystalline carbon material comprises a polycrystalline carbon flake resistivity switching material.

18. A method of programming a nonvolatile memory cell comprising a steering element located in series with a storage element, wherein the storage element comprises a non-monolithic carbon material, the method comprising:

applying a reset pulse to change a resistivity state of the carbon material from a first state to a second state which is higher than the first state; and

applying a set pulse to change a resistivity state of the carbon material from the second state to a third state which is lower than the second state, wherein a fall time of both of the reset pulse and the set pulse is 15 ns or less, a rise time of both of the reset pulse and the set pulse is 15 ns or less and a pulse duration of both of the reset pulse and the set pulse is 40 ns or less,

wherein the non-monolithic carbon material comprises carbon nanotubes and the steering element comprises a diode.