Methods for programming a floating body nonvolatile memory
View Patent ↗A technique to speed up the programming of a non-volatile memory device that has a floating body actively removes holes from the floating body that have accumulated after performing hot carrier injection (HCI). The steps of HCI and active hole removal can be alternated until the programming is complete. The active hole removal is faster than passively allowing holes to be removed, which can take milliseconds. The active hole removal can be achieved by reducing the drain voltage to a negative voltage and reducing the gate voltage as well. This results in directly withdrawing the holes from the floating body to the drain. Alternatively, reducing the drain voltage while maintaining current flow stops impact ionization while sub channel current collects the holes. Further alternatively, applying a negative gate voltage causes electrons generated by band to band tunneling and impact ionization near the drain to recombine with holes.
1. A method of programming a non-volatile memory (NVM) cell having a floating body, comprising
during a first programming phase:
applying a voltage at a first level to a drain of the NVM cell;
applying a voltage at a second level to a source of the NVM cell, wherein the second level is lower than the first level; and
applying a voltage at a third level to a gate of the NVM cell, wherein the third level is greater than the second level; and
during a second programming phase after the first programming phase, performing one of the following steps to remove holes in the floating body:
reducing the voltage on the drain to a fourth level, wherein current flows between the source and drain and wherein the fourth level is sufficiently low so as to result in minimal impact ionization;
reducing the voltage on the gate to a fifth level, wherein the fifth level is lower than the second level; or
reducing the voltage on the drain to a sixth level and reducing the voltage on the gate, wherein the sixth level is below the second level.
2. The method of claim 1 , wherein the second level is ground.
3. The method of claim 1 , wherein the sixth level of voltage is negative.
4. The method of claim 1 , wherein the first programming phase is of longer duration than the second programming phase.
5. The method of claim 1 , wherein the fourth level is greater than the second level.
6. The method of claim 1 , wherein the floating body comprises P-type silicon, the drain comprises N-type silicon, and the source comprises N-type silicon.
7. The method of claim 1 , wherein the NVM cell comprises a charge storage layer, wherein the charge storage layer comprises at least one of polysilicon, nanoclusters or silicon nitride.
8. A method of programming a non-volatile memory (NVM) cell in a floating body, comprising:
performing hot carrier injection on the NVM cell under a first set of electrical bias conditions; and
actively removing holes accumulated in the floating body during the performing hot carrier injection by altering the first set of electrical bias conditions to a second set of electrical bias conditions, wherein the altering the first set of electrical bias conditions comprises changing a voltage on a drain of the NVM cell and a voltage on a gate of the NVM cell.
9. The method of claim 8 , wherein the performing hot carrier injection occurs for a first time duration and the actively removing holes occurs for a second time duration, wherein the second time duration is less than the first time duration.
10. The method of claim 8 , wherein the altering the first set of electrical bias conditions comprises reducing the voltage on the gate and maintaining the voltage on the drain and a voltage on a source of the NVM cell.
11. The method of claim 8 , wherein the altering the first set of electrical bias conditions comprises changing the voltage on the gate to a level that is less than a level of a voltage on a source of the NVM cell.
12. The method of claim 8 , further comprising repeating the performing of hot carrier injection after the performing the actively removing holes.
13. The method of claim 8 , further comprising repeating the actively removing holes after the repeating the performing of hot carrier injection.
14. The method of claim 8 , wherein the altering the first set of electrical bias conditions comprises reducing the voltage on the drain and the voltage on the gate.
15. The method of claim 8 , wherein the altering the first set of electrical bias conditions comprises changing the voltage on the drain to be less than a voltage on a source of the NVM cell.
16. The method of claim 8 , wherein the altering the first set of electrical bias conditions comprises reducing the voltage on the drain so as to result in minimal impact ionization.
17. The method of claim 8 , wherein the floating body is P-type conductivity and wherein the NVM cell comprises a source and a drain that are N-type conductivity.
18. A method of programming a non-volatile memory (NVM) cell in a floating body, comprising:
performing hot carrier injection on the NVM cell under a first set of electrical bias conditions; and
actively removing holes accumulated in the floating body during the performing hot carrier injection by altering the first set of electrical bias conditions to a second set of electrical bias conditions, wherein the altering the first set of electrical bias conditions comprises lowering a voltage on a gate of NVM cell and applying a negative voltage to a drain of the NVM cell.