Negative voltage wordline methods and systems
A methodology and structure for driving a selected wordline to a negative voltage without the need for a negative wordline voltage generator. The methodology includes the step of boosting a non-selected wordline to a first positive voltage. The methodology proceeds with holding a selected wordline, which is adjacent to and capacitively coupled with the non-selected wordline, at zero voltage. The methodology continues with floating the selected wordline. The methodology proceeds with driving the non-selected wordline to a lower voltage to shift the selected wordline to less than zero volts due to capacitance effects. The methodology continues with the step of accelerating charge loss in a defective memory cell connected to the selected wordline while at a negative voltage during a soft erase operation.
1. A method for non-volatile memory, comprising:
boosting a non-selected wordline to a first positive voltage;
holding a selected wordline at zero volts, the selected wordline being adjacent to the non-selected wordline and being capacitively coupled to the non-selected wordline;
floating the selected wordline; and
during a soft erase operation, shifting the selected wordline to a negative voltage due to capacitance effects by driving the non-selected wordline to a voltage lower than the first positive voltage, thereby
accelerating charge loss in a defective memory cell connected to the selected wordline.
2. The method of claim 1 , further comprising applying a program pulse to the defective memory cell at an increased level.
3. The method of claim 1 ,
wherein the boosting comprises boosting sequential odd non-selected wordlines to the first positive voltage,
wherein the floating comprises floating an even wordline that is intermediate between the sequential odd non-selected wordlines as the selected wordline, and
wherein the shifting comprises driving both the sequential odd non-selected wordlines to the voltage lower than the first positive voltage, thereby shifting the selected wordline to the negative voltage.
4. A method for non-volatile memory, comprising:
issuing a program command to control a bitline associated with a memory cell connected to an even selected wordline;
driving odd non-selected wordlines, which are sequential and adjacent to the selected wordline and are capacitively coupled to the even selected wordline, to a pass voltage, thereby stepping the even selected wordline to a program voltage;
returning the odd non-selected wordlines and the even selected wordline to zero volts;
boosting the odd non-selected wordlines to a first positive voltage;
holding the even selected wordline at zero volts;
floating the even selected wordline; and
during a soft erase operation, shifting the even selected wordline to less than zero volts due to capacitance effects by driving at least one of the odd non-selected wordlines to a voltage lower than the first positive voltage, thereby accelerating charge loss in a defective memory cell connected to the even selected wordline.
5. The method of claim 4 , further comprising verifying an erase after accelerating the charge loss in the defective memory cell.
6. The method of claim 1 ,
wherein the boosting comprises boosting sequential odd non-selected wordlines to the first positive voltage,
wherein the floating comprises floating an even wordline that is intermediate between the sequential odd non-selected wordlines as the selected wordline, and
wherein the shifting comprises:
driving a first one of the sequential odd non-selected wordlines to zero volts, thereby shifting the selected wordline to the negative voltage, and
driving a second one of the sequential odd non-selected wordlines to a voltage less than the first positive voltage and greater than zero.
7. The method of claim 6 , wherein the boosting the sequential odd non-selected wordlines comprises boosting the first one of the sequential non-selected off wordlines to at least seven volts.
8. The method of claim 7 , further comprising shifting the even-selected wordline down to more than five volts while not connected to driver circuitry.
9. A non-volatile memory, comprising:
a plurality of even wordlines;
a plurality of odd wordlines alternating with ones of the plurality of even wordlines;
a plurality of memory cells in a vertical stack connected to the plurality of even wordlines and the plurality of odd wordlines;
a bit line connected at one end of the vertical stack of memory cells; and
controller circuitry configured to issue signals thereby:
boosting a non-selected wordline to a first positive voltage;
holding a selected wordline at zero volts, the selected wordline being adjacent to the non-selected wordline and being capacitively coupled to the non-selected wordline;
floating the selected wordline; and
during a soft erase operation, shifting the selected wordline to a negative voltage due to capacitance effects by driving the non-selected wordline to a voltage lower than the first positive voltage, thereby
accelerating charge loss in a defective memory cell connected to the selected wordline.
10. The memory of claim 9 , wherein the controller is further configured to issue control signals thereby applying apply a program pulse to the defective memory cell at an increased level.
11. The memory of claim 9 , wherein the controller is further configured to issue control signals such that:
the boosting comprises boosting sequential odd non-selected wordlines to the first positive voltage,
the floating comprises floating an even wordline that is intermediate between the sequential odd non-selected wordlines as the selected wordline, and
the shifting comprises driving both the sequential odd non-selected wordlines to the voltage lower than the first positive voltage, thereby shifting selected wordline to the negative voltage.
12. A non-volatile memory, comprising
a plurality of even wordlines;
a plurality of odd wordlines alternating with ones of the plurality of even wordlines;
a plurality of memory cells in a vertical stack connected to the plurality of even wordlines and the plurality of odd wordlines;
a bit line connected at one end of the vertical stack of memory cells; and
controller circuitry configured to issue signals thereby:
issuing a program command to control a bitline associated with s memory cell connected to an even selected wordline,
driving odd non-selected wordlines, which are sequential and adjacent to the selected wordline and are capacitively coupled to the even selected wordline, to a pass voltage, thereby stepping
the even selected wordline to a program voltage,
returning the odd non-selected wordlines and the even selected wordline to zero volts,
boosting the odd non-selected wordlines to a first positive voltage,
holding the even selected wordline at zero volts,
floating the even selected wordline, and
during a soft erase operation, shifting the even selected wordline to less than zero volts due to capacitance effects by driving at least one of the odd non-selected wordlines to a voltage lower than the first positive voltage, thereby accelerating charge loss in a defective memory cell connected to the even selected wordline.
13. The memory of claim 12 , wherein the controller is further configured to verify an erase after accelerating the charge loss in the defective memory cell.
14. The memory of claim 9 , wherein:
the boosting comprises boosting sequential odd non-selected wordlines to the first positive voltage,
the floating comprises floating an even wordline that is intermediate between the sequential odd non-selected wordlines as the selected wordline, and
the shifting comprises:
driving a first one of the sequential odd non-selected wordlines to zero volts thereby shifting the selected wordline to the negative voltage, and
driving a second one of the sequential odd non-selected wordlines to a voltage less that the first positive voltage and greater than zero.
15. The memory of claim 14 , wherein the boosting comprises boosting the first one of the sequential non-selected wordlines to at least seven volts.
16. The memory of claim 15 , wherein the selected wordline is shifted down to more than five volts while not connected to driver circuitry.