DATA STATE-BASED TEMPERATURE COMPENSATION DURING SENSING IN NON-VOLATILE MEMORY

• US 20100074014A1
• Filed: 09/19/2008
• Published: 03/25/2010
• Est. Priority Date: 09/19/2008
• Status: Active Grant

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: SanDisk Corporation (Western Digital Corporation)
• Inventors: Higashitani, Masaaki, Dunga, Mohan V.
• Granted Patent: US 7,755,946 B2
• Time in Patent Office: Days
• US Class Current: 365/185.170
• CPC Class Codes: G11C 11/5642 Sensing or reading circuits; Data output circuits
• CPC Class Codes: G11C 16/26 Sensing or reading circuits; Data output circuits
• CPC Class Codes: G11C 7/04 with means for avoiding disturbances due to temperature effects

Abstract

Temperature effects in a non-volatile storage device are addressed by providing a data state-dependent, and optionally temperature dependent, sense current during verify and read operations. A different sense current is provided for each data state, so that a common temperature coefficient is realized for storage elements with different data states. The temperature coefficient for higher states can be reduced to that of lower states. During sensing, a sense time can be adjusted to achieve a desired sense current when a selected storage element is in a conductive state. A fixed voltage trip point may be maintained. During the sense time, a pre-charged capacitor discharges into a selected storage element such as via a bit line and NAND string, when the selected storage element is in a conductive state. The discharge level is translated to a current which is compared to a state-dependent, and optionally temperature dependent, reference current.

Claims

1. A method for operating non-volatile storage, comprising:

applying a plurality of voltages, one at a time, to a control gate of a selected non-volatile storage element; and

while applying each voltage, coupling, to the selected non-volatile storage element, at least one current source;

sensing a current which flows through the selected non-volatile storage element; and

comparing the sensed current to a reference current which is different for at least two of the voltages.

2. The method of claim 1, wherein:

the reference current is set according to different temperature coefficient versus current relationships of different data states.

3. The method of claim 1, wherein:

the reference current is set to provide common temperature coefficient for the different data states.

4. The method of claim 1, wherein:

the reference current is higher for higher voltages.

5. The method of claim 1, wherein:

the selected non-volatile storage element is series-connected to other non-volatile storage elements in a string, and the at least one current source is coupled to a drain end of the string.

6. The method of claim 5, wherein:

the string comprises a NAND string, and the at least one current source is coupled to a bit line of the NAND string.

7. The method of claim 1, wherein:

the reference current is different for each voltage.

8. The method of claim 1, wherein:

the reference current is the same for at least two voltages.

9. The method of claim 1, wherein:

the at least one current source comprises a charge-storing component, and the sensing comprises determining an extent to which the charge-storing component discharges.

10. The method of claim 1, wherein:

the plurality of voltages are applied in a read or verify operation.

11. The method of claim 1, wherein:

the reference current for at least one of the voltages is temperature dependent.

12. The method of claim 1, wherein:

at least one of the voltages is temperature compensated.

13. A method for operating non-volatile storage, comprising:

applying a voltage to a control gate of at least one selected non-volatile storage element in a NAND string via a selected word line, the voltage separates lower and higher states;

if the at least one selected non-volatile storage element is made conductive by the applying the voltage, inducing a current through the selected non-volatile storage element; and

comparing the current to a reference current which is based on a reference temperature coefficient of the higher state.

14. The method of claim 13, wherein:

the voltage is applied in a verify operation.

15. The method of claim 13, wherein:

the level of the reference current is temperature-dependent.

16. A method for operating non-volatile storage, comprising:

applying a plurality of voltages, one at a time, to a control gate of a selected non-volatile storage element;

while applying each voltage, coupling, to the selected non-volatile storage element, a pre-charged capacitor, the capacitor discharges into the selected non-volatile storage element when the selected non-volatile storage element is in a conductive state; and

after a discharge time which differs for each of the voltages, determining whether the selected non-volatile storage element is in the conductive state based on whether the capacitor has discharged below a trip point.

17. The method of claim 16, wherein:

the trip point is the same for each of the voltages.

18. The method of claim 16, wherein:

when the selected non-volatile storage element is in the conductive state, the capacitor discharges into the selected non-volatile storage element resulting in a current through the selected non-volatile storage element, a level of the current differs for each of the voltages.

19. The method of claim 16, wherein:

the determining whether the capacitor has discharged below the trip point comprises comparing the current to a reference current which differs for each voltage.

20. The method of claim 16, wherein:

the discharge time for at least one of the voltages is temperature dependent.

21. A non-volatile storage system, comprising:

a set of non-volatile storage elements including a selected non-volatile storage element having a control gate;

at least one current source; and

at least one control circuit, the at least one control circuit applies voltages, one at a time, to the control gate of the selected non-volatile storage element of the set, while applying each voltage, couples, to the selected non-volatile storage element, the at least one current source, senses a current which flows through the selected non-volatile storage element, and compares the sensed current to a reference current which is different for at least two of the voltages.

22. The non-volatile storage system of claim 21, wherein:

the reference current is set according to different temperature coefficient versus current relationships of different data states.

23. The non-volatile storage system of claim 22, wherein:

the reference current is set to provide a common temperature coefficient for the different data states.