Word line kick during sensing: trimming and adjacent word lines

• US 9,318,210 B1
• Filed: 02/02/2015
• Issued: 04/19/2016
• Est. Priority Date: 02/02/2015
• Status: Active Grant

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: Sandisk Technologies Incorporated (Western Digital Corporation)
• Inventors: Louie, Kenneth, Nguyen, Khanh, Mui, Man, Hart, James V.
• Primary Examiner(s): Nguyen, Hien
• Application Number:
  US14/611,997
• Time in Patent Office: 442 Days
• US Class Current: 1/1
• CPC Class Codes: G11C 11/5642 Sensing or reading circuits; Data output circuits
• CPC Class Codes: G11C 16/0483 comprising cells having several storage transistors connected in series
• CPC Class Codes: G11C 16/08 Address circuits; Decoders; Word-line control circuits
• CPC Class Codes: G11C 16/26 Sensing or reading circuits; Data output circuits
• CPC Class Codes: G11C 16/3459 Circuits or methods to verify correct programming of nonvolatile memory cells
• CPC Class Codes: G11C 2211/5621 Multilevel programming verification

Abstract

When applying a sensing voltage at one end of a word line of a non-volatile memory circuit, an initial kick, where the voltage is initially raised somewhat above its final desired voltage, is used. Using on-chip circuitry for the determination of the RC time constant of the word lines allows for this kick to be trimmed to the specifics of the circuit. To further improve settling times for read operations is NAND type architectures, when raising the voltage to the desired read level on a selected word line, a reverse kick, where the non-selected word line'"'"'s voltage is dropped briefly, can be applied to neighboring non-selected word lines.

Claims

1. A method of operating a non-volatile memory array formed according to a NAND-type of architecture, comprising:

performing a sensing operation for memory cells along a selected word line with the word lines of the array biased to a first set of bias conditions, the first set of bias conditions including;

driving the selected word line at a first sensing voltage; and

driving non-selected word lines of the array at a voltage level to allow the memory cells therealong to conduct; and

prior to performing the sensing operation, establishing the first set bias conditions, including;

setting the non-selected word lines to the voltage to allow the memory cells therealong to conduct; and

subsequently raising the selected word line from an initial level to the first sensing voltage, wherein, while selected word line is being raised, the voltage level for a non-selected word line adjacent to the selected word line is lowered from, and then returned to, the voltage to allow the memory cells therealong to conduct.

2. The method of claim 1, wherein raising the selected word line from an initial level to the first sensing voltage including raising the selected word line from the initial level to a level above the first sensing voltage and subsequently lowering the selected word line to the first sensing voltage.

3. The method of claim 1, wherein the memory cells of the memory array store data in a multi-state format.

4. The method of claim 3, wherein the first sensing voltage and the initial level correspond to sensing voltages of different data states.

5. The method of claim 3, wherein the first sensing voltage corresponds to a data state and the initial level corresponds an idle condition.

6. The method of claim 1, wherein the sensing operation is a data read operation.

7. The method of claim 1, wherein the sensing operation is a program verify operation.

8. The method of claim 1, wherein the memory array is formed on a monolithic three-dimensional semiconductor memory device where the memory cells are arranged in multiple physical levels above a silicon substrate and comprise a charge storage medium, having NAND strings running in a vertical direction relative to the substrate and the word lines running in a horizontal direction relative to the substrate.

9. The method of claim 1, wherein a time and amplitude by which the voltage level for the non-selected word line adjacent to the selected word line is lowered from, and then returned to, the voltage to allow the memory cells therealong to conduct are settable parameters.

10. An integrated circuit comprising:

a plurality of control lines;

line driver circuitry for providing line voltage levels;

line decoding circuitry connected to the control lines and to the line driver circuitry by which the line voltage levels are selectively applied to the control lines at a first end thereof;

a time constant determination circuit connected to the line decoding circuitry for determining time constants for charging by the driver circuitry of the far end, relative to the first end, of the control lines; and

on-chip control circuitry connected to the line driver circuitry, the line decoding circuitry, and the time constant determination circuit, whereby when applying a first voltage level to a selected control line, the line driver circuitry initially ramps up the selected control line to a level higher than that the first voltage for a first interval, the duration of the first interval based upon the time constant of the selected control line as determined by the time constant determination circuit.

11. The integrated circuit of claim 10, wherein the integrated circuit is a non-volatile memory circuit having an array of non-volatile memory cells formed as a plurality of multi-cell erase blocks, wherein the control lines are word lines along which the memory cells are formed, and where the first voltage is a sensing voltage.

12. The non-volatile memory circuit of claim 11, wherein an amount by which the level higher than that the first sensing voltage exceeds the first sensing voltage is determined by the on-chip control circuitry.

13. The non-volatile memory circuit of claim 12, wherein each of the word lines of a corresponding block belongs to one of a plurality of word line zones, each of the word line zones containing one or more adjacent word lines of the corresponding block, wherein the amount by which the level higher than that the first sensing voltage exceeds the first sensing voltage is the same for the word lines of a common word line zone and differs between word lines of different word line zones.

14. The non-volatile memory circuit of claim 11, wherein the first sensing voltage is applied as part of a read operation.

15. The non-volatile memory circuit of claim 11, wherein the first sensing voltage is applied as part of a program verify operation.

16. The non-volatile memory circuit of claim 11, wherein each of the word lines of a corresponding block belongs to one of a plurality of word line zones, each of the word line zones containing one or more adjacent word lines of the corresponding block, wherein the word lines of a common word line zone use a common duration for the first interval and word lines of different word line zones use different durations for the first interval.

17. The non-volatile memory circuit of claim 11, wherein the array is formed according to a NAND type architecture.

18. The non-volatile memory circuit of claim 11, wherein the memory circuit is a monolithic three-dimensional semiconductor memory device where the memory cells are arranged in multiple physical levels above a silicon substrate and comprise a charge storage medium.

19. The non-volatile memory circuit of claim 18, wherein the plurality of blocks are formed of a plurality of NAND strings, each having multiple memory cells connected in series between one or more source select gates and one or more drain select gates, the memory cells being connected along word lines and the source and drain select gates being respectively connected along source and drain select lines, the NAND strings being formed above a P well and each connected, though the corresponding drain select gates, to an associated bit line, and

wherein the NAND strings run in a vertical direction relative to the substrate, and the word lines, and source and drain select lines, and bit lines run in a horizontal direction relative to the substrate.

20. The non-volatile memory circuit of claim 11, wherein a value of the duration is determined when the memory circuit is fresh.

21. The non-volatile memory circuit of claim 20, wherein a value of the duration is determined when the memory circuit has aged.