Sensing multiple reference levels in non-volatile storage elements

Patent metadata

Field	Value
Publication number	US-9576673-B2
Application number	US-201414508615-A
Country	US
Kind code	B2
Filing date	Oct 7, 2014
Priority date	Oct 7, 2014
Publication date	Feb 21, 2017
Grant date	Feb 21, 2017

Abstract

Disclosed herein are techniques for sensing multiple reference levels in non-volatile storage elements without changing the voltage on the selected word line. One aspect includes determining a first condition of a selected non-volatile storage element with respect to a first reference level based on whether a sensing transistor conducts in response to a sense voltage on a sense node. Then, a voltage on the source terminal of the sensing transistor is modified after determining the first condition with respect to the first reference level. A second condition of the selected non-volatile storage element is then determined with respect to a second reference level based on whether the sensing transistor conducts in response to the sense voltage on the sense node. This allows two different reference levels to be efficiently sensed. Dynamic power is saved due low capacitance of the sensing transistor relative to the sense node.

First claim

We claim:

1. A non-volatile storage device, comprising:
a selected non-volatile storage element;
a charge storage device coupled to the selected non-volatile storage element and a sensing device having a control terminal coupled to the charge storage device,
a pre-charge circuit and bit line connection circuit configured to develop a sense voltage on the charge storage device in response to a signal from a state machine, the sense voltage is developed based on connecting the selected non-volatile storage element to the charge storage device for a sense time;
a processor configured to determine whether the sensing device activates in response to the sense voltage that was developed on the charge storage device based on connecting the selected non-volatile storage element to the charge storage device for the sense time;
the processor further configured to determine a first condition of the selected non-volatile storage element with respect to a first reference level based on whether the sensing device activates in response to the sense voltage developed on the charge storage device,
a voltage supply configured to modify a voltage on a second terminal of the sensing device other than the control terminal after determining the first condition in response to a signal from the state machine;
the processor configured to determine whether the sensing device activates after modifying the voltage on the second terminal in response to the sense voltage that was developed on the charge storage device based on connecting the selected non-volatile storage element to the charge storage device for the sense time,
the processor configured to determine a second condition of the selected non-volatile storage element with respect to a second reference level based on whether the sensing device activates in response to the sense voltage developed on the charge storage device after modifying the voltage on the second terminal of the sensing device.

2. The non-volatile storage device of claim 1 , wherein the bit line connection circuit is configured to connect the charge storage device to a bit line for the sense time to allow a current from the bit line to discharge the charge storage device for the sense time.

3. The non-volatile storage device of claim 1 , wherein the voltage supply increases a voltage on the second terminal in response to a signal from the state machine in order to modify the voltage on the second terminal.

4. The non-volatile storage device of claim 1 , wherein the pre-charge circuit is configured to modify a voltage on the charge storage device after the first condition of the selected non-volatile storage element is determined with respect to the first reference level, the processor is configured to determine whether the sensing device activates in response to the modified voltage on the charge storage device, the processor is configured to determine a third condition of the selected non-volatile storage element with respect to a third reference level based on whether the sensing device activates in response to the modified voltage on the charge storage device, the voltage supply is configured to modify the voltage on the second terminal of the sensing device after it is determined whether the sensing device activates in response to the modified voltage on the charge storage device, the third reference level being between the first reference level and the second reference level.

5. The non-volatile storage device of claim 1 , further comprising a data latch that stores a first result in response to whether the sensing device activates in response to the sense voltage on the charge storage device prior to modifying the voltage on the second terminal of the sensing device, the first result indicates whether the selected non-volatile storage element has a threshold voltage above or below a first target threshold voltage, the data latch stores a second result in response to whether the sensing device activates in response to the sense voltage on the charge storage device after modifying the voltage on the second terminal of the sensing device, the second result indicates whether the selected non-volatile storage element has a threshold voltage above or below a second target threshold voltage.

6. The non-volatile storage device of claim 1 , wherein when the pre-charge circuit and bit line connection circuit develop the sense voltage on the charge storage device the voltage supply applies a voltage to a word line associated with the selected non-volatile storage element in response to a signal from the state machine.

7. The non-volatile storage device of claim 1 , wherein the selected non-volatile storage element is part of a 3D memory array.

8. The non-volatile storage device of claim 1 , wherein the selected non-volatile storage element comprises a charge trapping region that store data.

9. The non-volatile storage device of claim 1 , wherein the sensing device comprises a transistor having a source terminal, wherein the second terminal is the source terminal.

10. A method comprising:
developing a sense voltage on a sense node connected to a sensing device, including connecting the sense node to a selected non-volatile storage element to discharge the sense node for a sense time;
determining a first condition of the selected non-volatile storage element with respect to a first reference level based on whether the sensing device activates in response to the sense voltage that was developed on the sense node based on discharging the sense node for the sense time;
modifying a voltage on a node of the sensing device after determining the first condition with respect to the first reference level; and
determining a second condition of the selected non-volatile storage element with respect to a second reference level based on whether the sensing device activates after modifying the voltage on the node of the sensing device in response to the sense voltage that was developed on the sense node based on discharging the sense node for the sense time.

11. The method of claim 10 , wherein the modifying a voltage on the node of the sensing device comprises:
increasing a voltage on the sense node of the sensing device.

12. The method of claim 10 , wherein the developing a sense voltage on a sense node comprises:
charging the sense node;
connecting the sense node to a bit line that is associated with the selected non-volatile storage element; and
allowing a current from the bit line to discharge the sense node for the sense time.

13. The method of claim 10 , further comprising:
modifying a voltage on the sense node after determining the first condition of the selected non-volatile storage element with respect to the first reference level;
determining whether the sensing device activates in response to the modified voltage on the sense node prior to modifying the voltage on the node of the sensing device; and
determining a third condition of the selected non-volatile storage element with respect to a third reference level based on whether the sensing device activates in response to the modified voltage on the sense node prior to modifying the voltage on the node of the sensing device, wherein the modifying a voltage on a node of the sensing device is performed after determining whether the sensing device activates in response to the modified voltage on the sense node, the third reference level being between the first reference level and the second reference level.

14. The method of claim 10 , wherein the first reference level is whether the selected non-volatile storage element has a threshold voltage above or below a first threshold voltage, whe

Assignees

• Sandisk 3D Llc
• Sandisk Technologies Llc

Inventors

• Jiang Xiaowei
• Siau Chang
• Chan Siu Lung

Classifications

• G11C16/28 Primary

  using differential sensing or reference cells, e.g. dummy cells · CPC title

• G11C2211/5621

  Multilevel programming verification · CPC title

• G11C16/3459

  Circuits or methods to verify correct programming of nonvolatile memory cells · CPC title

• G11C16/26

  Sensing or reading circuits; Data output circuits · CPC title

• G11C16/0466

  comprising cells with charge storage in an insulating layer, e.g. metal-nitride-oxide-silicon [MNOS], silicon-oxide-nitride-oxide-silicon [SONOS] (G11C16/0483, G11C16/0491 take precedence) · CPC title