# US 10,121,521 B2 · Read threshold voltage selection

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- Number: US 10,121,521 B2
- Document ID: US10121521B2
- Status: Granted
- Kind: B2
- Application number: 15/837,036
- Filed: 2017-12-11
- Published: 2018-04-12
- Granted: 2018-11-06
- Earliest claimed: 2016-02-16
- Assignees: Micron Technology, Inc.
- Applicants: Micron Technology, Inc.
- Inventors: Chandra C. Varanasi
- Web page: https://patentgrep.com/patent/US10121521B2

## CPC

- G11C 7/00: Arrangements for writing information into, or reading information out from, a digital store (G11C5/00 takes precedence; auxiliary circuits for stores using semiconductor devices G11C11/4063, G11C11/413)
- G06F 11/1012: {using codes or arrangements adapted for a specific type of error (G06F11/1048 takes precedence)}
- G06F 11/1068: {in sector programmable memories, e.g. flash disk (G06F11/1072 takes precedence)}
- G11C 7/14: Dummy cell management; Sense reference voltage generators
- G11C 29/52: Protection of memory contents; Detection of errors in memory contents
- G11C 2207/2254: Calibration
- G11C: STATIC STORES (semiconductor memory devices H10B)
- G06F: ELECTRIC DIGITAL DATA PROCESSING (computer systems based on specific computational models G06N)

## Abstract

Apparatuses and methods for read threshold voltage selection are provided. One example method can include setting a first soft read threshold voltage and a second soft read threshold voltage based on a difference between a first number of memory cells that are read as being programmed to a first state when read using a first threshold voltage and a second number of memory that are read as being programmed to the first state when read using another threshold voltage.

## Claims

### Claim 1

A method for read threshold voltage selection, comprising:
setting a first soft read threshold voltage based on mutual information of two adjacent threshold voltage distributions, wherein:
the two adjacent threshold voltage distributions include a first threshold voltage distribution including memory cells programmed to a first state and a second threshold voltage distribution including memory cells programmed to a second state; and
the method includes setting the first soft read threshold voltage such that a read operation using the first soft read threshold voltage results in an amount of mutual information that is at least 99.5% of an achievable mutual information value for the two adjacent threshold voltage distributions.

### Claim 2 (depends on 1)

The method of claim 1, wherein the method includes setting the first soft read threshold voltage such that a read operation using the first soft read threshold voltage results in an amount of mutual information that is at least a particular percentage of an achievable peak mutual information value for the two adjacent threshold voltage distributions.

### Claim 3 (depends on 1)

The method of claim 1, the method includes setting the first soft read threshold voltage as an offset from a hard read threshold voltage for the two adjacent threshold voltage distributions.

### Claim 4 (depends on 1)

The method of claim 1, the method includes setting a second soft read threshold voltage as an offset from a hard read threshold voltage for the two adjacent threshold voltage distributions, wherein the offset from the hard read threshold voltage is equal for the first soft read threshold voltage and the second soft read threshold voltage.

### Claim 5

A method for read threshold voltage selection, comprising:
setting a first soft read threshold voltage based on mutual information of two adjacent threshold voltage distributions, wherein:
the two adjacent threshold voltage distributions include a first threshold voltage distribution including memory cells programmed to a first state and a second threshold voltage distribution including memory cells programmed to a second state; and
the method includes setting the first soft read threshold voltage such that a read operation using the first soft read threshold voltage results in an amount of mutual information that is at least 99% of an achievable peak mutual information value for the two adjacent threshold voltage distributions.

### Claim 6 (depends on 5)

The method of claim 5, wherein the method includes setting the first soft read threshold voltage such that a read operation using the first soft read threshold voltage results in an amount of mutual information that is at least a particular percentage of an achievable peak mutual information value for the two adjacent threshold voltage distributions.

### Claim 7 (depends on 5)

The method of claim 5, wherein the method includes setting the first soft read threshold voltage as an offset from a hard read threshold voltage for the two adjacent threshold voltage distributions.

### Claim 8 (depends on 5)

The method of claim 5, wherein the method includes setting a second soft read threshold voltage as an offset from a hard read threshold voltage for the two adjacent threshold voltage distributions, wherein the offset from the hard read threshold voltage is equal for the first soft read threshold voltage and the second soft read threshold voltage.