Method for reading data stored in a flash memory according to a voltage characteristic and memory controller thereof

• US 10,679,709 B2
• Filed: 12/20/2018
• Issued: 06/09/2020
• Est. Priority Date: 02/22/2012
• Status: Active Grant

• Current Assignee: Silicon Motion Incorporated California (Silicon Motion)
• Original Assignee: Silicon Motion Incorporated Taiwan (Silicon Motion)
• Inventors: Yang, Tsung-Chieh
• Primary Examiner(s): Yoha, Connie C
• Application Number:
  US16/228,007
• Publication Number:
  US 20190122738A1
• Time in Patent Office: 537 Days
• Field of Search: 3651859, 3651858, 36518529, 3651853, 36518509, 36518508
• CPC Class Codes: G11C 16/04 using variable threshold transistors, e.g. FAMOS
• CPC Class Codes: G11C 16/0408 comprising cells containing floating gate transistors G11C16/0483, G11C16/0491 take precedence
• CPC Class Codes: G11C 16/06 Auxiliary circuits, e.g. for writing into memory
• CPC Class Codes: G11C 16/10 Programming or data input circuits
• CPC Class Codes: G11C 16/16 for erasing blocks, e.g. arrays, words, groups
• CPC Class Codes: G11C 16/26 Sensing or reading circuits; Data output circuits
• CPC Class Codes: G11C 16/3418 Disturbance prevention or evaluation; Refreshing of disturbed memory data
• CPC Class Codes: G11C 16/3431 Circuits or methods to detect disturbed nonvolatile memory cells, e.g. which still read as programmed but with threshold less than the program verify threshold or read as erased but with threshold greater than the erase verify threshold, and to reverse the disturbance via a refreshing programming or erasing step

Abstract

A method for reading data stored in a flash memory. The flash memory comprises a plurality of memory cells and each memory cell has a particular threshold voltage. The method includes: obtaining a first threshold voltage distribution representing threshold voltages of a first group of the memory cells; obtaining a second threshold voltage distribution representing threshold voltages of a second group of the memory cells, wherein the second threshold voltage distribution is different from the first threshold voltage distribution, and the first group of the memory cells comprises at least a part of the second group of the memory cells; and controlling the flash memory to perform at least one read operation upon the first group of the memory cells according to the second threshold voltage distribution.

Claims

1. A method for reading data stored in a flash memory, wherein the flash memory comprises a first set of memory cells and a second set of memory cells, and each memory cell corresponds to a particular threshold voltage, and the method comprises:

obtaining a first counter number by reading the first set of the memory cells;

obtaining a first voltage characteristic of the first set of the memory cells according to the first counter number;

obtaining a second counter number by reading the second set of the memory cells;

obtaining a second voltage characteristic of the second set of the memory cells according to the first counter number and the second counter number; and

reading the first set of the flash memory by using the second voltage characteristic;

wherein the first set of memory cells comprises at least a part of the second set of the memory cells.

2. The method as claimed in claim 1, wherein the first voltage characteristic is different from the second voltage characteristic.

3. The method as claimed in claim 1, wherein the step of reading the first set of the flash memory by using the second threshold voltage information further comprises:

determining a shifting direction according to the first counter number and the second counter number; and

adjusting a control gate voltage for performing the read operation according to the shifting direction.

4. A memory controller for reading data stored in a flash memory, wherein the flash memory comprises a first set of memory cells and a second set of memory cells, and each memory cell corresponds to a particular threshold voltage, and the memory controller comprises:

a control logic, obtaining a first voltage characteristic of the first set of the memory cells according to the first counter number, obtaining a second voltage characteristic of the second set of the memory cells according to the first counter number and the second counter number, and reading the first set of the flash memory by using the second voltage characteristic;

wherein the first set of memory cells comprises at least a part of the second set of the memory cells.

5. The memory controller as claimed in claim 4, wherein the first voltage characteristic is different from the second voltage characteristic.

6. The memory controller as claimed in claim 4, wherein the step of reading the first set of the flash memory by using the second threshold voltage information further comprises:

determining a shifting direction according to the first counter number and the second counter number; and

adjusting a control gate voltage for performing the read operation according to the shifting direction.

7. A method for reading data stored in a flash memory, wherein the flash memory comprises a plurality of memory cells and each memory cell has a particular threshold voltage, the method comprising:

reading a part of the memory cells of the flash memory by a first control gate voltage;

detecting error bits of the memory cells;

correcting the error bits of the memory cell by reading the flash memory continuously;

obtaining a counter number by reading the first set of the memory cells;

obtaining a first voltage characteristic of the first set of the memory cells according to the counter number;

averaging the first voltage characteristic for obtaining a second voltage characteristic; and

reading a part of the flash memory again by using the second voltage characteristic;

wherein a first set of memory cells comprises at least a part of a second set of the memory cells.

8. A system for reading data stored in a flash memory, wherein the flash memory comprises a plurality of memory cells and each memory cell has a particular threshold voltage, the system comprising:

a control logic for reading a part of the memory cells of the flash memory by using a first control gate voltage;

a detector for detecting error bits of the memory cells;

a corrector for correcting the error bits of the memory cell by reading the flash memory continuously;

wherein the control logic further obtains a counter number by reading the first set of the memory cells, obtains a first voltage characteristic of the first set of the memory cells according to the counter number, averages the first voltage characteristic for obtaining a second voltage characteristic, and reads a part of the flash memory again by using the second voltage characteristic; and

wherein a first set of memory cells comprises at least a part of a second set of the memory cells.