High temperature methods for enhancing retention characteristics of memory ...

Illllllllllllllllllllllllllllllllllllllllllllllllll

US007839695B2

(12) United States Patent

Wu et al.

(io) Patent No.: (45) Date of Patent:

US 7,839,695 B2 Nov. 23, 2010

(54) HIGH TEMPERATURE METHODS FOR ENHANCING RETENTION CHARACTERISTICS OF MEMORY DEVICES

(75) Inventors: Chao-I Wu, Zhubei (TW); Tzu Hsuan Hsu, Jhongpu Township (TW)

(73) Assignee: Macronix International Co., Ltd.,

Hsinchu (TW)

( * ) Notice: Subject to any disclaimer, the term of this patent is extended or adjusted under 35 U.S.C. 154(b) by 865 days.

(21) Appl.No.: 11/741,053

(22) Filed: Apr. 27, 2007

(65) Prior Publication Data

US 2008/0268659 Al Oct. 30, 2008

(51) Int. CI.

G11C11/34 (2006.01)

(52) U.S. CI 365/185.24; 365/185.02;

365/185.28; 365/201

(58) Field of Classification Search 365/185 .02,

365/185.09, 185.22, 185.24, 185.28, 201 See application file for complete search history.

(56) References Cited

U.S. PATENT DOCUMENTS

6,075,724 A * 6/2000 Lietal 365/185.18

6.344.994 Bl 2/2002 Hamilton et al.

6,618,290 Bl* 9/2003 Wangetal 365/185.28

6,778,442 Bl * 8/2004 Hamilton etal 365/185.28

6,813,752 Bl 11/2004 Hsiaetal.

6,993,690 Bl * 1/2006 Okamoto 714/718

7.259.995 B2 * 8/2007 Shih et al 365/185.28

2007/0263444 Al * 11/2007 Gorobets et al 365/185.09

OTHER PUBLICATIONS

Janai, Meir et al., "Data Retention Reliability Model of NROM Nonvolatile Memory Products," IEEE Transactions on Device and Materials Reiliability vol. 4, No. 3, Sep. 2004, 12 pages.

* cited by examiner

Primary Examiner—Dang T Nguyen

Assistant Examiner—Alexander Sofocleous

(74) Attorney, Agent, or Firm—Haynes Beffel & Wolfeld

LLP

Methods are described for improving the retention of a memory device by execution of a retention improvement procedure. The retention improvement procedure comprises a baking process of the memory device in a high temperature environment, a verifying process of the memory device that checks the logic state of memory cells, and a reprogramming process to program the memory device once again by programming memory cells in a 0-state to a high-Vt state. The baking step of placing the memory device in a high temperature environment causes a charge loss by expelling shallow trapped charges, resulting in the improvement of retention reliability.

11 Claims, 9 Drawing Sheets