United States Patent 6,134,145
Wong Oct. 17, 2000
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High data rate write process for non-volatile flash memories
Abstract
A non-volatile semiconductor memory includes: multiple write pipelines, each including a memory array; a timing circuit which sequentially starts programming operations in the pipelines; and a shared charge pump and voltage regulation circuit that drives a current through the memory cells being programmed. Staggering the starts of programming operations reduces the current demand on the charge pump because spikes that occur at the starts of programming operations, for example, when using channel hot electron injection, are distributed over time rather than occurring all at once. Noise, which can reduce the accuracy of write operations, is also reduced because the total current required from the charge pump is more nearly constant. As further aspect of the invention, each write pipeline can perform a write operation as alternating programming cycles and verify cycles. During a programming cycle, the shared charge pump drives a current through a selected memory cell to change the threshold voltage of the selected memory cell. During a verify cycle, the write circuit determines whether the selected memory cell has reached its target threshold voltage level. The write pipelines can be partitioned into two banks where pipelines in one bank perform programming cycles while pipelines in the other bank perform verify cycles. More generally the write pipelines are partitioned into multiple banks where each bank starts programming cycles at times that differ from the starts of programming cycles in the other banks.
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Inventors: Wong; Sau C. (Hillsborough, CA).
Assignee: SanDisk Corporation (Campbell, CA).
Appl. No.: 128,225
Filed: Aug. 3, 1998
Related U.S. Application Data
Continuation-in-part of Ser No. 103,623, Jun. 23, 1998.
Intl. Cl. : G11C 16/00
Current U.S. Cl.: 365/185.22; 365/185.11; 365/185.28
Field of Search: 365/185.22, 185.11, 185.28, 185.23, 185.19, 185.33, 230.03; 711/169
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References Cited | [Referenced By]
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U.S. Patent Documents
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5,680,341 Oct., 1997 Wong et al. 365/77
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Foreign Patent Documents
0798739 Oct., 1995 EP
3644322 Jul., 1988 DE
Primary Examiner: Nguyen; Tan T.
Attorney, Agent or Firm: Majestic, Parsons, Siebert & Hsue
18 Claims, 7 Drawing Figures |
