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Patent Issued for Nonvolatile Memory Device and Program Verify Method

June 18, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- A patent by the inventor Choi, Won Yeol (Icheon-si, KR), filed on February 17, 2012, was published online on June 3, 2014, according to news reporting originating from Alexandria, Virginia, by VerticalNews correspondents.

Patent number 8743620 is assigned to SK Hynix Inc. (Gyeonggi-do, KR).

The following quote was obtained by the news editors from the background information supplied by the inventors: "Example embodiments relate to a nonvolatile memory device and a program verify method thereof and, more particularly, to a nonvolatile memory device and a program verify method thereof, which are capable of improving a distribution of threshold voltages of memory cells.

"A semiconductor memory device is a memory device in which data can be stored and from which stored data can be read. Semiconductor memory devices are chiefly divided into volatile memory devices, whose data stored therein is erased when power is off; and nonvolatile memory devices, whose data stored therein is not erased although power is off. From among the nonvolatile memory devices, flash memory is being widely used in computers, memory cards, etc. because it is capable of electrically erasing bundles of data of memory cells.

"Flash memory is divided into NOR-type flash memory and NAND-type flash memory according to a coupling state between memory cells and a bit line. The NOR-type flash memory has two or more cell transistors coupled in parallel to one bit line, stores data using a channel hot electron method, and erases data using a Fowler-Nordheim (F-N) tunneling method. The NAND-type flash memory has two or more cell transistors coupled in series to one bit line and stores or erases data using the F-N tunneling method. In general, the NOR-type flash memory requires higher current consumption, which hinders a high integration of the flash memory. The NOR-type flash memory, however, is superior in terms of having a higher speed. The NAND-type flash memory is able to achieve higher integration because it uses lower cell current than the NOR-type flash memory.

"In a program verify method of the nonvolatile memory device, a plurality of program verify operations is consecutively performed by skipping a bit line precharge time during the program verify operation in order to reduce the time taken to perform the program verify operations. If the program verify method is used, however, verify time points are different depending on the program states of memory cells. In this case, there is a problem in that a distribution of the threshold voltages of the memory cells is widened because a margin differs depending on a difference in a time of an evaluation interval when a page buffer detects the potential of a bit line."

In addition to the background information obtained for this patent, VerticalNews journalists also obtained the inventor's summary information for this patent: "Example embodiments relate to a nonvolatile memory device and a program verify method thereof, which can prevent an increase in the width of a threshold voltage distribution by regularly maintaining a bit line sense current, in such a way as to supply a bit line sense signal having a gradually lower voltage level whenever program verify voltages are changed when the threshold voltages of a memory cell are sensed by sequentially supplying the program verify voltages in program verify operations.

"A nonvolatile memory device according to an aspect of the present disclosure includes a memory cell array configured to include a plurality of memory cells, a voltage supply unit configured to supply operating voltages to a word line of the memory cell array, a page buffer unit coupled to the plurality of memory cells through a bit line, and a controller configured to control the operations of the page buffer unit and the voltage supply unit, wherein the controller performs control so that the voltage supply unit sequentially outputs a plurality of program verify voltages to the memory cell array when program verify operations are performed and generates a bit line sense signal so that the page buffer unit senses a voltage of the bit line, and the bit line sense signal having a gradually lower voltage level is generated whenever the program verify voltages are changed.

"A program verify method of the nonvolatile memory device according to an aspect of this disclosure includes supplying a first program verify voltage to a word line coupled to memory cells of a memory cell array, sensing a voltage of a bit line coupled to the memory cells in response to a first sense signal, supplying a second program verify voltage higher than the first program verify voltage to the word line, and sensing a voltage of the bit line in response to a second sense signal having a lower voltage level than the first sense signal.

"In an other embodiment, a program verify method of a nonvolatile memory device includes supplying a first program verify voltage to a word line coupled to memory cells of a memory cell array, evaluating a voltage of a bit line coupled to the memory cells according to threshold voltages of the memory cells during a first interval, sensing the voltage of the bit line coupled to the memory cells in response to a first sense signal, supplying a second program verify voltage higher than the first program verify voltage to the word line, evaluating a voltage of the bit line according to threshold voltages of the memory cells during a second interval shorter than the first interval, and sensing the voltage of the bit line coupled to the memory cells in response to a second sense signal."

URL and more information on this patent, see: Choi, Won Yeol. Nonvolatile Memory Device and Program Verify Method. U.S. Patent Number 8743620, filed February 17, 2012, and published online on June 3, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8743620.PN.&OS=PN/8743620RS=PN/8743620

Keywords for this news article include: Electronics, SK Hynix Inc., Semiconductor.

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Source: Electronics Newsweekly