Abstract
This report introduces the cryogenic operation and storage performance of 3-D flash memory. The cell transistor characteristics and the basic functionalities, including read and program and erase (P/E) operations, are investigated at an extremely low temperature of 77 K cooled by the liquid nitrogen. The cell transistor has a steep subthreshold slope at 77 K compared with at 300 K, and the read operation is fully functional even though the saturation current becomes relatively small. P/E operations at 77 K are not much different from those at 300 K, and the same incremental-step pulse programming (ISPP) and incremental-step pulse erase (ISPE) methods are applicable. In addition, the storage performance and the reliability characteristics of 3-D flash memory, such as the read noise, the disturb characteristics, the data retention, and the cycle endurance, are also investigated. While there is no degradation in the disturb characteristics, the read noise at 77 K was significantly minimized compared with that at 300 K. The data retention characteristics are about three times improved, and the cycle endurance is about ten times improved at 77 K compared with at 300 K. These storage performance improvements and high-reliability characteristics at cryogenic operation enable us to achieve the ultramultilevel cell. We show the successful demonstration of 6-bit per cell (HLC) and discuss the impact of additional cooling cost and the possibility of future storage devices beyond HLC. The cryogenic operation of 3-D flash memory can greatly improve the storage performance and opens the door for potential new applications and the bit cost scaling for future storage devices.
Highlights
S INCE NAND Flash memory, one of the lowest cost and highest bit density nonvolatile memory, was announced 30 years ago [1], the continuous increase in bit density and bit cost scaling has been achieved including evolutional conversion from 2D planar to 3D Flash memory [2, 3]
For 3D Flash memory, we previously reported that cryogenic operation of 3D Flash memory is fully functional and has the potential for ultra-multi-level operation by improving the read noise characteristics, the data retention and the cycle endurance [21]
We reported that the failure bit analysis and the cell transistor characteristics of our state-of-the-art 3D Flash memory at cryogenic temperature, and discussed the advantage of cryogenic operation for scaling in future 3D Flash memory [22]
Summary
S INCE NAND Flash memory, one of the lowest cost and highest bit density nonvolatile memory, was announced 30 years ago [1], the continuous increase in bit density and bit cost scaling has been achieved including evolutional conversion from 2D planar to 3D Flash memory [2, 3]. It has been reported that memory operation at 77 K (-196 °C) cooled by the liquid nitrogen instead of 4.2 K or lower is cost effective and sufficient to support superconducting operation [7] Another possible application of cryogenic operation is in the aerospace field [9]. We reported that the failure bit analysis and the cell transistor characteristics of our state-of-the-art 3D Flash memory at cryogenic temperature, and discussed the advantage of cryogenic operation for scaling in future 3D Flash memory [22]. We propose that cryogenic operation of 3D Flash memory is advantageous for the application to new fields and for the improvement of storage performance and the bit cost scaling of future storage devices
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