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http://dx.doi.org/10.6117/kmeps.2017.24.3.047

A Study on Threshold Voltage Degradation by Loss Effect of Trapped Charge in IPD Layer for Program Saturation in a MLC NAND Flash Memory  

Choi, Chae-Hyoung (Division. of Electronics & Information Engineering, Yeungnam University College)
Choi, Deuk-Sung (Division. of Electronics & Information Engineering, Yeungnam University College)
Jeong, Seung-Hyun (Division. of Electronics & Information Engineering, Yeungnam University College)
Publication Information
Journal of the Microelectronics and Packaging Society / v.24, no.3, 2017 , pp. 47-52 More about this Journal
Abstract
This research scrutinizes the data retention characteristics of the MLC NAND Flash Memory instigated by the loss effect of trapped charge when the memory is in the state of program saturation. It is attributed to the threshold voltage saturation phenomenon which engenders an interruption to the linear increase of the voltage in the memory cell. This phenomenon is occasioned by the outflow of the trapped charge from the floating gate to the control gate, which has been programmed by the ISPP (Incremental Step Pulse Programming), via Inter-Poly Dielectric (IPD). This study stipulates the significant degradation of thermal retention characteristics of threshold voltage in the saturation region in contrast to the ones in the linear region. Thus the current study evaluates the data retention characteristics of voltage after the program with a repeated reading test in various measurement conditions. The loss effect of trapped charge is found in the IPD layer located between the floating gate and the control gate especially in the nitride layer of the IPD. After the thermal stress, the trapped charge is de-trapped and displays the impediment of the characteristic of reliability. To increase the threshold saturation voltage in the NAND Flash Memory, the storage ability of the charge in the floating gate must be enhanced with a well-thought-out designing of the module in the IPD layer.
Keywords
MLC NAND Flash Memory; Inter-Poly Dielectric; saturation cell threshold voltage; saturation program voltage; trapped charge; data retention;
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