Effect of Noncircular Channel on Distribution of Threshold Voltage in 3D NAND Flash Memory

Donghyun Go; Gilsang Yoon; Jounghun Park; Donghwi Kim; Jiwon Kim; Jungsik Kim; Jeong-Soo Lee

doi:10.3390/mi14112007

Effect of Noncircular Channel on Distribution of Threshold Voltage in 3D NAND Flash Memory

Micromachines (Basel). 2023 Oct 28;14(11):2007. doi: 10.3390/mi14112007.

Authors

Donghyun Go¹, Gilsang Yoon¹, Jounghun Park¹, Donghwi Kim¹, Jiwon Kim¹, Jungsik Kim², Jeong-Soo Lee¹

Affiliations

¹ Department of Electrical Engineering, Pohang University of Science and Technology, Pohang 37673, Republic of Korea.
² Department of Electrical Engineering, Gyeongsang National University, Jinju 52828, Republic of Korea.

Abstract

The instability in threshold voltage (V_TH) and charge distributions in noncircular cells of three-dimensional (3D) NAND flash memory are investigated. Using TCAD simulation, we aim to identify the main factors influencing the V_TH of noncircular cells. The key focus is on the nonuniform trapped electron density in the charge trapping layer (CTL) caused by the change in electric field between the circular region and the spike region. There are less-trapped electron (LT) regions within the CTL of programmed noncircular cells, which significantly enhances current flow. Remarkably, more than 50% of the total current flows through these LT regions when the spike size reaches 15 nm. We also performed a comprehensive analysis of the relationship between charge distribution and V_TH in two-spike cells with different heights (H_Spike) and angles between spikes (θ). The results of this study demonstrate the potential to improve the reliability of next-generation 3D NAND flash memory.

Keywords: 3D NAND flash memory; TCAD simulation; noncircular cell; spike; threshold voltage distribution; trapped charge.

Abstract

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