Seoul National University Investigation of Retention Characteristics caused by Charge Loss for Charge Trap NAND Flash memory 2014년 06월 25일 School of EE, Seoul National University 대표 학생 김승현 과제 책임자 박병국 교수 1/12

Introduction NAND Flash memory Low cost, high density NVM memory  data storage SSD for PC storage & mobile application drive the NAND consumption 2/12

Lateral redistribution - Poole-frenkel emission Retention loss mechanisms Leakage components in a NAND string Poly O N Lateral redistribution Vertical charge loss O - Poole-frenkel emission - Trap-to-band tunneling - Trap-to-trap tunneling - Band-to trap tunneling - Thermal excitation - Poole-frenkel emission 3/12

Fabrication processes of SONOS 4/12

Fabrication processes of SONOS Lateral charge loss Cut - SONOS Non cut - SONOS 5/12

Electrical characteristics of SONOS Measurement Read voltage ∆ 𝑰 𝑫 6/12

Setting for retention measurement Gate, Drain : pulse voltage Source, Body : constant voltage It is very useful for the measurement of the long time response in the retention test 7/12

Electrical characteristics of SONOS Id-Vg characteristic and program characteristics of SONOS device Id-Vd curve of SONOS device. When drain bias is 0.1V, the device is in the linear region 𝑉 𝑝𝑔𝑚 =13𝑉,10𝑢𝑠 𝑉 𝐷 =0.1𝑉 𝑉 𝑝𝑔𝑚 =13𝑉,10𝑢𝑠 𝑉 𝐺 =3𝑉 8/12

Retention characteristics of SONOS Retention curve Drain current as a function of time (linear scale). It shows initial charge loss and subsequent charge loss It is estimated that the transient characteristic can be the form of superposition of a few exponential functions 9/12

Time-constant analysis for fitting Stretched exponential function form 𝐼= 𝑖=1 𝑛 𝛼 𝑖 exp⁡(−𝑡/ 𝜏 𝑖 ) + 𝐼 ∞ 10/12

Summary 【 4차년도 상반기 연구 내용 요약 및 인력 양성 & 연구 실적】 상반기 (’13.07~’13.12) 연구 내용 요약 SONOS device which width split into several is fab out Setting a fast response measurement to observe the retention characteristics Studying for mechanism about retention characteristics caused by charge loss 인력 양성 & 연구 실적 1. 인력 양성 실적 (본 산학협력위원회 관련 박사과정 산학 생 배출 수) - 4차년도 : 2명 - 1차년도 이후 누적 : 총 6명 2. 본 과제 관련 대표 논문 (1편만 기재) 논 문 제 목 발표지명 또는 학회명 1 Investigation of Gate Stacked Array (GSTAR) for 3D NAND Flash Memory ITC-CSCC 11/12

4차년도 하반기 주요 연구 계획 하반기 (’14.1~’14.6) 주요 연구 계획 Study for retention characteristics caused by charge loss Measuring SONOS device which widths split into several 12/12