Novel Vertical Channel-All-Around (CAA) In-Ga-Zn-O FET for 2T0C-DRAM With High Density Beyond 4F2 by Monolithic Stacking

• Published in: IEEE transactions on electron devices 2022-04, Vol.69 (4), p.2196-2202
• Main Authors: Duan, Xinlv, Huang, Kailiang, Feng, Junxiao, Niu, Jiebin, Qin, Haibo, Yin, Shihui, Jiao, Guangfan, Leonelli, Daniele, Zhao, Xiaoxuan, Wang, Zhaogui, Jing, Weiliang, Wang, Zhengbo, Wu, Ying, Xu, Jeffrey, Chen, Qian, Chuai, Xichen, Lu, Congyan, Wang, Wenwu, Yang, Guanhua, Geng, Di, Li, Ling, Liu, Ming
• Format: Article
• Language: English
• Subjects: 4F² bit cell; Atomic layer epitaxy; Cycle ratio; Density; Dynamic random access memory; dynamic random access memory (DRAM); Electrodes; Field effect transistors; Indium gallium zinc oxide; In–Ga–Zn-O (IGZO); Logic gates; Memory management; plasma-enhanced atomic layer deposition (PEALD); Plasmas; Power management; Random access memory; Semiconductor devices; Stacking; Zinc oxide
• ISSN: 0018-9383; 1557-9646
• DOI: 10.1109/TED.2022.3154693

For the first time, we propose a stackable vertical channel-all-around (CAA) In-Ga-Zn-O field-effect transistor (IGZO FET) for high-density 4F 2 and long-retention 2T0C dynamic random access memory (DRAM) application. The device is fabricated in a back-end-of-line (BEOL) compatible process flow where the channel and gate-stack are deposited by plasma-enhanced atomic layer deposition (PEALD). The impact of IGZO cycle ratio and plasma power on the device's electrical performance is studied. An optimized 50-nm channel-length CAA IGZO FET achieved {I}_{ \mathrm{\scriptscriptstyle ON}} > 30 ~\mu \text{A}/\mu \text{m} and {I}_{ \mathrm{\scriptscriptstyle OFF}} below 1.8\times10 −17 \mu \text{A}/\mu \text{m} at {V}_{\text {DS}} = 1 V. A long retention of 300 s has been experimentally verified for the CAA IGZO 2T0C bit cell, making it a potential candidate for low-power 2T0C DRAM with ultralow refresh frequency. Finally, by monolithically stacking the vertical CAA IGZO FETs with 130-nm critical dimension (CD) to form 2T0C bit cells, we demonstrate the feasibility of the proposed BEOL-compatible 2T0C DRAM for further density scaling beyond 4F 2 .