Ultra-thin gate insulator of atomic-layer-deposited AlO x and HfO x for amorphous InGaZnO thin-film transistors

Jiye Li; Yuhang Guan; Jinxiong Li; Yuqing Zhang; Yuhan Zhang; ManSun Chan; Xinwei Wang; Lei Lu; Shengdong Zhang

doi:10.1088/1361-6528/acc742

Ultra-thin gate insulator of atomic-layer-deposited AlO _x and HfO _x for amorphous InGaZnO thin-film transistors

Nanotechnology. 2023 Apr 12;34(26). doi: 10.1088/1361-6528/acc742.

Authors

Jiye Li¹, Yuhang Guan¹, Jinxiong Li², Yuqing Zhang³, Yuhan Zhang¹, ManSun Chan³, Xinwei Wang², Lei Lu¹, Shengdong Zhang^{1

4}

Affiliations

¹ School of Electronic and Computer Engineering, Peking University, Shenzhen, People's Republic of China.
² School of Advanced Materials, Peking University, Shenzhen, People's Republic of China.
³ Department of Electronic and Computer Engineering, Hong Kong University of Science and Technology, Hong Kong, People's Republic of China.
⁴ School of Integrated Circuits, Peking University, Beijing, People's Republic of China.

PMID: 36962937
DOI: 10.1088/1361-6528/acc742

Abstract

To strengthen the downscaling potential of top-gate amorphous oxide semiconductor (AOS) thin-film transistors (TFTs), the ultra-thin gate insulator (GI) was comparatively implemented using the atomic-layer-deposited (ALD) AlO_xand HfO_x. Both kinds of high-kGIs exhibit good insulating properties even with the physical thickness thinning to 4 nm. Compared to the amorphous indium-gallium-zinc oxide (a-IGZO) TFTs with 4 nm AlO_xGI, the 4 nm HfO_xenables a larger GI capacitance, while the HfO_x-gated TFT suffers higher gate leakage current and poorer subthreshold slope, respectively originating from the inherently small band offset and the highly defective interface between a-IGZO and HfO_x. Such imperfect a-IGZO/HfO_xinterface further causes noticeable positive bias stress instability. Both ALD AlO_xand HfO_xwere found to react with the underneath a-IGZO channel to generate the interface defects, such as metal interstitials and oxygen vacancies, while the ALD process of HfO_xgives rise to a more severe reduction of a-IGZO. Moreover, when such a defective interface is covered by the top gate, it cannot be readily restored using the conventional oxidizing post-treatments and thus desires the reduction-resistant pre-treatments of AOSs.

Keywords: AlO x; HfO x; a-IGZO; atomic-layer-deposition (ALD); gate insulators (GIs); thin-film transistors (TFTs).