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

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) AlOx and HfOx. Both kinds of high-k GIs 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 AlOx GI, the 4-nm HfOx enables a larger GI capacitance, while the HfOx-gated TFT suffers the 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 HfOx. Such imperfect a-IGZO/HfOx interface further causes the noticeable positive bias stress (PBS) instability. Both ALD AlOx and HfOx were 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 HfOx gives 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.

Photochargeable Semiconductors: in “Dark Photocatalysis” and Beyond

“…Generally, very good results were obtained thanks to the charge‐storing properties of QDs, functioning as electron pools. [ 122–127 ] These materials achieved among the best prolonged cathodic protection in the dark with excellent OPC shifts and R PC /R DC ratio ( Table 2 ), confirming QDs as state‐of‐the‐art charge‐storing semiconductors. In a few instances, introducing 2D carbon layers proved to be beneficial for enhanced charge separation and storage.…”

“…In particular, for most TiO 2 ‐based photoanodes the main semiconductor is fabricated in the form of nanotubes or other vertical arrays on the electrode. [ 108,113–116,118,125–127,136 ] It is believed that such morphology favors the oriented transfer of electrons, thus suppressing carrier recombination. [ 85,137 ] Alternatively, the increased surface area might provide more charge‐trapping sites.…”

Review of Material Properties of Oxide Semiconductor Thin Films Grown by Atomic Layer Deposition for Next-Generation 3D Dynamic Random-Access Memory Devices

“…HfO x experiences increased gate leakage and worsen subthreshold slope due to its small band offset and defective a-IGZO/HfO x interface, leading to significant positive bias stress instability. 246 In the study by Lin and Chou, a-IGZO TFTs with HfO 2 gate dielectric layers demonstrated electrical performance postannealing at 200 °C, evidenced by an I on /I off ratio reaching 10 7 V th of 1.5 V, and an SS value of 0.2 V/decade. Elevating the annealing temperature above 300 °C resulted in deteriorating electrical characteristics, notably at 400 °C, where the I on /I off ratio decreased to 10 6 , V th increased to over 3 V, and SS rose to 0.8 V/decade, signaling a compromise in interface integrity and oxide quality.…”

Editorial for focus on manipulations of atomic and molecular layers and its applications in energy, environment sciences and optoelectronic devices

“…This study provides a rational strategy to develop perovskite nanocrystals LEDs (PNCs-LED) with high efficiency and stable operation. Another study investigated the downscaling potential of top-gate amorphous oxide semiconductor (AOS) thin-film transistors (TFTs) with two ALD-deposited oxides as the ultra-thin gate insulators (GIs), AlO x and HfO x [14]. In the study, however, Li et al [14] revealed that both ALD AlO x and HfO x reacted with the underneath amorphous indiumgallium-zinc oxide (a-IGZO) TFTs to generate the interface defects.…”

“…Another study investigated the downscaling potential of top-gate amorphous oxide semiconductor (AOS) thin-film transistors (TFTs) with two ALD-deposited oxides as the ultra-thin gate insulators (GIs), AlO x and HfO x [14]. In the study, however, Li et al [14] revealed that both ALD AlO x and HfO x reacted with the underneath amorphous indiumgallium-zinc oxide (a-IGZO) TFTs to generate the interface defects. They pointed out that, to strengthen the downscaling capability of AOS TFTs using the high-k dielectrics, it is necessary to effectively suppress the ALD-induced interface reduction reaction.…”