Low-temperature fabrication of an HfO2 passivation layer for amorphous indium–gallium–zinc oxide thin film transistors using a solution process

Abstract

We report low-temperature solution processing of hafnium oxide (HfO2) passivation layers for amorphous indium–gallium–zinc oxide (a-IGZO) thin-film transistors (TFTs). At 150 °C, the hafnium chloride (HfCl4) precursor readily hydrolyzed in deionized (DI) water and transformed into an HfO2 film. The fabricated HfO2 passivation layer prevented any interaction between the back surface of an a-IGZO TFT and ambient gas. Moreover, diffused Hf4+ in the back-channel layer of the a-IGZO TFT reduced the oxygen vacancy, which is the origin of the electrical instability in a-IGZO TFTs. Consequently, the a-IGZO TFT with the HfO2 passivation layer exhibited improved stability, showing a decrease in the threshold voltage shift from 4.83 to 1.68 V under a positive bias stress test conducted over 10,000 s.

Self-Assembled Monolayers (SAMs)/Al2O3 Double Layer Passivated InSnZnO Thin-Film Transistor

“…All parameters mentioned above, except / , are affected by the charge carrier concentration of the channel layer, while / is affected by the total trap density consisting of the bulk trap density and interface trap density [19]. Therefore, the positive shift of Vth and the reduction of SS and Ioff are all benefits from the reduction of oxygen vacancies (VO) and electron concentration in the ITZO channel [17,18,20]. It is well known that VO (as donor-like states) is related to the electrons generated in the ITZO channel.…”

“…It is reported that Al 3+ as an oxygen binder can effectively reduce VO in AOS film [17,18]. This could be due to the lower standard electrode potential (SEP) (−1.66 V) of Al than that of In (−0.342 V), Zn (−0.761 V), and Sn (−0.13 V), which could combine easily with the oxygen vacancies (VO) [17,19,20]. This results in a reduction of oxygen vacancy and a decrease of electron concentration in the ITZO channel, and the Vth of the device is positively shifted accordingly.…”

“…4 (a) and (b). The O 1s peak was deconvoluted into two peaks centered at 530.3 eV and 531.7 eV, which is corresponded to the binding energy of the oxide and the hydroxyl groups [20]. After SAM treatment, the number of hydroxyl groups has a decrease for the Al2O3 PVL, which is from 10.7% to 6.8%.…”

“…After SAM treatment, the number of hydroxyl groups has a decrease for the Al2O3 PVL, which is from 10.7% to 6.8%. A small number of hydroxyl groups can ensure TFT reliability [20]. For the SAM treatment, the anchor groups of silane SAMs undergo dehydration, condensation reaction with the hydroxyl groups on the surface of the oxide to form a strong chemical bond, while the hydrophobic surface is formed by the hydrophobic functional group (-CH3) of silane SAMs, as shown in Fig.…”

Channel Defect Profiling and Passivation for ZnO Thin-Film Transistors

“…These oxygen vacancies serve as active trap sites and cause various reliability problems [ 15 , 16 , 17 ]. Although several countermeasures for this problem have been developed using passivation layers such as SiO 2 and HfO 2 [ 18 , 19 ], the detailed mechanisms of device degradation and recovery related with the oxygen vacancies have not been systematically investigated.…”