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The gate‐induced electrical instability of SnO thin‐film transistors (TFTs) with SiO2 and Al2O3/SiO2 gate dielectric layers is evaluated. The hysteresis voltage (Vhy) and threshold voltage (Vth) in the transfer characteristics of SnO TFTs depend on the sweep range and rate of gate voltage (VGS). The TFT with an Al2O3/SiO2 gate dielectric layer exhibit reduced Vhy and stable Vth compared with the device without an Al2O3 layer. The introduction of an Al2O3 layer between the SnO channel and the SiO2 layer suppresses the electron and hole trapping at the channel/dielectric interface and contains mobile oxygen vacancies that counteract the hole trapping effect. [ABSTRACT FROM AUTHOR]

The origin of hysteresis in the drain–source current (IDS)–gate‐source voltage (VGS) characteristics of atomic‐layer‐deposited (ALD) p‐type SnO thin‐film transistors (TFTs) is examined by adding ALD Al2O3 interfacial layers (IL) between the SnO channel layer and the SiO2 gate insulator (GI) layer. SnO TFTs with SiO2 GI exhibit a large hysteresis voltage (Vhy) due to the trap state density near the interface between the SnO active layer and the SiO2 GI (known as the border trap). Both experimental results and theoretical calculations show that the origin of border traps is the SnSi+0 gap states in SiO2, which is induced by the Sn diffusion into the SiO2 layer. The use of Al2O3 films as ILs suppresses this diffusion. The effectiveness, however, is dependent on the thickness, crystallinity, and density of the Al2O3 films. The Vhy of the SnO TFTs can be decreased when the thickness and density of the ILs is increased if the amorphous structure of the Al2O3 IL is maintained after the rapid thermal annealing process. p‐Type ALD SnO TFTs with optimum ILs exhibit a high on‐off ratio of IDS (1.2 × 105), high field‐effect mobility (1.6 cm2 V−1 s−1), and a small Vhy (0.2 V). [ABSTRACT FROM AUTHOR]

The electronic structure of the Sn-added p-type SnO thin film was examined using x-ray absorption spectroscopy (XAS). Sn was intentionally added to a pristine SnO film, and the film was annealed to form p-type SnO. Sn L 1 - and L 3 -edge XAS was used to examine the oxidation states of the Sn-added p-type SnO. Compared to the case of the reference SnO, the spectrum of the Sn-added SnO (after annealing) partly contained the lineshape for SnO 2 , suggesting that the oxidation of Sn  +  SnO was progressed such that the film became preferably SnO 2   +  SnO rather than Sn  +  SnO 2 . O K-edge XAS, x-ray photoelectron spectroscopy (XPS), and spectroscopic ellipsometry (SE) were also used to scrutinize the electronic structure. The direct bandgap of the annealed film was estimated to be ~3.6 eV, consistent with the reported SnO 2 bandgap, while that of the as-deposited Sn-added SnO was  <2.5 eV. The large bandgap after annealing suggests that the metallic Sn was no longer in existence and manifested the functionality of the annealed Sn  +  SnO as a p-type semiconductor.

The programming characteristics of charge trap flash memory device adopting amorphous In 2 Ga 2 ZnO 7 (a-IGZO) oxide semiconductors as channel layer were evaluated. Metal-organic chemical vapor deposition (MOCVD) and RF-sputtering processes were used to grow a 45 nm thick a-IGZO layer on a 20 nm thick SiO 2 (blocking oxide)/p ++ -Si (control gate) substrate, where 3 nm thick atomic layer deposited Al 2 O 3 (tunneling oxide) and 5 nm thick low-pressure CVD Si 3 N 4 (charge trap) layers were intervened between the a-IGZO and substrate. Despite the identical stoichiometry and other physicochemical properties of the MOCVD and sputtered a-IGZO, a much faster programming speed of MOCVD a-IGZO was observed. A comparable amount of oxygen vacancies was found in both MOCVD and sputtered a-IGZO, confirmed by x-ray photoelectron spectroscopy and bias-illumination-instability test measurements. Ultraviolet photoelectron spectroscopy analysis revealed a higher Fermi level (E F ) of the MOCVD a-IGZO (∼0.3 eV) film than that of the sputtered a-IGZO, which could be ascribed to the higher hydrogen concentration in the MOCVD a-IGZO film. Since the programming in a flash memory device is governed by the tunneling of electrons from the channel to charge trapping layer, the faster programming performance could be the result of a higher E F of MOCVD a-IGZO.