Ultrahigh-vacuum Sputtering Research Articles

Epitaxial growth and scanning tunneling microscopy of LiV2O4 thin films on SrTiO3(111)

LiV2O4 is a mixed-valent spinel oxide and one of a few transition-metal compounds to host a heavy fermion phase at low temperatures. Although numerous experimental studies have attempted to elucidate how its 3d electrons undergo giant mass renormalization, spectroscopic probes that may provide crucial hints, such as scanning tunneling microscopy (STM), remain to be applied. A prerequisite is atomically flat and pristine surfaces, which, in the case of LiV2O4, are difficult to obtain by the cleavage of small, three-dimensional crystals. We report the epitaxial growth of LiV2O4 thin films with bulklike properties on SrTiO3(111) via pulsed laser deposition and stable STM imaging of the LiV2O4(111) surface. The as-grown films were transferred ex situ to a room-temperature STM, where subsequent annealing with optional sputtering in ultrahigh vacuum enabled compact islands with smooth surfaces and a hexagonal 1 × 1 atomic lattice to be resolved. Our STM measurements provide insights into the growth mechanisms of LiV2O4 on SrTiO3(111) as well as demonstrate the feasibility of performing surface-sensitive measurements of this heavy fermion compound.

Disorder-induced 2D superconductivity in a NbTiN film grown on Si by ultrahigh-vacuum magneton sputtering

We report on the growth and characterization of a niobium titanium nitride (NbTiN) film on a Si substrate prepared by ultrahigh vacuum sputtering. We show that the superconducting transition temperature is lower than those of high-quality NbTiN films. Interestingly, even though the zero-temperature Ginzburg-Landau coherence length (=9.77 nm) is significantly shorter than the film thickness (=86 nm), we are still able to observe the Berezinskii-Kosterlitz-Thouless-like transition, indicating the two-dimensional (2D) signature of our three-dimensional (3D) sample. We propose that the mechanism of hidden 2D superconducting property is similar to the recently reported results of the disordered induced 3D to 2D superconductor transition. We suggest further theoretical work is required for studying our new experimental results.

Local Structure Properties of Hydrogenated and Nonhydrogenated Amorphous In–Ga–Zn–O Thin Films Using XAFS and High-Energy XRD

The strong effect of impurity hydrogen (H) on subgap electronic states in amorphous In–Ga–Zn–O thin-film transistors (a-IGZO TFTs) was confirmed using standard (STD) and ultrahigh-vacuum (UHV) sputtering systems with different base pressures of 10–4 and 10–7 Pa, respectively. However, comprehensive studies of the atomic-scale structure have yet to be reported. We investigated the correlations between the atomic-scale structure, the electronic state, and the impurity hydrogen content in a-IGZO by high-energy X-ray diffraction (HEXRD) coupled with reverse Monte Carlo (RMC) modeling and X-ray absorption fine structure (XAFS) spectroscopy. XAFS probed the distribution of unoccupied electronic states above the Fermi level and the local coordination structure around the In, Ga, and Zn atoms. A possible contribution for H from voids in the a-IGZO films was observed by the HEXRD and RMC configuration models. In contrast, the STD 3% film has many voids, which are occupied by impurity H. The proportion of lower coordinated M-O (M = Zn, Ga, In) structures is increased because of the H in voids. We revealed that this electronic and atomic-scale structure of the a-IGZO TFTs, which results in enhanced TFT characteristics, can be stabilized by the hydrogen-passivated defects resulting from STD sputtering with an optimum oxygen flow rate ratio of 3%.

Transition in a Magnetic Non-Collinear Spin-Flop State in a Fe/Pd/Gd/Pd Superlattice

The influence of a Pd spacer on the magnetic properties of Gd/Fe heterostructures has been studied. We have prepared using ultrahigh vacuum sputtering multilayered [Fe(3.5 nm)/Pd(1.2 nm)/Gd(5.0 nm)/Pd(1.2 nm)]12 structure. By using Polarized Neutron Reflectometry at temperature of 10 K we have observed strong increase in the intensity of neutron spin-flip scattering above magnetic field of 1.5 kOe. Combined analysis of magnetometry and polarized neutron reflectometry data allowed us to find out that the observed increase in spin-flip scattering is related to the spin-flop transition. Although the spin-flop transition were already seen in Fe/Gd systems, the use of Pd in our case allowed the suppression of the magnetic field of the transition making thus possible the use of Fe/Pd/Gd systems for diverse spintronic applications.

Electrodeposition of Epitaxial Co on Ru(0001)/Al2O3(0001)

The 60 nm-thick Ru(0001) layer was deposited epitaxially onto Al2O3(0001) by ultrahigh vacuum (UHV) sputter deposition at 500°C followed by a step anneal (ex situ) to 950°C. The Co layer was electrodeposited at room temperature from an acidic electrolyte (pH = 3.8) containing dilute Co metal ions. Previously unreported, evidence for the underpotential deposition (UPD) of Co on Ru(0001) is presented and was shown to affect the nucleation of Co during constant potential electrodeposition. This result demonstrates a strong interaction between Co and the Ru substrate necessary for epitaxial growth. Cross-sectional transmission electron imaging and diffraction confirmed the formation of an epitaxial layer of Co(0001) on Ru(0001) to practical thicknesses for interconnect gap-fill. This finding suggests the plausibility of electrodeposited, single crystal interconnects in future integrated circuit chips.

Compositional Dependence of Exchange Anisotropy in Pt$_x$Mn$_{100-}$$_x$/Co$_y$Fe$_{100-}$$_y$ Films

Bilayer films consisting of a 15 nm thick Pt x Mn 100-x (x = 48 or 15) layer and a 2 nm thick Co y Fe 100-y (0 ≤ y ≤ 90) layer were fabricated by ultrahigh-vacuum magnetron sputtering. The Pt 48 Mn 52 and Pt 15 Mn 85 films consisted of face-centered tetragonal (FCT) and face-centered cubic (FCC) structures, respectively. The effect of composition of CoFe films on the unidirectional anisotropy constant (Jk) in the Pt x Mn 100-x /Co y Fe 100- y bilayer films and the optimum conditions for producing large Jk were determined. The FCT and FCC PtMn films annealed at 370 °C for 6 h both exhibited maximum J k when the film composition was Co 70 Fe 30 . Blocking temperatures of the FCT and FCC PtMn films were 410 °C and 160 °C, respectively. All the bilayer films possess flat surfaces. These results indicate that the obtained Pt-Mn films-with low roughness, high exchange bias, and high blocking temperature-will be practical candidates as the antiferromagnetic layer in spintronic devices.

Optical properties of refractory metal based thin films

There is a growing interest in refractory metal thin films for a range of emerging nanophotonic applications including high temperature plasmonic structures and infrared superconducting single photon detectors. We present a detailed comparison of optical properties for key representative materials in this class (NbN, NbTiN, TiN and MoSi) with texture varying from crystalline to amorphous. NbN, NbTiN and MoSi have been grown in an ultra-high vacuum sputter deposition system. Two different techniques (sputtering and atomic layer deposition) have been employed to deposit TiN. We have carried out variable angle ellipsometric measurements of optical properties from ultraviolet to mid infrared wavelengths. We compare with high resolution transmission electron microscopy analysis of microstructure. Sputter deposited TiN and MoSi have shown the highest optical absorption in the infrared wavelengths relative to NbN, NbTiN or ALD deposited TiN. We have also modelled the performance of a semi-infinite metal air interface as a plasmonic structure with the above mentioned refractory metal based thin films as the plasmonic components. This study has implications in the design of next generation superconducting nanowire single photon detector or plasmonic nanostructure based devices.

Hetero-interface effect on Gilbert damping in nonmagnetic metal/permalloy/nonmagnetic metal trilayers

Gilbert damping in nonmagnetic metal (NM)/permalloy (Py)/nonmagnetic metal (NM) trilayers was studied using ferromagnetic resonance (FMR) measurements for different constituent materials (NM = Pt, Ta, Cu, and Ti) of varying Py thickness (t = 2, 3, 4, 5, 6, 8, and 10 nm) fabricated using an ultrahigh vacuum sputtering system. We found that the Gilbert damping constant increases with decreasing Py thickness and varies for different constituents of nonmagnetic metals. For NM = Pt, the damping constant of Py increases with decreasing Py thickness more remarkably than for other nonmagnetic metals. According to quantitative estimations of the effective spin-mixing conductance Geffmix, it was found that the value of Geffmix = 1.17 × 1015 Ω−1·m−2 for Pt is one order of magnitude greater than Geffmix = 0.13 × 1015 Ω−1·m−2 for Cu and 0.11 × 1015 Ω−1·m−2 for Ti. The large Geffmix value for Pt/Py/Pt is known to be caused by the strong spin-orbit coupling (SOC) of Pt. The effective spin-mixing conductance for Pt is 3 times greater than that (0.27 × 1015 Ω−1·m−2) for Ta despite the SOC of both Pt and Ta is similar in magnitude. This work allows not only for an understanding of the interface effect of the Gilbert damping constant on NM/Py/NM trilayers but also for optimal design of low-power-consumption spintronic devices that are composed of a variety of hetero-interfaces between the different magnetic and nonmagnetic layers.

Effects of Base Pressure on Growth and Optoelectronic Properties of Amorphous In‐Ga‐Zn‐O: Ultralow Optimum Oxygen Supply and Bandgap Widening

It is generally thought that deposition of device‐quality oxide semiconductors requires somewhat high oxygen supply in order to reduce oxygen deficiency and to suppress generation of free electrons. This paper reports that such high oxygen supply is not an essential requirement for a representative amorphous oxide semiconductor, amorphous In‐Ga‐Zn‐O (a‐IGZO). That is, the optimum oxygen flow rate ratio (RO2) is ≈3% for standard (STD) sputtering with the base pressure of ≈10−4 Pa, while it is reduced dramatically to 10−3–10−5% for ultrahigh vacuum (UHV) sputtering with the base pressure of ≈10−7 Pa. We consider that the ultralow optimum oxygen supply originates from residual hydrogen, because the STD and the UHV films have different hydrogen contents at the orders of 1020 and 1019 cm−3, respectively. This comparison also suggests that the inclusion of impurity hydrogen widens the optical bandgap by ≈0.1 eV, which causes a bandgap minimum by post annealing at ≈500 °C for the STD a‐IGZO films accompanying the removal of incorporated hydrogen as H2O. Furthermore, crystallization onset temperature is reduced remarkably by ≈100 K for the UHV a‐IGZO films.

Magnetic tunnel junctions with an equiatomic quaternary CoFeMnSi Heusler alloy electrode

Tunnel magnetoresistance (TMR) in MgO-based magnetic tunnel junctions (MTJs) with equiatomic quaternary CoFeMnSi Heusler and CoFe alloy electrodes is studied. The epitaxial MTJ stacking structures were prepared using ultrahigh-vacuum magnetron sputtering, where the CoFeMnSi electrode has a full B2 and partial L21 ordering crystal structure. Maximum TMR ratios of 101% and 521% were observed at room temperature and 10 K, respectively, for the MTJs. The large bias voltage dependence of the TMR ratio was also observed at low temperature (LT), as similarly observed in Co2MnSi Heusler alloy-based MTJs in the past. The physical origins of this relatively large TMR ratio at LT were discussed in terms of the half-metallicity of CoFeMnSi.

Hydrogen sensor based on palladium-yttrium alloy nanosheet

This paper presents a hydrogen sensor based on palladium-yttrium (Pd-Y) alloy nanosheet. Zigzag-shaped Pd-Y nanosheet with a thickness of 19.3 nm was deposited on a quartz substrate by using an ultrahigh-vacuum magnetron sputtering system and shadow mask. The atomic ratio of palladium to yttrium in the nanosheet was 0.92/0.08. The fabrication process was simple and low-cost, and the sensor can be mass-produced. The experimental results show the sensor has a superior sensitivity, reversibility, and reproducibility. The resistive-based hydrogen detection mechanism in this research is much simpler and more compact compared to the optical-based detection method.

Multiple Roles of Hydrogen Treatments in Amorphous In–Ga–Zn–O Films

The roles of hydrogen introduced by post-deposition hydrogen treatments were investigated for amorphous In–Ga–Zn–O (a-IGZO) films using room-temperature hydrogen plasma (H-plasma) and high-temperature H2 annealing. It was found that these treatments cause different effects as confirmed by hard X-ray photoemission spectroscopy and difference spectrum analyses. The H-plasma treatment increased both the near-valence band maximum (near-VBM) states (observed just above VBM) and the –OH bonds (confirmed by O 1s core spectrum) if a-IGZO films were deposited under an optimum condition, leading to the conclusion that the room-temperature H treatment incorporates H to a-IGZO films as –OH bonds, and the increase in the relatively shallow near-VBM states (peaked at ∼1.0 eV, extended to ∼2.4 eV from VBM) is ascribed to the generated –OH bonds. On the other hand, high-temperature H2 annealing did not increase the O 1s –OH signal, and its difference spectrum showed a different peak centered at ∼0.7 eV. This difference spectrum is similar to that of H-less a-IGZO films deposited without O2 supply by ultra-high vacuum sputtering and assigned to oxygen deficiency. These results will contribute to control the operation characteristics and the instability issues of a-IGZO TFTs. Further, the deconvoluted difference spectra will be the standard fingerprints of these defects in a-IGZO.

Surface and Near Surface Area Density of States for Magnetron-Sputtered ZnO and Al-ZnO: A MIES, UPS, and VBXPS Study Investigating Ultrahigh Vacuum Sputter Cleaning and UV Oxygen Plasma

The impact of nonsolvent-based cleaning methods on zinc oxide and aluminum-doped zinc oxide was investigated across a range of doping concentrations up to 25% aluminum. A combination of electron spectroscopic techniques was utilized in order to characterize the electronic states present on the surface and to discern the differences between the near surface area and outermost layer valence band states. Understanding the differences between the near surface area and outermost layer of an interface is crucial when optimizing devices for charge transfer. The techniques were valence band X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and metastable-induced electron spectroscopy. The band gap was also measured via ultraviolet/visible spectroscopy.

Correlation between structural, magnetic and transport properties of Co2FeSi thin films

Co2FeSi thin films are grown on a Si (1 0 0) substrate using ultrahigh-vacuum magnetron sputtering at different substrate temperatures from 300 °C to 550 °C. The films are characterized using grazing incidence x-ray diffraction, magnetization, and ferromagnetic resonance and temperature-dependent resistivity measurements. The films deposited at 450 °C (TS450) have better magnetic as well as structural properties with the minimum disorder. The temperature dependence of line-width () suggests two-magnon scattering is responsible for the line broadening. The correlation between the disorder and extrinsic broadening of the line-width is brought out clearly for the first time in Co2FeSi thin films. TS450 film has minimum (33 Oe) and Gilbert damping parameter (α = 0.005) at room temperature making it ideal for spintronic applications.

Effects of residual hydrogen in sputtering atmosphere on structures and properties of amorphous In-Ga-Zn-O thin films

We investigated the effects of residual hydrogen in sputtering atmosphere on subgap states and carrier transport in amorphous In-Ga-Zn-O (a-IGZO) using two sputtering systems with different base pressures of ∼10−4 and 10−7 Pa (standard (STD) and ultrahigh vacuum (UHV) sputtering, respectively), which produce a-IGZO films with impurity hydrogen contents at the orders of 1020 and 1019 cm−3, respectively. Several subgap states were observed by hard X-ray photoemission spectroscopy, i.e., peak-shape near-valence band maximum (near-VBM) states, shoulder-shape near-VBM states, peak-shape near-conduction band minimum (near-CBM) states, and step-wise near-CBM states. It was confirmed that the formation of these subgap states were affected strongly by the residual hydrogen (possibly H2O). The step-wise near-CBM states were observed only in the STD films deposited without O2 gas flow and attributed to metallic In. Such step-wise near-CBM state was not detected in the other films including the UHV films even deposited without O2 flow, substantiating that the metallic In is segregated by the strong reduction effect of the hydrogen/H2O. Similarly, the density of the near-VBM states was very high for the STD films deposited without O2. These films had low film density and are consistent with a model that voids in the amorphous structure form a part of the near-VBM states. On the other hand, the UHV films had high film densities and much less near-VBM states, keeping the possibility that some of the near-VBM states, in particular, of the peak-shape ones, originate from –OH and weakly bonded oxygen. These results indicate that 2% of excess O2 flow is required for the STD sputtering to compensate the effects of the residual hydrogen/H2O. The high-density near-VBM states and the metallic In segregation deteriorated the electron mobility to 0.4 cm2/(V s).

Structure and magnetic properties of tetragonal Heusler D022-Mn3Ge compound epitaxial films with high perpendicular magnetic anisotropy

We investigated the structure and magnetic properties of epitaxial films of D022-Mn3Ge tetragonal Heusler like compounds in detail. Epitaxial films with a stoichiometric composition were grown on Cr-buffered single crystalline (0 0 1) MgO substrates using ultra-high vacuum sputtering at different growth temperatures. X-ray diffraction showed that D022-ordered films were formed at growth temperatures of ⩾200 °C. Epitaxial growth was indicated by cross-sectional high-resolution transmission electron microscopy. Nanobeam diffraction patterns from the D022-Mn3Ge film grown at 400 °C suggests the absence of planar defects such as stacking faults and twins in the film. Out-of-plane magnetic hysteresis curves with perfect squareness were observed for the films grown at ⩾300 °C. These films also showed abrupt magnetization reversal at a coercivity of about 1 T, which is higher than that of other thin film materials with perpendicular magnetic anisotropy such as CoPt and FePt. A huge domain diameter in the D022-Mn3Ge films was indicated by the initial magnetization curves that were measured by the polar magneto-optical Kerr effect.

Thermal annealing effects on ZnO films grown on graphene buffered Si substrates.

ZnO films deposited on SiO2/Si substrate with a graphene single layer (GSL) were studied by using an ultra-high vacuum sputter. The as-prepared films were annealed at temperature ranges from 500 degrees C to 800 degrees C for 1 min under ambient N2 gas. When the annealing temperature was increased up to 800 degrees C, the root mean square roughness of the ZnO/Si sample surface decreased down to 3.4 nm, and the grain sizes increased about 50.8 nm with a clear grain boundary. From the photoluminescence (PL) spectra, the high intensity of near-band-edge UV emission at 380 nm (3.26 eV) and the broad band emission between 450 and 650 nm, known as the visible defect related PL band, decreased with increasing annealing temperature up to 800 degrees C. The ZnO thin films on the growth on the GSL and post-annealing at 700 degrees C for 1 min under ambient N2 gas had the best structural and optical properties.

Relationship Between Magnetostriction and Magnetic Domain Structure in Fe-Based Alloy Single-Crystal Films With bcc(001) Orientation

Fe, Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">94</sub> Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> , Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">98</sub> C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , and Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">95</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> (at. %) single-crystal thin films of bcc(001) orientation are prepared on MgO(001) substrates using an ultrahigh-vacuum magnetron sputtering system. The influence of magnetic anisotropy on the magnetostriction under rotating magnetic field is investigated. Fe, Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">94</sub> Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> , and Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">98</sub> C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> films show four-fold symmetries in in-plane magnetic anisotropy, where easy and hard magnetization directions are, respectively, observed along bcc[100] and bcc[110]. Higher saturation fields measured along bcc[110] are recognized in the order of Fe (6 kOe) > Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">98</sub> C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (5 kOe) > Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">94</sub> Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> (4 kOe). Triangle output waveforms of magnetostriction appear when these films are measured under low-rotating fields. The behavior is related with the motion of 90° magnetic domain walls in magnetically unsaturated film. With increasing the rotating field, the films approach to magnetic saturations and the waveform gradually shifts to usual sinusoidal shape. Larger threshold rotating field is observed in the order of Fe > Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">98</sub> C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> > Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">94</sub> Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> , which is related to the saturation field. On the contrary, Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">95</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> film possesses an almost isotropic property in in-plane measurement and shows sinusoidal waveforms even when the film is magnetically unsaturated. The waveform is affected by the symmetry and the strength of magnetic anisotropy.

Infrared spectroscopy study of adsorption and photodecomposition of formic acid on reduced and defective rutile TiO2 (110) surfaces

Adsorption and photodecomposition of formic acid on rutile TiO2 (110) have been investigated with infrared reflection–absorption spectroscopy (IRRAS) employing p- and s-polarized light along the [001] and [11¯0] crystal directions. The single crystal surfaces were prepared either by sputtering and annealing in ultrahigh vacuum (UHV) to obtain a reduced surface (r-TiO2), or by sputtering without annealing to create a rough, highly defective surface (sp-TiO2). Results are compared with corresponding measurements on rutile nanocrystals performed in synthetic air. IRRAS spectra obtained on r-TiO2 and rutile nanocrystals are very similar, and show that in both cases formic acid dissociates and is predominately adsorbed as a bridging bidentate formate species, and that the formate adsorption structure on the nanocrystals is dominated by interactions with majority (110) surfaces. In contrast, the IRRAS spectra on sp-TiO2 are different, with only minor spectral features associated with (110) surfaces and lost azimuthal symmetry, both of which imply changed adsorption geometry due to bonding to low-coordinated Ti atoms with lower valences. The UV-induced rate of formate photodecomposition is about 30 times higher on rutile nanocrystals in synthetic air compared with sp-TiO2 under UHV conditions, and even larger than on r-TiO2. These differences are explained by the lack of oxygen and limited hydroxyl coverage under UHV conditions. The difference in reactivity between the r-TiO2 and sp-TiO2 surfaces is attributed to a high concentration of strongly bonded bridging bidentate formate species on the (110) surface, which lowers its reactivity. The results point to a pressure gap where the availability of molecular oxygen and the hydroxyl concentration limit the photoreactivity in UHV leading to an almost 20-fold decrease of the formate degradation rate in UHV. In contrast, the structure represented by the single crystal (110) surface is shown to capture the essential structural properties, which dictates the formic acid adsorption and adsorption structure of rutile nanocrystals.

Roles of Hydrogen in Amorphous Oxide Semiconductor In-Ga-Zn-O: Comparison of Conventional and Ultra-High-Vacuum Sputtering

We investigated roles of hydrogen on physical properties of a-IGZO films and thin-film transistors (TFTs) by comparing standard and ultra-high vacuum (UHV) sputtering systems. It was confirmed that the impurity hydrogens come mainly from the residual gas in the deposition chamber and the molecules adsorbed to the surface of the sputtering target. It was found impurity hydrogen has unfavorable effects as follows; (i) enhances selective Zn desorption during film deposition, and (ii) weakens chemical bonds of the resulting film, causing temperature instability. On the other hand, the UHV a-IGZO films with less hydrogen had low density and exhibited structural instability, suggesting that some hydrogens would have a favorable effect to enhance structural relaxation rate and to form denser and more stable structures during film deposition at room temperature. The revealed hydrogen effects are discussed in relation to those in amorphous silicon and silicon dioxide.