Structural and electrical properties of sputtered indium-zinc oxide thin films

In this study, indium-zinc oxide (IZO) thin films have been prepared at a room temperature, 200 and 300 °C by radio frequency magnetron sputtering from a In₂O₃-12 wt.% ZnO sintered ceramic target, and their dependence of electrical and structural properties on the oxygen content in sputter gas, the substrate temperature and the post-heat treatment was investigated. X-ray diffraction measurements showed that amorphous IZO films were formed at room temperature (RT) regardless of oxygen content in sputter gas, and micro-crystalline and In₂O₃-oriented crystalline films were obtained at 200 and 300 °C, respectively. From the analysis on the electrical and the structural properties of annealed IZO films under Ar atmosphere at 200, 300, 400 and 500 °C, it was shown that oxygen content in sputter gas is a critical parameter that determines the local structure of amorphous IZO film, stability of amorphous phase as well as its eventual crystalline structure, which again decide the electrical properties of the IZO films. As-prepared amorphous IZO film deposited at RT gave specific resistivity as low as 4.48 × 10^− 4 Ω cm, and the highest mobility value amounting to 47 cm²/V s was obtained from amorphous IZO film which was deposited in 0.5% oxygen content in sputter gas and subsequently annealed at 400 °C in Ar atmosphere.     

Effect of annealing temperature on the properties of IZO films and IZO based transparent TFTs

This work shows the effect of the annealing temperature and atmosphere on the properties of r.f. magnetron sputtered indium-zinc oxide (IZO) thin-films of two types: one a conductive film (as-deposited, room temperature) that exhibits a resistivity of 3.5 × 10^− 4 Ω cm; the other, a semiconductor film with a resistivity ∼ 10² Ω cm. The annealing temperatures were changed between 125 and 500 °C. Crystallization of the more conductive films was already noticeable at temperatures around 400 °C. Three different annealing atmospheres were used — vacuum, air and oxygen. For the conductive films, only the oxygen atmosphere was critical, leading to an increase of the electrical resistivity of more than one order of magnitude, for temperatures of 250 °C and above. Concerning the semiconductor films, both temperature and atmosphere had a strong effect on the film's properties, and the resistivity of the annealed films was always considerably smaller than the as-deposited films. Finally, some results of the application of these films to transparent TFTs are shown.     

Influence of DC magnetron sputtering parameters on the properties of amorphous indium zinc oxide thin film

Amorphous or crystalline indium zinc oxide (IZO) thin films, which are highly transparent and conducting, were deposited by DC magnetron sputtering. X-Ray diffraction technique was used for analyzing microstructures of the films, and also differential thermal analysis was performed for observing their crystallization behavior. The IZO thin films prepared were crystallized at much higher temperature than ITO films were. The crystallized samples showed (222) preferred orientations. By varying process parameters, the optimum conditions for the highest electrical conductivity and optical transmittance, and the lowest surface roughness were found. The resistivity of IZO films decreased as the deposition temperature increased until 250 °C, but sharp rise occurred at or above 300 °C. The extinction coefficients diminished in the films prepared with the conditions of higher deposition temperature, sputtering gas of light mass, and heat treatment. However, excessive amount of oxygen flow during deposition brought about the increase of the extinction coefficients. The variations of extinction coefficients mainly influenced the transmittance of the samples. On the basis of X-ray photoelectron spectroscopy analysis, atomic force microscopy measurement, spectroscopic ellipsometry and spectrophotometer measurement, several characteristics of IZO thin films were discussed comparing with those of ITO thin films. Very low surface roughness of IZO thin films could satisfy the requirement for organic light-emitting diode.     

Transparent Ga and Zn co-doped In2O3 electrode prepared by co-sputtering of Ga:In2O3 and Zn:In2O3 targets at room temperature

This study examined the characteristics of Ga:In₂O₃ (IGO) co-sputtered Zn:In₂O₃ (IZO) films prepared by dual target direct current (DC) magnetron sputtering at room temperature in a pure Ar atmosphere for transparent electrodes in IGZO-based TFTs. Electrical, optical, structural and surface properties of Ga and Zn co-doped In₂O₃ (IGZO) electrodes were investigated as a function of IGO and IZO target DC power during the co-sputtering process. Unlike semiconducting InGaZnO₄ films, which were widely used as a channel layer in the oxide TFTs, the co-sputtered IGZO films showed a high transmittance (91.84%) and low resistivity (4.1 × 10^− 4 Ω cm) at optimized DC power of the IGO and IZO targets, due to low atomic percent of Ga and Zn elements. Furthermore, the IGO co-sputtered IZO films showed a very smooth and featureless surface and an amorphous structure regardless of the IGO and IZO DC power due to the room temperature sputtering process. This indicates that co-sputtered IGZO films are a promising S/D electrode in the IGZO-based TFTs due to their low resistivity, high transmittance and same elements with channel InGaZnO₄ layer.     

Anode material properties of Ga-doped ZnO thin films by pulsed DC magnetron sputtering method for organic light emitting diodes

This study examined the anode material properties of Ga-doped zinc oxide (GZO) thin films deposited by pulsed DC magnetron sputtering along with the device performance of organic light emitting diodes (OLEDs) using GZO as the anode. The structure and electrical properties of the deposited films were examined as a function of the substrate temperature. The electrical properties of the GZO film deposited at 200 °C showed the best properties, such as a low resistivity, high mobility and high work function of 5.3 × 10^− 4Ω cm, 9.9 cm²/Vs and 4.37 eV, respectively. The OLED characteristics with the GZO film deposited under the optimum conditions showed good brightness > 10,000 cd/m². These results suggest that GZO films can be used as the anode in OLEDs, and a lower deposition temperature of 200 °C is suitable for flexible devices.     

Deposition of Al-doped ZnO thin-films with radio frequency magnetron sputtering for a source/drain electrode for pentacene thin-film transistor

Al-doped ZnO thin-films were deposited with the radio frequency magnetron sputtering technique at various temperatures and sputtering powers for a source/drain electrode in the pentacene thin-film transistor. With the increase in the deposition temperature and the decrease in the radio frequency sputtering power, the crystallinity was increased and the surface roughness was decreased, which lead to the decrease in the electrical resistivity of the film. Al-doped ZnO film deposited at 200 °C and sputtering power of 50 W showed a low resistivity (9.73 × 10⁴ μΩcm), high crystallinity, low roughness and uniform surface morphology. The pentacene thin-film transistor fabricated with Al-doped ZnO film as a source/drain electrode showed a device performance, (mobility: 7.89 × 10^− 3 cm²/Vs and on/off ratio: ~ 5 × 10⁴) which is comparable with an indium tin oxide electrode grown at room temperature.     

Electrical and optical properties of Al-doped ZnO films deposited by hollow cathode gas flow sputtering

Al-doped ZnO (AZO) films were deposited on glass by hollow cathode gas flow sputtering using Zn-Al alloy targets. Sputtering power for all the depositions was fixed at 1500 W. Resistivities of 0.81-1.1 × 10^− 3 Ω cm were obtained for AZO films deposited at room temperature with an O₂ flow from 38 to 50 standard cubic centimetre/minute (SCCM), while static deposition rates were almost constant at 270-300 nm/min. On the other hand, lower resistivities of 5.2-6.4 × 10^− 4 Ω cm were obtained for AZO films deposited at 200 °C with an O₂ flow from 25 to 50 SCCM, while the static deposition rates were almost constant at 200-220 nm/min. Average transmittances in the visible light region were above 80% for both sets of films.     

Preparation of LaNiO3 thin films with very low room-temperature electrical resistivity by room temperature sputtering and high oxygen-pressure processing

LaNiO₃ (LNO) thin films were deposited by radio frequency magnetron sputtering on n-type Si (100) wafers at room temperature (RT). The as-sputtered LNO thin films were amorphous and had very high RT electrical resistivity even after post-annealing at 800 °C. The amorphous as-sputtered LNO films could be transformed to polycrystalline LNO films in rhombohedral phase by heating at 400 °C in an O₂ atmosphere at pressure ranging from 1.5 to 8.0 MPa. Very low RT resistivity of LNO films were obtained by this high oxygen-pressure processing. The lowest value was as low as 1.09 × 10^− 4 Ω cm by processing at oxygen pressure of 8 MPa. Such preparation of LNO thin films is compatible with the Si-based readout integrated circuits. Highly (100)-oriented perovskite structure of Pb(Zr_0.52Ti_0.48)O₃ thin films was formed on this rhombohedral phase LNO, and good ferroelectricity could also be obtained on these HOPP-processed rhombohedral phase LNO films.     

Effects of hydrogen gas on properties of tin-doped indium oxide films deposited by radio frequency magnetron sputtering method

Tin-doped indium oxide (ITO) films were deposited at ∼ 70 °C of substrate temperature by radio frequency magnetron sputtering method using an In₂O₃-10% SnO₂ target. The effect of hydrogen gas ratio [H₂ / (H₂ + Ar)] on the electrical, optical and mechanical properties was investigated. With increasing the amount of hydrogen gas, the resistivity of the samples showed the lowest value of 3.5 × 10^− 4 Ω·cm at the range of 0.8-1.7% of hydrogen gas ratio, while the resistivity increases over than 2.5% of hydrogen gas ratio. Hall effect measurements explained that carrier concentration and its mobility are strongly related with the resistivity of ITO films. The supplement of hydrogen gas also reduced the residual stress of ITO films up to the stress level of 110 MPa. The surface roughness and the crystallinity of the samples were investigated by using atomic force microscopy and x-ray diffraction, respectively.     

Properties of Ce-doped ITO films deposited on polymer substrate by DC magnetron sputtering

Ce-doped indium tin oxide (ITO:Ce) films were deposited on flexible polyimide substrates by DC magnetron sputtering using ITO targets containing various CeO₂ contents (CeO₂ : 0, 0.5, 3.0, 4.0, 6.0 wt.%) at room temperature and post-annealed at 200 °C. The crystallinity of the ITO films decreased with increasing Ce content, and it led to a decrease in surface roughness. In addition, a relatively small change in resistance in dynamic stress mode was obtained for ITO:Ce films even after the annealing at high temperature (200 °C). The minimum resistivity of the amorphous ITO:Ce films was 3.96 × 10^− 4 Ωcm, which was deposited using a 3.0 wt.% CeO₂ doped ITO target. The amorphous ITO:Ce films not only have comparable electrical properties to the polycrystalline films but also have a crystallization temperature > 200 °C. In addition, the amorphous ITO:Ce film showed stable mechanical properties in the bended state.     

Polycrystalline films of tungsten-doped indium oxide prepared by d.c. magnetron sputtering

Electrical and optical properties of polycrystalline films of W-doped indium oxide (IWO) were investigated. These films were deposited on glass substrate at 300 °C by d.c. magnetron sputtering using ceramic targets. The W-doping in the sputter-deposited indium oxide film effectively increased the carrier density and the mobility and decreased the resistivity. A minimum resistivity of 1.8 × 10^− 4 Ω cm was obtained at 3.3 at.% W-doping using the In₂O₃ ceramic targets containing 7.0 wt.% WO₃. The 2.2 at.% W-doped films obtained from the targets containing 5.0 wt.% WO₃, showed the high Hall mobility of 73 cm² V^− 1 s^− 1 and relatively low carrier density of 2.9 × 10²⁰ cm^− 3. Such properties resulted in novel characteristics of both low resistivity (3.0 × 10^− 4 Ω cm) and high transmittance in the near-infrared region.     

Study on inverse spinel zinc stannate, Zn2SnO4, as transparent conductive films deposited by rf magnetron sputtering

Inverse spinel zinc stannate (Zn₂SnO₄, ZTO) films were deposited onto fused quartz glass substrates heated at 800 °C by rf magnetron sputtering using a ceramic ZTO target (Zn:Sn = 2:1). H₂ flow ratios [H₂/(Ar + H₂)] were controlled from 0 to 30% during the depositions. ZTO films deposited at 800 °C possessed a polycrystalline inverse spinel structure. The lowest resistivity of 1.1 × 10^− 2 Ω cm was obtained for a ZTO film deposited at 20% H₂ flow ratio. The transmittance of the ZTO film was approximately 80% in the visible region.     

ITO thin films deposited by advanced pulsed laser deposition

Indium tin oxide thin films were deposited by computer assisted advanced PLD method in order to obtain transparent, conductive and homogeneous films on a large area. The films were deposited on glass substrates. We studied the influence of the temperature (room temperature (RT)-180 °C), pressure (1-6 × 10^− 2 Torr), laser fluence (1-4 J/cm²) and wavelength (266-355 nm) on the film properties. The deposition rate, roughness, film structure, optical transmission, electrical conductivity measurements were done. We deposited uniform ITO thin films (thickness 100-600 nm, roughness 5-10 nm) between RT and 180 °C on a large area (5 × 5 cm²). The films have electrical resistivity of 8 × 10^− 4 Ω cm at RT, 5 × 10^− 4 Ω cm at 180 °C and an optical transmission in the visible range, around 89%.     

Effects of oxygen concentration on the properties of sputtered SnO2:Sb films deposited at low temperature

Antimony doped tin oxide (SnO₂:Sb) films have been prepared by d.c. magnetron sputtering and the properties of the films depend on deposition conditions, such as O₂ gas ratio, were investigated. The gas composition was found to affect the properties of the films. With the incorporation additional oxygen, the electrical and optical properties of films significantly improved. The minimum value of resistivity of the films was 4.9 × 10^− 3 Ω cm at the oxygen concentration of 30% and the optical transmittance was over 80%.     

Effects of phosphorus doping source temperatures on fabrication and properties of p-type ZnO thin films

Phosphorus-doped p-type ZnO thin films have been deposited by metalorganic chemical vapor deposition using P₂O₅ as the dopant source. The conductivity types of the as-grown thin films were strongly temperature-dependent. When the substrate temperature maintains at the optimal one of 420 °C, the evaporating temperature of the phosphorus source plays significant roles in controlling the phosphorus content doping into films, then influences the films' performance. Optimizing the growth parameters, the optimal results were obtained with a resistivity of 6.49 Ω cm, a Hall mobility of 0.40 cm²/V s and a hole concentration of 2.42 × 10¹⁸ cm^− 3. The optical property of the optimal film was characterized by PL measurements, which indicated the film is of high optical quality.     

Fabrication of TiO2-based transparent conducting oxide on glass and polyimide substrates

We report on preparation and properties of anatase Nb-doped TiO₂ transparent conducting oxide films on glass and polyimide substrates. Amorphous Ti_0.96Nb_0.04O₂ films were deposited at room temperature by using sputtering, and were then crystallized through annealing under reducing atmosphere. Use of a seed layer substantially improved the crystallinity and resistivity (ρ) of the films. We attained ρ = 9.2 × 10^− 4 Ω cm and transmittance of ~ 70% in the visible region on glass by annealing at 300 °C in vacuum. The minimum ρ of 7.0 × 10^− 4 Ω cm was obtained by 400 °C annealing in pure H₂.     

Electrical and optical properties of amorphous indium zinc oxide films

Valence electron control and electron transport mechanisms on the amorphous indium zinc oxide (IZO) films were investigated. The amorphous IZO films were deposited by dc magnetron sputtering using an oxide ceramic IZO target (89.3 wt.% In₂O₃ and 10.7 wt.% ZnO). N-type impurity dopings, such as Sn, Al or F, could not lead to the increase in carrier density in the IZO. Whereas, H₂ introduction into the IZO deposition process was confirmed to be effective to increase carrier density. By 30% H₂ introduction into the deposition process, carrier density increased from 3.08 × 10²⁰ to 7.65 × 10²⁰ cm^− 3, which must be originated in generations of oxygen vacancies or interstitial Zn²⁺ ions. Decrease in the transmittance in the near infrared region and increase in the optical band gap were observed with the H₂ introduction, which corresponded to the increase in carrier density. The lowest resistivity of 3.39 × 10^− 4 Ω cm was obtained by 10% H₂ introduction without substrate heating during the deposition.     

Fabrication of transparent conducting amorphous Zn-Sn-In-O thin films by direct current magnetron sputtering

Amorphous ZnO-SnO₂-In₂O₃ films were grown by direct current magnetron sputtering from vacuum hot pressed ceramic oxide targets of Zn:In:Sn cation ratios 1:2:1 and 1:2:1.5 onto glass substrates. X-ray diffraction analysis showed that the microstructure remained amorphous during annealing at 200 °C for up to 5 hours. By monitoring the electrical resistivity, oxygen content and substrate temperature were optimized during deposition. The optimal films were characterized by Hall Effect, work function and optical spectroscopy measurements. Films of 1:2:1 composition showed the lowest resistivity (7.6 × 10^− 4 Ω-cm), when deposited onto substrates preheated to 300 °C. Transmissivity of all films exceeded 80% in the visible spectral region. The energy gap was 3.52-3.74 eV, and the work function ranged 5.08-5.22 eV, suitable for cathode applications in organic light emitting diodes. Overall, the film characteristics were comparable or superior to those of amorphous tin-doped indium oxide and zinc-doped indium oxide films and may serve as viable, lower-cost alternatives.     

Indium zinc oxide semiconductor thin films deposited by dc magnetron sputtering at room temperature

Amorphous indium zinc oxide (IZO) thin films were prepared on glass substrates by dc magnetron sputtering at room temperature. The resistivity of IZO films could be controlled between 3.8 × 10⁻³ and 2.5 × 10⁶ Ω cm by varying the oxygen partial pressure during deposition, while keep the average transmittance over 83%. With IZO films as channel layers, whose surface root-mean-square roughness was less than 1 nm, thin film transistors were fabricated at room temperature, showing enhanced mode operation with good saturation characteristics, mobility of 5.2 cm² V⁻¹ s⁻¹, threshold voltage of 0.94 V and on/off ratio of ∼10⁴.     

Effects of deposition parameters on tantalum films deposited by direct current magnetron sputtering

Effects of deposition parameters on tantalum films deposited by direct current magnetron sputtering were studied. The results indicated that the electrical properties were relative to the oxygen and other impurities rather than to growth orientation. As the sputtering power increases from 25 to 100 W, the preferred-growth orientation of Ta films changes from (200) to (202) and the oxygen and impurities content in the films decrease. The temperature coefficient of resistance also reduces from −289.79 to −116.65 ppm/°C. The O/Ta ratio decrease and grain size reduction related to a change of electrical resistivity were observed at substrate temperatures in the range 300-500 °C. At 650 °C, partial stable α-Ta associated with a sharp decrease of the electrical resistivity was also found.