Toshikazu Kakumu

Highly Transparent and Conductive Zn2In2O5 Thin Films Prepared by RF Magnetron Sputtering

A new transparent conducting Zn2In2O5 film is demonstrated. The film was prepared by rf magnetron sputtering using binary compound targets composed of In2O3 and ZnO (with a Zn content (Zn/(Zn+In)) of 5-45 at%). The electrical properties were relatively independent of the substrate temperatures between room temperature and 350° C. A resistivity of 3.9×10-4 Ω· cm and an average transmittance above 80% in the visible range were obtained for undoped Zn2In2O5 films with a thickness of about 400 nm. The spatial resistivity distribution on the substrate surface was minimal for Zn2In2O5 films. Optical measurements showed a band-gap energy of about 2.9 eV and a refractive index of about 2.4 for Zn2In2O5. It was found that the resistance of the undoped Zn2In2O5 films was more stable than that of undoped ZnO or In2O3 films in oxidizing environments at high temperatures.

Preparation of transparent and conductive In2O3–ZnO films by radio frequency magnetron sputtering

Highly transparent and conductive In2O3–ZnO films have been prepared by rf magnetron sputtering using targets composed of In2O3 and ZnO. Polycrystalline Zn2In2O5 films were deposited at a substrate temperature of 350 °C using targets with a Zn content [Zn/(Zn+In)] of about 10–60 at. %. A uniform spatial resistivity distribution on the substrate surface was obtained even in Zn2In2O5 films deposited at room temperature. A resistivity of 3.4×10−4 Ω cm was obtained in Sn‐doped Zn2In2O5 films deposited at 350 °C. A sheet resistance of 400 Ω/sq and an average transmittance above 90% in the visible range were obtained for an undoped Zn2In2O5 film with a thickness of about 20 nm. The etching rate of In2O3–ZnO films when using HCl as the etchant could be controlled by the Zn content in the films.

Physics of very thin ITO conducting films with high transparency prepared by DC magnetron sputtering

The preparation of very thin indium tin oxide (ITO) films with extremely high transparency and suitable resistivity, as well as resistivity stability for long term use, is described. In order to obtain these properties, amorphous suboxide films were first prepared and then annealed. Suboxide films with a thickness of 20 to 30 nm were prepared on PET film and glass substrates at a temperature of 60 °C using In2O3SnO2 targets with a SnO2 content of 0 to 10 wt% by DC magnetron sputtering in a pure argon gas atmosphere. The films were annealed at a temperature of 150 °C for 1 to 100 h in air. The resistivity of films on PET films was, depending on the SnO2 content, on the order of 10−3 ω cm. An average transmittance above 97% in the visible wavelength range and a resistivity of about 4 × 10−3 ω cm, as well as resistivity stability, were attained in ITO films with a SnO2 content of about 1 wt% prepared on PET films by the low-temperature process. It is thought that these properties result from crystallization which occurred during the annealing, duration up to about 25 h.

Highly transparent and conductive ZnOIn2O3 thin films prepared by d.c. magnetron sputtering

Abstract Transparent conducting In2O3Zn2In2O5ZnO thin films with electrical, optical and chemical properties that varied with the composition were prepared by d.c. magnetron sputtering. The maximum carrier concentration and minimum resistivity were obtained for a Zn2In2O5 film prepared on substrates at room temperature (RT) using a target with a Zn content ([Zn]/[Zn+In] atomic ratio) of 0.245, and those of a Zn2In2O5 film prepared at 350 °C were obtained with a Zn content of 0.422. A maximum refractive index of about 2.6 and minimum band gap energy of about 3 eV were obtained for the Zn2In2O5 films. A resistivity of 2.9 × 10−4 Ω cm was obtained in a Zn2In2O5 film deposited at RT. A sheet resistance of 250 Ω/□ and an average transmittance above 95% in the visible range were obtained for a Zn2In2O5 film with a thickness of about 20 nm. The etching rate of Zn2In2O5 films was about 500 nm min−1 when using a 0.2 M HCl solution.

New transparent conducting ZnO-In2O3-SnO2 thin films prepared by magnetron sputtering

Abstract New multicomponent ZnO–In 2 O 3 –SnO 2 system and new In 4 Sn 3 O 12 transparent conducting oxide thin films have been prepared by RF magnetron sputtering. The In 4 Sn 3 O 12 films, or In 2 O 3 –SnO 2 films with a Sn/(In+Sn) atomic ratio around 0.5, showed a resistivity of 3–4×10 −4 Ω cm and an average transmittance above 80% in the visible range when they were prepared at substrate temperatures of room temperature to 350°C. In addition, the electrical properties of multicomponent Zn 2 In 2 O 5 –ZnSnO 3 films changed monotonically as the ZnSnO 3 content was varied.

Preparation of transparent conducting In4Sn3O12 thin films by DC magnetron sputtering

Abstract Highly conductive and transparent In4Sn3O12 films have been prepared by DC magnetron sputtering using In2O3-SnO2 targets with a Sn content (Sn/(Sn+In) atomic ratio) of 45–55 atomic %. In4Sn3O12 films with a low resistivity on the order of 10−4 Ωcm were prepared in the substrate temperature range of room temperature (RT) to 350°C, at a sputter pressure of 0.2 Pa with an O2 gas content of 4%. The obtained resistivity decreased gradually as the film thickness was increased from 20 to 300 nm. In4Sn3O12 films prepared on substrates at RT exhibited a spatial resistivity distribution on their surface which was strongly dependent on the O2 gas content. The spatial resistivity distribution was mainly related to the amount of oxygen gas available locally at locations on the substrate. A resistivity of 2×10−4 Ωcm and an average transmittance above 80% in the visible range were obtained for films prepared at a substrate temperature of 350°C. A carrier concentration on the order of 1021 cm−3 and a Hall mobility as high as 20 cm2 V−1 s−1 were obtained in the In4Sn3O12 films.

New transparent conducting MgIn2O4Zn2In2O5 thin films prepared by magnetron sputtering

Abstract New materials for a transparent conducting oxide film are demonstrated. Highly transparent Zn2In2O5 films with a resistivity of 3.9 × 10−4 Ω cm were prepared on substrates at room temperature using a pseudobinary compound powder target composed of ZnO (50 mol.%) and In2O3 (50 mol.%) by r.f. magnetron sputtering. MgIn2O4Zn2In2O5 films were prepared using MgIn2O4 targets with a ZnO content of 0–100 wt.%. The resistivity of the deposited films gradually decreased from 2 × 10−3 to 3.9 × 10−4 Ω cm as the Zn (Mg + Zn) atomic ratio introduced into the films was increased. The greatest transparency was obtained in a MgIn2O4 film. The optical absorption edge of the films decreased as the Zn/(Mg + Zn) atomic ratio was increased, corresponding to the bandgap energy of their materials. It was found that the resistance of the undoped Zn2In2O5 films was more stable than either the undoped MgIn2O4, ZnO or In2O3 films in oxidizing environments at high temperatures.

Preparation of highly transparent and conducting Ga2O3–In2O3 films by direct current magnetron sputtering

Multicomponent Ga2O3–In2O3 films have been prepared by dc magnetron sputtering using targets with a Ga content [Ga/(In+Ga) atomic ratio] of 0–60 at. %. Transparent conducting thin films prepared with Ga contents up to about 40 at. % were identified as Ga-doped In2O3 (In2O3:Ga). A minimum resistivity of 5.8×10−4 Ω cm and a maximum carrier concentration of 5×1020 cm−3 were obtained in an In2O3:Ga film prepared at a substrate temperature of room temperature with a Ga content of 30 at. %. Transparent conducting thin films prepared with a Ga content of 45–50 at. % were identified as a ternary compound: gallium indium oxide, (Ga,In)2O3. The electrical properties exhibited by the (Ga,In)2O3 films were relatively independent of the substrate temperature from room temperature to 350 °C. A sheet resistance of 1–2 kΩ and an average transmittance above 95% were obtained in (Ga,In)2O3 films with a thickness of about 20 nm and prepared with a Ga content of 50 at. %.

Preparation of transparent conducting Zn2In2O5 films by d.c. magnetron sputtering

Highly transparent and conductive Zn2In2O5 films have been prepared by d.c. magnetron sputtering using targets composed of ZnO and In2O3. The films deposited on substrates at a temperature of 350°C using targets with a composition (Zn:(In+Zn) atomic ratio) of approximately 20 to 60 at.% were identified as Zn2In2O5. The etching rate of the films in a HCl solution was strongly dependent on the Zn:(In+Zn) atomic ratio and the substrate temperature. Zn2In2O5 films deposited on substrates at a temperature of room temperature to 350°C exhibited a resistivity of 2–4×10−4 Ω cm. An average transmittance of above 85% in the visible range was obtained in the films.

New Materials Consisting of Multicomponent Oxides for Thin‐Film Gas Sensors

High sensitivity for specific gas detection has been realized by new gas sensors incorporating multicomponent oxide thin films such as ZnO-In 2 O 3 , MgO-In 2 O 3 , and Zn 2 In0 5 -MgIn 2 O 4 systems. The sensing properties of the multicomponent oxide thin-film sensors were strongly dependent on the composition of the films used. Sensors using ternary compounds such as Zn 2 In 2 O 5 and MgIn 2 O 4 always exhibited a higher sensitivity than those using binary compounds such as ZnO and In 2 O 3 . The sensors only exhibited an increase in resistance with exposure to carbon tetrachloride (CCl 4 ) gas, whereas they exhibited a decrease in resistance for inflammable gases such as butane (C 4 H 10 ) and hexane (C 6 H 14 ). The highest sensitivity for CCl 4 gas was obtained in a sensor using a Zn 2 In 2 O 5 -MgIn 2 O 4 thin film prepared with a Zn 2 In 2 O 5 content of about 60 mole percent. The resistance of sensors operated at 300°C was increased by a factor of about 10 when exposed to CCl 4 gas with a concentration of 350 ppm. The increase in resistance is attributed to the trapping of free electrons resulting from chlorine being adsorbed on grain boundaries and/or the film surface.