CdGaO and CdInO amorphous transparent conducting oxide on flexible substrates

Abstract

In this study, Cd_1-xGa_xO films had been manufactured on glass, and flexible plastic substrates by sputtering at room temperature to investigate its electrical properties, optical properties and flexibility. The result shows that Cd_1-xGa_xO films had similar electrical properties and optical properties when grown on glass and plastic substrates. Depending on their composition, the films had electron concentrations in the range of ~2 − 7 × 10^20cm^-3, mobilities ~10 − 20cm^3/Vs and resistivities ~1 × 10^3Ω − cm while they are all ~80% transmission in the visible range. For films with composition 𝑥 > 3, their crystal structure are amorphous. To investigate the flexibility of Cd_1-xGa_xO films. Both crystalline and amorphous Cd_1-xGa_xO films were bent over different radius in both inward and outward directions. After bending their electrical properties were compared with their respective as-grown state. Results suggested that all the Cd_1-xGa_xO films were more resistive to the bending test up to a bending radius of 8 mm. The relative variations of the resistivity of amorphous films bent inside were smaller than crystalline films for different bending radius and repeated bending (up to 100 times). For outer bending, crystalline films show a lower change of the resistivity at first, but the variation became the same when bent ≥20 times for both crystalline and amorphous films. Our result shows that the amorphous Cd_1-xGa_xO films have high transparency, high conductivity and flexibility to be used as transparent conductors for flexible electronic applications.

Currently, Transparent Conducting Oxides (TCOs) could not use at flexible application since they need a high temperature deposition and annealing process to achieve good electrical properties. There is a new class of amorphous semiconductor call Amorphous Ionic Oxide Semiconductor has been found. It has a very good transparency and a low temperature deposition. Most Importantly, AIOSs have good electrical properties, which are the mobility above 10 cm^2V^-1s^-1, and conductivity above 1000 S/cm, so it has a huge potential on some application which require flexible substrate. In this experiment, 13 different compositions of Cd_xIn_1-xO_1+δ were form on both glass and plastic substrate with similar electrical properties. And the amorphous states are between composition from x=0.06 to x=0.35. To identify the flexibility of AIOS, three types of samples, crystalline, pseudocrystalline and amorphous were selected to do bending, after the bending procedure, the resistivities were compared. When those three samples were bent inner side once with different diameters, there is no change for the resistivity of amorphous state, from the diameter is above 18mm, but the performance was poor when bent outer side. Another comparison is bent the samples with multiple time until 100 times. The results show that when the diameter is close to 33mm, the flexibility of Cd_xIn_1-xO_1+δ is promised. Since the diameter of 33mm is still small, this Cd_xIn_1-xO_1+δ is suitable for flexible electronics.