Deposition, Characterization, and Performance of Spinel InGaZnO4

Polycrystalline indium-gallium-zinc oxide (IGZO) in the spinel phase was obtained by physical vapor deposition (PVD), using reactive sputtering from an IGZO target with In/Ga/Zn = 1:1:1 composition. The initial growth of spinel IGZO is investigated by X-ray diffraction measurements after annealing the film. Deposition of spinel IGZO initially starts as a mixed amorphous/c-axis-aligned crystalline (CAAC) film, after which a metastable spinel IGZO is formed. Using a template of polycrystalline spinel Ga2ZnO4, the growth of the spinel phase is immediately achieved and enables the electrical characterization of pure spinel IGZO channels in scaled thin-film field-effect transistors. The average effective channel field-effect mobility of spinel IGZO of 50 +/- 10 cm(2)/(V s) is slightly higher than amorphous IGZO in the same devices. This is in line with a slightly lower effective electron mass, as is calculated with density functional theory. The calculated total energies and band gaps have similar values to CAAC-IGZO. This metastable nature identifies spinel IGZO as an intermediate phase before the onset of CAAC-IGZO formation during PVD. Spinel IGZO is an interesting alternative to amorphous IGZO (a-IGZO) and CAAC-IGZO because of potentially higher robustness to oxygen vacancy formation.

Automated summary

Polycrystalline indium-gallium-zinc oxide (IGZO) in the spinel phase was successfully obtained by physical vapor deposition (PVD) and its growth process and electrical properties were investigated. It was found that spinel IGZO exhibited higher channel field-effect mobility and lower effective electron mass, indicating its potential for higher stability. Therefore, spinel IGZO is an interesting alternative to amorphous and CAAC phase IGZO.