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 cm2/(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.