We achieved the lowest contact resistance between a-IGZO and a metal electrode for >30 GHz operation of an oxide semiconductor device. For high-resolution display and high-speed electronic devices, both bulk and contact resistances need to be reduced. In this study, hydrogen plasma was used to lower the contact resistance significantly by modifying the surface of the a-IGZO thin film. The potential barrier width at the interface was decreased by increasing the carrier concentration, and weak M−OH bonds were sufficiently diffused out with optimized plasma process. The minimum contact resistance was measured to be 1.33 × 10 −6 Ω•cm 2 by the transfer line method, which is the lowest reported value to the best of our knowledge. Utilizing this enhanced contact property between a-IGZO and metal, the metal−insulator−semiconductor varactor was fabricated, and its operating frequency was measured to be higher than 30 GHz.

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