Amorphous indium gallium zinc oxide (a-IGZO) is a transparent semiconductor which has demonstrated excellent electrical performance as thin-film transistors (TFTs). However, a high-temperature activation process is generally required which is incompatible for next-generation flexible electronic applications. In this work, He+ irradiation is demonstrated as an athermal activation process for a-IGZO TFTs. Controlling the He+ dose enables the tuning of charge density, and a dose of 1 × 1014 He+/cm2 induces a change in charge density of 2.3 × 1012 cm-2. Time-dependent transport measurements and time-of-flight secondary ion mass spectroscopy (ToF-SIMS) indicate that the He+-induced trapped charge is introduced because of preferential oxygen-vacancy generation. Scanning microwave impedance microscopy confirms that He+ irradiation improves the conductivity of the a-IGZO. For realization of a permanent activation, IGZO was exposed with a He+ dose of 5 × 1014 He+/cm2 and then aged 24 h to allow decay of the trapped oxide charge originating for electron-hole pair generation. The resultant shift in the charge density is primarily attributed to oxygen vacancies generated by He+ sputtering in the near-surface region.
Keywords: IGZO; athermal; flexible electronics; helium ion; low-temperature activation; transistors.