Electrical property relaxation characteristics of UV-treated ZnO-based thin film transistors

• Published in: Thin solid films 2013-01, Vol.527, p.334-337
• Main Authors: Jin, Sun Moon, Cho, Nam-Ihn, Yun, Eui-Jung, Nam, Hyoung Gin
• Format: Article
• Language: English
• Subjects: Applied sciences; Channels; Charge carriers: generation, recombination, lifetime, trapping, mean free paths; Charge trapping; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Deionization; Diffusion; interface formation; Electrical properties; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Electronic transport phenomena in thin films and low-dimensional structures; Electronics; Exact sciences and technology; Gates; Oxygen vacancy ionization; Physics; Secondary ion mass spectrometry; Semiconductor devices; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Solid surfaces and solid-solid interfaces; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Thin film transistors; Transistors; Transparent thin film transistor; Ultraviolet photoelectron spectroscopy; Ultraviolet treatment; Voltage; X-ray photoelectron spectroscopy; Zinc oxide
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/j.tsf.2012.11.057

We investigated the transient electrical response of deep UV or near UV-treated ZnO-based bottom gate transparent thin film transistors (TTFTs). In both cases, the turn-on voltage (VON) negatively shifts due to the treatment and subsequently relaxes in the positive direction. The subthreshold swing as well as the off-current also decreases with time following the initial increase. However, VON of the near UV-treated TTFT apparently recovers its initial value, whereas that of the deep UV-treated TTFT fails to fully return. Furthermore, the relaxation of the electrical properties with time appears much faster in case of the near UV-treated TTFT. We demonstrated that exposure to the near UV illumination does not affect SiNx, the gate insulator (GI), and that the reversible variation of electrical properties in this case is a consequence of the ionization/deionization of oxygen vacancies present in ZnO. In case of the deep UV-treated TTFT, on the other hand, GI also absorbs the UV energy to induce inter-diffusion of oxygen and hydrogen near the ZnO/SiNx interface. We stated that these spectroscopic changes near the channel region brought about irreversible modifications to the electrical properties of the deep UV-treated TTFT as well as formation of new trap centers in GI. The slower recovery in this case is a consequence of de-trapping of the charges trapped by the centers newly formed in SiNx near the interface. ► We report property variation of UV-treated ZnO-based thin film transistors. ► Near UV-treatment results in reversible and fast electrical property variation. ► Near UV-treatment does not induce spectroscopic changes in both ZnO and SiNx. ► Deep UV-treatment results in irreversible and slow property variation. ► Deep UV-treatment induces spectroscopic changes in both ZnO and SiNx.