UV Illumination Technique for Leakage Current Reduction in a-Si:H Thin-Film Transistors

• Published in: IEEE transactions on electron devices Vol. 55; no. 11; pp. 3314 - 3318
• Main Authors: YIMING LI, HWANG, Chih-Hong, CHEN, Chung-Le, SHUOTING YAN, LOU, Jen-Chung
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.11.2008; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Amorphous silicon; Amorphous silicon thin-film transistors (a-Si:H TFTs); Applied sciences; band-to-band tunneling; device simulation and characterization; Devices; Electronics; Exact sciences and technology; Illumination; Leakage current; Reduction; Semiconductor devices; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Silicon; Thin film transistors; Thin films; Transistors; trap-assisted tunneling; Tunneling; ultraviolet (UV) illumination; trap-assisted tunneling; Amorphous material; Voltage current curve; Ultraviolet laser; Backlighting; Tunnel effect; device simulation and characterization; Active layer; Photoinduced effect; band-to-band tunneling; Charge carrier trapping; Ultraviolet irradiation; Fermi level; Amorphous silicon thin-film transistors (a-Si:H TFTs); Amorphous hydrogenated material; Illumination; SPICE; Leakage current; Thin film transistor; ultraviolet (UV) illumination; Photoconductivity
• ISSN: 0018-9383; 1557-9646
• DOI: 10.1109/TED.2008.2005133

The high photoconductivity of hydrogenated amorphous silicon thin-film transistors (a-Si:H TFTs) is responsible for the leakage current under illumination-particularly in projectors and displays with high-intensity backlight illumination. This work investigates a leakage current reduction approach, in which the inverted staggered a-Si:H TFTs are exposed to the ultraviolet (UV) laser. An 85% reduction in the leakage current in a-Si:H TFTs is experimentally observed. The general SPICE model (such as the RPI model) lacks the proper term to capture the photo-induced phenomena; therefore, the physical mechanisms that are associated with the illumination of a-Si:H TFTs under UV, including the energy state and the density of traps, are analyzed using device simulation. The I-V characteristics of the inverted staggered a-Si:H TFTs under different magnitudes of UV exposure are calibrated with experimentally measured data. The preliminary results show the change of trap states in amorphous silicon film and a shift of the Fermi level with UV illumination. UV illumination may induce traps in the active layer of the device and thereby reduce the OFF-state leakage current.