Electrode patterning and annealing processes of aluminum-doped zinc oxide thin films using a UV laser system

• Published in: Optics and lasers in engineering 2013-01, Vol.51 (1), p.15-22
• Main Authors: Hsiao, Wen-Tse, Tseng, Shih-Feng, Huang, Kuo-Cheng, Chiang, Donyau
• Format: Article
• Language: English
• Subjects: Ablation; Aluminum-doped zinc oxide (AZO); Annealing; Azo; Galvanometers; Laser pattern and anneal; Lasers; Mathematical analysis; Optoelectronic properties; Patterning; Scanning; Scanning electron microscopy; Structural properties; Thin films; Transmittance
• ISSN: 0143-8166; 1873-0302
• DOI: 10.1016/j.optlaseng.2012.08.003

This study presents the hybrid processing (patterning and annealing) of aluminum-doped zinc oxide (AZO) films in a one-step process using a diode-pumped-solid-state (DPSS) ultraviolet (UV) laser system. The focused laser beam had a diameter of 30μm and the positive defocused laser beam had a diameter of 1mm. Both beams were adjusted using a UV laser-processing system. AZO films were deposited on Corning Eagle 2000® optical glass sheets with a thickness of 0.7mm using a sputtering method. The deposited films were approximately 200nm. The optoelectronic properties of machined (patterning and annealing) AZO films depend on the laser pulse frequency and galvanometer scanning speed. The surface morphology, roughness, optical transmittance, and resistivity of the films after the laser patterning and annealing processes were measured using a three-dimensional confocal laser scanning microscope, a field emission scanning electron microscope (FE-SEM), a spectrophotometer, and a four-point probe instrument, respectively. Experimental results indicate that the ablation depth increased as the pulse repetition frequency increased. The ablation depth also decreased as the galvanometric scanning speed increased. The transmittance spectra of the film changes slightly after laser annealing, and the average transmittance in the visible region is approximately 83%. All resistivity values of laser-patterned and annealed AZO films decreased significantly. The structural properties grain size was calculated firm the X-ray diffraction (XRD) spectra using the Scherrer equation that increased from 7.4nm to 12nm as the annealing scanning speed decreased from 800mm/s to 400mm/s. The root mean square (RMS) values of annealed AZO films treated with a laser scanning speed of 500mm/s with a pulse repetition frequency of 40kHz, 55kHz, and 70kHz were 1.1nm, 1.2nm, and 1.8nm, respectively. ► Hybrid (patterning and annealing) processing approach of AZO films in one-step process using UV laser system. ► The ablation depth were depended on the pulse repetition frequency and galvanometric scan speed. ► After laser annealing, the average transmittance in visible region were approximately 83%. ► All resistivity values of laser-patterned and annealed AZO films decreased significantly. ► The grain size increased as the annealing scanning speed decreased.