Influence of negative metal ion bombardment on the properties of ITO/PET films deposited by dc magnetron sputtering

Transparent conducting indium tin oxide (ITO) thin films were deposited on a polyethylene terephthalate (PET) substrate at a low substrate temperature by dc magnetron sputtering using a negative metal ion source and an ITO target. During separate deposition runs, the cesium partial pressure was varied from 1 × 10−3 to 2.2 × 10-3 Pa to investigate the effect of ion beam bombardment on the surface morphological, electrical and optical properties of the films. The resistivity of ITO films decreased with PCs and reached as low as 6.2 × 10−4 Ω cm at PCs of 1.7 × 10−3 Pa. Optical transmittance compared with bare PET substrate also varied significantly with PCs and the highest optical transmittance of 87% (at λ=550 nm) was obtained at PCs of 1.7 × 10−3 Pa. According to a result obtained by AFM, surface roughness of the ITO/PET film showed remarkable change from 2.8 to 1.1 nm with PCs. However, above optimal PCs condition (>1.7 × 10−3 Pa), the electrical, optical property and surface morphological properties deteriorated. From SEM, AFM, and Hall measurements, relatively low resistivity and high transmittance of ITO film deposited at PCs=1.7×10−3 Pa is caused by an increase in charge carrier concentration and flat surface morphology with secondary negative metal ion beam bombardment.