Deposition of low emissivity filters for display applications

초록

A low emissivity (low-e) filter can be used not only to cut off the near infrared (NIR) but the hazardous EM-waves in the visual display unit (VDU). The filter of VDU is noteworthy for anti-static function and conductive property together with the NIR cut-off function since the high conductive Ag layer is used. In this study, we designed and deposited the low-e filters by the RF-magnetron sputtering. The basic structure of the filters was [air|TiO2|Ti|Ag|TiO2|glass] for high transmittance and low reflectance in the visible. A simple repetition of the structure four times was carried out to reduce the transmittance in the NIR and the electrical resistance. The transmittance and reflectance of low-e filters were measured by a spectrophotometer and the sheet resistance was measured by a 4-point probe. The photopic average transmittance and reflectance of the 13-layer low-e filter were 45% and 4.6% in the visible and the transmittance beyond 800 nm was under 15%. As the number of the repeating period was increased up to four, the sheet resistance and emissivity were decreased to 2.75 Ω/sq and 0.035, respectively. In this experiment, the best performance was achieved in the modified structure of three Ag layers, which had a thicker Ag layer of 20 nm in the final period. The photopic average transmittance and reflectance were 57 % and 3.8 % in the visible and the transmittance beyond 800 nm was under 6 %. Also, the sheet resistance and emissivity were reduced to 1.6 Ω/sq and 0.021, respectively.