Optical and structural properties of multi-period low-emissivity filters by RF magnetron sputtering

초록

Multi-period low-emissivity (low-e) filters based on the basic structure of [TiO2|Ti|Ag|TiO2] were designed and fabricated by RF magnetron sputtering method. The optical performance of the filters was examined by the measurement of transmittance and reflectance with a spectrophotometer. Also, the structural, chemical, and electrical properties were investigated by the scanning electron microscopy (SEM), Auger electron spectroscopy (AES), Rutherford backscattering spectrometry (RBS), and the four-point probe method. The optimized structure of [air|TiO2(24 nm)|Ti(1.5 nm)|Ag(17 nm)|TiO2(48 nm)|Ti(1.5 nm)|Ag(13 nm)|TiO2(48 nm)| Ti(1.5 nm)|Ag(13 nm)|TiO2(24 nm)|glass] showed the best optical and electrical performances : the average transmittance was 61.1% in the visible and the sheet resistance was 0.9 Ω/sq, but it turned out that the 1.5 nm thickness of Ti layers was not enough to protect the Ag layers completely and there was a little discrepancy between the measured and simulated transmittances in the visible. To prevent the diffusion effectively and eliminate the discrepancy, the thickness of the Ti layers was increased 1.8 nm so that the Ag layers were less destroyed and diffused and the measured optical spectra were in better agreement with the simulated one. However, the average transmittance was reduced to 53.4 % and the sheet resistance was increased to 1.16 Ω/sq, while the transmittance above 800 nm was below 5.7 %, less than the 6.6 % of the structure with the 1.5 nm barriers. Consequently, the transmittance of the optimized three periods filter was very low in the near IR and the sheet resistance was low enough to shield the electromagnetic waves. The results suggest that the multiple repetition of the basic structure can be used for display applications.