A comparative study of ITO Ti and Cu metal mesh resonant filters for THz applications

Demirhan, Yasemin
Kurt, Metin
Alaboz, Hakan
Semerci, Tuğçe
Özyüzer, Lütfi
Nebioğlu, Mehmet Ali
Takan, Taylan
Altan, Hakan
Sabah, Cumali
Terahertz (THz) radiation is part of the electromagnetic spectrum lying between microwaves and the far-IR. Sensing and imaging using terahertz waves is a rapidly progressing technology which has wide-range applications in different areas such as security, medicine, quality control and etc. The importance of developing passive and active devices which work in terahertz frequencies is ever more increasing in this popular field [1]. One of the most important devices in THz applications is band pass filters, which could be widely applied to imaging, spectroscopy, molecular sensing, security, drug identification, or other systems [2]. Cross-shaped apertures have advantages in fabrication of the bandpass filters. Periodicity G, cross member length K, and cross-member width J determine the performance of these filters. Provided that G is smaller with respect to the wavelength, it is possible to shift the filter profile by linearly scaling the dimensions G, K, and J and this fact very much simplifies the design of resonant meshes. In this study, we report on resonant metal-mesh bandpass filters made up of metal films (typically 100-500 nm thick) perforated with arrays of cross-shaped apertures. Design of the filter structures was created by CST microwave studio program. The layout of the filter design is shown in Fig. 1. We use 2 mm thick quartz as the substrate because of its low loss at THz. ITO, Ti and Cu were chosen as the metallic layer due to their good attachment to the substrate. These films were grown in high vacuum magnetron sputtering system. Terahertz resonant metal-mesh filters were fabricated using the UV photolithography and Ar ion beam etching techniques. After fabrication, the samples were measured using a Bruker Vertex V80 FTIR spectrometer. Transmission measurements have shown center frequencies and bandwidths close to the design predictions as seen in Fig. 2. The measured results showed an insertion loss, which is due to the finite conductivity of the metal films and some loss in the substrate. Finally the created structures were characterized using time-domain THz spectroscopy (THz-TDS) systems. The measurements will be discussed in the light of surface conductivity of deposited films.