# A High-Performance Thin-Film Sensor in 6G for Remote Sensing of the Sea Surface
## 2 Experimental Design
The Si substrate, which was coated with the thin film, was cut from the back side and positioned upright to measure the film thickness in the cross-section. The figure demonstrates that the coating thickness was consistent and measured at 4.24 \(\upmu\)m.  
Finally, copper (Cu) electrodes were fabricated on the prepared Te films with an electrode pitch of 5 mm. The fabrication process involved the following steps. First, the air pressure was reduced to 1 \(\times\) 10\({}^{-5}\) Pa, and argon gas was introduced into the cavity. The Cu target was then coated using a direct current (DC) drive mode. The specific parameters for this process were set as follows: an argon flow rate of 15 SCCM, a current of 0.2 A, and a duration time of 90 s.  
In order to investigate the properties of films in the THz band under various crystallization conditions, such as transmittance and complex conductivity, the transmittance spectra of the films were examined using THz-TDS. The laser used in THz-TDS had a central wavelength of 780 nm, a repetition frequency of 80 MHz, a pulse width of 90 fs, and a spectral width of 7 nm. Figure 3 illustrates the characterization of Te thin films in the THz band. The results of the tests indicated that the lowest THz transmittance was observed at an annealing temperature of 100 \({}^{\circ}\)C. This finding suggests that the degree of crystallization was optimal at this temperature, as the atoms became regularly arranged and the carriers were more uniformly bound around them. Consequently, the transmission rate of the incident THz wave decreased. The experimental data revealed the transmission rates of Te films with thicknesses of 4.24 \(\upmu\)m and varying degrees of crystallinity (annealed at 100 \({}^{\circ}\)C, 200 \({}^{\circ}\)C, and no annealing) in the THz range from 56% to 78%, 61% to 85%, and 67% to 94%, respectively. Figure 3: Characterization of Te thin films in the THz band. (**a**) THz pulses through thin films at different annealing temperatures. (**b**) Fourier transform results of (**a,c**) THz transmittance of thin films with different annealing temperatures. (**d**) Complex conductivity of thin films with different annealing temperatures in the THz band. Figure 2: Characterization of Te thin films. (**a**) Raman spectra of Te films at different annealing temperatures. (**b**) SEM images of film thickness. (**c**) Raman spectral intensity and incident angle of samples with different annealing temperatures and polarization. (**d**) Raman spectra of different laser polarization incidence for 100 \({}^{\circ}\)C annealing temperature Te film. Furthermore, variations in the degree of crystallinity result in distinct atomic binding capabilities of the carriers, consequently leading to notable disparities in the complex conductivity of the films. It is observed that a higher degree of crystallization corresponds to a greater magnitude of complex conductivity. Figure 2b shows the complex conductivity of the Te nanofilm at room temperature. The ordinary Drude equation was also employed to fit the frequency dependence of conductivity [37]:  
\[\sigma(\omega)=\sigma_{0}\frac{1}{1-i\omega\tau} \tag{2}\]  
Here, \(\omega\) indicates the frequency of the THz wave, \(\tau\) is the quasi-particle relaxation time, and \(\sigma_{0}\) is the DC conductivity. The results of the complex conductivity in the THz band show the best complex conductivity parameters at the preferred annealing temperature, i.e., 60 min at 100 \({}^{\circ}\)C. The Te films produced under these specific conditions exhibit enhanced suitability for devices operating within the THz frequency range.