## 3 Results and Discussion
\begin{table}
\begin{tabular}{l c c c c c} \hline Concentration of Ti [at.%] & 0 & 3.4 & 6.8 & 9.6 & 12.9 & 22.7 \\ \hline Grain sizes [nm] & 69.4 \(\pm\) 1.2 & 56.8 \(\pm\) 1.4 & 50.4 \(\pm\) 1.6 & 34.1 \(\pm\) 2.2 & 29.5 \(\pm\) 1.1 & 28.2 \(\pm\) 1.9 \\ \hline \end{tabular}
\end{table} 
Table 3: Grain sizes of the WTi films with respect to the Ti content. Figure 2: XRD patterns of WTi alloy films as a function of Ti concentrations. Due to the small thickness of the film sample, the resistance caused by the scattering of electrons on the film surface accounts for a large proportion of the total resistance, that is, the roughness of the film surface will affect the resistivity of the film. To study the surface roughness of the W and WTi alloy films, an AFM was used to characterize the surface roughness of the samples, as shown in Figure 4. The surface roughness of the pure W film was 14.8 nm. After Ti was added, the surface roughness of the WTi alloy film decreased. This is because the melting point of Ti is smaller than that of W, the undercooling degree of Ti is smaller in the sputtering process, and the diffusion ability is stronger. The roughness of the WTi alloy films with different Ti contents was about 10 nm, and the electron scattering ability of the film surface was similar. The resistivity of pure W film was 13.3 \(\mu\Omega\)-cm, which increased rapidly to 25.9 \(\mu\Omega\)-cm (3 at.% Ti) with the increase in Ti content. The highest resistivity was 33.5 \(\mu\Omega\)-cm when Ti content was 22.7 at.%, as shown in Figure 5a. After Ti was dissolved in W, some W atoms were replaced, and lattice distortion occurred, the lattice vibration increased, the scattering effect of the lattice on electrons increased, and the resistivity increased. Figure 5b shows the thermal resistance curves of the W and WTi films. The resistance of W and WTi alloy films increased with the increase in temperature, indicating that W and WTi alloys  
Figure 4: Surface AFM images and roughness of the WTi alloys films as a function of Ti concentrations. Figure 3: Surface and cross-section SEM images of the WTi alloys films as a function of Ti concentrations. have positive temperature coefficients. The TCR of pure W films was 5.4 \(\times\) 10\({}^{-4}\) K\({}^{-1}\), and the TCR increased rapidly to 14.2 \(\times\) 10\({}^{-4}\) K\({}^{-1}\) with the addition of a small amount of Ti. The resistance inside the grain was increased by the Ti replacement of part of W in the W lattice, which made the TCR increase. With the increase in the Ti content, the TCR of the WTi alloy films increased first and then decreased. When Ti content increased from 3.4 at.% to 6.8 at.%, the number of Ti atoms in the solid solution of the W lattice increased, which made the resistance inside the grain increase, the electron scattering ability of the lattice is enhanced, and the TCR increases. As the content of Ti continued to increase, the number of Ti atoms in solid solution further increased, and the TCR of Ti was less than that of W (TCR\({}_{\rm W}\) = 0.0049/K, TCR\({}_{\rm Ti}\) = 0.0041/K), which made the TCR of the alloy thin film decrease. Moreover, with the increase in Ti content, the grain size of the WTi alloy film decreased, which also led to a decrease in TCR. When Ti content was 6.8 at.%, TCR reached the maximum value of 19.5 \(\times\) 10\({}^{-4}\) K\({}^{-1}\). Compared with the pure W films, TCR increased by 3.6 times, and the linearity of linear fitting was very high, indicating that the WTi alloy films have good thermal resistance. The thermal resistance repeatability test was carried out for the WTi film with 6.8 at.% Ti content. Figure 6 shows the (a) thermal resistance curve and (b)TCR of the 6.8 at.% Ti alloy film after repeated tests. After being repeated at different times, the resistance of the WTi film increased with the increase in temperature, but the slope of the thermal resistance curve decreased gradually, the increase in resistance decreased, and the TCR decreased gradually.