## 3 Results and Discussion  
According to the theory of the conductive mechanism of films, the resistance of films is divided into the resistance within the grain and the resistance at the grain boundary. The increase in the resistance inside the grain increases the TCR, while the increase in the resistance at the grain boundary decreases the TCR. By adding a small number of other metal elements into W, a single-phase solid solution alloy film can be obtained, which can greatly improve the internal resistance of the grain and thus improve the thermal resistance of the film. A small number of Ti atoms in W was added to form a single-phase replacement solid solution, which can improve the thermal resistance of W film. By changing the clamping position of the matrix, WTi alloy films with Ti atomic ratios of 3.4 at.%, 6.8 at.%, 9.6 at.%, 12.9 at.%, and 22.7 at.% were obtained, which were compared with pure W films. The phase structures of W and WTi alloy thin films were characterized, as shown in Figure 2. The prepared pure W thin film was single-phase \(\alpha\)-W with (110) grain orientation (JCPDS No.040806). There were only (110) and (220) characteristic diffraction peaks of \(\alpha\)-W in the WTi alloy films with different Ti contents, but no characteristic peaks of Ti, which indicates that there is no elemental Ti in the alloy films, and Ti is all solid dissolved in the W lattice to form a single-phase solid solution. With the increase in the Ti content in the alloy film, the more Ti in the solid solution in the W lattice, the more serious the lattice distortion. The atomic radius of W is 1.41 A, and the atomic radius of Ti is 1.45 A. Ti is dissolved using a solution in the lattice of W. Replacing the W atom increased the lattice constant, and the diffraction peak of (110) shifted to a low angle. However, the Ti is soft and a further addition of Ti (9.6-22.7 at.%) reduces the residual stress of the WTi films. With the increase in the Ti content, the full width at half maximum (FWHM) of the (110) diffraction peak increased obviously, and the grain size of the alloy thin film decreased. The average grain sizes of the films were estimated by Debye-Scherrer formula, using the FWHM value of the (110) XRD diffraction peaks. The calculated grain sizes of the WTi films with respect to the Ti content are presented in Table 3. It can be seen that the grain size decreases from 69.4 \(\pm\) 1.2 nm down to 28.2 \(\pm\) 1.9 nm with increasing Ti content from 0 \begin{table}
\begin{tabular}{l c c c c c c} \hline
**Samples** & **T1** & **T2** & **T3** & **T4** & **T5** & **T6** \\ \hline Bias voltage [V] & & & \(-\)100 & & & \\ Deposition temperature [\({}^{\circ}\)C] & & & 300 & & & \\ Ar flow [sccm] & & & 100 & & & \\ Deposition pressure [Pa] & & & & 0.4 & & \\ Target power [kW] & & & & 2.3 & & \\ Deposition time [min] & & & & 30 & & \\ Film thickness [nm] & 613 & 591 & 664 & 656 & 624 & 631 \\ Ti concentrations in WTi [at.%] & 0 & 3.4 & 6.8 & 9.6 & 12.9 & 22.7 \\ \hline \end{tabular}
\end{table} 
Table 2: Parameters of deposition for the W and WTi films. to 22.7 at.%. Higher Ti concentrations mean more nucleation sites are provided and result in grain size refinement. Figure 3 shows the surface section topography of the W and WTi alloy thin films. The surface of both W and WTi films shows an obvious geometric cone shape, clear grain boundaries, and regular stacking, and is compact. The intersections show a dense columnar crystal structure. Compared with the WTi alloy films, the grain size of pure W films is much larger, indicating that the addition of Ti hinders the growth of W grains. The grain boundary of the alloy film is clear, the columnar crystal is obvious, and there is no other structural grain, which indicates that all Ti is solidly dissolved in W, and the single-phase solid solution of WTi alloy is obtained, which is also consistent with the results of XRD.