## 3 Results and Discussion
Then, it gradually decreased with increased source power, reaching 1.47 m\(\Omega\)\(\cdot\)cm at 175 W. An abrupt decrease in resistivity was observed because the stoichiometric TiN deposited at the higher source power remained stable against oxidation [21], and the transformation from Ti\({}_{2}\)N phase to TiN phase. At high source power, the resistivity was low, but \(\rm{R_{q}}\) was high. Accordingly, 150 W was selected for further studies to improve the surface roughness and electrical properties of TiN thin film. The surface morphology of TiN thin film on the Si/SiO\({}_{2}<\)100\(>\) substrate at various working pressure was investigated by SEM analysis (Figure 4). Figure 3: (**a**) XRD patters, (**b**) RMS roughness (\(\rm{R_{q}}\)) and resistivity of TiN thin film on the Si/SiO\({}_{2}<\)100\(>\) substrate with various source power. Figure 2: SEM surface morphology of TiN thin film deposited with various source power: (**a**) 50 W, (**b**) 75 W, (**c**) 100 W, (**d**) 125 W, (**e**) 150 W, and (**f**) 175 W, respectively. The inset presents a SEM image of TiN thickness. At a higher working pressure (P\({}_{\text{working}}\) = 5 \(\times\) 10\({}^{-3}\) Torr) during films preparations, the evaporated TiN atoms presumably lost considerable energy through their numerous collisions with Ar atoms before they were deposited onto the Si/SiO\({}_{2}\)\(<\)100\(>\) substrate, resulting in insufficient growth of TiN film. With decreased working pressure, the surface morphology of TiN film drastically improved with small grain and narrow grain boundary. The insets of Figure 4 presented the cross-sectional microstructures of TiN film. As the working pressure was adjusted, film thickness slightly changed owing to the formation on the target surface a gas compound layer with a lower sputtering rate than metals [22]. Moreover, the cross-sectional images revealed growth morphology containing a columnar microstructure of TiN film at high working pressure, consistent with the characterization of the Zone T structure [23]. At lower working pressure (P\({}_{\text{working}}\)\(\leq\) 1 mTorr), columnar structures were not clearly observed, and TiN thin films grew well on the Si/SiO\({}_{2}\)\(<\)100\(>\) substrate. The XRD patterns of films deposited at various working pressures are shown in Figure 5a. With decreasing working pressure, the peak intensity of Ti\({}_{2}\)N decreased and the TiN peak position shifted toward the lower diffraction angles. A low working pressure seemed to enhanced diffusion of nitrogen, resulting in the transformation from Ti\({}_{2}\)N to TiN. Figure 5b shows that the R\({}_{\text{q}}\) of TiN thin films continuously decreased from 1 nm to 0.3 nm at a working pressure of 5 \(\times\) 10\({}^{-3}\) and 1 \(\times\) 10\({}^{-3}\) Torr, respectively. However, R\({}_{\text{q}}\) suddenly increased to 0.6 nm at a low working pressure of 0.25 \(\times\) 10\({}^{-3}\) Torr. A smoother surface helped reduce electron scattering and improve the conductivity of TiN film [14]. Consequently, the resistivity of TiN film abruptly decreased from 1.05 m\(\Omega\cdot\)cm to 0.14 m\(\Omega\cdot\)cm at a working pressure of 2 \(\times\) 10\({}^{-3}\) and 1 \(\times\) 10\({}^{-3}\) Torr, respectively, and then slowly decreased to 0.1 m\(\Omega\cdot\)cm at a P\({}_{\text{working}}\) of about 0.5 \(\times\) 10\({}^{-3}\) Torr. The decreased resistivity can be attributed to the suppressed secondary phase (Ti\({}_{2}\)N) formation and the reduced electron scattering on smoother surface, which is also consistent with the results shown in Figure 3. The TiN thin films prepared under the optimum conditions at a source power of 150 W and working pressure of 0.5 \(\times\) 10\({}^{-3}\) Torr was utilized as a bottom electrode for MIM devices. Figure 6a reveals the high-frequency (1 MHz) capacitance-voltage (C-V) characteristic of Al\({}_{2}\)O\({}_{3}\) MIM capacitors of various dielectric thickness, and the inset of Figure 6a shows the schematic of the MIM structure.