# A TSV-Structured Room Temperature p-Type TiO\({}_{2}\) Nitric Oxide Gas Sensor
## 3 Results  
Figure 3a shows the top-view SEM image of the via-structured TiO\({}_{2}\) sensor. The via is almost square, with a side length of 270 um. Figure 3b shows the cross-sectional FIB image of the via-structured TiO\({}_{2}\) sensor. The via is 400 um deep. Figure 3c-e shows the FIB image of the top, middle, and bottom of the via structure, respectively. These figures show that the Al\({}_{2}\)O\({}_{3}\) and TiO\({}_{2}\) thin films are about 85 and 75 nm thick, respectively. The TiO\({}_{2}\) and Al\({}_{2}\)O\({}_{3}\) films which are produced using ALD are uniform and cover the surface of the Si. The Al electrode is 190 nm thick. Figure 4 shows the micro-Raman spectrum for TiO\({}_{2}\)/Si at room temperature using a 532 nm solid laser excitation source. There is a strong and sharp peak at 522 cm\({}^{-1}\). This is attributed to the Si substrate. In addition, there is one weaker peak at 300 cm\({}^{-1}\), which is attributed to the SiO\({}_{2}\) that is generated by the water vapor and the surface of the Si substrate during the fabrication of the TiO\({}_{2}\) thin film [31]. Then, there is one minor peak at 144 cm\({}^{-1}\) and three other significantly weaker peaks at 199, 400, and 638 cm\({}^{-1}\). These peaks are attributed to the TiO\({}_{2}\) thin film, which contains anatase crystals. The Raman peaks at 144, 199, and 638 cm\({}^{-1}\) are attributed to the Raman mode position E\({}_{g}\) mode for TiO\({}_{2}\). These Eg peaks are attributed to the symmetric stretching vibration of O-Ti-O [21]. The peak at 400 cm\({}^{-1}\) is attributed to the B1g mode, which is probably related to the bending vibration of O-Ti-O [32]. Figure 2: The sensor fabrication process diagram for (**a**) etching Si, (**b**) depositing Al\({}_{2}\)O\({}_{3}\), (**c**) depositing TiO\({}_{2}\), and (**d**) depositing Al, respectively. Figure 4: The micro-Raman spectrum for TiO\({}_{2}\)/Si at room temperature. Figure 3: (**a**) The top-view SEM image and (**b**) the cross-sectional FIB image of the via-structured TiO\({}_{2}\) sensor (**c**–**e**) show an enlarged image of the top, middle, and bottom of the via-structured sensor, respectively. To confirm the structure of the TiO\({}_{2}\) thin film, Figure 5 displays the XRD diffraction pattern of the TiO\({}_{2}\) thin film prepared by ALD. It was found that the main diffraction plane and sub-main peak are the (101) and (200) planes, respectively. Moreover, it was found that the reflections from the (101), (004), (200), (105), (211), and (204) planes correspond to peaks at 20 = 25.25\({}^{\circ}\), 38.41\({}^{\circ}\), 48.06\({}^{\circ}\), 53.63\({}^{\circ}\), 55.10\({}^{\circ}\), and 62.68\({}^{\circ}\), respectively. These features of the XRD pattern indicate the presence of an anatase phase of TiO\({}_{2}\) (JCPDS card no. 21-1272) [33]. Hall measurement is used to confirm the type of metal oxide semiconductor material. Figure 6 shows the I-V curve for the Hall measurement, which is linear. This shows that the probes at the sample and measurement are in ohmic contact. The carrier concentration is +3.84 \(\times\) 10\({}^{18}\) cm\({}^{-3}\). The TiO\({}_{2}\) thin film for this study that is produced using ALD is a p-type semiconductor material, as well as the experimental conclusions that can be drawn. Figure 5: The XRD diffraction pattern of the TiO\({}_{2}\) thin film prepared by ALD. Figure 6: The I-V curve for the Hall measurement. Electrons have an important role in the gas sensing mechanism for a p-type MOS sensor. When the sensor is placed in air at room temperature, oxidizing gases (such as O\({}_{2}\), nitric oxide (NO), etc.) are chemisorbed onto the surface of the MOS sensor. O\({}_{2}\) traps an electron from the sensor's surface to form oxygen ions (O\({}_{2}\)\({}^{-}\)).