# A TSV-Structured Room Temperature p-Type TiO\({}_{2}\) Nitric Oxide Gas Sensor
###### Abstract  
Planar MOS/MEMS gas sensors have been widely studied and applied, but the detection of exhaled gas has been little developed. The flow rate of exhaled gas affects the suspension structure of the MEMS gas sensor and the operating temperature of the gas sensor. Therefore, this study uses the Bosch process and the atomic layer deposition (ALD) process to prepare a room-temperature (RT) TSV-structured TiO\({}_{2}\) gas sensor. The results indicated that the TiO\({}_{2}\) sensing film is uniformed and covers the through-silicon via (TSV) structure and the TiO\({}_{2}\) sensing film is confirmed to be a p-type MOS. In terms of gas sensing at room temperature, the response of the sensor increases with the increasing NO concentration. The sensor response is 16.5% on average, with an inaccuracy of \(\rm{<\pm 0.5\%}\) for five cycles at 4 ppm NO concentration. For gas at 10 ppm, the response of the sensor to NO is 24.4%, but the sensor produces almost no response to other gases (CO, CO\({}_{2}\), SO\({}_{2}\), and H\({}_{2}\)S). The RT TiO\({}_{2}\) gas sensor with a TSV structure exhibits good stability, reversibility, and selectivity to NO gas.  
TiO\({}_{2}\); TSV; gas sensor Article  
A TSV-Structured Room Temperature Gas Sensor  
1  
Tianian 701, Taiwan Semiconductor Research Institute, Tainan 704, Taiwan 12 Taiwan Semiconductor Research Institute,  
(TiO\({}_{2}\)) is an n-type semiconductor with a 3.0 eV energy gap and with the advantage of chemical and thermal stability at room temperature, which contributes to its suitability for gas sensing [15]. Some p-type TiO\({}_{2}\) have been produced using a different growth technology [16; 17; 18].  
Three-dimensional (3D) through-silicon via (TSV) technology allows heterogeneous integration, low power consumption, and reduction in the size of component. Therefore, it is widely used in integrated circuits (IC), humidity sensors [19], light-emitting diodes [20; 21], field emissions [22], and photo detectors [23]. Recently, various TSV processes were widely developed, such as laser drilling [24], cryogenic etching [25], Bosch etching [26], and wet anisotropic etching [27]. Among them, the Bosch process is widely used due to its high etch rate, better profile control, and mask selectivity [26]. In addition, the Bosch process creates scallops on the sidewalls [26], which increase the sensing surface of the gas sensor. However, thin films are difficult to deposit on the surface of scallops. The atomic layer deposition (ALD) process was found to have good step coverage, especially for TSV structures [28].  
This study uses a via-structured p-type TiO\({}_{2}\) NO gas sensor that is produced by the Bosch and the ALD process. During the gas measurement, the sensor is operated at RT. A via-structured gas sensor makes the airflow considerably smoother than a MOS gas sensor with a general structure, which is more suitable for the detection of exhaled gas, especially for the detection of respiratory diseases, as shown in Figure 1. The via-structured formation, the TiO\({}_{2}\) fabrication, and the sensor's sensing mechanism are described and discussed.