氣體感測器是用於檢測和量化周圍環境中各種氣體存在的重要設備。它們在許多產業中扮演及其關鍵的角色，包含了環境汙染氣體的監測、工業安全、交通工具廢氣排出控制、室內空氣品質評估和醫療保健。氣體感測器提供氣體濃度的即時數據，從而能夠及時採取行動以減輕潛在危險並確保安全並符合氣體監控標準。氣體感測器依據不同的感測方式及技術又分類成不同種類，包括化學電阻、紅外線、光學等等。
　　在化學電阻感測器中，有一類被稱作是金屬氧化物半導體感測器，其為透過金屬氧化物與測量的目標氣體結合時所產生的電阻變化率來檢測周遭環境的特定目標氣體濃度大小。因金屬氧化半導體感測器雖然對特定氣體的反應時間較為迅速以及較高靈敏度，不過其仍舊極度容易受到周圍環境的溼度、溫度等等影響，且其需要定期校準才能夠維持此標準。本次研究即是以二氧化錫為前驅物感測材料，將其以硒化機與硒粒進行反應後，檢測層主要以硒化錫為材料，檢測其在四吋晶圓上初期的電阻值、四個象限的電阻分布、及其在不同溫度硒化的情況下初始電阻值的差異，以展示本論文整合半導體製程技術與在製程可控之硒化溫度區間內，所大量且低成本的製備氣體感測器元件陣列，在室溫下於晶圓上的初始電阻值的均一性極佳，提供新穎二維材料感測器商業化的解決方案。

Gas sensors are important devices used to detect and quantify the presence of various gases in the surrounding environment. They play a vital role in many industries and applications, including environmental monitoring, industrial safety, vehicle exhaust emission control, indoor air quality assessment and healthcare. Gas sensors provide instant data on gas concentrations, allowing timely action to be taken to mitigate potential hazards and ensure safety and compliance with gas monitoring standards. Among gas sensors, a specific type is called a metal oxide semiconductor sensor, which detects the specific target gas concentration in the surrounding environment through the resistance change rate generated when the metal oxide combines with the measured target gas concentration. Although metal oxide semiconductor sensors have fast response time and high sensitivity, they are still easily affected by the humidity, temperature, etc. of the surrounding environment, and they require regular calibration to maintain this standard. This research is based on tin dioxide. After reacting it with selenium particles using a selenization machine, the detection layer is mainly composed of tin diselenide, and check its initial resistance value, the resistance distribution of the four quadrants, and the difference in the initial resistance value under different temperature of selenization process. It is expected to reduce the initial resistance value and the normality of the gas sensor to extend its using durability, and break the struggle of commercializing production.

Abstract (Chinese)………………………………………………Ⅰ
Abstract (English)…………………………………………...…..Ⅱ
Contents…………………………………………………………Ⅲ
Figure Caption……………………………………………….….Ⅳ
Chapter 1 Introduction…………………………………………1
1.1 Gas sensors……………………………………………………………………...1
1.1.1 Physical characteristics of gas sensors……………………………...…...3
1.2 Optical gas sensors…………………………………………………...…......9
1.3 Electrochemical gas sensors…………………………………………………...11
1.4 MOS (metal oxide semiconductor) sensors…………………………………...13
1.5 2D material gas sensors……………………………………………………...15
1.5.1 Traditional manufacturing method of 2D gas sensors.………………...…...17
Chapter 2 Motivation…………………………………………...20
Chapter 3 Experimental Design………………………………...22
3.1 Structure of devices………………………………………………………...22
3.2 Fabrication of SnSe2 …………………………………………………………23
Chapter 4 Results and Discussion………………………………26
4.1 Whole 4” wafer resistance mapping………………………….…………….26
4.2 Comparison of different temperature selenization…………………….……29
Chapter 5 Conclusion and Future Work……………………..32
Chapter 6 Reference…………………………………………….34
Figure caption
Figure 1-1 Types of gases that require continuous monitoring for safety and health reasons1…………………………………………………………………3
Figure 1-2 Schematic diagram of response curve a MOS sensor1……………4
Figure 1-3 Gas response of the SnO2 nanofibers to 100 ppm VOCs (a) at several process temperatures (b) under 260°C29….………...….……………………6
Figure 1-4 Stability of SnO2 gas sensors in 50 days28…………………..………7
Figure 1-5 Various types of gas sensors1…………………………………8
Figure 1-6 A schematic representation of the NDIR sensor1...…………………9
Figure 1-7 Schematic representation of NDIR gas sensing of a specific gas concentration32……………………………………………………………10
Figure 1-8 Schematic of a typical electrochemical gas sensor1……………11
Figure 1-9 Schematic diagram of electrochemical cell34.………………….12
Figure 1-10 The mechanism of the adsorption of the oxygen molecules on the MOS surface1.…………………………………………………………..14
Figure 1-11 Top: schematic of the MoS2 gas-sensing device; bottom: charge transfer vs adsorption energy profile for NO2, NH3, H2 and CO2 gases on MoS2.34, 35, 36.……………………………………………………………16
Figure 1-12 Charge density of the pristine monolayer SnSe2 with NO2 (a, c) and NH3 (b, d) molecules, with c-axis and b-axis views23….………………….17
Figure 1-13 Schematic of CVD growth setup23.…………………………….18
Figure 1-14 Schematic of the synthesis process of WS2 nanowalls by the horizontal furnace38…………………………………………………………..…19
Figure 2-1 Schematic of plasma-assisted selenization process and the SnSe2 layered film for NO2 gas detection22…………………………….………………21
Figure 3-1 Flow chart of structure of a sensor on the wafer. (a) clean the wafer (b) e-beam deposition of SnO2 as precursor (c) e-beam deposition of Au interdigitated electrodes (d) PACVR (selenization machine) transformation of SnSe2…………………………………………………………………22
Figure 3-2 Schematic illustration of plasma assisted vertical furnace for selenization…………………………………………………………24
Figure 3-3 Temperature curves and the timing of applying plasma……25
Figure 4-1 Gas measuring response for six gases with 40nm SnSe2 sensing film under 250°C selenization process………………………………………...…27
Figure 4-2 Whole wafer mapping for (a) 225°C (b) 250°C (c) 275°C………28

Table caption
Table 4-1 Normality, consistency, and mode value res. of three wafer under different process temperature…………………………………..……29

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