有机薄膜晶体管气体传感器的制备及特性研究
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摘要
有机薄膜晶体管(OTFT)又名有机场效应管,是基于传统的无机场效应管(FET)的基础上发展起来的一种有机电子器件,它具有低功耗、重量轻及体积小等优点,因而自问世以来就受到了研究人员的普遍关注,目前它的性能已经接近或超过非晶硅薄膜晶体管的水平,并被广泛应用于有机电致发光显示、大规模和超大规模集成电路等领域。随着新型有机敏感材料的开发,有机薄膜晶体管也被尝试运用于化学分析物和气体的检测。
本文以n型硅为衬底、SiO2为绝缘层,分别采用旋涂和真空蒸发法制备了聚3-己基噻吩(P3HT)和并五苯薄膜,以其作为有源层制作了底栅极底接触结构的P3HT和并五苯有机薄膜晶体管器件。通过研究OTFT器件的电学特性,进一步地探讨了器件的工作机理,并分析了工艺条件对器件性能的影响,包括绝缘层和有源层的生长质量以及它们之间的界面特性等等。
为了论证有源层的晶形态与OTFT电学性能的关系,采用紫外-可见光谱分析、原子力显微镜分析和X射线衍射分析等方法对OTFT器件的有源层薄膜的形态和结构进行了表征分析,结果发现,结晶度越高、晶界越少,器件的性能更加优越。这也就解释了单晶OTFT器件具有比多晶器件更高的场效应迁移率的原因。除了薄膜生长条件,成膜方法也会影响薄膜的晶形态进而影响器件的性能,关于这一点在对P3HT有机薄膜晶体管的研究中也得到了证明。
有机薄膜晶体管虽然用途广泛,但将其应用为气体传感器的却并不多见。在实验中把制备的P3HT和并五苯有机薄膜晶体管暴露在不同的气体中,研究了OTFT器件对各种气体的响应特性,结果表明,基于P3HT的有机薄膜晶体管对NO2表现出了良好的响应重复性和可逆性及较高的灵敏度,对NH3也具有较好的响应特性和较短的响应恢复时间。另外,P3HT-TFT对甲醇、乙醇和正丁醇等有机蒸气也具有一定的敏感特性。与此同时,并五苯有机薄膜晶体管对乙醇蒸气也表现出了显著的敏感特性,而对甲醇蒸气、CO、SO2等气体不敏感。研究中还发现,OTFT器件对气体的响应强度和灵敏度可以通过栅极电压来调制,这意味着选择合适的栅压可以获得较高的响应灵敏度,这是传统的化学电阻式传感器所不具备的。最后,对OTFT气体传感器的敏感机理进行了初步的分析和探讨。
Organic thin-film transistors(OTFTs), also called organic field-effect transistors, are a kind of organic electronic devices which are developed on the basis of inorganic field-effect transistors. The OTFTs devices, with several advantages such as lower power consumption, less weight, and smaller size, have attracted great interests and concerns of the worldwide scientific researchers since they were reported for the first time. At present, the OTFTs, whose performance has approached or exceeded the level of a-Si:H TFTs, are widely used in OLED displays and large and very-large scale integrated circuit. With the development of organic sensitive materials, organic thin-film transistors are also applied in the detection of chemical analytes and gases.
In this paper, two kinds of the OTFTs with the‘‘bottom-gate’’and‘‘bottom-contact’’configuration were fabricated with poly(3-hexylthiophene)(P3HT) and pentacene as the active layer. P3HT and pentacene thin films were doposited onto a SiO2/n-Si substrate by spin coating and vacuum evaporation, respectively. The electrical characteristics of the OTFTs were investigated and its mechanism was in further discussion. Besides, the survey reveals that the OTFTs’performance is dependent on the processing techniques to a certain extent, including the quality of the insulating layer and active layer as well as the interfacial propeties.
The relationship between the morphology, crystalline state of the active layer and the device performance was studied by means of UV-Vis spectrophotometer, atomic force microscopy (AFM) and x-ray diffraction (XRD). It indicates that larger crystalline area and less grain boundary can improve the performance of the OTFTs. This is why the single crystal pentacene based OTFT has higher field effect mobility than the polycrystalline device. Besides, the thin film deposition methods can also affect its morphology and crystalline state, and eventually change the device performance.
Although organic thin-film transistors are widely used in many fields, there is few report about employing them as gas sensors. In the experiment the gas sensing properties of P3HT and pentacene based OTFTs exposed to different gases were tested. The results show that poly(3-hexylthiophene) based OTFTs exhibit a good level of performance particularly in terms of response repeatability and reversibility when exposed to NO2 gas. In particular, the devices show a excellent response and recovery characteristics upon exposure to NH3 gas. Besides, poly(3-hexylthiophene) based OTFTs are also sensitive to volatile organic vapors such as methanol, ethanol and n-butanol. Meanwhile, pentacene based OTFTs have a noticeable response when exposed to ethanol, but little response to methanol, CO and SO2. Moreover, the OTFTs devices possess a high sensitivity which can be adjusted by the gate-source voltage. It means that the sensitivity of the devices operated in a proper gate bias may be enhanced, which is superior to chemiresistor sensors. In the end, the mechanism of gas sensing was also discussed in organic thin-film transistor sensors.
本文以n型硅为衬底、SiO2为绝缘层,分别采用旋涂和真空蒸发法制备了聚3-己基噻吩(P3HT)和并五苯薄膜,以其作为有源层制作了底栅极底接触结构的P3HT和并五苯有机薄膜晶体管器件。通过研究OTFT器件的电学特性,进一步地探讨了器件的工作机理,并分析了工艺条件对器件性能的影响,包括绝缘层和有源层的生长质量以及它们之间的界面特性等等。
为了论证有源层的晶形态与OTFT电学性能的关系,采用紫外-可见光谱分析、原子力显微镜分析和X射线衍射分析等方法对OTFT器件的有源层薄膜的形态和结构进行了表征分析,结果发现,结晶度越高、晶界越少,器件的性能更加优越。这也就解释了单晶OTFT器件具有比多晶器件更高的场效应迁移率的原因。除了薄膜生长条件,成膜方法也会影响薄膜的晶形态进而影响器件的性能,关于这一点在对P3HT有机薄膜晶体管的研究中也得到了证明。
有机薄膜晶体管虽然用途广泛,但将其应用为气体传感器的却并不多见。在实验中把制备的P3HT和并五苯有机薄膜晶体管暴露在不同的气体中,研究了OTFT器件对各种气体的响应特性,结果表明,基于P3HT的有机薄膜晶体管对NO2表现出了良好的响应重复性和可逆性及较高的灵敏度,对NH3也具有较好的响应特性和较短的响应恢复时间。另外,P3HT-TFT对甲醇、乙醇和正丁醇等有机蒸气也具有一定的敏感特性。与此同时,并五苯有机薄膜晶体管对乙醇蒸气也表现出了显著的敏感特性,而对甲醇蒸气、CO、SO2等气体不敏感。研究中还发现,OTFT器件对气体的响应强度和灵敏度可以通过栅极电压来调制,这意味着选择合适的栅压可以获得较高的响应灵敏度,这是传统的化学电阻式传感器所不具备的。最后,对OTFT气体传感器的敏感机理进行了初步的分析和探讨。
Organic thin-film transistors(OTFTs), also called organic field-effect transistors, are a kind of organic electronic devices which are developed on the basis of inorganic field-effect transistors. The OTFTs devices, with several advantages such as lower power consumption, less weight, and smaller size, have attracted great interests and concerns of the worldwide scientific researchers since they were reported for the first time. At present, the OTFTs, whose performance has approached or exceeded the level of a-Si:H TFTs, are widely used in OLED displays and large and very-large scale integrated circuit. With the development of organic sensitive materials, organic thin-film transistors are also applied in the detection of chemical analytes and gases.
In this paper, two kinds of the OTFTs with the‘‘bottom-gate’’and‘‘bottom-contact’’configuration were fabricated with poly(3-hexylthiophene)(P3HT) and pentacene as the active layer. P3HT and pentacene thin films were doposited onto a SiO2/n-Si substrate by spin coating and vacuum evaporation, respectively. The electrical characteristics of the OTFTs were investigated and its mechanism was in further discussion. Besides, the survey reveals that the OTFTs’performance is dependent on the processing techniques to a certain extent, including the quality of the insulating layer and active layer as well as the interfacial propeties.
The relationship between the morphology, crystalline state of the active layer and the device performance was studied by means of UV-Vis spectrophotometer, atomic force microscopy (AFM) and x-ray diffraction (XRD). It indicates that larger crystalline area and less grain boundary can improve the performance of the OTFTs. This is why the single crystal pentacene based OTFT has higher field effect mobility than the polycrystalline device. Besides, the thin film deposition methods can also affect its morphology and crystalline state, and eventually change the device performance.
Although organic thin-film transistors are widely used in many fields, there is few report about employing them as gas sensors. In the experiment the gas sensing properties of P3HT and pentacene based OTFTs exposed to different gases were tested. The results show that poly(3-hexylthiophene) based OTFTs exhibit a good level of performance particularly in terms of response repeatability and reversibility when exposed to NO2 gas. In particular, the devices show a excellent response and recovery characteristics upon exposure to NH3 gas. Besides, poly(3-hexylthiophene) based OTFTs are also sensitive to volatile organic vapors such as methanol, ethanol and n-butanol. Meanwhile, pentacene based OTFTs have a noticeable response when exposed to ethanol, but little response to methanol, CO and SO2. Moreover, the OTFTs devices possess a high sensitivity which can be adjusted by the gate-source voltage. It means that the sensitivity of the devices operated in a proper gate bias may be enhanced, which is superior to chemiresistor sensors. In the end, the mechanism of gas sensing was also discussed in organic thin-film transistor sensors.
引文
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[3] Torsi L, Dodabalapur A, Sabbatini L and Zambonin P G., Multi-parameter gas sensors based on organic thin-film-transistors. Sensors and Actuators B,2000,67: 312-316.
[4] Crone B, Dodabalapur A et al. Electronic sensing of vapors with organic transistors. Appl. Phys. Lett.,2001,78:2229-2231.
[5] Liao F, Chen C, Subramanian V et al. Organic TFTs as gas sensors for electronic nose applications. Sensors and Actuators B,2005,107:849-855.
[6] Tanese M C, Fine D, Dodabalapur A, Torsi L. Interface and gate bias dependence responses of sensing organic thin-film transistors. Biosensors and Bioelectronics,2005, 21:782-788.
[7] Torsi L, Tanese M C, Cioffi N, Gallazzi M C et al. Side-Chain Role in Chemically Sensing Conducting Polymer Field-Effect Transistors. J. Phys. Chem. B, 2003,107:7589-7594
[8] Rafik Ben Chaabane, Adnène Ltaief, L. Kaabi et al. Influence of ambient atmosphere on the electrical properties of organic thin film transistors. Materials Science and Engineering, 2006,26:514-518.
[9] Tsumura A, Koezuka H, and Ando T. Macromolecular electronic device:Field-effect transistor with a polythiophene thin film. Appl. Phys. Lett.,1986,49(18):1210-1212.
[10] Tsumura A, Koezuka H, and Ando T. Polythiophene Field-Effect Transistor:Its Characteristics and Operation Mechanism. Synthetic Metals,1988,25:11-23.
[11] Gilles Horowitz, Denis Fichou, Xuezhou Peng, Zhigang Xu and Francis Garnier. A field-effect transistor based on conjugated alpha-sexithienyl.Solid State Communications,1989,72:381-384.
[12] Akimichi H, Waragai K, Hotta S, Kano H, and Sakakia H. Field-effect Transistors using alkyl substituted oligothiophenes. Appl. Phys. Lett.,1991,58(14):1500-1502.
[13] Garnier F, Hajlaoui R, Yassar A, Srivastava P. All-Polymer Field-Effect Transistor Realized by Printing Techniques. Science,1994,265(5179):1684-1686.
[14] Dodabalapur A, Katz H E, Torsi L, and Haddon R C. Organic Heterostructure Field-Effect Transistors. Science,1995,269:1560-1562.
[15] Zhenan Bao, Andrew J Lovinger, and Ananth Dodabalapur. Organic field-effect transistors with high mobility based on copper phthalocyanine. Appl. Phys. Lett.,1996, 69:3066.
[16] Dodabalapur A, Laquindanum J, Katz H E, and Bao Z. Complementary circuits with organic transistors. Appl. Phys. Lett.,1996,69:4227.
[17] Gundlach D J, Klauk H, Sheraw C D et al. High-mobility, low voltage organic thin film transistors. International Electron Devices Meeting,1999,111-114.
[18] Klauk H, Halik M et al. High-mobility polymer gate dielectric pentacene thin film transistors. Journal of Applied Physics,2002,92:5259.
[19] Fukuda H, Yamagishi Y et al. Gas sensing properties of poly-3-hexylthiophene thin film transistors. Sensors and Actuators B,2005,108:414-417.
[20] Wei Hu, Yi Zhao et al. Improving the performance of the organic thin-film transistors with thin insulating lithium fluoride buffer layer. Microelectronics Journal, 2007,38:632-636.
[21] Leufgen M, Rost O, Gould C et al. High-mobility tetrathiafulvalene organic field-effect transistors from solution processing. Organic Electronics,2008,9:1101-1106.
[22] Mayumi Uno, Y. Tominari, J. Takeya. Fabrication of high-mobility organic single-crystal field-effect transistors with amorphous fluoropolymer gate insulators. Organic Electronics, 2008,9:753-756.
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