Low power consumption micro C2H5OH gas sensor based on micro-heater and screen printing technique
Introduction
Semiconductors based gas sensors have been studied for several applications in detecting inflammable, toxic, and odorless gases due to several merits, such as, small size and high sensitivity [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11]. Moreover to reduce the power consumption of the device, the micro-heater to enhance the sensing and desorption of the target gas has been normally adopted.
In the group of hazardous gases, C2H5OH sensor is being focused to detect drunk driving or to detect leak in fuel cell. An extensive research is being carried out using various metal oxides like SnO2, ZnO, TiO2, WO3, In2O3, LaFeO3, Co3O4 as sensor materials [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24]. Due to the difficulties in micro electro mechanical systems (MEMS) design, fabrication technique and higher production cost for micro gas sensor, few commercial devices based on bulk micromachining technique are selling by pioneering company. This technology needs further improvement in handling device wafer and cost reduction for dry Si etching technique [25], [26], [27], [28], [29], [30].
In this study we report surface micromachined gas sensors based on micro-heater and the SnO2 thick film, which show low power consumption and high sensitivity for C2H5OH detection. The fabrication process for the micro gas sensor was based on the conventional complementary metal-oxide semiconductor (CMOS) compatible MEMS processes for mass-production, which is possible to integrate with other devices and electronic circuitry.
Section snippets
Experimental
Semiconducting SnO2 nano-powders were synthesized by homogeneous co-precipitation method. (CH3CO2)2Cax·H2O, H2PtCl6·6H2O and NH4OH solution was slowly added to the aqueous solution of SnCl4·5H2O to control the pH value of the solutions, which is one of main parameters to determine the characteristics of nano-powders. The main roles of Ca and Pt are to suppress the growth of crystal in sintering process and to activate the reaction to the C2H5OH [31], [32]. The resulting gel was washed several
Results and discussion
Fig. 1 shows the XRD patterns of the doped SnO2 thick film. All peaks belong to SnO2 phase except one, which corresponds to Sn2O3 phase. The calculated average crystallite size of the SnO2 nano-powders using Scherrer formula was 57 ± 6 nm, which grain size was proper to detect gas.
Fig. 2 presents the SEM image and energy dispersive X-ray (EDAX) analysis result of the SnO2 thick films on Si substrate, From the Fig. 2(a), the distribution of the crystallite size of the SnO2 nano-powders was uniform
Summary
Micro C2H5OH gas sensor was fabricated by using surface micromachined micro-heater and doped SnO2 thick film with low power consumption and high response. The device based on 6 in. Si wafer was fabricated by using CMOS compatible MEMS processes including screen printing technique. Our micro gas sensor showed substantial response down to 0.5 ppm alcohol at much lower power consumption (35 mW) than those of the commercial alcohol gas sensors with high mechanical endurance.
Acknowledgements
This work was supported by Technology Innovation Program (Innovation Cluster Program) through the Korea Innovation Cluster Foundation funded by the Ministry of Knowledge Economy (MKE, Korea) and by the IT R&D Program of the MKE/KEIT [10035570, development of self-powered smart sensor node platform for smart&green building].
Seung Eon Moon received the BS, MS, and PhD degree in Physics from Seoul National University, Seoul, Korea in 1990, 1994 and 2000, respectively. Since 2000, he has been working for Electronics and Telecommunications Research Institute (ETRI) in the area of various application devices based on oxide materials. His current research activities are the development of MEMS gas sensor, piezoelectric energy harvester, ferroelectric phase shifter and ferroelectric or oxide non-volatile memory.
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Seung Eon Moon received the BS, MS, and PhD degree in Physics from Seoul National University, Seoul, Korea in 1990, 1994 and 2000, respectively. Since 2000, he has been working for Electronics and Telecommunications Research Institute (ETRI) in the area of various application devices based on oxide materials. His current research activities are the development of MEMS gas sensor, piezoelectric energy harvester, ferroelectric phase shifter and ferroelectric or oxide non-volatile memory.
Hyung-Kun Lee is a senior researcher of Components & Materials Research Laboratory at Electronics and Telecommunications Research Institute (ETRI) in South Korea. Prior to joining ETRI, he carried out postdoctoral experience in Center for Smart Supramolecules, Korea in 2004 and Materials Science and Engineering at Northwestern University, USA from 2005 until 2006. He completed Ph.D. in Chemistry from the Pohang University of Science and Technology (POSTECH) in 2004, studying self-assembly of soft materials such as liquid crystals and supramolecular vesicles. His current research interests are mainly focused on gas sensors and their applications in actuators.
Nak-Jin Choi received his B.S. from Pukyong National University, Korea in 1996 and M.S. and Ph.D from Kyungpook National University in 1998 and 2005, respectively. Since 2005, he has been working for Electronics and Telecommunications Research Institute (ETRI) in the area of various application devices based on oxide materials. He has been involved with research on e-nose since 1997, and also conducted research on actuators by polymer.
Jaewoo Lee received the B.S. degree in electrical and electronics engineering from Korea University, Seoul, Korea, in 2000, and the M.S. degree in information and communication engineering from Gwang-Ju Institute of Science and Technology (GIST), Gwangju, Korea, in 2002.After that, He joined a micro-system team at Electronics and Telecommunication Research Institute (ETRI), Daejeon, Korea. He focused on RF MEMS switches for the front-end Antenna module. Since 2006, he has developed MEMS microphones for mobile application.
Chang Auck Choi was born in Taegu, Korea, in 1954. He received his M.S. and PhD degrees in electronic engineering from Kyungpook National University, Taegu, Korea, in 1988 and 1999, respectively. Since 1980, he is working for the ETRI in the area of developing micro-electro-mechanical-system (MEMS) devices and advanced semiconductor process technology.He is currently the project manager of the MEMS sensor technology development. His research interests are physical sensors and integrated MEMS sensor and process.
Woo Seok Yang received the BS, MS and PhD degrees in materials science and engineering from Pohang University of Science and Technology, Pohang, Korea, in 1991, 1993 and 1998, respectively. From 1998 to 2001, he worked on FeRAM and DRAM at Hynix Semiconductor Inc. He has been with Electronics and Telecommunications Research Institute since 2001. His recent research interests are in the fields of physical MEMS devices and USN sensors.
Jongdae Kim received the BS and MS degrees in electronics engineering from Kyungpook National University, in 1982 and 1984, respectively. In 1994, he received the PhD degree in electrical and computer engineering from the University of New Mexico, Albuquerque, USA. From 1984, he has been working in Electronics and Telecommunications Research Institute (ETRI) with silicon-based device design and process integration. His research interests include power integrated circuits for FED, PDP, and OLED driving ICs; micro DC-DC converters; and circuit design and IPs based on the nanotechnology. He is now a director of the Strategy and Planning Division.
Jong-Jin Jung received his B.S.degree at Andong National University in 2006. Since 2006, he works as a manager of the research & development center at Sentech Korea Co. Ltd. His research interests include fabrication of chemical gas sensors.
Do-Jun Yoo received his B.S., M.S., and Ph.D. degrees from Seoul National University in 1990, 1992, and 1996, respectively. He was a Visitor Researcher at KyushuUniversity (Japan) from 1994 to 1995 and a Researcher at the Korea ElectronicTechnology Institute (KETI) from 1995 to 1996. He worked as a Senior Researcherat ResearchInstitute of Industrial Science & Technology (RIST) from1996 to 1998. In 1999, he established Sentech Korea Co. Ltd. Since 1999, he is CEO at Sentech Korea Co. Ltd. His research interests include fabrication of chemical gas sensors.