Available online at www.sciencedirect.com ScienceDirect Physics Procedia 72 (2015) 485 – 489 Conference of Physics of Nonequilibrium Atomic Systems and Composites, PNASC 2015, 18-20 February 2015 and the Conference of Heterostructures for microwave, power and optoelectronics: physics, technology and devices (Heterostructures), 19 February 2015 Fabrication of Microhotplates Based on Laser Micromachining of Zirconium Oxide Konstantin Oblova, Anastasia Ivanovaa, Sergey Solovieva, Nikolay Samotaeva,*, Alexandr Lipilinb, Alexey Vasilievc, Andrey Sokolovc a Micro- and Nanoelectronics Department, National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), Kashirskoe higway 31, Moscow 115409, Russia b Institute of Electrophysics of Ural Branch of RAS, Amundsen str., 106, Ekaterinburg, 620016, Russia c Center of Physical and Chemical Technology, NRC Kurchatov Institute, Academician Kurchatov square 1, Moscow 123098, Russia Abstract We present a novel approach to the fabrication of MEMS devices, which can be used for gas sensors operating in harsh environment in wireless and autonomous information systems MEMS platforms based on ZrO2/Y2O3 (YSZ) are applied in these devices The methods of ceramic MEMS devices fabrication with laser micromachining are considered It is shown that the application of YSZ membranes permits a decrease in MEMS power consumption at 450 0C down to ~75 mW at continuous heating and down to ~ mW at pulse heating mode The application of the platforms is not restricted by gas sensors: they can be used for fast thermometers, bolometric matrices, flowmeteres and other MEMS devices working under harsh environmental conditions © 2015 The Authors Published by Elsevier B.V © 2015 The Authors Published by Elsevier B.V This isResearch an open access article under the CC BY-NC-ND license Nuclear University MEPhI (Moscow Engineering Peer-review under responsibility ofthe National (http://creativecommons.org/licenses/by-nc-nd/4.0/) Physics Institute) Peer-review under responsibility of the National Research Nuclear University MEPhI (Moscow Engineering Physics Institute) Keywords: laser ; MEMS; microhotplate; gas sensor; * Corresponding author Tel.:+7-495-5858273; fax: +7-499-3242111 E-mail address: nnsamotaev@mephi.ru 1875-3892 © 2015 The Authors Published by Elsevier B.V This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the National Research Nuclear University MEPhI (Moscow Engineering Physics Institute) doi:10.1016/j.phpro.2015.09.057 486 Konstantin Oblov et al / Physics Procedia 72 (2015) 485 – 489 Introduction Many research groups worldwide investigate now the possibility of the fabrication of gas sensors of metal oxide semiconductor, thermocatalytic, and IR optic types based on micromachining technologies, which present by Simon et al (2001) All these types of gas sensors require typical working temperature ranges from approximately 150 to 4500C Mainly the following technologies are used for the fabrication of MEMS microhotplate platforms: silicon technology (CVD which present by Vincenzi et al (2001)], SOI which present by Friedberger et al (2003), porous silicon which present by Maccagnani et al (1998)); ceramic (thin alumina films which present in Karpov et al (2013) and Vasiliev et al.(2008), LTCC which present by Teterycz et al (1998) or Rettig and Moos (2004)); thick film (screen printing which present in Samotaev et al (2007) or Samotaev et al (2013)); flexible substrate (polyimide film which present in Kim (2006) or Oprea et al (2009)) The application of bulk structure or thick film microhotplates leads to relatively high heating power consumption (> 150 mW) on the other hand silicon technology gives record 20 mW power consumption at 4500C constant heating mode Wieldy, MEMS sensors and systems based on silicon technology not able to long term operate under harsh environmental conditions (ambient temperature up to 250 0C and humidity up to 100%) for long enough time (at least, for several days) As example, silicon based MEMS are not stable at high operation temperature because of poor adhesion of Pt to SiO2 and Si3N4, oxidation of thin films of materials other than Pt, hydrolysis of Si 3N4, and internal strains in SiO2/Si3N4 multilayer membrane The same problem with adhesion of Pt metallization and high temperature stability of membrane made by organic materials has flexible substrate Stable to harsh environmental condition only technologies working with ceramics materials, but one have relativity large size of microhotplates (This is explained by complexity of micromachining of ceramics materials) and leads as result more high power consumption compare with technologies using silicon as material for substrate In our work, we tried to develop a fast, low cost and technology effective process for ceramic MEMS microhotplates fabrication possible to use in middle-scale mass production of gas sensors, up to several thousand units per day Our main goal in this work was to fabricate low power consuming MEMS microhotplate with short thermal response time comparable with the level typical for ceramic MEMS or screen-print technologies Also additional requirement for material for microhotplate is stability up to 600 0С for using in wireless sensor applications with harsh environmental condition which describing by Samotaev et al (2014) or Vasiliev et al (2014) there are survey present in works Samotaev et al (2014), Somov et al (2013), Somov et al (2011), Somov et al (2014) show that low power consumption of MEMS platform are critical Fig Technological sequence of YSZ microhotplate manufacturing: (a) Photo of 10 μm thickness YSZ membrane; (b) YSZ ceramic substrate (0.5 mm thick) with mm holes made by laser micromachining; (c) Top view of YSZ substrate YSZ membrane glued with glass; (d) Layout of the MEMS heater of semiconductor gas sensor fabricated by magnetron sputtering The area of the heater is of about 400 x 250 microns, the width of platinum lines is of about 40 microns; (e) YSZ ceramic substrate with microhotplates chips after platinum sputtering through shadow mask; (f) Single MEMS microhotplates chips (6x6 mm size) after cutting YFZ substrate by laser facility Konstantin Oblov et al / Physics Procedia 72 (2015) 485 – 489 Experiment We fabricated experimental samples of ceramic MEMS platforms with thin membranes of zirconium dioxide stabilized with yttrium (YSZ) Ceramic film was made by slip casting with consequent annealing under mechanical load Ceramic slip consists of small particles with size of about 20 nm, therefore satisfactory quality of the film sintering was obtained at relatively low temperature of about 11500C and sintering time of 12 hours Resulting membrane has thickness of about 10 microns, SEM photos of this membrane (top view and cleaving, respectively) are presented in Figs 2a and 2b respectively After sintering, the membrane consists of roundish particles with size of ~ 0.2 μm This particle size and surface roughness enables easy deposition of platinum heater layer using magnetron sputtering The main advantage of ZrO2 ceramics compared to all other ceramic materials is extremely low coefficient of thermal conductivity It is equal to about 2.5 W/m•K This value is approximately one order of magnitude lower that the thermal conductivity of wieldy used for ceramic MEMS application aluminum oxide Therefore, MEMS device made of zirconia ceramics will consume considerably lower power compared to the device made of alumina Fig (a) SEM photo of the ceramic membrane made of yttria stabilized zirconia (cross section (cleaving) of the membrane); (b) SEM photo of the ceramic membrane made of yttria stabilized zirconia (top view of the membrane) The membrane was glued to ceramic substrate (0.5 mm thick) with mm holes made by laser micromachining of the same YSZ material as membrane (Fig 1b) For gluing we used the ink including melted glass with the expansion coefficient close to the expansion coefficient of YSZ material (Fig 1c) After ink deposition, the membrane was carefully pressed to the substrate, dried at 150 0C, and annealed at 9500C for the melting of glass binder Microheater was fabricated by magnetron sputtering of platinum trough shadow mask After sputtering substrate was cut to single chips (6x6 mm size) by the MiniMarker-2 laser facility which parameters are present in Table The chips were packaged in TO-8 package Table Main characteristic of the laser facility MiniMarker -2 Laser pulsed source type ytterbium fiber Wavelength, μm 1,064 Pulse frequency (regulated), kHz from 20 to 100 Power (average),W 20 Pulse energy, mJ 1,0 Focused spot diameter, μm 50 Laser position system - two-axis scanner G325DT Maximum speed of the laser beam, mm/s 8700 line width with automatic filling, mm From 0,05 to Software and hardware solution, μm 2,5 487 488 Konstantin Oblov et al / Physics Procedia 72 (2015) 485 – 489 Fig (a) Cantilever element fabricated by laser cutting view from membrane side ; (b) Cantilever shaped element fabricated by laser cutting view from frame side (c) Heating power of the heater presented in Fig 1f as a function of its temperature Result and Discussion The most important characteristics of the microhotplate – power consumption as a function of temperature – was determined after the measurement of volt-ampere characteristics of the device The results of the measurement are presented in Fig 3c The microheater consumes approximately 75 mW at working temperature of 450 0C sufficient for the efficient measurement of methane concentrations in air Further decrease in power consumption is possible with the application of microcantilevers similar to those presented in Fig 2a and 2b fabricated by laser micromachining already glued YSZ membranes on substrate Another way available for a decrease in power consumption is related to the application of pulsing heating of the sensor In this way, it is possible to decrease power consumption of the sensor down to approximately mW (duty cycle of 1%) at methane detection Conclusion The application of YSZ membranes enables significant decrease in power consumption of the sensor working at 4500C This power is equal to about 75 mW at constant heating of the sensor and to about mW in average at pulsing heating with duty cycle of 0.01 Such level of power consumption gives possibility using developed microhotplates in wireless sensor applications Also experiments show that technologies with using YSZ membrane and laser micromachining can be adapted successfully to mass production of ceramic MEMS platforms for semiconductor and thermocatalytic sensors of combustible gases, gas fire detectors, and electrochemical sensors of oxygen Acknowledgements The research was performed within a frame of Russian Federation President Grant for support young scientists №14.Y30.15.7910-MK from 16.02.2015 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network for combustible gas monitoring Sensors and Actuators A: Physical 171, 398-405 Somov, A., Baranov, A., Spirjakin, D., 2014 A wireless sensor-actuator system for hazardous gases detection and control Sensors and Actuators A: Physical 210, 157-164 489 ... harsh environmental condition only technologies working with ceramics materials, but one have relativity large size of microhotplates (This is explained by complexity of micromachining of ceramics... detection Conclusion The application of YSZ membranes enables significant decrease in power consumption of the sensor working at 4500C This power is equal to about 75 mW at constant heating of the... application of bulk structure or thick film microhotplates leads to relatively high heating power consumption (> 150 mW) on the other hand silicon technology gives record 20 mW power consumption at