ISSN 1023-1935, Russian Journal of Electrochemistry, 2007, Vol. 43, No. 5, pp. 561–569. © Pleiades Publishing, Ltd. 2007. Original Russian Text © A.A. Vasiliev, V.I. Filippov, Yu.A. Dobrovolsky, A.V. Pisareva, W. Moritz, R. Palombari, 2007, published in Elektrokhimiya, 2007, Vol. 43, No. 5, pp. 593−601. 561 INTRODUCTION The interest in the development of hydrogen sensors operating at room temperature, which can be manufac- tured using silicon technology, is due to the possibility of creation of a new generation of fire alarms (detec- tors) that are capable of detecting the odor of the smol- dering combustible material, rather than the smoke pro- duced by fire or the temperature rise in the room caused by the flames. This possibility is specified in relatively recent standards EN54/6, ISO 7240/6, and NPB 98. One of the most important gases that are emitted by smoldering combustible materials in the early stages of a fire is hydrogen. The large diffusion coefficient of hydrogen and its low background content in atmo- sphere (~0.5 ppm) make hydrogen a very appealing candidate for manufacturing gas fire alarms. On the other hand, detecting this gas is of importance for fuel cells that are rapidly developing at the present time. Sensors that are used in gas fire alarms must possess the following most important properties: low electric power consumption, high sensitivity (a value of H 2 con- centration of 10 ppm is typical of fire), low cost, and, consequently, the possibility of manufacture with the aid of an adequate technology, preferably, the silicon technology. To our minds, there exist two most important kinds of sensors for the application in gas fire alarms, specif- ically, metal oxide sensors manufactured using the technology of silicon micromachining, i.e., thin dielec- tric membranes of silicon oxide or nitride (“nano-per- micron” technology) and sensors on the basis of the metal–insulator–semiconductor (MIS) structures. In this paper we will focus our attention on the MIS sensors and especially on the MIS sensors with an undergate layer formed out of a proton-conducting solid electrolyte. The principle underlying the method of measuring a gas concentration with the aid of an MIS structure with Hydrogen Sensors Based on Metal–Insulator–Semiconductor Structures with a Layer of a Proton-Conducting Solid Electrolyte* A. A. Vasiliev a,b , V. I. Filippov b , Yu. A. Dobrovolsky c , A. V. Pisareva c , W. Moritz d , and R. Palombari e a Institute Rovira i Virzhili, DEEEA, Av. Paisos Catalans 26, Tarragona, 43007 Spain b Institute of Applied Chemical Physics, Russian Research Centre Kurchatov Institute, pl. Kurchatova 1, Moscow, 123182 Russia c Institute of Problems of Chemical Physics, Russian Academy of Sciences, pr. Akademika Semenova 1, Chernogolovka, Moscow oblast, 142432 Russia d Institute of Chemistry, Humboldt Universit of Berlin, Berlin, Germany e University of Perugia, Perugia, Italy Received June 30, 2006 Abstract—Application of solid electrolytes as undergate layers accelerates the response of a sensor at room temperature as compared with ordinary hydrogen sensors manufactured on the basis of the metal–insulator– semiconductor (MIS) structures with a palladium gate. The proton-conducting solid electrolytes under study include NAFION, zirconium hydrophosphate, and etherified polyvinyl alcohol (PVA) with heteropolyacids and phenoldisulfonic acid, which can be deposited under the platinum gate. Sensors based on the MIS structures with these solid electrolytes show a high sensitivity toward hydrogen (~120 mV per concentration decade). The response time τ 0.63 of a freshly manufactured sensor with a layer of zirconium hydrophosphate amounts to about 2 min. The maximum mechanical stability, especially at relative humidities in excess of 80% is intrinsic to sensors containing layers of PVA with heteropolyacids. The response time of such sensors is nearly 10 min. DOI: 10.1134/S1023193507050096 Key words: hydrogen sensor, MIS structure, proton-conducting solid electrolyte, gas fire alarms (detectors) * Based on the paper delivered at the 8th Meeting “Fundamental Problems of Solid-State Ionics”, Chernogolovka (Russia), 2006.