Sensors and Actuators B 146 (2010) 165–170 Contents lists available at ScienceDirect Sensors and Actuators B: Chemical j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / s n b WO 3 -based NO 2 sensors fabricated through low frequency AC electrophoretic deposition Elham Kamali Heidari a , Cyrus Zamani b,∗ , Ehsan Marzbanrad a , Babak Raissi a , Soroush Nazarpour c a Ceramic Department, Materials and Energy Research Center, Tehran, Iran b ME2, XaRMAE, Department Electrònica, Universitat de Barcelona, Martí i Franquès 1, 08028 Barcelona, Spain c MIND/IN2UB, Departament d’Electrònica, Universitat de Barcelona, Martí i Franquès 1, 08028 Barcelona, Spain a r t i c l e i n f o Article history: Received 14 October 2009 Received in revised form 7 December 2009 Accepted 4 January 2010 Available online 16 February 2010 Keywords: NO2 sensor Mesoporous WO 3 Low frequency electrophoretic deposition Sensitivity a b s t r a c t Mesoporous tungsten oxide was synthesized based on hard template method using silica as template. The produced material was investigated structurally using X-ray diffraction and high resolution TEM. The material was deposited on patterned alumina substrates through low frequency AC electrophoresis of which, the deposition pattern was studied using optical microscopy and SEM. Exposure of the sensors to NO2 in the temperature range of 150–300 ◦ C resulted in highest sensitivity at 200 ◦ C. Increasing tem- perature was found to produce faster response and recovery processes while the sensitivity decreased. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Exhaust gases generated by cars and factories are the focus of many researches as the main source of air pollution. NOx (NO, NO 2 ) as a toxic is of great importance and many researchers have reported metal oxide based sensors for NOx detection.Based on American standards, concentration of NO and NO 2 should not exceed 3 and 25 ppm respectively while in Japan, these fall in ppb range. Thus, there is an increasing need to highly sensitive sen- sors targeting NOx. A great number of sensors are reported so far with their advantages and drawbacks [1,2]. Solid-state NOx sensors reported so far can be categorized in several groups among which, resistive-type (based on semiconducting oxides),amperometric- and potentiometric-type (based on solid-electrolyte materials), and capacitive-type are of great importance. Combined structures are also reported presenting a combination of the properties of individual elements used in their structure [3–6]. Although a large number of works have been focusing on solid-electrolyte sensors which show a high sensitivity at elevated temperatures, progress in oxide materials and their novel structures is the motivation for research on resistive-sensors which operate at lower tempera- tures and benefit a simple structure. SnO 2 , In 2 O 3 , TiO 2 , ZnO, Fe 2 O 3 , WO 3 and several combinations of these (in some cases doped with a catalytic material) have been studied so far [7–13]. Of the ∗ Corresponding author. Tel.: +34 934039174; fax: +34 934021148. E-mail address: cyrus zamani@yahoo.com (C. Zamani). oxide materials used for sensing, WO 3 shows promising properties especially if possesses a large surface area [14]. In this scenario, mesoporous materials are so far one of the best candidates pre- senting a high sensitivity thanks to their large specific surface area. The possibility of manipulating mesoporous materials with desired structural features is an advantage which makes the products suit- able for sensing gases like amines which are difficult to be sensed by other structures [15,16]. On the other hand, the deposition process affects the device per- formance largely since it affects the morphology and structure of the sensing material (and thus,its properties) [17].Thus, various deposition methods have been implemented such as melting and quenching [4,5],micro dropping [15,18],dip coating [19], screen printing [12], sputtering [10], etc. Low frequency electrophoresis is a method with high potentiality to deposit nanomaterials in a con- trolled way [20–23]. In this article, we present the application of low frequency AC electrophoretic deposition in sensor fabrication where WO 3 nanopowder is deposited on interdigitated electrodes. Fabricated devices are exposed to various concentrations of NO 2 for which, results are presented. 2. Experimental 2.1. WO 3 nano particles synthesis Mesoporous SiO 2 was synthesized, as a template for impreg- nation of WO 3 nano particles based on method reported earlier [24,25]. A solution of 6 g polyethylene oxide–polypropylene oxide 0925-4005/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2010.01.073