Polyaniline based impedance humidity sensors M. Tariq Saeed Chani a, b, * , Kh.S. Karimov a, c , F. Ahmad Khalid a , S. Abdul Moiz d a GIK Institute of Engineering Sciences and Technology, Topi 23640, Swabi, Pakistan b Center of Excellence for Advanced Materials Research (CEAMR), King Abdulaziz University, Jeddah 21589, P.O. Box 80203, Saudi Arabia c Physical Technical Institute, Aini St. 299/1, Dushanbe 734063, Tajikistan d Department of Electrical Engineering, College of Engineering and Islamic Architecture, Umm Al-Qura University, Makkah, Saudi Arabia article info Article history: Received 6 December 2011 Received in revised form 22 November 2012 Accepted 14 January 2013 Available online 26 January 2013 Keywords: Humidity sensor Conducting polymer Polyaniline Dielectric permittivity Simulation abstract In this study, the fabrication and sensing response of humidity sensor based on the polyaniline (PANI) thin film have been studied. PANI thin films with 30e70 mm thickness were deposited on glass substrates between pre-deposited silver and gold electrodes. It was found that the sensing mechanism is based on the impedance and capacitance variations. For change in Relative Humidity (RH) from 36 to 90%, the change in sensor’s capacitance and impedance is 167 and 471 times, respectively. The impedance ehumidity relationship is more uniform as compared to capacitanceehumidity relationship for this range of humidity. It is also observed that annealing enhanced the sensitivity of the sensor by two times. The consequence of measuring frequency and absorptionedesorption behavior of the humidity sensor are also discussed in detail. Response (s res ) and recovery (s rec ) times are 8 and 27 s respectively. Results are examined by simulation and found in good agreement with experimental data. Ó 2013 Elsevier Masson SAS. All rights reserved. 1. Introduction Investigation and modification of electrical, optical and photo- voltaic response [1e5] of organic semiconductors reveal their po- tential for a variety of applications. Organic materials are very sensitive to humidity [1,2,6], temperature [5,7], radiations [8] and different types of gases etc [9e11]. Measurement and control of humidity is very important not only for human comfort but also for manufacturing processes and industrial products [12] because of universal existence of water, which affects the human health and physical properties of mate- rials [13]. Humidity sensors are widely used in semiconductor, automobile, medical, pharmaceutical, health caring, textile, paper, agriculture and food industry [14,15]. Commercially available humidity sensors are fabricated by conventional sensing materials like alumina, ceramics and elec- trolytic metal oxides [14]. Depending upon the nature of materials these sensors may be expansive or require high operational power/ temperature and high cost of maintenance [6,15]. Organic materials due to light weight, flexibility, simple technology, low cost and large surface area have developed great interest for their use in humidity sensors. The humidity sensors based on organic sensing materials are classified in to capacitive, resistive [14] oscillating, mechanical [16], and thermoelemental [17] type sensors depending upon basic sensing principle. Based on its unique advantages each type of sensor has specific applications. To make the sensor suitable for commercialization; the wide range sensitivity, linear response, small hysteresis, short response and recovery time, low cost and low power along with long term physical and chemical stability are the required characteristics [16,17]. The polyaniline (PANI) is one of the most interesting polymers due to its good stability, easy preparation and its potential for fabrication of different microelectronic devices [18e21]. The tai- loring of conductivity of PANI by doping level of oxidation and protonation makes it unique among such other polymers. The ex- istence of oxidation states in PANI provides basis for its sensitivity to water [22]. The change in resistance of polyaniline with change in relative humidity was studied by Ref. [23]. In this study 0.55e0.89 mm thick pellets of polyaniline with 13 mm diameter were prepared by using 7 ton hydraulic press. The change in resistance from 5.8 GU to 13.9 MU is reported for change in humidity from 15 to 90% RH, while response and recovery time was 1 min for 30% change in humidity. A rapid response humidity sensor based on ultra thin film layer by layer (LBL) assembly of poly(anilinesulfonic acid) (SPANI) were fabricated by Ref. [15] and compared with SPANI based * Corresponding author. Faculty of Materials Sciences and Engineering (FMSE), GIK Institute of Engineering Sciences and Technology, Topi 23640, District Swabi, Pakistan. Tel.: þ92 938 271 858x2669; fax: þ92 938 271868. E-mail addresses: tariq_chani@yahoo.com, tariqchani1@gmail.com (M.T.S. Chani). Contents lists available at SciVerse ScienceDirect Solid State Sciences journal homepage: www.elsevier.com/locate/ssscie 1293-2558/$ e see front matter Ó 2013 Elsevier Masson SAS. All rights reserved. http://dx.doi.org/10.1016/j.solidstatesciences.2013.01.005 Solid State Sciences 18 (2013) 78e82