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    Capacitive Humidity Sensor Based on Polymer Composite Thin Film
    Fakhra Aziz1; Nosheen Fatima2; Lih W. Lim3; Khaulah Sulaiman3;
    1UNIVERSITY OF PESHAWAR, Peshawar, Pakistan; 2CAPITAL UNIVERSITY OF SCIENCE AND TECHNOLOGY (CUST), Islamabad, Pakistan; 3UNIVERSITY OF MALAYA, Kuala Lumpur, Malaysia;
    PAPER: 17/Composite/Regular (Oral)
    SCHEDULED: 11:45/Tue./Grego (50/3rd)



    ABSTRACT:
    Nowadays humidity sensors are used in every industry, such as in food, pharmaceuticals [1], medicine, [2] and agriculture [3, 4]. These commercial humidity sensors are quite expensive, complicated in operation, and have low sensitivity and stability because of the materials used as a sensing element [5]. It is difficult to maintain their operational cost, power losses, sensitivity and stability [4]. Therefore, it is essential for a sensor to have high sensitivity and stability, low cost, small hysteresis, wide linear range, simple operation, short response, and short recovery time [5, 6]. Electrical conduction is affected significantly by dipoles of water molecules, which makes it important for researchers to investigate the magnitude of change in impedance and capacitance of the samples with respect to varying relative humidity. The investigation becomes more important for composite materials due to the contribution of properties by two or more ingredients. Changing the constituting ratio of the ingredients in the composites results in modification of properties in composite materials. The choice of compatible ingredients is also important to fabricate stable samples so as to overcome the degradation processes [7]. The present work demonstrates a humidity sensor based on a composite of polythieno [3,4-b]-thiophene-co-benzodithiophene (PTB7) and [6,6]-phenyl-C-butyric-acid methyl ester (PCBM). The capacitive type humidity sensor is fabricated using simple cost effective spin coating approach in the Al/ PTB7:PCBM/Al surface type geometry with different ratios of PTB7: PCBM i.e., 1:0, 1.5:1, 1:1, 1:1.5 and 0:1 respectively. The sensing behavior of the prepared devices has been observed at ~1V of AC operational bias over a wide range of relative humidity i.e. 20-95 % RH. The sensors are also examined at different frequencies i.e., 100 Hz, 1 kHz, 10 kHz and 100 kHz. The optimum frequency and volumetric ratio are selected as 100 Hz and 1.5:1 (PTB7:PCBM). The sensor shows better sensitivity of 1.325 nF/%RH with negligible hysteresis. The composite sensor indicates remarkable improvement in the sensing behavior as compared to single material based sensors. These properties make it a potential candidate for the state-of-the-art sensor applications.

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