Cerium and Titanium Oxide Interdigitated Capacitors for Pressure Sensing Applications Khalil I. Arshak*, Deirdre Morris + , Olga Korostynska*, Arousian Arshak + *Department of Electronic and Computer Engineering + Department of Physics, University of Limerick, Limerick, Ireland khalil.arshak@ul.ie Abstract Pressure measurement is an essential tool in understanding environmental and biological processes. However, devices for such applications need to be small in size and easy to adhere to a wide range of surfaces. It is also preferable that the data gathered by such a device be transferred wirelessly to a receiver, remote from the sensing environment, for the safety of personnel or patient comfort. With this in mind, the pressure sensing properties of thick film cerium oxide (CeO 2 ) and titanium oxide (TiO 2 ) interdigitated capacitors were investigated. The devices were fabricated on flexible polymer substrates so that they could be attached to both planar and cylindrical surfaces. Each sensor was then placed under hydrostatic pressure ranging from 0 – 17 kPa. It was found that sensors based on TiO 2 were most sensitive. It is thought that this is due to differences in the materials particle size. Keywords: cerium oxide, titanium oxide, interdigitated capacitors, pressure sensors 1 Introduction The ability to remotely measure physical and chemical changes in difficult to reach areas has a number of applications in both biological and environmental monitoring [1]. There is a particularly high demand for reliable and cost-effective pressure sensitive devices as they are considered a useful tool for clinical studies in such areas as cardiology, neurology and rehabilitation [2]. To date, MEMS sensors have been the preferred method of creating miniature sensors, particularly for biomedical applications [3, 4]. Typically, these devices are based on the capacitive principle as they are more sensitive and have lower power consumption than piezoresistive sensors [5]. However, the presence of moving parts makes packaging, which is particularly important for biomedical sensors, a difficult task [6]. A further disadvantage is the fact that MEMS are only cost-effective if 10 5 – 10 6 devices are produced per year. Thick film technology offers a cost effective and reliable alternative to sensor fabrication, which is capable of meeting the demand for medical sensors [5]. The most common method of thick film sensor fabrication is screen-printing. This technique can achieve high line resolution with economical use of paste thus lowering production costs [7]. In addition, capacitors with no moving parts and high sensitivity can be fabricated [8]. A large number of materials are suitable for use and as a result, devices with the desired physical properties can be achieved [9]. Previous investigations into the properties of interdigitated capacitors with a polyvinylidene fluoride (PVDF) dielectric layer have shown high sensitivity to pressure [10]. Interdigitated electrodes with a polymer based dielectric layer have also been popular in the development of strain gauges [11]. In this work, interdigitated capacitors were fabricated using either cerium oxide (CeO 2 ) or titanium oxide (TiO 2 ) as the dielectric layer. Cerium oxide has unique electrical properties, which make it useful for applications involving microelectronic and optoelectronic devices [12]. On the other hand, TiO 2 is a popular material for use in medical applications, as it is biocompatible due to its chemical stability [13]. Both materials were prepared and deposited on interdigitated electrodes by screen-printing. Each material was then examined using SEM in order to gain an understating of their morphology and particle size. Their sensitivity was tested by placing the devices under hydrostatic pressure ranging from 0 – 17 kPa. 2 Experimental Procedure To fabricate interdigitated capacitors, the conductive and insulative layers were deposited by screen- printing onto polymer substrates. DuPont 4929 conductive paste was used for the electrodes, while the CeO 2 and TiO 2 dielectric pastes were developed in house. To form the dielectric paste, the functional material (either CeO 2 or TiO 2 , supplied by Sigma Aldrich and Riedel-De Haen Ag Seelze-Hannover respectively) was mixed with 7 wt.% of binder, which in this case is polyvinyl butyral (PVB). Finally, the solvent 1st International Conference on Sensing Technology November 21-23, 2005 Palmerston North, New Zealand 442