A Novel Fully Printed and Flexible Capacitive Pressure Sensor B. B. Narakathu 1* , A. Eshkeiti 1 , A. S. G. Reddy 1 , M. Rebros 2 , E. Rebrosova 2 , M. K. Joyce 2 , B. J. Bazuin 1,2 , M. Z. Atashbar 1,2 1 Department of Electrical and Computer Engineering 2 Center for the Advancement of Printed Electronics Western Michigan University Kalamazoo, MI, USA * binubaby.narakathu@wmich.edu Abstract—A novel fully printed flexible capacitive pressure sensor was fabricated using conventional screen and gravure printing techniques. The sensor was successfully printed on a flexible polyethylene terephthalate (PET) substrate with silver (Ag) nanoparticle (NP) ink as the metallization layer and polydimethylsiloxane (PDMS) as the dielectric layer. The capacitive response of the sensor demonstrated a percentage change of 5 % and 40 % for minimum and maximum detectable compressive forces of 800 kPa and 18 MPa, respectively when compared to the base capacitance of 26 pF. At the minimum detectable pressure, the stability measurements resulted in a maximum variation of ± 0.15 % from the average capacitance value of 28 pf. The response of the printed device demonstrated the feasibility of employing traditional printing techniques for the fabrication of flexible pressure sensing devices. I. INTRODUCTION Recently, there has been a growing interest in the development of pressure sensors on flexible substrates for applications in the aerospace, automotive, and biomedical engineering fields [1-3]. Pressure sensors are typically manufactured using conventional CMOS processes which are often expensive and fabricated on rigid substrates [4-7]. Almost all pressure sensing systems built to date utilize hanging structures or cavity based sensor design configurations [8-12]. However, none of these configurations offer the high flexibility, stability and conformability, required for various pressure sensing applications. A continuous layer- on-layer configuration is envisioned as a promising approach that will overcome the drawbacks associated with conventional pressure sensing systems. The development of fully flexible and conformal pressure sensors, due to the availability of diverse manufacturing materials and the rapid development of modern fabrication techniques, is thus poised to have a significant impact on the modern society. Over the last decade, a steady and considerable effort has been directed towards the development of printed electronics using conventional printing technologies. To name a few, organic thin film transistors (OTFT’s) using inkjet printing [13-15], flexible displays by means of screen printing [16-18] and electrochemical sensors by rotogravure printing [19, 20]. The use of printing technologies overcomes some of the drawbacks associated with conventional silicon technology, which involves high-vacuum and high- temperature deposition processes along with sophisticated photolithographic patterning techniques [21]. The advantages of printing include improved cost efficiency, reduction of material wastage during fabrication, flexibility in the substrate and low manufacturing temperatures. Even though a steady and considerable effort has been directed towards the development of flexible electronics, there have been no reports on fully printed flexible pressure sensors. This has led to the research of traditional printing techniques for the manufacture of flexible pressure sensors. Gravure printing is known for its high quality and high printing speed; use of low viscosity inks and robustness of the process [22, 23]. Screen printing has an added advantage of producing a relatively larger wet film thickness which is difficult to attain by other print methods [24]. A typical gravure system is comprised of an engraved gravure cylinder (image carrier), doctor blade, impression roller and ink pan whereas a screen printer consists of a squeegee and a screen printing mask which consists of a frame (steel or aluminum), screen fabric and stencil. Gravure printing is a direct ink transfer process while screen printing is a push through process in which the substrate is not in direct contact with the mask. In this work, conventional screen and gravure printing techniques were used to fabricate a fully printed flexible capacitive pressure sensor. A laboratory scale gravure press was used to print highly a conductive silver (Ag) nanoparticle (NP) based ink as the electrode metallization layer on a flexible polyethylene terephthalate (PET) substrate. A dielectric layer of polydimethylsiloxane (PDMS) was deposited using a screen printer. The capability of the fabricated device to be used as a pressure sensor was demonstrated by investigating the capacitive response based on varying compressive forces applied. 978-1-4577-1767-3/12/$26.00 ©2012 IEEE