Abstract² We present a novel and flexible system to be employed for tactile transduction in the realization of artificial ‡URERW VNLQ· 7KH PHFKDQLFDO GHIRUPDWLRQ GHWHFWLRQ ZKLFK functionally reproduces the sense of touch, is based on Organic Thin Film Transistors (OTFTs) assembled on a flexible plastic foil, where each device acts as a strain sensor. OTFT-based mechanical sensors were fabricated employing a solution- processable organic semiconductor, namely 6,13- bis(triisopropylsilylethynyl)-pentacene (TIPS-pentacene) deposited by drop casting. It will be shown that the surface deformation induced by an external mechanical stimulus gives rise in both cases to a marked, reproducible, and reversible (within a certain range of surface deformation) variation of the device output current. Starting from these results, more complex structures, such as arrays and matrices of OTFT-based mechanical sensors, have been fabricated by means of inkjet printing. Thanks to the flexibility of the introduced structure, we will show that the presented system can be transferred on different surfaces (hard and soft) and employed for a wide range of applications. In particular, it can be successfully employed for tactile transduction in the realizDWLRQ RI DUWLILFLDO ‡robot skin· INTRODUCTION HE light weight, low-cost processing, and the mechanical flexibility of conjugated polymers led them to be considered as a valuable alternative to most common inorganic materials for the realization of electronic devices. Organic Thin Film Transistors (OTFTs) are recognized as key tools/building blocks for the implementation of electronic logic circuits [1-3] and have been intensively studied for many applications, such as displays, smart tags and sensors [4-6]. Despite the low mobility of organic materials (compared to crystalline semiconductors, it is about three orders of magnitude lower) there are applications, as the recently suggested electronic skin [3, 7, 8], in which the lower speed is tolerable and the use of organic materials seems to be more beneficial than Manuscript received January 31 st 2012. 1 Department of Electrical and Electronic Engineering, University of &DJOLDUL 3LD]]D G¶$UPL  &DJOLDUL ,WDO\ 2 CNR- Institute of Nanoscience S3 Via Campi 213A, I-41100 Modena, Italy 3 Dipartimento di Informatica, Sistemistica e Telematica, Università di Genova, via Opera Pia 13, 16145 Genova (*email address: piero.cosseddu@diee.unica.it) detrimental. In fact, being able to obtain large sensing areas is certainly a benefit for a wide set of applications and using printing techniques for creating sensing devices on unusual substrates could surely widen the set of possible applications where sensing is required. Reproducing the human sense of touch with an artificial system is a very challenging task, primarily because the term "touch" is actually the combined term for several senses. In fact, when a person touches something or somebody this gives rise to various feelings: the perception of pressure (hence shape, softness, texture, vibration, etc.), relative temperature and sometimes pain. The high degree of dexterity which characterizes grasping and manipulative functions in humans, and the sophisticated capability of recognizing the features of an object are the result of a powerful sensory-motor integration which fully exploits the wealth of information provided by the cutaneous and kinaesthetic neural afferent systems [9]. A very accurate description of tactile units is available [9], where a classification of these units according to receptive fields and response time is given. Several approaches have been introduced over the past years for the fabrication of flexible tactile sensors for bio- inspired applications. The tentative specifications for tactile sensors have been defined [10] as: i) the sensor surface or its covering should be both robust and durable; ii) the sensor should provide stable and repeatable output signals. Loading and unloading hysteresis should be minimal; iii) linearity is important, while a monotonic response is absolutely necessary. Some degree of non-linearity can be corrected through signal processing; iv) the sensor transduction bandwidth should not be less than 100 Hz, intended as tactile image frame frequency. Individual sensing units should accordingly possess faster responses to allow multiplexing; v) spatial resolution should be at least of the order of 1-2 mm, as a reasonable compromise between gross grasping and fine manipulation tasks. The development of tactile sensors is one of the most challenging aspects of robotics research. Many technologies have been explored, including carbon-loaded elastomers, piezoelectric materials, and micro-electromechanical systems. Artificial skin examples, able to detect pressure, already exist, but these are difficult to manufacture in large enough quantities to cover a robot body, and, moreover, they GR QRW VWUHWFK 7KH PRVW SURPLVLQJ H[DPSOHV RI ‡HOHFWURQLF Inkjet printed Organic Thin Film Transistors based tactile transducers for artificial robotic skin Piero Cosseddu 1, 2* , Laura Basiricò 1, 2 , Alberto Loi 1 , Stefano Lai 1 , P. Maiolino 3 , E. Baglini 3 , S. Denei 3 , F. Mastrogiovanni 3 , G. Cannata 3 , Annalisa Bonfiglio 1, 2 T The Fourth IEEE RAS/EMBS International Conference on Biomedical Robotics and Biomechatronics Roma, Italy. June 24-27, 2012 978-1-4577-1200-5/12/$26.00 ©2012 IEEE 1907