Wireless system for biological signal recording with Gallium Arsenide high electron mobility transistors as sensing elements Leonardo Sileo a,b,⇑ , Luigi Martiradonna a , Paola Arcuti b , Giuseppina Monti b , Vittorianna Tasco c , Marco Dal Maschio d , Giacomo Pruzzo d , Benedetto Bozzini b , Luciano Tarricone b , Massimo De Vittorio a,b,c a Center for Biomolecular Nanotechnologies@UniLe, Istituto Italiano di Tecnologia, Arnesano (LE) 73010, Italy b Dip. di Ingegneria dell’Innovazione, Università del Salento, Lecce 73100, Italy c National Nanotechnology Laboratory, Istituto Nanoscienze-CNR, Lecce 73100, Italy d Istituto Italiano di Tecnologia (IIT), Genova I-16163, Italy article info Article history: Available online xxxx Keywords: Biosensors HEMTs Radiofrequency Wireless power transmission Inductive link abstract We propose the realization of a compact fully-passive biotelemetry tag composed of a high-electron mobility transistor (HEMT) connected to a wireless link. The Gallium Arsenide based gateless HEMT serves both as the environmental sensing element and as the amplitude modulator of the carrier signal received by the antenna. A prototype demonstrator operating in the MHz range has been developed: it consists of an array of transistors with different gate geometries and two spiral loop resonators imple- menting the wireless link. More specifically, one resonator (Tag-resonator) is connected to the array of transistors, while the other one (Reader-resonator) is connected to a power generator/reader device; the wireless link uses the magnetic coupling between the two resonators. Experimental results demon- strate that the reader-resonator exhibits an intensity modulation of the resonance dip depending on the voltage applied to the HEMT gate. These results will be used as a guideline for the realization of biocompatible sub-millimeter tags operating in the Gigahertz frequency range. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction Remote and real-time monitoring of human body vital signs can be considered the main goal of biosensors research. Advanced bio- telemetry systems date back to the human space travel era, when Spacelabs Healthcare Company developed the first recording sys- tem able to transmit vital parameters of astronauts to Earth [1]. Nowadays, the development of wearable [2] or implantable [3–5] sensors is mainly focused to improve the quality of health care sys- tem, allowing doctors and caregivers to follow patients’ state of health thoroughly and continuously, while significantly reducing both hospitalization and first-aid intervention times. Wireless systems for neuroscience could allow microelectrode monitoring of neuronal activity on a large scale, without the draw- back of cumbersome connecting wires tethering the brain [4–6]. However, such technology is particularly challenging due to the main constraint of miniaturization. For this reason, the project of radio-frequency identification (RFID) systems, and in particular of the implantable transponder, must be carefully evaluated bearing in mind the requirements of compactness, lightness and biocompat- ibility. Active transponders carrying batteries or power harvesting circuits on board, or semi-active systems requiring rectifiers for con- version of the received alternating current into direct current [6,7] are hardly corresponding to these needs. Fully-passive schemes, where the role of the transponder is limited to back-scatter the re- ceived power after modulation with the information previously stored in it, are instead potentially simpler and more suited for min- iaturization and implantation. Examples of such approaches can also be found in literature [6], where fully-passive biotelemetry sensors are proposed by exploiting varactors to modulate a biological signal with the received electromagnetic carrier. We here propose the use of Gallium Arsenide (GaAs) – based high electron mobility transis- tors (HEMTs) connected to a wireless link to realize a novel biote- lemetry sensor with several advantages as compared to diodes based approaches. Field effect transistors (FETs) analogous to HEM- Ts have been largely employed as sensors for the detection of biolog- ical activity, ranging from pH variations to macromolecules sensing and to electrical activity from cultured neuronal networks [8–10]. Moreover, FETs fabrication technology is nowadays extremely ad- vanced, allowing implementation on very small areas with unvaried performances and reduced noise figures as compared to miniaturized diode mixers. GaAs – based HEMTs are, among FET devices, the best perform- ing in terms of transconductance (and, therefore, in sensitivity to gate modulation) and high frequency communications [11,12]. In 0167-9317/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.mee.2013.02.089 ⇑ Corresponding author. Address: Center for Biomolecular Nanotechnolo- gies@UniLe, Istituto Italiano di Tecnologia, Via Barsanti Arnesano (LE) 73010, Italy. Tel.: +39 0832295732; fax: +39 0832295708. E-mail addresses: leonardo.sileo@iit.it, sileoleo@gmail.com (L. Sileo). Microelectronic Engineering xxx (2013) xxx–xxx Contents lists available at SciVerse ScienceDirect Microelectronic Engineering journal homepage: www.elsevier.com/locate/mee Please cite this article in press as: L. Sileo et al., Microelectron. Eng. (2013), http://dx.doi.org/10.1016/j.mee.2013.02.089