Domain of specialization

Henrique Leonel Gomes graduated in Physics (1989). He subsequently obtained his PhD from University College of North Wales (UK) for work on the electrical properties of semiconducting organic thin films under the supervision of Prof. David Martin Taylor. He moved to the University of the Algarve (Portugal) where is Associated Professor in the Electronics Engineering department.

Area of scientific activity

The major research interest areas are: Electrical characterization, electronic devices, biosensors and new materials for electronic and bio-sensing applications.He has a recognized expertise in electrical characterization techniques for assessing organic based devices. His research group based in Faro has developed particular strength in techniques for device characterization. The experimental facilities include extensive electrical characterization systems for charge carrier concentration and mobility determination, while information concerning defect parameters is obtained using Deep Level Transient Spectroscopy (DLTS), Thermally Stimulated Currents (TSC) and Admittance Spectroscopy (AS) methods and electrical noise techniques

Present research interests

The major research interest areas are: Electrical characterization, electronic devices, biosensorsand new materials for electronic and bio-sensing applications.

Other skills/activities

Recently his research activities have expanded to encompass also the interaction between conducting polymers and biological materials. He has a special interest in the application ofsuch materials to electronic and optoelectronic devices with application as biosensors.

Research topics

1-Electronic devices based on thin film diamonds

Research in diamond electronics started as joint collaborative project with the Physics department of the University of Aveiro. The research was mostly focused on Schottky type of diodes. As major contributions to this research field was the effect of the diamond structure had in the device performance. Ana Rodrigues working as an assistant at the university did her PhD in 2004 under my supervision in this topic with thesis title “Electrical characterization of electronic devices from thin film diamonds”. The device performance was dramatically affected by grain boundaries, improvement in processing revealed to be a challenge. This research field was abandon after the completion of the PhD thesis following worldwide trend.

2-Organic electronics

My interest in this topic was directly from my PhD work. Back in 1990, I published one of the first organic based transistors. My major contribution was to elucidate the role of the oxygen as a dopant species in semiconducting polymers.(this article has now more than 90 citations). The PhD work also helps me to establish a reputation on small-signal techniques to characterize devices

When established at the University of the Algarve as an Auxiliary Professor. The research in organic based electronics received an important boost when I was invited to join a Training and mobility network of excellence (TMR-SELOA). Thanks to the support of Prof. Sir. Richard Friend. A post-doc (Peter Stallinga) has hired and my expertise in small-signal impedance measurements was highly appreciated within the network.  Later we joined another European Network (Mona Lisa) and we start to interact directly with Dago de Leeuw at Philips research labs in Eindhoven. An important outcome of this work was the finding that the source of the electrical instability in organic based electronics was water-contamination in the surface of the dielectric layers. The first paper in 2004 had already received more than100 citations and it is becoming a reference in the field. The finding that water was the chemical agent responsible for the instability received more than 34 citations but more important the paper motivated an intense research by other groups in devising solutions to eliminate water using hydrophobic layers and the citations are rising exponentially.  Following this successful experiment. Philips invited us to solve a reliability problem occurring in Light emitting diodes (PLEDs) processed at the PLED prepilot line at Philips Research. Organic light emitting diodes (OLED), either based on polymers or small molecules, suffer from early failure: an unpredictable sudden increase in current with a total loss of light output. The origin is claimed to be formation of shorts induced by defects such as particles. This reliability problem, despite a decade of investigations, could not be solved. The origin is not an electrical short. The “dead” OLED is a non-volatile organic memory. In order to understand the reason for failure we had to move into the physical mechanisms leading to a resistive switching phenomena and into a complete and complex of memristors (see later research in RRAMs). This research was fully supported by the Ducth Polymer Institute (DPI) a industrial private organization and for the first time we secure for the university of the Algarve 300 K€ of direct funding

3-Printed electronics

This research is motivated by the potential of organic (plastic) electronics to greatly impact the future semiconductor industry by low-cost, high diversity and low power consumption. Examples of plastic electronics applications include: OLED (organic light emitting diode) TVs, flexible plastic solar cells, flexible displays, RF identification tags wearable (textile) electronics, chemical and biological sensors. My group is currently involved in a FP7 project entitle TDK4PE.

Among our task forces is to produce device models, and simulation tools. This is highly important to design large area circuits. This research topic also represent a movement of the group to a more technological area and to a strong interaction of companies involved in mass production of large area circuits. Thin-film transistors made of organic materials are potentially low-cost and compatible with flexible substrates. Soluble organic materials can be designed and synthesized for printing electronic components similar to how newspapers are printed. For the above applications to become reality, Novel completely new simulation and design tools are necessary.

4- Non-volatile resistive switching memories

My research group joins efforts together with Eindhoven University of Technology TU/e, Philips research labs and the University of Groningen in a project financially supported by the Dutch Polymer Institute (DPI). Two PhD students were allocated to my group and a state of the art noise measuring system to understand why dead OLEDs become memories.

The final goals of the project arrive at a characterization method that predicts early failure or the absence directly after fabrication. This diagnostic quality too can be used by Philips at the production stage.

The spin-off of this research is enormous, because the metal oxide – organic diode is a generic device. The operation mechanism holds not only for the reliability of OLEDs, but to varying degrees also for the electron emission of oxides, field emission of cold cathodes, the dielectric breakdown of ELCO’s  and the so-called forming of classical thyristors.

Our group got already some international recognition and our papers on resistive switching memories are now highly cited and our PhD students got a high number of oral talks at international conferences and we participated in a invitation to write a with paper on theories. “Non-volatile, rewritable polymer memory diodes” presented at Spring 2010 ITRS Meeting, Emerging Research Memory Assessment Workshop in Italy on April 6 & 7  (2010),.We had an invited presentation at the plastics electronics conference. In parallel with this project a research, we explore the role of nanoparticles in electrical conduction systems.

5- Bioelectronic devices

Bioelectronics deals with the coupling of the worlds of electronics and biology, and this coupling can go both ways. The natural ability for “recognition” in the biological world. At the same time, electronic devices can help “guide” biological events, for example cell growth, thereby creating new tools for biomedical research. This cross-fertilization between the two disciplines improves our understanding of life processes and forms the basis for advanced disease detection and treatment. Tools generated in this arena, such as medical diagnostics and bioelectronics implants, will dominate the future of healthcare and help increase the span and quality of our lives.

Key to these new technologies is a fundamental understanding of the interface between electronic materials and biology. Organic electronics – an emerging technology that relies on carbon-based semiconductors and promises to deliver devices with unique properties – seems to be ideally suited for the interface with biology. The “soft” nature of organic materials offers better mechanical compatibility with tissue than traditional electronic materials, while their natural compatibility with mechanically flexible substrates suits the non-planar form factors often required for biomedical implants. More importantly, their ability to conduct ions in addition to electrons and holes opens up a new communication channel with biology.