Giulia Casula

Ultralow Voltage, OTFT‐Based Sensor for Label‐Free DNA Detection

An organic ultralow voltage field effect transistor for DNA hybridization detection is presented. The transduction mechanism is based on a field-effect modulation due to the electrical charge of the oligonucleotides, so label-free detection can be performed. The device shows a sub-nanometer detection limit and unprecedented selectivity with respect to single nucleotide polymorphism.

7.5–15 MHz organic frequency doubler made with pentacene-based diode and paper substrate

This work describes the realization of a fully organic “chip-less” tag, based on the harmonic RFID architecture, operating at 7.5 and 15 MHz. The tag is fabricated on paper substrate and includes an organic pentacene-based diode, as a non-linear component, to generate harmonics. The communication between reader and tag is provided by coupled resonators operating at the fundamental and harmonic frequencies. A measure campaign of the complete reader-tag system has been performed and the results are here reported.

Flexible non-volatile memory devices based on organic semiconductors

The possibility of developing fully organic electronic circuits is critically dependent on the ability to realize a full set of electronic functionalities based on organic devices. In order to complete the scene, a fundamental element is still missing, i.e. reliable data storage. Over the past few years, a considerable effort has been spent on the development and optimization of organic polymer based memory elements. Among several possible solutions, transistor-based memories and resistive switching-based memories are attracting a great interest in the scientific community. In this paper, a route for the fabrication of organic semiconductor-based memory devices with performances beyond the state of the art is reported. Both the families of organic memories will be considered. A flexible resistive memory based on a novel combination of materials is presented. In particular, high retention time in ambient conditions are reported. Complementary, a low voltage transistor-based memory is presented. Low voltage operation is allowed by an hybrid, nano-sized dielectric, which is also responsible for the memory effect in the device. Thanks to the possibility of reproducibly fabricating such device on ultra-thin substrates, high mechanical stability is reported.

Combined AFM and ToF-SIMS analyses for the study of filaments in organic resistive switching memories

The resistive switching mechanism in organic and hybrid resistive memories has been intensively studied in the last years. A particular interest have been directed to solution processed resistive layers based on an organic or polymer compounds for which convincing direct and indirect evidences indicated that the switching mechanism is based on the formation of conductive filaments (CFs) bridging the two metal electrodes. However, the CF composition, formation and rupture dynamics and evolution during the prolonged cycling are still poorly explored. Experiments are rare because of the well-known challenges in characterizing nanoscale filaments. In this work, we combine time-of-flight secondary ion mass spectrometry (ToF-SIMS) 3D imaging and in-situ atomic force microscopy (AFM), acquired at different profile depths, to characterize the CF composition and dynamics in high-performance and environmental stable crossbar Ag/parylene C/Ag printed memories. The results allow characterizing the filaments composition, their formation mechanism by electrochemical metallization and their evolution upon cycling. Moreover, the AFM images allow for a more clear interpretation of ToF-SIMS 3D reconstructions of molecular ions and to highlight artifacts arising from the different sputtering rate of metals as compared to the organic material.

Towards all inkjet printed electronics (Conference Presentation)

Organic electronics has been thoroughly investigated as technology for the fabrication of flexible devices enabling a wide range of applications including disposable electronics, smart cards, flexible displas, wearable electronics and sensors. However, in order to make such technology suitable for real applications, reliable, cost efficient approaches for large area fabrication, such as inkjet printing, have to be properly optimized. Moreover, in order to increase the final system portability, and as a consequence, its application range, such devices must be also operated at relatively low voltages. In this work we present the different solutions we have developed for the routinely fabrication of inkjet printed organic transistors, operating a very low voltages and we report about their employment in the realization of different kinds of sensor devices for monitoring physical (pressure/temperature) and biochemical (eg. pH and/or DNA) stimuli and/or ionizing radiations. Moreover, the development of organic electronics systems requires also the integration of such smart sensing systems with reliable data storage devices. Among several possible solutions, we will demonstrate that inkjet printing can be employed for the fabrication of high performing memory devices using different approaches, based on printed transistors and resistive switching elements, and that, such devices, can be easily integrated with electrical sensors for the fabrication of printed, flexible smart tags.