Annalisa Bonfiglio

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.

Low voltage organic charge modulated FETs: A flexible approach for the fabrication of high sensitive biosensors (Conference Presentation)

Charge Modulated OTFTs represent a versatile tool for the realization of a wide range of sensing applications. The architecture is based on a floating gate organic transistor whose sensitivity to a specific target is obtained by properly functionalizing a part of the floating gate with a sensing layer that can be chosen according to the specific external stimulus to be sensed.nIn this work we will show that such devices can be routinely fabricated on highly flexible, ultra-conformable thin films and that they can be employed, with no need of any chemical modification of the sensing area, for monitoring pH variations featuring a super-nernstian sensitivity. Interestingly, we will also show that the proposed approach has been applied for monitoring cell metabolic activity, demonstrated with a preliminary validation. In addition this device can be used for monitoring electrical activity of excitable cells, thus giving rise to a new family of highly sensitive, reference-less, and low-cost devices for a wide range of bio-sensing applications.nFinally, we will also demonstrate that using a different sensing layer it is possible to employ the same device architecture for the realization of matrices of multimodal tactile transducers capable to detect at the same time temperature and pressure stimuli, and that being fabricated on sub-micrometer thin film can be conformably transferred on whatever kind of surface allowing the reproduction of the sense of touch.

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. nIn 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.nMoreover, 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.