20 research outputs found
Flexible oxide thin film transistors: device fabrication and kelvin probe force microscopy analysis
I transistor a film sottile basati su ossidi amorfi semiconduttori sono ottimi candidati nell'ambito dell'elettronica su larga scala. Al contrario delle tecnologie basate su a-Si:H a poly-Si, gli AOS presentano un'elevata mobilitĂ elettrica (m > 10 cm^2/ Vs) nonostante la struttura amorfa. Inoltre, la possibilitĂ di depositare AOS a basse temperature e su substrati polimerici, permette il loro impiego nel campo dell'elettronica flessibile.
Al fine di migliorare questa tecnologia, numerosi TFT basati su AOS sono stati fabbricati durante 4 mesi di attività all'Università Nova di Lisbona. Tutti i transistor presentano un canale formato da a-GIZO, mentre il dielettrico è stato realizzato con due materiali differenti: Parylene (organico) e 7 strati alternati di SiO2
e SiO2 + Ta2O5. I dispositivi sono stati realizzati su substrati
flessibili sviluppando una nuova tecnica per la laminazione e la delaminazione di fogli di PEN su supporto rigido. L'ottimizzazione del processo di fabbricazione ha permesso la realizzazione
di dispositivi che presentano caratteristiche paragonabili a quelle previste per TFT costruiti su substrati rigidi (m = 35.7 cm^2/Vs; VON = -0.10 V; S = 0.084 V/dec).
Al Dipartimento di Fisica dell'UNIBO, l'utilizzo del KPFM ha permesso lo studio a livello microscopico delle prestazioni presentate dai dispositivi analizzati. Grazie a questa tecnica di indagine, è stato possibile analizzare l'impatto delle resistenze di contatto sui dispositivi meno performanti e identificare l'esistenza di cariche intrappolate nei TFT basati su Parylene.
Gli ottimi risultati ottenuti dall'analisi KPFM suggeriscono un futuro impiego di questa tecnica per lo studio del legame tra stress meccanico e degradazione elettrica dei dispositivi. Infatti, la comprensione dei fenomeni microscopici dovuti alla deformazione strutturale sarĂ un passaggio indispensabile per lo sviluppo dell'elettronica flessibile
Novel Semiconducting Materials and Thin Film Technologies for High Energy Radiation Detection
Nowadays the development of real-time ionizing radiation detection system operating over large areas is crucial. Increasing quest for flexible, portable, low cost and low power consumption sensors pushed the scientific community to look for alternative materials and technologies able to fulfill these new requirements. In this thesis the potentiality of organic semiconductors and metal oxides as material platforms for novel ionizing radiation sensors is demonstrated. In particular, organic semiconductors are human tissue-equivalent and this represents a unique and desirable property for the development of dosimeters to be employed in the medical field. The ionizing radiation sensors described in this thesis have been designed, fabricated and characterized during my PhD research and are realized onto polymeric foils leading to flexible devices operating at low voltages, in ambient condition and able to directly detect X-rays, gamma-rays and protons. Following the study of the properties and of the mechanisms of interaction between the radiation and the active layers of the sensors, several strategies have been adopted to enhance the efficiency of these detectors. X-rays dosimeters based on organic semiconductors have been realized presenting record sensitivity values compared with the state of the art for large area radiation detection. The unprecedentedly reported performance led to the possibility to testing these devices in actual medical environments. Moreover, the proof-of-principle demonstration of a dosimetric detection of proton beams by organic-based sensors is reported. Finally, a new sensing platform based on metal oxides is introduced. Combining the advantages of amorphous high mobility oxide semiconductors with a multilayer dielectric, novel devices have been designed, capable of providing a sensitivity one order of magnitude higher than the one shown by the standard RADFETs. Thanks to their unique properties, these sensors have been integrated with a wireless readout system based on a commercial RFID tag and its assessment is presented
Direct Detection of 5-MeV Protons by Flexible Organic Thin-Film Devices
The direct detection of 5-MeV protons by flexible organic detectors based on thin films is here demonstrated. The organic devices act as a solid-state detector, in which the energy released by the protons within the active layer of the sensor is converted into an electrical current. These sensors can quantitatively and reliably measure the dose of protons impinging on the sensor both in real time and in integration mode. This study shows how to detect and exploit the energy absorbed both by the organic semiconducting layer and by the plastic substrate, allowing to extrapolate information on the present and past irradiation of the detector. The measured sensitivity, S = (5.15 Âą 0.13) pC Gyâ1, and limit of detection, LOD = (30 Âą 6) cGy sâ1, of the here proposed detectors assess their efficacy and their potential as proton dosimeters in several fields of application, such as in medical proton therapy
Medical Applications of Tissue-Equivalent, Organic-Based Flexible Direct X-Ray Detectors
The aim of this study is to assess direct X-ray detectors based on organic thin films, fabricated onto flexible plastic substrates, and operating at ultra-low bias (<1 V), for different medical applications. With this purpose, flexible fully organic pixelated X-ray detectors have been tested at the imaging beamline SYRMEP (SYnchrotron Radiation for MEdical Physics) at the Italian synchrotron Elettra, Trieste. The detectors' performance has been assessed for potential employment both as reliable wearable personal dosimeters for patients and as flexible X-ray medical imaging systems. A spatial resolution of 1.4 lp mmâ1 with a contrast of 0.37 has been evaluated. Finally, we validate the detector using X-ray doses and energies typically employed for actual medical radiography, and using X-ray beam pulses provided by a commercial dental radiography system, recording a sensitivity of 1.6 Ă 105 ÎźC Gyâ1 cmâ3 with a linear response with increasing of the dose rates and a reliable signal to 100 ms X-rays pulses
Molecular Weight Tuning of Organic Semiconductors for Curved Organic-Inorganic Hybrid X-Ray Detectors
Curved X-ray detectors have the potential to revolutionize diverse sectors due to benefits such as reduced image distortion and vignetting compared to their planar counterparts. While the use of inorganic semiconductors for curved detectors are restricted by their brittle nature, organic-inorganic hybrid semiconductors which incorporated bismuth oxide nanoparticles in an organic bulk heterojunction consisting of poly(3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl C71 butyric acid methyl ester (PC70BM) are considered to be more promising in this regard. However, the influence of the P3HT molecular weight on the mechanical stability of curved, thick X-ray detectors remains less well understood. Herein, high P3HT molecular weights (>40 kDa) are identified to allow increased intermolecular bonding and chain entanglements, resulting in X-ray detectors that can be curved to a radius as low as 1.3 mm with low deviation in X-ray response under 100 repeated bending cycles while maintaining an industry-standard dark current of mu C Gy(-1) cm(-2). This study identifies a crucial missing link in the development of curved detectors, namely the importance of the molecular weight of the polymer semiconductors used
Tissue Equivalent Curved Organic X-ray Detectors Utilizing High Atomic Number Polythiophene Analogues
Organic semiconductors are a promising material candidate for X-ray detection. However, the low atomic number (Z) of organic semiconductors leads to poor X-ray absorption thus restricting their performance. Herein, the authors propose a new strategy for achieving high-sensitivity performance for X-ray detectors based on organic semiconductors modified with high âZ heteroatoms. X-ray detectors are fabricated with p-type organic semiconductors containing selenium heteroatoms (poly(3-hexyl)selenophene (P3HSe)) in blends with an n-type fullerene derivative ([6,6]-Phenyl C71 butyric acid methyl ester (PC70BM). When characterized under 70, 100, 150, and 220 kVp X-ray radiation, these heteroatom-containing detectors displayed a superior performance in terms of sensitivity up to 600 Âą 11 nC Gyâ1 cmâ2 with respect to the bismuth oxide (Bi2O3) nanoparticle (NP) sensitized organic detectors. Despite the lower Z of selenium compared to the NPs typically used, the authors identify a more efficient generation of electron-hole pairs, better charge transfer, and charge transport characteristics in heteroatom-incorporated detectors that result in this breakthrough detector performance. The authors also demonstrate flexible X-ray detectors that can be curved to a radius as low as 2 mm with low deviation in X-ray response under 100 repeated bending cycles while maintaining an industry-standard ultra-low dark current of 0.03 Âą 0.01 pA mmâ2
Perinatal and 2-year neurodevelopmental outcome in late preterm fetal compromise: the TRUFFLE 2 randomised trial protocol
Introduction: Following the detection of fetal growth restriction, there is no consensus about the criteria that should trigger delivery in the late preterm period. The consequences of inappropriate early or late delivery are potentially important yet practice varies widely around the world, with abnormal findings from fetal heart rate monitoring invariably leading to delivery. Indices derived from fetal cerebral Doppler examination may guide such decisions although there are few studies in this area. We propose a randomised, controlled trial to establish the optimum method of timing delivery between 32 weeks and 36 weeks 6âdays of gestation. We hypothesise that delivery on evidence of cerebral blood flow redistribution reduces a composite of perinatal poor outcome, death and short-term hypoxia-related morbidity, with no worsening of neurodevelopmental outcome at 2 years. Methods and analysis: Women with non-anomalous singleton pregnancies 32+0 to 36+6 weeks of gestation in whom the estimated fetal weight or abdominal circumference is <10th percentile or has decreased by 50 percentiles since 18-32 weeks will be included for observational data collection. Participants will be randomised if cerebral blood flow redistribution is identified, based on umbilical to middle cerebral artery pulsatility index ratio values. Computerised cardiotocography (cCTG) must show normal fetal heart rate short term variation (âĽ4.5âmsec) and absence of decelerations at randomisation. Randomisation will be 1:1 to immediate delivery or delayed delivery (based on cCTG abnormalities or other worsening fetal condition). The primary outcome is poor condition at birth and/or fetal or neonatal death and/or major neonatal morbidity, the secondary non-inferiority outcome is 2-year infant general health and neurodevelopmental outcome based on the Parent Report of Children's Abilities-Revised questionnaire. Ethics and dissemination: The Study Coordination Centre has obtained approval from London-Riverside Research Ethics Committee (REC) and Health Regulatory Authority (HRA). Publication will be in line with NIHR Open Access policy. Trial registration number: Main sponsor: Imperial College London, Reference: 19QC5491. Funders: NIHR HTA, Reference: 127â976. Study coordination centre: Imperial College Healthcare NHS Trust, Du Cane Road, London, W12 0HS with Centre for Trials Research, College of Biomedical & Life Sciences, Cardiff University. IRAS Project ID: 266â400. REC reference: 20/LO/0031. ISRCTN registry: 76â016â200
Rivelatori di raggi X basati su cristalli organici semiconduttori
Negli ultimi anni, i progressi della ricerca scientifica nell'ambito dell'elettronica organica hanno messo in luce le proprietĂ dei cristalli organici che rendono possibile un loro potenziale utilizzo nel campo della rivelazione di radiazioni ionizzanti.
All'interno di questa tesi, analizzeremo le prestazioni di rivelazione di raggi X da parte di due cristalli che si distinguono tra loro per proprietĂ chimiche e fisiche: l'NTI e il Rubrene. Questi due materiali verranno sottoposti a misure elettriche, svolte in diverse condizioni di irraggiamento, e dai dati ottenuti sarĂ possibile analizzare la risposta alla radiazione da parte di ciascun dispositivo. Verranno valutate le capacitĂ di rivelazione da parte dei due materiali studiati, in base ai parametri che caratterizzano i rivelatori di radiazione a stato solido, e sarĂ inoltre possibile mettere a confronto i risultati ottenuti dai due diversi cristalli e osservare eventuali comportamenti differenti
Morphology and mobility as tools to control and unprecedentedly enhance X-ray sensitivity in organic thin-films
Organic semiconductor materials exhibit a great potential for the realization of large-area solution-processed devices able to directly detect high-energy radiation. However, only few works investigated on the mechanism of ionizing radiation detection in this class of materials, so far. In this work we investigate the physical processes behind X-ray photoconversion employing bis-(triisopropylsilylethynyl)-pentacene thin-films deposited by bar-assisted meniscus shearing. The thin film coating speed and the use of bis-(triisopropylsilylethynyl)-pentacene:polystyrene blends are explored as tools to control and enhance the detection capability of the devices, by tuning the thin-film morphology and the carrier mobility. The so-obtained detectors reach a record sensitivity of 1.3â¡â104 ÂľC/Gy¡cm2, the highest value reported for organic-based direct X-ray detectors and a very low minimum detectable dose rate of 35 ÂľGy/s. Thus, the employment of organic large-area direct detectors for X-ray radiation in real-life applications can be foreseen.I.F., L.B., A.C., and B.F. acknowledge funding from INFN through the CSN5 FIRE project. This work was also funded by the ERC StG 2012-306826 e-GAMES and the DGI (Spain) project FANCY CTQ2016-80030-R. The authors also thank the Generalitat de Catalunya (2017-SGR-918), the Networking Research Center on Bioengineering, Biomaterials, and Nanomedicine (CIBER-BBN), and the Spanish Ministry of Economy and Competitiveness, through the âSevero Ochoaâ Programme for Centers of Excellence in R&D (SEV-2015-0496). I.T. and A.T. are enrolled in the Materials Science PhD program of Universitat Autònoma de Barcelona and acknowledge FPU fellowship from the Spanish Ministry.Peer reviewe
Boosting Direct XâRay Detection in Organic Thin Films by Small Molecules Tailoring
The attention focused on the application of organic electronics for the detection of ionizing radiation is rapidly growing among the international scientific community, due to the great potential of organic technology to enable largeâarea conformable sensor panels. However, highâenergy photon absorption is challenging as organic materials are constituted of atoms with low atomic numbers. Here it is reported how, by synthesizing new solutionâprocessable organic molecules derived from 6,13âbis(triisopropylsilylethynyl)pentacene (TIPSâpentacene) and 2,8âdifluoroâ5,11âbis(triethylsilylethynyl)anthradithiophene, with Geâsubstitution in place of the Si atoms to increase the material atomic number, it is possible to boost the Xâray detection performance of organic thin films on flexible plastic substrates. Bis(triisopropylgermylethynyl)âpentacene based flexible organic thin film transistors show high electrical performance with higher mobility (0.4 cm2 Vâ1 sâ1) and enhanced Xâray sensitivity, up to 9.0 Ă 105 ÂľC Gyâ1 cmâ3, with respect to TIPSâpentaceneâbased detectors. Moreover, similar results are obtained for 5,11âbis(triethylgermylethynyl)anthradithiophene devices, confirming that the proposed strategy, that is, increasing the atomic number of organic molecules by chemical tailoring to improve Xâray sensitivity, can be generalized to organic thin film detectors, combining high Xâray absorption, mechanical flexibility, and largeâarea processing