Suchergebnisse

Low-voltage organic field-effect transistors (OFETs) promise for low power consumption logic circuits. To enhance the efficiency of the logic circuits, the control of the threshold voltage of the transistors are based on is crucial. We report the systematic control of the threshold voltage of electrolyte-gated OFETs by using various gate metals. The influence of the work function of the metal is investigated in metal-electrolyte-organic semiconductor diodes and electrolyte-gated OFETs. A good correlation is found between the flat-band potential and the threshold voltage. The possibility to tune the threshold voltage over half the potential range applied and to obtain depletion-like (positive threshold voltage) and enhancement (negative threshold voltage) transistors is of great interest when integrating these transistors in logic circuits. The combination of a depletion-like and enhancement transistor leads to a clear improvement of the noise margins in depleted-load unipolar inverters. ; Funding Agencies|Onnesjo Foundation||Swedish Foundation for Strategic Research (OPEN)||Swedish government||Vinnova||EU-ERDF (PEA)||EU-commision (BIOEGOFET)||

Electrolyte-gated organic field-effect transistors (EGOFETs) represent a class of organic thin-film transistors suited for sensing and biosensing in aqueous media, often at physiological conditions. The EGOFET device includes electrodes and an organic semiconductor channel in direct contact with an electrolyte. Upon operation, electric double layers are formed along the gate-electrolyte and the channel-electrolyte interfaces, but ions do not penetrate the channel. This mode of operation allows the EGOFET devices to run at low voltages and at a speed corresponding to the rate of forming electric double layers. Currently, there is a lack of a detailed quantitative model of the EGOFETs that can predict device performance based on geometry and material parameters. In the present paper, for the first time, an EGOFET model is proposed utilizing the Nernst-Planck-Poisson equations to describe, on equal footing, both the polymer and the electrolyte regions of the device configuration. The generated calculations exhibit semi-qualitative agreement with experimentally measured output and transfer curves. ; Funding Agencies|Swedish Research CouncilSwedish Research CouncilEuropean Commission [2017-04474]; Swedish Government Strategic Research Area in Materials Science on Advanced Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009-00971]; French National Research Agency (Agence Nationale de la Recherche) through the project EGOFLEXFrench National Research Agency (ANR) [ANR-17-CE08-0025]

The influence of external electric fields on the vibrational properties of Pentacene-based field effect transistors were investigated by Ramanspectroscopy.ThemonitoredRamanbandswereintherangefrom 1100cm−1 to1200cm−1,whereabroadbandispresentandenhanceddue to the external electric field. The process is modeled by density functional theory (DFT) at the B3LYP/3–21G level. Additionally, the relaxation of the Raman bands after the removal of the external field was determined from an exponential Debye like decay fitting to be approximately 94 min, this finding indicates that a long relaxation time ca. 8 h is required in order to recover the original structure. Experimentally and theoretically was demonstrated that the applied electric fields induce artificial traps in the organic layer mediated by charge carrier–dipole interaction.

Here, we study the temperature-dependent transport properties of OFETs with the prototypical OSC 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) co-processed with polystyrene (PS) as the active layer. The active layer is deposited directly on SiO2 using the bar-assisted meniscus shearing (BAMS) method. The co-processing with PS favors a consequential decrease in interfacial trap densities as previously reported. Furthermore, we demonstrate how this processing method leads to devices exhibiting activation energies well below the current state of the art for TIPS-pentacene on SiO2 or other dielectrics. Altogether, our study reports on TIPS-pentacene thin films exhibiting an activation energy (Ea) as low as 15 meV when the active material is blended with PS and processed via BAMS. Such an unprecedentedly low value originates not only from a decrease in the interfacial trap densities but also from trapping energies much shallower than previously reported elsewhere for the same material. This allows us to clarify the previously reported notion that significant passivation of interfacial traps occurs following the separation of PS from TIPS-pentacene into an individual layer at the interface with the insulator and to confirm that the enhanced transport originates from a synergistic effect wherein both trapping density and depth are reduced. ; E.O. and I.S. acknowledge the financial support of the Natural Sciences and Engineering Research Council of Canada (NSERC) (funding Reference Nos. RGPIN-201805092 and RGPIN-2017-06748), the Fonds de recherche du Québec-Nature et technologies (FRQNT). E.O. also acknowledges the financial support of the Canadian Foundation for Innovation (CFI) through the John R. Evans Leaders Fund (JELF). M.M.T. acknowledges funding by the Spanish Ministry with the Project No. GENESIS PID2019-111682RB-I00 and through the "Severo Ochoa" Programme for Centers of Excellence in R&D (No. FUNFUTURE CEX2019-000917-S) and the Generalitat de Catalunya (No. 2017-SGR-918). A.T. acknowledges his FPU fellowship and is enrolled in the UAB Materials Science Ph.D. program. M.B.R. cordially thanks NSERC for support through the Canada Graduate Scholarships–Master's program and the Centre québécois sur les matériaux fonctionnels (CQMF) for his summer scholarship. ; With funding from the Spanish government through the 'Severo Ochoa Centre of Excellence' accreditation (CEX2019-000917-S). ; Peer reviewed

Fundamental understanding of the charge transport physics of hybrid lead halide perovskite semiconductors is important for advancing their use in high-performance optoelectronics. We use field-effect transistors (FETs) to probe the charge transport mechanism in thin films of methylammonium lead iodide (MAPbI$_{3}$). We show that through optimization of thin-film microstructure and source-drain contact modifications, it is possible to significantly minimize instability and hysteresis in FET characteristics and demonstrate an electron field-effect mobility (μ$_{FET}$) of 0.5 cm$^{2}$/Vs at room temperature. Temperature-dependent transport studies revealed a negative coefficient of mobility with three different temperature regimes. On the basis of electrical and spectroscopic studies, we attribute the three different regimes to transport limited by ion migration due to point defects associated with grain boundaries, polarization disorder of the MA$^{+}$ cations, and thermal vibrations of the lead halide inorganic cages. ; S.P.S. acknowledges funding from the Royal Society London for a Newton Fellowship. B.Y. acknowledges support from China Council Scholarship and Cambridge Overseas Trust. A.S. and R.H.F. acknowledge funding and support from the Engineering and Physical Sciences Research Council (EPSRC) through the India-U.K. APEX project. P.D. acknowledges support from the European Union through the award of a Marie Curie Intra-European Fellowship. X.M. is grateful for the support from the Royal Society. B.N. is grateful for the support from Gates Cambridge and the Winton Program for the Physics of Sustainability. We acknowledge funding from the EPSRC through a program grant (EP/M005143/1). We acknowledge funding from the German Federal Ministry of Education and Research under agreement number 01162525/1. This work was performed in part on the SAXS/WAXS beamline of the Australian Synchrotron, Victoria, Australia (55, 56). C.R.M. acknowledges support from the Australian Research Council (DP13012616).

Under the terms of the Creative Commons Attribution (CC BY) license to their work. ; We have used a multi-scale physics-based model to predict how the grain size and different grain boundary morphologies of polycrystalline graphene will impact the performance metrics of graphene field-effect transistors. We show that polycrystallinity has a negative impact on the transconductance, which translates to a severe degradation of the maximum and cutoff frequencies. On the other hand, polycrystallinity has a positive impact on current saturation, and a negligible effect on the intrinsic gain. These results reveal the complex role played by graphene grain boundaries and can be used to guide the further development and optimization of graphene-based electronic devices. ; We acknowledge support from SAMSUNG within the Global Innovation Program. The research leading to these results has received funding from Ministerio de Economía y Competitividad of Spain under the Project Nos. TEC2012-31330 and MAT2012-33911, and from the European Union Seventh Framework Programme under Grant Agreement No. 604391 Graphene Flagship. ; Peer Reviewed

In this work we present an automatic thermoregulation system for biosensors based on field-effect transistors with a nanowire channel, which provides full control on the required temperature regime in bioanalytical analises. The system elements, including field-effect transistors with a nanowire channel, temperature sensors and heaters, were fabricated on a single silicon cristal using electron beam lithography, reactive ion etching and high-vacuum deposition techniques. Unicue electronics have been developed to control and maintain temperature. The dependence of thermometer readout on heating power was measured, which is in good agreement with the results of numerical simulation. A demonstration of a thermoregulation system with PID-feedback was carried out, ensuring the establishment of a desiered temperature in the range of 30-70◦ C in 18 s in liquid. A demonstration of a thermoregulation system for detecting nucleic acids was carried out using synthetic single-stranded DNA, which is a gene fragment from the bacterium Escherichia coli. The minimal detectable response was observed for a sample with a concentration of 3 fM.

AlxGa1-xN/GaN Heterostructure Field Effect Transistors (HFETs) have come under increased study, in recent years, owing to their highly desirable material and electrical properties, ruggedness, and survivability even during and after exposure to extreme temperature and radiation environments. These devices or similar devices constructed of AlGaN and/or GaN materials are being researched for their potential applications in many military and space based systems. In this study, unpassivated and SiN passivated Al0.27Ga0.73N/GaN HFETs were subjected to electron radiation at incident energies of 0.5MeV and 1.0MeV and fluences from 5x1014 to 5x1015 [e-/cm2] while maintained in a 10-6 Torr or higher vacuum at liquid nitrogen temperature (LN). The primary focus of the research was the effects of electron radiation and temperature on drain current, gate leakage current, threshold voltage shift, and gate-channel capacitance. Measurements were taken of transistor current, gate-channel capacitance, and gate leakage current vs. gate bias at 4°K temperature intervals beginning at LN through room temperature (RT). The resulting gate leakage currents were fitted to a Trap-Assisted Tunneling model and transistor currents were compared to a Charge Control model to evaluate post-irradiation change mechanisms to the parameters of these models. Post-irradiation drain currents increased for all devices, with a consistently lesser increase observed for passivated devices. Most post-irradiation increases returned to nearly pre-irradiation levels after an RT anneal period. Threshold voltage shifts averaged -0.5V for unpassivated and -0.2V for passivated HFETs, showed negligible temperature dependence, and returned to near pre-irradiation values, after RT anneal periods. Gate leakage currents showed post-irradiation increases for all devices.

International audience ; The ability to detect minute traces of chemical warfare agents is mandatory both for military forces and homeland security. Various detectors based on different technologies are available but still suffer from serious drawbacks such as false positives. There is still a need for the development of innovative reliable sensors, in particular for organophosphorus nerve agents like Sarin. We report herein on the fabrication of a portable, battery-operated, microprocessor-based prototype sensor system relying on silicon nanowire field-effect transistors for the detection of nerve agents. A fast, supersensitive and highly selective detection of organophosphorus molecules is reported. The results show also high selectivity in complex mixtures and on contaminated materials.