The effect of the dielectric end groups on the positive bias stress stability of N2200 organic field effect transistors

Bias stress degradation in conjugated polymer field-effect transistors is a fundamental problem in these disordered materials and can be traced back to interactions of the material with environmental species,[1,2,3] as well as fabrication-induced defects.[4,5] However, the effect of the end groups of the polymer gate dielectric and the associated dipole-induced disorder on bias stress stability has not been studied so far in high-performing n-type materials, such as N2200.[6,7] In this work, the performance metrics of N2200 transistors are examined with respect to dielectrics with different end groups (Cytop-M and Cytop-S).[8] We hypothesize that the polar end groups would lead to increased dipole-induced disorder, and worse performance.[1,9,10] The long-time annealing scheme at lower temperatures used in the paper is assumed to lead to better crystallization by allowing the crystalline domains to reorganize in the presence of the solvent.[11] It is hypothesized that the higher crystallinity could narrow down the range at which energy carriers are induced and thus decrease the gate dependence of the mobility. The results show that the dielectric end groups do not influence the bias stress stability of N2200 transistors. However, long annealing times result in a dramatic improvement in bias stress stability, with the most stable devices having a mobility that is only weakly dependent on or independent of gate voltage

Structural and dynamic disorder, not ionic trapping, controls charge transport in highly doped conducting polymers

Doped organic semiconductors are critical to emerging device applications, including thermoelectrics, bioelectronics, and neuromorphic computing devices. It is commonly assumed that low conductivities in these materials result primarily from charge trapping by the Coulomb potentials of the dopant counter-ions. Here, we present a combined experimental and theoretical study rebutting this belief. Using a newly developed doping technique, we find the conductivity of several classes of high-mobility conjugated polymers to be strongly correlated with paracrystalline disorder but poorly correlated with ionic size, suggesting that Coulomb traps do not limit transport. A general model for interacting electrons in highly doped polymers is proposed and carefully parameterized against atomistic calculations, enabling the calculation of electrical conductivity within the framework of transient localisation theory. Theoretical calculations are in excellent agreement with experimental data, providing insights into the disordered-limited nature of charge transport and suggesting new strategies to further improve conductivities

Structural and dynamic disorder, not ionic trapping, controls charge transport in highly doped conducting polymers

Doped organic semiconductors are critical to emerging device applications, including thermoelectrics, bioelectronics, and neuromorphic computing devices. It is commonly assumed that low conductivities in these materials result primarily from charge trapping by the Coulomb potentials of the dopant counter-ions. Here, we present a combined experimental and theoretical study rebutting this belief. Using a newly developed doping technique, we find the conductivity of several classes of high-mobility conjugated polymers to be strongly correlated with paracrystalline disorder but poorly correlated with ionic size, suggesting that Coulomb traps do not limit transport. A general model for interacting electrons in highly doped polymers is proposed and carefully parameterized against atomistic calculations, enabling the calculation of electrical conductivity within the framework of transient localisation theory. Theoretical calculations are in excellent agreement with experimental data, providing insights into the disordered-limited nature of charge transport and suggesting new strategies to further improve conductivities

Electrolyte‐gated organic field‐effect transistors with high operational stability and lifetime in practical electrolytes

A key component of organic bioelectronics is electrolyte‐gated organic field‐effect transistors (EG‐OFETs), which have recently been used as sensors to demonstrate label‐free, single‐molecule detection. However, these devices exhibit limited stability when operated in direct contact with aqueous electrolytes. Ultrahigh stability is demonstrated to be achievable through the utilization of a systematic multifactorial approach in this study. EG‐OFETs with operational stability and lifetime several orders of magnitude higher than the state of the art have been fabricated by carefully controlling a set of intricate stability‐limiting factors, including contamination and corrosion. The indacenodithiophene‐co‐benzothiadiazole (IDTBT) EG‐OFETs exhibit operational stability that exceeds 900 min in a variety of widely used electrolytes, with an overall lifetime exceeding 2 months in ultrapure water and 1 month in various electrolytes. The devices were not affected by electrical stress‐induced trap states and can remain stable even in voltage ranges where electrochemical doping occurs. To validate the applicability of our stabilized device for biosensing applications, the reliable detection of the protein lysozyme in ultrapure water and in a physiological sodium phosphate buffer solution for 1500 min was demonstrated. The results show that polymer‐based EG‐OFETs are a viable architecture not only for short‐term but also for long‐term biosensing applications

OptiJ: Open-source optical projection tomography of large organ samples

Abstract: The three-dimensional imaging of mesoscopic samples with Optical Projection Tomography (OPT) has become a powerful tool for biomedical phenotyping studies. OPT uses visible light to visualize the 3D morphology of large transparent samples. To enable a wider application of OPT, we present OptiJ, a low-cost, fully open-source OPT system capable of imaging large transparent specimens up to 13 mm tall and 8 mm deep with 50 µm resolution. OptiJ is based on off-the-shelf, easy-to-assemble optical components and an ImageJ plugin library for OPT data reconstruction. The software includes novel correction routines for uneven illumination and sample jitter in addition to CPU/GPU accelerated reconstruction for large datasets. We demonstrate the use of OptiJ to image and reconstruct cleared lung lobes from adult mice. We provide a detailed set of instructions to set up and use the OptiJ framework. Our hardware and software design are modular and easy to implement, allowing for further open microscopy developments for imaging large organ samples

OptiJ: Open-source optical projection tomography of large organ samples

The three-dimensional imaging of mesoscopic samples with Optical Projection Tomography (OPT) has become a powerful tool for biomedical phenotyping studies. OPT uses visible light to visualize the 3D morphology of large transparent samples. To enable a wider application of OPT, we present OptiJ, a low-cost, fully open-source OPT system capable of imaging large transparent specimens up to 13 mm tall and 8 mm deep with 50 µm resolution. OptiJ is based on off-the-shelf, easy-to-assemble optical components and an ImageJ plugin library for OPT data reconstruction. The software includes novel correction routines for uneven illumination and sample jitter in addition to CPU/GPU accelerated reconstruction for large datasets. We demonstrate the use of OptiJ to image and reconstruct cleared lung lobes from adult mice. We provide a detailed set of instructions to set up and use the OptiJ framework. Our hardware and software design are modular and easy to implement, allowing for further open microscopy developments for imaging large organ samples

High‐Efficiency Ion‐Exchange Doping of Conducting Polymers

Abstract: Molecular doping—the use of redox‐active small molecules as dopants for organic semiconductors—has seen a surge in research interest driven by emerging applications in sensing, bioelectronics, and thermoelectrics. However, molecular doping carries with it several intrinsic problems stemming directly from the redox‐active character of these materials. A recent breakthrough was a doping technique based on ion‐exchange, which separates the redox and charge compensation steps of the doping process. Here, the equilibrium and kinetics of ion exchange doping in a model system, poly(2,5‐bis(3‐alkylthiophen‐2‐yl)thieno(3,2‐b)thiophene) (PBTTT) doped with FeCl3 and an ionic liquid, is studied, reaching conductivities in excess of 1000 S cm−1 and ion exchange efficiencies above 99%. Several factors that enable such high performance, including the choice of acetonitrile as the doping solvent, which largely eliminates electrolyte association effects and dramatically increases the doping strength of FeCl3, are demonstrated. In this high ion exchange efficiency regime, a simple connection between electrochemical doping and ion exchange is illustrated, and it is shown that the performance and stability of highly doped PBTTT is ultimately limited by intrinsically poor stability at high redox potential

Water stability of organic and electrolyte-gated field-effect transistors

Organic bioelectronics is an emerging field that utilizes electronic devices made from a large family of aromatic compounds (conjugated polymers and small molecules) for biological applications. Organic materials seem ideal candidates for bioelectronics due to their softness, biocompatibility, stretchability, and their ability to conduct both electrons and ions. Many fundamental studies have been conducted, utilizing devices such as the Organic Field Effect Transistor (OFET), the Electrolyte-Gated OFET (EG-OFET), and the Organic Electro-Chemical Transistor (OECT). However, water constitutes a key factor in charge trapping and device degradation in organic materials, due to its strong dipole moment, high dielectric constant, and its omnipresence in almost all processing, environmental, and operational conditions. In this dissertation, we used an additives-based approach to stabilize OFETs immersed in DI water and saline solution, for periods up to a month, making the first high-performance water-stable OFETs reported in the literature. We then repeated the long-term water stability experiments on EG-OFETs, and demonstrated that cleanly fabricated EG-OFETs can remain stable within the course of an overnight measurement (16 hours), without needing the additive stabilization process. By comparing the water stability of OFETs and EG-OFETs, we highlighted the different requirements involved in stabilizing these two architectures, challenging the notion that organic materials are intrinsically unstable in water.D. Simatos acknowledges support from the EPSRC Centre for Doctoral Training (CDT) in Sensor Technologies and Application (EP/L015889/1), as well as support by the Henry Royce Institute facilities grant (EP/P024947/1)

SONOS memory devices with ion beam modified nitride layers

135 σ.Οι διατάξεις μνήμης τύπου SONOS αποτελούν μια πολλά υποσχόμενη εναλλακτική επιλογή των μνημών αιωρούμενης πύλης, ειδικά σε ότι αφορά τα ενσωματωμένα συστήματα. Όμως, αυτή η κατηγορία μη πτητικών μνημών, που χρησιμοποιούν συνήθως διηλεκτρικές στοίβες οξειδίου-νιτριδίου του πυριτίου-οξειδίου, απαιτεί βελτιώσεις, κυρίως σε ότι αφορά τη λειτουργία της διαγραφής. Μία μέθοδος βελτίωσης των ηλεκτρικών χαρακτηριστικών των διατάξεων αυτών είναι μέσω ιοντικής εμφύτευσης χαμηλής ενέργειας στο νιτρίδιο του πυριτίου και στη συνέχεια υγρή οξείδωση. Διατάξεις οξειδίου-νιτριδίου του πυριτίου (2.5nm/6nm) κατασκευάστηκαν σε υπόστρωμα πυριτίου τύπου n. Στη συνέχεια εμφυτεύθηκαν ιόντα πυριτίου, αζώτου και αργού με δόση 1E16 ions/cm^2 σε χαμηλή ενέργεια 1keV και ακολούθησε υγρή οξείδωση στους 850 βαθμούς Κελσίου για 15 λεπτά. Ο ηλεκτρικός χαρακτηρισμός των τελικών διατάξεων πραγματοποιήθηκε χρησιμοποιώντας συνηθισμένους πυκνωτές MONOS με πύλη αλουμινίου. Ο δομικός χαρακτηρισμός τύπου TEM έδειξε ότι το πάχος του οξειδίου φραγής επηρεάζεται σημαντικά από την ιοντική εμφύτευση και κυμαίνεται από 1nm (για το μη εμφυτευμένο δείγμα), 4-5nm (για N και Ar) μέχρι 10nm για Si. Οι διατάξεις εμφυτευμένες με ιόντα πυριτίου παρουσίασαν το μεγαλύτερο δυνατό παράθυρο, περίπου 9V. Οι μετρήσεις διατήρησης φορτίου σε θερμοκρασία δωματίου αποκάλυψαν ότι ο ρυθμός απώλειας ηλεκτρονίων είναι πιο μεγάλος στα δείγματα εμφυτευμένα με Si, παρά με N, πράγμα που οδηγεί σε ένα παράθυρο της τάξης των 1.7V και 2.5V αντίστοιχα μετά από 10 χρόνια. Αυτή η διαφορά στη διατήρηση φορτίου πιστώνεται κυρίως στη διαφορετική φύση των παγίδων που δημιουργούνται.The SONOS type memory devices constitute a promising scaling alternative to the conventional floating-gate cells, especially for embedded applications. However, this class of non-volatile memory cells, which typically make use of oxide-nitride-oxide (ONO) charge-trapping stacks, requires improvements mainly in regards of the erase operation. A method to accomplish significant advances in device performance is via low-energy silicon ion implantation into oxide-nitride stacks followed by a low-thermal budget wet-oxidation. Typical oxide-nitride stacks (2.5nm/6nm) were formed on n-type silicon substrates. The stacks were implanted with 1keV Si, N and Ar to a dose of 1E16 ions/cm^2, and further wet oxidized at 850 degrees Celsius for 15 min. Electrical characterization of the final structures was performed using standard aluminum gate MONOS capacitors. TEM imaging showed that the thickness of the blocking oxide layer is strongly affected by the implantation process going from 1nm (non-implanted sample), 4-5nm (N and Ar) and 10nm (Si). Si implanted stacks showed the highest attainable memory window (ca 9V). Room temperature charge retention measurements of the programming state revealed that the electron loss rate is faster in samples implanted with Si than N, allowing for a memory window of 1.7V and 2.5V respectively after ten years extrapolation. This retention behavior is mainly attributed to the different nature of the traps generated in these materials.Δημήτριος Π. Σιμάτο