Neuromorphic device architectures with global connectivity through electrolyte gating.

Information processing in the brain takes place in a network of neurons that are connected with each other by an immense number of synapses. At the same time, neurons are immersed in a common electrochemical environment, and global parameters such as concentrations of various hormones regulate the overall network function. This computational paradigm of global regulation, also known as homeoplasticity, has important implications in the overall behaviour of large neural ensembles and is barely addressed in neuromorphic device architectures. Here, we demonstrate the global control of an array of organic devices based on poly(3,4ethylenedioxythiophene):poly(styrene sulf) that are immersed in an electrolyte, a behaviour that resembles homeoplasticity phenomena of the neural environment. We use this effect to produce behaviour that is reminiscent of the coupling between local activity and global oscillations in the biological neural networks. We further show that the electrolyte establishes complex connections between individual devices, and leverage these connections to implement coincidence detection. These results demonstrate that electrolyte gating offers significant advantages for the realization of networks of neuromorphic devices of higher complexity and with minimal hardwired connectivity

Efficient Gating of Organic Electrochemical Transistors with In-Plane Gate Electrodes

AbstractOrganic electrochemical transistors (OECTs) are electrolyte‐gated transistors, employing an electrolyte between their gate and channel instead of an insulating layer. For efficient gating, non‐polarizable electrodes, for example, Ag/AgCl, are typically used but unfortunately, this simple approach limits the options for multiple gate integration. Patterned polarizable Au gates on the other hand, show strongly reduced gating due to a large voltage drop at the gate/electrolyte interface. Here, an alternative, simple yet effective method for efficient OECT gating by scalable in‐plane gate electrodes, is demonstrated. The fact that poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) exhibits a volumetric capacitance in an electrolyte is made use of. As a result, the capacitance of PEDOT:PSS‐based gates can be strongly enhanced by increasing their thickness, thereby reducing the voltage loss at the gate/electrolyte interface. By combining spin coating and electrodeposition, planar electrodes of various thicknesses are created on a multi‐gated OECT chip and their effect on the gating efficiency, examined. It is shown that the gating performed by an in‐plane PEDOT:PSS electrode can be tuned to be comparable to the one obtained by a Ag/AgCl electrode. Overall, the realization of efficient gating with in‐plane electrodes paves the way toward integration of OECT‐based biosensors and "organ‐on‐a‐chip" platforms

Orientation selectivity in a multi-gated organic electrochemical transistor.

UNLABELLED: Neuromorphic devices offer promising computational paradigms that transcend the limitations of conventional technologies. A prominent example, inspired by the workings of the brain, is spatiotemporal information processing. Here we demonstrate orientation selectivity, a spatiotemporal processing function of the visual cortex, using a poly(3,4ethylenedioxythiophene):poly(styrene sulfonate) ( PEDOT: PSS) organic electrochemical transistor with multiple gates. Spatially distributed inputs on a gate electrode array are found to correlate with the output of the transistor, leading to the ability to discriminate between different stimuli orientations. The demonstration of spatiotemporal processing in an organic electronic device paves the way for neuromorphic devices with new form factors and a facile interface with biology

Brain-Inspired Organic Electronics:Merging Neuromorphic Computing and Bioelectronics Using Conductive Polymers

Neuromorphic computing offers the opportunity to curtail the huge energy demands of modern artificial intelligence (AI) applications by implementing computations into new, brain-inspired computing architectures. However, the lack of fabrication processes able to integrate several computing units into monolithic systems and the need for new, hardware-tailored training algorithms still limit the scope of application and performance of neuromorphic hardware. Recent advancements in the field of organic transistors present new opportunities for neuromorphic systems and smart sensing applications, thanks to their unique properties such as neuromorphic behavior, low-voltage operation, and mixed ionic-electronic conductivity. Organic neuromorphic transistors push the boundaries of energy efficient brain-inspired hardware AI, facilitating decentralized on-chip learning and serving as a foundation for the advancement of closed-loop intelligent systems in the next generation. The biocompatibility and dual ionic-electronic conductivity of organic materials introduce new prospects for biointegration and bioelectronics. Their ability to sense and regulate biosystems, as well as their neuro-inspired functions can be combined with neuromorphic computing to create the next-generation of bioelectronics. These systems will be able to seamlessly interact with biological systems and locally compute biosignals in a relevant matter

Bio-inspired multimodal learning with organic neuromorphic electronics for behavioral conditioning in robotics

Biological systems interact directly with the environment and learn by receiving multimodal feedback via sensory stimuli that shape the formation of internal neuronal representations. Drawing inspiration from biological concepts such as exploration and sensory processing that eventually lead to behavioral conditioning, we present a robotic system handling objects through multimodal learning. A small-scale organic neuromorphic circuit locally integrates and adaptively processes multimodal sensory stimuli, enabling the robot to interact intelligently with its surroundings. The real-time handling of sensory stimuli via low-voltage organic neuromorphic devices with synaptic functionality forms multimodal associative connections that lead to behavioral conditioning, and thus the robot learns to avoid potentially dangerous objects. This work demonstrates that adaptive neuro-inspired circuitry with multifunctional organic materials, can accommodate locally efficient bio-inspired learning for advancing intelligent robotics

Monitoring Reversible Tight Junction Modulation with a Current‐Driven Organic Electrochemical Transistor

AbstractThe barrier functionality of a cell layer regulates the passage of nutrients into the blood. Modulating the barrier functionality by external chemical agents like poly‐l‐lysine (PLL) is crucial for drug delivery. The ability of a cell layer to impede the passage of ions through it and therefore to act as a barrier, can be assessed electrically by measuring the resistance across the cell layer. Here, an organic electrochemical transistor (OECT) is used in a current‐driven configuration for the evaluation of reversible modulation of tight junctions in Caco‐2 cells over time. Exposure to low and medium concentrations of PLL initiates reversible modulation, whereas a too high concentration induces an irreversible barrier disruption due to nonfunctional tight junction proteins. The results demonstrate the suitability of OECTs to in situ monitor temporal barrier modulation and recovery, which can offer valuable information for drug delivery applications

Unravelling the operation of organic artificial neurons for neuromorphic bioelectronics

Organic artificial neurons operating in liquid environments are crucial components in neuromorphic bioelectronics. However, the current understanding of these neurons is limited, hindering their rational design and development for realistic neuronal emulation in biological settings. Here we combine experiments, numerical non-linear simulations, and analytical tools to unravel the operation of organic artificial neurons. This comprehensive approach elucidates a broad spectrum of biorealistic behaviors, including firing properties, excitability, wetware operation, and biohybrid integration. The non-linear simulations are grounded in a physics-based framework, accounting for ion type and ion concentration in the electrolytic medium, organic mixed ionic-electronic parameters, and biomembrane features. The derived analytical expressions link the neurons spiking features with material and physical parameters, bridging closer the domains of artificial neurons and neuroscience. This work provides streamlined and transferable guidelines for the design, development, engineering, and optimization of organic artificial neurons, advancing next generation neuronal networks, neuromorphic electronics, and bioelectronics

Current-Driven Organic Electrochemical Transistors for Monitoring Cell Layer Integrity with Enhanced Sensitivity

AbstractIn this progress report an overview is given on the use of the organic electrochemical transistor (OECT) as a biosensor for impedance sensing of cell layers. The transient OECT current can be used to detect changes in the impedance of the cell layer, as shown by Jimison et al. To circumvent the application of a high gate bias and preventing electrolysis of the electrolyte, in case of small impedance variations, an alternative measuring technique based on an OECT in a current‐driven configuration is developed. The ion‐sensitivity is larger than 1200 mV V‐1dec‐1 at low operating voltage. It can be even further enhanced using an OECT based complementary amplifier, which consists of a p‐type and an n‐type OECT connected in series, as known from digital electronics. The monitoring of cell layer integrity and irreversible disruption of barrier function with the current‐driven OECT is demonstrated for an epithelial Caco‐2 cell layer, showing the enhanced ion‐sensitivity as compared to the standard OECT configuration. As a state‐of‐the‐art application of the current‐driven OECT, the in situ monitoring of reversible tight junction modulation under the effect of drug additives, like poly‐l‐lysine, is discussed. This shows its potential for in vitro and even in vivo toxicological and drug delivery studies

High-Performance Organic Electrochemical Transistors and Neuromorphic Devices Comprising Naphthalenediimide-Dialkoxybithiazole Copolymers Bearing Glycol Ether Pendant Groups

Organic electrochemical transistors (OECTs) have emerged as building blocks for low power circuits, biosensors, and neuromorphic computing. While p-type polymer materials for OECTs are well developed, the choice of high-performance n-type polymers is limited, despite being essential for cation and metabolite biosensors, and crucial for constructing complementary circuits. N-type conjugated polymers that have efficient ion-to-electron transduction are highly desired for electrochemical applications. In this contribution, three non-fused, planar naphthalenediimide (NDI)-dialkoxybithiazole (2Tz) copolymers, which systematically increase the amount of polar tri(ethylene glycol) (TEG) side chains: PNDI2OD-2Tz (0 TEG), PNDIODTEG-2Tz (1 TEG), PNDI2TEG-2Tz (2 TEG), are reported. It is demonstrated that the OECT performance increases with the number of TEG side chains resulting from the progressively higher hydrophilicity and larger electron affinities. Benefiting from the high electron mobility, excellent ion conduction capability, efficient ion-to-electron transduction, and low-lying lowest unoccupied molecular orbital energy level, the 2 TEG polymer achieves close to 105 on-off ratio, fast switching, 1000 stable operation cycles in aqueous electrolyte, and has a long shelf life. Moreover, the higher number TEG chain substituted polymer exhibits good conductance state retention over two orders of magnitudes in electrochemical resistive random-access memory devices, highlighting its potential for neuromorphic computing

Electronic memory devices based on composite polymeric materials and proton carriers

The present thesis concentrates on the study of new electrochemical processes of suitable complex polymer films. The main aim of this thesis is the evaluation of the appropriateness of these processes in order to fabricate an organic non volatile memory. The basic concept of this non volatile memory is based on ionic transport and ionic trapping phenomena of complex polymer films. It should be noticed that the present thesis is not restricted to the fabrication of an organic non volatile memory, but concentrates on the investigation of the ionic transport and interfacial phenomena of these complex polymer films. These complex polymer films consist of poly-methyl methacrylate matrix (PMMA) doped with 12-phosphotungstic acid molecules (POM). The conduction carriers of these complex polymer films are in the form of protons. Various electrolytic capacitor devices were fabricated during thesis research and were studied using several electrical characterization methods such as time and frequency domain dielectric spectroscopy. An in-depth investigation of ionic transport mechanisms and interfacial phenomena was conducted using dielectric spectroscopy measurements in both domains. Additionally, hysteresis phenomena were observed in electrolytic capacitors, as a result of macroscopic ion transport within the electrolyte film. The observed hysteresis is a first sign evidence for memory phenomena in these electrolytic capacitors. Ionic transport mechanisms and interfacial phenomena were also studied as a function of various physicochemical parameters (i.e., electrolyte film thickness in the micro and nanoscale, POM molecule concentration inside the PMMA matrix, moisture effect), by using the aforementioned electrical characterization methods. Finally, the physicochemical properties of the electrolytic films were studied using supplementary spectroscopic techniques such as infra red and ultra violet – visible measurements. The results of this thesis, interpret a series of ionic transport and interfacial phenomena that are evident in several classes of disordered electrolytes.Η παρούσα διατριβή πραγματεύεται τη μελέτη ηλεκτροχημικών διαδικασιών, κατάλληλων σύνθετων πολυμερικών υλικών. Σκοπός της διατριβής αυτής είναι η αξιολόγηση της καταλληλότητας των φαινομένων αυτών, για τη δημιουργία μιας οργανικής μνήμης μόνιμης αποθήκευσης δεδομένων. Η αρχή λειτουργίας αυτής της οργανικής μνήμης στηρίζεται σε φαινόμενα ιοντικής μεταφοράς και παγίδευσης κατάλληλων σύνθετων πολυμερικών στρωμάτων. Θα πρέπει να σημειωθεί ότι η διατριβή αυτή δεν αποσκοπεί αποκλειστικά στην δημιουργία μιας οργανικής μνήμης, αλλά περισσότερο στην εκτενή μελέτη των διεπιφανειακών φαινομένων και φαινομένων ιοντικής μεταφοράς που παρουσιάζουν οι τα στρώματα αυτά. Τα σύνθετα αυτά στρώματα δημιουργούνται με τον εμπλουτισμό πολυμερικής μήτρας πολύ-μεθακρυλικού μεθυλεστέρα (PMMA) με μόρια 12-φώσφο-βολφαμικού οξέος (POM). Οι φορείς αγωγιμότητας των σύνθετων αυτών στρωμάτων είναι τα πρωτόνια. Κατά τη διάρκεια της διατριβής κατασκευάστηκαν ηλεκτρολυτικοί πυκνωτές, οι οποίοι μελετήθηκαν με διάφορες μεθόδους ηλεκτρικού χαρακτηρισμού, όπως για παράδειγμα μέσω μετρήσεων διηλεκτρικής φασματοσκοπίας στο χώρο των χρόνων και σε αυτό των συχνοτήτων. Από τις μετρήσεις διηλεκτρικής φασματοσκοπίας μελετήθηκαν σε βάθος τόσο τα φαινόμενα ιοντικής μεταφοράς του ηλεκτρολύτη, όσο και τα φαινόμενα της διεπιφάνειας μετάλλου/ηλεκτρολύτη. Επιπλέον, μελετήθηκαν τα φαινόμενα υστέρησης που παρουσιάζουν οι ηλεκτρολυτικοί πυκνωτές, λόγω της μακροσκοπικής κίνησης των ιόντων μέσα στον ηλεκτρολύτη. Τα φαινόμενα αυτά αποτελούν μια ένδειξη των φαινομένων μνήμης που παρουσιάζουν οι εν λόγο διατάξεις πυκνωτών. Χρησιμοποιώντας τις μεθόδους ηλεκτρικού χαρακτηρισμού, μελετήθηκε εκτενώς η επίδραση της μεταβολής των φυσικοχημικών παραμέτρων του ηλεκτρολύτη POM/PMMA (πάχος του ηλεκτρολύτη στην μίκρο και νανοκλίμακα, συγκέντρωση των μορίων POM μέσα στην μήτρα του PMMA, επίδραση της υγρασίας του περιβάλλοντος), στα διεπιφανειακά φαινόμενα και φαινόμενα μεταφοράς αυτού. Τέλος οι φυσικοχημικές ιδιότητες των ηλεκτρολυτικών υμενίων μελετήθηκαν μέσω συμπληρωματικών μετρήσεων φασματοσκοπίας υπεριώδους και ορατού-υπερύθρου. Τα αποτελέσματα της διατριβής ερμηνεύουν φαινόμενα ιοντικής μεταφοράς και διεπιφανειακά φαινόμενα, μιας πληθώρας άμορφων ηλεκτρολυτών, όπως άλλωστε είναι και ο ηλεκτρολύτης που μελετάται στην παρούσα διατριβή