An electronic skin (e-skin) for the next generation of robots is expected to have biological skin-like multimodal sensing, signal encoding, and preprocessing. To this end, it is imperative to have high-quality, uniformly responding electronic devices distributed over large areas and capable of delivering synaptic behavior with long- and short-term memory. Here, we present an approach to realize synaptic transistors (12-by-14 array) using ZnO nanowires printed on flexible substrate with 100% yield and high uniformity. The presented devices show synaptic behavior under pulse stimuli, exhibiting excitatory (inhibitory) post-synaptic current, spiking rate-dependent plasticity, and short-term to long-term memory transition. The as-realized transistors demonstrate excellent bio-like synaptic behavior and show great potential for in-hardware learning. This is demonstrated through a prototype computational e-skin, comprising event-driven sensors, synaptic transistors, and spiking neurons that bestow biological skin-like haptic sensations to a robotic hand. With associative learning, the presented computational e-skin could gradually acquire a human body–like pain reflex. The learnt behavior could be strengthened through practice. Such a peripheral nervous system–like localized learning could substantially reduce the data latency and decrease the cognitive load on the robotic platform.
Touch is a complex sensing modality owing to large number of receptors (mechano, thermal, pain) nonuniformly embedded in the soft skin all over the body. These receptors can gather and encode the large tactile data, allowing us to feel and perceive the real world. This efficient somatosensation far outperforms the touch-sensing capability of most of the state-of-the-art robots today and suggests the need for neural-like hardware for electronic skin (e-skin). This could be attained through either innovative schemes for developing distributed electronics or repurposing the neuromorphic circuits developed for other sensory modalities such as vision and audio. This Review highlights the hardware implementations of various computational building blocks for e-skin and the ways they can be integrated to potentially realize human skin–like or peripheral nervous system–like functionalities. The neural-like sensing and data processing are discussed along with various algorithms and hardware architectures. The integration of ultrathin neuromorphic chips for local computation and the printed electronics on soft substrate used for the development of e-skin over large areas are expected to advance robotic interaction as well as open new avenues for research in medical instrumentation, wearables, electronics, and neuroprosthetics.
Memristors can mimic the functions of biological synapse, where it can simultaneously store the synaptic weight and modulate the transmitted signal. Here, we report Nb/Nb 2 O 5 /Pt based memristors with bipolar resistive switching, exhibiting synapse like property of gradual and continuously change of conductance with subsequent voltage signals. Mimicking of basic functions of remembering and forgetting processes of biological brain were demonstrated through short term plasticity, spike rate dependent plasticity, paired pulse facilitation and post-titanic potentiation. The device layer interface tuning was shown to affect the device properties shift from digital to analog behaviour. Demonstration of basic synaptic functions in the NbOx based devices makes them suitable for neuromorphic applications.
Memory devices based on resistive switching (RS) have not been fully realised due to lack of understanding of the underlying switching mechanisms. Nature of ion transport responsible for switching and growth of conducting filament in transition metal oxide based RS devices is still in debate. Here, we investigated the mechanism in Niobium oxide based RS devices, which shows unipolar switching with high ON/OFF ratio, good endurance cycles and high retention times. We controlled the boundary conditions between low-conductance insulating and a high-conductance metallic state where conducting filament (CF) can form atomic point contact and exhibit quantized conductance behaviour. Based on the statistics generated from quantized steps data, we demonstrated that the CF is growing atom by atom with the applied voltage sweeps. We also observed stable quantized states, which can be utilized in multistate switching. ==============
A detailed understanding of quantization conductance (QC), their correlation with resistive switching phenomena and controlled manipulation of quantized states is crucial for realizing atomic-scale multilevel memory elements. Here, we demonstrate highly stable and reproducible quantized conductance states (QC-states) in Al/Niobium oxide/Pt resistive switching devices. Three levels of control over the QC-states, required for multilevel quantized state memories, like, switching ON to different quantized states, switching OFF from quantized states, and controlled inter-state switching among one QC-states to another has been demonstrated by imposing limiting conditions of stop-voltage and current compliance. The well defined multiple QC-states along with a working principle for switching among various states show promise for implementation of multilevel memory devices.
Ella Gale opened discussion of the introductory lecture by Rainer Waser: At the end of your talk you introduced complementary resistance switches, which you used for binary pattern matching. Do you have any insight into how you might use these systems to do computation in the real number space? Rainer Waser answered: We are currently working on this. (2:[2]2) Ilia Valov said: From your point of view, at the moment, what are the hottest points of research in memristive cells? What are the main challenges? Rainer Waser answered: The hot points of research are the physical understanding of the reliability-limiting processes in conjunction with the material's treasure map and, from the application side, the development of a convincing neuromorphic circuit that shows clear benet compared to standard CMOS solutions (4:[4]4) Hans Hilgenkamp asked: Most memristor embodiments shown in the papers are based on stacked devices with the current ow perpendicular to the plane. Do all applications necessarily favour this type of conguration, or are there also applications for which an in-plane conguration would be preferred? DIS C8FD90059K
Noise not only deteriorates image quality but also may result in loss of important information hidden in images (i.e. medical applications
We report unipolar resistive switching of Pt/Nb2O5/Al device with orthorhombic crystalline phase prepared by reactive sputtering method. It showed non-volatile reproducible unipolar switching with ON/OFF resistance ratio of 10 3 or higher. The range of SET and RESET voltage was 1.0-2.0 V and 0.3-0.8 V, respectively, depending on devices and their dimension. The charge carriers followed Ohmic and space-charge-limited conduction (SCLC) behaviour in lowresistance state (LRS) and high-resistance state (HRS), respectively. An impedance spectroscopy analysis as well as a drift and diffusion of oxygen ion vacancy model are presented to explain the conducting filament formation and its rupture during the SET and RESET processes.
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