Recently, the interest in neuromorphic computing that can mimic the human brain to combine computation and storage with energy efficiency into a compact space, has created a new artificial computing architecture distinguished from the traditional von Neumann ones. As one of the key components in artificial computing architectures, synaptic devices play very important roles in detecting and processing the environmental information. Copper oxide is one of the transition metal oxides with unique electronic, mechanical, magnetic and optical properties. However, there have been few reports on the investigation of synaptic devices based on copper oxide semiconductors. Most of the reported synaptic devices respond to electrical excitation but few of them can work under light excitation. Here, we report the fabrication of an optoelectronic synaptic device structured as ITO/CuOx/Pt that is based on monolayer copper oxide film only, and demonstrate the multiple synaptic properties. It is found that the device could effectively absorb and respond to the stimulating light at 450 nm and 520 nm, and the generated photocurrent could be modulated by regulating the defects and the composition of the memristive film inside the device. Additionally, a series of important synaptic functions, including excitatory postsynaptic current (EPSC), paired-pulse facilitation (PPF), short-term potentiation (STP) to long-term potentiation (LTP) transition, have been successfully simulated on the device. Our newly fabricated optoelectronic synaptic device shows a great potential in neuromorphic computing.
The visual nervous system is the main channel for perceiving the surrounding environment and obtaining external information. However, due to the von Neumann bottleneck, new computing architecture is urgently needed to meet the growing demands of big data processing. So, it is a new frontier in the field of computing to develop artificial neural networks comparable to biological neural networks. Synapses, which form the basis of neuromorphic computing, have attracted great interest in recent years. In this study, we synthesized ZnO nanorods by chemical method and introduced NiO as the second functional layer to modify the interface by taking advantage of ZnO's large specific surface area. We report the fabrication of the optoelectronic synaptic device based on NiO/ZnO bilayer films and demonstrate its diverse synaptic plasticity. The device could respond to light stimuli at the wavelength of 450 nm or 520 nm respectively, and present varied synaptic behaviors, such as short-term plasticity (STP), paired-pulse facilitation (PPF), long-term plasticity (LTP), and STP to LTP transition and “Learning behavior”. It is worth confirming that our optoelectronic synapse has simple ITO/NiO/ZnO/ITO structure but excellent synaptic behavior, which has a potential to be used in artificial vision and neuromorphic computing systems in the near future.
With the rapid development of intelligent era, machine vision based on von Neumann architecture will face a bottleneck, while the developing neuromorphic computing is one of the most promising options to solve the bottleneck. The key step is to enable the artificial devices to simulate the behaviors of biological synapses, and light-modulated memristors can be applied in neuromorphic computing to build artificial visual systems. Here, a bilayer memristive film of SrTiO3 /CuAlO2 was chosen to construct a two-terminal artificial synaptic sample with construction of ITO/SrTiO3:Ru/CuAlO2/ITO, in which the SrTiO3 layer was doped by Ruthenium (Ru) in order to enhance the light response from ultraviolet to visible range. It is found that the number of interior carries in the memristor could be generated by exterior stimulation of light, and the fabricated memristor could successfully mimic multiple synaptic functions of the biological synapse like excitatory postsynaptic current, short/long-term plasticity transform, paired-pulse facilitation and so on. The obtained excellent synaptic plasticities and optoelectronic properties of our light-modulated memristor have shown a potential in the machine vision and artificial neuromorphic computing systems in the near future.
Synapse is one of the key components of brain nervous system. As the fourth electronic component, memristor can be used to act as synaptic device and construct bionic neural network, in which the synapses can be stimulated by either electrical excitation or optical irradiation. Up to now, there have been many researches on the optoelectronic synaptic devices and the main functional materials include binary oxides, perovskite complex oxides, solid electrolytes, organic and polymer materials, etc. Here, we report anoptoelectronic synaptic device based on SnO2monolayer embedded with Ag nanocrystals and structured as ITO/SnO2:Ag/p++-Si. It is found that the SnO2:Ag thin film can effectively absorb light illumination in the broadband range of 450 nm to 635 nm, and that the device has been successfully simulated with multiple synaptic behaviors in the broadband range, including excitatory postsynaptic current (EPSC), paired pulse facilitation (PPF) and the transition from short-term plasticity (STP) to long-term plasticity (LTP). Our newly developed optoelectronic synapse device shows great application potential in neuromorphological computing.
Neuromorphic computing refers to one of the most promising choices to solve the von Neumann bottleneck. The key to develop neuromorphic computing is to make the device able of simulating biological synaptic behavior. Optically stimulated synaptic devices have the advantages of fast speed and low energy consumption. Many materials including carbon group materials, oxide materials and 2D materials have been used to make photoelectronic synaptic devices. However, most of the devices can only respond by violet and/or ultraviolet light stimulation, and very few of them can work in the near-infrared range. Here, we report an optoelectronic synaptic device based on SiOy/a-Si1-xRux bilayer memristive materials. By doping with ruthenium (Ru), the optical bandgap of amorphous silicon (a-Si) film could be engineered, making the doped a-Si1-xRux film infrared sensitive. Therefore, a-Si1-xRux film can effectively absorb light illumination in a wideband range from 450 nm to 905 nm. Many photoelectronic synaptic behaviors including excitatory postsynaptic current (EPSC), paired-pulse facilitation (PPF) and short-term plasticity (STP) to long-term plasticity (LTP) transition, have been simulated successfully by using different light spikes at wavelengths of 450 nm, 635 nm and 905 nm, respectively. We refer the obtained synaptic plasticities to originate from the trapping and de-trapping of photogenerated carriers by light-induced defects inside the silicon oxide (SiOy) which was deposited directly on a-Si1- xRux film, and to the generation of electron-hole pairs from the underlying a-Si1-xRux film. Our newly fabricated optoelectronic synaptic device shows a great application potential in neuromorphic computing.
Memristors are emerging and being considered to be used as candidates to realize multiple bio-synaptic plasticities and to act in the developed neuromorphic computing systems. Simulating the human visual neural network is an effective way to build a new generation of artificial visual systems and a realistic method to break the von Neumann bottleneck. In this article, we report for the first time a newly proposed and fabricated oxide-based optoelectronic synaptic device with a structure of ITO/Ag:SrTiO3/CuAlO2/ITO, and demonstrate its diverse synaptic plasticities. It is found that the device can respond light stimulation from visible to near-IR (450 nm-905 nm) wavelengths, and also can exhibit interestingly various synaptic behaviors including short-term plasticity (STP), paired-pulse facilitation (PPF), long-term plasticity (LTP) and the transition from STP to LTP, respectively. More importantly, our optoelectronic synaptic device has successfully simulated several artificial vision properties as image memory, image preprocessing and color recognition. It is worth acknowledging that our optoelectronic synaptic device has a simple structure of ITO/Ag:SrTiO3/CuAlO2/ITO and an excellent synaptic behavior, showing a potential to be used in the artificial vision and neuromorphic computing systems in the near future.
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