S. G. Hu

Associative memory realized by a reconfigurable memristive Hopfield neural network

Although synaptic behaviours of memristors have been widely demonstrated, implementation of an even simple artificial neural network is still a great challenge. In this work, we demonstrate the associative memory on the basis of a memristive Hopfield network. Different patterns can be stored into the memristive Hopfield network by tuning the resistance of the memristors, and the pre-stored patterns can be successfully retrieved directly or through some associative intermediate states, being analogous to the associative memory behaviour. Both single-associative memory and multi-associative memories can be realized with the memristive Hopfield network.

Emulating the paired-pulse facilitation of a biological synapse with a NiOx-based memristor

We study the paired-pulse-induced response of a NiOx-based memristor. The behavior of the memristor is surprisingly similar to the paired-pulse facilitation of a biological synapse. When the memristor is stimulated with a pair of electrical pulses, the current of the memristor induced by the second pulse is larger than that by the first pulse. In addition, the magnitude of the facilitation decreases with the pulse interval, while it increases with the pulse magnitude or pulse width.

Emulating the Ebbinghaus forgetting curve of the human brain with a NiO-based memristor

The well-known Ebbinghaus forgetting curve, which describes how information is forgotten over time, can be emulated using a NiO-based memristor with conductance that decreases with time after the application of electrical pulses. Here, the conductance is analogous to the memory state, while each electrical pulse represents a memory stimulation or learning event. The decrease in the conductance with time depends on the stimulation parameters, including pulse height and width and the number of pulses, which emulates memory loss behavior well in that the time taken for the memory to be lost depends on how the information is learned.

Synaptic long-term potentiation realized in Pavlov's dog model based on a NiOx-based memristor

Synaptic Long-Term Potentiation (LTP), which is a long-lasting enhancement in signal transmission between neurons, is widely considered as the major cellular mechanism during learning and memorization. In this work, a NiOx-based memristor is found to be able to emulate the synaptic LTP. Electrical conductance of the memristor is increased by electrical pulse stimulation and then spontaneously decays towards its initial state, which resembles the synaptic LTP. The lasting time of the LTP in the memristor can be estimated with the relaxation equation, which well describes the conductance decay behavior. The LTP effect of the memristor has a dependence on the stimulation parameters, including pulse height, width, interval, and number of pulses. An artificial network consisting of three neurons and two synapses is constructed to demonstrate the associative learning and LTP behavior in extinction of association in Pavlovs dog experiment.

Design of an electronic synapse with spike time dependent plasticity based on resistive memory device

This paper presents a design of electronic synapse with Spike Time Dependent Plasticity (STDP) based on resistive memory device. With the resistive memory device whose resistance can be purposely changed, the weight of the synaptic connection between two neurons can be modified. The synapse can work according to the STDP rule, ensuring that the timing between pre and post-spikes leads to either the long term potentiation or long term depression. By using the synapse, a neural network with three neurons has been constructed to realize the STDP learning.

Effect of Heat Diffusion During State Transitions in Resistive Switching Memory Device Based on Nickel-Rich Nickel Oxide Film

The switching behaviors of the resistive switching device based on Ni-rich nickel oxide thin film during the set and reset processes in the pulse voltage experiment have been examined. In the switching from a high-resistance state (HRS) to a low-resistance state (LRS) during the set process, the formation of filament is the dominant process. The switching is easier to occur with a shorter off time between pulses, indicating that heat diffusion plays an important role. On the other hand, in the switching from the LRS to the HRS during the reset process, there is a competition between the formation and deformation of filament, which is much stronger than that in the set process. The heat diffusion during the off time between pulses affects both the formation and deformation of filaments. Thus, there is no definite relationship in statistics between the off time and the occurrence of the reset switching.

VCO-BASED CONTINUOUS-TIME SIGMA DELTA ADC BASED ON A DUAL-VCO-QUANTIZER-LOOP STRUCTURE

This paper explores a continuous time (CT) sigma delta (ΣΔ) analog-to-digital converter (ADC) based on a dual-voltage-controlled oscillator (VCO)-quantizer-loop structure. A third-order filter is adopted to reduce quantization noise and VCO nonlinearity. Even-order harmonics of VCO are significantly reduced by the proposed dual-VCO-quantizer-loop structure. The prototype with 10 MHz bandwidth and 400 MHz clock rate is designed using a 0.18 μm RF CMOS process. Simulation results show that the signal-to-noise ratio and signal-to-noise distortion ratio (SNDR) are 76.9 and 76 dB, respectively, consuming 37 mA at 1.8 V. The key module of the ADC, which is a 4-bit VCO-based quantizer, can convert the voltage signal into a frequency signal and quantize the corresponding frequency to thermometer codes at 400 MS/s.

γ-Ray Radiation Effects on an HfO 2 -Based Resistive Memory Device

In this paper, electrical characteristics of an HfO2-based resistive switching memory device are investigated before and after γ-ray radiation with various total ionizing doses (TIDs). The device can still function properly even if irradiated with a TID of 20 Mrad(Si). The small changes of resistance states and set/reset voltages induced by γ-ray radiation can hardly influence the proper function of the device. The γ-ray radiation does not significantly degrade both retention and endurance characteristics even after a high-TID exposure. The radiation effects on the resistive switching memory device show little dependence on the cell area. The results suggest that the HfO2-based resistive switching memory device has good γ-ray radiation-resistant capability.

Smart electronic skin having gesture recognition function by LSTM neural network

Rapid growth of soft electronics has enabled various approaches for developing artificial skin. However, currently existing electronic skin is still facing some problems such as high fabrication complexity, high production cost, and smartness of recognizing the stimulus automatically. In this work, we report a simple, low-cost Polydimethylsiloxane (PDMS)-based smart electronic skin system, consisting of a sensor array and a data processing system. The sensor array can be easily mounted on the human body or robot hand as a result of excellent softness, stretchability, and bendability of PDMS. Signals from the sensor array are processed by a Long and Short Term Memory neural network algorithm in the data processing system. The trained data processing system can recognize four types of gestures at an accuracy of 85 ± 5%, even taking into account environmental variations including folding, curvature, tensile strength, temperature, and endurance cycles. This work proves that this type of skin can be endowed with intelligence with a proper neural network algorithm and fabricated at low cost and reduced complexity.

An HfO 2 -based resistive switching memory device with good anti-radiation capability

Electrical characteristics of an HfO2-based resistive switching memory device are investigated before and after exposure to γ ray radiation for various total ionizing doses (TIDs). The device can still function properly after radiation, showing a good anti-radiation capability. After exposure to radiation, the set and reset voltages of the device decrease very slightly, and the resistance of the low-resistance state and the high-resistance state shows little increase. The very small changes of set voltage, reset voltage and resistance after radiation do not influence the proper function of the device. The γ ray radiation does not significantly degrade both retention and endurance characteristics even after a high-TID exposure.