ABSTRACT
The Niobium Dioxide (NbO2) oscillator neuron has garnered significant interest because of its simple structure compared to conventional CMOS-based circuits. However, the limited on/off resistance ratio narrows the range of series resistances that satisfy the self-oscillation conditions and limits its use in large-scale synaptic arrays. In this study, we report the possibility of improving the performance of NbO2-based oscillator neuron devices through cryogenic operation. The study emphasizes two crucial parameters: the on/off resistance ratio and the oscillation amplitude, both of which are essential for accurate weighted sum classification. The data suggest that these parameters can be effectively enhanced under cryogenic conditions. In addition, we revealed that 120 K is the optimal temperature for cryogenic operation, as it represents the temperature where the on/off resistance ratio ceases to increase. As a result, we revealed that the series resistance range satisfying the self-oscillation condition in a single oscillator increases from 20 to 126 kΩ. The research also probes the maximum possible array size at each temperature. At 300 K, representation is only possible for a 5 × 5 array, but at 120 K, a 30 × 30 array can be represented as a frequency. The evidence implies that the 120 K conditions not only broaden the range of series resistors that can be connected to a single oscillator but also increases the array size, thereby representing different weighted sum currents as frequencies. The research indicates that using carefully optimized cryogenic operation could be a viable method to enhance the necessary NbO2properties for an oscillator neuron device.
ABSTRACT
In this study, a two-dimensional electron gas (2DEG), which is a conductive layer formed at the interface of Al2O3and TiO2, was used as an electrode for resistive random access memory (RRAM) and implemented in a cell size down to 30 nm. For an RRAM device comprising W/2DEG/TiO2/W, we confirmed that the dominant switching mechanism changed from interfacial to filamentary as the cell size decreased from 500 nm to 30 nm. Through analyses of changes in forming characteristics and conduction mechanisms in the low resistive state depending on the cell size, it was identified that the 2DEG acted as an oxygen-scavenging layer of TiO2during the resistive switching process. By comparing the switching characteristics of RRAM devices with and without 2DEG for a 30 nm cell size, we confirmed that a high-performance 2DEG RRAM was realized, with highly uniform current-voltage characteristics, a low operating voltage (â¼1 V), and a high on/off ratio (>102). Finally, the applicability of the proposed device to a crossbar array was validated by evaluating 1S1R operation with an NbO2-based selector. Considering the improved switching uniformity, the 2DEG RRAM shows promise for high-density memory applications.
ABSTRACT
BACKGROUND: Generally, treadmill-walking training focuses on weight bearing and the speed of walking. However, changes in direction, speed, and slope while walking require adaptation. OBJECTIVE: The effects of task-oriented treadmill-walking training (TOTWT) on the walking ability of stroke patients were evaluated. METHODS: Subjects were randomly divided into two groups: the task-oriented treadmill-walking training (TOTWT) group and the conventional treadmill-walking training (CTWT) group. Evaluation was performed before the commencement of the training and again 4 and 8 wk after training was initiated. The OptoGait system measured gait parameters. The Timed Up and Go test and 6-min walk test were also performed. RESULTS: Within each group, both the TOTWT and the CTWT groups significantly differed before and after the intervention in all tests (P < 0.05); the CTWT group showed greater improvement in all tests following TOTWT (P < 0.05). CONCLUSION: TOTWT improves gait and rehabilitation in the stroke-affected limb, and also improves general gait characteristics.