Spontaneous Threshold Lowering Neuron using Second-Order Diffusive Memristor for Self-Adaptive Spatial Attention.

Intrinsic plasticity of neurons, such as spontaneous threshold lowering (STL) to modulate neuronal excitability, is key to spatial attention of biological neural systems. In-memory computing with emerging memristors is expected to solve the memory bottleneck of the von Neumann architecture commonly used in conventional digital computers and is deemed a promising solution to this bioinspired computing paradigm. Nonetheless, conventional memristors are incapable of implementing the STL plasticity of neurons due to their first-order dynamics. Here, a second-order memristor is experimentally demonstrated using yttria-stabilized zirconia with Ag doping (YSZ:Ag) that exhibits STL functionality. The physical origin of the second-order dynamics, i.e., the size evolution of Ag nanoclusters, is uncovered through transmission electron microscopy (TEM), which is leveraged to model the STL neuron. STL-based spatial attention in a spiking convolutional neural network (SCNN) is demonstrated, improving the accuracy of a multiobject detection task from 70% (20%) to 90% (80%) for the object within (outside) the area receiving attention. This second-order memristor with intrinsic STL dynamics paves the way for future machine intelligence, enabling high-efficiency, compact footprint, and hardware-encoded plasticity.

Effects of CuO addition on the sinterability and electric properties in PbNb2O6-based ceramics.

PbNb2O6 (PN)-based ceramics with tungsten bronze structure are promising piezoelectric materials in high-temperature devices such as piezoelectric vibration transducers. However, the PN-based ceramics usually exhibit a low bulk density, which greatly limits their practical applications. In this work, CuO was used as the sintering aid to form a liquid-phase bridge, leading to an obvious increase of the bulk density of PN-based ceramics by 11% (from 5.25 to 5.85 g cm-3) and the improvement of the piezoelectric constant (d 33) (from 168 to 190 pC/N) and the Curie temperature (T C) from 367 to 395 °C. The positive influence of CuO on densification has been proved by SEM and fracture toughness. The XRD patterns confirmed that there was no secondary phase introduced by CuO addition. The Raman spectra revealed that part of Cu2+ ions has probably diffused into host lattice of the PN and preferred to occupy on A-sites. These results not only demonstrate the high potential of the CuO added PN-based ceramics for high-temperature piezoelectric applications, but also reveal the corresponding structure-properties relationship as well as provide a way to improve the sinterability, d 33, and T C simultaneously.