our brain would solve this dilemma, that is, the von Neumann bottleneck. Thus, neuromorphic engineering comes into being. Basically, data-driven neuromorphic engineering needs to complete a large number of data processing tasks. Presently, one of the main tasks in the state-ofthe-art neuromorphic computing system is to optimize neuromorphic algorithm. Due to the use of von Neumann architecture, such neuromorphic systems always consume extremely high energy. In fact, our brain nervous system is consisted of ≈10 11 neurons connected by ≈10 15 synapses. [3] Neurons and synapses are basic units in brain information processing. Brain cognitive behaviors occur through synaptic responses and neural functions. And the synaptic plasticity is the most important characteristics of synapse. Such architecture makes our brain operate in extremely high energy efficiency with certain fault tolerance to respond to our surroundings. Thus, brain-inspired neuromorphic devices have been proposed for mimicking biological synaptic responses and neural functions. [4][5][6] It is getting a new branch for neuromorphic engineering.Recently, with the developments of microelectronics, optoelectronics, and material technologies, solid-state neuromorphic devices have been proposed to mimic biological synaptic functions. Such devices include two-terminal resistance change memory devices [7][8][9][10] and field-effect transistor based neuromorphic transistors. [11][12][13][14][15] Due to the simple sandwich structure, two-terminal memristors have the inherent priority in 3D integrity. They have been widely investigated for high density storage applications. [16,17] With nonlinear electrical characteristics and nonvolatile resistance modulation effects, two-terminal memristors are very suitable for neuromorphic device applications. Such devices include ferroelectric random access memory (FeRAM), phase change random access memory (PCRAM), resistive random access memory (RRAM), etc. [18][19][20][21][22] In fact, most of the recent reported neuromorphic devices are based on two-terminal memristors. Especially with the deep understanding of the operation mechanisms of memristors, neural operation and typical Modified National Institute of Standards and Technology (MNIST) pattern recognition have also been demonstrated by using memristor arrays. [23][24][25] In addition, energy consumption is another important index in neuromorphic device applications. Recently, several works have been reported on neuromorphic device with low energy consumption. [26][27][28][29][30] Xu et al. [26] obtained organic nanowire synaptic transistors with energy consumption of ≈1.23 fJ per Recently, neuromorphic devices have attracted great attention due to their potential to overcome the von Neumann bottleneck. Due to their nonlinear electrical characteristics and nonvolatile resistance, memristors have been proposed for use in neuromorphic device applications. Bilayered HfO 2 /TiO x -based cognitive memristors are proposed. They demonstrate conductance-modulation capabilit...