Ultrathin HfO<sub>2</sub>/Al<sub>2</sub>O<sub>3</sub> bilayer based reliable 1T1R RRAM electronic synapses with low power consumption for neuromorphic computing
Qiang Wang, Yankun Wang, Ren Luo, Jianjian Wang, Lanlong Ji, Zhuangde Jiang, Christian Wenger, Zhitang Song, Sannian Song, Wei Ren, Jinshun Bi, Gang Niu
Abstract
Abstract Neuromorphic computing requires highly reliable and low power consumption electronic synapses. Complementary-metal-oxide-semiconductor (CMOS) compatible HfO 2 based memristors are a strong candidate despite of challenges like non-optimized material engineering and device structures. We report here CMOS integrated 1-transistor-1-resistor (1T1R) electronic synapses with ultrathin HfO 2 /Al 2 O 3 bilayer stacks (<5.5 nm) with high-performances. The layer thicknesses were optimized using statistically extensive electrical studies and the optimized HfO 2 (3 nm)/ Al 2 O 3 (1.5 nm) sample shows the high reliability of 600 DC cycles, the low Set voltage of ∼0.15 V and the low operation current of ∼6 µ A. Electron transport mechanisms under cycling operation of single-layer HfO 2 and bilayer HfO 2 /Al 2 O 3 samples were compared, and it turned out that the inserted thin Al 2 O 3 layer results in stable ionic conduction. Compared to the single layer HfO 2 stack with almost the same thickness, the superiorities of HfO 2 /Al 2 O 3 1T1R resistive random access memory (RRAM) devices in electronic synapse were thoroughly clarified, such as better DC analog switching and continuous conductance distribution in a larger regulated range (0–700 µ S). Using the proposed bilayer HfO 2 /Al 2 O 3 devices, a recognition accuracy of 95.6% of MNIST dataset was achieved. These results highlight the promising role of the ultrathin HfO 2 /Al 2 O 3 bilayer RRAM devices in the application of high-performance neuromorphic computing.