Ferroelectric Tunneling Junctions for Neurosynaptic Computing

Ferroelectric tunneling junctions (FTJs) with tunable tunneling electroresistance (TER) are promising for many emerging applications including non-volatile memories and neurosynaptic computing. Traditional FTJs were mainly based on perovskites, such as lead zirconate titanate (PZT). Recently, doped hafnium oxide (HfO) emerged as a new class of ferroelectric materials [1]. As compared to traditional perovskites, doped HfO has the advantages of high coercive field and full compatibility with CMOS processes. Among various doped HfO, Zr-doped HfO (HZO) is particularly attractive due to its low annealing temperature and excellent scalability [2]-[3]. In FTJs based on metal/HZO/metal structure, in order to achieve a sizable on-current, the thickness of HZO needs to be scaled down below 5 nm. However, the polarization in these ultra-thin HZO film is very small, which leads to a low TER ratio [4]. In this project, we propose and demonstrate a new type of FTJ based on metal/AlO/HZO/Si structure. The interfacial AlO layer and semiconducting substrate enable sizable TERs even when the thickness of HZO is above 10 nm. We demonstrate FTJ synapses with symmetric potentiation and depression characteristics and widely tunable conductance. We also show that spike-timing-dependent plasticity (STDP) can be harnessed from HZO based FTJs.