Neuromorphic computing on the hardware level is promising for performing ever‐increasing data‐centric tasks owing to its superiority to conventional von Neumann architecture in terms of energy efficiency and learning ability. One key aspect to its implementation is the development of artificial synapses that can effectively emulate the multiple functionalities exhibited by their biological counterparts. Here, building on an inorganic ferroelectric gate stack integrated with a 2D layered semiconductor (WS2), a new type of ferroelectricity‐based synaptic transistor that differs from those relying on interface traps or floating gate configuration is reported. By virtue of a 6 nm thick ferroelectric hafnium zirconium oxide by atomic layer deposition and postannealing treatment, the device shows a channel resistance change ratio above 105 corresponding to opposite ferroelectric polarization direction. Furthermore, by applying electrical stimulus to the gate, it demonstrates good capability to mimic various synaptic behaviors including long‐term potentiation, long‐term depression, spike‐amplitude‐dependent plasticity, and spike‐rate‐dependent plasticity. Given the inherent compatibility of the ferroelectric gate stack with existing fabrication technology, and the reliability of ferroelectricity engineering, this work paves the way toward practical implementation of synaptic devices in neuromorphic circuits.

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We present measurements of the low temperature electrical transport properties of the two dimensional carrier gas that forms at the interface of (111) (La 0.3 Sr 0.7 )(Al 0.65 Ta 0.35 )/SrTiO 3 (LSAT/STO) as a function of applied back gate voltage, V g . As is found in (111) LaAlO 3 /SrTiO 3 interfaces, the low-field Hall coefficient is electron-like, but shows a sharp reduction in magnitude below V g ∼ 20 V, indicating the presence of holelike carriers in the system. This same value of V g correlates approximately with the gate voltage below which the magnetoresistance evolves from nonhysteretic to hysteretic behavior at millikelvin temperatures, signaling the onset of magnetic order in the system. We believe our results can provide insight into the mechanism of magnetism in SrTiO 3 based systems.For more than ten years, the two dimensional carrier gas in SrTiO 3 (STO) based heterostructures has provided us with a model system to study a wide variety of physical phenomena, such as magnetism, superconductivity, spinorbit interaction, and localization effects. [1][2][3][4][5][6][7] Adding to the interest is the fact that these interfacial phenomena can be tuned by a range of experimental handles, including applied electric fields, 3 oxygen partial pressure during growth, 5,8,9 capping layers, 10 post growth annealing treatment, 11,12 crystal orientation, 14 and strain. 15 So far, most studies on these heterostructures have focused on LaAlO 3 (LAO) deposited on a (001) oriented STO substrate. However, it was recently discovered that changing the surface crystal orientation can vastly change the properties of the carrier gas.14 In particular, a tunable anisotropy in transport parameters was observed in (110) and (111) oriented LAO/STO. 12,13,[16][17][18] The (111) oriented interface has also been predicted to show novel topological phases, given that the surface Ti atoms in STO form a honeycomb lattice that hosts orbitals with hexagonal symmetry. 19-23(La 0.3 Sr 0.7 )(Al 0.65 Ta 0.35 ) (LSAT) is a commonly used substrate for the growth of other perovskite films. When LSAT is grown on STO, a two-dimensional carrier gas forms at the LSAT/STO interface.24 LSAT has a band gap of 4.9 eV, 25 smaller than the LAO band gap of 5.6 eV, 26 which can affect the relative importance of the different mechanisms contributing to the formation of the conducting gas. LSAT has a 1 % lattice mismatch with STO, as opposed to a 3 % mismatch in the case of LAO, which means the interfacial STO layers experience a smaller strain in the case of LSAT/STO. Also, unlike LAO, but similar to STO, LSAT undergoes a cubic to tetragonal transition at about 100 K, 27,28 which is also expected to reduce strain effects. Earlier work on (001) LAO/STO interfaces 15 demonstrated that strain at the interface can drastically change conduction, whereas recent studies of LSAT grown on (001) STO suggested that the lower strain compared to LAO significantly increased the carrier mobility.24,29 However, there have been only a few transport experiments performed ...

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