BiFe_1–xCr_xO₃ Ferroelectric Tunnel Junctions for Neuromorphic Systems

Abstract

We report on the fabrication of ferroelectric tunnel junctions of BiFe0.45Cr0.55O3 as a tunneling barrier, Nb-doped (111) SrTiO3 as a bottom electrode, and platinum as a top electrode. BiFeO3 is a generic multiferroic material with perspectives for multiferroic tunnel junctions, with chromium being introduced to shift and enhance the magnetic ordering from canted magnetization to ferrimagnetism. We deposit the ferroelectric films by radio frequency magnetron sputtering, an industry-compatible synthesis method. After confirming the BiFe1–x Cr x O3 film composition and its partial crystallinity, we found possible indications of ferroelectricity through piezoresponse force microscopy. X-ray photoelectron spectroscopy together with optical band measurements provide the electronic band profile of the Nb:SrTiO3/BiFe1–x Cr x O3/Pt structures. Pulsed electrical characterization reveals resistive switching with very high fatigue resistance (>106 cycles) consistent with direct tunneling across a trapezoidal barrier for a surface fraction of the film. These results make BiFe1–x Cr x O3 a promising candidate for ferroelectric tunnel junctions in particular, as they are able to operate as artificial synapses for neuromorphic circuit tiles as evidenced by spike-timing-dependent plasticity.

The promise of spintronics for unconventional computing

“…The integration of multiferroic materials in the field of spintronics seems to be very promising not only for memories, for example magnetoelectric switching being very energy efficient, 60 but also for new scalable energy-efficient logic devices combining magnetoelectricity and spin-orbit coupling 61 . Broadly, multiferroics that have been proposed to date are either single-phase materials, which exhibit intriguing characteristics but allow for only limited degrees of freedom to engineer devices, or heterostructures coupling ferroelectric and ferromagnetic phases (e.g., via strain 62,63,64 ), which provide more design flexibility but may present their own integration challenges.…”

Progressive and Stable Synaptic Plasticity with Femtojoule Energy Consumption by the Interface Engineering of a Metal/Ferroelectric/Semiconductor

“…[ 5 , 8 ] Among the various two‐terminal memristors, metal/ferroelectric/semiconductor (MFS) memristors utilizing Nb‐doped SrTiO 3 as a semiconducting substrate have exhibited high performance in resistive switching behaviors owing to the modulation of the ferroelectric barrier and depletion region in Nb‐doped SrTiO 3 semiconductors by ferroelectric polarization reversal. [ 9 , 10 , 11 , 12 , 13 , 14 , 15 ] Progressive polarization reversal of the ferroelectric domain in MFS can improve the electrical modulation of the band profile between the high resistance state (HRS) and low resistance state (LRS), which can lead to high linearity/symmetry of the synaptic weight update when using a smart programming pulse. [ 9 , 10 , 11 , 12 , 13 , 16 ] However, parameter enhancement in weight update (linearity, symmetry, and variation) caused by interface engineering between the ferroelectric material and top electrode has not been addressed in MFS memristors reported earlier.…”

“…[ 9 , 10 , 11 , 12 , 13 , 16 ] However, parameter enhancement in weight update (linearity, symmetry, and variation) caused by interface engineering between the ferroelectric material and top electrode has not been addressed in MFS memristors reported earlier. [ 4 , 8 , 11 , 14 , 15 ] Moreover, high reading currents of the order of µA during synaptic operation pose a major challenge in implementing energy‐efficient large‐scale synaptic arrays based on MFS devices, although ultrafast synaptic operation with low energy consumption has been achieved. [ 2 , 3 , 4 , 8 , 11 , 14 , 15 ]…”

“…[ 4 , 8 , 11 , 14 , 15 ] Moreover, high reading currents of the order of µA during synaptic operation pose a major challenge in implementing energy‐efficient large‐scale synaptic arrays based on MFS devices, although ultrafast synaptic operation with low energy consumption has been achieved. [ 2 , 3 , 4 , 8 , 11 , 14 , 15 ]…”

Optoelectronic Memory Capacitor Based on Manipulation of Ferroelectric Properties

“…However, because of cost issues and operation problems, these memories have not been very popular in commercial usage. , Beyond the destructive readout of the data from transistor-based ferroelectric memories, a variety of nondestructive readout methods have been introduced for these memories. One of them is atomic force microscopy (AFM), in which a probe sweeps the entire ferroelectric surface to read information. , In other works, high-speed reading has been successfully implemented by ferroelectric tunnel junctions, although the deposition of ultrathin films over large areas without defects is still a challenge. − Recently, researchers have demonstrated that the conductivity of the domain walls in monocrystalline ferroelectrics can change based on the direction of the polarization. , However, the resistivity in this method remains challenging for the high-speed data readout …”