Harnessing The Competing Roles of Charge to Design Ferroelectric-Gated Mott Transistors

The device concept of ferroelectric-gated Mott field effect transistors (FETs) has been intensively studied for the past three decades as a promising building block for developing energy-efficient nanoelectronics that can transcend the scaling limits of conventional semiconductor technology. The nearly metallic density of carriers within the Mott channel, however, imposes a major bottleneck for achieving substantial field effect modulation via a solid-state gate. In this study, we report a record high room temperature resistance switching in a rare earth nickelate (<i>R</i>NiO₃) channel controlled by a ferroelectric PbZr_0.2Ti_0.8O₃ (PZT) gate. We have systematically studied the ferroelectric field effect in <i>R</i>NiO₃ (<i>R</i> = Sm, Nd, La) to identify the optimal channel materials for constructing nonvolatile Mott transistors. For single-layer <i>R</i>NiO₃ channels, the resistance switching ratio Δ<i>R</i>/<i>R</i>_on peaks near the electrical dead layer thickness and then decreases abruptly due to strong depolarization in PZT. Switching the polarization of PZT induces a metal-insulator transition in the 4 uc single-layer LaNiO₃ channel. At 300 K, the highest Δ<i>R</i>/<i>R</i>_on of 1,619% is observed in 2 unit cell (uc) LaNiO₃ channels as it possesses the smallest electrical dead layer thickness. Devices with <i>R</i>NiO₃/La_0.67Sr_0.33MnO₃ (LSMO) composite channels exhibit up to three orders of magnitude higher Δ<i>R</i>/<i>R</i>_on compared with the single layer channel FETs with the same channel thickness. A record high Δ<i>R</i>/<i>R</i>_on of 38,540% is observed in the 2.5 uc LaNiO₃/2 uc LSMO bilayer channel at 300 K. Such an enhancement has been attributed to the interfacial charge transfer between <i>R</i>NiO₃ and LSMO, which reduces the net carrier density in <i>R</i>NiO₃ without compromising the screening of depolarization field in PZT. First principles calculations reveal about 0.1 electron/Mn transfer from interfacial Mn to Ni layers (or hole transfer from Ni to Mn). Both the magnitude and length scale of the charge transfer have been confirmed by atomically resolved EELS mapping. We have also studied the retention and cycling behaviors of the PZT/LaNiO₃/LSMO FETs, which reveal superior device performance compared with those of single-layer Mott channels and FeFETs exploiting polycrystalline PZT gates. Our study addresses one of the critical material challenges that limit the application potential of epitaxial ferroelectric-gated Mott transistors.<br/><br/>This work was primarily supported by National Science Foundation (NSF) Grant No. DMR-1710461 and EPSCoR RII Track-1: Emergent Quantum Materials and Technologies (EQUATE), Award No. OIA-2044049, and Semiconductor Research Corporation (SRC) under GRC Task Number 2831.001