Proximity Engineered Tunable Phase Transitions in Ferroelectric Hafnia and Steep Switching Phase Change FETs

Ferroelectric hafnia has emerged as a transformative material in advanced electronics, with Complementary Metal Oxide Semiconductor (CMOS) compatibility, robust ferroelectricity, and scalability for applications including memory and ferroelectric field effect transistors (FEFETs). We demonstrate wake‐up‐free, robust ferroelectricity in solution‐processed La‐doped hafnia (LHO, 40 nm thick). By leveraging a metal‐insulator transition (MIT) in the bottom electrode, TiO x (N y ), a Mott Insulator, we engineer a depolarization‐field‐controlled reversible polar‐to‐non‐polar phase transitions via the proximity effect in the ferroelectric hafnia layer. We further show that capping the ferroelectric layer with Al 2 O 3 of various thicknesses, allows for subtle oxidation of the bottom electrode, resulting in tunable phase transitions between 140 and 260 K. Using the idea of proximity‐coupled phase‐transitioning ferroelectric layers, we demonstrate phase‐change ferroelectric field‐effect transistor (PCFE‐FET) integrated onto a 2D MoS 2 channel. Near the induced phase transition temperatures, our devices show steep subthreshold slopes surpassing the Boltzmann limit. The temperature tunability of the phase transitions renders our PC‐FEFETs highly promising for low‐power computing solutions for both cryogenic and near‐room temperature applications.