New paradigms in computing architectures require the development of devices based on materials that extend beyond conventional semiconductor components. Memristors[1] have emerged as main building blocks for these next-generation technologies. Current research explores several systems—such as resistive random-access memories, spin-torque magnetic memories, phase-change memories, and other resistive-based elements—as potential memristors. However, all these approaches rely on current injection through the device, which leads to disadvantages primarily related to device reliability and power consumption [2]. Ferroelectric materials can overcome many of these challenges. As insulating materials capable of operating under open-circuit conditions, they avoid current flow during switching and offer inherently low-power operation.[2] Despite these advantages, their technological impact was limited by the difficulty of integrating ferroelectric compounds into highly dense memory architectures [3,4]. This situation changed with the discovery of ferroelectricity in doped HfO₂ [5]. Hafnium oxide—and its doped variants—is fully compatible with CMOS processes, making it an attractive material for neuromorphic devices where it can function as a memristive element [6]. In recent years, progress in understanding the memristive and neuromorphic characteristics of ferroelectric HfO₂ has been remarkable. The majority of studies have focused on polycrystalline films, which are directly compatible with industrial fabrication. However, their functional properties are difficult to interpret because polycrystalline hafnia typically contains mixed phases, multiple orientations, and diffuse interfaces. These structural complexities hinder a clear understanding of the intrinsic ferroelectric and neuromorphic behavior.

Epitaxial ferroelectric HfO₂ films offer a powerful alternative platform for fundamental studies [7]. These films exhibit atomically flat surfaces, well-defined interfaces, and single-phase structures, enabling more precise investigation of switching mechanisms. Epitaxial films also avoid the wake-up effect commonly observed in polycrystalline hafnia [8], and they show fast neuromorphic responses [9] together with large polarization and exceptional endurance [10] even in ultrathin layers [11]. These features position epitaxial ferroelectric HfO₂ as an excellent model system for exploring new phenomena relevant to multi-input/multi-output neuromorphic devices. In this work, we highlight several recent developments using epitaxial ferroelectric HfO₂ systems. First, we present the creation of a robust multiferroic heterostructure capable of achieving magnetoelectric neuromorphic-like responses [12]. This system demonstrates the potential of coupling ferroelectric and magnetic orders to achieve neuromorphic magnetoelectric response. Second, we summarize our recent investigations into the interaction between ferroelectric order and light. We show that photovoltaic conversion can be used to monitor polarization via short-circuit photocurrent signals [13]. This voltage-free readout enables non-destructive detection of multilevel ferroelectric states—an especially valuable feature for neuromorphic architectures requiring energy efficiency. In addition, light can be used to remotely manipulate the ferroelectric polarization state, enabling multi-state optoelectrical response. Taken together, these results underscore the broad potential of epitaxial ferroelectric HfO₂ films for advancing neuromorphic device technologies.