Ferroelectric thin films are investigated for their potential in photovoltaic (PV) applications, owing to their high open-circuit voltage and switchable photovoltaic effect. The direction of the ferroelectric polarization can control the sign of the photocurrent through the ferroelectric layer, theoretically allowing for 100 percent switchability of the photocurrent with the polarization, which is particularly interesting for photo-ferroelectric memories. However, the quantitative relationship between photocurrent and polarization remains little studied. In this work, a careful investigation of the polarization-dependent photocurrent of epitaxial Pb(Zr,Ti)O3 thin films has been carried out, and has provided a quantitative determination of the unswitchable part of ferroelectric polarization. These results represent a systematic approach to study and optimize the switchability of photocurrent, and more broadly to get important insights on the ferroelectric behavior in all types of ferroelectric layers in which pinned polarization is difficult to investigate.
Intensive research into functional oxides has been triggered by the quest for a solid-state universal memory with high-storage density, non-volatility, high read/write speed, and random access. The ferroelectric random-access memory (FeRAM), in which the information is stored in the spontaneous ferroelectric polarization of the material, offers great promise as nonvolatile and multistate memory, but its destructive electrical reading step requires a rewrite step after each reading, increasing energy consumption. As an alternative, optical nondestructive readout is based on the ferroelectric polarization dependence of the photovoltaic response in materials and has been reported in two-states ferroelectric memories and multistate devices with limited photocurrent switchability due to asymmetric interfacial effects. In this work, we report a nonvolatile oxide memory device based on a symmetric heterostructure with eight stable and well-controlled remanent polarization (Pr) states, written electrically by voltage pulse and read optically through polarization-dependent short-circuit photocurrent Isc or open circuit photovoltage Voc. This symmetric capacitor demonstrates a clear proportionality between Isc (Voc) and Pr, allowing to achieve a 100% switchability of the photovoltaic response. The memory devices based on 3-bit data storage show good performance in terms of data retention, fatigue behavior, and repeatability of writing and reading cycles. Thanks to the very high sensitivity of the optical reading method, the number of states could largely exceed eight, being limited only by the electrical writing step precision. These results are particularly exciting for the development of next-generation ferroelectric memory devices with increased memory storage density and lower power consumption.
The large switchable ferroelectric polarization and lead-free composition of BiFeO3 make it a promising candidate as an active material in numerous applications, in particular, in micro-electro-mechanical systems (MEMS) when BiFeO3 is integrated in a thin film form on a silicon substrate. Here, 200-nm-thick Mn-doped BiFeO3 thin films have been epitaxially grown on a SrRuO3/SrTiO3/Si substrate and patterned into microcantilevers as prototype device structures for piezoelectric actuation. The devices demonstrate excellent ferroelectric response with a remanent polarization of 55 μC/cm2. The epitaxial BiFeO3 MEMS exhibit very high piezoelectric response with transverse piezoelectric coefficient d31 reaching 83 pm/V. The BiFeO3 cantilevers show larger electromechanical performance (the ratio of curvature/electric field) than that of state-of-art piezoelectric cantilevers, including well-known PZT (Pb(Zr,Ti)O3) and the hyper-active PMN–PT (Pb(Mg1/3Nb2/3)O3-PbTiO3). In addition, the piezoelectricity in BiFeO3 MEMS is found to depend on the ferroelectric polarization direction, which could originate from the flexoelectric effect and be exploited to further enhance the electromechanical performance of the devices. These results could potentially lead to a replacement of lead-based piezoelectrics by BiFeO3 in many microdevices.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.