Robust ferroelectricity in HfO2-based bulk crystals via polymorphic engineering

Abstract The discovery of ferroelectricity in hafnium dioxide (HfO2) thin films over the past decade has revolutionized the landscape of ferroelectrics. HfO2-based ferroelectrics exhibit extraordinary switching capabilities and integrability in existing semiconductor chips, making them a promising candidate for next-generation ferroelectrics beyond the constraints of Moore’s law. However, the underlying mechanism of their ferroelectricity remains a topic of debate, possibly related to the presence of a metastable and volatile ferroelectric phase. Herein, we have achieved the successful growth of HfO2-based bulk crystals, revealing a remarkable remanent polarization of 26 μC/cm2 by a comprehensive understanding of the polymorphic engineering strategy. This result not only rivals the performances observed in extensively studied ultra-thin films but also underscores the universal feature of HfO2-based ferroelectricity. Our investigation has unveiled the intricate local structural transitions during the development of the ferroelectric phase in bulk crystals, clearly elucidating that the ferroelectric orthorhombic Pbc21 phase originates from the metastable tetragonal phase. This groundbreaking discovery clarifies the ferroelectric origin of HfO2 and provides a strategic approach for designing robust ferroelectricity. Our findings hold the potential to advance the comprehension of ferroelectric mechanisms in fluorite-structured materials, paving the way for significant strides in the subsequent development of HfO2-based nonvolatile electronic and photonic devices.