Origin and mitigation of the imprint effect in hafnia-based ferroelectrics

Abstract

The potential of hafnia-based ferroelectric materials for Ferroelectric Random Access Memory (FeRAM) applications is limited by the imprint effect, which compromises readout reliability. Here, we systematically investigate the asymmetric imprint behavior in W/Hf_0.5Zr_0.5O₂/W ferroelectric capacitors, demonstrating that the imprint direction correlates directly with the ferroelectric polarization state. Notably, a pre-pulse of specific polarity can temporarily suppress the imprint effect. Combined experimental and theoretical analyses reveal that the directional segregation of oxygen vacancies (V_O) at the electrode/ferroelectric interface, coupled with their dynamic charge trapping and detrapping processes, constitutes the core mechanism driving the imprint phenomenon. These processes modulate the built-in electric field, resulting in a shift of the coercive voltage. Building on these findings, we propose an oxygen vacancy segregation–charge trapping model that accounts for critical observations, including the dependence of imprint direction on polarization history and its reversible modulation by pre-pulses. Leveraging this model, we introduce three practical strategies for imprint recovery: charge compensation, oxygen vacancy redistribution, and the design of a bidirectional alternating polarization circuit architecture. Experimental results confirm that these approaches markedly enhance the device's resilience to imprinting, offering innovative pathways to address the reliability challenges of hafnia-based FeRAM.