Authors:

Rana Yuvraj

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About Paper:

Hafnia-based ferroelectrics offer great promise for emerging memories but are impeded by imprint that presents a consistent hurdle for read-out reliability; however, the origin of this phenomenon remains unclear. This study investigates the imprint in Hf(Zr)O2 (HZO) Metal-Ferroelectric- Metal (MFM) capacitor stacks and proposes a mechanism considering charged O-vacancies as a primary factor affecting imprint. Capacitor stacks-50 nm of W at the bottom electrode, 10 nm HZO ferroelectric layer, 5 nm of W and 5 nm of Pt to create semi-transparent top contact-are placed under a spectroscopy system while contacted to a Radiant Ferroelectric Tester. The capacitors are initially poled to either have their polarization pointing down (i.e. towards bottom electrode) or up. The measurements include an initial PL scan, a polarization hysteresis loop (PE-Loop), a so-called "wake up process" to ensure consistent ferroelectric response followed by a final polarizing pulse to ensure uniform poling of a film in a certain direction. After poling, PL measurements were taken continually during a 3-hour period during which the device was not electrically disturbed from the final polarizing pulse. After the 3-hour period, a final PE-loop was acquired to assess changes in the HZO with time. Variations in PL-intensity and the PE- loop with time were then compared. For films held in an upward polarization, an increase in coercive field with time (i.e., the amount of imprint) correlated to a larger variation in PL-intensity over the first hour. In preceding work, changes in PL were indicative of changes in the number and charge-states of O-vacancies in HZO. Here, using this knowledge, the correlation suggests that O-vacancies are an underlying cause of imprint. Specificially, we speculate that the increase in PL intensity observed after poling upward suggests that as more domains switch and guide electrons to the top interface, O-vacancies gain charge that generates an electric field, leading to an increased voltage requirement for switching. Findings of this mechanism can help mitigate imprint and improve reliability of Hafnia-based ferroelectrics. † Presenting Undergrad Author; ‡ Contributing Undergrad Author; * Undergrad Acknowledgment Keywords: Hafnia-Based Ferroelectrics; Imprint; O-Vacancies; Hf(Zr)O2 (HZO); Metal-Ferroelectric-Metal Capacitor

Source:

Purdue University / 2025

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Co-authors:

Rana Yuvraj