Relaxation Induced by Imprint Phenomena in Low-Temperature (400 °C) Processed Hf0.5Zr0.5O2-Based Metal-Ferroelectric-Metal Capacitors

Ferroelectricity in Hf0.5Zr0.5O2 (HZO) has garnered increasing interest due to its potential applications in neuromorphic and nonvolatile memory devices. However, with time, the adverse shift in the coercive voltage (Vc) observed in a prepoled HZO ferroelectric capacitor can lead to insufficient polarization switching from one polarity owing to the development of a built-in voltage, causing reliability concerns. Another consequence of developed built-in voltage is polarization relaxation, that is, the rapid loss of stored polarization with time (t < 6 s). In this work, the correlation between the data retention issues in ferroelectric films, namely, imprint (Vc shift with time) and polarization relaxation, is studied carefully by pulse measurement techniques in HZO-based metal-ferroelectric-metal capacitors. In a nonaged ferroelectric, there are no significant relaxation effects for a switching time delay up to 6 s, even at higher measurement temperatures until 125 °C. After a baking process was performed at higher temperatures (25–125 °C) to a prepoled ferroelectric capacitor, an apparent systematic imprint was observed with increasing baking time (up to 200 h). Conjunctively, we also see that the imprinted ferroelectric capacitor shows a strong polarization relaxation effect even for short time periods due to the generated built-in voltages. For the 2.0 V operation, based on the delay time between the re-WRITE pulse and READ pulses, the lifetime extracted for a 65 °C bake can show a stable 10-year lifetime using a 10 μs delay time compared to a 0.5 year lifetime when using a delay time of 6 s. This work explores the drastic relaxation effects due to imprint in ferroelectric HZO films and the need to mitigate defects/space charges causing these issues.