Thermally Stable and Radiation Hard Ferroelectric Hf_0.5Zr_0.5O₂ Thin Films on Muscovite Mica for Flexible Nonvolatile Memory Applications

Abstract

Metal–ferroelectric–metal (MFM) capacitors on flexible substrates are promising for flexible nonvolatile memory applications, while the insufficient scalability of perovskite-based ferroelectric thin films and the difficulty of direct integration of high performance ferroelectric thin films on current conventional flexible substrates are the most serious obstacles to their practical applications. Meanwhile, performance under harsh conditions (such as high temperature and high total ionized dose (TID) radiation) is highly demanded due to the growing applications for nonvolatile memory. Here, we integrate highly scalable ferroelectric Hf0.5Zr0.5O2 (HZO) thin films on potential flexible mica substrates using atomic layer deposition (ALD) to form flexible MFM capacitors and investigate the ferroelectric properties, the retention behaviors, and endurance characteristics of the TaN/HZO/TaN/mica flexible MFM capacitors under various tensile and compressive bending radii. In addition, these characteristics of the HZO-based MFM flexible capacitors are explored in a wide temperature range from 25 up to 125 °C. The ferroelectricity of the film can be retained under a bending radius down to 7.5 mm after 1000 bending cycles, and the retention properties can be reserved under a bake time of 104 s at 125 °C, with an extrapolated retention time-to-failure longer than 10 years. Furthermore, the flexible devices display robust ferroelectric performance against radiation of 60Co γ-rays with a total dose of 1 Mrad (Si). Our work represents a critical step in HfO2-based ferroelectric memory implemented on mica toward flexible nonvolatile memory operated under harsh conditions.

Stabilization of the Ferroelectric Phase in Epitaxial Hf1–xZrxO2 Enabling Coexistence of Ferroelectric and Enhanced Piezoelectric Properties

“…The integrated peak intensity of the o(111)/t(101) reflection as a function of temperature (Figure 2f) shows a gradual decrease with temperature and the absence of phase transition. For HfO 2 , Hf 0.5 Zr 0.5 O 2 , and ZrO 2 films, polarization dependence on temperature shows a small decrease with temperature with the absence of phase transition in the explored temperature range (Supporting Information, Figure S9) in agreement with the reported results in polycrystalline 39 and epitaxial 40 films. Thus, only the HfO 2 film undergoes a phase transition to the high temperature stable monoclinic phase.…”

Large‐Scale Hf0.5Zr0.5O2 Membranes with Robust Ferroelectricity

“…[41] Previous studies showed that HZO thin films directly grown on flexible mica substrates had robust ferroelectricity and promising application potential in flexible electronics. [42][43][44][45] The distinct advantage of our freestanding HZO membranes is that they can be easily transferred to almost any substrate to fabricate electronic devices, including substrates that cannot be annealed at high temperatures. Here we transferred the HZO capacitors onto mica as an example to demonstrate the robust ferroelectricity of our freestanding HZO membranes in flexible electronic devices.…”

Ferroelectric Properties and Polarization Fatigue of La:HfO2 Thin‐Film Capacitors

“…Although there are observations of large polarizations that are comparable with those of perovskite‐oxide ferroelectrics, doped HfO 2 thin films suffer from severe fatigue problems during bipolar electric field cycling. [ 21–30 ] Switchable polarizations ( P SW ) have been observed to be degraded to zero after ≈10 9 cycles in Hf 0.5 Zr 0.5 O 2 and Y:HfO 2 thin films. [ 22,28 ] In addition, dramatically increased leakage currents and dielectric breakdown appeared in fatigued HfO 2 thin films.…”