Influence of the Ozone Dose Time during Atomic Layer Deposition on the Ferroelectric and Pyroelectric Properties of 45 nm-Thick ZrO₂ Films

Over a decade ago, ferroelectricity was discovered in doped HfO₂ thin films. The HfO₂-based thin films have attracted much attention due to their remarkable scalability and CMOS compatibility. Other than the HfO₂-based thin films, the undoped ZrO₂ thin films are understudied despite their commonly reported antiferroelectric behavior. However, being of the same fluorite structure as HfO₂-based thin films, the undoped ZrO₂ also displayed considerable ferroelectricity as demonstrated in recent studies. In this work, 45 nm-thick polycrystalline undoped ZrO₂ films are synthesized using atomic layer deposition with different ozone dose times. The ZrO₂ films are crystallized after atomic layer deposition at 350 °C without anneals. In general, the longer ozone dose time causes a lower in-plane tensile stress and oxygen vacancy content, which help facilitate an irreversible non-polar tetragonal to polar orthorhombic phase transition with electric-field cycling. However, the lower in-plane tensile stress and oxygen vacancy content also stabilize the monoclinic phase so that a long ozone dose time (>17.5 s) reduces the ferroelectric behavior. After wake-up cycles, the ZrO₂ thin film with an ozone dose time of 17.5 s exhibits a remanent polarization of 6 μC·cm^-2 and a pyroelectric coefficient of −35 μC·K^-1·m^-2. Moreover, the wake-up behavior is consistent between the ferroelectric and pyroelectric response. As essential factors in optimizing the growth of fluorite-structure thin films for ferroelectric applications, the in-plane tensile stress and oxygen vacancy content significantly influence the ferroelectric and pyroelectric properties. Additionally, the low thermal budget for processing ferroelectric ZrO₂ thin films is valuable for semiconductor back-end-of-line processes.