Abstract
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.
