Novel Non-Perovskite Ferroelectric Oxides and Nitrides

Ferroelectricity in wurtzite-based crystals was observed in 2019 and immediately introduced exciting opportunities to explore and discover new structure-property relationships in novel formulation spaces, and to investigate new integration and device implementations given new process compatibilities. The seminal discovery of ferroelectric Al_1-xSc_xN by University of Kiel reserchers initiated this excitement and was followed by comparable observations of polarization reversal in the structurally similar Al_1-xB_xN and the Zn_1-xMg_xO systems. These observations lead one to speculate that ferroelectricity might be found much more broadly, even “everywhere”, by introducing the appropriate disorder.<br/><br/>In this presentation the structure-process-property relationships in the B-substituted AlN and Mg-substituted ZnO wurtzite systems will be demonstrated. The B-substituted materials exhibit square hysteresis loops with polarization values between 150 µC/cm² and 120 µC/cm² when boron concentrations range between 2% and 15% respectively. Coercive field values fall with additional boron, from 5.5MV/cm to about 5 MV/cm at B saturation. Bandgap values are approximately 5 eV or above in all cases. Material can be prepared between 100 °C and 350 °C with very little difference in electrical properties. W bottom and top electrodes are used in all cases. Capacitors can be prepared down to 50 nm thick before leakage current becomes problematic during low frequency hysteresis measurements.<br/><br/>Comparable results are found in the Zn_1-xMg_xO system. Between 25% and 35% Mg substitution, square hysteresis loops with remanent polarization values above 100 µC/cm² are readily achieved. Transmission measurements show bandgap values between 4.0 eV and 4.2 eV in this range. In comparison to AlBN, coercive field values for ZMO are as low as 1.7 MV/cm.<br/><br/>In addition to a discussion of properties and preferred synthesis routes, we will discuss the limitations to property engineering and scaling, and provide a complete update on observations/explorations in additional compositional and structural families. Finally, we will present our efforts to integrate these new ferroelectric crystals using "ground rules" that are consistent with the conventional semiconductor back end, addressing issues of temperature, chemical reactions, CMOS-accepted elements, and crystallographic texture.