An ultra-thin InO interlayer as an oxygen reservoir for defect passivation and enhanced ferroelectricity in hafnia devices

Abstract

We report an interface engineering approach to enhance the ferroelectric properties and reliability of ultra-thin hafnium zirconium oxide (HZO) capacitors by introducing an indium oxide (InO) interlayer. Acting as an oxygen reservoir, the InO interlayer mitigates interface-driven degradation by replenishing oxygen vacancies at the HZO–electrode interface during thermal processing, thereby suppressing sub-oxide formation and improving interfacial stability. The TiN/InO/HZO/TiN metal–ferroelectric–metal (MFM) stack demonstrates up to a 35% increase in remanent polarization (P_r) and approximately one-order reduction in leakage current in representative devices compared to control devices without InO. Spectroscopic analyses, including X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS), confirm a significant reduction in sub-oxide fractions, validating the oxygen-supplying role of InO. Furthermore, transient current analysis and the conductance method reveal that the InO interlayer effectively passivates interfacial “dead layers,” enhancing interfacial capacitance and charge transport. Nucleation-limited switching (NLS) analysis indicates improved domain switching kinetics with a more uniform switching time distribution. Endurance and retention tests demonstrate robust reliability, sustaining over 10⁸ switching cycles and stable polarization retention for more than a decade. These findings provide critical insights into oxygen-mediated defect passivation in ferroelectric hafnia-based devices and offer a scalable strategy for advanced memory and logic applications.