Metal Interlayer Insertion for Grain Engineering in Ferroelectric Hf₀.₅Zr₀.₅O₂

Abstract

Since its discovery in the previous decade, ferroelectricity (FE) in zirconium-doped hafnium oxide (HZO) has been studied intensively. With HZO being incorporated in multiple applications, grain size reduction has become essential to enhance the ferroelectric performance and scalability. A common method is implementing a dielectric interlayer (IL) in the middle of HZO films while sacrificing operating power caused by voltage drop across the additional material. This research implemented W and Mo metal ILs in the middle of the HZO stack to prevent grain growth. The effects of the ILs on ferroelectric performance were studied using metal-ferroelectric–insulator-silicon structure. Transmission electron microscopy (TEM) and grazing-incidence X-ray diffraction were used to examine the grain formation in HZO. The results show that metal ILs have successfully improved the ferroelectric performance by suppressing the nonferroelectric monoclinic phase while promoting the formation of the orthorhombic phase. The sample with W IL acting as electrodes for both upper and under HZO thin films was more resilient to fatigue than that with the Mo IL. Hence, W metal ILs can enable HZO implementation in a wider range of application.