Impact of CeOx layer insertion on ferroelectric properties of Hf-Zr-O films prepared by chemical solution deposition

Abstract

Multivalent oxide, CeOx has been formed at top or bottom of the Hf-Zr-O (HZO) layer by chemical solution deposition (CSD) to obtain ferroelectric properties of HZO layer. It is shown that the insertion of thin CeOx layer significantly enhances the ferroelectric properties of Y-doped HZO layer. It is found by transmission electron microscope (TEM) observation that CeOx(12 nm)/Y-HZO(33 nm) layered structure can be clearly fabricated by CSD process in spite of high temperature crystallization anneal at 800 oC.

Visualization of oxygen vacancies at CeO x /Y-HZO interface by spectrum imaging method and multivariate analysis

“…23,24) In addition, there is another report on the improvement of ferroelectricity by doping some solid solution oxides to HfO 2 . 25) However, in our previous work, 16) we found the diffusion of Ce into the Y-HZO layer is negligible. Hence, we focus on the interface structures between the CeO x and Y-HZO layers in the present study.…”

“…21,22) We previously showed clear CeO x /Y-HZO/CeO x layered structure with no serious interdiffusion of constituent elements by depth profile analysis of X-ray photoelectron spectroscopy (XPS). 16) In this paper, we found in the highresolution STEM image that an interface layer existed between CeO x and Y-HZO layers. The interface layer consists of nanometer-size grains with a few nm to 10 nm in size although some parts of the interface were unclear.…”

“…CeO x /Y-HZO/CeO x layered structures were prepared by the CSD with 800 °C, 3 min annealing process, as reported previously. 16) At first, the CeO x source solution on spincoated on Pt/Ti/SiO 2 /Si substrate and dried on a hot plate at 250 °C. Next, the Y-HZO source solution was spin-coated on the dried CeO x layer and dried at 250 °C.…”

“…Then the CeO x /Y-HZO/CeO x sample was crystallized simultaneously at 800 °C for 3 min under N 2 atmosphere of a reduced pressure of 50 Pa. We estimated that the concentration of Ce in the middle of the Y-HZO layer was as small as 1%. 16) The thicknesses of CeO x and Y-HZO layers were 12 and 33 nm, respectively. As shown in Fig.…”

“…15) In our previous work, to improve the ferroelectric properties of HZO films made by the CSD, we have prepared undoped and Y-doped HZO (Y-HZO) films with CeO x layers inserted on top and/or bottom trying to control oxygen vacancy in HZO films and successfully demonstrated that the CeO x -capped films enhanced their ferroelectric properties. 16) However, its mechanism remains unclear. It is important to clarify the microstructure of CeO x film, in particular the CeO x /Y-HZO interface, that contributes to the improved characteristics of Y-HZO film.…”