Signatures of enhanced out-of-plane polarization in asymmetric BaTiO3 superlattices integrated on silicon

Binbin Chen,Stefan Abel,Felix Eltes,Daen Jannis,Sizhao Huang,Manfred Fiebig,Martin F Sarott,Gertjan Koster,Jean Fompeyrine,Minh Duc Nguyen,Matjaž Spreitzer,Guus Rijnders,Morgan Trassin,Nicolas Gauquelin,Mark Huijben,Nives Strkalj,Johan Verbeeck,Ufuk Halisdemir

doi:10.1038/s41467-021-27898-x

Abstract

In order to bring the diverse functionalities of transition metal oxides into modern electronics, it is imperative to integrate oxide films with controllable properties onto the silicon platform. Here, we present asymmetric LaMnO3/BaTiO3/SrTiO3 superlattices fabricated on silicon with layer thickness control at the unit-cell level. By harnessing the coherent strain between the constituent layers, we overcome the biaxial thermal tension from silicon and stabilize c-axis oriented BaTiO3 layers with substantially enhanced tetragonality, as revealed by atomically resolved scanning transmission electron microscopy. Optical second harmonic generation measurements signify a predominant out-of-plane polarized state with strongly enhanced net polarization in the tricolor superlattices, as compared to the BaTiO3 single film and conventional BaTiO3/SrTiO3 superlattice grown on silicon. Meanwhile, this coherent strain in turn suppresses the magnetism of LaMnO3 as the thickness of BaTiO3 increases. Our study raises the prospect of designing artificial oxide superlattices on silicon with tailored functionalities.

Highlights

In order to bring the diverse functionalities of transition metal oxides into modern electronics, it is imperative to integrate oxide films with controllable properties onto the silicon platform
The SrTiO3 (STO) buffer layer prepared by molecular beam epitaxy (MBE) has been widely used as a template to overcome this limitation, but the defective STO layer usually induces a relaxation of the crystalline film at the growth temperature, and the typically large thermal-expansion coefficients in oxides leads to biaxial thermal tension to the ferroelectric film, favouring an in-plane polarization[3,4]
Ferroelectric BTO is tetragonal at room temperature with a = b = 3.992 Å and c = 4.036 Å27

Summary

Introduction

In order to bring the diverse functionalities of transition metal oxides into modern electronics, it is imperative to integrate oxide films with controllable properties onto the silicon platform. By harnessing the coherent strain between the constituent layers, we overcome the biaxial thermal tension from silicon and stabilize c-axis oriented BaTiO3 layers with substantially enhanced tetragonality, as revealed by atomically resolved scanning transmission electron microscopy. Optical second harmonic generation measurements signify a predominant out-of-plane polarized state with strongly enhanced net polarization in the tricolor superlattices, as compared to the BaTiO3 single film and conventional BaTiO3/SrTiO3 superlattice grown on silicon This coherent strain in turn suppresses the magnetism of LaMnO3 as the thickness of BaTiO3 increases. Resolved scanning transmission electron microscopy (STEM) reveals c-axis-oriented BTO layers with remarkably enhanced tetragonality (c/a) This is accomplished by taking advantages of the compressive strain from neighboring STO and LMO layers, which overcomes the biaxial thermal tension from silicon

Methods

Results

Conclusion