Wassim Hamouda1,Ines Häusler2,Florian Maudet1,Hafiz Muhammad Hamid Raza1,Keerthana Shajil Nair1,3,Marco Holzer1,3,Zora Chalkley1,3,Christoph Schlueter4,Adnan Hammud5,Christoph T. Koch2,Veeresh Deshpande1,Catherine Dubourdieu1,3
Helmholtz-Zentrum Berlin für Materialien und Energie1,Humboldt-Universität zu Berlin2,Freie Universitat Berlin, Physical Chemistry3,Photon Science, Deutsches Elektronen-Synchrotron DESY4,Fritz-Haber Institute of the Max-Planck Society5
Wassim Hamouda1,Ines Häusler2,Florian Maudet1,Hafiz Muhammad Hamid Raza1,Keerthana Shajil Nair1,3,Marco Holzer1,3,Zora Chalkley1,3,Christoph Schlueter4,Adnan Hammud5,Christoph T. Koch2,Veeresh Deshpande1,Catherine Dubourdieu1,3
Helmholtz-Zentrum Berlin für Materialien und Energie1,Humboldt-Universität zu Berlin2,Freie Universitat Berlin, Physical Chemistry3,Photon Science, Deutsches Elektronen-Synchrotron DESY4,Fritz-Haber Institute of the Max-Planck Society5
Ferroelectric tunnel junctions (FTJs) have been intensively explored for future low power non-volatile data storage and information processing applications. Among various studied ferroelectric (FE) materials, polycrystalline HfO<sub>2</sub> and Hf<sub>0.5</sub>Zr<sub>0.5</sub>O<sub>2</sub> (HZO) solid solution thin films have the advantage of CMOS process compatibility and remarkable energy efficiency.<br/>Ferroelectricity in these systems has been attributed to the stabilization of a polar orthorhombic phase. However, the remnant polarization and the overall device performance depends strongly on several parameters such as the nature of the bottom and top electrodes, the presence of interfacial layers (whether intentional or not), and the oxygen defect content.<br/>In this study, we discuss the role of processing conditions of double layer FTJ devices consisting of 10 nm Hf<sub>0.5</sub>Zr<sub>0.5</sub>O<sub>2 </sub>(HZO) / 3 nm Al<sub>2</sub>O<sub>3</sub> with bottom TiN and top W electrodes on the chemistry of interfaces, on the crystallinity and the ferroelectric polarization in HZO. The latter is crystallized at a low temperature of 400C for full CMOS back-end of-line compatibility.<br/>First, as observed in electrical characterization, processing of the ultrathin Al<sub>2</sub>O<sub>3</sub> tunneling barrier plays a key role in the ability to stabilize and switch the electrical polarization in the HZO layer. Moreover, a strong dependence of the remnant polarization with the voltage pulse width is observed, which points to the major role of charge traps in minimizing the depolarizing field. Soft and hard X-ray photoelectron spectroscopy techniques were therefore used to probe the physical chemistry of the different buried interfaces and to quantify the oxygen vacancy content across the stack. We performed measurements at different synchrotron X-ray energies and beam angles to probe various depths of the HZO layer while the top alumina/W layers were investigated by combining laboratory XPS with low energy Ar ion sputtering. In addition, scanning transmission electron microscopy and electron energy loss spectroscopy (EELS) were performed to further investigate the chemistry of the films and interfaces. Based on the electrical, XPS and STEM/EELS measurements, we will discuss the influence of the processing conditions on providing the needed amount of electronic traps for sufficient screening charges, essential to maintain the non-volatile property of the device.