Structural Correlation of Ferroelectric Behavior in Mixed Hafnia-Zirconia High-k Dielectrics for FeRAM and NCFET Applica
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MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.148
Structural Correlation of Ferroelectric Behavior in Mixed Hafnia-Zirconia High-k Dielectrics for FeRAM and NCFET Applications Vineetha Mukundan*, Karsten Beckmann*, Kandabara Tapily^, Steven Consiglio^, Robert Clark^, Gert Leusink^, Nathaniel Cady*, Alain C Diebold* *SUNY Polytechnic Institute, Albany, NY
^TEL Technology Center, America, LLC, Albany, NY
ABSTRACT The recent discovery of ferroelectric behavior in doped hafnia-based dielectrics, attributed to a non-centrosymmetric orthorhombic phase, has potential for use in attractive applications such as negative differential capacitance field-effect-transistors (NCFET) and ferroelectric random access memory devices (FeRAM). Alloying with similar oxides like ZrO2, doping with specific elements such as Si, novel processing methods, encapsulation and annealing schemes are also some of the techniques that are being explored to target structural modifications and stabilization of the non-centrosymmetric phase. In this study, we utilized synchrotron-based xray diffraction in the grazing incidence in plane geometry (GIIXRD) to determine the crystalline phases in hafnia-zirconia (HZO) compositional alloys deposited by atomic layer deposition (ALD). Here we compare and contrast the structural phases and ferroelectric properties of mechanically confined HZO films in metal-insulator-metal (MIM) and metalinsulator-semiconductor (MIS) structures. Both MIM and MIS structures reveals a host of reflections due to non-monoclinic phases in the d-spacing region between 1.75Å to 4Å. The non-monoclinic phases are believed to consist of tetragonal and orthorhombic phases. Compared to the MIS structures a suppression of the monoclinic phase in MIM structures with 50% zirconia or less was observed. The correlation of the electrical properties with the structural analysis obtained by GIIXRD highlights the importance of understanding the effects of the underlying substrate (metal vs. Si) for different target applications. Email: [email protected]
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INTRODUCTION Ferroelectricity in hafnium oxide was discovered in 2011 in thin films doped with SiO2 and aided by TiN encapsulation [1,2]. Since then, hafnia with different doping elements and alloying with similar oxides have been under investigation for applications in ferroelectric RAM and negative differential capacitance FETs [3,4]. Further, electric field controlled partial polarization switching in ferroelectric FETs made from hafnia zirconia (HZO) films makes these an interesting candidate for synaptic memory devices for application in neuromorphic computing [4, 5]. At the core of these new-generation technologies is an ALD grown HZO nanoscale film which exhibits ferroelectricity when stabilized in a non-centrosymmetric
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