@misc{hsain_lee_materano_mittmann_payne_mikolajick_schroeder_parsons_jones_2022, title={Many routes to ferroelectric HfO2: A review of current deposition methods}, volume={40}, ISSN={["1520-8559"]}, url={https://doi.org/10.1116/6.0001317}, DOI={10.1116/6.0001317}, abstractNote={Although 10 years have passed since the initial report of ferroelectricity in hafnia (HfO2), researchers are still intensely fascinated by this material system and the promise it holds for future applications. A wide variety of deposition methods have been deployed to create ferroelectric HfO2 thin films such as atomic layer deposition, chemical solution deposition, and physical vapor deposition methods such as sputtering and pulsed laser deposition. Process and design parameters such as deposition temperature, precursor choice, target source, vacuum level, reactive gases, substrate strain, and many others are often integral in stabilizing the polar orthorhombic phase and ferroelectricity. We examine processing parameters across four main different deposition methods and their effect on film microstructure, phase evolution, defect concentration, and resultant electrical properties. The goal of this review is to integrate the process knowledge collected over the past 10 years in the field of ferroelectric HfO2 into a single comprehensive guide for the design of future HfO2-based ferroelectric materials and devices.}, number={1}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={Hsain, Hanan Alexandra and Lee, Younghwan and Materano, Monica and Mittmann, Terence and Payne, Alexis and Mikolajick, Thomas and Schroeder, Uwe and Parsons, Gregory N. and Jones, Jacob L.}, year={2022}, month={Jan} }
 @article{hsain_lee_lancaster_materano_alcala_xu_mikolajick_schroeder_parsons_jones_2022, title={Role of Oxygen Source on Buried Interfaces in Atomic-Layer- Deposited Ferroelectric Hafnia-Zirconia Thin Films}, volume={9}, ISSN={["1944-8252"]}, url={https://doi.org/10.1021/acsami.2c11073}, DOI={10.1021/acsami.2c11073}, abstractNote={Hafnia-zirconia (HfO2-ZrO2) solid solution thin films have emerged as viable candidates for electronic applications due to their compatibility with Si technology and demonstrated ferroelectricity at the nanoscale. The oxygen source in atomic layer deposition (ALD) plays a crucial role in determining the impurity concentration and phase composition of HfO2-ZrO2 within metal-ferroelectric-metal devices, notably at the Hf0.5Zr0.5O2 /TiN interface. The interface characteristics of HZO/TiN are fabricated via sequential no-atmosphere processing (SNAP) with either H2O or O2-plasma to study the influence of oxygen source on buried interfaces. Time-of-flight secondary ion mass spectrometry reveals that HZO films grown via O2-plasma promote the development of an interfacial TiOx layer at the bottom HZO/TiN interface. The presence of the TiOx layer leads to the development of 111-fiber texture in HZO as confirmed by two-dimensional X-ray diffraction (2D-XRD). Structural and chemical differences between HZO films grown via H2O or O2-plasma were found to strongly affect electrical characteristics such as permittivity, leakage current density, endurance, and switching kinetics. While HZO films grown via H2O yielded a higher remanent polarization value of 25 μC/cm2, HZO films grown via O2-plasma exhibited a comparable Pr of 21 μC/cm2 polarization and enhanced field cycling endurance limit by almost 2 orders of magnitude. Our study illustrates how oxygen sources (O2-plasma or H2O) in ALD can be a viable way to engineer the interface and properties in HZO thin films.}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Hsain, Hanan Alexandra and Lee, Younghwan and Lancaster, Suzanne and Materano, Monica and Alcala, Ruben and Xu, Bohan and Mikolajick, Thomas and Schroeder, Uwe and Parsons, Gregory N. and Jones, Jacob L.}, year={2022}, month={Sep} }
 @misc{lee_lee_yang_park_kim_reddy_materano_mulaosmanovic_mikolajick_jones_et al._2021, title={Domains and domain dynamics in fluorite-structured ferroelectrics}, volume={8}, ISSN={["1931-9401"]}, DOI={10.1063/5.0047977}, abstractNote={Ferroelectricity in fluorite-structured ferroelectrics such as HfO2 and ZrO2 has been attracting increasing interest since its first publication in 2011. Fluorite-structured ferroelectrics are considered to be promising for semiconductor devices because of their compatibility with the complementary metal–oxide–semiconductor technology and scalability for highly dense information storage. The research on fluorite-structured ferroelectrics during the first decade of their conceptualization has been mainly focused on elucidating the origin of their ferroelectricity and improving the performance of electronic devices based on such ferroelectrics. Furthermore, as is known, to achieve optimal performance, the emerging biomimicking electronic devices as well as conventional semiconductor devices based on the classical von Neumann architecture require high operating speed, sufficient reliability, and multilevel data storage. Nanoscale electronic devices with fluorite-structured ferroelectrics serve as candidates for these device systems and, thus, have been intensively studied primarily because in ferroelectric materials the switching speed, reliability, and multilevel polarizability are known to be strongly correlated with the domains and domain dynamics. Although there have been important theoretical and experimental studies related to domains and domain dynamics in fluorite-structured ferroelectrics, they are yet to be comprehensively reviewed. Therefore, to provide a strong foundation for research in this field, herein, domains, domain dynamics, and emerging applications, particularly in neuromorphic computing, of fluorite-structured ferroelectrics are comprehensively reviewed based on the existing literature.}, number={2}, journal={APPLIED PHYSICS REVIEWS}, author={Lee, Dong Hyun and Lee, Younghwan and Yang, Kun and Park, Ju Yong and Kim, Se Hyun and Reddy, Pothala Reddi Sekhar and Materano, Monica and Mulaosmanovic, Halid and Mikolajick, Thomas and Jones, Jacob L. and et al.}, year={2021}, month={Jun} }
 @article{shekhawat_hsain_lee_jones_moghaddam_2021, title={Effect of ferroelectric and interface films on the tunneling electroresistance of the Al2O3/Hf0.5Zr0.5O2 based ferroelectric tunnel junctions}, volume={32}, ISSN={["1361-6528"]}, DOI={10.1088/1361-6528/ac1ebe}, abstractNote={Ferroelectric random-access memory (FRAM) based on conventional ferroelectric materials is a non-volatile memory with fast read/write operations, high endurance, and 10 years of data retention time. However, it suffers from destructive read-out operation and lack of CMOS compatibility. HfO2-based ferroelectric tunnel junctions (FTJ) may compensate for the shortcomings of FRAM by its CMOS compatibility, fast operation speed, and non-destructive readout operation. In this study, we investigate the effect of ferroelectric and interface film thickness on the tunneling electroresistance or ON/OFF current ratio of the Hf0.5Zr0.5O2/Al2O3 based FTJ device. Integrating a thick ferroelectric layer (i.e. 12 nm Hf0.5Zr0.5O2) with a thin interface layer (i.e. 1 nm Al2O3) resulted in an ON/OFF current ratio of 78. Furthermore, to elucidate the relationship between ON/OFF current ratio and interfacial properties, the Hf0.5Zr0.5O2-Al2O3 films and Ge-Al2O3 interfaces are examined via time-of-flight secondary ion mass spectrometry depth profiling mode. A bilayer oxide heterostructure (Hf0.5Zr0.5O2/Al2O3) is deposited by atomic layer deposition (ALD) on the Ge substrate. The ON/OFF current ratio is enhanced by an order of magnitude when the Hf0.5Zr0.5O2 film deposition mode is changed from exposure (H2O) ALD to sequential plasma (sequential O2–H2) ALD. Moreover, the interfacial engineering approach based on the in situ ALD H2-plasma surface pre-treatment of Ge increases the ON/OFF current ratio from 9 to 38 by reducing the interfacial trap density state at the Ge-Al2O3 interface and producing Al2O3 with fewer oxygen vacancies as compared to the wet etch (HF + H2O rinse) treatment of the Ge substrate. This study provides evidence of strong coupling between Hf0.5Zr0.5O2 and Al2O3 films in controlling the ON/OFF current ratio of the FTJ.}, number={48}, journal={NANOTECHNOLOGY}, author={Shekhawat, Aniruddh and Hsain, H. Alex and Lee, Younghwan and Jones, Jacob L. and Moghaddam, Saeed}, year={2021}, month={Nov} }
 @article{lee_hsain_fields_jaszewski_horgan_edgington_ihlefeld_parsons_jones_2021, title={Unexpectedly large remanent polarization of Hf0.5Zr0.5O2 metal-ferroelectric-metal capacitor fabricated without breaking vacuum}, volume={118}, ISSN={["1077-3118"]}, url={https://doi.org/10.1063/5.0029532}, DOI={10.1063/5.0029532}, abstractNote={We introduce an Atomic Layer Deposition (ALD) technique referred to here as Sequential, No-Atmosphere Processing (SNAP) to fabricate ferroelectric Hf0.5Zr0.5O2 capacitors in Metal–Ferroelectric–Metal (MFM) structures. SNAP involves the ALD of each layer sequentially while maintaining the sample under vacuum process conditions without ambient exposure during the entire sequential deposition processes. We first use plasma enhanced ALD to fabricate 002-textured TiN films and study the degree of texture and quality of the film by X-ray Diffraction (XRD), Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), and transmission electron microscopy. Building upon the textured TiN film, we fabricate MFM capacitors with 10-nm-thick Hf0.5Zr0.5O2 via SNAP deposition and observe an unexpectedly large remanent polarization (2Pr = 54.2 μC/cm2). We report that annealing at T <800 °C and at T = 800 °C results in different ferroelectric behaviors and phases determined by grazing incidence XRD patterns. We infer that the nonpolar tetragonal phase is dominant in films treated at T <800 °C, whereas the polar orthorhombic phase is dominant in films treated at T = 800 °C. Using ToF-SIMS and x-ray spectroscopy depth profiling on MFM capacitors, we observe an increase in the concentration of defects in the Hf0.5Zr0.5O2 layer after annealing. We believe that the absence of the native passive layer between Hf0.5Zr0.5O2 and TiN layers made via SNAP deposition is responsible for the unexpectedly large remanent polarization. In addition, we associate the 002-textured TiN as potentially playing a role in realizing the unexpectedly large remanent polarization.}, number={1}, journal={APPLIED PHYSICS LETTERS}, author={Lee, Younghwan and Hsain, H. Alex and Fields, Shelby S. and Jaszewski, Samantha T. and Horgan, Madison D. and Edgington, Patrick G. and Ihlefeld, Jon F. and Parsons, Gregory N. and Jones, Jacob L.}, year={2021}, month={Jan} }
 @article{park_yang_lee_kim_lee_reddy_jones_park_2020, title={A perspective on semiconductor devices based on fluorite-structured ferroelectrics from the materials-device integration perspective}, volume={128}, ISSN={["1089-7550"]}, DOI={10.1063/5.0035542}, abstractNote={Ferroelectric materials are known to be ideal materials for nonvolatile memory devices, owing to their two electrically switchable spontaneous polarization states. However, difficulties in scaling down devices with ferroelectric materials have hindered their practical applications and research. The discovery of ferroelectricity in fluorite-structured ferroelectrics has revived research on semiconductor devices based on ferroelectrics. With their scalability and established fabrication techniques, the performance of nanoscale electronic devices with fluorite-structured ferroelectrics is being rapidly developed. However, the fundamental physics behind the superior ferroelectricity is yet to be elucidated. From this Perspective, the status of research on fluorite-structured ferroelectrics and state-of-the-art semiconductor devices based on them are comprehensively reviewed. In particular, the fundamental physics of fluorite-structured oxides is critically reviewed based on a newly developed theory as well as on the classical theory on ferroelectrics. A perspective on the establishment of emerging semiconductor devices based on fluorite-structured ferroelectrics is provided from the viewpoint of materials science and engineering.}, number={24}, journal={JOURNAL OF APPLIED PHYSICS}, author={Park, Ju Yong and Yang, Kun and Lee, Dong Hyun and Kim, Se Hyun and Lee, Younghwan and Reddy, P. R. Sekhar and Jones, Jacob L. and Park, Min Hyuk}, year={2020}, month={Dec} }
 @article{hsain_lee_parsons_jones_2020, title={Compositional dependence of crystallization temperatures and phase evolution in hafnia-zirconia (HfxZr1-x)O-2 thin films}, volume={116}, ISSN={["1077-3118"]}, url={https://doi.org/10.1063/5.0002835}, DOI={10.1063/5.0002835}, abstractNote={Polymorphic (HfxZr1−x)O2 (HZO) thin films exhibit ferroelectric, dielectric, and antiferroelectric properties across a wide compositional range due to the existence of orthorhombic, monoclinic, and tetragonal phases. To better understand the phase stability across the HfO2–ZrO2 compositional range, we investigate the structural evolution of HZO thin films in situ via high-temperature x-ray diffraction (HTXRD) for five different compositions [ZrO2, (Hf0.23Zr0.77)O2, (Hf0.43Zr0.57)O2, (Hf0.67Zr0.33)O2, and HfO2]. The real-time monitoring of HZO crystallization reveals a competing driving force between the tetragonal and monoclinic phase stabilities for HfO2-rich vs ZrO2-rich compositions. Additionally, we confirm an XRD peak shift toward lower 2θ with increasing temperature in ZrO2, (Hf0.23Zr0.77)O2, and (Hf0.43Zr0.57)O2 films, which we ascribe to the appearance of a metastable orthorhombic phase during heating. A monotonic trend for the onset crystallization temperature is reported for five compositions of HZO and reveals an increase in onset crystallization temperature for HfO2-rich compositions. Relative intensity fraction calculations suggest a higher fraction of monoclinic phase with increasing annealing temperature for (Hf0.67Zr0.33)O2. This study of phase stability and onset crystallization temperatures offers insight for managing the thermal budget for HZO thin films, especially for temperature-constrained processing.}, number={19}, journal={APPLIED PHYSICS LETTERS}, author={Hsain, H. Alex and Lee, Younghwan and Parsons, Gregory N. and Jones, Jacob L.}, year={2020}, month={May} }
 @article{strader_lee_teska_li_jones_2019, title={Approaches for Characterizing Surfaces Damaged by Disinfection in Healthcare}, volume={9}, ISSN={["1793-9852"]}, DOI={10.1142/S1793984419500028}, abstractNote={ Healthcare-Associated Infections (HAIs) are a significant cause of morbidity and mortality and occur in many healthcare facilities including hospitals, surgery centers and long-term care facilities. It is well known that some pathogens can persist on healthcare surfaces for weeks to months and spread readily to new surfaces. It is current practice to disinfect or clean surfaces routinely in order to reduce the risk of HAIs. However, routine cleaning can damage the surface chemically or mechanically, which may actually increase the surface contamination. Fundamental knowledge is therefore needed to understand the influence of cleaning and disinfection on healthcare surfaces in order to mitigate pathogen persistence. In this study, materials and objects found in healthcare facilities were selected and exposed to disinfection procedures including wiping and soaking with readily available chemical disinfectants. A variety of chemical disinfectants were selected which contain hydrogen peroxide, quaternary ammonia, and chlorine, respectively. Optical microscopy, contact angle measurement, atomic force microscopy (AFM), Fourier Transform Infrared (FTIR) spectroscopy and nanoindentation are used to analyze surface characteristics before and after disinfection in order to study the effect of disinfection on material properties. Disinfection procedures are found to cause changes to surface properties of materials and objects which can be detected and observed or quantified by the approaches used in this study. The methods should become regular practice in the studies of healthcare surfaces and their role in HAIs. Each method in this study may not be reliably applied to every object or disinfection scenario. Sample geometry and features may influence response during measurement and affect results. The combination of the approaches is able to sufficiently characterize chemical, mechanical, and topological changes to the surface. }, number={4}, journal={NANO LIFE}, author={Strader, Phillip and Lee, Younghwan and Teska, Peter and Li, Xiaobao and Jones, Jacob L.}, year={2019}, month={Dec} }