Shelby S. Fields

While ferroelectric HfO2 shows promise for use in memory technologies, limited endurance is one factor that challenges its widespread application. Herein, endurance is investigated through field cycling W/Hf0.5Zr0.5O2/W capacitors above the coercive field while manipulating the time under field using bipolar pulses of varying pulse duration or duty cycle. Both remanent polarization and leakage current increase with increasing pulse duration. Additionally, an order of magnitude decrease in the pulse duration from 20 to 2 μs results in an increase in endurance lifetime of nearly two orders of magnitude from 3 × 106 to 2 × 108 cycles. These behaviors are attributed to increasing time under field allowing for charged oxygen vacancy migration, initially unpinning domains, or driving phase transformations before segregating to grain boundaries and electrode interfaces. This oxygen vacancy migration causes …

Altermagnetism is an emerging phenomena of significantly high interest to the spintronics community. While spintronics has persisted for decades across a wide array of memory and computing paradigms, it has reached a threshold. Ferromagnetic spintronics have the clear downsides of low switching speeds, stray fields and low packing densities which have hindered any new novel spin related paradigms from wide adaptation by our modern nanoelectronics. While Antiferromagnetics has breathed new life by promising to increase the switching speed of spintronic devices by multiple orders of magnitude by Neel vector manipulation, their diminishingly low spin polarizations prohibit spin current enabled electric readout. Altermagnets however promise to be a new subset of antiferromagnetism described as combining the ultra-high switching speeds of an antiferromagnet, with the spin polarization of a ferromagnet …

Q23. 00005: Characterization of Altermagnetic MnTe Films Grown by Molecular Beam Epitaxy on Al 2 O 3 (0001) Substrates

B20. 00006: Combinatorial Synthesis and Characterization of α''-Fe x M 1‑x N 2 for Rare-Earth-Free Permanent Magnet Applications

The impact of the high-power impulse magnetron sputtering (HiPIMS) pulse width on the crystallization, microstructure, and ferroelectric properties of undoped HfO2 films is investigated. HfO2 films were sputtered from a hafnium metal target in an Ar/O2 atmosphere, varying the instantaneous power density by changing the HiPIMS pulse width with fixed time-averaged power and pulse frequency. The pulse width is shown to affect the ion-to-neutral ratio in the depositing species with the shortest pulse durations leading to the highest ion fraction. In situ x-ray diffraction measurements during crystallization demonstrate that the HiPIMS pulse width impacts nucleation and phase formation, with an intermediate pulse width of 110 μs stabilizing the ferroelectric phase over the widest temperature range. Although the pulse width impacts the grain size with the lowest pulse width resulting in the largest grain size, the grain size …

La-doped BaSnO3 (LBSO) epitaxial thin films were grown on (001) MgO substrates by pulsed laser deposition using a La0.04Ba0.96SnO3 target. The structural, electrical, and optical properties of the LBSO films were investigated as a function of oxygen pressure during deposition. The carrier mobility can be tuned from 13 cm2V−1s−1 to 44 cm2V−1s−1 by varying oxygen partial pressure from 2 Pa to 12 Pa, respectively. This improved mobility is attributed to the reduced film strain via reducing oxygen defect concentration or reducing off-stoichiometry in the film. The optical permittivity of LBSO films can also be modified as a function of the oxygen pressure during deposition, allowing tuning of their epsilon-near-zero wavelength from 1.9 µm to 5.6 µm. These results demonstrate that LBSO thin films grown on MgO can be used for plasmonic devices at mid-wave infrared wavelengths.

Ferroelectric HfO 2 holds promise for many applications, including non-volatile on-chip memory and ferroelectric field-effect transistors. One challenge preventing the integration of ferroelectric HfO 2 into devices is the difficulty to unambiguously prepare phase-pure material without the benefits of epitaxy. Here, a new method for preparing ferroelectric HfO 2 is presented using High-Power Impulse Magnetron Sputtering (HiPIMS). HiPIMS offers a unique combination of processing parameters such as incident ion energy and gas atmosphere that are inaccessible through conventional HfO 2 synthesis by atomic layer deposition (ALD). In this work, the impact of plasma oxygen content on the crystallization, phase constitution, microstructure, and ferroelectric properties of undoped HfO 2 films deposited by HiPIMS is investigated. HfO 2 thin films were reactively sputtered with plasma oxygen content varied from 7.1 to 8.0 …

Phase identification in HfO2-based thin films is a prerequisite to understanding the mechanisms stabilizing the ferroelectric phase in these materials, which hold great promise in next-generation nonvolatile memory and computing technology. While grazing-incidence X-ray diffraction is commonly employed for this purpose, it has difficulty unambiguously differentiating between the ferroelectric phase and other metastable phases that may exist due to similarities in the d-spacings, their low intensities, and the overlapping of reflections. Infrared signatures provide an alternative route. However, their use in phase identification remains limited because phase control has overwhelmingly been accomplished via substituents, thereby convoluting infrared signatures between the substituents and the phase changes that they induce. Herein, we report the infrared optical responses of three undoped hafnium oxide films where …

As ferroelectric hafnium zirconium oxide (HZO) becomes more widely utilized in ferroelectric microelectronics, integration impacts of intentional and nonintentional dielectric interfaces and their effects upon the ferroelectric film wake-up (WU) and circuit parameters become important to understand. In this work, the effect of the addition of a linear dielectric aluminum oxide, Al2O3, below a ferroelectric Hf0.58Zr0.42O2 film in a capacitor structure for FeRAM applications with niobium nitride (NbN) electrodes was measured. Depolarization fields resulting from the linear dielectric is observed to induce a reduction of the remanent polarization of the ferroelectric. Addition of the aluminum oxide also impacts the WU of the HZO with respect to the cycling voltage applied. Intricately linked to the design of a FeRAM 1C/1T cell, the metal–ferroelectric–insulator–metal (MFIM) devices are observed to significantly shift charge related …

Ferroelectricity in binary oxides including hafnia and zirconia has riveted the attention of the scientific community due to the highly unconventional physical mechanisms and the potential for the integration of these materials into semiconductor workflows. Over the last decade, it has been argued that behaviours such as wake-up phenomena and an extreme sensitivity to electrode and processing conditions suggest that ferroelectricity in these materials is strongly influenced by other factors, including electrochemical boundary conditions and strain. Here we argue that the properties of these materials emerge due to the interplay between the bulk competition between ferroelectric and structural instabilities, similar to that in classical antiferroelectrics, coupled with non-local screening mediated by the finite density of states at surfaces and internal interfaces. Via the decoupling of electrochemical and electrostatic controls …

Non‐volatile memory device structures such as ferroelectric random‐access memory and ferroelectric tunnel junctions employ switchable spontaneous polarization to hold binary states. These devices can potentially benefit from the imposition of spontaneous internal biases and their resulting effect on the polarization properties of the ferroelectric (or field‐induced ferroelectric/antiferroelectric) layer. While HfO2‐based thin films are ideal candidates for implementation into these devices due to their scalability and silicon compatibility, the phase purity of these oxides is sensitive to the selection of electrode material, preventing incorporation of asymmetric electrode layers into such structures. Within this work, electrode replacement following post‐metallization anneal processing is introduced as a route to achieve ferroelectric and field‐induced ferroelectric HfxZr1−xO2 (HZO) thin films with electrode‐independent …

Ferroelectric thin film hafnium oxide (HfO 2) is an especially promising candidate for next generation non-volatile memory applications because of its compatibility with complementary metal-oxide-semiconductor (CMOS) technology. Although the metastable polar orthorhombic Pca2 1 phase is generally thought to be responsible for ferroelectricity in thin film HfO 2, this identification is not absolutely certain because multiple structurally similar phases are present in the polycrystalline films. Moreover, the mechanism stabilizing the relevant crystal phases is not fully understood. Scanning transmission electron microscopy (STEM) can identify crystal phases, but usually is insensitive to polarization. Electron-beam induced current (EBIC) imaging can map electric fields directly. Using STEM EBIC imaging along with the positive-up-negative-down (PUND) method, we map the polarization state and measure the global …

Machine learning (ML) and artificial intelligence (AI) have been applied to determine the physical mechanisms involved in phenomena encoded within microscopy data [1], enabling ML/AI to rapidly become an indispensable part of physics research. However, the real-time connection between ML and microscopy—which enables automated and autonomous experiments for microscopy imaging and spectroscopy measurements—still lags. Until now, the search for interesting functionalities in microscopy experiments has been guided by auxiliary information from microscopy to identify potential objects of interest based on human intuition; the exploration and verification of physical mechanisms depend on human-based decision making, ie, operators determine the parameters for subsequent experiments according to the previous experiment. Here, we developed a ML-driven automated experiment (AE) scanning …

Electronic conduction pathways in dielectric thin films are explored using automated experiments in scanning probe microscopy (SPM). Here, we use large field of view scanning to identify the position of localized conductive spots and develop an SPM workflow to probe their dynamic behavior at higher spatial resolution as a function of time, voltage, and scanning process in an automated fashion. Using this approach, we observe the variable behaviors of the conductive spots in a 20-nm-thick ferroelectric Hf 0.54 Zr 0.48 O 2 film, where conductive spots disappear and reappear during continuous scanning. There are also fresh conductive spots that develop during scanning. The automated workflow is universal and can be integrated into a wide range of microscopy techniques, including SPM, electron microscopy, optical microscopy, and chemical imaging.

Ferroelectric microelectronic devices utilizing NbN / Nb electrodes with thin film ferroelectric (Hf,Zr)O Page 1 Exceptional service in the national interest Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the US Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. Ferroelectric microelectronic devices utilizing NbN / Nb electrodes with thin film ferroelectric (Hf,Zr)O 2 M. David Henry1, Shelby Fields2, Samantha Jaszewski2, Giovanni Esteves1, Travis Young1, Steve Wolfley1, and Jon Ihlefeld2 1Microsystems Engineering, Science and Applications, Sandia National Laboratories, Albuquerque, New Mexico, 87123, USA 2Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia, …

The presence of the top electrode on hafnium oxide‐based thin films during processing has been shown to drive an increase in the amount of metastable ferroelectric orthorhombic phase and polarization performance. This “Clamping Effect,” also referred to as the Capping or Confinement Effect, is attributed to the mechanical stress and confinement from the top electrode layer. However, other contributions to orthorhombic phase stabilization have been experimentally reported, which may also be affected by the presence of a top electrode. In this study, it is shown that the presence of the top electrode during thermal processing results in larger tensile biaxial stress magnitudes and concomitant increases in ferroelectric phase fraction and polarization response, whereas film chemistry, microstructure, and crystallization temperature are not affected. Through etching experiments and measurement of stress evolution …

Since the first report of ferroelectricity in hafnium oxide (HfO2) doped with SiO2 in 2011 [1], significant research efforts have been directed toward understanding the switchable spontaneous polarization in this material. HfO2 is chemically compatible with silicon [2], is currently used as a high-κ dielectric in complementary metal oxide semiconductor (CMOS) devices [3], and in the ferroelectric phase is not susceptible to the thickness scaling effects that impose application limitations on traditional ferroelectrics [4, 5]. Thus, this material presents opportunities for technological developments in devices, such as renewed scaling of ferroelectric random access memory (FeRAM), ferroelectric field effect transistors (FeFETS), and new devices such as ferroelectric tunnel junctions (FTJs) that previously required epitaxial growth. The wide-scale adoption of ferroelectric HfO2 into devices is constrained, in part, by an inability to prepare phase-pure films. In equilibrium at room temperature and atmospheric pressure, HfO2 exists in the nonpolar monoclinic P21/c phase. Multiple metastable phases exist, including an orthorhombic Pca21 phase and a tetragonal P42/nmc phase, which can be stabilized by various factors. Ferroelectricity in HfO2 has been attributed to the non-centrosymmetric Pca21 orthorhombic phase.[6] The factors that have been shown to impact phase constitution include dopant type and concentration [6–10], biaxial stress [11], oxygen vacancies [12], and film thickness or grain size [13, 14].The majority of research on ferroelectric HfO2 thus far has utilized atomic layer deposition (ALD) for film preparation. These films are typically amorphous as …

Commonly employed as a high-k dielectric in the semiconductor industry, thin film hafnia (HfO2) was discovered to exhibit ferroelectricity in 2011 [1]. Hafnia consequently became the leading candidate material for ferroelectric random access memory (FRAM)[2], and much effort has been devoted to better understanding the origins, characteristics, and optimization of its ferroelectricity. The orthorhombic Pca21 phase is generally thought to be responsible for hafnia’s ferroelectricity [3, 4], but this identification is not entirely certain because of the structural similarities between the various phases present in polycrystalline hafnia films [5, 6]. Here we use scanning transmission electron microscopy (STEM) and electron beam-induced current (EBIC) imaging to study the ferroelectric properties of hafnium-zirconium-oxide (HZO).We fabricate a metal-insulator-metal (MIM) capacitor on an electron-transparent Si3N4 …

Ferroelectric oxides interfaced with transition metal dichalcogenides (TMDCs) offer a promising route toward ferroelectric-based devices due to lack of dangling bonds on the TMDC surface leading to a high-quality and abrupt ferroelectric/TMDC interface. In this work, the thermal stability of this interface is explored by first depositing hafnium zirconium oxide (HZO) directly on geological MoS2 and as-grown WSe2, followed by sequential annealing in ultra-high vacuum (UHV) over a range of temperatures (400–800 °C), and examining the interface through X-ray photoelectron spectroscopy (XPS). We show that the nucleation and stability of HZO grown through atomic layer deposition (ALD) varied depending on functionalization of the TMDC, and the deposition conditions can cause tungsten oxidation in WSe2. It was observed that HZO deposited on non-functionalized MoS2 was unstable and volatile upon annealing …

The elastic moduli of amorphous and crystalline atomic layer-deposited Hf 1-x Zr x O 2 (HZO, x= 0, 0.31, 0.46, 0.79, 1) films prepared with TaN electrodes on silicon substrates were investigated using picosecond acoustic measurements. The moduli of the amorphous films were observed to increase between 211±6 GPa for pure HfO 2 and 302±9 GPa for pure ZrO 2. In the crystalline films, it was found that the moduli increased upon increasing the zirconium composition from 248±6 GPa for monoclinic HfO 2 to 267±9 GPa for tetragonal ZrO 2. Positive deviations from this increase were observed for the Hf 0.69 Zr 0.31 O 2 and Hf 0.54 Zr 0.46 O 2 compositions, which were measured to have moduli of 264±8 GPa and 274±8 GPa, respectively. These two compositions contained the largest fractions of the ferroelectric orthorhombic phase, as assessed from polarization and diffraction data. The biaxial stress states of the …