The recently proposed dynamical multiferroic effect describes the generation of magnetization fro... more The recently proposed dynamical multiferroic effect describes the generation of magnetization from temporally varying electric polarization. Here, we show that the effect can lead to a magnetic field at moving ferroelectric domain walls, where the rearrangement of ions corresponds to a rotation of ferroelectric polarization in time. We develop an expression for the dynamical magnetic field, and calculate the relevant parameters for the example of 90 • and 180 • domain walls in BaTiO3 using a combination of density functional theory and phenomenological modeling. We find that the magnetic field reaches the order of several µT at the center of the wall, and we propose two experiments to measure the effect with nitrogen-vacancy center magnetometry.
Phase transitions and octahedral rotations in epitaxial Ag(Ta x Nb 1Àx )O 3 thin films under tens... more Phase transitions and octahedral rotations in epitaxial Ag(Ta x Nb 1Àx )O 3 thin films under tensile strain," J. Appl. Phys. 117, 085309 (2015).
This paper reports the fatigue and retention behavior for Al1-xBxN thin films, a member of the no... more This paper reports the fatigue and retention behavior for Al1-xBxN thin films, a member of the novel family of wurtzite ferroelectrics, with an emphasis on the role of capacitor architecture. By modifying the capacitor architecture, and thus thermal and electrical boundary conditions, we create insight regarding the relative importance of intrinsic and extrinsic contributors to the degradation tendencies. Our experiments suggest that bipolar cycling of metal (Pt/W)/Al0.93B0.07N/W/Al2O3 film stacks first induced wake-up, then a region of constant switchable polarization. On additional cycling, the film leakage current increased, and then films underwent dielectric breakdown. For unpatterned first generation Al0.93B0.07N films with 100 nm thick Pt top electrodes survive ~10 4 bipolar cycles, whereas films with 1000 nm W top electrodes survive ~10 5 cycles before thermal dielectric breakdown. Sentaurus modeling was used to design an SU8 field plate which improved the performance to ~10 6 fatigue cycles. It was found that the thermal failures during fatigue were not due to surface flashover events but were associated with hard breakdown events in the dielectric. The films showed excellent retention of the stored polarization state. As expected, data retention was slightly inferior in the opposite state (OS) measurements. However, it is noted that even after 3.6×10 6 sec (1000 hr). at 200°C, the OS signal margin still exceeded 200 C/cm 2 . The predicted OS retention is 82% after 10 years baking at 200 o C.
Journal of the American Ceramic Society, Jun 1, 2021
Potassium sodium niobate (KNN) thin films are potentially useful for energy harvesting devices an... more Potassium sodium niobate (KNN) thin films are potentially useful for energy harvesting devices and for lead-free piezoelectric microelectromechanical systems. This work reports the activation energies for nucleation, growth and perovskite phase transformation from a 0.5% manganese-doped KNN 2-methoxyethanol-based solution modified with acetylacetone and excess alkali precursors. The films were annealed in a rapid thermal processor (RTP) with a hold step at temperatures from 500 to 550°C. The activation energies for perovskite transformation and growth, determined by electron micrograph observation, were 687 ± 13 and 194 ± 10 kJ/mol. The activation energy for nucleation was 341 ± 20 kJ/mol. Based on these data, crystallization in KNN is found to be nucleation-limited; thus, it should be possible to reduce the crystallization temperature by utilizing a seed layer which provides nucleation sites, provided the organics are removed from the film.
thin films are attractive for applications in MicroElectroMechanical Systems (MEMS) due to the co... more thin films are attractive for applications in MicroElectroMechanical Systems (MEMS) due to the combination of high energy density and low power requirements relative to other on-chip actuation mechanisms. As such, they can be utilized for applications as diverse as the pumping systems in miniature analytical instrumentation, high sensitivity accelerometers and hydrophones, miniature motors, and high frequency biomedical ultrasound, for example. Critical in all of these applications is the magnitude of the electromechanical response that can be generated. This paper will focus on the factors which affect the measured piezoelectric response of ferroelectric thin films. Particular emphasis will be placed on the effects of substrate clamping, clamping of the extrinsic contributions to the properties, and the role of preferred polarization directions in increasing the long-term reliability of ferroelectric films for piezoelectric applica tions.
Medical ultrasound and other devices that require transducer arrays are difficult to manufacture,... more Medical ultrasound and other devices that require transducer arrays are difficult to manufacture, particularly for high frequency devices (>30 MHz). To enable focusing and beam steering, it is necessary to reduce the center-to-center element spacing to half of the acoustic wavelength. Conventional methodologies prevent co-sintering ceramic-polymer composites due to the low decomposition temperatures of the polymer. Moreover, for ultrasound transducer arrays exceeding 30 MHz, methods such as dice-and-fill cannot provide the dimensional tolerances required. Other techniques in which the ceramic is formed in the green state often fail to retain the required dimensions without distortion on firing the ceramic. This paper explores the use of the cold sintering process to produce dense lead zirconate titanate (PZT) ceramics for application in high frequency transducer arrays. PZT-polymer 2-2 composites were fabricated by cold sintering tape cast PZT with Pb nitrate as a sintering aid and ZnO as the sacrificial layer. PZT beams of 35 µm width with ~5.4 µm kerfs were produced by this technique. The ZnO sacrificial layer was also found to serve as a liquid phase sintering aid that led to grain growth in adjacent PZT. This composite produced resonance frequencies of >17 MHz.
Journal of Astronomical Telescopes, Instruments, and Systems, Mar 23, 2019
Piezoelectric adjustable x-ray optics use magnetron sputtered thin film coatings on both sides of... more Piezoelectric adjustable x-ray optics use magnetron sputtered thin film coatings on both sides of a thin curved glass substrate. To produce an optic suitable for a mission requiring high-angular resolution like "Lynx," the integrated stresses (stress × thickness) of films on both sides of the optic must be approximately equal. Thus, understanding how sputtered film thickness distributions change for convex and concave curved substrates is necessary. To address this, thickness distributions of piezoelectric Pb 0.995 ðZr 0.52 Ti 0.48 Þ 0.99 Nb 0.01 O 3 films are studied on flat, convex, and concave cylindrical substrates with a 220-mm radius of curvature. A mathematical model of the film thickness distribution is derived based on the geometric properties of the sputter tool and the substrate, and film thicknesses deposited with a commercially available sputtering tool are measured with spectroscopic ellipsometry. Experiment and modeled results for flat and convex curved substrates demonstrate good agreement, with average relative thickness distribution difference of 0.19% and -0.10% respectively, and a higher average difference of 1.4% for concave substrates. The calculated relative thickness distributions are applied to the convex and concave sides of a finite-element analysis (FEA) model of an adjustable x-ray optic prototype. The FEA model shows that, left uncorrected, the relative film thickness variation will yield an optic with an optical performance of 2.6 arc sec half power diameter (HPD) at 1 keV. However, the mirror figure can be corrected to diffraction-limited performance (0.3 arc sec HPD) using the piezoelectric adjusters, suggesting that the tolerances for applying a balanced integrated stress on both sides of a mirror are alleviated for adjustable x-ray optics as compared to traditional static x-ray mirrors. Furthermore, the piezoelectric adjusters will also allow changes in mirror figure over the telescope lifetime due to drift in the stress states of the x-ray surfaces to be corrected on orbit.
Additive manufacturing has dramatically transformed the design and fabrication of advanced object... more Additive manufacturing has dramatically transformed the design and fabrication of advanced objects. Printed electronicsan additive thin-film processing technol-ogyaims to realize low-cost, large-area electronics, and fabrication of devices with highly customized architectures. Recent advances in printing technology have led to several innovative applications; however, layer-on-layer deposition persists as a challenging issue. Here, the additive manufacturing of functional oxide devices by inkjet printing is presented. Two conditions appear critical for successful layer-on-layer printing: (i) preservation of stable surface properties and (ii) suppression of the material accumulation at the edges of a feature upon drying. The former condition was satisfied by introducing a surface modification layer of a polymer with nanotextured topography, and the latter was satisfied by designing the solvent composition of the ink. The developed process is highly efficient and enables conformal stacking of functional oxide layers according to the user-defined geometry, sequence arrangement, and layer thickness. To prove the effectiveness of this concept, we demonstrate an additive manufacture of all-oxide ferroelectric multilayer capacitors/transducers. Printed multilayer devices offer a significant increase in the capacitance density and the electromechanical voltage response in comparison to the single-layer devices. Further growth in the number of available functional oxide inks will enable arbitrary device architectures with novel functionalities.
Radio frequency (RF) microelectromechanical systems (MEMS) based on Al 1-x Sc x N are replacing A... more Radio frequency (RF) microelectromechanical systems (MEMS) based on Al 1-x Sc x N are replacing AlN-based devices because of their higher achievable bandwidths, suitable for the fifth-generation (5G) mobile network. However, overheating of Al 1-x Sc x N film bulk acoustic resonators (FBARs) used in RF MEMS filters limits power handling and thus the phone's ability to operate in an increasingly congested RF environment while maintaining its maximum data transmission rate. In this work, the ramifications of tailoring of the piezoelectric response and microstructure of Al 1-x Sc x N films on the thermal transport have been studied. The thermal conductivity of Al 1-x Sc x N films (3-8 W m -1 K -1 ) grown by reactive sputter deposition was found to be orders of magnitude lower than that for c-axis-textured AlN films due to alloying effects. The film thickness dependence of the thermal conductivity suggests that higher frequency FBAR structures may suffer from limited power handling due to exacerbated overheating concerns. The reduction of the abnormally oriented grain (AOG) density was found to have a modest effect on the measured thermal conductivity. However, the use of low AOG density films resulted in lower insertion loss and thus less power dissipated within the resonator, which will lead to an overall enhancement of the device thermal performance.
Methylammonium lead iodide (MAPbI 3 ) exhibits exceptional photovoltaic performance, but there re... more Methylammonium lead iodide (MAPbI 3 ) exhibits exceptional photovoltaic performance, but there remains substantial controversy over the existence and impact of ferroelectricity on the photovoltaic response. We confirm ferroelectricity in MAPbI 3 single crystals and demonstrate mediation of the electronic response by ferroelectric domain engineering. The ferroelectric response sharply declines above 57°C, consistent with the tetragonal-to-cubic phase transition. Concurrent band excitation piezoresponse force microscopy-contact Kelvin probe force microscopy shows that the measured response is not dominated by spurious electrostatic interactions. Large signal poling (>16 V/cm) orients the permanent polarization into large domains, which show stabilization over weeks. X-ray photoemission spectroscopy results indicate a shift of 400 meV in the binding energy of the iodine core level peaks upon poling, which is reflected in the carrier concentration results from scanning microwave impedance microscopy. The ability to control the ferroelectric response provides routes to increase device stability and photovoltaic performance through domain engineering.
The dielectric and piezoelectric properties of an epitaxial PbZr 0.8 Ti 0.2 O 3 /PbZr 0.6 Ti 0.4 ... more The dielectric and piezoelectric properties of an epitaxial PbZr 0.8 Ti 0.2 O 3 /PbZr 0.6 Ti 0.4 O 3 ferroelectric bilayer film were studied. Time-resolved synchrotron x-ray microdiffraction provided access to layer-specific structural information during electric-field induced changes. The observed dielectric and electro-mechanical responses are consistent with a weak electrostatic polarization coupling and can be described using a thermodynamic model of epitaxial ferroelectric bilayers. The weak electrostatic coupling between ferroelectric layers can enable unusual tail-to-tail and head-to-head polarization configurations. X-ray measurements of the piezoelectric response of the ferroelectric bilayer at a microsecond time scale confirmed a possible tail-to-tail polarization domain configuration.
In order to advance significantly scientific objectives, future x-ray astronomy missions will lik... more In order to advance significantly scientific objectives, future x-ray astronomy missions will likely call for x-ray telescopes with large aperture areas (≈ 3 m 2 ) and fine angular resolution (≈ 1²). Achieving such performance is programmatically and technologically challenging due to the mass and envelope constraints of space-borne telescopes and to the need for densely nested grazing-incidence optics. Such an x-ray telescope will require precision fabrication, alignment, mounting, and assembly of large areas (≈ 600 m 2 ) of lightweight (≈ 2 kg/m 2 areal density) high-quality mirrors, at an acceptable cost (≈ 1 M$/m 2 of mirror surface area). This paper reviews relevant programmatic and technological issues, as well as possible approaches for addressing these issues-including direct fabrication of monocrystalline silicon mirrors, active (in-space adjustable) figure correction of replicated mirrors, static post-fabrication correction using ion implantation, differential erosion or deposition, and coating-stress manipulation of thin substrates.
In this study, a flexible magnetoelectric (ME) heterostructure of PZT/Ni was fabricated by deposi... more In this study, a flexible magnetoelectric (ME) heterostructure of PZT/Ni was fabricated by depositing a (001) oriented Pb(Zr 0.52 Ti 0.48 )O 3 (PZT) film on a thin, flexible Ni foil buffered with LaNiO 3 /HfO 2 . Excellent ferroelectric properties and large ME voltage coefficient of 3.2 V/cm•Oe were realized from the PZT/Ni heterostructure. The PZT/Ni composite's high performance was attributed to strong texturing of the PZT film, coupled with the compressive stress in the piezoelectric film. Besides, reduced substrate clamping in the PZT film due to the film on the foil structure and strong interfacial bonding in the PZT/LaNiO 3 /HfO 2 /Ni heterostructure could also have contributed to the high ME performance of PZT/Ni.
Journal of the American Ceramic Society, Jun 11, 2021
Various processing methods such as hydrothermal sintering, 1 spark plasma sintering, 2,3 microwav... more Various processing methods such as hydrothermal sintering, 1 spark plasma sintering, 2,3 microwave sintering, 4 liquid phase sintering, 5 and cold sintering 6 have been developed in an effort to lower sintering temperatures for bulk ceramics. In many of these approaches, a secondary liquid phase, often called a sintering aid, is used to lower processing temperatures significantly 7-9 via a liquid phase sintering mechanism. For example, compounds such as Cu 2 O/PbO, V 2 O 5 , P 2 O 5 , or LiBiO 2 facilitate densification of lead zirconate titanate (PZT) ceramics at <1000°C; without such liquid phases, PZT is typically sintered at 1200-1300°C. Gutmanas et al. 14 first coined the term "cold sintering" in 1983 to refer to a plastic deformation in metals at low temperatures by utilizing extremely high uniaxial pressure: ~GPa's. Recently, the cold sintering process (CSP) has enabled densification of a number of ceramic materials at temperatures of 25-300°C in the presence of a transient liquid phase and applied uniaxial pressure: ~100 to 500 MPa (in an open system). A broad range of material chemistries and material structures including metal oxides, 16 inorganic salts, 17 composites, and multilayer systems 20 have been
Strain, temperature, and electric-field effects on the phase transition and piezoelectric respons... more Strain, temperature, and electric-field effects on the phase transition and piezoelectric responses of K 0.5 Na 0.5 NbO 3 thin films
We develop and implement an automated experiment in multimodal imaging to probe structural, chemi... more We develop and implement an automated experiment in multimodal imaging to probe structural, chemical, and functional behaviors in complex materials and elucidate the dominant physical mechanisms that control device function. Here the emergence of non-linear electromechanical responses in piezoresponse force microscopy (PFM) is explored. Non-linear responses in PFM can originate from multiple mechanisms, including intrinsic material responses often controlled by domain structure, surface topography that affects the mechanical phenomena at the tip-surface junction, and, potentially, the presence of surface contaminants. Using an automated experiment to probe the origins of non-linear behavior in model ferroelectric lead titanate (PTO) and ferroelectric Al0.93B0.07N films, it was found that PTO showed asymmetric nonlinear behavior across a/c domain walls and a broadened high nonlinear response region around c/c domain walls. In contrast, for Al0.93B0.07N, well-poled regions showed high linear piezoelectric responses paired with low non-linear responses and regions that were multidomain indicated low linear responses and high nonlinear responses. We show that formulating dissimilar exploration strategies in deep kernel learning as alternative hypotheses allows for establishing the preponderant physical mechanisms behind the non-linear behaviors, suggesting that this approach automated experiments a
The recently proposed dynamical multiferroic effect describes the generation of magnetization fro... more The recently proposed dynamical multiferroic effect describes the generation of magnetization from temporally varying electric polarization. Here, we show that the effect can lead to a magnetic field at moving ferroelectric domain walls, where the rearrangement of ions corresponds to a rotation of ferroelectric polarization in time. We develop an expression for the dynamical magnetic field, and calculate the relevant parameters for the example of 90 • and 180 • domain walls in BaTiO3 using a combination of density functional theory and phenomenological modeling. We find that the magnetic field reaches the order of several µT at the center of the wall, and we propose two experiments to measure the effect with nitrogen-vacancy center magnetometry.
Phase transitions and octahedral rotations in epitaxial Ag(Ta x Nb 1Àx )O 3 thin films under tens... more Phase transitions and octahedral rotations in epitaxial Ag(Ta x Nb 1Àx )O 3 thin films under tensile strain," J. Appl. Phys. 117, 085309 (2015).
This paper reports the fatigue and retention behavior for Al1-xBxN thin films, a member of the no... more This paper reports the fatigue and retention behavior for Al1-xBxN thin films, a member of the novel family of wurtzite ferroelectrics, with an emphasis on the role of capacitor architecture. By modifying the capacitor architecture, and thus thermal and electrical boundary conditions, we create insight regarding the relative importance of intrinsic and extrinsic contributors to the degradation tendencies. Our experiments suggest that bipolar cycling of metal (Pt/W)/Al0.93B0.07N/W/Al2O3 film stacks first induced wake-up, then a region of constant switchable polarization. On additional cycling, the film leakage current increased, and then films underwent dielectric breakdown. For unpatterned first generation Al0.93B0.07N films with 100 nm thick Pt top electrodes survive ~10 4 bipolar cycles, whereas films with 1000 nm W top electrodes survive ~10 5 cycles before thermal dielectric breakdown. Sentaurus modeling was used to design an SU8 field plate which improved the performance to ~10 6 fatigue cycles. It was found that the thermal failures during fatigue were not due to surface flashover events but were associated with hard breakdown events in the dielectric. The films showed excellent retention of the stored polarization state. As expected, data retention was slightly inferior in the opposite state (OS) measurements. However, it is noted that even after 3.6×10 6 sec (1000 hr). at 200°C, the OS signal margin still exceeded 200 C/cm 2 . The predicted OS retention is 82% after 10 years baking at 200 o C.
Journal of the American Ceramic Society, Jun 1, 2021
Potassium sodium niobate (KNN) thin films are potentially useful for energy harvesting devices an... more Potassium sodium niobate (KNN) thin films are potentially useful for energy harvesting devices and for lead-free piezoelectric microelectromechanical systems. This work reports the activation energies for nucleation, growth and perovskite phase transformation from a 0.5% manganese-doped KNN 2-methoxyethanol-based solution modified with acetylacetone and excess alkali precursors. The films were annealed in a rapid thermal processor (RTP) with a hold step at temperatures from 500 to 550°C. The activation energies for perovskite transformation and growth, determined by electron micrograph observation, were 687 ± 13 and 194 ± 10 kJ/mol. The activation energy for nucleation was 341 ± 20 kJ/mol. Based on these data, crystallization in KNN is found to be nucleation-limited; thus, it should be possible to reduce the crystallization temperature by utilizing a seed layer which provides nucleation sites, provided the organics are removed from the film.
thin films are attractive for applications in MicroElectroMechanical Systems (MEMS) due to the co... more thin films are attractive for applications in MicroElectroMechanical Systems (MEMS) due to the combination of high energy density and low power requirements relative to other on-chip actuation mechanisms. As such, they can be utilized for applications as diverse as the pumping systems in miniature analytical instrumentation, high sensitivity accelerometers and hydrophones, miniature motors, and high frequency biomedical ultrasound, for example. Critical in all of these applications is the magnitude of the electromechanical response that can be generated. This paper will focus on the factors which affect the measured piezoelectric response of ferroelectric thin films. Particular emphasis will be placed on the effects of substrate clamping, clamping of the extrinsic contributions to the properties, and the role of preferred polarization directions in increasing the long-term reliability of ferroelectric films for piezoelectric applica tions.
Medical ultrasound and other devices that require transducer arrays are difficult to manufacture,... more Medical ultrasound and other devices that require transducer arrays are difficult to manufacture, particularly for high frequency devices (>30 MHz). To enable focusing and beam steering, it is necessary to reduce the center-to-center element spacing to half of the acoustic wavelength. Conventional methodologies prevent co-sintering ceramic-polymer composites due to the low decomposition temperatures of the polymer. Moreover, for ultrasound transducer arrays exceeding 30 MHz, methods such as dice-and-fill cannot provide the dimensional tolerances required. Other techniques in which the ceramic is formed in the green state often fail to retain the required dimensions without distortion on firing the ceramic. This paper explores the use of the cold sintering process to produce dense lead zirconate titanate (PZT) ceramics for application in high frequency transducer arrays. PZT-polymer 2-2 composites were fabricated by cold sintering tape cast PZT with Pb nitrate as a sintering aid and ZnO as the sacrificial layer. PZT beams of 35 µm width with ~5.4 µm kerfs were produced by this technique. The ZnO sacrificial layer was also found to serve as a liquid phase sintering aid that led to grain growth in adjacent PZT. This composite produced resonance frequencies of >17 MHz.
Journal of Astronomical Telescopes, Instruments, and Systems, Mar 23, 2019
Piezoelectric adjustable x-ray optics use magnetron sputtered thin film coatings on both sides of... more Piezoelectric adjustable x-ray optics use magnetron sputtered thin film coatings on both sides of a thin curved glass substrate. To produce an optic suitable for a mission requiring high-angular resolution like "Lynx," the integrated stresses (stress × thickness) of films on both sides of the optic must be approximately equal. Thus, understanding how sputtered film thickness distributions change for convex and concave curved substrates is necessary. To address this, thickness distributions of piezoelectric Pb 0.995 ðZr 0.52 Ti 0.48 Þ 0.99 Nb 0.01 O 3 films are studied on flat, convex, and concave cylindrical substrates with a 220-mm radius of curvature. A mathematical model of the film thickness distribution is derived based on the geometric properties of the sputter tool and the substrate, and film thicknesses deposited with a commercially available sputtering tool are measured with spectroscopic ellipsometry. Experiment and modeled results for flat and convex curved substrates demonstrate good agreement, with average relative thickness distribution difference of 0.19% and -0.10% respectively, and a higher average difference of 1.4% for concave substrates. The calculated relative thickness distributions are applied to the convex and concave sides of a finite-element analysis (FEA) model of an adjustable x-ray optic prototype. The FEA model shows that, left uncorrected, the relative film thickness variation will yield an optic with an optical performance of 2.6 arc sec half power diameter (HPD) at 1 keV. However, the mirror figure can be corrected to diffraction-limited performance (0.3 arc sec HPD) using the piezoelectric adjusters, suggesting that the tolerances for applying a balanced integrated stress on both sides of a mirror are alleviated for adjustable x-ray optics as compared to traditional static x-ray mirrors. Furthermore, the piezoelectric adjusters will also allow changes in mirror figure over the telescope lifetime due to drift in the stress states of the x-ray surfaces to be corrected on orbit.
Additive manufacturing has dramatically transformed the design and fabrication of advanced object... more Additive manufacturing has dramatically transformed the design and fabrication of advanced objects. Printed electronicsan additive thin-film processing technol-ogyaims to realize low-cost, large-area electronics, and fabrication of devices with highly customized architectures. Recent advances in printing technology have led to several innovative applications; however, layer-on-layer deposition persists as a challenging issue. Here, the additive manufacturing of functional oxide devices by inkjet printing is presented. Two conditions appear critical for successful layer-on-layer printing: (i) preservation of stable surface properties and (ii) suppression of the material accumulation at the edges of a feature upon drying. The former condition was satisfied by introducing a surface modification layer of a polymer with nanotextured topography, and the latter was satisfied by designing the solvent composition of the ink. The developed process is highly efficient and enables conformal stacking of functional oxide layers according to the user-defined geometry, sequence arrangement, and layer thickness. To prove the effectiveness of this concept, we demonstrate an additive manufacture of all-oxide ferroelectric multilayer capacitors/transducers. Printed multilayer devices offer a significant increase in the capacitance density and the electromechanical voltage response in comparison to the single-layer devices. Further growth in the number of available functional oxide inks will enable arbitrary device architectures with novel functionalities.
Radio frequency (RF) microelectromechanical systems (MEMS) based on Al 1-x Sc x N are replacing A... more Radio frequency (RF) microelectromechanical systems (MEMS) based on Al 1-x Sc x N are replacing AlN-based devices because of their higher achievable bandwidths, suitable for the fifth-generation (5G) mobile network. However, overheating of Al 1-x Sc x N film bulk acoustic resonators (FBARs) used in RF MEMS filters limits power handling and thus the phone's ability to operate in an increasingly congested RF environment while maintaining its maximum data transmission rate. In this work, the ramifications of tailoring of the piezoelectric response and microstructure of Al 1-x Sc x N films on the thermal transport have been studied. The thermal conductivity of Al 1-x Sc x N films (3-8 W m -1 K -1 ) grown by reactive sputter deposition was found to be orders of magnitude lower than that for c-axis-textured AlN films due to alloying effects. The film thickness dependence of the thermal conductivity suggests that higher frequency FBAR structures may suffer from limited power handling due to exacerbated overheating concerns. The reduction of the abnormally oriented grain (AOG) density was found to have a modest effect on the measured thermal conductivity. However, the use of low AOG density films resulted in lower insertion loss and thus less power dissipated within the resonator, which will lead to an overall enhancement of the device thermal performance.
Methylammonium lead iodide (MAPbI 3 ) exhibits exceptional photovoltaic performance, but there re... more Methylammonium lead iodide (MAPbI 3 ) exhibits exceptional photovoltaic performance, but there remains substantial controversy over the existence and impact of ferroelectricity on the photovoltaic response. We confirm ferroelectricity in MAPbI 3 single crystals and demonstrate mediation of the electronic response by ferroelectric domain engineering. The ferroelectric response sharply declines above 57°C, consistent with the tetragonal-to-cubic phase transition. Concurrent band excitation piezoresponse force microscopy-contact Kelvin probe force microscopy shows that the measured response is not dominated by spurious electrostatic interactions. Large signal poling (>16 V/cm) orients the permanent polarization into large domains, which show stabilization over weeks. X-ray photoemission spectroscopy results indicate a shift of 400 meV in the binding energy of the iodine core level peaks upon poling, which is reflected in the carrier concentration results from scanning microwave impedance microscopy. The ability to control the ferroelectric response provides routes to increase device stability and photovoltaic performance through domain engineering.
The dielectric and piezoelectric properties of an epitaxial PbZr 0.8 Ti 0.2 O 3 /PbZr 0.6 Ti 0.4 ... more The dielectric and piezoelectric properties of an epitaxial PbZr 0.8 Ti 0.2 O 3 /PbZr 0.6 Ti 0.4 O 3 ferroelectric bilayer film were studied. Time-resolved synchrotron x-ray microdiffraction provided access to layer-specific structural information during electric-field induced changes. The observed dielectric and electro-mechanical responses are consistent with a weak electrostatic polarization coupling and can be described using a thermodynamic model of epitaxial ferroelectric bilayers. The weak electrostatic coupling between ferroelectric layers can enable unusual tail-to-tail and head-to-head polarization configurations. X-ray measurements of the piezoelectric response of the ferroelectric bilayer at a microsecond time scale confirmed a possible tail-to-tail polarization domain configuration.
In order to advance significantly scientific objectives, future x-ray astronomy missions will lik... more In order to advance significantly scientific objectives, future x-ray astronomy missions will likely call for x-ray telescopes with large aperture areas (≈ 3 m 2 ) and fine angular resolution (≈ 1²). Achieving such performance is programmatically and technologically challenging due to the mass and envelope constraints of space-borne telescopes and to the need for densely nested grazing-incidence optics. Such an x-ray telescope will require precision fabrication, alignment, mounting, and assembly of large areas (≈ 600 m 2 ) of lightweight (≈ 2 kg/m 2 areal density) high-quality mirrors, at an acceptable cost (≈ 1 M$/m 2 of mirror surface area). This paper reviews relevant programmatic and technological issues, as well as possible approaches for addressing these issues-including direct fabrication of monocrystalline silicon mirrors, active (in-space adjustable) figure correction of replicated mirrors, static post-fabrication correction using ion implantation, differential erosion or deposition, and coating-stress manipulation of thin substrates.
In this study, a flexible magnetoelectric (ME) heterostructure of PZT/Ni was fabricated by deposi... more In this study, a flexible magnetoelectric (ME) heterostructure of PZT/Ni was fabricated by depositing a (001) oriented Pb(Zr 0.52 Ti 0.48 )O 3 (PZT) film on a thin, flexible Ni foil buffered with LaNiO 3 /HfO 2 . Excellent ferroelectric properties and large ME voltage coefficient of 3.2 V/cm•Oe were realized from the PZT/Ni heterostructure. The PZT/Ni composite's high performance was attributed to strong texturing of the PZT film, coupled with the compressive stress in the piezoelectric film. Besides, reduced substrate clamping in the PZT film due to the film on the foil structure and strong interfacial bonding in the PZT/LaNiO 3 /HfO 2 /Ni heterostructure could also have contributed to the high ME performance of PZT/Ni.
Journal of the American Ceramic Society, Jun 11, 2021
Various processing methods such as hydrothermal sintering, 1 spark plasma sintering, 2,3 microwav... more Various processing methods such as hydrothermal sintering, 1 spark plasma sintering, 2,3 microwave sintering, 4 liquid phase sintering, 5 and cold sintering 6 have been developed in an effort to lower sintering temperatures for bulk ceramics. In many of these approaches, a secondary liquid phase, often called a sintering aid, is used to lower processing temperatures significantly 7-9 via a liquid phase sintering mechanism. For example, compounds such as Cu 2 O/PbO, V 2 O 5 , P 2 O 5 , or LiBiO 2 facilitate densification of lead zirconate titanate (PZT) ceramics at <1000°C; without such liquid phases, PZT is typically sintered at 1200-1300°C. Gutmanas et al. 14 first coined the term "cold sintering" in 1983 to refer to a plastic deformation in metals at low temperatures by utilizing extremely high uniaxial pressure: ~GPa's. Recently, the cold sintering process (CSP) has enabled densification of a number of ceramic materials at temperatures of 25-300°C in the presence of a transient liquid phase and applied uniaxial pressure: ~100 to 500 MPa (in an open system). A broad range of material chemistries and material structures including metal oxides, 16 inorganic salts, 17 composites, and multilayer systems 20 have been
Strain, temperature, and electric-field effects on the phase transition and piezoelectric respons... more Strain, temperature, and electric-field effects on the phase transition and piezoelectric responses of K 0.5 Na 0.5 NbO 3 thin films
We develop and implement an automated experiment in multimodal imaging to probe structural, chemi... more We develop and implement an automated experiment in multimodal imaging to probe structural, chemical, and functional behaviors in complex materials and elucidate the dominant physical mechanisms that control device function. Here the emergence of non-linear electromechanical responses in piezoresponse force microscopy (PFM) is explored. Non-linear responses in PFM can originate from multiple mechanisms, including intrinsic material responses often controlled by domain structure, surface topography that affects the mechanical phenomena at the tip-surface junction, and, potentially, the presence of surface contaminants. Using an automated experiment to probe the origins of non-linear behavior in model ferroelectric lead titanate (PTO) and ferroelectric Al0.93B0.07N films, it was found that PTO showed asymmetric nonlinear behavior across a/c domain walls and a broadened high nonlinear response region around c/c domain walls. In contrast, for Al0.93B0.07N, well-poled regions showed high linear piezoelectric responses paired with low non-linear responses and regions that were multidomain indicated low linear responses and high nonlinear responses. We show that formulating dissimilar exploration strategies in deep kernel learning as alternative hypotheses allows for establishing the preponderant physical mechanisms behind the non-linear behaviors, suggesting that this approach automated experiments a
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Papers by Susan Trolier-McKinstry