Clamping enables enhanced electromechanical responses in antiferroelectric thin films.

Thin-film materials with large electromechanical responses are fundamental enablers of next-generation micro-/nano-electromechanical applications. Conventional electromechanical materials (for example, ferroelectrics and relaxors), however, exhibit severely degraded responses when scaled down to submicrometre-thick films due to substrate constraints (clamping). This limitation is overcome, and substantial electromechanical responses in antiferroelectric thin films are achieved through an unconventional coupling of the field-induced antiferroelectric-to-ferroelectric phase transition and the substrate constraints. A detilting of the oxygen octahedra and lattice-volume expansion in all dimensions are observed commensurate with the phase transition using operando electron microscopy, such that the in-plane clamping further enhances the out-of-plane expansion, as rationalized using first-principles calculations. In turn, a non-traditional thickness scaling is realized wherein an electromechanical strain (1.7%) is produced from a model antiferroelectric PbZrO3 film that is just 100 nm thick. The high performance and understanding of the mechanism provide a promising pathway to develop high-performance micro-/nano-electromechanical systems.

Defect-Induced, Ferroelectric-Like Switching and Adjustable Dielectric Tunability in Antiferroelectrics.

Antiferroelectrics, which undergo a field-induced phase transition to ferroelectric order that manifests as double-hysteresis polarization switching, exhibit great potential for dielectric, electromechanical, and electrothermal applications. Compared to their ferroelectric cousins, however, considerably fewer efforts have been made to understand and control antiferroelectrics. Here, it is demonstrated that the polarization switching behavior of an antiferroelectric can be strongly influenced and effectively regulated by point defects. In films of the canonical antiferroelectric PbZrO3 , decreasing oxygen pressure during deposition (and thus increasing adatom kinetic energy) causes unexpected "ferroelectric-like" polarization switching although the films remain in the expected antiferroelectric orthorhombic phase. This "ferroelectric-like" switching is correlated with the creation of bombardment-induced point-defect complexes which pin the antiferroelectric-ferroelectric phase boundaries, and thus effectively delay the phase transition under changing field. The effective pinning energy is extracted via temperature-dependent switching-kinetics studies. In turn, by controlling the concentration of defect complexes, the dielectric tunability of the PbZrO3 can be adjusted, including being able to convert between "positive" and "negative" tunability near zero field. This work reveals the important role and strong capability of defects to engineer antiferroelectrics for new performance and functionalities.

Infective endocarditis and rheumatic heart disease in the north of Australia.

BACKGROUND: To prevent infective endocarditis (IE), Australian guidelines recommend providing prophylactic antibiotics to Indigenous patients with rheumatic heart disease (RHD) prior to procedures which may cause bacteremia. In northern Australia RHD remains prevalent. We aimed to determine whether RHD is associated with an increased risk of IE, which risk factors are associated with IE, and the incidence and aetiology of IE. METHODS: A retrospective review of IE patients who fulfilled modified Duke criteria at two tertiary centres in northern Australia. RESULTS: 89 patients were reviewed. The rate of IE was 6.5/100,000 person-years. IE was more common in people with RHD (relative risk (RR) 58), Indigenous Australians (RR 2.0) and men (RR 1.7). RHD-associated IE was not confined to Indigenous Australians with 42% being non-Indigenous. The commonest risk factors for IE were intracardiac prosthetic material, injecting drug use and previous IE. One in five patients died. CONCLUSIONS: In northern Australia the principle risk factor for IE is not RHD. Whilst RHD increased the risk of IE it was not restricted to Indigenous Australians. Current Australian recommendations of providing prophylactic antibiotics to Indigenous patients with RHD prior to procedures which may cause bacteremia may need to be broadened to include non-Indigenous patients.

High-Temperature Ferroelectric Behavior of Al0.7Sc0.3N.

Currently, there is a lack of nonvolatile memory (NVM) technology that can operate continuously at temperatures > 200 °C. While ferroelectric NVM has previously demonstrated long polarization retention and >1013 read/write cycles at room temperature, the largest hurdle comes at higher temperatures for conventional perovskite ferroelectrics. Here, we demonstrate how AlScN can enable high-temperature (>200 °C) nonvolatile memory. The c-axis textured thin films were prepared via reactive radiofrequency magnetron sputtering onto a highly textured Pt (111) surface. Photolithographically defined Pt top electrodes completed the capacitor stack, which was tested in a high temperature vacuum probe station up to 400 °C. Polarization−electric field hysteresis loops between 23 and 400 °C reveal minimal changes in the remanent polarization values, while the coercive field decreased from 4.3 MV/cm to 2.6 MV/cm. Even at 400 °C, the polarization retention exhibited negligible loss for up to 1000 s, demonstrating promise for potential nonvolatile memory capable of high−temperature operation. Fatigue behavior also showed a moderate dependence on operating temperature, but the mechanisms of degradation require additional study.

Self-Folding PCB Kirigami: Rapid Prototyping of 3D Electronics via Laser Cutting and Forming.

This paper demonstrates laser forming, localized heating with a laser to induce plastic deformation, can self-fold 2D printed circuit boards (PCBs) into 3D structures with electronic function. There are many methods for self-folding but few are compatible with electronic materials. We use a low-cost commercial laser writer to both cut and fold a commercial flexible PCB. Laser settings are tuned to select between cutting and folding with higher power resulting in cutting and lower power resulting in localized heating for folding into 3D shapes. Since the thin copper traces used in commercial PCBs are highly reflective and difficult to directly fold, two approaches are explored for enabling folding: plating with a nickel/gold coating or using a single, high-power laser exposure to oxidize the surface and improve laser absorption. We characterized the physical effect of the exposure on the sample as well as the fold angle as a function of laser passes and demonstrate the ability to lift weights comparable with circuit packages and passive components. This technique can form complex, multifold structures with integrated electronics; as a demonstrator, we fold a commercial board with a common timing circuit. Laser forming to add a third dimension to printed circuit boards is an important technology to enable the rapid prototyping of complex 3D electronics.

Exploring the Pb1- x Srx HfO3 System and Potential for High Capacitive Energy Storage Density and Efficiency.

The hafnate perovskites PbHfO3 (antiferroelectric) and SrHfO3 ("potential" ferroelectric) are studied as epitaxial thin films on SrTiO3 (001) substrates with the added opportunity of observing a morphotropic phase boundary (MPB) in the Pb1- x Srx HfO3 system. The resulting (240)-oriented PbHfO3 (Pba2) films exhibited antiferroelectric switching with a saturation polarization ≈53 µC cm-2 at 1.6 MV cm-1 , weak-field dielectric constant ≈186 at 298 K, and an antiferroelectric-to-paraelectric phase transition at ≈518 K. (002)-oriented SrHfO3 films exhibited neither ferroelectric behavior nor evidence of a polar P4mm phase . Instead, the SrHfO3 films exhibited a weak-field dielectric constant ≈25 at 298 K and no signs of a structural transition to a polar phase as a function of temperature (77-623 K) and electric field (-3 to 3 MV cm-1 ). While the lack of ferroelectric order in SrHfO3 removes the potential for MPB, structural and property evolution of the Pb1- x Srx HfO3 (0 ≤ x < 1) system is explored. Strontium alloying increased the electric-breakdown strength (EB ) and decreased hysteresis loss, thus enhancing the capacitive energy storage density (Ur ) and efficiency (η). The composition, Pb0.5 Sr0.5 HfO3 produced the best combination of EB  = 5.12 ± 0.5 MV cm-1 , Ur  = 77 ± 5 J cm-3 , and η = 97 ± 2%, well out-performing PbHfO3 and other antiferroelectric oxides.

Printing a Pacinian Corpuscle: Modeling and Performance.

The Pacinian corpuscle is a highly sensitive mammalian sensor cell that exhibits a unique band-pass sensitivity to vibrations. The cell achieves this band-pass response through the use of 20 to 70 elastic layers entrapping layers of viscous fluid. This paper develops and explores a scalable mechanical model of the Pacinian corpuscle and uses the model to predict the response of synthetic corpuscles, which could be the basis for future vibration sensors. The -3dB point of the biological cell is accurately mimicked using the geometries and materials available with off-the-shelf 3D printers. The artificial corpuscles here are constructed using uncured photoresist within structures printed in a commercial stereolithography (SLA) 3D printer, allowing the creation of trapped fluid layers analogous to the biological cell. Multi-layer artificial Pacinian corpuscles are vibration tested over the range of 20-3000 Hz and the response is in good agreement with the model.

Vibration sensing the mammalian way: an artificial Pacinian corpuscle.

A vibration sensor is presented mimicking the structure of the Pacinian corpuscle. A multi-step casting process is used to create a 5 mm diameter sensor with a liquid metal core, elastomer dielectric, and graphite counter electrode creating a spherical capacitive sensing element with sensitivities on the order of 10 Δ pF/mm-1. A model for the capacitance change of the spherical capacitor as it is formed is developed and its findings support the sensitivities observed. Various elastomer dielectric compositions with integrated barium titanate nanoparticles are tested to increase the dielectric constant. The biological acoustic filter within the corpuscle is mimicked using alternating cast layers of oligomers and elastomers around the spherical sensor element. Vibration sensing is characterized over the low frequency range of 10-300 Hz and the minimum detectable sensitivity is found to be 1 µm with a low power requirement of 7 mW. The artificial Pacinian corpuscle has potential applications in tactile sensing and seismic monitoring devices.