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[IEEE 2019 IEEE International Symposium on Applications of Ferroelectrics (ISAF) - Lausanne, Switzerland (2019.7.14-2019.7.19)] 2019 IEEE International Symposium on Applications of Ferroelectrics (ISAF) - Vibrating Piezoelectric Energy Conversion Efficiency of Sol-Gel PZT Films with Various Crystal Orientations on MEMS Buckled Diaphragm Structures
摘要： Vibrating energy conversion efficiency was investigated on piezoelectric transducers fabricated on MEMS buckled diaphragm structures from the viewpoint of crystal orientation of sol-gel derived lead-zirconate-titanate (PZT) films. The crystal orientation dominates in-plane stress and spontaneous polarization direction of the PZT films. The in-plane stress affects the static buckling of the diaphragm where a large convex buckling results in a high mechanical conversion efficiency from the flexural vibration to the in-plain vibration. The polarization direction affects the intrinsic piezoelectric conversion efficiency. The crystal orientation of the sol-gel PZT was controlled through pyrolysis temperature between 250?C and 350?C, resulting in a texture variation from (100)-oriented films to (111)-oriented ones. Highly (111)-oriented films showed large polarizations but small buckling deflections, while highly (100)-oriented films showed vice versa. Intermediately textured films with 40–45% (111)-orientation index showed the highest conversion efficiency.
关键词： Piezoelectric,Sol-gel,Residual stress,Buckling,PZT,Polarization,Energy conversion,Diaphragm
更新于2025-09-19 17:13:59
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Enhanced bonding strength of InP/Si chip-on-wafer by plasma-activated bonding using stress-controlled interlayer
摘要： This study demonstrates high-yield InP/Si CoW plasma-activated bonding using a chip holder with pockets, the depth of which is precisely controlled. Additionally, finite element simulations are used to determine that the stress-controlled interlayer consisting of InP-based epitaxial layers with tensile strain effectively suppresses stress at the InP/Si bonding interface, which affects the bonding strength. Thus, a high bonding strength of 20 MPa in 2 mm × 2 mm InP chips on the Si substrate was achieved by introducing a superlattice structure consisting of GaInAsP and InP (with tensile strain) as the stress-controlled interlayer.
关键词： chip-on-wafer,plasma-activated bonding,bonding strength,InP/Si,stress-controlled interlayer
更新于2025-09-19 17:13:59
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Interface Stress for Bidirectional Frequency Tuning of Prebuckled Vanadium Dioxide MEMS Resonators
摘要： Interface stress between structural materials and thin film coatings has a significant influence on the resonant frequency of microelectromechanical system (MEMS) resonators. In this work, the axial stress on different types of buckled bridge MEMS resonator structures is controlled through the solid-to-solid phase transition of a VO2 thin film coating. The devices have identical dimensions, but different buckling orientations and profiles due to the combined effect of overetching and residual thermal stress mismatch. Thermal actuation is used to tune the resonant frequency of the device, but the changes in frequency are found to be dependent on the type of buckling for the device. Thermal actuation is achieved by applying an electrical current to integrated heaters, or by uniform substrate heating. Bidirectional tunability is found when substrate heating is used, while Joule heating shows a monotonic change in frequency. This phenomenon can be attributed to the transition in boundary conditions, where the turning points are indicated by the prominent changes in buckling amplitude. In addition, devices with opposite buckling orientations exhibit different tuning behaviors which can be explained by different bending moments induced by beam stress interface modification.
关键词： MEMS resonators,interface stress,buckling,vanadium dioxide,resonant frequency tuning
更新于2025-09-19 17:13:59
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[IEEE IGARSS 2019 - 2019 IEEE International Geoscience and Remote Sensing Symposium - Yokohama, Japan (2019.7.28-2019.8.2)] IGARSS 2019 - 2019 IEEE International Geoscience and Remote Sensing Symposium - Measuring Leaf Equivalent Water Thickness of Short-Rotation Coppice Willow Canopy Using Terrestrial Laser Scanning
摘要： Accurate measurements of leaf Equivalent Water Thickness (EWT) can help in early detection of vegetation stress. Terrestrial Laser Scanning (TLS) intensity data have the potential to provide 3D estimates of EWT, overcoming the limitations of the 2D estimates provided by remote sensing optical data. Such limitations include the sensors being solar illumination dependent and unable to provide information about the vertical variation in EWT. In this study, intensity data from the Leica P20 and P40 commercial TLS instruments were combined in a Normalized Difference Index (NDI). NDI was used to measure EWT in six short-rotation coppice willow (Salix spp.) plots from different varieties with an average error of 7.3% (R2 = 0.8, RMSE = 0.0011 g cm-2). The effects of wind and senescence of leaves on the accuracy of the EWT estimation were also investigated.
关键词： agricultural crops,ground LiDAR,biomass energy,water stress,Vegetation water content
更新于2025-09-19 17:13:59
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Interfacial and structural modifications in perovskite solar cells
摘要： The rapid and continuous progress in perovskite solar cells (PSCs) has drawn lots of attention from the photovoltaic research community and urges them to apply perovskite in other electronic devices such as photo detectors, light-emitting diodes, and batteries. Thanks to the diversity of the device configuration, optimization of the film deposition and exploration of material system, the power conversion efficiency (PCE) of PSCs has boosted to a certified 25.2%, making this solar cell to date the fastest advancing technology. As demonstrated by worldwide researchers, controlling the morphology and defects of the perovskite film is essential for attaining high performance of PSCs. In this regard, interface engineering has proven a very efficient way to address these issues, obtaining better charge collection efficiency and reducing recombination losses. In this review, the interfacial modification between perovskite films and charge-transport layers (CTLs) as well as CTLs and electrodes of PSCs has been widely summarized. Grain boundary (GB) engineering and stress engineering are also included since these are closely related with the improvement of device performance and stability.
关键词： grain boundaries,stress engineering,perovskite solar cell,structural,Interfacial,defects
更新于2025-09-19 17:13:59
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Fatigue Life Behavior of Laser Shock Peened Duplex Stainless Steel with Different Samples Geometry
摘要： Two different stress raiser geometries (fillet and notched) were treated by laser shock peening (LSP) in order to analyze the effect of sample geometry on fatigue behavior of 2205 duplex stainless steel (DSS). The LSP treatment was carried through Nd:YAG pulsed laser with 1064 nm wavelength, 10 Hz frequency, and 0.85 J/pulse. Experimental and MEF simulation results of residual stress distribution after LSP were assessed by hole drilling method and ABAQUS/EXPLICIT software, respectively. The fatigue tests (tensile-tensile axial stress) were realized with stress ratio of R = 0.1 and 20 Hz. A good comparison of residual stress simulation and experimental data was observed. The results reveal that the fatigue life is increased by LSP treatment in the notched samples, while it decreases in the fillet samples. This is related to the residual stress distribution after LSP that is generated in each geometry type. In addition, the fatigue crack growth direction is changed according to geometry type. Both the propagation direction of fatigue crack and the anisotropy of this steel results detrimental in fillet samples, decreasing the number of cycles to the fatigue crack initiation. It is demonstrated that the LSP effect on fatigue performance is influenced by the specimen geometry.
关键词： laser shock peening,residual stress,duplex stainless steel,fatigue life,sample geometry
更新于2025-09-19 17:13:59
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Crack closure mechanisms in residual stress fields generated by laser shock peening: A combined experimental-numerical approach
摘要： Laser shock peening (LSP) is successfully applied to retard fatigue cracks in metallic lightweight structures by introducing specific, in particular compressive, residual stress fields. In this work, experiments and a multi-step simulation strategy are used to explain the fatigue crack retarding and accelerating mechanisms within these LSP-induced residual stress fields. Crack face contact is identified as main mechanism to retard the fatigue crack as the stress distribution changes and the stress intensity factor range decreases. Crack face contact is experimentally detected by load vs. crack opening displacement (COD) curves and scanning electron microscopy (SEM) of the crack faces, as well as during numerical simulations. The convincing agreement between experiment and simulation, especially regarding the specific crack face contact areas, allowed the proper evaluation of the stress intensity factors depending on the crack length. It is found that crack closure is indeed one of the main reasons for the efficient application of LSP for fatigue crack retardation. Furthermore, the occurrence of crack closure does not indicate a zero value stress intensity factor in complex residual stress fields, as the areas of crack face contact depend strongly on the LSP-induced compressive residual stresses.
关键词： Stress intensity factor,Laser shock peening,Residual stress,Fatigue crack growth,Crack closure
更新于2025-09-16 10:30:52
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Controlled oxidation of Ni for stress-free hole transport layer of large-scale perovskite solar cells
摘要： The effect of the residual thermal stress of NiO films on the performance of an inverted type perovskite solar cell was studied. In this study, NiO films were grown on fluorine doped tin oxide (FTO) substrates of different surface roughness by thermally oxidizing Ni film and were tested as a hole transport layer for large-scale perovskite solar cells. Experimental and simulation results show that it is very important to suppress the appearance of the residual stress at the NiO–FTO interface during the oxidation of the Ni film for effective hole extraction. The Ni oxidation on the flat FTO film produced in-plane compressive stress in the NiO film due to the Ni film volume expansion. This led to the formation of defects including small blisters. These residual stress and defects increased leakage current through the NiO film, preventing holes from being selectively collected at the NiO-perovskite interface. However, when Ni was deposited and oxidized on the rough surface, the residual stress of the NiO film was negligible and its inherent high resistance was maintained. Stress-free NiO film is an excellent hole transport layer that stops the photogenerated electrons of the perovskite layer from moving to FTO. The improvements in the structural and electrical qualities of the NiO film by engineering the residual stress reduce the carrier recombination and increase the power conversion efficiency of the perovskite solar cells to 16.37%.
关键词： perovskite solar cells,large scale processing,nickel oxidation,residual stress,surface roughness
更新于2025-09-16 10:30:52
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[IEEE 2019 20th International Conference on Solid-State Sensors, Actuators and Microsystems & Eurosensors XXXIII (TRANSDUCERS & EUROSENSORS XXXIII) - Berlin, Germany (2019.6.23-2019.6.27)] 2019 20th International Conference on Solid-State Sensors, Actuators and Microsystems & Eurosensors XXXIII (TRANSDUCERS & EUROSENSORS XXXIII) - Fabrication of Cavity-Sealed Optical Interferometric Surface Stress Biosensor by thin Film Transfer Technique
摘要： We developed a surface stress sensor based on a MEMS Fabry-Perot interferometer with cavity-sealed structure by technique of nanometer-thick parylene sheet for highly sensitive label-free biosensing. The proposed MEMS interferometer can measure the membrane deflection caused by target molecule adsorption as the spectral shift. The proposed cavity-sealed optical interferometer can prevent physical adsorption to the backside of membrane and refractive index drift in the cavity, leading to improvement of sensitivity. We successfully obtained the spectral shift of 77 nm in 10 minutes with the color change associated with the antigen-antibody reaction with a concentration of 1 ng/ml, which improved by 16.7-fold compared with the conventional sensor.
关键词： MEMS biosensor,Surface stress sensor,label-free biosensing,film transfer technique,Fabry-Perot interferometer
更新于2025-09-16 10:30:52
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Photovoltaic Modules (Technology and Reliability) || 10. Accelerated aging tests
摘要： All environmental simulation tests which allow an accelerated analysis of material degradation processes through intensified environmental stress levels compared to real life can be summarized under the notion of accelerated aging tests. This type of test is especially useful for products with long service lifetimes, such as photovoltaic modules. As guarantees for PV modules cover up to 30 years of service life, accelerated aging tests are of high economic importance for PV modules manufacturers. As PV manufactures aim for utilizing materials which are both economically and technically suitable, accelerated aging tests on full PV modules as well as on separate materials and material combinations are necessary. It is in the interest of the customer as well the investor and the insurance that the product achieves the expected service life without major performance losses. The aim of accelerated aging tests is to achieve reliable results within a very short period of time and with minimum costs in order to keep pace with the rapid innovation cycles. In order to ensure the transferability of the testing result on real life performance, a specific adaptation of the test conditions to the specific materials and stress factors is indispensable. Otherwise, climatic conditions may be induced which either exceed or undermine those under standard operation, and this may subsequently lead to altered physical or chemical degradation processes. Thus, the processes which occur under standard operation should be accelerated but at the same time simulated as close to reality as possible.
关键词： photovoltaic modules,service life,environmental stress,material degradation,accelerated aging tests
更新于2025-09-16 10:30:52