An enhanced self-powered near-ultraviolet photodetection phenomenon was observed in epitaxial gal... more An enhanced self-powered near-ultraviolet photodetection phenomenon was observed in epitaxial gallium nitride (GaN) nanorod networks grown on an intermediate layer of N:GaN on a nitridated HfO2(N:HfO2)/SiO2/p-Si substrate.
The solid solution of relaxor and lead titanate single crystals have been an excellent choice for... more The solid solution of relaxor and lead titanate single crystals have been an excellent choice for electromechanical applications such as energy harvesters, SONARs, transducers, and biomedical equipment. The mechanical quality factor (Qm) plays a crucial role in such applications using high power resonance condition. In this work, 32 mode (011) oriented along thickness direction, Generation-III piezoelectric single crystals based on PMN-PZT [71Pb(Mg1/3Nb2/3)O3–29PbZrTiO3] have been grown by solid state single crystal growth method. The Mn doping concentration in the crystals were systematically controlled within the range of 0 to 1.0 mol.%. The piezoelectric properties noticeably varied with the Mn doping concentration when the content is over 0.1 mol.%. In order to obtain significant enhancement in Qm in PMN-PZT single crystals, especially, the Mn doping concentration should be higher than 0.7 mol.% (which offers highest figure of merit) for high power resonance applications.
The electrocaloric effect (ECE), in which the change in the material temperature with an applicat... more The electrocaloric effect (ECE), in which the change in the material temperature with an application or removal of an electric field is one of the key phenomena of future highly...
Abstract Resistive switching behavior in Graphene oxide (GO) is well studied, however, the variou... more Abstract Resistive switching behavior in Graphene oxide (GO) is well studied, however, the various mechanisms responsible for this phenomenon are still under extensive debate. We present repeatable bipolar resistive switching in GO thin films sandwiched between two insulating polymer PVDF (Polyvinylidene Fluoride) grown on conducting indium tin oxide (ITO) covered glass substrate. The device heterostructure (Al/PVDF/GO/PVDF/ITO) showed bipolar resistance states switching between low resistance state (LRS) to high resistance state (HRS) with a large ON/OFF ratio of 103 and resistance retention potential up to 104 s. In LRS, in the low applied voltage region, ohmic conduction was the main reason for current conduction in devices; however, traps filled/assisted conduction mechanism dominates in the higher voltage region. The PVDF/GO/PVDF heterostructure shows that oxygen vacancies are responsible for the formation of current conducting filaments. The low operating voltage (
A small amount of illumination of visible light on ultra thin films (∼5 nm) hafnium oxide demonst... more A small amount of illumination of visible light on ultra thin films (∼5 nm) hafnium oxide demonstrated giant irreversible resistive switching, changed band off set and permanently developed trap charge states.
Among the various forms of natural energies, heat is the most prevalent and least harvested energ... more Among the various forms of natural energies, heat is the most prevalent and least harvested energy. Scavenging and detecting stray thermal energy for conversion into electrical energy can provide a cost-effective and reliable energy source for modern electrical appliances and sensor applications. Along with this, flexible devices have attracted considerable attention in scientific and industrial communities as wearable and implantable harvesters in addition to traditional thermal sensor applications. This review mainly discusses thermal energy conversion through pyroelectric phenomena in various lead-free as well as lead-based ceramics and polymers for flexible pyroelectric energy harvesting and sensor applications. The corresponding thermodynamic heat cycles and figures of merit of the pyroelectric materials for energy harvesting and heat sensing applications are also briefly discussed. Moreover, this study provides guidance on designing pyroelectric materials for flexible pyroelec...
We report giant resistive switching of an order of 104, long-time charge retention characteristic... more We report giant resistive switching of an order of 104, long-time charge retention characteristics up to 104 s, non-overlapping SET and RESET voltages, ohmic in low resistance state (LRS) and space charge limited current (SCLC) mechanism in high resistance state (HRS) properties in polycrystalline perovskite Cobalt Titanate (CoTiO3 ~ CTO) thin films. Impedance spectroscopy study was carried out for both LRS and HRS states which illustrates that only bulk resistance changes after resistance switching, however, there is a small change (<10% which is in pF range) in the bulk capacitance value in both states. These results suggest that in LRS state current filaments break the capacitor in many small capacitors in a parallel configuration which in turn provides the same capacitance in both states even there was 90 degree changes in phase-angle and an order of change in the tangent loss.
Future nanoelectronics for nonvolatile memory elements require novel materials and devices that c... more Future nanoelectronics for nonvolatile memory elements require novel materials and devices that can switch logic states with a low power consumption, minimum heat dissipation, high-circuit density, fast switching speed, large endurance and long charge retention period. Herein, we report novel high resistance resistive switching in a polar beta-polyvinylidene fluoride (b-PVDF) and graphene oxide (GO) composite. A high resistance switching ratio was achieved without the realization of the essential current-filament forming condition mainly responsible for switching the device from high to low resistance states. b-PVDF is a well known ferroelectric/piezoelectric material which changes shape and size after application of an external electric field. We propose a model which describes how the present b-PVDF–GO composite changes shape after application of an external electric field (E) which provides a favorable environment for the formation of the current linkage path of GO in the PVDF ma...
Among various energy harvester paradigms, the simple cantilever-structured magneto-mechano-electr... more Among various energy harvester paradigms, the simple cantilever-structured magneto-mechano-electric (MME) energy generator comprises a piezoelectric material laminated on a magnetostrictive metal plate and permanent magnets as proof mass, exhibiting excellent magnetic energy-harvesting performance. The current challenge in using MME energy harvesters is the mechano-electric coupling at the interface between the piezoelectric material and magnetostrictive metal layer, which depends significantly on the mechanical properties of the interfacial adhesive layer. In this study, the effects of four types of adhesive interfacial layers on the output power and environmental and fatigue resistances of MME harvesters are systematically investigated. An optimized MME energy generator with an adhesive interfacial layer of 18.8 μm thickness and elastic modulus of 3.1 GPa achieves colossal enhancement (∼300%) with a maximum output power density of 0.92 mW/cm2, while a 10 Oe (=10 G = 1 mT in air; 60 Hz) magnetic field is applied. In addition, the generator exhibits a robust endurance of continuous 108 fatigue cycles and excellent temperature stability in the range of -30 to 70 °C. The presented MME generator, which harvests stray magnetic energy reliably, is promising as a low-cost and efficient autonomous power source for Internet of Things devices, wireless sensor networks, and so on.
A thin dielectric layer of Al2O3 was grown by atomic layer deposition on a relaxor ferroelectric ... more A thin dielectric layer of Al2O3 was grown by atomic layer deposition on a relaxor ferroelectric 65Pb(Mg1/3Nb2/3)O3–35PbTiO3 (PMN–PT)/Pt/Si thick film fabricated by the aerosol deposition technique to artificially induce ferroelectric behaviour.
A robust and reproducible resistance switching in iron substituted strontium titanate is reported... more A robust and reproducible resistance switching in iron substituted strontium titanate is reported which shows giant high to low resistance state ratio (∼105) and stable charge retention.
Conventional thin-film processing techniques remain inadequate for obtaining superior dense ceram... more Conventional thin-film processing techniques remain inadequate for obtaining superior dense ceramic thick films. The incompatibility of ceramic films prepared via other methods, such as screen printing, spin coating, and sputtering, is a major obstacle in the fabrication of thick film-based ceramic electronic components. The granule spray in vacuum (GSV) processes and aerosol deposition (AD) are important coating approaches for forming dense ceramic thick films featuring nanoscale crystallite structures at room temperature, which offer excellent material properties and facilitate cost-effective production. AD ceramic coatings require the acceleration of solid-state submicron ceramic particles via gas streams with a velocity of a few hundred meters per second, which are then wedged onto a substrate. This process is economical and particularly useful for the fabrication of piezoelectric thick film-based microactuators, energy harvesters, sensors, and optoelectronic devices. More recen...
(Pb0.89La0.11)(Zr0.70Ti0.30)O3 (PLZT 11/70/30) relaxor ferroelectric (RFE) films were fabricated ... more (Pb0.89La0.11)(Zr0.70Ti0.30)O3 (PLZT 11/70/30) relaxor ferroelectric (RFE) films were fabricated on Pt/Si substrates by aerosol deposition, which not only enabled the deposition of a film at room temperature but also increased the dielectric breakdown strength. Perovskite phase and microstructural analyses were carried out by x-ray diffraction and scanning electron microscopy techniques. A PLZT 11/70/30 RFE AD film annealed at 550 °C exhibited the best dielectric properties (εr ~ 1090, tanδ ~ 0.028) and typical relaxor-type slim polarization–electric field (P–E) hysteresis loop with relatively low remanent polarization (Pr ~ 6.81 µC/cm2) and coercive field (Ec ~ 118 kV/cm) even at a high applied electric field (~ 2500 kV/cm). These superior properties were achieved due to high phase purity, low defect densities, and well-tuned grain sizes of an annealed PLZT 11/70/30 RFE AD film. The PLZT 11/70/30 RFE AD film exhibited a high energy-storage density (Wrec ~ 44 J/cm3) which is attributed to the high dielectric breakdown strength, low hysteresis loss (Wloss ~ 10.3 J/cm3), and almost-electric-field-independent efficiency (η ~ 81%, change of ~ 6% with the change from low to high electric fields), calculated using the unipolar P–E hysteresis loop. The excellent temperature stability of the energy efficiency of the PLZT 11/70/30 RFE AD film makes it a promising material for high-temperature energy-storage capacitor applications.
An enhanced self-powered near-ultraviolet photodetection phenomenon was observed in epitaxial gal... more An enhanced self-powered near-ultraviolet photodetection phenomenon was observed in epitaxial gallium nitride (GaN) nanorod networks grown on an intermediate layer of N:GaN on a nitridated HfO2(N:HfO2)/SiO2/p-Si substrate.
The solid solution of relaxor and lead titanate single crystals have been an excellent choice for... more The solid solution of relaxor and lead titanate single crystals have been an excellent choice for electromechanical applications such as energy harvesters, SONARs, transducers, and biomedical equipment. The mechanical quality factor (Qm) plays a crucial role in such applications using high power resonance condition. In this work, 32 mode (011) oriented along thickness direction, Generation-III piezoelectric single crystals based on PMN-PZT [71Pb(Mg1/3Nb2/3)O3–29PbZrTiO3] have been grown by solid state single crystal growth method. The Mn doping concentration in the crystals were systematically controlled within the range of 0 to 1.0 mol.%. The piezoelectric properties noticeably varied with the Mn doping concentration when the content is over 0.1 mol.%. In order to obtain significant enhancement in Qm in PMN-PZT single crystals, especially, the Mn doping concentration should be higher than 0.7 mol.% (which offers highest figure of merit) for high power resonance applications.
The electrocaloric effect (ECE), in which the change in the material temperature with an applicat... more The electrocaloric effect (ECE), in which the change in the material temperature with an application or removal of an electric field is one of the key phenomena of future highly...
Abstract Resistive switching behavior in Graphene oxide (GO) is well studied, however, the variou... more Abstract Resistive switching behavior in Graphene oxide (GO) is well studied, however, the various mechanisms responsible for this phenomenon are still under extensive debate. We present repeatable bipolar resistive switching in GO thin films sandwiched between two insulating polymer PVDF (Polyvinylidene Fluoride) grown on conducting indium tin oxide (ITO) covered glass substrate. The device heterostructure (Al/PVDF/GO/PVDF/ITO) showed bipolar resistance states switching between low resistance state (LRS) to high resistance state (HRS) with a large ON/OFF ratio of 103 and resistance retention potential up to 104 s. In LRS, in the low applied voltage region, ohmic conduction was the main reason for current conduction in devices; however, traps filled/assisted conduction mechanism dominates in the higher voltage region. The PVDF/GO/PVDF heterostructure shows that oxygen vacancies are responsible for the formation of current conducting filaments. The low operating voltage (
A small amount of illumination of visible light on ultra thin films (∼5 nm) hafnium oxide demonst... more A small amount of illumination of visible light on ultra thin films (∼5 nm) hafnium oxide demonstrated giant irreversible resistive switching, changed band off set and permanently developed trap charge states.
Among the various forms of natural energies, heat is the most prevalent and least harvested energ... more Among the various forms of natural energies, heat is the most prevalent and least harvested energy. Scavenging and detecting stray thermal energy for conversion into electrical energy can provide a cost-effective and reliable energy source for modern electrical appliances and sensor applications. Along with this, flexible devices have attracted considerable attention in scientific and industrial communities as wearable and implantable harvesters in addition to traditional thermal sensor applications. This review mainly discusses thermal energy conversion through pyroelectric phenomena in various lead-free as well as lead-based ceramics and polymers for flexible pyroelectric energy harvesting and sensor applications. The corresponding thermodynamic heat cycles and figures of merit of the pyroelectric materials for energy harvesting and heat sensing applications are also briefly discussed. Moreover, this study provides guidance on designing pyroelectric materials for flexible pyroelec...
We report giant resistive switching of an order of 104, long-time charge retention characteristic... more We report giant resistive switching of an order of 104, long-time charge retention characteristics up to 104 s, non-overlapping SET and RESET voltages, ohmic in low resistance state (LRS) and space charge limited current (SCLC) mechanism in high resistance state (HRS) properties in polycrystalline perovskite Cobalt Titanate (CoTiO3 ~ CTO) thin films. Impedance spectroscopy study was carried out for both LRS and HRS states which illustrates that only bulk resistance changes after resistance switching, however, there is a small change (<10% which is in pF range) in the bulk capacitance value in both states. These results suggest that in LRS state current filaments break the capacitor in many small capacitors in a parallel configuration which in turn provides the same capacitance in both states even there was 90 degree changes in phase-angle and an order of change in the tangent loss.
Future nanoelectronics for nonvolatile memory elements require novel materials and devices that c... more Future nanoelectronics for nonvolatile memory elements require novel materials and devices that can switch logic states with a low power consumption, minimum heat dissipation, high-circuit density, fast switching speed, large endurance and long charge retention period. Herein, we report novel high resistance resistive switching in a polar beta-polyvinylidene fluoride (b-PVDF) and graphene oxide (GO) composite. A high resistance switching ratio was achieved without the realization of the essential current-filament forming condition mainly responsible for switching the device from high to low resistance states. b-PVDF is a well known ferroelectric/piezoelectric material which changes shape and size after application of an external electric field. We propose a model which describes how the present b-PVDF–GO composite changes shape after application of an external electric field (E) which provides a favorable environment for the formation of the current linkage path of GO in the PVDF ma...
Among various energy harvester paradigms, the simple cantilever-structured magneto-mechano-electr... more Among various energy harvester paradigms, the simple cantilever-structured magneto-mechano-electric (MME) energy generator comprises a piezoelectric material laminated on a magnetostrictive metal plate and permanent magnets as proof mass, exhibiting excellent magnetic energy-harvesting performance. The current challenge in using MME energy harvesters is the mechano-electric coupling at the interface between the piezoelectric material and magnetostrictive metal layer, which depends significantly on the mechanical properties of the interfacial adhesive layer. In this study, the effects of four types of adhesive interfacial layers on the output power and environmental and fatigue resistances of MME harvesters are systematically investigated. An optimized MME energy generator with an adhesive interfacial layer of 18.8 μm thickness and elastic modulus of 3.1 GPa achieves colossal enhancement (∼300%) with a maximum output power density of 0.92 mW/cm2, while a 10 Oe (=10 G = 1 mT in air; 60 Hz) magnetic field is applied. In addition, the generator exhibits a robust endurance of continuous 108 fatigue cycles and excellent temperature stability in the range of -30 to 70 °C. The presented MME generator, which harvests stray magnetic energy reliably, is promising as a low-cost and efficient autonomous power source for Internet of Things devices, wireless sensor networks, and so on.
A thin dielectric layer of Al2O3 was grown by atomic layer deposition on a relaxor ferroelectric ... more A thin dielectric layer of Al2O3 was grown by atomic layer deposition on a relaxor ferroelectric 65Pb(Mg1/3Nb2/3)O3–35PbTiO3 (PMN–PT)/Pt/Si thick film fabricated by the aerosol deposition technique to artificially induce ferroelectric behaviour.
A robust and reproducible resistance switching in iron substituted strontium titanate is reported... more A robust and reproducible resistance switching in iron substituted strontium titanate is reported which shows giant high to low resistance state ratio (∼105) and stable charge retention.
Conventional thin-film processing techniques remain inadequate for obtaining superior dense ceram... more Conventional thin-film processing techniques remain inadequate for obtaining superior dense ceramic thick films. The incompatibility of ceramic films prepared via other methods, such as screen printing, spin coating, and sputtering, is a major obstacle in the fabrication of thick film-based ceramic electronic components. The granule spray in vacuum (GSV) processes and aerosol deposition (AD) are important coating approaches for forming dense ceramic thick films featuring nanoscale crystallite structures at room temperature, which offer excellent material properties and facilitate cost-effective production. AD ceramic coatings require the acceleration of solid-state submicron ceramic particles via gas streams with a velocity of a few hundred meters per second, which are then wedged onto a substrate. This process is economical and particularly useful for the fabrication of piezoelectric thick film-based microactuators, energy harvesters, sensors, and optoelectronic devices. More recen...
(Pb0.89La0.11)(Zr0.70Ti0.30)O3 (PLZT 11/70/30) relaxor ferroelectric (RFE) films were fabricated ... more (Pb0.89La0.11)(Zr0.70Ti0.30)O3 (PLZT 11/70/30) relaxor ferroelectric (RFE) films were fabricated on Pt/Si substrates by aerosol deposition, which not only enabled the deposition of a film at room temperature but also increased the dielectric breakdown strength. Perovskite phase and microstructural analyses were carried out by x-ray diffraction and scanning electron microscopy techniques. A PLZT 11/70/30 RFE AD film annealed at 550 °C exhibited the best dielectric properties (εr ~ 1090, tanδ ~ 0.028) and typical relaxor-type slim polarization–electric field (P–E) hysteresis loop with relatively low remanent polarization (Pr ~ 6.81 µC/cm2) and coercive field (Ec ~ 118 kV/cm) even at a high applied electric field (~ 2500 kV/cm). These superior properties were achieved due to high phase purity, low defect densities, and well-tuned grain sizes of an annealed PLZT 11/70/30 RFE AD film. The PLZT 11/70/30 RFE AD film exhibited a high energy-storage density (Wrec ~ 44 J/cm3) which is attributed to the high dielectric breakdown strength, low hysteresis loss (Wloss ~ 10.3 J/cm3), and almost-electric-field-independent efficiency (η ~ 81%, change of ~ 6% with the change from low to high electric fields), calculated using the unipolar P–E hysteresis loop. The excellent temperature stability of the energy efficiency of the PLZT 11/70/30 RFE AD film makes it a promising material for high-temperature energy-storage capacitor applications.
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