Search

The piezotronics effect utilizes a piezopotential to modulate and control current in piezo-semiconductors. Ferroelectric materials, as a type of piezoelectric materials, possess piezoelectric coefficients that are significantly larger than those found in conventional piezoelectric materials. Here, we propose a strain modulated ferroelectric field-effect transistor (St-FeFET) utilizing external strain instead of gate voltage to achieve ferroelectric modulation, which eliminates the need for gate voltage. By applying a very small strain (0.01%), the St-FeFET can achieve a maximum on-off current ratio of 1250% and realizes a gauge factor (GF) of 1.19 × 106, which is much higher than that of conventional strain sensors. This work proposes a new method for realizing highly sensitive strain sensors and presents innovative approaches to the operation methods of ferroelectric field-effect transistors as well as potential applications for coupling of strain sensors and various devices across different fields. [ABSTRACT FROM AUTHOR]

Recently, a great deal of interest has been focused on developing sensors that can measure both pressure and light. However, traditional sensors are difficult to integrate into silicon (Si)-based integrated circuits. Therefore, it is particularly important to design a sensor that operates on a new principle. In this paper, junction piezotronic transistor (JPT) arrays based on zinc oxide (ZnO) nanowire are demonstrated. And the JPT arrays show high spatial resolution pressure and light mapping with 195 dpi. Because ZnO nanowires are arranged vertically above the p-type Si channel's center of the transistor, the width of the heterojunction depletion region is constricted by the positive piezoelectric potential generated by strained ZnO. In addition, photogenerated charge carriers can be created in the Si channel when JPT is stimulated by light, which increases its electrical conductivity. Consequently, the external pressure and light distribution information can be obtained from the variation in the output current of the device. The prepared JPT arrays can be compatible with Si transistors, which make them highly competitive and make it possible to incorporate both pressure and light sensors into large integrated circuits. This work will contribute to many applications, such as intelligent clothing, human–computer interaction, and electronic skin. [ABSTRACT FROM AUTHOR]

Nitrides are the leading semiconductor material used for the fabrication of high electron mobility transistors (HEMTs). They exhibit piezoelectric properties, which, coupled with their high mechanical stiffness, expand their versatile applications into the fabrication of piezoelectric devices. Today, due to advances in device technology that result in a reduction in the size of individual transistor elements and due to increased structural complexity (e.g., multi-gate transistors), the integration of piezoelectric materials into HEMTs leads to an interesting occurrence, namely acoustic emission from the transistor gate due to piezoelectric effects. This could affect the device's performance, reliability, and durability. However, this phenomenon has not yet been comprehensively described. This paper aims to examine this overlooked aspect of AlGaN/GaN HEMT operation, that is, the acoustic emission from the gate region of the device induced by piezoelectric effects. For this purpose, dedicated test structures were designed, consisting of two narrow 1.7 μm-wide metallization strips placed at distances ranging from 5 μm to 200 μm fabricated in AlGaN/GaN heterostructures to simulate and examine the gate behavior of the HEMT transistor. For comparison, the test device structures were also fabricated on sapphire, which is not a piezoelectric material. Measurements of acoustic and electrical interactions in the microwave range were carried out using the "on wafer" method with Picoprobe's signal–ground–signal (SGS)-type microwave probes. The dependence of reflectance |S11| and transmittance |S21| vs. frequency was investigated, and the coupling capacitance was determined. An equivalent circuit model of the test structure was developed, and finite element method simulation was performed to study the distribution of the acoustic wave in the nitride layers and substrate for different frequencies using Comsol Multiphysics software. At frequencies up to 2–3 GHz, the formation of volume waves and a surface wave, capable of propagating over long distances (in the order of tens of micrometers) was observed. At higher frequencies, the resulting distribution of displacements as a result of numerous reflections and interferences was more complicated. However, there was always the possibility of a surface wave occurrence, even at large distances from the excitation source. At small gate distances, electrical interactions dominate. Above 100 µm, electrical interactions are comparable to acoustic ones. With further increases in distance, weakly attenuated surface waves will dominate. [ABSTRACT FROM AUTHOR]

Recently, a great deal of interest has been focused on developing sensors that can measure both pressure and light. However, traditional sensors are difficult to integrate into silicon (Si)-based integrated circuits. Therefore, it is particularly important to design a sensor that operates on a new principle. In this paper, junction piezotronic transistor (JPT) arrays based on zinc oxide (ZnO) nanowire are demonstrated. And the JPT arrays show high spatial resolution pressure and light mapping with 195 dpi. Because ZnO nanowires are arranged vertically above the p-type Si channel’s center of the transistor, the width of the heterojunction depletion region is constricted by the positive piezoelectric potential generated by strained ZnO. In addition, photogenerated charge carriers can be created in the Si channel when JPT is stimulated by light, which increases its electrical conductivity. Consequently, the external pressure and light distribution information can be obtained from the variation in the output current of the device. The prepared JPT arrays can be compatible with Si transistors, which make them highly competitive and make it possible to incorporate both pressure and light sensors into large integrated circuits. This work will contribute to many applications, such as intelligent clothing, human–computer interaction, and electronic skin.

This study investigates the piezoelectric and piezotronic properties of a novel composite material comprising polyvinylidene fluoride (PVDF) and antimony sulphoiodide (SbSI) nanowires. The material preparation method is detailed, showcasing its simplicity and reproducibility. The material's electrical resistivity, piezoelectric response, and energy-harvesting capabilities are systematically analyzed under various deflection conditions and excitation frequencies. The piezoelectric response is characterized by the generation of charge carriers in the material due to mechanical strain, resulting in voltage output. The fundamental phenomena of charge generation, along with their influence on the material's resistivity, are proposed. Dynamic strain testing reveals the composite's potential as a piezoelectric nanogenerator (PENG), converting mechanical energy into electrical energy. Comparative analyses highlight the composite's power density advantages, thereby demonstrating its potential for energy-harvesting applications. This research provides insights into the interplay between piezoelectric and piezotronic phenomena in nanocomposites and their applicability in energy-harvesting devices. [ABSTRACT FROM AUTHOR]

Herein, the influence of stresses on parameters of 2D electron gas (2DEG) in AlGaN/GaN high‐electron‐mobility transistor‐type heterostructures grown on sapphire substrate by metal–organic vapor‐phase epitaxy technique is presented. The as‐grown heterostructures as well as Schottky diodes fabricated in them are subjected to compressive stress. The custom stressing system induces a homogeneous state of compressive stress in the samples without causing electrical side effects. Time‐dependent heterostructures characteristics of electron concentration, electron mobility, and bandgap width are measured. Additionally, in the case of the Schottky diodes, current–voltage characteristics and charge flow in the contact are measured. The measurements are performed in cycles with and without applied stresses to determine the repeatability of effects and to separate the influence of thermal and electrical factors. Additionally, electrical simulations are performed using APSYS software package. The obtained results lead to conclusions that are different to those reported in existing literature, especially in regard to the time dependence of the measured effects, that is essential to proper explanation. It is also shown that a key role in the change of 2DEG parameters is played by deep surface states and interlayer piezoelectric effects. Finally, the anisotropic character of the derived relations is demonstrated. [ABSTRACT FROM AUTHOR]

Piezoelectricity is the electric charge which accumulates in certain materials in response to mechanical stimuli, while piezoelectric nanogenerators (PENGs) converting mechanical energy into electricity can be widely used for energy harvesting and self-powered systems. The group IV–VI monochalcogenides may exhibit strong piezoelectricity because of their puckered C2v symmetry and electronic structure, making them promising for flexible PENG. Herein, we investigated the synthesis and piezoelectric properties of multilayer SnSe nanosheets grown by chemical vapor deposition (CVD). The SnSe nanosheets exhibited high single-crystallinity, large area, and good stability. The strong layer-dependent in-plane piezoelectric coefficient of SnSe nanosheets showed a saturated trend to be ∼ 110 pm/V, which overcomes the weak piezoelectric response or odd-even effects in other layered nanosheets. A high energy conversion efficiency of 9.3% and a maximum power density of 538 mW/cm2 at 1.03% strain have been demonstrated in a SnSe-based PENG. Based on the enhanced piezoelectricity of SnSe and attractive output performance of the nanogenerator, a self-powered sensor for human motion monitoring is further developed. These results demonstrate the strong piezoelectricity in high quality CVD-grown SnSe nanosheets, allowing for application in flexible smart piezoelectric sensors and advanced microelectromechanical devices. [ABSTRACT FROM AUTHOR]

Driven by the urgent demands for information technology, energy, and intelligent industry, third-generation semiconductor GaN has emerged as a pivotal component in electronic and optoelectronic devices. Fundamentally, piezoelectric polarization is the most essential feature of GaN materials. Incorporating piezotronics and piezo-phototronics, GaN materials synergize mechanical signals with electrical and optical signals, thereby achieving multi-field coupling that enhances device performance. Piezotronics regulates the carrier transport process in micro–nano devices, which has been proven to significantly improve the performance of devices (such as high electron mobility transistors and microLEDs) and brings many novel applications. This review examines GaN material properties and the theoretical foundations of piezotronics and phototronics. Furthermore, it delves into the fabrication and integration processes of GaN devices to achieve state-of-the-art performance. Additionally, this review analyzes the impact of introducing three-dimensional stress and regulatory forces on the electrical and optical output performance of devices. Moreover, it discusses the burgeoning applications of GaN devices in neural sensing, optoelectronic output, and energy harvesting. The potential of piezotronic-controlled GaN devices provides valuable insights for future research and the development of multi-functional, diversified electronic devices.

With the arrival of the era of artificial intelligence (AI) and big data, the explosive growth of data has raised higher demands on computer hardware and systems. Neuromorphic techniques inspired by biological nervous systems are expected to be one of the approaches to breaking the von Neumann bottleneck. Piezotronic neuromorphic devices modulate electrical transport characteristics by piezopotential and directly associate external mechanical motion with electrical output signals in an active manner, with the capability to sense/store/process information of external stimuli. In this review, we have presented the piezotronic neuromorphic devices (which are classified into strain-gated piezotronic transistors and piezoelectric nanogenerator-gated field effect transistors based on device structure) and discussed their operating mechanisms and related manufacture techniques. Secondly, we summarized the research progress of piezotronic neuromorphic devices in recent years and provided a detailed discussion on multifunctional applications, including bionic sensing, information storage, logic computing, and electrical/optical artificial synapses. Finally, in the context of future development, challenges, and perspectives, we have discussed how to modulate novel neuromorphic devices with piezotronic effects more effectively. It is believed that the piezotronic neuromorphic devices have great potential for the next generation of interactive sensation/memory/computation to facilitate the development of the Internet of Things, AI, biomedical engineering, etc.

Piezotronic and piezo-phototronic effects can effectively modulate the Schottky barrier height (SBH) of the metal-semiconductor contact and the built-in electric field. Most models focus on the built-in electric field of perovskite solar cells, and polarization-modulated SBH is missing. We investigated piezotronic and piezo-phototronic effects on the Schottky barrier and built-in electric field of perovskite solar cells. A model of the surface potential induced by polarization was developed. The analytical and numerical results are calculated for perovskite solar cells. We found that the piezo-phototronic effect can significantly increase the performance of perovskite solar cells by reducing the height of the Schottky barrier. This model not only provides a fundamental physical picture of the piezotronic and piezo-phototronic effect on perovskite solar cells, but also paves a new path to develop high-efficiency perovskite solar cells. [Display omitted] • Piezotronic and piezo-phototronic effect can improve the performance of perovskite solar cells. • The model of piezotronics and piezo-phototronics on perovskite solar cells was proposed. • This model provides a basic physics picture for piezotronic and piezo-phototronic effect on perovskite solar cell. [ABSTRACT FROM AUTHOR]

Abstract Introducing polarization field of piezoelectric materials is an effective strategy to improve photocatalytic performance. In this study, a new type of BaTiO3/CuO heterostructure catalyst was designed and synthesized to achieve high piezo-photocatalytic activity through the synergy of heterojunction and piezoelectric effect. The BaTiO3/CuO heterostructure shows a significantly enhanced piezo-photocatalytic degradation efficiency of organic pollutants compared with the individual BaTiO3 nanowires (NWs) and CuO nanoparticles (NPs). Under the co-excitation of ultrasonic vibration and ultraviolet radiation, the optimal degradation reaction rate constant k of polarized BaTiO3/CuO heterostructure on methyl orange (MO) dye can reach 0.05 min− 1, which is 6.1 times of photocatalytic rate and 7 times of piezocatalytic rate. The BaTiO3/CuO heterostructure with remarkable piezo-photocatalytic behavior provides a promising strategy for the development of high-efficiency catalysts for wastewater purification, and it also helps understand the coupling mechanism between piezoelectric effect and photocatalysis.

Mechanical characterization of quasi one-dimensional nanostructures is essential for the design of novel nanoelectromechanical systems. However, the results obtained on basic mechanical quantities, such as Young's modulus and fracture strength, show significant standard deviation in the literature. This is partly because of diversity in the quality of the nanowire, and partly because of inappropriately performed mechanical tests and simplified mechanical models. Here we present orientation-controlled bending and fracture studies on wet chemically grown vertical ZnO nanowires, using lateral force microscopy. The lateral force signal of the atomic force microscope was calibrated by a diamagnetic levitation spring system. By acquiring the bending curves of 14 nanowires, and applying a two-segment mechanical model, an average bending modulus of 108 ± 17 GPa was obtained, which was 23% lower than the Young's modulus of bulk ZnO in the [0001] direction. It was also found that the average fracture strain and stress inside the nanowire was above 3.1 ± 0.3 % and 3.3 ± 0.3 GPa, respectively. However, the fracture of the nanowires was governed by the quality of the nanowire/substrate interface. The demonstrated technique is a relatively simple and productive way for the accurate mechanical characterization of vertical nanowire arrays. [ABSTRACT FROM AUTHOR]

This study investigates the piezoelectric and piezotronic properties of a novel composite material comprising polyvinylidene fluoride (PVDF) and antimony sulphoiodide (SbSI) nanowires. The material preparation method is detailed, showcasing its simplicity and reproducibility. The material’s electrical resistivity, piezoelectric response, and energy-harvesting capabilities are systematically analyzed under various deflection conditions and excitation frequencies. The piezoelectric response is characterized by the generation of charge carriers in the material due to mechanical strain, resulting in voltage output. The fundamental phenomena of charge generation, along with their influence on the material’s resistivity, are proposed. Dynamic strain testing reveals the composite’s potential as a piezoelectric nanogenerator (PENG), converting mechanical energy into electrical energy. Comparative analyses highlight the composite’s power density advantages, thereby demonstrating its potential for energy-harvesting applications. This research provides insights into the interplay between piezoelectric and piezotronic phenomena in nanocomposites and their applicability in energy-harvesting devices.

Abstract The fascinating two‐dimensional (2D) materials are being potentially applied in various fields from science to engineering benefitting from the charming physical and chemical properties on optics, electronics, and magnetism, compared with the bulk crystal, while piezotronics is a universal and pervasive phenomenon in the materials with broking center symmetry, promoting the new field and notable achievements of piezotronics in 2D materials with higher accuracy and sensitivity. For example, 20 parts per billion of the detecting limitations in NO2 sensor, 500 μm of spatial strain resolution in flexible devices, and 0.363 eV output voltage in nanogenerators. In this review, three categories of 2D piezotronics materials are first introduced ranging from organic to inorganic data, among which six types of 2D inorganic materials are emphasized based on the geometrical arrangement of different atoms. Then, the microscopic mechanism of carrier transport and separation in 2D piezotronic materials is highlighted, accompanied with the presentation of four measured methods. Subsequently, the developed applications of 2D piezotronics are discussed comprehensively including different kinds of sensors, piezo‐catalysis, nanogenerators and information storage. Ultimately, we suggest the challenges and provide the ideas for qualitative–quantitative research of microscopic mechanism and large‐scale integrated applications of 2D piezotronics.

Metal‐halide perovskites have emerged as versatile materials for various electronic and optoelectronic devices such as diodes, solar cells, photodetectors, and sensors due to their interesting properties of high absorption coefficient in the visible regime, tunable bandgap, and high power conversion efficiency. Recently, metal‐free organic perovskites have also emerged as a particular class of perovskites materials for piezoelectric applications. This broadens the chemical variety of perovskite structures with good mechanical adaptability, light‐weight, and low‐cost processability. Despite these achievements, the fundamental understanding of the underlying phenomenon of piezoelectricity in metal‐free perovskites is still lacking. Therefore, this perspective emphasizes the overview of piezoelectric properties of metal‐halide, metal‐free perovskites, and their recent progress which may encourage material designs to enhance their applicability towards practical applications. Finally, challenges and outlooks of piezoelectric metal‐free perovskites are highlighted for their future developments. [ABSTRACT FROM AUTHOR]

• The piezotronic fields in non-uniform piezo-semiconductive fibers are solved using a power series expansion method. • The convergence and correctness of the method are proved. • The antisymmetry of the electromechanical fields is broken due to the contoured profile. • A necking heterogeneous piezoelectric semiconductor PN junction is more conveniently modulated. In order to evidently improve the working performance of piezotronic devices, non-uniform piezoelectric semiconductor fibers with contoured profiles are designed. However, apart from the finite element method, it's hard to achieve analytical descriptions of the electromechanical fields in these non-uniform piezoelectric semiconductor fibers because of the governing equations with variable coefficients. For solving this bottleneck and exploring improved performance and new phenomena caused by the non-uniform profile, a power series expansion method is proposed based on the framework of the one-dimensional linearized model and is further applied to analyze the piezotronic performances of n-type non-uniform piezoelectric semiconductor fibers and PN junctions. It is revealed via systematical numerical simulations that the antisymmetry of the electromechanical fields in piezoelectric semiconductor fibers is broken because of the contoured profile and the piezotronic coupling. Meanwhile, the barrier configuration in a non-uniform PN junction is sensitive to the variation of cross-sectional area. Furthermore, the current-voltage relation of a necking heterogeneous piezoelectric semiconductor PN junction can be manipulated more conveniently by external mechanical loadings, meaning that the sensitivity of the device is improved. Not limited by non-uniform piezoelectric semiconductor fibers with contoured profiles, this method exhibits broad applicability, which is still available for solving multiple-coupled properties of functional graded piezoelectric semiconductor media. [ABSTRACT FROM AUTHOR]

Abstract Metal‐halide perovskites have emerged as versatile materials for various electronic and optoelectronic devices such as diodes, solar cells, photodetectors, and sensors due to their interesting properties of high absorption coefficient in the visible regime, tunable bandgap, and high power conversion efficiency. Recently, metal‐free organic perovskites have also emerged as a particular class of perovskites materials for piezoelectric applications. This broadens the chemical variety of perovskite structures with good mechanical adaptability, light‐weight, and low‐cost processability. Despite these achievements, the fundamental understanding of the underlying phenomenon of piezoelectricity in metal‐free perovskites is still lacking. Therefore, this perspective emphasizes the overview of piezoelectric properties of metal‐halide, metal‐free perovskites, and their recent progress which may encourage material designs to enhance their applicability towards practical applications. Finally, challenges and outlooks of piezoelectric metal‐free perovskites are highlighted for their future developments.

Based on the surface elasticity theory established by Gurtin and Murdoch, one-dimensional (1D) multi-field coupling model incorporating surface effects for piezoelectric semiconductor (PS) nanostructures is developed, in which the surface effect is treated as a non-classical mechanical boundary condition. With the derived equations, we conduct a theoretical analysis of static bending and free vibration of a simply supported n-type PS beam with open-circuit and electrically isolated boundary conditions at two ends. Numerical results show that the surface effect can stiffen the PS beam, and thus enhance its natural frequencies. Due to the influence of surface effects, the physical quantities such as the effective rigidity and natural frequencies of the PS beam exhibit a considerably significant size-dependent property when the radius R of the PS beam's cross-section is smaller than 400 nm. For the free vibration of the PS beam, the motion of electrons causes a damping effect. Both the surface effect and initial concentration of electrons have an effect on the quasi-damping ratio of the PS beam. The surface effect tends to enhance the damping effect. [ABSTRACT FROM AUTHOR]

Mechanical characterization of quasi one-dimensional nanostructures is essential for the design of novel nanoelectromechanical systems. However, the results obtained on basic mechanical quantities, such as Young’s modulus and fracture strength, show significant standard deviation in the literature. This is partly because of diversity in the quality of the nanowire, and partly because of inappropriately performed mechanical tests and simplified mechanical models. Here we present orientation-controlled bending and fracture studies on wet chemically grown vertical ZnO nanowires, using lateral force microscopy. The lateral force signal of the atomic force microscope was calibrated by a diamagnetic levitation spring system. By acquiring the bending curves of 14 nanowires, and applying a two-segment mechanical model, an average bending modulus of 108 ± 17 GPa was obtained, which was 23% lower than the Young’s modulus of bulk ZnO in the [0001] direction. It was also found that the average fracture strain and stress inside the nanowire was above 3.1 ± 0.3 % and 3.3 ± 0.3 GPa, respectively. However, the fracture of the nanowires was governed by the quality of the nanowire/substrate interface. The demonstrated technique is a relatively simple and productive way for the accurate mechanical characterization of vertical nanowire arrays.

The fascinating two‐dimensional (2D) materials are being potentially applied in various fields from science to engineering benefitting from the charming physical and chemical properties on optics, electronics, and magnetism, compared with the bulk crystal, while piezotronics is a universal and pervasive phenomenon in the materials with broking center symmetry, promoting the new field and notable achievements of piezotronics in 2D materials with higher accuracy and sensitivity. For example, 20 parts per billion of the detecting limitations in NO2 sensor, 500 μm of spatial strain resolution in flexible devices, and 0.363 eV output voltage in nanogenerators. In this review, three categories of 2D piezotronics materials are first introduced ranging from organic to inorganic data, among which six types of 2D inorganic materials are emphasized based on the geometrical arrangement of different atoms. Then, the microscopic mechanism of carrier transport and separation in 2D piezotronic materials is highlighted, accompanied with the presentation of four measured methods. Subsequently, the developed applications of 2D piezotronics are discussed comprehensively including different kinds of sensors, piezo‐catalysis, nanogenerators and information storage. Ultimately, we suggest the challenges and provide the ideas for qualitative–quantitative research of microscopic mechanism and large‐scale integrated applications of 2D piezotronics. [ABSTRACT FROM AUTHOR]

Smart, flexible, and self‐powered sensory systems represent the developmental trend of information technology beyond Moore's law with versatility and diversity toward artificial intelligence. Piezo/tribotronics offer a direct linkage/triggering of the electrical output sensing signals with external mechanical actions in an active way, which is highly promising in smart and flexible sensors, intelligent human–machine interaction, and self‐powered systems. Starting with the origin of piezo/triboelectric nanogenerators (PENGs/TENGs), herein, a review on the piezotronic devices based on 1D nanowires, 2D materials, 1D/2D mixed dimensional structures, PENG/TENG‐gated three‐terminal devices, and their applications in various multifunctional sensors is covered. In addition, a discussion is provided around how to improve the effectiveness in utilizing the piezo/triboelectric potential and fabricate smarter and more sophisticated electronic devices. Finally, future research concerns on piezo/triboelectric potential applications are summarized. There remains a massive space for the further development of piezotronics/tribotronics, which will be a multidisciplinary subject closely associated with soft electronics, neuromorphic devices, artificial intelligence, self‐powered systems, and even ocean/space technologies.

We study electric currents in a piezoelectric semiconductor fiber under a constant voltage and time-dependent axial stresses applied locally. From a nonlinear numerical analysis based on a one-dimensional phenomenological model using the commercial software COMSOL, it is found that pulse electric currents can be produced by periodic or time-harmonic stresses. The pulse currents can be tuned by the amplitude and frequency of the applied stress. The result obtained provides a new approach for the mechanical control of electric currents in piezoelectric semiconductor fibers and has potential applications in piezotronics. [ABSTRACT FROM AUTHOR]

Smart, flexible, and self‐powered sensory systems represent the developmental trend of information technology beyond Moore's law with versatility and diversity toward artificial intelligence. Piezo/tribotronics offer a direct linkage/triggering of the electrical output sensing signals with external mechanical actions in an active way, which is highly promising in smart and flexible sensors, intelligent human–machine interaction, and self‐powered systems. Starting with the origin of piezo/triboelectric nanogenerators (PENGs/TENGs), herein, a review on the piezotronic devices based on 1D nanowires, 2D materials, 1D/2D mixed dimensional structures, PENG/TENG‐gated three‐terminal devices, and their applications in various multifunctional sensors is covered. In addition, a discussion is provided around how to improve the effectiveness in utilizing the piezo/triboelectric potential and fabricate smarter and more sophisticated electronic devices. Finally, future research concerns on piezo/triboelectric potential applications are summarized. There remains a massive space for the further development of piezotronics/tribotronics, which will be a multidisciplinary subject closely associated with soft electronics, neuromorphic devices, artificial intelligence, self‐powered systems, and even ocean/space technologies. [ABSTRACT FROM AUTHOR]

• A new Kirchhoff–Love composite piezoelectric semiconductor shell is established. • The principle of virtual work is applied for the governing equations. • Static bending and forced vibration analyses are analytically conducted. • Coupling relations between mechanical deformation and charge behavior are obtained. • New structures and analytical solutions are helpful for sensing and energy harvesting. We study electromechanical effects and piezotronic behaviors in a Kirchhoff–Love laminated composite piezoelectric semiconductor circular cylindrical thin shell, which is composed of a non-piezoelectric semiconductor core and two piezoelectric dielectric layers. A second-order assumption for electric potentials and carrier concentration perturbations is utilized to capture accurate descriptions of the electric field and charge distributions within the composite shell, where the zeroth-order, first-order, and second-order forms represent constant, antisymmetric, and symmetric distributions along the thickness, respectively. The field equations and boundary conditions are simultaneously derived through a principle of virtual work and the fundamental lemma of the calculus of variation. The new governing equations derived show a new coupling relation between mechanical deformation and charge behavior in the composite shell, where all mechanical deformations (extension, bending of the shell) and all distribution forms of electric potential (zeroth-, first-, second-order electric potentials) are coupled, which is different from piezoelectric semiconductor beams and plates. Then, the numerical results of electromechanical effects and piezotronic behaviors in static bending and forced vibration problems of the shell are conducted with the derived theoretical model. Numerical studies of static bending graphically show some fundamental coupling relations between mechanical forces and charge distributions in deformed piezoelectric semiconductor shells. The new results from the forced vibration analysis given by the current model show that the deflection amplitude and the electric potential distribution in the thin shell are frequency-dependent and can be adjusted by controlling the excitation frequency. In addition, the semiconducting properties (dependence of mechanical behavior on doping level) are studied in both static and dynamic problems. The mechanically controlled charge distribution suggests that shell-shaped piezoelectric semiconductor shells could serve as an effective means of sensing or energy harvesting by converting mechanical energy into electricity. [ABSTRACT FROM AUTHOR]

Abstract Piezoelectricity has already found a multitude of applications, including voltage generation, quartz oscillators, mechanical sensors and actuators, piezoelectric transformers and more. However, in the last years, intense research efforts worldwide are demonstrating that nanoscale piezoelectricity can offer outstanding advantages in comparison with conventional piezoelectrics. Nevertheless, so far, no systematic analysis of these advantages and of the associated challenges has been reported. Here, we critically review 16 unique advantages of piezoelectricity at nanoscale and also consider some of the most important open challenges, together with promising general strategies to address them. Our analysis confirms that nanotechnology can open the way to piezoelectric transducers with unprecedented performance for several applications, including mechanical energy harvesting, piezotronics, piezophototronics, implantable systems, wireless piezoelectric nanotransducers, and more. Graphical abstract Image 1 Highlights • First systematic analysis of 16 unique advantages of piezoelectricity at nanoscale. • Review of some most important open challenges and strategies to address them. • Nanotechnology can open the way to superior piezoelectric transducers. [ABSTRACT FROM AUTHOR]

Abstract Electronic skins have received substantial attention in recent years and found great potential in prosthetics, robots, wearable devices, medical equipment, and many other areas. The development of the emerging field of nanogenerators and piezotronics unveiled new types of flexible electronic skins. These devices demonstrated high sensitivity, rapid response, and self-power capability. This review gives the research progress of electronic skins based on principles found in nanogenerators and piezotronics. The role of the piezoelectric effect and the piezotronic effect in sensors is explored, materials used in devices are discussed, and different sensors for electronic skins are provided in this review. The review concludes with an outlook of electronic skins enabled by nanogenerators and piezotronics. Graphical abstract fx1 [ABSTRACT FROM AUTHOR]

Abstract The development of recently discovered two-dimensional (2D) piezotronics will benefit from the comprehensive understanding of the piezopotential properties of 2D materials. Taking two most widely studied 2D piezoelectric nanomaterials (PNMs), hexagonal boron nitride and molybdenum disulfide for examples, in this paper we investigate the piezopotential properties of 2D PNMs based on numerical simulations and analytical modelling. Our molecular dynamics (MD) simulations show that the piezopotential coefficients of 2D PNMs can be significantly enhanced by small-scale effects at the nanoscale, which becomes more aggressive as the length of 2D PNMs decreases. In addition, a complicated piezopotential distribution is also observed in the stretched 2D PNMs due to the influence of small-scale effects. The influence of small-scale effects on piezopotential properties of 2D PNMs is beyond the reach of previously widely used classical electromechanical theories. To consider the small-scale effects in the analytical modelling of 2D PNMs, we propose here a novel nonlocal electromechanical model based on Eringen's nonlocal theory. Analytical expressions of the piezopotential distribution and piezopotential coefficient of intrinsic 2D PNMs are obtained from the proposed nonlocal models, which show good agreements with MD simulation results. In addition to the electromechanical properties, small-scale effects can also affect the piezopotential of 2D PNMs by changing their semiconducting properties, since it is observed in our density functional theory calculations that the conduction band edges of 2D PNMs can be greatly downwards shifted by small-scale effects. Graphical abstract fx1 Highlights • Piezopotential properties of 2D materials are studied analytically and numerically. • Small-scale effects can significantly affect the piezopotential of 2D materials. • A length-dependent piezopotential coefficient is observed in 2D materials. • A novel nonlocal electromechanical model is proposed for 2D materials. [ABSTRACT FROM AUTHOR]

Abstract This paper reports the fabrication of arrays of vertical piezoelectric nanowires which are individually contacted at their base, and demonstrates that an electrical response to strain can be obtained from individual nanowires from the array, without external biasing exploiting the piezotronic effect. Such a technology could thus be used for the fabrication of self-powered sensors for mechanical strain mapping, where each individually contacted nanowire would act as the strain sensing equivalent of a pixel. Lateral mapping resolutions in the micrometer range can be obtained. Here, the hydrothermal method was used to grow vertical ZnO nanowires selectively between two electrodes that had been patterned beforehand. For the sake of demonstration, nanowires deflection was produced by subjecting the array of nanowires to an incident lateral gas flow of controlled rate, which was switched on and off repeatedly across the sample while electrical response was measured. Different experimental configurations were tested in terms of flow rate, flow orientation, or nanowire position with respect to tube outlet. Experiments were carried out with compressed nitrogen and air. The experimental results are fully consistent with the piezoelectric and piezotronic response which can be expected with this geometry. Moreover, it is shown that the electrical response under nitrogen flow is a linear function of flow rate and that its sign provides information about flow direction. These results demonstrate the very promising prospects of this new technology for high-resolution mapping, with potential applications in gas or liquid flow sensing, fingerprints detection or human-machine interfaces. Graphical abstract fx1 Highlights • Experimental demonstration of individually contacted vertical ZnO NWs based sensors. • The fabrication used is large scale compatible and allows the matrices arrangement. • Results show a linear response with flow rate and consistent with orientation. • It exhibits prospect for high-resolution mapping of force/ deformation distribution. [ABSTRACT FROM AUTHOR]

Abstract The piezoelectric coefficient is a measure to quantify the potential use of a material in energy harvesting and sensor applications. High concentration of free charge carriers in piezoelectric materials can significantly impede the use of generated piezoelectric charge. In this study, undoped semiconducting ZnO single crystals with both Ohmic and Schottky contacts were prepared to quantify the effective piezoelectric response at temperatures from 20 °C to −140 °C and frequencies of mechanical loading from 0.5 Hz to 160 Hz. It was demonstrated that the formation of an electrostatic potential barrier at the metal-semiconductor interface increases the overall resistance, which provides access to unbiased piezoelectric coefficients of ZnO single crystals even at room temperature. These findings were verified using semiconducting ZnO for energy harvesting at room temperature and relatively low loading frequency. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Abstract Thin film is a good choice for in-plane strain sensing and is also technical compatible with modern electronic industry. In this paper, a thin film based piezotronic transistors array was demonstrated for the first time. The piezotronic effect of the sensing units was investigated and qualitative characterized. The strain sensitivity (gauge factor) of the units was derived up to 199, which is around 100 times of the sensitivity of the commercial foil gauge. After calibration on every sensing unit, the distribution of the strain applied on the device was successfully measured and mapped by the sensor array, which show the big potential of the thin film based piezotronic transistors array on the application of high space resolution, high sensitivity field deformation sensing. Graphical abstract fx1 Highlights • Li-doped ZnO shows better strain-tuned I-V characteristic than un-doped ZnO due to the decrease of screening effect. • The in-plane strain sensor based on Li-doped ZnO is 100 times more sensitive than that of the commercial foil gauge. • A high spatial resolution in-plane strain sensor array has fabricated by using Li-doped ZnO film. [ABSTRACT FROM AUTHOR]

Abstract Self-powered nanodevices are highly desirable for green energy technology, internet of things, wearable devices, sensors, and implanted biomedical devices. In this aspect, piezoelectric nanogenerators (PENGs) that involve energy harvest from mechanical vibrations and piezotronic effect enhanced various sensors, including strain sensor, gas sensor, humidity sensor, pressure sensor, and bio sensors are highly attractive, prompting a rapid surge in research on enhancing their performance. Due to the lack of inversion symmetry in wurtzite materials, external stress induced piezoelectric potential (piezopotential) is a well-known mechanism behind energy harvesting. By the coupling of semiconducting and piezoelectric properties, the resulting piezopotential can effectively tune the Schottky barrier height (SBH) at the interfaces of the devices, which can act as the virtual gate to modulate the carrier transportation in various electronic devices. In order to enhance the performances of piezotronics devices and PENGs, one of the main approaches is to search for new materials with higher piezoelectric coefficients. However, development of new materials is often impeded by available synthesis techniques. Alternatively, enhancing the piezoelectric properties of most common wurtzite piezoelectric semiconductors by microstructure modification is considered to be a viable approach. For this purpose, several strategies have been demonstrated to enhance the performances of piezotronics and PENGs, such as, surface modification, doping, altering orientation and aspect ratio of 1D nanostructures, etc. In this review, we systematically analyze the current developments in enhancing the performance of piezotronics and PENGs by microstructure modification of 1D nanostructures. Graphical abstract fx1 Highlights • Self-powered nanodevices are highly desirable. • Current developments in enhancing the performances of piezotronics devices and PENGs. • Enhancement by microstructure modification of well-known 1D nanostructures is discussed. • Surface modification, doping, altering orientation and aspect ratio of 1D nanostructures. [ABSTRACT FROM AUTHOR]

Piezotronics and piezo-phototronics are two emerging fields that involve high performance piezoelectric semiconductor devices. The nonuniform strain can create nonlinear piezopotential even in nonpiezoelectric materials such as silicon. Here, we propose theory of quantum piezotronics under nonuniform strain using a typical example of the interaction between independently trapped charges under nonlinear piezopotential. The trapped-ion motional frequency along the x direction can increase from 4 MHz to 25 MHz, and the electric-field noise can decrease by 15 times under nonuniform strain. This piezotronic harmonic oscillator based on trapping wells not only provides a good understanding of quantum piezotronics but also a guide for developing peizotronic devices for quantum computing. [Display omitted] • The nonuniform strain can create quadratic piezo-potential to control the axis motional frequency of trapped ions qubit. • The trapped-ion motional frequency along the x direction can reach up to 25 MHz under nonuniform strain. • The surface electric-field noise is decreased by 15 times under nonuniform strain. [ABSTRACT FROM AUTHOR]

Abstract Group-III nitride nano-dimensional materials with noncentrosymmetric crystal structure offer an exciting area of piezotronics for energy conversion applications. We experimentally report the piezotronic and piezo-phototronic effects of n -InGaN nanowires (NWs) having an emission wavelength in the visible region (≈510 nm). The n -type InGaN NWs, exhibiting high structural and optical quality, were grown by plasma-assisted molecular beam epitaxy (PAMBE) on Ti/TaN/Si substrates to facilitate the direct bottom electrical contact to the NWs. Further, we use Pt/Ir conductive atomic force microscopy (c-AFM) tip as a top electrical contact to the NW. Applying compressive strain on the NWs using a c-AFM tip, the Schottky barrier height (SBH) formed at the metal-semiconductor NW interface was tuned by means of strain induced piezo-potential. Thus, we study the two-way coupling of mechanical and electrical energy results in piezotronics of n -InGaN NWs. Such measurements were further carried out under optical excitation with 405 nm laser to understand its effect on change in SBH. Thereby, we demonstrate the three-way coupling of the piezo-phototronics of n -InGaN NWs by exploiting their excellent visible optoelectronic properties. The photogenerated carriers reduce the SBH while they play a lesser role at higher tip deflection force on NWs. This revealed that at the higher strain on NW, the piezo fields screen the photoexcited carriers hence resulting in a negligible change in I-V characteristics for ≥ 6 nN tip force with and without illumination. Thus, the investigation of nanoscale piezotronic and piezo-phototronic effects of n -InGaN NWs provides an opportunity to enable piezoelectric functional devices to be used as strain-tunable, self-powered electronics and optoelectronics applications. Graphical abstract The two-way coupling of mechanical and electrical energy is examined by applying external compressive strain on the n-InGaN nanowires (NWs), using a c-AFM Pt/Ir conductive tip, which induced a piezoelectric potential in the NW. Furthermore, the piezo-phototronic effect associated with the three-way coupling of n -InGaN NWs is demonstrated by exploiting their excellent visible optoelectronic properties. Under optical excitation, the photogenerated carriers reduce the strain induced SBH. At higher compressive strain, no change in the I-V characteristics was observed which reveals the dominant role of strain induced piezo fields. fx1 Highlights • We report the first systematic study on the piezotronic and piezo-phototronic effects in n-type InGaN nanowires (NWs) with the well-revealed mechanism. • The two-way coupling of mechanical and electrical energy is verified by applying external compressive strain on the NWs using a c-AFM Pt/Ir conductive tip. • The piezo-phototronics effect using the three-way coupling of n -InGaN NWs is demonstrated by exploiting their excellent visible optoelectronic properties. Under optical excitation, the photogenerated carriers reduce the strain induced SBH. • The change in SBH with and without illumination exhibited a linear relationship with the external compressive strain. • At higher compressive strain, the piezo fields have a dominant role over the optical excitation induced fields. [ABSTRACT FROM AUTHOR]

The humidity effect is inevitable in the fabrication and operation of zinc oxide (ZnO) nanowires (NWs). In this paper, the piezopotential properties of ZnO NWs under the humidity condition are compressively investigated based on atomic-scale simulations. Through molecular dynamics simulations, we find a mixed molecular and dissociative adsorption of water on the surface of ZnO NWs under the humidity condition. Absorptions of molecular and dissociative water both structurally reconstruct the surface atoms of ZnO NWs and thus modify their surface properties, which finally make the material properties of ZnO NWs under the humidity condition significantly different from those of their counterparts under the vacuum condition. Applying the obtained material properties to the numerical and analytical calculations of the piezopotential of ZnO NWs, we find a significant reduction in the piezopotential induced by the humidity effect. Similar to the results observed in the previous experiments, the reduction in the piezopotential is found to become more significant as the humidity level increases, since in this process more surface atoms of ZnO NWs will be adsorbed by molecular or dissociated water. Moreover, our density functional theory calculations indicate that the humidity effect can also influence the semiconducting properties of ZnO NWs by downward shifting their conduction band edges. However, the change in semiconducting properties induced by the humidity effect is found to have trivial effect on the piezopotential of ZnO NWs. [ABSTRACT FROM AUTHOR]

Piezotronics and piezo-phototronics have received increasing attention in flexible energy-harvesting devices, self-powered sensor systems utilizing piezoelectric semiconductor materials, such as ZnO, GaN and monolayer MoS 2 . Piezoelectric potentials induced by the externally applied strain can effectively control the generation, recombination and transport of the charge carriers for achieving high-performance devices. In this study, we describe the piezotronics effect on the GaN/InN/GaN quantum well, which can induce performances resembling those of topological insulators by a piezoelectric field polarized under the externally applied mechanical strain. The transport properties of bulk and edge states of this quantum well device have been investigated by calculating the electron density distribution under different widths of the quantum point contact (QPC), which is the origin of more conductance plateaus. In addition, we postulate the mechanical - electronic logic operation mechanisms based on the piezotronics effect adjusting the transport of edge states in the quantum well device. Fundamental logic units such as NOT, NAND and NOR gates have been innovatively designed for performing the logic computation functions from external mechanical stimuli. The logic nanodevices based on the topological insulator have near zero-power consumption and ultrahigh ON/OFF ratio. This work provides a deep insight into the piezotronics effect on the transport of bulk and edge states of the quantum well device, and offers novel solutions to design high-performance low-power mechanical-electronic logic devices. [ABSTRACT FROM AUTHOR]

Due to the coupling of piezoelectric and semiconductor properties, the wurtzite structure semiconductors have been used for fabricating high performance piezotronic devices. The carrier transport behavior can be effectively controlled by the polarized charges induced by applied strain. High-sensitive piezotronic strain sensors have potential application in next generation self-powered, flexible electronics and wearable systems. In this study, a piezotronic bipolar transistor has been studied through theoretical calculation and numerical simulation. The output current, gauge factor and carrier concentration have been simulated under the influence of different strains. The piezotronic bipolar transistor based strain sensor has ultrahigh sensitivity and the gauge factor can reach over 10 4 . This investigation not only provides a theoretical insight into the piezotronic effect on bipolar transistor, but also presents a new approach to design ultra-high sensitivity strain sensor. [ABSTRACT FROM AUTHOR]

Piezotronics have shown great promises in promoting the efficiency of photoelectrochemical (PEC) reactions, while their full-gear functionalities are constrained by the longstanding contradiction between the charge collection of semiconductors and the screening effect of polarization materials. In this report, we tackle this issue by decoupling the collecting and screening trajectories using graphene as the charge collector. The moderate charge density of graphene ensures minimal screen of the adjacent electrical polarizations and concurrently delivers photogenerated free carriers toward the counter electrode. Based on a PMN-PT/graphene/TiO 2 piezotronic PEC system, substantial performance gains were received through tuning the interfacial electronic energy level via ferroelectric polarizations. Forward poling could lead to a 50% improvement of photocurrent density at 1 V vs. RHE and a favorably shifted onset potential. Both calculation and experimental results suggest this outcome was beneficial from the low screening effect from graphene. In contrast, gold electrode will fully screen the polarization from PMN-PT and yield similar PEC performance despite of the poling conditions. This work reveals graphene could be an ideal conductive electrode selection for freeing piezotronic PEC devices from the performance capstone imposed by the trade-off between carrier collecting and charge screening. [ABSTRACT FROM AUTHOR]

Nanotransducers can offer crucial advantages in comparison with conventional sensors and actuators. However, interfacing and packaging nanostructures into complete electronic systems is very complex. Here we describe a wet chemical method for cointegrating arrays of ZnO nanowires into systems on printed circuit boards (PCBs). First, we deposit on the PCB a MnOOH layer for reproducibly increasing the nanowires density. Afterwards, we numerically demonstrate that the ligand ethylenediamine, at the isoelectric point of the ZnO nanowires tips, can effectively control, at very low concentrations, both zinc speciation and supersaturation in the nutrient solution. Accordingly, we combine potassium chloride and ethylenediamine, produced in situ from a safer precursor (ethanolamine), for concurrently thinning the nanowires (top width around 60 nm) and stabilizing their top faces. Our synergic approach enables the solution growth of ZnO nanowires which are untapered and have high densities (> 8/μm 2 ) and record length (> 15 µm) and aspect ratio (> 200) for plastic substrates which may not withstand high temperatures. These characteristics permit to simultaneously add the top electrode, package the nanowires, improve their mechanical robustness and connect to the electronic interface by a simple flip chip adhesive bonding procedure. As proofs of concept we describe flexible PCB heaters (electrical to thermal energy conversion) with power densities comparable with state of the art flexible heaters and a wearable piezotronic heartbeat detector comprising both ZnO nanowires (mechanical to electric energy conversion) and electronics on a single flexible PCB. Our results open the way to the cointegration of nanotransducers and electronics on conventional PCBs. [ABSTRACT FROM AUTHOR]

We report a novel approach to achieve piezotronic analog-to-digital converters (ADCs) based on strain gated transistors (SGTs). A single SGT can act as voltage converter, comparator, and amplifier. The new piezotronic ADC devices benefit from high sensitivity of the piezotronic SGT responding to the external strains. This design can significantly reduce the power consumption and the size of these devices, which are considered as crucial factors in self-powered systems. The fundamental concept of the device design has been demonstrated by three piezotronic ADC architectures formed by various networks comprised of SGTs and resistors. Analog-to-digital conversion and logic operations of these piezotronic ADCs blocks are analyzed and logic truth tables for all those configurations are presented. This design has immense potential for enormous applications in future human-machine interfaces, internet of things, and sensor networks. [ABSTRACT FROM AUTHOR]