This study utilized finite element simulation and experimental methods to investigate the evolution of crack detection performanceof a flexible differential fractal Koch eddy current probe at different excitation freq...This study utilized finite element simulation and experimental methods to investigate the evolution of crack detection performanceof a flexible differential fractal Koch eddy current probe at different excitation frequencies as the lift-off distance increases.As the lift-off distanceincreased,the distribution shape of induced eddy currents changed,leading to reduced similarity in the shape of the excitation coil and an expandeddistribution range of induced eddy currents,ultimately resulting in weakened output signal strength.The experimental results showed that forexcitation frequencies of 10 kHz,20 kHz,50 kHz,100 kHz,200 kHz,500 kHz,and1000 kHz,the maximum lift distances of the real partof the output signal when cracks were detected were 5.0 mm,7.0 mm,8.0 mm,8.0 mm,8.0 mm,6.5 mm,and 4.0 mm,respectively.Theimaginary parts were 6.5 mm,6.5 mm,7.5 mm,5.5 mm,8.0 mm,6.5 mm,and 6.5 mm,respectively.展开更多
Lift-off velocity of saltating sand particles in wind-blown sand located at 1.0 mm above the sand bed surface was measured using a phase Doppler particle analyzer in a wind tunnel. The results show that the probabilit...Lift-off velocity of saltating sand particles in wind-blown sand located at 1.0 mm above the sand bed surface was measured using a phase Doppler particle analyzer in a wind tunnel. The results show that the probability distribution of lift-off velocity can be expressed as a lognormal function, while that of lift-off angle follows an exponential function. The probability distribution of lift-off angle conditioned for each lift-off velocity also follows an exponential function, with a slope that becomes steeper with increasing lift-off velocity. This implies that the probability distribution of lift-off velocity is strongly dependent on the lift-off angle. However, these lift-off parameters are generally treated as an independent joint probability distribution in the literature. Numerical simulations were carried out to investigate the effects of conditional versus independent joint probability distributions on the vertical sand mass flux distribution. The simulation results derived from the conditional joint probability distribution agree much better with experimental data than those from the independent ones. Thus, it is better to describe the lift-off velocity of saltating sand particles using the conditional joint probability distribution. These results improve our understanding of saltation processes in wind-blown sand.展开更多
The probability distributions of sand particles＇ lift-off and incident velocities in a wind-blown sand flux play very important roles in the simulation of the wind-blown sand movement. In this paper, the vertical and...The probability distributions of sand particles＇ lift-off and incident velocities in a wind-blown sand flux play very important roles in the simulation of the wind-blown sand movement. In this paper, the vertical and the horizontal speeds of sand particles located at 1.0 mm above a sand-bed in a wind-blown sand flux are observed with the aid of Phase Doppler Anemometry （PDA） in a wind tunnel. Based on the experimental data, the probability distributions of not only the vertical lift-off speed but also the lift-off velocity as well as its horizontal component and the incident velocity as well as its vertical and horizontal components can be obtained by the equal distance histogram method. It is found, according to the results of the X^2-test for these probability distributions, that the probability density functions （pdf＇s） of the sand particles＇ lift-off and incident velocities as well as their vertical com- ponents are described by the Gamma density function with different peak values and shapes and the downwind incident and lift-off horizontal speeds, respectively, can be described by the lognormal and the Gamma density functions, These pdf＇s depend on not only the sand particle diameter but also the wind speed.展开更多
The influence of the picosecond(ps) pulsed burst with a nanosecond scale of temporal separation(50 ns) on filamentary traces in sapphire substrate is investigated. The spatiotemporal evolution of the filamentary plasm...The influence of the picosecond(ps) pulsed burst with a nanosecond scale of temporal separation(50 ns) on filamentary traces in sapphire substrate is investigated. The spatiotemporal evolution of the filamentary plasma string induced by sub-pulses of the burst-mode is revealed according to the analysis of the instantaneous photoluminescence images. Due to the presence of residual plasma, the energy loss of sub-pulse during the balancing of self-focusing effect is reduced, and thus refreshes the plasma via refocusing. The refreshed plasma peak generated by the subsequent subpulse appears at relatively low density positions in the formed filamentary plasma string, which results in more uniform densities and less spatial overlap among the plasma peaks. The continuity and uniformity of the filamentary trace in sapphire are enhanced by the burst-mode. Besides, the burst filamentary propagation can also remain effective when the sub-pulse energy is below the self-focusing threshold. Based on this uniform and precise energy propagation mode, the feasibility of its use for the laser lift-off(LLO) process is verified.展开更多
High-electron-mobility transistors(HEMTs)are a promising device in the field of radio frequency and wireless communication.However,to unlock the full potential of HEMTs,the fabrication of large-size flexible HEMTs is ...High-electron-mobility transistors(HEMTs)are a promising device in the field of radio frequency and wireless communication.However,to unlock the full potential of HEMTs,the fabrication of large-size flexible HEMTs is required.Herein,a large-sized(>2 cm^(2))of AlGaN/AlN/GaN heterostructure-based HEMTs were successfully stripped from sapphire substrate to a flexible polyethylene terephthalate substrate by an electrochemical lift-off technique.The piezotronic effect was then induced to optimize the electron transport performance by modulating/tuning the physical properties of two-dimensional electron gas(2DEG)and phonons.The saturation current of the flexible HEMT is enhanced by 3.15%under the 0.547%tensile condition,and the thermal degradation of the HEMT was also obviously suppressed under compressive straining.The corresponding electrical performance changes and energy diagrams systematically illustrate the intrinsic mechanism.This work not only provides in-depth understanding of the piezotronic effect in tuning 2DEG and phonon properties in GaN HEMTs,but also demonstrates a low-cost method to optimize its electronic and thermal properties.展开更多
首先以α-萘酚、间甲酚、甲醛为单体,通过缩聚反应合成了萘酚基酚醛树脂NAPR,随后与二碳酸二叔丁酯(DBDC)反应制备了一系列t-BOC改性的萘酚基酚醛树脂NAPR-BOC。用红外(FT-IR)、核磁(1 H NMR)、凝胶色谱(GPC)、热失重分析(TGA)对其结构...首先以α-萘酚、间甲酚、甲醛为单体,通过缩聚反应合成了萘酚基酚醛树脂NAPR,随后与二碳酸二叔丁酯(DBDC)反应制备了一系列t-BOC改性的萘酚基酚醛树脂NAPR-BOC。用红外(FT-IR)、核磁(1 H NMR)、凝胶色谱(GPC)、热失重分析(TGA)对其结构及性能进行了表征。以NAPR-BOC-2为基体树脂配制成lift-off光刻胶,测试了光刻胶的分辨率、形貌和耐热性,得到的光刻胶分辨率最大为0.6μm,耐热可达130℃。展开更多
The microfabrication technique for THz dipole antenna,"lift-off" was studied in this paper.Its procedure has been examined in detail,and discreetly tweaked.Particularly,Chlorobenzene is suggested to assist t...The microfabrication technique for THz dipole antenna,"lift-off" was studied in this paper.Its procedure has been examined in detail,and discreetly tweaked.Particularly,Chlorobenzene is suggested to assist the formation of undercut indispensible for fulfilling "lift-off".The experimental results of fabricated antennas confirm the effectiveness of this method.展开更多
Due to the wide range of potential applications for next-generation multi-functional devices,the flexible selfpowered photodetector(PD)with polarity-switchable behavior is essential but very challenging to be realized...Due to the wide range of potential applications for next-generation multi-functional devices,the flexible selfpowered photodetector(PD)with polarity-switchable behavior is essential but very challenging to be realized.Herein,a wearable bidirectional self-powered PD based on detached(Al,Ga)N and(In,Ga)N nanowires has been proposed and demonstrated successfully.Arising from the photovoltage-competing dynamics across(Al,Ga)N and(In,Ga)N nanowire photoelectrodes,such PD can generate the positive(33.3 mA W−1)and negative(-0.019 mA W−1)photo-responsivity under ultraviolet(UV)and visible illumination,respectively,leading to the bidirectional photocurrent behavior.Thanks to the introduction of quasi solid-state hydrogel,the PD can work without the liquid-electrolyte,thus remarkably reducing the volume from about 482 cm3 to only 0.18 cm3.Furthermore,the use of hydrogel is found to enhance response speed in the UV range by reducing the response time for more than 95%,which is mainly attributed to the increased open circuit potential and reduced ion transport distance.As the GaN connecting segment is pretty thin,the piezoelectric charges generated by stress are proposed to have only a limited effect on the photocurrent density.Therefore,both the stable on-off switching characteristics and photocurrent densities can still be achieved after being bent 400 times.With an excellent flexibility,this work creates opportunities for technological applications of bidirectional photocurrent PDs in flexible optoelectronic devices,e.g.,wearable intelligent sensors.展开更多
It is increasingly crucial for flexible electronics to efficiently and reliably peel large-area, ultra-thin flexible films off from rigid substrate serving as substrates of flexible electronics device, especially in i...It is increasingly crucial for flexible electronics to efficiently and reliably peel large-area, ultra-thin flexible films off from rigid substrate serving as substrates of flexible electronics device, especially in industrial production. This paper experimentally investigated the mechanism and technologic characteristics of laser lift-off(LLO) process of ultra-thin(～ 2 μm) polyimide(PI)film. It was found increasingly difficult to obtain desirable ultra-thin PI film by LLO with the decrease of the film thickness. The optimal process parameters were achieved considering laser fluence and accumulated irradiation times(AIT), which were found to be strongly correlative to the thickness of PI film. The process mechanism of LLO of PI film was disclosed that laser ablation of interfacial PI will result in the formation of gas products between the PI and glass substrate, enabling the change of interface microstructures to reduce the interface bond strength. The amount of gas products mainly determines the result of LLO process for ultra-thin PI film, from residual adhesion to wrinkles or cracking. The strategy of multi-scanning based on multiple irradiations of low-energy laser pulses was presented to effectively achieve a reliable LLO process of ultra-thin PI film. This study provides an attractive route to optimize the LLO process for large-scale production of ultra-thin flexible electronics.展开更多
A process methodology has been adopted to transfer GaN thin films grown on sapphire substrates to Si substrates using metal bonding and laser lift-off techniques. After bonding, a single KrF （248 nm） excimer laser p...A process methodology has been adopted to transfer GaN thin films grown on sapphire substrates to Si substrates using metal bonding and laser lift-off techniques. After bonding, a single KrF （248 nm） excimer laser pulse was directed through the transparent sapphire substrates followed by low-temperature heat treatment to remove the substrates. The influence of bonding temperature and energy density of the excimer laser on the structure and optical properties of GaN films were investigated systemically. Atomic force microscopy, X-ray diffraction and photoluminescence measurements showed that （1） the quality of the GaN film was higher at a lower bonding temperature and lower energy density; （2） the threshold of the energy density of the excimer laser lift-off GaN was 300 mJ/cm^2. The root-mean-square roughness of the transferred GaN surface was about 50 nm at a bonding temperature of 400 ℃.展开更多
AZ15nXT is a chemically-amplified negative-tone thick film photoresist.The resist has vertical profile and is widely used for redistribution layer(RDL)and through silicon vias(TSV)applications.For lift-off applicati...AZ15nXT is a chemically-amplified negative-tone thick film photoresist.The resist has vertical profile and is widely used for redistribution layer(RDL)and through silicon vias(TSV)applications.For lift-off applications,however,the inverted profile is needed.In this paper,we report the effects of process conditions on the resist profile and process window for lift off applications.展开更多
基金supported by the National Nature Science Foundation of China(Nos.62471206,52467002)。
文摘This study utilized finite element simulation and experimental methods to investigate the evolution of crack detection performanceof a flexible differential fractal Koch eddy current probe at different excitation frequencies as the lift-off distance increases.As the lift-off distanceincreased,the distribution shape of induced eddy currents changed,leading to reduced similarity in the shape of the excitation coil and an expandeddistribution range of induced eddy currents,ultimately resulting in weakened output signal strength.The experimental results showed that forexcitation frequencies of 10 kHz,20 kHz,50 kHz,100 kHz,200 kHz,500 kHz,and1000 kHz,the maximum lift distances of the real partof the output signal when cracks were detected were 5.0 mm,7.0 mm,8.0 mm,8.0 mm,8.0 mm,6.5 mm,and 4.0 mm,respectively.Theimaginary parts were 6.5 mm,6.5 mm,7.5 mm,5.5 mm,8.0 mm,6.5 mm,and 6.5 mm,respectively.
基金supported by the Fundamental Research Funds for the Central Universities of China(GK201503053)the National Natural Science Foundation of China(41601002)
文摘Lift-off velocity of saltating sand particles in wind-blown sand located at 1.0 mm above the sand bed surface was measured using a phase Doppler particle analyzer in a wind tunnel. The results show that the probability distribution of lift-off velocity can be expressed as a lognormal function, while that of lift-off angle follows an exponential function. The probability distribution of lift-off angle conditioned for each lift-off velocity also follows an exponential function, with a slope that becomes steeper with increasing lift-off velocity. This implies that the probability distribution of lift-off velocity is strongly dependent on the lift-off angle. However, these lift-off parameters are generally treated as an independent joint probability distribution in the literature. Numerical simulations were carried out to investigate the effects of conditional versus independent joint probability distributions on the vertical sand mass flux distribution. The simulation results derived from the conditional joint probability distribution agree much better with experimental data than those from the independent ones. Thus, it is better to describe the lift-off velocity of saltating sand particles using the conditional joint probability distribution. These results improve our understanding of saltation processes in wind-blown sand.
基金The project supported by the National Natural Science Foundation of China(10532040)the Hundred Talents Project.the Knowledge Innovation Project of Chinese Academy of Sciences(KZCX2-304).
文摘The probability distributions of sand particles＇ lift-off and incident velocities in a wind-blown sand flux play very important roles in the simulation of the wind-blown sand movement. In this paper, the vertical and the horizontal speeds of sand particles located at 1.0 mm above a sand-bed in a wind-blown sand flux are observed with the aid of Phase Doppler Anemometry （PDA） in a wind tunnel. Based on the experimental data, the probability distributions of not only the vertical lift-off speed but also the lift-off velocity as well as its horizontal component and the incident velocity as well as its vertical and horizontal components can be obtained by the equal distance histogram method. It is found, according to the results of the X^2-test for these probability distributions, that the probability density functions （pdf＇s） of the sand particles＇ lift-off and incident velocities as well as their vertical com- ponents are described by the Gamma density function with different peak values and shapes and the downwind incident and lift-off horizontal speeds, respectively, can be described by the lognormal and the Gamma density functions, These pdf＇s depend on not only the sand particle diameter but also the wind speed.
基金Project(51975017) supported by the National Natural Science Foundation of ChinaProject(KZ202110005012) supported by the Scientific Research Project of Beijing Educational Committee+1 种基金ChinaProject(2018YFB1107500) supported by the National Key R&D Program of China。
文摘The influence of the picosecond(ps) pulsed burst with a nanosecond scale of temporal separation(50 ns) on filamentary traces in sapphire substrate is investigated. The spatiotemporal evolution of the filamentary plasma string induced by sub-pulses of the burst-mode is revealed according to the analysis of the instantaneous photoluminescence images. Due to the presence of residual plasma, the energy loss of sub-pulse during the balancing of self-focusing effect is reduced, and thus refreshes the plasma via refocusing. The refreshed plasma peak generated by the subsequent subpulse appears at relatively low density positions in the formed filamentary plasma string, which results in more uniform densities and less spatial overlap among the plasma peaks. The continuity and uniformity of the filamentary trace in sapphire are enhanced by the burst-mode. Besides, the burst filamentary propagation can also remain effective when the sub-pulse energy is below the self-focusing threshold. Based on this uniform and precise energy propagation mode, the feasibility of its use for the laser lift-off(LLO) process is verified.
基金Key-Area Research and Development Program of Guangdong Province(Nos.2020B010172001,2020B010174004)GDAS’Project of Science and Technology Development(No.2018GDASCX-0112)+3 种基金Science and Technology Program of Guangzhou(No.2019050001)National Key Research and Development Program of China(No.2017YFB0404100)National Natural Science Foundation of China(Grant No.11804103)Guangdong Natural Science Foundation for Distinguished Young Scholars(Grant No.2018B030306048).
文摘High-electron-mobility transistors(HEMTs)are a promising device in the field of radio frequency and wireless communication.However,to unlock the full potential of HEMTs,the fabrication of large-size flexible HEMTs is required.Herein,a large-sized(>2 cm^(2))of AlGaN/AlN/GaN heterostructure-based HEMTs were successfully stripped from sapphire substrate to a flexible polyethylene terephthalate substrate by an electrochemical lift-off technique.The piezotronic effect was then induced to optimize the electron transport performance by modulating/tuning the physical properties of two-dimensional electron gas(2DEG)and phonons.The saturation current of the flexible HEMT is enhanced by 3.15%under the 0.547%tensile condition,and the thermal degradation of the HEMT was also obviously suppressed under compressive straining.The corresponding electrical performance changes and energy diagrams systematically illustrate the intrinsic mechanism.This work not only provides in-depth understanding of the piezotronic effect in tuning 2DEG and phonon properties in GaN HEMTs,but also demonstrates a low-cost method to optimize its electronic and thermal properties.
文摘首先以α-萘酚、间甲酚、甲醛为单体,通过缩聚反应合成了萘酚基酚醛树脂NAPR,随后与二碳酸二叔丁酯(DBDC)反应制备了一系列t-BOC改性的萘酚基酚醛树脂NAPR-BOC。用红外(FT-IR)、核磁(1 H NMR)、凝胶色谱(GPC)、热失重分析(TGA)对其结构及性能进行了表征。以NAPR-BOC-2为基体树脂配制成lift-off光刻胶,测试了光刻胶的分辨率、形貌和耐热性,得到的光刻胶分辨率最大为0.6μm,耐热可达130℃。
文摘The microfabrication technique for THz dipole antenna,"lift-off" was studied in this paper.Its procedure has been examined in detail,and discreetly tweaked.Particularly,Chlorobenzene is suggested to assist the formation of undercut indispensible for fulfilling "lift-off".The experimental results of fabricated antennas confirm the effectiveness of this method.
基金National Natural Science Foundation of China(62174172,61875224 and 61827823)Key Research and Development Program of Jiangsu Province(BE2018005)+4 种基金Key Research Program of Frontier Sciences,CAS(ZDBS-LY-JSC034)support from Natural Science Foundation of Jiangxi Province(20192BBEL50033)Research Program of Scientific Instrument and Equipment of CAS(YJKYYQ20200073)SINANO(Y8AAQ21001)support from Vacuum Interconnected Nanotech Workstation(Nano-X,F2201),Platform for Characterization&Test of SINANO,CAS.
文摘Due to the wide range of potential applications for next-generation multi-functional devices,the flexible selfpowered photodetector(PD)with polarity-switchable behavior is essential but very challenging to be realized.Herein,a wearable bidirectional self-powered PD based on detached(Al,Ga)N and(In,Ga)N nanowires has been proposed and demonstrated successfully.Arising from the photovoltage-competing dynamics across(Al,Ga)N and(In,Ga)N nanowire photoelectrodes,such PD can generate the positive(33.3 mA W−1)and negative(-0.019 mA W−1)photo-responsivity under ultraviolet(UV)and visible illumination,respectively,leading to the bidirectional photocurrent behavior.Thanks to the introduction of quasi solid-state hydrogel,the PD can work without the liquid-electrolyte,thus remarkably reducing the volume from about 482 cm3 to only 0.18 cm3.Furthermore,the use of hydrogel is found to enhance response speed in the UV range by reducing the response time for more than 95%,which is mainly attributed to the increased open circuit potential and reduced ion transport distance.As the GaN connecting segment is pretty thin,the piezoelectric charges generated by stress are proposed to have only a limited effect on the photocurrent density.Therefore,both the stable on-off switching characteristics and photocurrent densities can still be achieved after being bent 400 times.With an excellent flexibility,this work creates opportunities for technological applications of bidirectional photocurrent PDs in flexible optoelectronic devices,e.g.,wearable intelligent sensors.
基金the National Natural Science Foundation of China(Grant Nos.51635007&51705180)Hubei Province Technology Innovation Special Projects(2017AAA002)
文摘It is increasingly crucial for flexible electronics to efficiently and reliably peel large-area, ultra-thin flexible films off from rigid substrate serving as substrates of flexible electronics device, especially in industrial production. This paper experimentally investigated the mechanism and technologic characteristics of laser lift-off(LLO) process of ultra-thin(～ 2 μm) polyimide(PI)film. It was found increasingly difficult to obtain desirable ultra-thin PI film by LLO with the decrease of the film thickness. The optimal process parameters were achieved considering laser fluence and accumulated irradiation times(AIT), which were found to be strongly correlative to the thickness of PI film. The process mechanism of LLO of PI film was disclosed that laser ablation of interfacial PI will result in the formation of gas products between the PI and glass substrate, enabling the change of interface microstructures to reduce the interface bond strength. The amount of gas products mainly determines the result of LLO process for ultra-thin PI film, from residual adhesion to wrinkles or cracking. The strategy of multi-scanning based on multiple irradiations of low-energy laser pulses was presented to effectively achieve a reliable LLO process of ultra-thin PI film. This study provides an attractive route to optimize the LLO process for large-scale production of ultra-thin flexible electronics.
基金supported by the National Natural Science Foundation of China(Nos.50672079,60676027,60837001,60776007)the State Key Development Program for Basic Research of China(No.2007CB613404)+1 种基金the Natural Science Foundation of Fujian Province (No.2008J 0221)the Science and Technology Program of the Educational Office of Fujian Province(No.JB08215)
文摘A process methodology has been adopted to transfer GaN thin films grown on sapphire substrates to Si substrates using metal bonding and laser lift-off techniques. After bonding, a single KrF （248 nm） excimer laser pulse was directed through the transparent sapphire substrates followed by low-temperature heat treatment to remove the substrates. The influence of bonding temperature and energy density of the excimer laser on the structure and optical properties of GaN films were investigated systemically. Atomic force microscopy, X-ray diffraction and photoluminescence measurements showed that （1） the quality of the GaN film was higher at a lower bonding temperature and lower energy density; （2） the threshold of the energy density of the excimer laser lift-off GaN was 300 mJ/cm^2. The root-mean-square roughness of the transferred GaN surface was about 50 nm at a bonding temperature of 400 ℃.
文摘AZ15nXT is a chemically-amplified negative-tone thick film photoresist.The resist has vertical profile and is widely used for redistribution layer(RDL)and through silicon vias(TSV)applications.For lift-off applications,however,the inverted profile is needed.In this paper,we report the effects of process conditions on the resist profile and process window for lift off applications.
