Effect of flip chip bonding parameters on microstructure at the interconnect interface and shear properties of 64.8Sn35.2Pb microbumps were investigated in this work.Results show that the main intermetallic compound(I...Effect of flip chip bonding parameters on microstructure at the interconnect interface and shear properties of 64.8Sn35.2Pb microbumps were investigated in this work.Results show that the main intermetallic compound(IMC)at the interconnect interface is(Ni,Cu)_(3)Sn_(4)phase,and meanwhile a small amount of(Cu,Ni)_(6)Sn_(5)phase with a size of 50−100 nm is formed around(Ni,Cu)_(3)Sn_(4)phase.The orientation relationship of[-1-56](Ni,Cu)_(3)Sn_(4)//[152](Cu,Ni)_(6)Sn_(5)and(601)(Ni,Cu)_(3)Sn_(4)//(-201)(Cu,Ni)_(6)Sn_(5)is found between these two phases,and the atomic matching at the interface of the two phases is low.The highest shear force of 77.3 gf is achieved in the 64.8Sn35.2Pb microbump at the peak temperature of 250℃and parameter V1 because dense IMCs and no cracks form at the interconnect interface.Two typical fracture modes of microbumps are determined as solder fracture and mixed fracture.The high thermal stress presenting in the thick IMCs layer induces crack initiation,and cracks propagate along theα/βphase boundaries in the Sn-Pb solder under shear force,leading to a mixed fracture mode in the microbumps.展开更多
Effects of ultrasonic bonding parameters on atomic diffusion, microstructure at the Al-Au interface, and shear strength of Al-Au ultrasonic bonding were investigated by the combining experiments and finite element (FE...Effects of ultrasonic bonding parameters on atomic diffusion, microstructure at the Al-Au interface, and shear strength of Al-Au ultrasonic bonding were investigated by the combining experiments and finite element (FE) simulation. The quantitative model of atomic diffusion, which is related to the ultrasonic bonding parameters, time and distance, is established to calculate the atomic diffusion of the Al-Au interface. The maximum relative error between the calculated and experimental fraction of Al atom is 7.35%, indicating high prediction accuracy of this model. During the process of ultrasonic bonding, Au8Al3 is the main intermetallic compound (IMC) at the Al-Au interface. With larger bonding forces, higher ultrasonic powers and longer bonding time, it is more difficult to remove the oxide particles from the Al-Au interface, which hinders the atomic diffusion. Therefore, the complicated stress state and the existence of oxide particles both promotes the formation of holes. The shear strength of Al-Au ultrasonic bonding increases with increasing bonding force, ultrasonic power and bonding time. However, combined with the presence of holes at especial parameters, the optimal ultrasonic bonding parameter is confirmed to be a bonding force of 23 gf, ultrasonic power of 75 mW and bonding time of 21 ms.展开更多
For large diameter radio telescope construction,it is essential to suppress radio frequency interference from various equipment.Considering that some electronic devices have extremely high electromagnetic compatibilit...For large diameter radio telescope construction,it is essential to suppress radio frequency interference from various equipment.Considering that some electronic devices have extremely high electromagnetic compatibility(EMC)requirements and are characterized by compact size and high integration,their EMC control poses significant technical challenges.To address these issues,this paper investigated the technical challenges involved in the EMC control process and performance measurement of small electronic devices.Based on the electromagnetic leakage mechanism of shielding protection and drawing upon engineering experience,a solution was proposed to replace the original shielding enclosure with an interface conversion board,and the window testing method was employed to measure the shielding effectiveness,resolving the technical issue of measuring the shielding performance of small-scale shielding enclosures.Furthermore,this methodology was applied to the EMC control process of actuators,such as EMC design,performance measurement,and optimization,which successfully addressed the EMC issues.The proposed method has further upgraded the EMC control process for large radio telescopes,effectively solving the EMC challenges posed by small electronic devices during the construction and operation of the telescope.展开更多
The reentry trajectory planning for hypersonic vehicles is critical and challenging in the presence of numerous nonlinear equations of motion and path constraints, as well as guaranteed satisfaction of accuracy in mee...The reentry trajectory planning for hypersonic vehicles is critical and challenging in the presence of numerous nonlinear equations of motion and path constraints, as well as guaranteed satisfaction of accuracy in meeting all the specified boundary conditions. In the last ten years, many researchers have investigated various strategies to generate a feasible or optimal constrained reentry trajectory for hypersonic vehicles. This paper briefly reviews the new research efforts to promote the capability of reentry trajectory planning. The progress of the onboard reentry trajectory planning, reentry trajectory optimization, and landing footprint is summarized. The main challenges of reentry trajectory planning for hypersonic vehicles are analyzed, focusing on the rapid reentry trajectory optimization, complex geographic constraints, and coop- erative strategies.展开更多
This paper reports that a 4H-SiC MESFET （Metal Semiconductor Field Effect Transistor） large signal drain current model based on physical expressions has been developed to be used in CAD tools. The form of drain curr...This paper reports that a 4H-SiC MESFET （Metal Semiconductor Field Effect Transistor） large signal drain current model based on physical expressions has been developed to be used in CAD tools. The form of drain current model is based on semi-empirical MESFET model, and all parameters in this model are determined by physical parameters of 4H-SiC MESFET. The verification of the present model embedded in CAD tools is made, which shows a good agreement with measured data of large signal DC I-V characteristics, PAE （power added efficiency）, output power and gain.展开更多
The effect of graphite surface modification on the thermal conductivity(TC) and bending strength of graphite flakes/Al composites(Gf/Al) prepared by gas pressure infiltration were investigated. Al3 Ni and Al4C3 phase ...The effect of graphite surface modification on the thermal conductivity(TC) and bending strength of graphite flakes/Al composites(Gf/Al) prepared by gas pressure infiltration were investigated. Al3 Ni and Al4C3 phase may form at the interface in Ni-coated Gf/Al and uncoated Gf/Al composites, respectively, while the Al-Cu compound cannot be observed in Cu-coated Gf/Al composites. The Cu and Ni coatings enhance TC and the bending strength of the composites in the meantime. TC of Cu-coated Gf/Al composites reach 515 Wm^-1·K^-1 with 75 vol% Gf, which are higher than that of Ni-coated Gf/Al. Meanwhile, due to Al3 Ni at the interface, the bending strength of Ni-coated Gf/Al composites are far more than those of the uncoated and Cu-coated Gf/Al with the same content of Gf. The results indicate that metal-coated Gf can effectively improve the interfacial bonding between Gf and Al.展开更多
Paint removal from steel structure is executed for shipyards of marine and offshore engineering.Due to environmental unfriendliness and unhealthy drawbacks of sand blasting technique, laser ablation technique is propo...Paint removal from steel structure is executed for shipyards of marine and offshore engineering.Due to environmental unfriendliness and unhealthy drawbacks of sand blasting technique, laser ablation technique is proposed as a substituting method.By absorbing high energy of the 1064 nm pulsed laser, the paint is vaporized quickly.The ablated debris is then collected by using a suction pump.Initial metal surface of the steel is exposed when laser beam irradiates perpendicularly and scans over it.The cleaned surface fulfills the requirements of surface preparation standards ISO 8501 of SA2.The adhesion is further characterized with pull-off test after carrying out painting with Jotamastic 87 aluminum paint.The repainting can be embedded onto the laser cleaned surface to bond much more tightly.The excellent adhesion strength of 20 MPa between repainted coating and the substrate is achieved, which is higher than what is required by shipyards applications.展开更多
Based on the heat diffusion equation of multilevel interconnects, a novel analytical thermal model for multilevel nano-scale interconnects considering the via effect is presented, which can compute quickly the tempera...Based on the heat diffusion equation of multilevel interconnects, a novel analytical thermal model for multilevel nano-scale interconnects considering the via effect is presented, which can compute quickly the temperature of multilevel interconnects, with substrate temperature given. Based on the proposed model and the 65 nm complementary metal oxide semiconductor （CMOS） process parameter, the temperature of nano-scale interconnects is computed. The computed results show that the via effect has a great effect on local interconnects, but the reduction of thermal conductivity has little effect on local interconnects. With the reduction of thermal conductivity or the increase of current density, however, the temperature of global interconnects rises greatly, which can result in a great deterioration in their performance. The proposed model can be applied to computer aided design （CAD） of very large-scale integrated circuits （VLSIs） in nano-scale technologies.展开更多
In the existing models of estimating the yield and critical area, the defect outline is usually assumed to be circular, but the observed real defect outlines are irregular in shape. In this paper, estimation of the yi...In the existing models of estimating the yield and critical area, the defect outline is usually assumed to be circular, but the observed real defect outlines are irregular in shape. In this paper, estimation of the yield and critical area is made using the Monte Carlo technique and the relationship between the errors of yield estimated by circular defect and the rectangle degree of the defect is analysed. The rectangular model of a real defect is presented, and the yield model is provided correspondingly. The models take into account an outline similar to that of an original defect, the characteristics of two-dimensional distribution of defects, the feature of a layout routing, and the character of yield estimation. In order to make the models practicable, the critical area computations related to rectangular defect and regular （vertical or horizontal） routing are discussed. The critical areas associated with rectangular defect and non- regular routing are developed also, based on the mathematical morphology. The experimental results show that the new yield model may predict the yield caused by real defects more accurately than the circular model. It is significant that the yield is accurately estimated using the proposed model for IC metals.展开更多
A semi-insulating layer is obtained in n-type 4H-SiC by vanadium-ion implantation. A little higher resistivity is obtained by increasing the annealing temperature from 1450 to 1650 ℃. The resistivity at room temperat...A semi-insulating layer is obtained in n-type 4H-SiC by vanadium-ion implantation. A little higher resistivity is obtained by increasing the annealing temperature from 1450 to 1650 ℃. The resistivity at room temperature is as high as 7.6 ×10^6 Ω. cm. Significant redistribution of vanadium is not observed even after 1650 ℃ annealing. Temperaturedependent resistivity and optical absorption of V-implanted samples are measured. The activation energy of vanadium acceptor level is observed to be at about Ec - 1.1 eV.展开更多
The effects of adding small amounts of cerium(Ce) to Sn-3.3 Ag-0.2 Cu-4.7 Bi solder on microstructure,wettability characteristic,interfacial morphology and the growth of interfacial intermetallic compound(IMC) during ...The effects of adding small amounts of cerium(Ce) to Sn-3.3 Ag-0.2 Cu-4.7 Bi solder on microstructure,wettability characteristic,interfacial morphology and the growth of interfacial intermetallic compound(IMC) during thermal cycling were investigated by optical microscopy(OM),scanning electron microscopy(SEM) and solderability tester.It is found that the p-Sn phase,Ag_(3)Sn phase and Cu6 Sn5 phase in the solder are refined and the wetting force increases.Ce is an active element;it more easily accumulates at the solder/flux interface in the molten state,which decreases the interfacial surface energy and reduces the driving force for IMC formation on Cu substrate;therefore,the thickness of IMC at the solder/Cu interface decreases when appropriate Ce was added into the solder.Moreover,the Ce-containing solders have lower growth rate of interfacial IMC than solders without Ce during the thermal cycling between-55 and 125℃.When the Ce content is 0.03 wt% in the Sn-3.3 Ag-0.2 Cu-4.7 Bi solder,the solder has the best wettability and the minimum growth rate of interfacial IMC layer.展开更多
In current critical area models, it is generally assumed the defect outlines are circular and the conductors to be rectangle or the merger of rectangles. However, real defects and conductors associated with optimal la...In current critical area models, it is generally assumed the defect outlines are circular and the conductors to be rectangle or the merger of rectangles. However, real defects and conductors associated with optimal layout design exhibit a great variety of shapes. Based on mathematical morphology, a new critical area model is presented, which can be used to estimate the critical area of short circuit, open circuit and pinhole. Based on the new model, the efficient validity check algorithms are explored to extract critical areas of short circuit, open circuit and pinhole from layouts. The results of experiment on an approximate layout of 4 × 4 shifts register show that the new model predicts the critical areas accurately. These results suggest that the proposed model and algorithm could provide new approaches for yield prediction.展开更多
Low Voltage Differential Signaling (LVDS) has become a popular choice for high-speed serial links to conquer the bandwidth bottleneck of intra-chip data transmission. This paper presents the design and the implementat...Low Voltage Differential Signaling (LVDS) has become a popular choice for high-speed serial links to conquer the bandwidth bottleneck of intra-chip data transmission. This paper presents the design and the implementation of LVDS Input/Output (I/O) interface circuits in a standard 0.18 μm CMOS technology using thick gate oxide devices (3.3 V), fully compatible with LVDS standard. In the proposed transmitter, a novel Common-Mode FeedBack (CMFB)circuit is utilized to keep the common-mode output voltage stable over Process, supply Voltage and Temperature (PVT) variations. Because there are no area greedy resistors in the CMFB circuitry, the disadvantage of large die area in existing transmitter structures is avoided. To obtain sufficient gain, the receiver consists of three am- plifying stages: a voltage amplifying stage, a transconductance amplifying stage, and a transimpedance amplifying stage. And to exclude inner nodes with high RC time constant, shunt-shunt negative feedback is introduced in the receiver. A novel active inductor shunt peaking structure is used in the receiver to fulfill the stringent requirements of high speed and wide Common-Mode Input Region (CMIR) without voltage gain, power dissipation and silicon area penalty. Simulation results show that data rates of 2 Gbps and 2.5 Gbps are achieved for the transmitter and receiver with power con- sumption of 13.2 mW and 8.3 mW respectively.展开更多
This paper proposes a reasonable radiation-resistant composite channel structure for In P HEMTs.The simulation results show that the composite channel structure has excellent electrical properties due to increased mod...This paper proposes a reasonable radiation-resistant composite channel structure for In P HEMTs.The simulation results show that the composite channel structure has excellent electrical properties due to increased modulation doping efficiency and carrier confinement.Moreover,the direct current(DC)and radio frequency(RF)characteristics and their reliability between the single channel structure and the composite channel structure after 75-ke V proton irradiation are compared in detail.The results show that the composite channel structure has excellent radiation tolerance.Mechanism analysis demonstrates that the composite channel structure weakens the carrier removal effect.This phenomenon can account for the increase of native carrier and the decrease of defect capture rate.展开更多
We demonstrate in-plane field-free-switching spin-orbit torque(SOT)magnetic tunnel junction(MTJ)devices that are capable of low switching current density,fast speed,high reliability,and,most importantly,manufactured u...We demonstrate in-plane field-free-switching spin-orbit torque(SOT)magnetic tunnel junction(MTJ)devices that are capable of low switching current density,fast speed,high reliability,and,most importantly,manufactured uniformly by the 200-mm-wafer platform.The performance of the devices is systematically studied,including their magnetic properties,switch-ing behaviors,endurance and data retention.The successful integration of SOT devices within the 200-mm-wafer manufactur-ing platform provides a feasible way to industrialize SOT MRAMs.It is expected to obtain excellent performance of the devices by further optimizing the MTJ film stacks and the corresponding fabrication processes in the future.展开更多
The electrochemical dissolution and passivation of laser additive manufactured Ti6Al4V were investigated through Tafel polarization,potentiostatic polarization and AC impedance measurements.The results show that the s...The electrochemical dissolution and passivation of laser additive manufactured Ti6Al4V were investigated through Tafel polarization,potentiostatic polarization and AC impedance measurements.The results show that the solution treatment−aging(STA)process aggravates the element micro-segregation compared to the annealing process,leading to varied Al and V contents of the phases from different samples.It is proven that either Al-rich or V-rich condition can highly affect the electrochemical dissolution behaviors due to thermodynamical instability caused by element segregation.The dissolution rate in the metastable passivation process is controlled by the stability of the produced film that is affected by phases distribution,especially the difficult-to-dissolve phase.And then,the dissolution rate of the phases in the transpassivation region is consistent with the rank in the activation process because the dense film is not capable of being produced.Compared to the annealed sample,the higher dissolution rate of the STA sample is beneficial to the electrochemical machining(ECM)of Ti6Al4V.展开更多
To reveal the internal physics of the low-temperature mobility of two-dimensional electron gas （2DEG） in Al- GaN/GaN heterostructures, we present a theoretical study of the strong dependence of 2DEG mobility on Al c...To reveal the internal physics of the low-temperature mobility of two-dimensional electron gas （2DEG） in Al- GaN/GaN heterostructures, we present a theoretical study of the strong dependence of 2DEG mobility on Al content and thickness of AlGaN barrier layer. The theoretical results are compared with one of the highest measured of 2DEG mobility reported for AlGaN/GaN heterostructures. The 2DEG mobility is modelled as a combined effect of the scat- tering mechanisms including acoustic deformation-potential, piezoelectric, ionized background donor, surface donor, dislocation, alloy disorder and interface roughness scattering. The analyses of the individual scattering processes show that the dominant scattering mechanisms are the alloy disorder scattering and the interface roughness scattering at low temperatures. The variation of 2DEG mobility with the barrier layer parameters results mainly from the change of 2DEG density and distribution. It is suggested that in AlGaN/GaN samples with a high Al content or a thick AlGaN layer, the interface roughness scattering may restrict the 2DEG mobility significantly, for the AlGaN/GaN interface roughness increases due to the stress accumulation in AlGaN layer.展开更多
In the GaN-based heterostructures, this paper reports that the strong electric fields induced by polarization effects at the structure boundaries complicate the electric-static equilibrium and the boundary conditions....In the GaN-based heterostructures, this paper reports that the strong electric fields induced by polarization effects at the structure boundaries complicate the electric-static equilibrium and the boundary conditions. The basic requirements of electric-static equilibrium for the heterostructure systems are discussed first, and it is deduced that in the application of the coupled Schroedinger-Poisson model to the heterostructures of electric static equilibrium state, zero external electric field guarantees the overall electric neutrality, and there is no need to introduce the charge balance equation. Then the relation between the screening of the polar charges in GaN-based heterostructures and the possible boundary conditions of the Poisson equation is analysed, it is shown that the various boundary conditions are equivalent to each other, and the surface charge, which can be used in studying the screening of the polar charges, can be precisely solved even if only the conduction band energy is correctly known at the surface. Finally, through the calculations on an AlGaN/GaN heterostructure with typical structure parameters by the coupled Schroedinger-Poisson model under the various boundary conditions, the correctness of the above analyses are validated.展开更多
Machine learning(ML)methods with good applicability to complex and highly nonlinear sequences have been attracting much attention in recent years for predictions of complicated mechanical properties of various materia...Machine learning(ML)methods with good applicability to complex and highly nonlinear sequences have been attracting much attention in recent years for predictions of complicated mechanical properties of various materials.As one of the widely known ML methods,back-propagation(BP)neural networks with and without optimization by genetic algorithm(GA)are also established for comparisons of time cost and prediction error.With the aim to further increase the prediction accuracy and efficiency,this paper proposes a long short-term memory(LSTM)networks model to predict the dynamic compressive performance of concrete-like materials at high strain rates.Dynamic explicit analysis is performed in the finite element(FE)software ABAQUS to simulate various waveforms in the split Hopkinson pressure bar(SHPB)experiments by applying different stress waves in the incident bar.The FE simulation accuracy is validated against SHPB experimental results from the viewpoint of dynamic increase factor.In order to cover more extensive loading scenarios,60 sets of FE simulations are conducted in this paper to generate three kinds of waveforms in the incident and transmission bars of SHPB experiments.By training the proposed three networks,the nonlinear mapping relations can be reasonably established between incident,reflect,and transmission waves.Statistical measures are used to quantify the network prediction accuracy,confirming that the predicted stress-strain curves of concrete-like materials at high strain rates by the proposed networks agree sufficiently with those by FE simulations.It is found that compared with BP network,the GA-BP network can effectively stabilize the network structure,indicating that the GA optimization improves the prediction accuracy of the SHPB dynamic responses by performing the crossover and mutation operations of weights and thresholds in the original BP network.By eliminating the long-time dependencies,the proposed LSTM network achieves better results than the BP and GA-BP networks,since smaller mean square error(MSE)and higher correlation coefficient are achieved.More importantly,the proposed LSTM algorithm,after the training process with a limited number of FE simulations,could replace the time-consuming and laborious FE pre-and post-processing and modelling.展开更多
It was reported by Shen et al that the two-dimensional electron gas （2DEG） in an AlGaN/AlN/GaN structure showed high density and improved mobility compared with an AlGaN/GaN structure, but the potential of the AlGaN...It was reported by Shen et al that the two-dimensional electron gas （2DEG） in an AlGaN/AlN/GaN structure showed high density and improved mobility compared with an AlGaN/GaN structure, but the potential of the AlGaN/AlN/GaN structure needs further exploration. By the self-consistent solving of one-dimensional Schroedinger- Poisson equations, theoretical investigation is carried out about the effects of donor density （0-1×10^19 cm^-3） and temperature （50-500 K） on the electron systems in the AlGaN/AlN/GaN and AlGaN/GaN structures. It is found that in the former structure, since the effective △Ec is larger, the efficiency with which the 2DEG absorbs the electrons originating from donor ionization is higher, the resistance to parallel conduction is stronger, and the deterioration of 2DEG mobility is slower as the donor density rises. When temperature rises, the three-dimensional properties of the whole electron system become prominent for both of the structures, but the stability of 2DEG is higher in the former structure, which is also ascribed to the larger effective △Ec. The Capacitance-Voltage （C - V） carrier density profiles at different temperatures are measured for two Schottky diodes on the considered heterostructure samples separately, showing obviously different 2DEG densities. And the temperature-dependent tendency of the experimental curves agrees well with our calculations.展开更多
基金Project(U2341254)supported by Ye Qisun Science Foundation of National Natural Science Foundation of ChinaProject(52475406)supported by the National Nature Science Foundation of ChinaProject(2024CY2-GJHX-32)supported by the Key R&D Program of Shaanxi Province,China。
文摘Effect of flip chip bonding parameters on microstructure at the interconnect interface and shear properties of 64.8Sn35.2Pb microbumps were investigated in this work.Results show that the main intermetallic compound(IMC)at the interconnect interface is(Ni,Cu)_(3)Sn_(4)phase,and meanwhile a small amount of(Cu,Ni)_(6)Sn_(5)phase with a size of 50−100 nm is formed around(Ni,Cu)_(3)Sn_(4)phase.The orientation relationship of[-1-56](Ni,Cu)_(3)Sn_(4)//[152](Cu,Ni)_(6)Sn_(5)and(601)(Ni,Cu)_(3)Sn_(4)//(-201)(Cu,Ni)_(6)Sn_(5)is found between these two phases,and the atomic matching at the interface of the two phases is low.The highest shear force of 77.3 gf is achieved in the 64.8Sn35.2Pb microbump at the peak temperature of 250℃and parameter V1 because dense IMCs and no cracks form at the interconnect interface.Two typical fracture modes of microbumps are determined as solder fracture and mixed fracture.The high thermal stress presenting in the thick IMCs layer induces crack initiation,and cracks propagate along theα/βphase boundaries in the Sn-Pb solder under shear force,leading to a mixed fracture mode in the microbumps.
基金Project(2022YFB3707201) supported by the National Key R&D Program of ChinaProject(U2341254) supported by the Ye Qisun Science Foundation of National Natural Science Foundation of China+1 种基金Projects(0604022GH0202143,0604022SH0201143) supported by the NPU Aoxiang Distinguished Young Scholars,ChinaProject supported by the Funding of Young Top-notch Talent of the National Ten Thousand Talent Program,China。
文摘Effects of ultrasonic bonding parameters on atomic diffusion, microstructure at the Al-Au interface, and shear strength of Al-Au ultrasonic bonding were investigated by the combining experiments and finite element (FE) simulation. The quantitative model of atomic diffusion, which is related to the ultrasonic bonding parameters, time and distance, is established to calculate the atomic diffusion of the Al-Au interface. The maximum relative error between the calculated and experimental fraction of Al atom is 7.35%, indicating high prediction accuracy of this model. During the process of ultrasonic bonding, Au8Al3 is the main intermetallic compound (IMC) at the Al-Au interface. With larger bonding forces, higher ultrasonic powers and longer bonding time, it is more difficult to remove the oxide particles from the Al-Au interface, which hinders the atomic diffusion. Therefore, the complicated stress state and the existence of oxide particles both promotes the formation of holes. The shear strength of Al-Au ultrasonic bonding increases with increasing bonding force, ultrasonic power and bonding time. However, combined with the presence of holes at especial parameters, the optimal ultrasonic bonding parameter is confirmed to be a bonding force of 23 gf, ultrasonic power of 75 mW and bonding time of 21 ms.
基金supported by the National Key Research and Development Program of China(grant No.2021YFC2203503)the Tianshan Talent Training Program(grant No.2023TSYCCX0042)+1 种基金the Scientific Instrument Developing Project of the Chinese Academy of Sciences(grant No.PTYQ2022YZZD01)Open Foundation of China-Belarus Belt and Road Joint Laboratory on Electromagnetic Environment Effect(grant No.2BKF2024031001)。
文摘For large diameter radio telescope construction,it is essential to suppress radio frequency interference from various equipment.Considering that some electronic devices have extremely high electromagnetic compatibility(EMC)requirements and are characterized by compact size and high integration,their EMC control poses significant technical challenges.To address these issues,this paper investigated the technical challenges involved in the EMC control process and performance measurement of small electronic devices.Based on the electromagnetic leakage mechanism of shielding protection and drawing upon engineering experience,a solution was proposed to replace the original shielding enclosure with an interface conversion board,and the window testing method was employed to measure the shielding effectiveness,resolving the technical issue of measuring the shielding performance of small-scale shielding enclosures.Furthermore,this methodology was applied to the EMC control process of actuators,such as EMC design,performance measurement,and optimization,which successfully addressed the EMC issues.The proposed method has further upgraded the EMC control process for large radio telescopes,effectively solving the EMC challenges posed by small electronic devices during the construction and operation of the telescope.
基金supported by the National Natural Science Foundation of China(6127334961203223+1 种基金61175109)the Innovation Foundation of BUAA for Ph.D.Graduates(YWF-14-YJSY-013)
文摘The reentry trajectory planning for hypersonic vehicles is critical and challenging in the presence of numerous nonlinear equations of motion and path constraints, as well as guaranteed satisfaction of accuracy in meeting all the specified boundary conditions. In the last ten years, many researchers have investigated various strategies to generate a feasible or optimal constrained reentry trajectory for hypersonic vehicles. This paper briefly reviews the new research efforts to promote the capability of reentry trajectory planning. The progress of the onboard reentry trajectory planning, reentry trajectory optimization, and landing footprint is summarized. The main challenges of reentry trajectory planning for hypersonic vehicles are analyzed, focusing on the rapid reentry trajectory optimization, complex geographic constraints, and coop- erative strategies.
文摘This paper reports that a 4H-SiC MESFET （Metal Semiconductor Field Effect Transistor） large signal drain current model based on physical expressions has been developed to be used in CAD tools. The form of drain current model is based on semi-empirical MESFET model, and all parameters in this model are determined by physical parameters of 4H-SiC MESFET. The verification of the present model embedded in CAD tools is made, which shows a good agreement with measured data of large signal DC I-V characteristics, PAE （power added efficiency）, output power and gain.
基金Funded by the Research Fund of the State Key Laboratory of Solidification Processing(NWPU),China(No.126-QP-2015).
文摘The effect of graphite surface modification on the thermal conductivity(TC) and bending strength of graphite flakes/Al composites(Gf/Al) prepared by gas pressure infiltration were investigated. Al3 Ni and Al4C3 phase may form at the interface in Ni-coated Gf/Al and uncoated Gf/Al composites, respectively, while the Al-Cu compound cannot be observed in Cu-coated Gf/Al composites. The Cu and Ni coatings enhance TC and the bending strength of the composites in the meantime. TC of Cu-coated Gf/Al composites reach 515 Wm^-1·K^-1 with 75 vol% Gf, which are higher than that of Ni-coated Gf/Al. Meanwhile, due to Al3 Ni at the interface, the bending strength of Ni-coated Gf/Al composites are far more than those of the uncoated and Cu-coated Gf/Al with the same content of Gf. The results indicate that metal-coated Gf can effectively improve the interfacial bonding between Gf and Al.
基金supported by the National Natural Science Foundation of China (U1609209)National Natural Science Foundation of China (61605162)+2 种基金NSFC-Liaoning Province united foundation (U1608259)National Natural Science Foundation of China (51501219)the financial support from the China Scholarship Council
文摘Paint removal from steel structure is executed for shipyards of marine and offshore engineering.Due to environmental unfriendliness and unhealthy drawbacks of sand blasting technique, laser ablation technique is proposed as a substituting method.By absorbing high energy of the 1064 nm pulsed laser, the paint is vaporized quickly.The ablated debris is then collected by using a suction pump.Initial metal surface of the steel is exposed when laser beam irradiates perpendicularly and scans over it.The cleaned surface fulfills the requirements of surface preparation standards ISO 8501 of SA2.The adhesion is further characterized with pull-off test after carrying out painting with Jotamastic 87 aluminum paint.The repainting can be embedded onto the laser cleaned surface to bond much more tightly.The excellent adhesion strength of 20 MPa between repainted coating and the substrate is achieved, which is higher than what is required by shipyards applications.
基金Project supported by the National Natural Science Foundation of China (Grant Nos 60676009 and 60725415)the National High Technology Research and Development Program of China (Grant Nos 2009AA01Z258 and 2009AA01Z260)
文摘Based on the heat diffusion equation of multilevel interconnects, a novel analytical thermal model for multilevel nano-scale interconnects considering the via effect is presented, which can compute quickly the temperature of multilevel interconnects, with substrate temperature given. Based on the proposed model and the 65 nm complementary metal oxide semiconductor （CMOS） process parameter, the temperature of nano-scale interconnects is computed. The computed results show that the via effect has a great effect on local interconnects, but the reduction of thermal conductivity has little effect on local interconnects. With the reduction of thermal conductivity or the increase of current density, however, the temperature of global interconnects rises greatly, which can result in a great deterioration in their performance. The proposed model can be applied to computer aided design （CAD） of very large-scale integrated circuits （VLSIs） in nano-scale technologies.
文摘In the existing models of estimating the yield and critical area, the defect outline is usually assumed to be circular, but the observed real defect outlines are irregular in shape. In this paper, estimation of the yield and critical area is made using the Monte Carlo technique and the relationship between the errors of yield estimated by circular defect and the rectangle degree of the defect is analysed. The rectangular model of a real defect is presented, and the yield model is provided correspondingly. The models take into account an outline similar to that of an original defect, the characteristics of two-dimensional distribution of defects, the feature of a layout routing, and the character of yield estimation. In order to make the models practicable, the critical area computations related to rectangular defect and regular （vertical or horizontal） routing are discussed. The critical areas associated with rectangular defect and non- regular routing are developed also, based on the mathematical morphology. The experimental results show that the new yield model may predict the yield caused by real defects more accurately than the circular model. It is significant that the yield is accurately estimated using the proposed model for IC metals.
基金Project supported by the National Natural Science Foundation of China （Grant No 60376001）, the National Basic Research Program of China （Grant No 2002CB311904） and the National Defense Basic Research Program of China （Grant No 51327020202）. Acknowledgments The authors would like to thank Li Cheng-Ji and Ye Xiao-Ling of Institute of Semiconductors, Chinese Academy of Sciences for measuring the temperaturedependent resistivity and absorption, respectively, and they also thank Ma Nong-Nong at the Centre of Electronic Materials Characterization of Tianjin Electronic Materials Research Institute for performing SIMS measurements.
文摘A semi-insulating layer is obtained in n-type 4H-SiC by vanadium-ion implantation. A little higher resistivity is obtained by increasing the annealing temperature from 1450 to 1650 ℃. The resistivity at room temperature is as high as 7.6 ×10^6 Ω. cm. Significant redistribution of vanadium is not observed even after 1650 ℃ annealing. Temperaturedependent resistivity and optical absorption of V-implanted samples are measured. The activation energy of vanadium acceptor level is observed to be at about Ec - 1.1 eV.
基金financially supported by the National Science and Technology Major Project of China(No.2011ZX02607)。
文摘The effects of adding small amounts of cerium(Ce) to Sn-3.3 Ag-0.2 Cu-4.7 Bi solder on microstructure,wettability characteristic,interfacial morphology and the growth of interfacial intermetallic compound(IMC) during thermal cycling were investigated by optical microscopy(OM),scanning electron microscopy(SEM) and solderability tester.It is found that the p-Sn phase,Ag_(3)Sn phase and Cu6 Sn5 phase in the solder are refined and the wetting force increases.Ce is an active element;it more easily accumulates at the solder/flux interface in the molten state,which decreases the interfacial surface energy and reduces the driving force for IMC formation on Cu substrate;therefore,the thickness of IMC at the solder/Cu interface decreases when appropriate Ce was added into the solder.Moreover,the Ce-containing solders have lower growth rate of interfacial IMC than solders without Ce during the thermal cycling between-55 and 125℃.When the Ce content is 0.03 wt% in the Sn-3.3 Ag-0.2 Cu-4.7 Bi solder,the solder has the best wettability and the minimum growth rate of interfacial IMC layer.
文摘In current critical area models, it is generally assumed the defect outlines are circular and the conductors to be rectangle or the merger of rectangles. However, real defects and conductors associated with optimal layout design exhibit a great variety of shapes. Based on mathematical morphology, a new critical area model is presented, which can be used to estimate the critical area of short circuit, open circuit and pinhole. Based on the new model, the efficient validity check algorithms are explored to extract critical areas of short circuit, open circuit and pinhole from layouts. The results of experiment on an approximate layout of 4 × 4 shifts register show that the new model predicts the critical areas accurately. These results suggest that the proposed model and algorithm could provide new approaches for yield prediction.
文摘Low Voltage Differential Signaling (LVDS) has become a popular choice for high-speed serial links to conquer the bandwidth bottleneck of intra-chip data transmission. This paper presents the design and the implementation of LVDS Input/Output (I/O) interface circuits in a standard 0.18 μm CMOS technology using thick gate oxide devices (3.3 V), fully compatible with LVDS standard. In the proposed transmitter, a novel Common-Mode FeedBack (CMFB)circuit is utilized to keep the common-mode output voltage stable over Process, supply Voltage and Temperature (PVT) variations. Because there are no area greedy resistors in the CMFB circuitry, the disadvantage of large die area in existing transmitter structures is avoided. To obtain sufficient gain, the receiver consists of three am- plifying stages: a voltage amplifying stage, a transconductance amplifying stage, and a transimpedance amplifying stage. And to exclude inner nodes with high RC time constant, shunt-shunt negative feedback is introduced in the receiver. A novel active inductor shunt peaking structure is used in the receiver to fulfill the stringent requirements of high speed and wide Common-Mode Input Region (CMIR) without voltage gain, power dissipation and silicon area penalty. Simulation results show that data rates of 2 Gbps and 2.5 Gbps are achieved for the transmitter and receiver with power con- sumption of 13.2 mW and 8.3 mW respectively.
基金the National Natural Science Foundation of China(Grant No.11775191)the Natural Science Foundation of Henan Province,China(Grant No.202300410379)+2 种基金the Promotion Funding for Excellent Young Backbone Teacher of Henan Province,China(Grant No.2019GGJS017)Key Technologies Research and Development Program of Henan Province,China(Grant No.202102210321)the Promotion Project for Physics Discipline in Zhengzhou University,China(Grant No.2018WLTJ01)。
文摘This paper proposes a reasonable radiation-resistant composite channel structure for In P HEMTs.The simulation results show that the composite channel structure has excellent electrical properties due to increased modulation doping efficiency and carrier confinement.Moreover,the direct current(DC)and radio frequency(RF)characteristics and their reliability between the single channel structure and the composite channel structure after 75-ke V proton irradiation are compared in detail.The results show that the composite channel structure has excellent radiation tolerance.Mechanism analysis demonstrates that the composite channel structure weakens the carrier removal effect.This phenomenon can account for the increase of native carrier and the decrease of defect capture rate.
基金supported by the National Key Research and Development Program of China(Grant Nos.2021YFB3601303,2021YFB3601304,2021YFB3601300)National Natural Science Foundation of China(Nos.62001014 and 62171013)。
文摘We demonstrate in-plane field-free-switching spin-orbit torque(SOT)magnetic tunnel junction(MTJ)devices that are capable of low switching current density,fast speed,high reliability,and,most importantly,manufactured uniformly by the 200-mm-wafer platform.The performance of the devices is systematically studied,including their magnetic properties,switch-ing behaviors,endurance and data retention.The successful integration of SOT devices within the 200-mm-wafer manufactur-ing platform provides a feasible way to industrialize SOT MRAMs.It is expected to obtain excellent performance of the devices by further optimizing the MTJ film stacks and the corresponding fabrication processes in the future.
基金The authors are grateful for the financial supports from the project of Ministry of Industry and Information Technology of China(No.2019-00899-1-1)the Natural Science Foundation of Shaanxi Province,China(No.2021JM-060)Fundamental Research Funds for the Central Universities,China(No.3102019QD0409).
文摘The electrochemical dissolution and passivation of laser additive manufactured Ti6Al4V were investigated through Tafel polarization,potentiostatic polarization and AC impedance measurements.The results show that the solution treatment−aging(STA)process aggravates the element micro-segregation compared to the annealing process,leading to varied Al and V contents of the phases from different samples.It is proven that either Al-rich or V-rich condition can highly affect the electrochemical dissolution behaviors due to thermodynamical instability caused by element segregation.The dissolution rate in the metastable passivation process is controlled by the stability of the produced film that is affected by phases distribution,especially the difficult-to-dissolve phase.And then,the dissolution rate of the phases in the transpassivation region is consistent with the rank in the activation process because the dense film is not capable of being produced.Compared to the annealed sample,the higher dissolution rate of the STA sample is beneficial to the electrochemical machining(ECM)of Ti6Al4V.
基金supported by the Key Program of the National Natural Science Foundation of China (Grant No 60736033)Xi’an Applied Materials Innovation Fund of China (Grant No XA-AM-200703)the Open Fund of Key Laboratory of Wide Bandgap Semiconductors Material and Devices,Ministry of Education,China
文摘To reveal the internal physics of the low-temperature mobility of two-dimensional electron gas （2DEG） in Al- GaN/GaN heterostructures, we present a theoretical study of the strong dependence of 2DEG mobility on Al content and thickness of AlGaN barrier layer. The theoretical results are compared with one of the highest measured of 2DEG mobility reported for AlGaN/GaN heterostructures. The 2DEG mobility is modelled as a combined effect of the scat- tering mechanisms including acoustic deformation-potential, piezoelectric, ionized background donor, surface donor, dislocation, alloy disorder and interface roughness scattering. The analyses of the individual scattering processes show that the dominant scattering mechanisms are the alloy disorder scattering and the interface roughness scattering at low temperatures. The variation of 2DEG mobility with the barrier layer parameters results mainly from the change of 2DEG density and distribution. It is suggested that in AlGaN/GaN samples with a high Al content or a thick AlGaN layer, the interface roughness scattering may restrict the 2DEG mobility significantly, for the AlGaN/GaN interface roughness increases due to the stress accumulation in AlGaN layer.
文摘In the GaN-based heterostructures, this paper reports that the strong electric fields induced by polarization effects at the structure boundaries complicate the electric-static equilibrium and the boundary conditions. The basic requirements of electric-static equilibrium for the heterostructure systems are discussed first, and it is deduced that in the application of the coupled Schroedinger-Poisson model to the heterostructures of electric static equilibrium state, zero external electric field guarantees the overall electric neutrality, and there is no need to introduce the charge balance equation. Then the relation between the screening of the polar charges in GaN-based heterostructures and the possible boundary conditions of the Poisson equation is analysed, it is shown that the various boundary conditions are equivalent to each other, and the surface charge, which can be used in studying the screening of the polar charges, can be precisely solved even if only the conduction band energy is correctly known at the surface. Finally, through the calculations on an AlGaN/GaN heterostructure with typical structure parameters by the coupled Schroedinger-Poisson model under the various boundary conditions, the correctness of the above analyses are validated.
基金supported by the National Natural Science Foundation of China (No. 52175148)the Natural Science Foundation of Shaanxi Province (No. 2021KW-25)+1 种基金the Open Cooperation Innovation Fund of Xi’an Modern Chemistry Research Institute (No. SYJJ20210409)the Fundamental Research Funds for the Central Universities (No. 3102018ZY015)
文摘Machine learning(ML)methods with good applicability to complex and highly nonlinear sequences have been attracting much attention in recent years for predictions of complicated mechanical properties of various materials.As one of the widely known ML methods,back-propagation(BP)neural networks with and without optimization by genetic algorithm(GA)are also established for comparisons of time cost and prediction error.With the aim to further increase the prediction accuracy and efficiency,this paper proposes a long short-term memory(LSTM)networks model to predict the dynamic compressive performance of concrete-like materials at high strain rates.Dynamic explicit analysis is performed in the finite element(FE)software ABAQUS to simulate various waveforms in the split Hopkinson pressure bar(SHPB)experiments by applying different stress waves in the incident bar.The FE simulation accuracy is validated against SHPB experimental results from the viewpoint of dynamic increase factor.In order to cover more extensive loading scenarios,60 sets of FE simulations are conducted in this paper to generate three kinds of waveforms in the incident and transmission bars of SHPB experiments.By training the proposed three networks,the nonlinear mapping relations can be reasonably established between incident,reflect,and transmission waves.Statistical measures are used to quantify the network prediction accuracy,confirming that the predicted stress-strain curves of concrete-like materials at high strain rates by the proposed networks agree sufficiently with those by FE simulations.It is found that compared with BP network,the GA-BP network can effectively stabilize the network structure,indicating that the GA optimization improves the prediction accuracy of the SHPB dynamic responses by performing the crossover and mutation operations of weights and thresholds in the original BP network.By eliminating the long-time dependencies,the proposed LSTM network achieves better results than the BP and GA-BP networks,since smaller mean square error(MSE)and higher correlation coefficient are achieved.More importantly,the proposed LSTM algorithm,after the training process with a limited number of FE simulations,could replace the time-consuming and laborious FE pre-and post-processing and modelling.
文摘It was reported by Shen et al that the two-dimensional electron gas （2DEG） in an AlGaN/AlN/GaN structure showed high density and improved mobility compared with an AlGaN/GaN structure, but the potential of the AlGaN/AlN/GaN structure needs further exploration. By the self-consistent solving of one-dimensional Schroedinger- Poisson equations, theoretical investigation is carried out about the effects of donor density （0-1×10^19 cm^-3） and temperature （50-500 K） on the electron systems in the AlGaN/AlN/GaN and AlGaN/GaN structures. It is found that in the former structure, since the effective △Ec is larger, the efficiency with which the 2DEG absorbs the electrons originating from donor ionization is higher, the resistance to parallel conduction is stronger, and the deterioration of 2DEG mobility is slower as the donor density rises. When temperature rises, the three-dimensional properties of the whole electron system become prominent for both of the structures, but the stability of 2DEG is higher in the former structure, which is also ascribed to the larger effective △Ec. The Capacitance-Voltage （C - V） carrier density profiles at different temperatures are measured for two Schottky diodes on the considered heterostructure samples separately, showing obviously different 2DEG densities. And the temperature-dependent tendency of the experimental curves agrees well with our calculations.
