A non-recessed-gate quasi-E-mode double heterojunction A1GaN/GaN high electron mobility transistor （quasi-E- DHEMT） with a thin barrier, high breakdown voltage and good performance of drain induced barrier lowering ...A non-recessed-gate quasi-E-mode double heterojunction A1GaN/GaN high electron mobility transistor （quasi-E- DHEMT） with a thin barrier, high breakdown voltage and good performance of drain induced barrier lowering （DIBL） was presented. Due to the metal organic chemical vapor deposition （MOCVD） grown 9-nm undoped A1GaN barrier, the effect that the gate metal depleted the two-dimensiomal electron gas （2DEG） was greatly impressed. Therefore, the density of carriers in the channel was nearly zero. Hence, the threshold voltage was above 0 V. Quasi-E-DHEMT with 4.1%tm source-to-drain distance, 2.6-μm gate-to-drain distance, and 0.5-μm gate length showed a drain current of 260 mA/mm. The threshold voltage of this device was 0.165 V when the drain voltage was 10 V and the DIBL was 5.26 mV/V. The quasi-E-DHEMT drain leakage current at a drain voltage of 146 V and a gate voltage of -6 V was below 1 mA/mm. This indicated that the hard breakdown voltage was more than 146 V.展开更多
By means of a coaxial apparatus, microsecond charging have been carried out with ferent ethylene glycol concentrations of ethylene pressurized water breakdown experiments with different surface roughness of electrodes...By means of a coaxial apparatus, microsecond charging have been carried out with ferent ethylene glycol concentrations of ethylene pressurized water breakdown experiments with different surface roughness of electrodes and difglycol/water mixture. The experimental results about the breakdown stress and the effective time are presented. The breakdown stress is normalized to the situation that the effective time is transformed to 1 μs and analyzed. The conclusions are as follows： （1） the breakdown stress formula is modified to E = 0.561MA^-1/10teff^-1/^NP^1/8 ;（2） the coefficient M is significantly increased by surface polishing and ethylene glycol additive; （3） it is accumulative for the capacity of improving electrical breakdown strength for surface polishing, ethylene glycol additive, and pressurization, of which pressurization is the most effective method; （4） the highest stress of 235.5 kV/cm is observed in ethylene glycol/water mixture with an ethylene glycol concentration of 80% at a hydrostatic pressure of 1215.9 kPa and is about one time greater than that in pure water at constant pressure; （5） for pressurization and surface polishing, the primary mechanism to improve the breakdown strength of water dielectric is the increase in the breakdown time delay. Research results indicate great potential in the application of the high power pulse conditioning system of water dielectric.展开更多
By means of a coaxial apparatus, high electrical breakdown experiments are carried out in the rest state and the low speed rolling state with microsecond charging and the experimental results are analyzed. The conclus...By means of a coaxial apparatus, high electrical breakdown experiments are carried out in the rest state and the low speed rolling state with microsecond charging and the experimental results are analyzed. The conclusions are： （1） the breakdown stress of water dielectric in the rolling state is in good agreement with that in Martin formula, and so is that in the rest state; （2） the breakdown stress of water dielectric in the rolling state is about 5% higher than that in the rest state; （3） the results simulated with ANSYS demonstrate that the breakdown stress of water dielectric decreases when the bubbles appear near the surface of electrodes; （4） the primary mechanism to increase the breakdown stress of water dielectric in the rolling state is that the bubbles are driven away and the number of bubbles near the surface of electrodes is decreased by rolling movement.展开更多
High-voltage thermal breakdown has great potential application in permeability enhancement of coal seam. The characteristics of the breakdown channel, coal element, porosity and microscopic coal petrography of coal un...High-voltage thermal breakdown has great potential application in permeability enhancement of coal seam. The characteristics of the breakdown channel, coal element, porosity and microscopic coal petrography of coal under high-voltage electric load were experimentally studied. The coal interior left apparent tracks due to electric current burning with high temperature. The percentage of C, O, Al, Fe, and Si had slightly decreased, while the content of element N increased obviously. Low-pressure nitrogen gas adsorption(LP-N_2GA) and mercury intrusion analysis showed that coal porosity increased. The increases of micropores and mesopores are beneficial to promotion of the ability of gas storage, and the increase of macropores could enhance the gas seepage and migration. The results of scanning electron microscope(SEM) show that there are many exogenous fractures in coal, which is also beneficial to gas seepage and migration. The results lay a theoretical foundation for application of high-voltage thermal breakdown in coal mines.展开更多
The evolution of euteelie carbide in as CaSl M2 high speed steeL was invesligated with hot compression test and metallographic examination. Initial rodlike or irregular eutectic carbides were broken into smaller parti...The evolution of euteelie carbide in as CaSl M2 high speed steeL was invesligated with hot compression test and metallographic examination. Initial rodlike or irregular eutectic carbides were broken into smaller particles during hot deformation by thermomechanical disintegration, while diffusion controlled phase transformation was not remarkable. Combining with numerical simulation, the relationship between breakdown ratio of carbide network and deformation parameters was obtained. Strain was the most important driving force to shatter euteclic carbides and disperse products. Furthermore, critical strain values were obtained, beyond which carbide network disappeared, and fractured carbides kept a stable profile and they were deformed with matrix coordinately. A higher temperature or lower strain rate resulted in a lower crilical strain.展开更多
Herein, the effect of high chloride ion(Cl^-) concentration on the corrosion behavior and passive film breakdown of 13Cr martensitic stainless steel under CO_2 environment was demonstrated. The Cl^- concentration was ...Herein, the effect of high chloride ion(Cl^-) concentration on the corrosion behavior and passive film breakdown of 13Cr martensitic stainless steel under CO_2 environment was demonstrated. The Cl^- concentration was varied from 30 to 150 g/L and cyclic potentiodynamic polarization was conducted to investigate the influence of the Cl^- concentration on the corrosion potential(E_(corr)), passive breakdown potential(E_(pit)), and repassivation potential(E_(rep)). The results of the polarization curves revealed that 13Cr stainless steel is susceptible to pitting under high Cl^- concentration. The passive breakdown potential and repassivation potential decreased with the increase of Cl-concentration. The semiconducting behavior of the passive film was investigated by Mott-Schottky analysis and the point defect model(PDM). It was observed that the iron cation vacancies and oxygen vacancies were continuously generated by autocatalytic reactions and the higher Cl^- concentration resulted in higher vacancies in the passive film. Once the excess vacancies condensed at the metal/film interface, the passive film became locally detached from the metal, which led to the breakdown of the passive film.展开更多
A novel A1GaN/GaN high electron mobility transistor （HEMT） with double buried p-type layers （DBPLs） in the GaN buffer layer and its mechanism are studied. The DBPL A1GaN/GaN HEMT is characterized by two equi-long ...A novel A1GaN/GaN high electron mobility transistor （HEMT） with double buried p-type layers （DBPLs） in the GaN buffer layer and its mechanism are studied. The DBPL A1GaN/GaN HEMT is characterized by two equi-long p-type GaN layers which are buried in the GaN buffer layer under the source side. Under the condition of high-voltage blocking state, two reverse p-n junctions introduced by the buried p-type layers will effectively modulate the surface and bulk electric fields. Meanwhile, the buffer leakage is well suppressed in this structure and both lead to a high breakdown voltage. The simulations show that the breakdown voltage of the DBPL structure can reach above 2000 V from 467 V of the conventional structure with the same gate-drain length of 8μm.展开更多
The critical electric fields of hot SF6 are calculated including both electron and ion kinetics in wide ranges of temperature and pressure, namely from 300 K up to 4000 K and 2 atmospheres up to 32 atmospheres respect...The critical electric fields of hot SF6 are calculated including both electron and ion kinetics in wide ranges of temperature and pressure, namely from 300 K up to 4000 K and 2 atmospheres up to 32 atmospheres respectively. Based on solving a multi-term electron Boltz- mann equation the calculations use improved electron-gas collision cross sections for twelve SF6 dissociation products with a particular emphasis on the electron-vibrating molecule interactions. The ion kinetics is also considered and its role on the critical field becomes non negligible as the temperature is above 2000 K. These critical fields are then used in hydrodynamics simulations which correctly predict the circuit breaker behaviours observed in the case of breaking tests.展开更多
The effects of gate length L_G on breakdown voltage VBRare investigated in AlGaN/GaN high-electron-mobility transistors（HEMTs） with L_G= 1 μm^20 μm. With the increase of L_G, VBRis first increased, and then satura...The effects of gate length L_G on breakdown voltage VBRare investigated in AlGaN/GaN high-electron-mobility transistors（HEMTs） with L_G= 1 μm^20 μm. With the increase of L_G, VBRis first increased, and then saturated at LG= 3 μm. For the HEMT with L_G= 1 μm, breakdown voltage VBRis 117 V, and it can be enhanced to 148 V for the HEMT with L-_G= 3 μm. The gate length of 3 μm can alleviate the buffer-leakage-induced impact ionization compared with the gate length of 1 μm, and the suppression of the impact ionization is the reason for improving the breakdown voltage.A similar suppression of the impact ionization exists in the HEMTs with LG〉 3 μm. As a result, there is no obvious difference in breakdown voltage among the HEMTs with LG= 3 μm^20 μm, and their breakdown voltages are in a range of 140 V–156 V.展开更多
The fluid model is proposed to investigate the gas breakdown driven by a short-pulse（such as a Gaussian pulse） highpower microwave at high pressures.However,the fluid model requires specification of the electron ene...The fluid model is proposed to investigate the gas breakdown driven by a short-pulse（such as a Gaussian pulse） highpower microwave at high pressures.However,the fluid model requires specification of the electron energy distribution function（EEDF）;the common assumption of a Maxwellian EEDF can result in the inaccurate breakdown prediction when the electrons are not in equilibrium.We confirm that the influence of the incident pulse shape on the EEDF is tiny at high pressures by using the particle-in-cell Monte Carlo collision（PIC-MCC） model.As a result,the EEDF for a rectangular microwave pulse directly derived from the Boltzmann equation solver Bolsig＋ is introduced into the fluid model for predicting the breakdown threshold of the non-rectangular pulse over a wide range of pressures,and the obtained results are very well matched with those of the PIC-MCC simulations.The time evolution of a non-rectangular pulse breakdown in gas,obtained by the fluid model with the EEDF from Bolsig＋,is presented and analyzed at different pressures.In addition,the effect of the incident pulse shape on the gas breakdown is discussed.展开更多
A new SOI power device with multi-region high-concentration fixed charge（MHFC） is reported. The MHFC is formed through implanting Cs or I ion into the buried oxide layer（BOX）, by which the high-concentration dynam...A new SOI power device with multi-region high-concentration fixed charge（MHFC） is reported. The MHFC is formed through implanting Cs or I ion into the buried oxide layer（BOX）, by which the high-concentration dynamic electrons and holes are induced at the top and bottom interfaces of BOX. The inversion holes can enhance the vertical electric field and raise the breakdown voltage since the drain bias is mainly generated from the BOX. A model of breakdown voltage is developed, from which the optimal spacing has also been obtained. The numerical results indicate that the breakdown voltage of device proposed is increased by 287% in comparison to that of conventional LDMOS.展开更多
A multi-deposition multi-annealing technique （MDMA） is introduced into the process of high-k/metal gate MOSFET for the gate last process to effectively reduce the gate leakage and improve the device＇s performance. ...A multi-deposition multi-annealing technique （MDMA） is introduced into the process of high-k/metal gate MOSFET for the gate last process to effectively reduce the gate leakage and improve the device＇s performance. In this paper, we systematically investigate the electrical parameters and the time-dependent dielectric breakdown （TDDB） characteristics of positive channel metal oxide semiconductor （PMOS） under different MDMA process conditions, including the depo- sition/annealing （D＆A） cycles, the D＆A time, and the total annealing time. The results show that the increases of the number of D＆A cycles （from 1 to 2） and D＆A time （from 15 s to 30 s） can contribute to the results that the gate leakage current decreases by about one order of magnitude and that the time to fail （TTF） at 63.2% increases by about several times. However, too many D＆A cycles （such as 4 cycles） make the equivalent oxide thickness （EOT） increase by about 1A and the TTF of PMOS worsen. Moreover, different D＆A times and numbers of D＆A cycles induce different breakdown mechanisms.展开更多
A new ultra-low specific on-resistance （Ron,sp） vertical double diffusion metal-oxide-semiconductor field-effect tran- sistor （VDMOS） with continuous electron accumulation （CEA） layer, denoted as CEA-VDMOS, is p...A new ultra-low specific on-resistance （Ron,sp） vertical double diffusion metal-oxide-semiconductor field-effect tran- sistor （VDMOS） with continuous electron accumulation （CEA） layer, denoted as CEA-VDMOS, is proposed and its new current transport mechanism is investigated. It features a trench gate directly extended to the drain, which includes two PN junctions. In on-state, the electron accumulation layers are formed along the sides of the extended gate and introduce two continuous low-resistance current paths from the source to the drain in a cell pitch. This mechanism not only dramatically reduces the Ron,sp but also makes the Ron,sp almost independent of the n-pillar doping concentration （Am）. In off-state, the depletion between the n-pillar and p-pillar within the extended trench gate increases the Nn, and further reduces the Ron,sp. Especially, the two PNjunctions within the trench gate support a high gate--drain voltage in the off-state and on-state, re- spectively. However, the extended gate increases the gate capacitance and thus weakens the dynamic performance to some extent. Therefore, the CEA-VDMOS is more suitable for low and medium frequencies application. Simulation indicates that the CEA-VDMOS reduces the Ron,sp by 80% compared with the conventional super-junction VDMOS （CSJ-VDMOS） at the same high breakdown voltage （BV）.展开更多
In this paper, a novel structure of a 4H-SiC lateral bipolar junction transistor （LBJT） with a base tield plate and double RESURF in the drift region is presented. Collector-base junction depletion extension in the ...In this paper, a novel structure of a 4H-SiC lateral bipolar junction transistor （LBJT） with a base tield plate and double RESURF in the drift region is presented. Collector-base junction depletion extension in the base region is restricted by the base field plate. Thin base as well as low base doping of the LBJT therefore can be achieved under the condition of avalanche breakdown. Simulation results show that thin base of 0.32 μm and base doping of 3 × 1017 cm 3 are obtained, and corresponding current gain is as high as 247 with avalanche breakdown voltage of 3309 V when the drift region length is 30 μm. Besides, an investigation of a 4H-SiC vertical BJT （VBJT） with comparable breakdown voltage （3357 V） shows that the minimum base width of 0.25 ~tm and base doping as high as 8 × 10^17 cm^-3 contribute to a maximum current gain of only 128.展开更多
A comparative investigation of the resistance and ability to trigger high voltage（HV） discharge for a single filament（SF） and multiple filaments（MFs） has been carried out.The experimental results show that the t...A comparative investigation of the resistance and ability to trigger high voltage（HV） discharge for a single filament（SF） and multiple filaments（MFs） has been carried out.The experimental results show that the trend of the breakdown threshold of the SF exactly follows that of its resistance,but this is not the case for the MF.The MF＇s resistance is much smaller than the SF＇s.However,the MF shows a slightly higher HV breakdown threshold than the SF.The underlying physics is that the measured resistance of the MF is collectively contributed by every filament in the MF while the HV breakdown threshold is determined by only one single discharging path.展开更多
An ultra-low specific on-resistance trench gate vertical double-diffused metal-oxide semiconductor with a high-k dielectric-filled extended trench（HK TG VDMOS） is proposed in this paper.The HK TG VDMOS features a hi...An ultra-low specific on-resistance trench gate vertical double-diffused metal-oxide semiconductor with a high-k dielectric-filled extended trench（HK TG VDMOS） is proposed in this paper.The HK TG VDMOS features a high-k（HK） trench below the trench gate.Firstly,the extended HK trench not only causes an assistant depletion of the n-drift region,but also optimizes the electric field,which therefore reduces Ron,sp and increases the breakdown voltage（BV）.Secondly,the extended HK trench weakens the sensitivity of BV to the n-drift doping concentration.Thirdly,compared with the superjunction（SJ） vertical double-diffused metal-oxide semiconductor（VDMOS）,the new device is simplified in fabrication by etching and filling the extended trench.The HK TG VDMOS with BV = 172 V and Ron,sp = 0.85 mΩ·cm2 is obtained by simulation;its Ron,sp is reduced by 67% and 40% and its BV is increased by about 15% and 5%,in comparison with those of the conventional trench gate VDMOS（TG VDMOS） and conventional superjunction trench gate VDMOS（SJ TG CDMOS）.展开更多
The air breakdown is easily caused by the high-power microwave, which can have two mutually orthogonal and heterophase electric field components. For this case, the electron momentum conservation equation is employed ...The air breakdown is easily caused by the high-power microwave, which can have two mutually orthogonal and heterophase electric field components. For this case, the electron momentum conservation equation is employed to deduce the electric field power and effective electric field for heating electrons. Then the formula of the electric field power is introduced into the global model to simulate the air breakdown. The breakdown prediction from the global model agrees well with the experimental data. Simulation results show that the electron temperature is sensitive to the phase difference between the two electron field components, while the latter can affect obviously the growth of the electron density at low electron temperature amplitudes. The ionization of nitrogen and oxygen induces the growth of electron density, and the density loss due to the dissociative attachment and dissociative recombination is obvious only at low electron temperatures.展开更多
This paper presents a new silicon-on-insulator(SOI) lateral-double-diffused metal-oxide-semiconductor transistor(LDMOST) device with alternated high-k dielectric and step doped silicon pillars(HKSD device). Due to the...This paper presents a new silicon-on-insulator(SOI) lateral-double-diffused metal-oxide-semiconductor transistor(LDMOST) device with alternated high-k dielectric and step doped silicon pillars(HKSD device). Due to the modulation of step doping technology and high-k dielectric on the electric field and doped profile of each zone, the HKSD device shows a greater performance. The analytical models of the potential, electric field, optimal breakdown voltage, and optimal doped profile are derived. The analytical results and the simulated results are basically consistent, which confirms the proposed model suitable for the HKSD device. The potential and electric field modulation mechanism are investigated based on the simulation and analytical models. Furthermore, the influence of the parameters on the breakdown voltage(BV) and specific on-resistance(R_(on,sp)) are obtained. The results indicate that the HKSD device has a higher BV and lower R_(on,sp) compared to the SD device and HK device.展开更多
We have demonstrated the first carrier density model for AlGaN channel with AlN buffer using spontaneous and piezoelectric polarization comparison with experimental and theoretical results. From the results we proved ...We have demonstrated the first carrier density model for AlGaN channel with AlN buffer using spontaneous and piezoelectric polarization comparison with experimental and theoretical results. From the results we proved that the formation of 2DEG in undoped structure relied both on spontaneous and piezoelectric polarization. The electron distribution of Al concentration (0 < x < 0.5) was measured for both AlGaN channel and barrier. Barrier thickness assumed between 20 and 25 nm for validating the experimental results. The carrier concentration was observed at the specific interface of the N- and Ga-face by assuming x1, x2 = 0. The model results are verified with previously reported experimental data.展开更多
A new analytical model of high voltage silicon on insulator （SOI） thin film devices is proposed, and a formula of silicon critical electric field is derived as a function of silicon film thickness by solving a 2D Po...A new analytical model of high voltage silicon on insulator （SOI） thin film devices is proposed, and a formula of silicon critical electric field is derived as a function of silicon film thickness by solving a 2D Poisson equation from an effective ionization rate, with a threshold energy taken into account for electron multiplying. Unlike a conventional silicon critical electric field that is constant and independent of silicon film thickness, the proposed silicon critical electric field increases sharply with silicon fihn thickness decreasing especially in the case of thin films, and can come to 141V/μm at a film thickness of 0.1 μm which is much larger than the normal value of about 30 V/μm. From the proposed formula of silicon critical electric field, the expressions of dielectric layer electric field and vertical breakdown voltage （VB,V） are obtained. Based on the model, an ultra thin film can be used to enhance dielectric layer electric field and so increase vertical breakdown voltage for SOI devices because of its high silicon critical electric field, and with a dielectric layer thickness of 2 μm the vertical breakdown voltages reach 852 and 300V for the silicon film thicknesses of 0.1 and 5μm, respectively. In addition, a relation between dielectric layer thickness and silicon film thickness is obtained, indicating a minimum vertical breakdown voltage that should be avoided when an SOI device is designed. 2D simulated results and some experimental results are in good agreement with analytical results.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.61334002)the Opening Project of Science and Technology on ReliabilityPhysics and Application Technology of Electronic Component Laboratory,China(Grant No.ZHD201206)
文摘A non-recessed-gate quasi-E-mode double heterojunction A1GaN/GaN high electron mobility transistor （quasi-E- DHEMT） with a thin barrier, high breakdown voltage and good performance of drain induced barrier lowering （DIBL） was presented. Due to the metal organic chemical vapor deposition （MOCVD） grown 9-nm undoped A1GaN barrier, the effect that the gate metal depleted the two-dimensiomal electron gas （2DEG） was greatly impressed. Therefore, the density of carriers in the channel was nearly zero. Hence, the threshold voltage was above 0 V. Quasi-E-DHEMT with 4.1%tm source-to-drain distance, 2.6-μm gate-to-drain distance, and 0.5-μm gate length showed a drain current of 260 mA/mm. The threshold voltage of this device was 0.165 V when the drain voltage was 10 V and the DIBL was 5.26 mV/V. The quasi-E-DHEMT drain leakage current at a drain voltage of 146 V and a gate voltage of -6 V was below 1 mA/mm. This indicated that the hard breakdown voltage was more than 146 V.
基金National 863 Project of China (No. 807-2020, 803-5051)
文摘By means of a coaxial apparatus, microsecond charging have been carried out with ferent ethylene glycol concentrations of ethylene pressurized water breakdown experiments with different surface roughness of electrodes and difglycol/water mixture. The experimental results about the breakdown stress and the effective time are presented. The breakdown stress is normalized to the situation that the effective time is transformed to 1 μs and analyzed. The conclusions are as follows： （1） the breakdown stress formula is modified to E = 0.561MA^-1/10teff^-1/^NP^1/8 ;（2） the coefficient M is significantly increased by surface polishing and ethylene glycol additive; （3） it is accumulative for the capacity of improving electrical breakdown strength for surface polishing, ethylene glycol additive, and pressurization, of which pressurization is the most effective method; （4） the highest stress of 235.5 kV/cm is observed in ethylene glycol/water mixture with an ethylene glycol concentration of 80% at a hydrostatic pressure of 1215.9 kPa and is about one time greater than that in pure water at constant pressure; （5） for pressurization and surface polishing, the primary mechanism to improve the breakdown strength of water dielectric is the increase in the breakdown time delay. Research results indicate great potential in the application of the high power pulse conditioning system of water dielectric.
基金supported by the National 863 Project of China(No. 807-2020, 803-5051)
文摘By means of a coaxial apparatus, high electrical breakdown experiments are carried out in the rest state and the low speed rolling state with microsecond charging and the experimental results are analyzed. The conclusions are： （1） the breakdown stress of water dielectric in the rolling state is in good agreement with that in Martin formula, and so is that in the rest state; （2） the breakdown stress of water dielectric in the rolling state is about 5% higher than that in the rest state; （3） the results simulated with ANSYS demonstrate that the breakdown stress of water dielectric decreases when the bubbles appear near the surface of electrodes; （4） the primary mechanism to increase the breakdown stress of water dielectric in the rolling state is that the bubbles are driven away and the number of bubbles near the surface of electrodes is decreased by rolling movement.
基金provided by the Scientific Research Foundation of the State Key Lab.of Coal Mine Disaster Dynamics and Control(No.2011DA105287-FW201509)the National Natural Science Foundation of China(No.51474211)the Innovation Team of CUMT(No.2014QN001)
文摘High-voltage thermal breakdown has great potential application in permeability enhancement of coal seam. The characteristics of the breakdown channel, coal element, porosity and microscopic coal petrography of coal under high-voltage electric load were experimentally studied. The coal interior left apparent tracks due to electric current burning with high temperature. The percentage of C, O, Al, Fe, and Si had slightly decreased, while the content of element N increased obviously. Low-pressure nitrogen gas adsorption(LP-N_2GA) and mercury intrusion analysis showed that coal porosity increased. The increases of micropores and mesopores are beneficial to promotion of the ability of gas storage, and the increase of macropores could enhance the gas seepage and migration. The results of scanning electron microscope(SEM) show that there are many exogenous fractures in coal, which is also beneficial to gas seepage and migration. The results lay a theoretical foundation for application of high-voltage thermal breakdown in coal mines.
基金Item Sponsored by National Key Basic Research and Development Program of China(2006CB705401)National Natural Science Foundation of China(50675133)
文摘The evolution of euteelie carbide in as CaSl M2 high speed steeL was invesligated with hot compression test and metallographic examination. Initial rodlike or irregular eutectic carbides were broken into smaller particles during hot deformation by thermomechanical disintegration, while diffusion controlled phase transformation was not remarkable. Combining with numerical simulation, the relationship between breakdown ratio of carbide network and deformation parameters was obtained. Strain was the most important driving force to shatter euteclic carbides and disperse products. Furthermore, critical strain values were obtained, beyond which carbide network disappeared, and fractured carbides kept a stable profile and they were deformed with matrix coordinately. A higher temperature or lower strain rate resulted in a lower crilical strain.
基金financially supported by the National Science and Technology Major Project of China (No. 2016ZX05028-004)
文摘Herein, the effect of high chloride ion(Cl^-) concentration on the corrosion behavior and passive film breakdown of 13Cr martensitic stainless steel under CO_2 environment was demonstrated. The Cl^- concentration was varied from 30 to 150 g/L and cyclic potentiodynamic polarization was conducted to investigate the influence of the Cl^- concentration on the corrosion potential(E_(corr)), passive breakdown potential(E_(pit)), and repassivation potential(E_(rep)). The results of the polarization curves revealed that 13Cr stainless steel is susceptible to pitting under high Cl^- concentration. The passive breakdown potential and repassivation potential decreased with the increase of Cl-concentration. The semiconducting behavior of the passive film was investigated by Mott-Schottky analysis and the point defect model(PDM). It was observed that the iron cation vacancies and oxygen vacancies were continuously generated by autocatalytic reactions and the higher Cl^- concentration resulted in higher vacancies in the passive film. Once the excess vacancies condensed at the metal/film interface, the passive film became locally detached from the metal, which led to the breakdown of the passive film.
基金Supported by the National Natural Science Foundation of China under Grant Nos 61334002,61106106,and 61204085the China Postdoctoral Science Foundation Funded Project under Grant No 2015M582610
文摘A novel A1GaN/GaN high electron mobility transistor （HEMT） with double buried p-type layers （DBPLs） in the GaN buffer layer and its mechanism are studied. The DBPL A1GaN/GaN HEMT is characterized by two equi-long p-type GaN layers which are buried in the GaN buffer layer under the source side. Under the condition of high-voltage blocking state, two reverse p-n junctions introduced by the buried p-type layers will effectively modulate the surface and bulk electric fields. Meanwhile, the buffer leakage is well suppressed in this structure and both lead to a high breakdown voltage. The simulations show that the breakdown voltage of the DBPL structure can reach above 2000 V from 467 V of the conventional structure with the same gate-drain length of 8μm.
文摘The critical electric fields of hot SF6 are calculated including both electron and ion kinetics in wide ranges of temperature and pressure, namely from 300 K up to 4000 K and 2 atmospheres up to 32 atmospheres respectively. Based on solving a multi-term electron Boltz- mann equation the calculations use improved electron-gas collision cross sections for twelve SF6 dissociation products with a particular emphasis on the electron-vibrating molecule interactions. The ion kinetics is also considered and its role on the critical field becomes non negligible as the temperature is above 2000 K. These critical fields are then used in hydrodynamics simulations which correctly predict the circuit breaker behaviours observed in the case of breaking tests.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61334002,61106106,and 61204085)
文摘The effects of gate length L_G on breakdown voltage VBRare investigated in AlGaN/GaN high-electron-mobility transistors（HEMTs） with L_G= 1 μm^20 μm. With the increase of L_G, VBRis first increased, and then saturated at LG= 3 μm. For the HEMT with L_G= 1 μm, breakdown voltage VBRis 117 V, and it can be enhanced to 148 V for the HEMT with L-_G= 3 μm. The gate length of 3 μm can alleviate the buffer-leakage-induced impact ionization compared with the gate length of 1 μm, and the suppression of the impact ionization is the reason for improving the breakdown voltage.A similar suppression of the impact ionization exists in the HEMTs with LG〉 3 μm. As a result, there is no obvious difference in breakdown voltage among the HEMTs with LG= 3 μm^20 μm, and their breakdown voltages are in a range of 140 V–156 V.
基金supported by the National Basic Research Program of China(Grant No.2013CB328904)the NSAF of China(Grant No.U1330109)2012 Doctoral Innovation Funds of Southwest Jiaotong University
文摘The fluid model is proposed to investigate the gas breakdown driven by a short-pulse（such as a Gaussian pulse） highpower microwave at high pressures.However,the fluid model requires specification of the electron energy distribution function（EEDF）;the common assumption of a Maxwellian EEDF can result in the inaccurate breakdown prediction when the electrons are not in equilibrium.We confirm that the influence of the incident pulse shape on the EEDF is tiny at high pressures by using the particle-in-cell Monte Carlo collision（PIC-MCC） model.As a result,the EEDF for a rectangular microwave pulse directly derived from the Boltzmann equation solver Bolsig＋ is introduced into the fluid model for predicting the breakdown threshold of the non-rectangular pulse over a wide range of pressures,and the obtained results are very well matched with those of the PIC-MCC simulations.The time evolution of a non-rectangular pulse breakdown in gas,obtained by the fluid model with the EEDF from Bolsig＋,is presented and analyzed at different pressures.In addition,the effect of the incident pulse shape on the gas breakdown is discussed.
基金supported by the State Key Laboratory of Electronic Thin Films and Integrated Devices of China(Grant No.KFJJ201205)the Department of Education Project of Guangxi Province,China(Grant No.201202ZD041)+1 种基金the Postdoctoral Science Foundation Project of China(Grant Nos.2012M521127 and2013T60566)the National Natural Science Foundation of China(Grant Nos.61361011,61274077,and 61464003)
文摘A new SOI power device with multi-region high-concentration fixed charge（MHFC） is reported. The MHFC is formed through implanting Cs or I ion into the buried oxide layer（BOX）, by which the high-concentration dynamic electrons and holes are induced at the top and bottom interfaces of BOX. The inversion holes can enhance the vertical electric field and raise the breakdown voltage since the drain bias is mainly generated from the BOX. A model of breakdown voltage is developed, from which the optimal spacing has also been obtained. The numerical results indicate that the breakdown voltage of device proposed is increased by 287% in comparison to that of conventional LDMOS.
基金supported by the National High Technology Research and Development Program of China(Grant No.SS2015AA010601)the National Natural Science Foundation of China(Grant Nos.61176091 and 61306129)
文摘A multi-deposition multi-annealing technique （MDMA） is introduced into the process of high-k/metal gate MOSFET for the gate last process to effectively reduce the gate leakage and improve the device＇s performance. In this paper, we systematically investigate the electrical parameters and the time-dependent dielectric breakdown （TDDB） characteristics of positive channel metal oxide semiconductor （PMOS） under different MDMA process conditions, including the depo- sition/annealing （D＆A） cycles, the D＆A time, and the total annealing time. The results show that the increases of the number of D＆A cycles （from 1 to 2） and D＆A time （from 15 s to 30 s） can contribute to the results that the gate leakage current decreases by about one order of magnitude and that the time to fail （TTF） at 63.2% increases by about several times. However, too many D＆A cycles （such as 4 cycles） make the equivalent oxide thickness （EOT） increase by about 1A and the TTF of PMOS worsen. Moreover, different D＆A times and numbers of D＆A cycles induce different breakdown mechanisms.
基金supported by the National Natural Science Foundation of China(Grant Nos.61176069 and 61376079)the Fundamental Research Funds for the Central Universities,China(Grant No.ZYGX2014Z006)
文摘A new ultra-low specific on-resistance （Ron,sp） vertical double diffusion metal-oxide-semiconductor field-effect tran- sistor （VDMOS） with continuous electron accumulation （CEA） layer, denoted as CEA-VDMOS, is proposed and its new current transport mechanism is investigated. It features a trench gate directly extended to the drain, which includes two PN junctions. In on-state, the electron accumulation layers are formed along the sides of the extended gate and introduce two continuous low-resistance current paths from the source to the drain in a cell pitch. This mechanism not only dramatically reduces the Ron,sp but also makes the Ron,sp almost independent of the n-pillar doping concentration （Am）. In off-state, the depletion between the n-pillar and p-pillar within the extended trench gate increases the Nn, and further reduces the Ron,sp. Especially, the two PNjunctions within the trench gate support a high gate--drain voltage in the off-state and on-state, re- spectively. However, the extended gate increases the gate capacitance and thus weakens the dynamic performance to some extent. Therefore, the CEA-VDMOS is more suitable for low and medium frequencies application. Simulation indicates that the CEA-VDMOS reduces the Ron,sp by 80% compared with the conventional super-junction VDMOS （CSJ-VDMOS） at the same high breakdown voltage （BV）.
基金supported by the Ministry of Education of China (Grant No. 20100101110056)the Natural Science Foundation for Distinguished Young Scholars of Zhejiang Province of China (Grant No. R1100468)
文摘In this paper, a novel structure of a 4H-SiC lateral bipolar junction transistor （LBJT） with a base tield plate and double RESURF in the drift region is presented. Collector-base junction depletion extension in the base region is restricted by the base field plate. Thin base as well as low base doping of the LBJT therefore can be achieved under the condition of avalanche breakdown. Simulation results show that thin base of 0.32 μm and base doping of 3 × 1017 cm 3 are obtained, and corresponding current gain is as high as 247 with avalanche breakdown voltage of 3309 V when the drift region length is 30 μm. Besides, an investigation of a 4H-SiC vertical BJT （VBJT） with comparable breakdown voltage （3357 V） shows that the minimum base width of 0.25 ~tm and base doping as high as 8 × 10^17 cm^-3 contribute to a maximum current gain of only 128.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 11074027,60978014,61178022,11274053,and 11211120156)the Funds from Sci. & Tech. Deparment of Jilin Province,China (Grant No. 20111812)
文摘A comparative investigation of the resistance and ability to trigger high voltage（HV） discharge for a single filament（SF） and multiple filaments（MFs） has been carried out.The experimental results show that the trend of the breakdown threshold of the SF exactly follows that of its resistance,but this is not the case for the MF.The MF＇s resistance is much smaller than the SF＇s.However,the MF shows a slightly higher HV breakdown threshold than the SF.The underlying physics is that the measured resistance of the MF is collectively contributed by every filament in the MF while the HV breakdown threshold is determined by only one single discharging path.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 60806025 and 61176069 )the Program for New Century Excellent Talents in University of Ministry of Education of China (Grant No. NCET-11-0062)
文摘An ultra-low specific on-resistance trench gate vertical double-diffused metal-oxide semiconductor with a high-k dielectric-filled extended trench（HK TG VDMOS） is proposed in this paper.The HK TG VDMOS features a high-k（HK） trench below the trench gate.Firstly,the extended HK trench not only causes an assistant depletion of the n-drift region,but also optimizes the electric field,which therefore reduces Ron,sp and increases the breakdown voltage（BV）.Secondly,the extended HK trench weakens the sensitivity of BV to the n-drift doping concentration.Thirdly,compared with the superjunction（SJ） vertical double-diffused metal-oxide semiconductor（VDMOS）,the new device is simplified in fabrication by etching and filling the extended trench.The HK TG VDMOS with BV = 172 V and Ron,sp = 0.85 mΩ·cm2 is obtained by simulation;its Ron,sp is reduced by 67% and 40% and its BV is increased by about 15% and 5%,in comparison with those of the conventional trench gate VDMOS（TG VDMOS） and conventional superjunction trench gate VDMOS（SJ TG CDMOS）.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61501358,61431010,and 61627901)the Fundamental Research Funds for the Central Universities,China
文摘The air breakdown is easily caused by the high-power microwave, which can have two mutually orthogonal and heterophase electric field components. For this case, the electron momentum conservation equation is employed to deduce the electric field power and effective electric field for heating electrons. Then the formula of the electric field power is introduced into the global model to simulate the air breakdown. The breakdown prediction from the global model agrees well with the experimental data. Simulation results show that the electron temperature is sensitive to the phase difference between the two electron field components, while the latter can affect obviously the growth of the electron density at low electron temperature amplitudes. The ionization of nitrogen and oxygen induces the growth of electron density, and the density loss due to the dissociative attachment and dissociative recombination is obvious only at low electron temperatures.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61704084 and 61874059)。
文摘This paper presents a new silicon-on-insulator(SOI) lateral-double-diffused metal-oxide-semiconductor transistor(LDMOST) device with alternated high-k dielectric and step doped silicon pillars(HKSD device). Due to the modulation of step doping technology and high-k dielectric on the electric field and doped profile of each zone, the HKSD device shows a greater performance. The analytical models of the potential, electric field, optimal breakdown voltage, and optimal doped profile are derived. The analytical results and the simulated results are basically consistent, which confirms the proposed model suitable for the HKSD device. The potential and electric field modulation mechanism are investigated based on the simulation and analytical models. Furthermore, the influence of the parameters on the breakdown voltage(BV) and specific on-resistance(R_(on,sp)) are obtained. The results indicate that the HKSD device has a higher BV and lower R_(on,sp) compared to the SD device and HK device.
文摘We have demonstrated the first carrier density model for AlGaN channel with AlN buffer using spontaneous and piezoelectric polarization comparison with experimental and theoretical results. From the results we proved that the formation of 2DEG in undoped structure relied both on spontaneous and piezoelectric polarization. The electron distribution of Al concentration (0 < x < 0.5) was measured for both AlGaN channel and barrier. Barrier thickness assumed between 20 and 25 nm for validating the experimental results. The carrier concentration was observed at the specific interface of the N- and Ga-face by assuming x1, x2 = 0. The model results are verified with previously reported experimental data.
基金Project supported by the National Natural Science Foundation of China (Grant No 60436030)National Laboratory of Analogue Integrated Circuits,China (Grant No 9140C090305060C09)
文摘A new analytical model of high voltage silicon on insulator （SOI） thin film devices is proposed, and a formula of silicon critical electric field is derived as a function of silicon film thickness by solving a 2D Poisson equation from an effective ionization rate, with a threshold energy taken into account for electron multiplying. Unlike a conventional silicon critical electric field that is constant and independent of silicon film thickness, the proposed silicon critical electric field increases sharply with silicon fihn thickness decreasing especially in the case of thin films, and can come to 141V/μm at a film thickness of 0.1 μm which is much larger than the normal value of about 30 V/μm. From the proposed formula of silicon critical electric field, the expressions of dielectric layer electric field and vertical breakdown voltage （VB,V） are obtained. Based on the model, an ultra thin film can be used to enhance dielectric layer electric field and so increase vertical breakdown voltage for SOI devices because of its high silicon critical electric field, and with a dielectric layer thickness of 2 μm the vertical breakdown voltages reach 852 and 300V for the silicon film thicknesses of 0.1 and 5μm, respectively. In addition, a relation between dielectric layer thickness and silicon film thickness is obtained, indicating a minimum vertical breakdown voltage that should be avoided when an SOI device is designed. 2D simulated results and some experimental results are in good agreement with analytical results.
