This paper details the design, simulation, and optimization of a low-impedance high repetition ra... more This paper details the design, simulation, and optimization of a low-impedance high repetition rate magnetically insulated transmission line oscillator (MILO) driven by a compact Marx generator. The project goals require the MILO to generate an radio frequency (RF) pulse within the S-band frequency range with a peak output power greater than 1 GW with greater than 10% efficiency. Its design is based on a set of base equation which provide critical component dimensions applied to a three-dimensional model constructed within CST studio suite used in a particle-in-cell (PIC) simulation. Additional to the geometric model, simulation of the MILO with non-ideal material properties and a lumped element modeling of the Marx generator were performed. The results of these simulations then informed changes to the model as to the optimizing performance of the device. Within the framework of the model, the final MILO design achieves the design goals with an approximate RF peak power of 4.5 GW at...
The use of nanosecond-duration-pulsed voltages with high-intensity electric fields (∼100 kV=cm) i... more The use of nanosecond-duration-pulsed voltages with high-intensity electric fields (∼100 kV=cm) is a promising development with many biomedical applications. Electroporation occurs in this regime, and has been attributed to the high fields. However, here we focus on temperature gradients. Our numerical simulations based on molecular dynamics predict the formation of nanopores and water nanowires, but only in the presence of a temperature gradient. Our results suggest a far greater role of temperature gradients in enhancing biophysical responses, including possible neural stimulation by infrared lasers.
Electric pulse driven membrane poration finds applications in the fields of biomedical engineerin... more Electric pulse driven membrane poration finds applications in the fields of biomedical engineering and drug/gene delivery. Here we focus on nanosecond, high-intensity electroporation and probe the role of pulse shape (e.g., monopolar-vs-bipolar), multiple electrode scenarios, and serial-versus-simultaneous pulsing, based on a three-dimensional time-dependent continuum model in a systematic fashion. Our results indicate that monopolar pulsing always leads to higher and stronger cellular uptake. This prediction is in agreement with experimental reports and observations. It is also demonstrated that multi-pronged electrode configurations influence and increase the degree of cellular uptake.
This contribution presents a model analysis for the initiation of explosive emission; a phenomena... more This contribution presents a model analysis for the initiation of explosive emission; a phenomena that is observed at cathode surfaces under high current densities. Here, localized heating is quantitatively evaluated on ultrashort time scales as a potential mechanism that initiates explosive emission, based on a two-temperature, relaxation time model. Our calculations demonstrate a strong production of nonequilibrium phonons, ultimately leading to localized melting. Temperatures are predicted to reach the cathode melting point over nanosecond times within the first few monolayers of the protrusion. This result is in keeping with the temporal scales observed experimentally for the initiation of explosive emission.
Experimental observation of photoionization capable extreme ultraviolet and vacuum ultraviolet em... more Experimental observation of photoionization capable extreme ultraviolet and vacuum ultraviolet emission from nanosecond timescale, developing low temperature plasmas (i.e. streamer discharges) in atmospheric air is presented. Applying short high voltage pulses enabled the observation of the onset of plasma formation exclusively by removing the external excitation before spark development was achieved. Contrary to the common assumption that radiative transitions from the b Π u 1 (Birge-Hopfield I) and b′ Σ + u 1 (Birge-Hopfield II) singlet states of N 2 are the primary contributors to photoionization events, these results indicate that radiative transitions from the c Σ ′ + u 4 1 (Carroll-Yoshino) singlet state of N 2 are dominant in developing low temperature plasmas in air. In addition to c ′ 4 transitions, photoionization capable transitions from atomic and singly ionized atomic oxygen were also observed. The inclusion of c Σ ′ + u 4 1 transitions into a statistical photoionization model coupled with a fluid model enabled streamer growth in the simulation of positive streamers.
Particle-in-cell simulations are performed to analyze the efficiency, output power and leakage cu... more Particle-in-cell simulations are performed to analyze the efficiency, output power and leakage currents in a 12-Cavity, 12-Cathode rising-sun magnetron with diffraction output (MDO). The central goal is to conduct a parameter study of a rising-sun magnetron that comprehensively incorporates performance enhancing features such as transparent cathodes, axial extraction, the use of endcaps, and cathode extensions. Our optimum results demonstrate peak output power of about 2.1 GW, with efficiencies of ∼70% and low leakage currents at a magnetic field of 0.45 Tesla, a 400 kV bias with a single endcap, for a range of cathode extensions between 3 and 6 centimeters.
Digest of Technical Papers. 12th IEEE International Pulsed Power Conference. (Cat. No.99CH36358)
Electron injection and the subsequent formation of a trap filled region leads to premature device... more Electron injection and the subsequent formation of a trap filled region leads to premature device failure in an opposed contact, EL2/carbon compensated GaAs photoconductive switch, made through the liquid encapsulated Czochralski process. Due to the electrostatic properties associated with a n +/semi-insulating junction, the introduction of a n+ region next to the cathode suppresses electron injection until higher bias. The doping level, length, and the thickness of the high n + region are some of the parameters that affect hold-off characteristics. Extending the length of the n + region well beyond the cathode does not increase the hold-off voltage but confines current flow to a narrow strip, which may trigger local heating burnout. Suppression of the effects of the EL2 traps at the n + /SI interface also does not improve the hold-off characteristics. Opposed contact switches, made from intrinsic GaAs have the characteristics of 'relaxation' semiconductors. The injection of minority carrier results in initial recombination and the formation of a large number of recombination regions may contribute to switching delays and jitters. 15. SUBJECT TERMS 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT SAR 18. NUMBER OF PAGES 4 19a. NAME OF RESPONSIBLE PERSON
The 31st IEEE International Conference on Plasma Science, 2004. ICOPS 2004. IEEE Conference Record - Abstracts.
Approved bw Ravindra P. Joshi (Member) Moimir Laroussi (Member) Reproduced with permission of the... more Approved bw Ravindra P. Joshi (Member) Moimir Laroussi (Member) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Analysis of the electrical double layer at the electrode-water interface for voltages close to th... more Analysis of the electrical double layer at the electrode-water interface for voltages close to the breakdown point has been carried out based on a static, Monte Carlo approach. It is shown that strong dipole realignment, ion-ion correlation, and finite-size effects can greatly modify the electric fields and local permittivity (hence, leading to optical structure) at the electrode interface. Dramatic enhancements of Schottky injection, providing a source for electronic controlled breakdown, are possible. It is also shown that large pressures associated with the Maxwell stress tensor would be created at the electrode boundaries. Our results depend on the ionic density, and are in keeping with recent observations. A simple, perturbative analysis shows that high field regions with a sharp variation in permittivity can potentially be critical spots for instability initiation. This suggests that the use of polished electrodes, or composite materials, or alternative nonpolar liquids might ...
Multipactor in a rectangular waveguide is studied using numerical simulations. Particular attenti... more Multipactor in a rectangular waveguide is studied using numerical simulations. Particular attention is given to the secondary electron emission characteristics including their energy spectrum (hence velocity spread) and angular distribution. Elastically scattered, rediffused and true secondary electrons are all comprehensively included based on the Furman-Pivi model [1] for the TE10 mode. The focus is on small waveguides and lowest order resonance conditions.
The behavior of the breakdown electric field versus frequency (DC to 100 MHz) for different gap l... more The behavior of the breakdown electric field versus frequency (DC to 100 MHz) for different gap lengths has been studied numerically at atmospheric pressure. Unlike previous reports, the focus here is on much larger gap lengths in the 1-5 cm range. A numerical analysis, with transport coefficients obtained from Monte Carlo calculations, is used to ascertain the electric field thresholds at which the growth and extinction of the electron population over time are balanced. Our analysis is indicative of a U-shaped frequency dependence, lower breakdown fields with increasing gap lengths, and trends qualitatively similar to the frequency-dependent field behavior for microgaps. The low frequency value of $34 kV/cm for a 1 cm gap approaches the reported DC Paschen limit.
Calculations of electron impact ionization of nitrogen gas at atmospheric pressure are presented ... more Calculations of electron impact ionization of nitrogen gas at atmospheric pressure are presented based on the kinetic Monte Carlo technique. The emphasis is on energy partitioning between primary and secondary electrons, and three different energy sharing schemes have been evaluated. The ionization behavior is based on Wannier's classical treatment. Our Monte Carlo results for the field-dependent drift velocities match the available experimental data. More interestingly, the field-dependent first Townsend coefficient predicted by the Monte Carlo calculations is shown to be in close agreement with reported data for E/N values ranging as high as 4000 Td, only when a random assignment of excess energies between the primary and secondary particles is used.
Erratum: "Spectroscopic ellipsometry-based study of optical properties of amorphous and crystalli... more Erratum: "Spectroscopic ellipsometry-based study of optical properties of amorphous and crystalline ZnSnO alloys and Zn 2 SnO 4 thin films grown using sputtering deposition: Dielectric function and subgap states" [
An electrical breakdown model for liquids in response to a submicrosecond (∼100ns) voltage pulse ... more An electrical breakdown model for liquids in response to a submicrosecond (∼100ns) voltage pulse is presented, and quantitative evaluations carried out. It is proposed that breakdown is initiated by field emission at the interface of pre-existing microbubbles. Impact ionization within the microbubble gas then contributes to plasma development, with cathode injection having a delayed and secondary role. Continuous field emission at the streamer tip contributes to filament growth and propagation. This model can adequately explain almost all of the experimentally observed features, including dendritic structures and fluctuations in the prebreakdown current. Two-dimensional, time-dependent simulations have been carried out based on a continuum model for water, though the results are quite general. Monte Carlo simulations provide the relevant transport parameters for our model. Our quantitative predictions match the available data quite well, including the breakdown delay times and obser...
Multipactor growth in rectangular waveguides is probed based on a kinetic approach. Unlike most s... more Multipactor growth in rectangular waveguides is probed based on a kinetic approach. Unlike most studies relying on the Vaughan model, a probabilitic approach for random multiple secondary particle emissions is used. Spread in electron emission velocities, the angular dependence of secondary emission yields, and an external radio frequency (RF) driving field due to a TE10 mode, were all built in. The calculations predict the secondary emission yield for copper, probe the population growth dynamics, and obtain the susceptibility diagram. Despite a maximum field at the waveguide center from the RF excitation, maximum electron densities are predicted at locations symmetrically displaced from the center. The secondary electron yield (SEY) characteristics, its local maxima, and the role of oblique incident angles, collectively lead to multipactor finding its place at off-center locations.
Time-dependent, two-dimensional, electrothermal simulations based on random Voronoi networks have... more Time-dependent, two-dimensional, electrothermal simulations based on random Voronoi networks have been developed to study the internal heating, current distributions and breakdown effects in ZnO varistors in response to high-voltage pulsing. The simulations allow for dynamic predictions of internal failures and to track the progression of hot-spots and thermal stresses. The focus is on internal grain-size variations and relative disorder including micropores. Our results predict that parameters such as the hold-off voltage, internal temperature, and average dissipated energy density would be higher with more uniform grains. This uniformity is also predicted to produce lower thermal stresses and to allow for the application of longer duration pulses. It is shown that the principal failure mechanism arises from internal localized melting, while thermal stresses are well below the thresholds for cracking. Finally, detrimental effects of micropores have been quantified and shown to be in agreement with experimental trends.
We report on the intensity-dependent behavior of the absorption coefficient (α) in semi-insulatin... more We report on the intensity-dependent behavior of the absorption coefficient (α) in semi-insulating 4H–SiC material. Data from as-received samples show a monotonic decrease in α with incident energy density, with a pronounced change in slope at around 10 mJ cm−2. Annealed samples, on the other hand, exhibit an experimental trend of increasing α with intensity. Qualitative explanation of the observed behavior is presented that probes the possible role of spontaneous and stimulated emission for as-received samples. With annealing, trap related recombination is strongly reduced leading to higher carrier densities and increased free-carrier absorption with incident intensity. The role of band-filling and permittivity changes are shown to be inconsequential, while changes in internal fields could contribute to decreases in absorption.
We focus on a simulation study to probe the mitigation of electric fields, especially at the edge... more We focus on a simulation study to probe the mitigation of electric fields, especially at the edges of metal contacts to SiC-based photoconductive switches. Field reduction becomes germane given that field-induced failures near contacts have been reported. A dual strategy of extending metal contacts to effectively spread the electric field over a larger distance and to employ HfO2 as a high-k dielectric, is discussed. Simulation results show that peak electric fields can be lowered by up to ~67% relative to a standard design. Finally, our calculations predict that the internal temperature rise for a ~7-ns laser pulse and applied voltages around 20 kV (typical experimental values) would also be effectively controlled.
This paper details the design, simulation, and optimization of a low-impedance high repetition ra... more This paper details the design, simulation, and optimization of a low-impedance high repetition rate magnetically insulated transmission line oscillator (MILO) driven by a compact Marx generator. The project goals require the MILO to generate an radio frequency (RF) pulse within the S-band frequency range with a peak output power greater than 1 GW with greater than 10% efficiency. Its design is based on a set of base equation which provide critical component dimensions applied to a three-dimensional model constructed within CST studio suite used in a particle-in-cell (PIC) simulation. Additional to the geometric model, simulation of the MILO with non-ideal material properties and a lumped element modeling of the Marx generator were performed. The results of these simulations then informed changes to the model as to the optimizing performance of the device. Within the framework of the model, the final MILO design achieves the design goals with an approximate RF peak power of 4.5 GW at...
The use of nanosecond-duration-pulsed voltages with high-intensity electric fields (∼100 kV=cm) i... more The use of nanosecond-duration-pulsed voltages with high-intensity electric fields (∼100 kV=cm) is a promising development with many biomedical applications. Electroporation occurs in this regime, and has been attributed to the high fields. However, here we focus on temperature gradients. Our numerical simulations based on molecular dynamics predict the formation of nanopores and water nanowires, but only in the presence of a temperature gradient. Our results suggest a far greater role of temperature gradients in enhancing biophysical responses, including possible neural stimulation by infrared lasers.
Electric pulse driven membrane poration finds applications in the fields of biomedical engineerin... more Electric pulse driven membrane poration finds applications in the fields of biomedical engineering and drug/gene delivery. Here we focus on nanosecond, high-intensity electroporation and probe the role of pulse shape (e.g., monopolar-vs-bipolar), multiple electrode scenarios, and serial-versus-simultaneous pulsing, based on a three-dimensional time-dependent continuum model in a systematic fashion. Our results indicate that monopolar pulsing always leads to higher and stronger cellular uptake. This prediction is in agreement with experimental reports and observations. It is also demonstrated that multi-pronged electrode configurations influence and increase the degree of cellular uptake.
This contribution presents a model analysis for the initiation of explosive emission; a phenomena... more This contribution presents a model analysis for the initiation of explosive emission; a phenomena that is observed at cathode surfaces under high current densities. Here, localized heating is quantitatively evaluated on ultrashort time scales as a potential mechanism that initiates explosive emission, based on a two-temperature, relaxation time model. Our calculations demonstrate a strong production of nonequilibrium phonons, ultimately leading to localized melting. Temperatures are predicted to reach the cathode melting point over nanosecond times within the first few monolayers of the protrusion. This result is in keeping with the temporal scales observed experimentally for the initiation of explosive emission.
Experimental observation of photoionization capable extreme ultraviolet and vacuum ultraviolet em... more Experimental observation of photoionization capable extreme ultraviolet and vacuum ultraviolet emission from nanosecond timescale, developing low temperature plasmas (i.e. streamer discharges) in atmospheric air is presented. Applying short high voltage pulses enabled the observation of the onset of plasma formation exclusively by removing the external excitation before spark development was achieved. Contrary to the common assumption that radiative transitions from the b Π u 1 (Birge-Hopfield I) and b′ Σ + u 1 (Birge-Hopfield II) singlet states of N 2 are the primary contributors to photoionization events, these results indicate that radiative transitions from the c Σ ′ + u 4 1 (Carroll-Yoshino) singlet state of N 2 are dominant in developing low temperature plasmas in air. In addition to c ′ 4 transitions, photoionization capable transitions from atomic and singly ionized atomic oxygen were also observed. The inclusion of c Σ ′ + u 4 1 transitions into a statistical photoionization model coupled with a fluid model enabled streamer growth in the simulation of positive streamers.
Particle-in-cell simulations are performed to analyze the efficiency, output power and leakage cu... more Particle-in-cell simulations are performed to analyze the efficiency, output power and leakage currents in a 12-Cavity, 12-Cathode rising-sun magnetron with diffraction output (MDO). The central goal is to conduct a parameter study of a rising-sun magnetron that comprehensively incorporates performance enhancing features such as transparent cathodes, axial extraction, the use of endcaps, and cathode extensions. Our optimum results demonstrate peak output power of about 2.1 GW, with efficiencies of ∼70% and low leakage currents at a magnetic field of 0.45 Tesla, a 400 kV bias with a single endcap, for a range of cathode extensions between 3 and 6 centimeters.
Digest of Technical Papers. 12th IEEE International Pulsed Power Conference. (Cat. No.99CH36358)
Electron injection and the subsequent formation of a trap filled region leads to premature device... more Electron injection and the subsequent formation of a trap filled region leads to premature device failure in an opposed contact, EL2/carbon compensated GaAs photoconductive switch, made through the liquid encapsulated Czochralski process. Due to the electrostatic properties associated with a n +/semi-insulating junction, the introduction of a n+ region next to the cathode suppresses electron injection until higher bias. The doping level, length, and the thickness of the high n + region are some of the parameters that affect hold-off characteristics. Extending the length of the n + region well beyond the cathode does not increase the hold-off voltage but confines current flow to a narrow strip, which may trigger local heating burnout. Suppression of the effects of the EL2 traps at the n + /SI interface also does not improve the hold-off characteristics. Opposed contact switches, made from intrinsic GaAs have the characteristics of 'relaxation' semiconductors. The injection of minority carrier results in initial recombination and the formation of a large number of recombination regions may contribute to switching delays and jitters. 15. SUBJECT TERMS 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT SAR 18. NUMBER OF PAGES 4 19a. NAME OF RESPONSIBLE PERSON
The 31st IEEE International Conference on Plasma Science, 2004. ICOPS 2004. IEEE Conference Record - Abstracts.
Approved bw Ravindra P. Joshi (Member) Moimir Laroussi (Member) Reproduced with permission of the... more Approved bw Ravindra P. Joshi (Member) Moimir Laroussi (Member) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Analysis of the electrical double layer at the electrode-water interface for voltages close to th... more Analysis of the electrical double layer at the electrode-water interface for voltages close to the breakdown point has been carried out based on a static, Monte Carlo approach. It is shown that strong dipole realignment, ion-ion correlation, and finite-size effects can greatly modify the electric fields and local permittivity (hence, leading to optical structure) at the electrode interface. Dramatic enhancements of Schottky injection, providing a source for electronic controlled breakdown, are possible. It is also shown that large pressures associated with the Maxwell stress tensor would be created at the electrode boundaries. Our results depend on the ionic density, and are in keeping with recent observations. A simple, perturbative analysis shows that high field regions with a sharp variation in permittivity can potentially be critical spots for instability initiation. This suggests that the use of polished electrodes, or composite materials, or alternative nonpolar liquids might ...
Multipactor in a rectangular waveguide is studied using numerical simulations. Particular attenti... more Multipactor in a rectangular waveguide is studied using numerical simulations. Particular attention is given to the secondary electron emission characteristics including their energy spectrum (hence velocity spread) and angular distribution. Elastically scattered, rediffused and true secondary electrons are all comprehensively included based on the Furman-Pivi model [1] for the TE10 mode. The focus is on small waveguides and lowest order resonance conditions.
The behavior of the breakdown electric field versus frequency (DC to 100 MHz) for different gap l... more The behavior of the breakdown electric field versus frequency (DC to 100 MHz) for different gap lengths has been studied numerically at atmospheric pressure. Unlike previous reports, the focus here is on much larger gap lengths in the 1-5 cm range. A numerical analysis, with transport coefficients obtained from Monte Carlo calculations, is used to ascertain the electric field thresholds at which the growth and extinction of the electron population over time are balanced. Our analysis is indicative of a U-shaped frequency dependence, lower breakdown fields with increasing gap lengths, and trends qualitatively similar to the frequency-dependent field behavior for microgaps. The low frequency value of $34 kV/cm for a 1 cm gap approaches the reported DC Paschen limit.
Calculations of electron impact ionization of nitrogen gas at atmospheric pressure are presented ... more Calculations of electron impact ionization of nitrogen gas at atmospheric pressure are presented based on the kinetic Monte Carlo technique. The emphasis is on energy partitioning between primary and secondary electrons, and three different energy sharing schemes have been evaluated. The ionization behavior is based on Wannier's classical treatment. Our Monte Carlo results for the field-dependent drift velocities match the available experimental data. More interestingly, the field-dependent first Townsend coefficient predicted by the Monte Carlo calculations is shown to be in close agreement with reported data for E/N values ranging as high as 4000 Td, only when a random assignment of excess energies between the primary and secondary particles is used.
Erratum: "Spectroscopic ellipsometry-based study of optical properties of amorphous and crystalli... more Erratum: "Spectroscopic ellipsometry-based study of optical properties of amorphous and crystalline ZnSnO alloys and Zn 2 SnO 4 thin films grown using sputtering deposition: Dielectric function and subgap states" [
An electrical breakdown model for liquids in response to a submicrosecond (∼100ns) voltage pulse ... more An electrical breakdown model for liquids in response to a submicrosecond (∼100ns) voltage pulse is presented, and quantitative evaluations carried out. It is proposed that breakdown is initiated by field emission at the interface of pre-existing microbubbles. Impact ionization within the microbubble gas then contributes to plasma development, with cathode injection having a delayed and secondary role. Continuous field emission at the streamer tip contributes to filament growth and propagation. This model can adequately explain almost all of the experimentally observed features, including dendritic structures and fluctuations in the prebreakdown current. Two-dimensional, time-dependent simulations have been carried out based on a continuum model for water, though the results are quite general. Monte Carlo simulations provide the relevant transport parameters for our model. Our quantitative predictions match the available data quite well, including the breakdown delay times and obser...
Multipactor growth in rectangular waveguides is probed based on a kinetic approach. Unlike most s... more Multipactor growth in rectangular waveguides is probed based on a kinetic approach. Unlike most studies relying on the Vaughan model, a probabilitic approach for random multiple secondary particle emissions is used. Spread in electron emission velocities, the angular dependence of secondary emission yields, and an external radio frequency (RF) driving field due to a TE10 mode, were all built in. The calculations predict the secondary emission yield for copper, probe the population growth dynamics, and obtain the susceptibility diagram. Despite a maximum field at the waveguide center from the RF excitation, maximum electron densities are predicted at locations symmetrically displaced from the center. The secondary electron yield (SEY) characteristics, its local maxima, and the role of oblique incident angles, collectively lead to multipactor finding its place at off-center locations.
Time-dependent, two-dimensional, electrothermal simulations based on random Voronoi networks have... more Time-dependent, two-dimensional, electrothermal simulations based on random Voronoi networks have been developed to study the internal heating, current distributions and breakdown effects in ZnO varistors in response to high-voltage pulsing. The simulations allow for dynamic predictions of internal failures and to track the progression of hot-spots and thermal stresses. The focus is on internal grain-size variations and relative disorder including micropores. Our results predict that parameters such as the hold-off voltage, internal temperature, and average dissipated energy density would be higher with more uniform grains. This uniformity is also predicted to produce lower thermal stresses and to allow for the application of longer duration pulses. It is shown that the principal failure mechanism arises from internal localized melting, while thermal stresses are well below the thresholds for cracking. Finally, detrimental effects of micropores have been quantified and shown to be in agreement with experimental trends.
We report on the intensity-dependent behavior of the absorption coefficient (α) in semi-insulatin... more We report on the intensity-dependent behavior of the absorption coefficient (α) in semi-insulating 4H–SiC material. Data from as-received samples show a monotonic decrease in α with incident energy density, with a pronounced change in slope at around 10 mJ cm−2. Annealed samples, on the other hand, exhibit an experimental trend of increasing α with intensity. Qualitative explanation of the observed behavior is presented that probes the possible role of spontaneous and stimulated emission for as-received samples. With annealing, trap related recombination is strongly reduced leading to higher carrier densities and increased free-carrier absorption with incident intensity. The role of band-filling and permittivity changes are shown to be inconsequential, while changes in internal fields could contribute to decreases in absorption.
We focus on a simulation study to probe the mitigation of electric fields, especially at the edge... more We focus on a simulation study to probe the mitigation of electric fields, especially at the edges of metal contacts to SiC-based photoconductive switches. Field reduction becomes germane given that field-induced failures near contacts have been reported. A dual strategy of extending metal contacts to effectively spread the electric field over a larger distance and to employ HfO2 as a high-k dielectric, is discussed. Simulation results show that peak electric fields can be lowered by up to ~67% relative to a standard design. Finally, our calculations predict that the internal temperature rise for a ~7-ns laser pulse and applied voltages around 20 kV (typical experimental values) would also be effectively controlled.
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