| Nowadays,circuit systems are under growing threats of strong electromagnetic interference.The strong electromagnetic interference source can be generated outside the circuit systems,such as the wireless communication equipment in the civil field and the high-power microwave weapons in the military field.Moreover,electromagnetic interference can also be generated by the high-frequency devices inside the circuit systems.Strong electromagnetic interference can result in strong electromagnetic effects.As a result,the semiconductor devices in the circuit will be temporarily or permanently fail due to semiconductor junction breakdown,temperature rise,etc.Therefore,it is of great significance to study the strong electromagnetic effects of circuit systems.In addition to experimental analysis,numerical simulation is an effective and essential way to study the strong electromagnetic effects of circuit systems.However,two key problems must be solved in the simulation of the strong electromagnetic effects of circuit systems:Firstly,the nonlinear electrical characteristics of semiconductor devices are critical for circuit system performance,so it is necessary to accurately characterize the nonlinear electrical characteristics of semiconductor devices under strong electromagnetic interference.For a long time,the equivalent circuit model of semiconductor devices is widely used in circuit simulation.But when simulating the strong electromagnetic effects,the following problems exist:(1)in general,the semiconductor manufacturers only provide the equivalent circuit model of semiconductor devices under normal-working conditions.The lack of the corresponding large-signal equivalent circuit model leads to the large calculation error and even wrong results;(2)due to the lack of a corresponding equivalent circuit model,it is impossible to simulate the strong electromagnetic effects such as the burndown and breakdown of semiconductor devices;(3)the equivalent circuit model conceals the internal physical process of the device,which cannot be used to analyze the physical mechanisms of the strong electromagnetic effects of circuit systems.Secondly,the physical processes of the strong electromagnetic effects include the propagation and coupling of electromagnetic waves and the nonlinear response of the lumped circuit.Hence,the simulation cannot be completed by the electromagnetic simulation or the circuit simulation alone.Instead,the field-circuit hybrid method is widely used to analyze the strong electromagnetic effects of the circuit systems.Moreover,the semiconductor device physical model-based circuit simulation method solves the semiconductor equations and Kirchhoff’s circuit equation,which can characterize the nonlinear electrical characteristics of semiconductor devices under strong electromagnetic interference.However,the lack of electromagnetic simulation cannot characterize the transmission and coupling of electromagnetic energy in the electromagnetic distribution structure,including air space,the circuit substrate,the cable,and the via,etc.To solve the above problems,our research team proposed a physical model-based multi-physics simulation method in the previous work.In the proposed method,based on the finite-difference time-domain(FDTD)field-circuit hybrid method,the physical model is adopted to model the semiconductor devices.Maxwell’s equations,Kirchhoff equations,and the physical equations of semiconductor devices are coupled and numerically solved.Therefore,when simulating the strong electromagnetic effect of the circuit systems,the method can characterize the critical physical processes,including the propagation and coupling of electromagnetic waves,and the large-signal nonlinear characteristics of semiconductor devices.However,this method still has some shortcomings:(1)when the physical model of semiconductor devices is used to characterize the device damage characteristics,it lacks the characterization of the high-electric field and high-temperature physical effects,such as the impact ionization of carriers and the saturation effect of drift velocity;(2)it is an urgent problem to obtain accurate physical model parameters of the semiconductor devices.To solve the above problems,this thesis studied the multi-physics simulation of the strong electromagnetic effects of the circuit systems based on the previous work of our team.In terms of theory,the physical model-based multi-physics simulation method is improved by adding the characterization of the high-electric field and high-temperature physical effects of devices.Moreover,by analyzing the relationship between carrier motion characteristics and the working frequency,a physical model parameters extraction method for semiconductor devices is proposed.This method can be applied to the precise simulation of semiconductor devices from DC(direct current)to microwave frequencies.In terms of application,two typical application examples are studied by using the multi-physics simulation.Taking the PIN diode limiter as a typical example,the damage effects under the electromagnetic pulse are simulated,which are in good agreement with the experiments.The damage mechanisms are also analyzed,which show that the current filamentation causes the temperature rise and damage.Furthermore,the electrostatic discharge effects of a cellphone protection circuit were accurately simulated and analyzed,which fully verified the multi-physics simulation in the engineering application.The main research contents and innovations are as follows.1.Because the multi-physics simulation method lacks the characterization of the strong electromagnetic characteristics of semiconductor devices,the multi-physics simulation method is improved by adding the high-electric field and high-temperature physical effects,including the carrier generation rate,high-electric field and high-temperature mobility,and Auger recombination rate.The solving process after adding the above models is analyzed,and the automatic selection mechanism of the time step for solving the numerical-divergence problem in breakdown simulation is added.Moreover,the reverse breakdown characteristics of the Schottky diode and the current-voltage curve are simulated.The experimental results show that the improved method can accurately simulate the breakdown characteristics and the high-voltage nonlinear characteristics of the Schottky diode.2.By analyzing the relationship between carrier motion characteristics and operating frequency,the operation modes of the PIN diode can be divided into three cases,so a physical model parameters extraction method for precise simulation of the semiconductor device from DC to microwave frequency is proposed.Specifically,because the transit-time effects are dependent on the working frequencies and input power levels,the operation modes of the PIN diode can be divided into three cases from DC to microwave frequencies,including the low-frequency mode,the high-frequency mode with small signal inputs,and the high-frequency mode with large signal inputs.Therefore,the proposed method extracts the parameters based on the optimization algorithm from three measured curves,including the DC I-V curve,a small-signal,and a large-signal voltage waveform,both at a microwave frequency.Experiments of a PIN diode SMP1330 circuit show that the error of the conventional method is about 45% at frequencies above 300 MHz,but the maximum error of the proposed method is only 9.5% from DC to 2 GHz.3.The damage effects of the PIN diode limiter circuit under the electromagnetic pulse are analyzed,and the damage mechanism of current filamentation caused by the electrical instability of negative differential resistance is revealed.Through the ultra-fast transmission line pulse test,a diode voltage drop is observed and permanent damage was caused after the inputting of square-wave pulse with amplitude of 490 V.Multi-physics simulation is used to analyze the damage process.The trends of quasi-static current-voltage curves by simulation and experiment are in good agreement,and a rapid decrease of voltage is observed in both the simulation and experiments during the damage process.Compared with the experiments,the simulation error of the threshold current is only 19.5%.The mechanism causing the voltage drop is analyzed by using the multi-physics simulation.It is found that a negative differential resistance is formed by the avalanche process after the first breakdown.It causes current filamentation and local overheating at the filament position,which overheats and damages the PIN diode.4.As a typical example of strong electromagnetic effects in engineering application,the electrostatic discharge(ESD)effects of a cellphone protection circuit are simulated and analyzed by the multi-physics simulation.The frequency band of an ESD pulse ranges from DC to microwave,and its amplitude is above several kilovolts.Hence,ESD is a major threat to the normal work of the internal circuit of a cellphone.Firstly,the ESD discharging characteristics are analyzed,and the equivalent circuit model of the ESD pulse generator is established.An ESD protection circuit is fabricated.The SEED(system-efficient ESD design)method is widely used in the simulation of ESD discharging characteristics,so it is adopted to analyze the fabricated ESD protection circuit as a comparison.Moreover,the physical model of a transient voltage suppressor(TVS)diode is established,and its physical parameters are extracted.Based on the physical model and the parameters,the multi-physics simulation is used to simulate the protection circuit.The results simulated by the two methods are compared,including the DC,AC(alternating current),and ESD discharging characteristics.The experiments show that compared with the SEED method with the maximum error of 219.2%,the multi-physics simulation method can characterize the AC characteristics well,and the maximum error is only 7.8%.Furthermore,the multi-physics simulation method can accurately simulate the voltage waveforms across the TVS diode under the ESD discharging and explain the physical mechanisms.The results fully verify the multi-physics simulation in the engineering application of the strong electromagnetic effects. |
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