Research On The Intense Electromagnetic Pulse Damage Effect Of GaAs PHEMT

Intense electromagnetic pulse can couple into the electronic system through a variety of ways,and makes it disturbed,degraded or even damaged,which brings a serious threat to the reliability of the electronic system.As the core unit of the electronic system,the research on the damage effect and mechanism of the semiconductor device induced by the intense electromagnetic pulse is of great significance.At present,the research methods on the intense electromagnetic pulse effect of semiconductor devices are mainly experiment and numerical simulation.Although the experiment research can reflect the damage effect of the devices truly,its research achievements do not have universality and are more costly due to the restriction of varieties of device types,difference of manufacturing process technologies between producers,complexity of systems and electromagnetic environments and other factors.Therefore,it has great realistic significance and practical use to study the damage effect and mechanism of semiconductor devices in theory by numerical simulation method.This dissertation takes typical GaAs pseudomorphic high electron mobility transistor(PHEMT)with ?-doped structure,establishes the damage model of the device under intense electromagnetic pulse,and analyses the damage effect and mechanism of GaAs PHEMT device induced by the electromagnetic pulse(EMP),repetitive pulses and high power microwave(HPM).The main research contents and results are as follows:1.With the help of the device simulation software Sentaurus TCAD,an intense electromagnetic pulse-induced damage model is established from three aspects: device structure,numerical model and signal model.Based on the typical delta-doping GaAs PHEMT,this model fully considers the electro-thermal effect,the carrier mobility degradation effect,the carrier mobility high-field saturation effect and the carrier avalanche generation effect of the device under the intense electromagnetic pulse.Meanwhile,the field-circuit conversion of two typical intense electromagnetic pulse sources is analyzed,and establishing the circuit form of EMP and HPM signals,which makes the analysis of the damage effect induced by the intense electromagnetic pulse more convenient.Therefore,the damage model established in this dissertation can reflect the GaAs PHEMT damage effect under the action of intense electromagnetic pulse more realistically.2.Based on the GaAs PHEMT damage model,the EMP-induced damage effect and mechanism of the device are studied from the analysis of the distribution and variation of the electric field,the current density and the temperature.Research results indicate that under the action of EMP there are a current path and intense electric field occurring between the gate and channel layer of the device,which causes the hot spot of the device located under the gate area.Furthermore,the hot spot is not always in the same position,which moves from the location beneath the gate area near the source side to the middle region with the happen of the electric field transfer phenomenon caused by the device thermal breakdown.Meanwhile,the influence of the external conditions on the damage effect of device is discussed from the signal parameters and external resistances.It is shown that the variation of external conditions can significantly affect the damage progression of the device: the increase of the signal amplitude can enhance the absorbing energy of the device with same time,which makes the energy value required to the thermal breakdown easier to reach and accelerates the damage progression of the device;the change of the signal rising time can speed or delay the breakdown point of the device,and influence the damage progression of the device;the external resistance at drain and source can change the width of the current path between the gate and channel layer to affect the damage progression of the device,and the source resistance is more obvious.In the practical design of the device,the ability of anti-electromagnetic pulse of device can be enhanced by increasing appropriate source resistance with the compromise of the device performance index.3.Traditionally,researchers always assume the device as two-dimensional or three-dimensional thermal model,and resolve the heat conduction equation to obtain the damage power and energy threshold of the device based on the hot spot uniqueness.This dissertation on the damage threshold of the device is completely different from the traditional method,which combines the EMP damage effect and mechanism of the GaAs PHEMT with structure property.Meanwhile,the damage power threshold formula of the GaAs PHEMT is established by the curve fitting software.Research results show that the damage power and energy threshold of GaAs PHEMT is different from the empirical threshold due to the damage characteristic of the device that the hot spot is not fixed in one position during the EMP action.In the damage process of the device,the undamaged hot spot will consume a portion of the signal energy,and thus the device needs more energy to get damage point in general,which causes that the time index of the damage power threshold formula is higher than that of the empirical formula.With the increase of the signal amplitude,the damage time of the device decreases,which leads to the little energy consumed on the undamaged hot spot and then the damage energy of the device reduced.When the signal amplitude increases to a certain degree,the device has damaged before the happen of the electric field transfer phenomenon.There is a fixed hot spot during the damage process of the deivce,which cause the damage energy threshold being almost a constant which is similar to the empirical formula.4.Based on the equation of thermal equivalent circuit,this dissertation establishes the repetitive pulse-induced failure model of devices,and get the relationship between the device temperature,pulse power and pulse time.A simple formula to calculate the thermal delay time of devices is established,which can work out the safe pulse interval much faster and more easily.Combined the damage model of GaAs PHEMT,the relationship between signal parameters and damage time is analyzed,and the necessary condition for the existence of potential damage of the device is discussed.Research results show that the pulse width is inversely proportional to the damage time: the longer the pulse width,the more heat the device produces during the same pulse period,and the easier it damages.When the variation of the pulse period is due to the change of pulse width,the variation rule of damage time on the pulse period is similar to that on the pulse width;when the variation of the pulse period is due to the change of pulse interval,it is proportional to the damage time: the longer the pulse period,the longer the pulse interval,and then the heat dissipation becomes larger which cause the device damage difficult.The variation of the pulse duty cycle can affect simultaneously the heat generation and heat dissipation device,which is inversely proportional to the damage time.There exists a safe threshold of the pulse period and duty cycle.When the pulse period of the injection signal is larger than the pulse period threshold or the duty cycle is less than the duty cycle threshold,the device will not have the potential damage.No matter how long the signal functions,the device will not be damaged.5.Based on the damage model of GaAs PHEMT,the damage effect and mechanism of GaAs PHEMT induced by HPM are studied.Research results show that during the action of HPM the peak temperature of the device behaves a periodic “rise-fall-rise” process,which rise process mainly happens before the wave crest of the signal.As the signal time continues,the thermal breakdown occurs when the device accumulates a certain energy,which leads to a sharp rise in the temperature and then damages the device.A comparison of damage effect is made between EMP,repetitive pulse and HPM.It is shown that the damage types induced by these three signal are all energy damage;the damage mechanisms are all thermal breakdown;the damage location are all under the gate near the middle region.The difference is that the device absorbs energy continuously under the action of EMP which always makes the temperature rise,and displays a periodic “heat production-heat dissipation” process under the action of repetitive pulse and HPM,which makes the temperature behave a periodic “rise-fall-rise” process.With the same amplitude,the EMP signal is most likely to damage the device.Thus,it is the most safe and reliable to use the EMP-induced damage threshold as the protection standard of system and circuit in the face of the complex electromagnetic environment.A HPM-injected effect experiment is carried out in the low noise amplifier(LNA)which consists of GaAs PHEMT device.Experimental results show that the first-stage transistor is the weak element of LNA under the action of HPM.With the help of the scanning electron microscope(SEM),it is found that there are various degrees of pit under the gate region of the first-stage transistor,which is consistent with the simulation result.In practice,designer should strengthen protect the gate region of the first-stage transistor of LNA.