Effects On Low Noise Amplifiers With Microwave Pulses

The High Power Microwave has become an important threat to electronic system because its output power has reached several GW or even above ten GW.As the core and most susceptible device of the RF front end,the Low Noise Amplifier(LNA)is easily interfered or even damaged by the microwave pulses from other microwave transmitting source.The effects on LNA based on Bipolar Junction Transistor(BJT)and Pseudomophic High Electron Mobility Transistor(PHEMT)with microwave pulses are studied by theoretical analysis,simulation,injection experiment and failure analysis to obtain the parameters of microwave pulses with better effect to electronic system and the approaches to improve the semiconductor device against microwave pulses.The non-linear property and damage property of the device with microwave pulses are studied and the influence rules of the different pulse parameters and working states of the device upon the damage power are analyzed.The main contents and conclusions are as follows:1.The effect mechanism on LNA with microwave pulses is studied by theoretical analysis and simulation.The theoretical model is established to analyze the influence of frequency on heat effect of semiconductor device.And,it is obtained that the device is easily damaged when the frequency is lower.The mechanism of non-linear effect and damage effect of semiconductor device are studied by establishing simulation model of BJT and PHEMT with microwave pulses.The feature of the collector current of BJT with microwave pulses injected from base is from linear increase,saturation,reduction to reversion and increase again as the amplitude of input voltage increases;the base region near emitter junction,base electrode and emitter electrode are the vulnerable parts.The feature of the drain current of PHEMT with microwave pulses injected from gate is also from linear increase,saturation to reversion and increase again as the amplitude of input voltage increases;the region below the gate near the source,gate electrode and source electrode are the vulnerable parts.In addition,the influence rule on damage effect of semiconductor device by the frequency and pulse width of microwave pulses and the bias voltage of device is obtained.2.The injection experiment on LNA based on BJT and PHEMT with microwave pulses is carried out to study the non-linear effect and damage effect of LNA.The variation characteristics of the output waveform of LNA as the input power increases measured by experiment are consistent with the simulation results.The influence rules of the different pulse parameters(including pulse width,frequency and pulse number)and working states of the device upon the damage power are analyzed.The typical damage waveform of LNA is analyzed as well.The change of the damage power of LNA as pulse width increases can be divided into two sections: in the first section,the relation between damage power and pulse width is P? t-1 when the pulse width is from 20 ns to 100 ns;in the second section,the relation between damage power and pulse width is P? t-1/2 when the pulse width is from 100 ns to 2000 ns.The damage power firstly increases and then decreases as the frequency increases when the frequency is from 1.5 GHz to 10 GHz measured by experiment.The frequency is near to 6 GHz when the damage power reaches maximum.The results of experimental measurement are consistent with those of three-dimensional simulation.The damage power of LNA based on BJT hardly changes when the pulse number increases.The damage power of LNA based on PHEMT decreases as the pulse number increases,when the pulse number is less than 100.The damage power hardly changes when LNA is biased or not.The energy for damage of device is from microwave pulses which is consistent with the simulation results.With large signal injection,the multiple frequency component of the output signal increases obviously.Step change occurs to the input impedance when the device is damaged.The impedance mismatch of the amplified circuit causes the abrupt increase of reflection signal and sudden decrease of output signal.3.The electrical properties are measured before and after damage of semiconductor device for comparison.The resistance among the electrodes of the damaged BJT is the same at both positive and negative bias,and the resistance obviously decreases.The resistance between base and emitter decreases the most.The breakdown voltage of the PN junction tends to be zero,so the emitter junction and collector junction lose PN junction properties.The short circuit path of low resistance is formed due to the breakdown of emitter junction and collector junction,therefore the device is permanently damaged.The resistance of gate-source and gate-drain of the damaged PHEMT is the same at both positive and negative bias,and the resistance obviously decreases.Meanwhile,the saturated drain current and gate leakage current are increased significantly;the output property of the transistor presents a resistive property and the gate voltage loses control ability over the drain current.The short circuit path of low resistance is formed due to the breakdown of Schottky junction.4.The microscopic damage images of the semiconductor devices in different damage conditions are analyzed.The vulnerable parts of BJT are the input terminal of the base electrode and the Si materials below with microwave pulses injected from base,which are consistent with the simulation results.In different injection conditions,there are obvious differences on damage degree of BJT.The input terminal of the base electrode is burnt out and broken with several pulses injection while the input terminal of the base electrode is only melted with single pulse injection.The damage degree is severer with several pulses injection.The longer the pulse width,the severer the damage and the larger the damage area.The gate metal strip and its surroundings are the vulnerable parts of PHEMT with microwave pulses injected from gate,which are consistent with the simulation results.In different damage conditions,there is no obvious difference of the microscopic damage image of PHEMT.5.The damage mode of two models of Ga As PHEMT Monolithic Microwave Integrated Circuit(MMIC)chip damaged with microwave pulses is analyzed by statistics.The results show that there is obvious difference on the damage position of different MMIC chips.Both active structure and passive device of the MMIC chip may be damaged.The active structure is easier to be damaged.The vulnerable device is the planar spiral inductor in passive device.