Study On Mechanism And Key Techniques Of Pulsed Power Switch RSD

Pulsed power technology has been developing very fast in recent years and it has a wide application prospects in military and industry areas. Pulsed power switch is one of the core elements in pulsed power system. Because semiconductor devices have the advantage of small volume, long lifetime and high reliability, pulsed power switch tends to turn into semiconductor now. Proposed by Russian scientists in 1980s based on the controllable plasma layer commutation principle, RSD(reversely switched dynistor) is a kind of new semiconductor switches specially applied to pulsed power area. It has advantage in operation principle and can reach several tens of kilovolts high voltage, several hundreds of kiloamperes great current and 105A/μs high current rise rate at the same time.The commutation characteristics of RSD are analyzed in detail firstly. The shortest n-base is acquired while the blocking condition is satisfied by introducing an optimal factor. Based on the plasma bipolar drift model, the turn-on condition of RSD described by the critical triggering electric charge amount is obtained. The experimental results show that the higher the triggering voltage is, the more uniform the turn-on process is in a certain range. Then the analytical expression of di/dt capability of RSD is deduced and the influence factors to di/dt are discussed and proved by experiments. According to the expressions of turn-on voltage on RSD and the loop equations, the power dissipation on RSD is calculated quantitively. The results show that the total dissipation on RSD is trivial and the proportion of commutation dissipation in total is little. It is proposed that skin effect exists in the short pulse discharge application of RSD. The current density distribution on the chip is calculated taken skin effect into account. The natural turn-off model of RSD is set up and the reverse recovery time is calculated.The thin emitter theory is proposed to apply to RSD in order to improve its turn-on characteristics. The new structure of“thin base-buffer-transparent anode”is presented further so as to get a good tradeoff among the on-state, off-state and switching characteristics. According to the turn-on condition of RSD, the thin anode emitter is capable of keeping the triggering plasma layer from being exhausted in the turn-on process. By setting up the asymmetric pin diode model of the thin emitter RSD, it is discovered that the forward voltage drop of RSD is reduced as the emitter doping concentration decreases in a certain range. The introduction of buffer layer makes the distribution of electric field in RSD become trapezoid from triangle, so the thickness of chip can be reduced on the condition of the same blocking voltage. The transparent anode structure makes the electrons penetrate through the anode directly and accelerates the turn-off speed.The key technics of RSD is studied. Firstly, two sets of preparation scheme are given out according to the different formation of the emitter in anode. Then the layouts of anode and cathode are designed. The multi-cell structure in anode should satisfy the requirement that the sum of the characteristics size of thyristor and transistor units is smaller than the width of the long base region. Finally, the new technics in the process of preparing RSD are introduced, including the chemical eroding method of silicon and the formation technics of“thin base - buffer - transparent anode”.The pulse generation circuit based on RSD is also researched into combined with its practical application. The inductance and volt-second product formulas of the saturable core choke are deduced. The delay time of the magnetic switch is researched into by theory and experiments. The relationships between the parameters of pulse discharge main loop and the output current waveforms are studied by simulations and experiments. The great power pulse generation circuit of 120kA is designed. The peak current of 132.2kA has passed through in experiment, with the pulse width of 330μs. The repetitive frequency turn-on experiment is carried out with the resonant triggering way, in which output waveform of 20Hz is obtained at 4kV. According to the skin effect, the multi-cell parallel of RSD is proposed to enlarge the current capability in order to make a full use of the chip area. The multi-cell parallel model is set up and the influence factor of current unbalance rate is discussed. It is presented that the blocking voltage of single chip is reduced and the number in series is increased in order to increase the operating speed and prolong the lifetime of device.