| SOI(Silicon On Insulator,referred to as SOI)devices have been widely used in power switch conversion circuits due to their advantages of high speed,low power consumption,high reliability,radiation resistance and excellent isolation performance.However,during the actual circuit switching operation,the SOI device will experience a deep depletion effect due to the fact that the SOI device will withstand a fast turn-off voltage with a fast rate of change.The deep depletion effect of the substrate will lead to the development of the depletion region to the substrate and the RESURF effect of the SOI device to change,resulting in the device's static withstand voltage becomes less practical in the actual switching converter circuit.In response to this problem,this article made a related research,the main content can be summarized as the following three aspects:1)The influencing factors of substrate deep depletion effect of SOI-LDMOS devices are discussed,and it is proposed to optimize the deep depletion effect of the substrate by changing the doping concentration of the substrate.The deep depletion effect of the substrate,the main influencing factor is the length of life of minority carriers in the substrate semiconductor.According to the expression of the relaxation times of minority minority carriers,in the second chapter of this paper,we discuss the deep depletion of the substrate due to factors such as silicon lattice constant,ambient temperature,carrier lifetime in silicon,and interface states.The effect of the effect.At the same time,using a simple SOI-LDMOS device designed as an example,through the MEIDICI simulation experiment,the effects of different substrate doping concentrations on deep depletion of the device substrate and dynamic voltage withstand,static withstand voltage,and device Conductive characteristics and other aspects were discussed.2)Proposed SOI device dynamic voltage under two-dimensional electric field analytical model.After relevant research,it is found that the width of the depletion region of the substrate is the largest at the turn-off of the device,and the deep depletion effect of the substrate has the most obvious effect on the device performance.Since then,with the passage of time,the substrate fewer children began to appear,the substrate inversion layer is established,the substrate deep depletion effect disappears.Therefore,in this paper,we will select the device off the moment,the establishment of the corresponding two-dimensional electric field analysis model.According to the proposed analytical model,the two-dimensional Poisson's equation of the depletion region and the drift region of the substrate is solved simultaneously according to the principle of continuous potential to obtain the expression of surface potential and surface electric field under dynamic withstand voltage.According to the new expression,the influence of substrate depletion region on thebreakdown characteristics of the device under dynamic withstand voltage is analyzed,and the physical mechanism of the voltage withstand characteristics of the device under dynamic withstand voltage is expounded.3)optimize the parameters of the device,its use in the ZVS-QRC switching power supply circuit simulation.In the ZVS-QRC switching circuit,due to the resonance effect,the device will withstand instantaneous over-voltage at the turn-off instant.In order to ensure the reliability of the work of the device,in the actual circuit design generally choose a higher breakdown voltage power devices.However,higher breakdown voltage will reduce the conversion efficiency of the entire circuit.Through the analytical model proposed,it is found that optimizing the substrate doping concentration of the SOI device can make the device withstand the dynamic voltage at the moment of turn-off more than the device's static withstand voltage.Therefore,the use of this feature can provide a new idea for switching power supply circuits such as ZVS to solve the transient over-voltage generated by the resonance. |
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