The Characteristics Research Of75V Trench Power Mosfet

Power MOSFETs are widely used in various fields of consumer electronics. Compared to other structures, the trench power MOSFET(UMOS,short for UMOSFET) structure often used in high frequency with low and medium power applications because of its low on-resistance, fast switching speed and good frequency characteristics.With the energy conservation policies proposed,which demand that the power MOSFETs have to ensure a certain degree of breakdown voltage and continue to reduce power consumption.From a point of reduce conduction losses, we complete the design of the cell of75V UMOS and finally optimize this structure in this paper.Pbody region is researched firstly in this paper.With the different implant dose, energy and annealing time, we get the results of UMOS parameters which affected by changing the Pbody junction depth and shape.When a gate oxide process is determined, the threshold voltage is only impact by Pbody doping profile.With the increase of Pbody depth, on-resistance and breakdown voltage increase too.But the gate-drain capacitance decreases on the contrary. To guarantee the breakdown voltage, we choose the Pbody junction depth which is parallel to the gate trench depth in this paper.In order to impove the current density and reduce the cell pitch of the chip, the body trench contact is adopted in this article.This method will be change the breakdown current path when the body trench contact is deeper and reduce the specific on-resistance. Finally we select0.45μm to be the most appropriate depth. In the above two cases,BV of the device is83.04V;the threshold voltage is2.903V;The on-resistance is42240.830Ohm while Vgs is biased10V;When VDS=25V, the gate-drain capacitance is3.415E-02fF.We adopt a new approach to optimization of on-resistance, that is an extra implant of high energy and low dose N type ion which is used for offset the P type ion of groove surface before N plus area is formed. This method is either guarantee the device breakdown voltage or there is no extra mask. Furthermore, it can be effective to reduce the on-resistance and the threshold voltage. By this way, the breakdown voltage remains and the on-resistance decreased by10.4%.In addition, we also apply another way to attain low on-resistance, which is called shallow junction model in the paper. Decreasing the channel length can get smaller on-resistance.Heavily doped P type ion of trench bottom after forming body trench contact and it will prevent punch through effect.Furthermore, we can dispose a metal layer in the trench and on top of gate trench to reduce the contact resistance. In this advanced structure, the specific on-resistance of this device can be reduced by deepening the body trench contact depth,and it will also improve the breakdown characteristics of the shallow junction model.