For the conventional VDMOS device structure, Rdson and BV are contradictory relations. In order to improve BV, we should start from reducing the EPI impurity concentration, but the epitaxial layer is also a channel of forward current flow. When the EPI impurity concentration decreases, the resistance will inevitably increase, and Rdson will increase. Rdson directly determines the loss of MOS monomer. Therefore, for ordinary VDMOS, the contradiction between the two is irreconcilable, which is the limitation of conventional VDMOS. For COOLMOS, however, this contradiction is not so obvious. By setting up a P-zone deep into the EPI, the BV is greatly improved, while having no impact on Rdson. For conventional VDMOS, the reverse voltage resistance mainly depends on the PN junction at the interface between N-type EPI and body region. For a PN junction, the voltage resistance mainly depends on the depletion region, the size of the electric field in the depletion region and the area of the width of the depletion region. The concentration of conventional VDSMO and Pbody is greater than that of NEPI, and it should also be clear to everyone that the depletion region of PN junction mainly diffuses to the low-impurity side, so under this structure, the depletion region on the side of the Pbody region has a small expansion, which basically does not contribute much to the pressure. The pressure is mainly caused by the area of P body-- NEPI on the side of the N-type. The electric field intensity in this region changes gradually, and the closer the PN junction is, the greater the electric field intensity E is. For the COOLMOS structure, due to the setting of a P region with a lower concentration of P body, the depletion region on one side of the P region will be greatly expanded, and this region goes deep into EPI, resulting in a large voltage on both sides of the PN junction. In other words, the peak electric field Ec is transferred from close to the device surface. Moving deeper into the device.

The advantages of Cool-MOS

1. Small on-state impedance, small on-state loss.

Since the Rdson of SJ-MOS is much lower than that of VDMOS, the on-off loss of SJ-MOS in system power products must be reduced much more than that of VDMOS. It greatly improves the on-loss of the monomer MOSFET above the system product and improves the efficiency of the system product. This advantage of SJ-MOS is particularly prominent in the power supply products with high power and high current.

2. With the same power specifications, the package is small, which is conducive to the improvement of power density.

First of all, under the same current and voltage specifications, the crystal source area of SJ-MOS is smaller than that of VDMOS process, so that as a MOS manufacturer, a relatively small volume product can be packaged for the same specification, which is conducive to the improvement of power density of the power supply system.

Secondly, due to the reduction of the on-off loss of SJ-MOS, the loss of power supply products is reduced, because these losses are dissipated in the form of heat, we often increase the heat sink in practice to reduce the temperature rise of the MOS monomer, so that it can ensure that it is in the appropriate temperature range. Since SJ-MOS can effectively reduce the heat generation and reduce the volume of the radiator, for some slightly lower power supplies, the radiator can even be completely removed after using SJ-MOS. Effectively improve the power density of system power supply products.

3. The grid charge is small, and the driving capacity of the circuit is reduced.

The gate charge of traditional VDMOS is relatively large, we often encounter the temperature rise problem caused by the insufficient drive capacity of IC in practical applications, some products in the circuit design in order to increase the drive capacity of IC to ensure the fast conduction of MOSFET, we have to increase the push-pull or other types of drive circuit, thereby increasing the complexity of the circuit. The gate capacitance of SJ-MOS is relatively small, which can reduce its requirements for driving capacity and improve the reliability of system products.

4. The power saving capacity is small, the switching speed is accelerated, and the switching loss is small.

Due to the change of the structure of SJ-MOS, the output power saving capacity is also greatly reduced, thus reducing the loss in the process of switching on and off. At the same time, because the response of SJ-MOS gate capacitance is also reduced, the capacitor charging time is shortened, and the switching speed of SJ-MOS is greatly improved. For the power supply with fixed frequency, it can effectively reduce its opening and closing losses. Improve the efficiency of the entire power system.