MOSFETs can be broadly divided into the following categories: planar MOSFETs; trench MOSFETs, mainly for low-voltage applications; SGT (Shielded Gate Transistor, shielded gate trench) MOSFETs, mainly for medium-voltage and low-voltage applications; SJ (super junction) - MOSFETs, mainly for high-voltage applications. With the rise of fast charger for cell phones, electric vehicles, brushless motors and lithium batteries, the demand for medium voltage MOSFETs is growing and medium voltage power devices are beginning to flourish. Because of its huge market share, many domestic and foreign manufacturers have been increasing their investment in the research and development of corresponding new technologies. SGT MOSFETs, as a representative of medium MOSFETs, are core power control components and widely being used as switching devices in motor drive systems, inverter systems and power management systems. The SGT MOSFET structure has a charge-coupled effect that introduces horizontal depletion based on the vertical depletion of the PN junction in conventional trench MOSFET devices. By changing the electric field of the device from a triangular distribution to an approximately rectangular distribution, the device can achieve a higher breakdown voltage with the same doping concentration of the epitaxial material specifications. The deeper trench depth allows more silicon volume to be used to absorb EAS energy, so SGT is more tolerant of avalanche breakdown and inrush current during avalanche. In applications such as switching power supplies, motor control, and power battery systems, SGT MOSFETs with advanced packaging are very helpful in improving system performance and power density.
Figure 1: Trench MOS and SGT MOS Device Structure
The technical advantages of SGT are as follows:
Advantage 1: Increase power density
The trench digging depth of SGT is three to five times deeper than conventional Trench, allowing more epitaxial volume to be used laterally to block the voltage, significantly reducing the on-resistance (Specific Resistance) of MOSFETs. For example, using the same package profile PDFN5*6, lower on-resistance can be obtained using SGT chip technology.
Figure 2: Specific Resistance Comparison of Trench MOS and SGT MOS
Figure 3: Min Rdson Comparison of PDFN5*6 Package
Advantage 2: Very low switching losses
SGT features low Qg compared to conventional Trench structure. The introduction of the shielded gate structure can reduce the Miller capacitance CGD of MOSFETs by up to 10 times or more, which helps to reduce the switching losses of the device in switching power supply applications. In addition, the low ratio of CGD/CGS is also a key indicator for suppressing shoot-through in current synchronous rectification applications, which can be obtained by using SGT structure.
Gate Charge Qg (nC)
Figure 4: Qg Comparison of Trench MOS and SGT MOS
Advantage 3: Better EMI
The built-in resistor-capacitor buffer structure in the SGT MOS suppresses transient oscillations when the DS voltage is turned off. As shown in Figure 5 below, the parasitic CD-shield and Rshield in the SGT structure in switching power supply applications can absorb spikes and oscillations caused by dv/dt variations when the device is turned off, further reducing application risk.
Figure 5: SGT MOS built-in Sunbber Structure
It is worth mentioning that, relying on the huge local market demand for medium-voltage MOSFETs, domestic devices in the medium- and low-voltage field have great potential to replace imported brands. WAYON is actively laying out SGT MOSFETs with high power density and low internal resistance. Combining market and customer needs, WAYON is continuing innovation in product process and packaging.
For different application scenarios, the recommended selection in terms of product series and specification sizes are as follows：
(1) PC, notebook, wireless charger, etc.
(2) PD, adapter synchronous rectification
(3) BMS and Motor Control
(4) Communication power supply, 5G base station