The Evolution of Power MOSFETs and the Role of Process Technologies

Feb 1, 2010 12:00 PM
Davis, Sam, PET

A new generation of PowerTrench MOSFETs will enhance the performance of power converters and switches by boosting their switching speed and efficiency.

As shown in Fig. 1, Fairchild Semiconductor's PowerTrench MOSFETs have exhibited significant improvements from one generation to the next. The company's original PowerTrench, which presented improvements over previous planar MOSFETs, is shown in Fig. 1a, while in Fig. 1b, the oxide underneath the gate region was extended, resulting in improved Q_GD (reduced switching loss). Fairchild's newest generation is a shielded-gate power MOSFET (Fig. 1c).

The new shielded gate device is said to offer performance improvements such as:

• Lower C_OSS (output capacitance)
• Lower Q_RR (reverse recovery charge)
• Lower t_RR (reverse recovery time)
• Enhanced low-side efficiency performance due to the lower C_OSS and t_RR
• Low R_DS(ON)
• Low Q_G (total gate charge)
• Very low Q_GD

THE SHIELDED GATE

The equivalent circuit of Fig. 2 demonstrates the impact of the shielded gate. Two capacitances, C_Drain-Shield and C_Gate-Shield — inserted with dashed lines in the equivalent circuit — act as virtual snubbers to minimize ringing when the MOSFET switches.

Fig. 3 compares the switching characteristics of a new shielded-gate PowerTrench MOSFET (Fig. 3a) with one of the competitor's lateral processes (Fig. 3b). The shielded-gate device exhibits considerably less ringing than the competitor MOSFET.

THE IMPORTANCE OF PACKAGING

Also helping switching performance is the use of a molded lead package (MLP) to minimize parasitic capacitance and inductance from the silicon die to the output terminals. The small die also allows for a dual-MOSFET package that simplifies the design of synchronous rectifiers. Fig. 4 shows a typical version of dual PowerTrench MOSFETs configured as synchronous rectifiers. The package contains two dice. The bottom device is a PowerTrench SyncFET™ with an integrated Schottky diode, and the top device is a conventional PowerTrench MOSFET with its standard body diode.

MOSFET FAMILY COMPARISONS

	PART NO.	PACKAGE	VDS (V)	25°C ID CONT.(A)	25°C POWER (W)	TYPICAL VGS(TH) (V)	TYPICAL RDS(ON) 10V ID/(mΩ)	10 V QG (NC)	FIGURE OF MERIT	RθJC °C/W	TYP. COSS VGS=0 F = 1 MHz VDS/(PF)
Old	FDMC8854	Power 33	30	15	2.0	1.9	15 A/4.4	41	180	3.0	10 V/515
SG	FDMC7570S	3 × 3 MLP	25	27	2.3	1.7	27 A/1.6	49	79	2.1	10 V/1,010
Old	FDMS3672	Power 56	100	22	2.5	3.1	7.4 A/19	31	589	1.6	50 V/210
SG	FDMS86101	Power 56	100	49	2.5	2.9	13 A/6.3	39	246	1.2	50 V/460
*SG = shielded gate

Related Articles

TrenchFETs Enhance DC-DC Converter Performance Generation 3 TrenchFETs enhance dc-dc converter performance/size.... Scaling New Heights in Power MOSFETs Although the development of power MOSFETs began with the V-MOS structure, the first commercially successful devices were based on the DMOS structure.... Are Trench FETs Too Fragile for Linear Applications? A comparison of the forward-biased safe-operating-area (FB-SOA) performance of one trench and one planar device of similar die size is presented. The results educate designers on issues concerning trench and planar MOSFETs in the linear region of the device operating characteristics.... Improved MOSFET Model Achieves Higher Accuracy A SPICE model based on the BSIM3 core eliminates shortcomings in the existing level 1 and level 3 subcircuit models, enabling better simulation of trench-type power MOSFETs....

Acceptable Use Policy blog comments powered by Disqus