MOSFETs switch to different production processMOSFETs switch to different production process

Sunnyvale, CA--Power MOSFETs are usually created using a Double-Diffused MOSFET (DMOS) process. Power Trench(TM) MOSFETs for dc-dc conversion from Fairchild Semiconductor come into being through a trench etching technique that allows the channel to be tipped on its side and formed on the silicon wafer trench's vertical sidewalls.

This Power Trench process is nothing new. However, Fairchild has tried to optimize this Power Trench process with certain applications in mind, such as those which require heavy switching, to optimize the process, according to Steve Sapp, new product development manager for the MOSFET business unit for Fairchild's Discrete Power and Signal Technologies Div.

The MOSFET works like a conventional MOSFET, with a drain, source, and gate. The gate in this case is a polysilicone one that is a plug in the trench. When voltage is applied to the gate, it inverts a channel on the trench sidewalls, and that connects the drain and source and allows current to flow between the two, Sapp says.

The FDS6680A MOSFETs, which took a year and a half to develop, are N-Channel and logic-level and feature low RDS(on) and low gate charge. Sapp says the idea is to keep conduction losses also low.

"With this technology, we've been able to get a very good combination of two features--low resistance and good switching characteristics," Sapp says.

"We haven't really sacrificed anything in terms of the on resistance," he adds.

MOSFETs have evolved over the last 10 years, Sapp says, and a key element of future development is how well the switch.

"The main issue is that there are a lot more voltages required in systems than used to be the case," Sapp says. "With microprocessors in particular, requiring a lot of different voltages, the need for very high efficiency dc-dc conversion is an important consideration."

By minimizing switching losses, Sapp adds, the MOSFET can take advantage of applications to improve the overall efficiency of the dc-dc converter.

Fairchild started sampling key customers in October 1997. The MOSFET made its commercial debut in January 1998.