The use of trench MOSFETs has become the standard for most of today's automotive applications. Historically, planar MOSFETs were built on the surface of the silicon wafer. Trench MOSFETs etch vertical trenches into the silicon allowing higher cell density and lower on resistance for the power switches.

Because most of these electro-mechanical systems utilize MOSFET H bridge motor drive configurations, two devices are always in series thus allowing the use of lower voltage MOSFETs while still withstanding the traditional high voltage automotive transients. These lower voltage breakdown devices can offer up to a 50% reduction in the switch on resistance as compared to 60V MOSFETs. This translates directly into a 50% reduction in system power dissipation, reducing system heat and minimizing heat sinking requirements.

As automotive system designers gain more experience in working with these lower voltage power MOSFETs and begin to realize the performance and cost advantages to lower voltage power MOSFETs, their use is expanding into other lower power systems such as braking and display control.

Today's power trench MOSFETs have switch on resistance (R_DS(ON)) down to 1 or 2 milliohms. This reduces system power dissipation dramatically but adds another complexity for the automotive system designer—it is now probable that the interconnect resistance including the board interconnection, system wiring, and even the bond wires in the package add more resistance to the system than the actual MOSFET.

Hybrid modules
One way to drive continual reduction in on resistance and get improved power density is the use of hybrid modules. Many applications are moving away from the traditional power package solutions to use bare die mounted on insulating substrates made from IMS (insulated metal substrate) or DBC (direct bond copper) material. These modules offering higher energy and higher current capability as compared to discrete power packages even when using the same power silicon die.

Modules offer higher density bonding or larger wire bonding of the die, lowering the connection resistance while also minimizing the distance between power components. This higher density energy capability comes at an increased component cost over discrete package alternatives. However, system size and performance improvements in high energy systems more than compensate for this increased device cost.

Another direction that automotive power MOSFETs are taking is the increased ability to sense, control, and protect the power switch. Power devices are being integrated with the intelligence of the automotive system. At the lowest level, MOSFETs are now available with sense elements included on the power device. These sense elements can measure current or temperature and can be connected to electronics to monitor the system performance and protect the power device in the event of an over-current or over-temperature condition.