Volume 31 (Nov 15, 2004)

The path traveled by the creators of the NP Series of ultra-low on-resistance power MOSFETs for automobiles (1/2)

Part 1: Breaking the 2m ohm barrier

Power MOSFETs: The key to the computerization of automobiles

On May 17, 2004, shipment of samples began for the NP Series of automotive power MOSFETs, which were the first in the industry* to realize an on-resistance value of less than 2m ohm. It took NEC Electronics more than two years to finally bring this epoch-making product to market. The advent of the NP Series, which realizes an on-resistance value of 1.4m ohm (maximum guaranteed value of 1.8m ohm) at a withstand voltage of 40V and has a high current capacity of 110A, gained a great deal of industry attention. This is because it was believed that the series would spur the wave of computerization of automobiles through the diffusion of electronic power steering-which was already being employed in compact cars-in large-size vehicles.

* As of May 21, 2004

Although it is an unfamiliar term for many, a power MOSFET is an electronic component used to perform the electric switching function necessary for activating electrical systems. Power MOSFETs are now used to control actuators in power steering equipment, power windows, airbags and anti-lock braking systems (ABS) (Figure 1). Unlike mechanical relays, which have traditionally been used as switches, power MOSFETs have no degradation due to contact, and also have the advantage of boasting an extremely fast response speed. Moreover, in comparison with various types of hydraulic equipment that use engine power to conduct control, electrically operated equipment employing power MOSFETs can be simplified and lightened, thereby realizing improved fuel consumption and decreasing environmental load at a higher level.

The only problem that needed to be dealt with was on-resistance. On-resistance is the resistance that occurs during the flow of electric current (on-state). When this resistance value is high, the power MOSFET experiences a large voltage drop and heat generation. For large-size vehicles (the electrical systems of which require a great deal of power) in particular, it is necessary for power MOSFETs to be able to handle the flow of large amounts of electric current, and also to possess high-voltage endurance characteristics. This is why the on-resistance value of 2m ohm was a major barrier. Though we eventually overcame the 2m ohm barrier, there were numerous challenges along the way.

Dispelling the myth of "If we manufacture it, it'll sell"

Photo 1 Shingo Yamada,
Senior System Integrator,
Power Management Device Division,
technical marketing and planning

In February 2002, another manufacturer had begun marketing a new power MOSFET that realized the industry's lowest on-resistance value of 2.3m ohm. The on-resistance value of NEC Electronics' power MOSFET, however, was 4.3m ohm, and the difference was enormous. Furthermore, even the target value for the next product under development by NEC Electronics at that time was 2.4m ohm.

With eight generations of power MOSFETs created for automobile use and over twenty years of experience, NEC Electronics (formerly NEC) had been able to follow its product roadmap and develop new products that they would sell. The company also prided itself on the fact that it manufactured the industry's top products. Yet in this case, achieving that distinction wouldn't be so easy.

Shingo Yamada of the Product Planning Section reflected on the anxiety felt by the team members at that time saying, "At that point, we didn't even know if we would be able to continue in this field in the future." Until then, we felt that all we really had to do was steadily develop new technologies. And in a way, it had been an ideal environment for the engineers. However, all of that changed in the blink of an eye. Team members had no choice but to reconsider their roadmap.

Reversing the tides and taking on the challenge of striving to become the industry leader
The launch of the project thanks to the cooperation of NEC Kansai