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EB201 Datasheet PDF : 8 Pages
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EB201/D
High Cell Density MOSFETs
Low On–Resistance Affords
New Design Options
Prepared by: Kim Gauen and Wayne Chavez
ON Semiconductor
http://onsemi.com
ENGINEERING BULLETIN
Just a few years ago an affordable 60 V, 10 mΩ power
transistor was a dream. After all, 10 mΩ is the resistance of
about 20 cm of #22 gauge wire. Today a sub–10 mΩ power
MOSFET is not only available, it is housed in a standard
TO–220. Such are the advances that have occurred lately in
“high cell density” power MOSFET technology.
Furthermore, Motorola’s high cell density technology,
HDTMOS®, brings other advantages such as greatly
improved body diode performance. The technological
advances are sufficiently great that they are fundamentally
changing low voltage power transistor technology.
Cutting the MOSFET’s On–Resistance
A cross section of the power MOSFET is shown in
Figure 1. The major contributors to the standard MOSFET’s
SOURCE
GATE
on–resistance are its spreading, channel, JFET,
accumulation region, and substrate resistances. To achieve
ultra–low RDS(on), device designers must decrease the
resistance of all these components. Most of the resistive
elements can be reduced by shrinking cell size and adding
more cells per square centimeter of silicon. However, there
is a limit to maximum packing density. As cell density
becomes very high, on–resistance actually increases due to
a higher JFET resistance. With today’s processes and cell
geometries, the optimum cell density is about five times that
of standard power MOSFETs. Devices built with ON
Semiconductor’s high cell density process (HDTMOS)
employ about 6 M cells/in2, up from the 1.2 M cells/in2 used
in standard power MOSFETs. Figure 2 illustrates the
marked difference in cell density.
SOURCE
R (PACKAGE)
P+
P–
R (ACCUM) R (JFET)
R (CH)
R(N+)
R (METAL)
R (CONTACT)
P+
Nepi
R (SPREAD)
R (BULK)
N + SUBSTRATE
R (SUBSTRATE)
DRAIN
Figure 1. HDTMOS Cross Section
© Semiconductor Components Industries, LLC, 2002
1
February, 2002 – Rev. 1
Publication Order Number:
EB201/D
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