Technology Characteristics; Figure 1 Cross Section Of A Fet In Soi-Technology - Infineon EiceDRIVER 6ED Series Application Note

6ED family - 2nd generation
Technical Description

Technology Characteristics

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SOI is the abbreviation of Silicon-On-Insulator and is an advanced technique for MOS/CMOS fabrications. It
differs from the conventional bulk process by placing the active transistor layer on the top of an insulator, as
shown in Figure 1.
Figure 1 Cross section of a FET in SOI-technology
The silicon is separated by a buried silicon oxide layer to one layer on the top and the other on the bottom. The
one on the top, which is the silicon film, is used to produce the transistor and the one on the bottom is used as
the silicon substrate. The buried silicon oxide provides an insulation barrier between the active layer and silicon
substrate and hence reduces the parasitic capacitance tremendously. Moreover, this insulation barrier disables
leakage or latch-up currents between adjacent devices.
A major technological advantage of the Thin-Film-SOI technology is the easy way of lateral insulation of
elements inside the silicon film. The thin film technology allows each device to be separated from all other
devices by a simple local oxidation (LOCOS) process. Thus, there is no need for CMOS-wells for preventing the
"latch-up" effect and reducing the chip size.
The small size of PN-junctions inside the thin silicon film leads to higher switching speed, lower leakage
currents and consequently higher temperature stability. In order to obtain a proper body contact for the thin SOI-
MOS transistor the channel doping is extended and connected to a common source contact (split source
contact). Hence the thin-film SOI-MOS transistor exhibits an anti-paralleled diode that safeguards the device in
case of polarity reversal.
In spite of the thin drift regions inside the silicon films, reasonable low on-resistance per area is achieved. This
allows a cost effective layout of the output driver transistors.
The SOI technology is also implemented for the 600 V level-shift transistors and high-voltage diodes. The 600V-
NMOSFET is based on the low-voltage SOI-NMOSFET structure in conjunction with a very long Drain-
extension. The buried oxide insulation barrier cuts off parasitic current paths between substrate and silicon film.
This prevents the latch-up effect even in case of high dv/dt switching under elevated temperature and hence
provides improved robustness.
Besides these improvements, the thin-film SOI-technology provides additional benefits like lower power
consumption and higher immunity to radioactive radiation or cosmic rays.
Application Note 8 Rev. 1.3, 2014-03-23
AN-EICEDRIVER-6EDL04-1