The schematic cross sections of the simulated devices are shown in Figure 4.1
to Figure 4.3. Generally, the BV of conventional SOI LDMOSFETs,
is limited by the buried oxide thickness, SOI thickness and the drift layer length.
Figure 4.1 shows a cross-sectional view of a conventional -channel SOI-LDMOSFET
designed for a BV of 300V with an SOI thickness
of 7
m,
and with a buried oxide thickness
of 2
m.
The drift region of the device
is doped according to the RESURF principle to achieve a maximum
BV.
-channel P-SOI LDMOSFETs with a silicon window under the drain
and under the source are shown in Figure 4.2 and Figure 4.3, respectively.
As shown in the figures, silicon is used as a window instead of some part of the
buried oxide layer. The major variable parameters are the
-substrate doping
concentration and the
-drift layer length. The
,
, and SOI layer
doping concentration of the P-SOI LDMOSFETs are the same as those of conventional
SOI LDMOSFETs shown in Figure 4.1.
Jong-Mun Park 2004-10-28