In simple words we can tell that double diffusion layer permit contact to the substrate from the surface.......................
The Laterally Diffused MOSFET is an asymmetric power MOSFET designed for low on-resistance and high blocking voltage. These features are obtained by creating a diffused p-type channel region in a low-doped n-type drain region. The low doping on the drain side results in a large depletion layer with high blocking voltage. The channel region diffusion can be defined with the same mask as the source region, resulting in a short channel with high current handling capability. The relatively deep p-type diffusion causes a large radius of curvature at the edges, which eliminates the edge effects. Diffusion can be used in addition to further increase the junction depth and radius of curvature.
EDGE EFFECT: Few p-n diodes are truly planar and typically have higher electric fields at the edges. Since the diodes will break down in the regions where the breakdown field is reached first, one has to take into account the radius of curvature of the metallurgical junction at the edges. Most doping processes including diffusion and ion implantation yield a radius of curvature on the order of the junction depth, xj. The p-n diode interface can then be approximated as having a cylindrical shape along a straight edge and a spherical at a corner of a rectangular pattern. Both structures can be solved analytically as a function of the doping density, N, and the radius of curvature, xj.
The resulting breakdown voltages and depletion layer widths are plotted below as a function of the doping density of an abrupt one-sided junction.
Figure 4.5.1 : Breakdown voltage and depletion layer width at breakdown versus doping density of an abrupt one-sided p-n diode. Shown are the voltage and width for a planar (top curves), cylindrical (middle curves) and spherical (bottom curves) junction with 1 mm radius of curvature.
https://www.circuitstoday.com/double-diffused-mos-dmos
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The Laterally Diffused MOSFET is an asymmetric power MOSFET designed for low on-resistance and high blocking voltage. These features are obtained by creating a diffused p-type channel region in a low-doped n-type drain region. The low doping on the drain side results in a large depletion layer with high blocking voltage. The channel region diffusion can be defined with the same mask as the source region, resulting in a short channel with high current handling capability. The relatively deep p-type diffusion causes a large radius of curvature at the edges, which eliminates the edge effects. Diffusion can be used in addition to further increase the junction depth and radius of curvature.
EDGE EFFECT: Few p-n diodes are truly planar and typically have higher electric fields at the edges. Since the diodes will break down in the regions where the breakdown field is reached first, one has to take into account the radius of curvature of the metallurgical junction at the edges. Most doping processes including diffusion and ion implantation yield a radius of curvature on the order of the junction depth, xj. The p-n diode interface can then be approximated as having a cylindrical shape along a straight edge and a spherical at a corner of a rectangular pattern. Both structures can be solved analytically as a function of the doping density, N, and the radius of curvature, xj.
The resulting breakdown voltages and depletion layer widths are plotted below as a function of the doping density of an abrupt one-sided junction.
Figure 4.5.1 : Breakdown voltage and depletion layer width at breakdown versus doping density of an abrupt one-sided p-n diode. Shown are the voltage and width for a planar (top curves), cylindrical (middle curves) and spherical (bottom curves) junction with 1 mm radius of curvature.
https://www.circuitstoday.com/double-diffused-mos-dmos
