High-breakdown-voltage devices in ultra-thin SOI

The possible advantages of an SOI (silicon-on-insulator) RESURF (reduced surface electric field) device are explored with an idealized lateral diode structure consisting of a P⁺ diffusion into an N-silicon-on-insulator film, supported by an N⁺ silicon substrate. An optimized structure is shown to have a uniform lateral electric field and a vanishing vertical electric field along the top surface of the depletion region. An analytical model based on ionization integrals indicates that, for very thin SOI, the breakdown voltage increases with decreasing SOI thickness. Two-dimensional numerical breakdown simulations also support this finding. Experimentally, breakdown voltages in excess of 700 V have been demonstrated on diodes having approximately 0.1-μm-thick SOI layers and 2-μm-thick buried oxide layers, in excellent agreement with theory. An obvious advantage of this concept lies in the integration of high-voltage devices with high-performance SOI CMOS circuits on a single chip