Measurement and modeling of circuit speed of CMOS on oxygen-implanted SOI

The dependence of the stage delay of CMOS ring oscillators on the voltage applied to the underlying silicon substrate has been investigated for SOI substrates formed by high-dose oxygen ion implantation. Improvements in speed of up to 30 percent are produced when the silicon under the isolating oxide is depleted. This situation occurs naturally for zero applied voltage when the substrate is lightly doped p-type and gives the oxygen-implanted SOI similar speed performance to other forms of SOI with thicker isolation layers. The increased speed is in good agreement with predictions made using SPICE simulation and modeled circuit capacitances.