Suppression of parasitic bipolar effects in thin-film SOI transistors

In order to correctly estimate the bipolar holding voltage of thin-film SOI transistors with submicrometer gate lengths, it is necessary to obtain the correct balance between the bipolar current gain and impact ionization. The bipolar current gain was found to be strongly dependent upon bandgap narrowing in the heavily doped source, while impact ionization may be most accurately modeled with a nonlocal ballistic model employing a composite electron mean-free path of 9.2 nm. Simulation with the improved models suggests that a reduction in the lateral electric field of the n/sup -/ drain region, and hence an increased bipolar holding voltage, may be achieved by using ultrathin highly doped SOI films. For a 0.5- mu m gate length, a maximum holding voltage in excess of 6 V has been simulated.<>