CONTOURED-TUB FERMI-THRESHOLD FIELD EFFECT TRANSISTOR AND METHOD OF FORMING SAME

摘要

A Fermi-threshold field effect transistor includes a contoured-tub region of the same conductivity type as the source, drain and channel regions and having nonuniform tub depth. The contoured-tub is preferably deeper under the source and/or drain regions than under the channel region. Thus, the tub-substrate junction is deeper under the source and/or drain regions than under the channel region. The diffusion capacitance is thereby reduced compared to a tub having a uniform tub depth, so that a high saturation current is produced at low voltages. The contoured-tub may be formed by an additional implant into the substrate using the gate as a mask.