Threshold voltage control in buried-channel MOSFETs

The analytical calculation of the threshold voltage in the buried-channel MOSFET (BCMOSFET) is revisited in connection with its widespread use in CMOS VLSI electronics. This device class is shown to comprise two distinct varieties, i.e., metallurgical-channel and field-induced-channel, depending on the thickness of the channel layer and the doping levels in the channel and body regions. The threshold voltage equations of the metallurgical-channel variety are reviewed briefly, and a first-order model is derived for the field-induced-channel variety. The long-channel threshold voltage of BCMOSFETs is calculated analytically providing a complete set of practical design equations and plots. The analytical model is validated by 2-D numerical calculations, and also by independent statistical observations on manufacturing data. It enables a clear theoretical assessment of the advantages and limitations of the BCMOSFET device architecture in the concert of VLSI miniaturization. (C) 1997 Elsevier Science Ltd.