A model for the relation between substrate and gate currents in n-channel MOSFET's

The gate current in n-channel MOSFET's normalized to the source current is expressed as a function of the substrate current normalized to the source current by means of an impact ionization model. The ratio of the electron mean free path for impact ionization to that for optical phonon scattering, which is the most important among the various related device parameters, is determined by indirect measurement of the gate current using stacked-gate MOSFET's. The present model has been applied to interpret the experimental results obtained from samples with a variety of device dimensions. Limitation by the hot-electron emission, which is an important design constraint for submicrometer-gate MOS devices, is studied for single-gate and stacked-gate MOSFET's in comparison with other limiting factors.