The poor electron mobility presently observed
in metal-insulator-semiconductor devices using high-k insulators may be due
to a variety of processing and material-related issues. However, in this
talk it will be argued that the high-k itself may present an intrinsic, unavoidable
cause of this poor performance. Indeed, the high dielectric constant is usually
accompanied by the presence of soft optical phonons. The long-range dipole
field associated with the interface excitations, while small in the case
of SiO2, for most high-k materials is sufficiently large to depress
the effective electron mobility in the inversion layer of the Si substrate.
We study the dispersion of the interfacial coupled phonon-plasmon modes,
their electron-scattering strength, and their effect on the electron mobility
for Si-gate structures employing films of SiO2, Al2O3, AlN, ZrO2, HfO2 and ZrSiO4 for `SiO2-equivalent' thicknesses ranging from 5 nm to 0.5 nm.
* In collaboration with Deborah A. Neumayer, and Eduard A. Cartier