No surprise
Asked in an interview to reconcile the differences between the IMEC and TI presentations, Fischetti said, "I'm not surprised that these labs are reporting inconsistent results. While we are all learning fast, these processes are not very well-controlled yet. The annealing steps, the deposition and growth techniques, all require a lot more optimization-but we don't have much time before these new materials may be needed."
The industry has seen "pretty promising results" from silicates, such as zirconium silicate and hafnium silicate, he said, but "when we try to measure the mobility, for most transistors with these high-k materials it is pretty bad." Degradation ranges "from 30 percent up to a factor of two compared with the universal mobility curve. A 30 percent hit is not good news."
The hit to mobility is intrinsic, Fischetti said, because as the dielectric constant increases, the electrons tend to polarize, and the bandgap decreases sharply. The phonons in high-k materials vibrate with a frequency that results in softer atomic bonds, which lead to charge trapping.
"There are dark areas in the theory, and at the experimental level we don't know exactly where we are with some deposition techniques," Fischetti said. "So I take some of these early results with a grain of salt. But if the problems are intrinsic because of remote scattering of the optical phonons-if that is true-then we could be in bad shape."
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