Merlin, the current cost of normal silicon wafers is between $1 to $2 per square inch. Your calculations of the mass of an athlon chip is somewhat flawed, since typically the tickness of the wafer is twice as thick (20 mils) and that is without taking into account kerf losses, which bring the boule mass to twice as much. You also have to take into account that while raw Si-28 might go for $75,000, single crystal Si-28 will go for at least twice as much (actually by the time a Kg of normal silicon is turned into a cheap wafer of $1/sq inch, the price per Kg has blown to about $1,400/ kg, or close to a factor of 20 of the raw material costs) and much more than half will be wasted. What you really need to compare is the roughly $2500/kg of high quality wafer to at least $150,000/kg (probably much more)for high quality Si-28 wafers.
As for Si having a neat native oxide, and Ga2O3 being unstable, that problem was solved some 15 to 20 years ago (Ga nitride was one solution, I am not certain what the current state of the art "native dielectric" are used, but deposition of thin SiO2 layers where also investigated at the time), and today quite a number of companies are doing a sizeable business (ANAD, TQNT and VTSS for example) in GaAs devices. It just cost too much to make sub GHz devices in GaAs, and and silicon keeps pushing the frequency limit (by feature reduction to sub .18 microns) and could conceivably reach the 2 GHz in the not too distant future.
Zeev |
