Comment Re:Seems simple enough (Score 1) 168
Single isotope silicon? Silicon wafers surfaces (where the transistors are) are generally doped with ions using diffusion and etched, and the most serious defects are usually parametric due to patterning issues. We've go a long ways to go before actually isotope purity is going to be a limiting factor...
Conductivity of gold vs copper? Copper is a better conductor than gold (although silver is a better conductor than both of them). The reason that gold is used for *connections* is that it is more malleable than copper allowing it to make a more robust physical connection. For conduction, copper or silver is much better. The reason that silver isn't used today is that the processes needed to etch it are their infancy. Also, there's a reluctance to go there, because it's known that silver is much more prone to electro-migration issues than copper and the gain in conductivity is relatively small (compared from the step between aluminum and copper).
Also, silicon on insulator isn't w/o problems. The main problems today are the floating-body problem** which will likely render SOI impractical for devices that need high frequency switching (e.g, a CPU) in future process nodes. This is why after a brief commercial taste of this technology, many companies are moving away from it except for specialty products (like Z-ram).
Also, if your assertion is true that insulators don't conduct heat (very well), now you can't get heat away from one hemisphere of your circuit (instead of heat conducting up and down). Wouldn't that tend to make more problems than it solves?
**As I understand it, in bulk silicon, there is a leakage path that bleeds the capacitance away, but on an insulator, the body of a transistor is effectively a large parasitic capacitor. Failure to fully discharge the transistor body after switching creates somewhat of a memory effect limiting performance and potentially causing a parasitic transistors to drain floating nodes (e.g., in latches and xor-gates) in a operational sequence indeterminate way influenced by neighboring transistors. This makes it hard to margin for and may ultimately make it unworkable to obtain the tolerances needed for high speed design.