Integrating an Inductor on a Chip / Die / Package?

[nekto]

Can someone tell me what the benefit of this is, and why it's been traditionally very hard?

I've heard that many RF applications now do an S-i-P integration of an inductor, possibly for spatial and cost reasons.. What would be some considerations, though (i.e. does the inductor add any noise / interference, or is it just hard to make it very small, as opposed to transistors that are shrinking with each process node)? Also wondering if one can go beyond SiP and just put it directly on the same die.

 

[yungman]

Hard to make it small. You can only put so many turns in the inductor if it is inside the IC. Also I can see one of the major problem is the area in the middle of the coil. The inductance goes down with the area. So the smaller the inductor, the lower the inductance you can get. This is not the same as shrinking the transistors where small transistor can still perform the job.

There might be other reasons, the two mentioned above is very obvious.