Patterned Ground Shileding

Hi Guys:

Why is it a common practice to use poly layer or silicided poly layer in realizing patterned ground shielding for inductor and not other llayers such as metal. Thanks in advance

Rgds

I think there are two reasons.

Why we need shielding?
1. we need to reduce substrate coupling between adjacent inductors.
2. we need to reduce the capacitance between inductor and lossy substrate.

Thus, if poly is conductive enough to reduce the coupling, it is ok to use it. Poly has another advantage, it is more away from inductor layers, thus lower parasitic capacitance.