What does a doped silicon layer mean?

[hrkhari]

Hi Guys:

I came across this statement while going through a Journal:

The advantage of using doped silicon layer for shield versus one of the closer metal layers is that the capacitance is less and the characteristic impedance higher.

What does it mean by doped silicon layer in this context?. Can anyone explain using an example of this layer?. Thanks in advance

Rgds

 

[SkyHigh]

Re: Doped silicon layer

Doped Silicon layer is basically a layer of Silicon doped with impurities such as Phosphor or Boron by Ion Implantation or Diffusion to improve the electrical properties such as conductivity and permittivity.

In your case that compares a metal with doped Silicon, this doped Silicon is probably doped PolySilicon or doped Poly-Si used in gate interconnect which is usually doped by impurities to improve conductivity and reduce permittivity to achieve low-k, thus low capacitance.

Characteristic impedance being higher? Are you sure? I seriously don't think so. Characteristic impedance is not a physical quantity to be quantified by length or material variables.

However with the introduction of doped Poly-Si instead of metal, sheet resistance is reduced due to improved conductivity, sheet capacitance is reduced due to reduced permittivity, thus the impedance over a unit length of interconnect is reduced, thus dissipates less power.

 

[flatulent]

Re: Doped silicon layer

It might also mean that the main silicon is further away than another metal layer. This will reduce the capacitance to the shield layer.