Why we always make resistors with poly or nwell ?

[penchal_gv]

Hi All,
why we make always resistor with poly,nwell.......but not with active even though active(P+/N+) having more resistance than poly and well. plz clarify me

Thanks
Penchal

 

[leohart]

making resistor

active should always been made as low sheet resistor as possible,because they will affect the parasitic s,d resistance.You can use it as a resistor if u like,but this kind of resistor and nwell resistor is not so precise as poly.

 

[siskam]

Re: making resistor

Hi All,
why we make always resistor with poly,nwell.......but not with active even though active(P+/N+) having more resistance than poly and well. plz clarify me

Thanks
Penchal

In integrated circuit (e.g. such as procesor) there are active resistors for pull-down (or pull-down).
Inside out, in "active load" (for testing el. equipment) are used FET as a electronic resistor.

Martin

 

[n1cm0c]

Re: making resistor

active is always covered with silicide, to reduce the resistance of the source/drain.

You can ask for a silicide block mask that will allow you to have "native" active, this is very common in esd protection devices.

The resistance value can be relatively well controlled, but the parasitic capacitance is a problem. It's also non-linear, so you'll have distortion. The resistance itself is actually rather like a JFET.