Effects of poly doping on mos varactor

[ustc_tweeg]

hi, I meet with a problem about mosvar and need some help.
I make two mosvar and test them at 2GHz with bias voltage sweeping from -1.8v to 1.8v.

mosvar1: n+ poly; n+ source/drain in n-well
mosvar2: p+ poly; n+ source/drain in n-well

As for the mosvar1 the c-v curve soon reaches a maximum value at about 1v, and then holds on for higher bias voltage. While the mosvar2 keeps rising upon positive bias, and no sign of slowing down.

I wonder why the poly doping makes so big a difference?

 

[lladnar23]

mosvaractor question

The gate material makes a big difference. Check out Muller & Kamins. There are issues like surface states, pinned Fermi level, etc...