Simulation in PGS (simulating in HFSS)

[Hyao89]

Hello experts,

I have a question on the PGS performance. I am now simulating a silicon-based transformer in HFSS and want to see the performance of the Patterned Ground Shield (PGS). From the simulation results it seems that the polysilicon PGS can give a higher Q-Factor than the metal PGS with the same size, shape and clearance to the coils. I was wondering if you can help me to analyze why the polysilicon is better in the sense of Q improvement even though poly's conductivity is low?

Thank you in advance!

Hyao

 

[shar2013]

Couple of reasons

1. The poly silicon is a lower layer so the parasitic capacitance is lower.
2. If the pattern is not well designed it is allowing eddy currents which degrade the performance , since poly-silicon has higher resistance the eddy currents arer of lower magnitude and the Q increases.

Good Luck !

 

[Hyao89]

Hello shar2013, thank you for replying. It seems the inductance of the transformer is enhanced with the polysilicon PGS comparing to the Metal PGS. Is this due to the reduction of the eddy current? Thank you!

Couple of reasons

1. The poly silicon is a lower layer so the parasitic capacitance is lower.
2. If the pattern is not well designed it is allowing eddy currents which degrade the performance , since poly-silicon has higher resistance the eddy currents arer of lower magnitude and the Q increases.

Good Luck !

 

[shar2013]

Is it a single ended Inductor or differential ?
if it is a single ended it might be the eddy currents check the SRF (self resonance frequency) if the polysilicon has lower SRF it is probably the eddy currents, since it is lower than the metal the SRF should increase (less parasitic capacitance) and if it doesnt it means the eddy currents in the metal are reducing the inductance thus increasing the SRF.