Interdigital capacitor hfss simulation

[vfurlan]

Dear all,

I need help with HFSS design of IDC.
As you can see in the attachment, I made the model of IDC on a 200nm ferroelectric material. Fed with two waveports and microstrip. The airbox is big because I made it lambda/4 for the lowest frequency.
I made a model in Sonnet also, so the compare results. HFSS model resonates way to low (see Y parameters) and C is about 100 time to high. Can you advise how to change the model.

Thank you

 

[Manjunatha_hv]

Hello vfurlan ,


Upload your sonnet em model too, then we can se how you have setup the settings for em simulation....
Basically just see how you entered the ferroelectric material properties...

---manju---

 

[vfurlan]

Here it is. Sonnet model should be correct. I get resonable results (I have some mathematical models so I know approximatively what should I get).
I modeled ferroelectric as a simple epsilon = 500, tan = 0.01, 200nm substrate (BST in the model).

 

[Manjunatha_hv]

Hello vfurlan ,

I see you have setup the sonnet model pretty nice...Except I could find couple of initial preliminary issues...
1. Grid needs to be fined specially Y Grid, set it to 1 um instead of 5 um as conductor itself 5um wide
2. Remove the Symmetry option this is not suitable for this kind of circuit (in Box Settings)
3. Since conductor thickness & below BST dielectric thickness are comparable or less so you need to use conductor as thick metal

Then you simulate you may get good results....
Finally you can also try anisotropic dielectric option for BST in Sonnet...


---manju---

 

[vfurlan]

Thank you for suggestions. Why is Symmetry not suitable?

 

[Manjunatha_hv]

Hello vfurlan ,

Nice to know it helped you...
Regarding Symmetry option...It should divide the Ports on both side (which is okay in your case ) & as well as equally divide the circuit in both top & bottom
(in your case it is just dividing on the Gap or space & not on the metal finger)...So symmetry not applicable...
See more help on Sonnet user Guide for "Port Placement with Symmetry On" topic...

May be if you fine the Y Grid then check the Symmetry & see how it divides....

---manju---