[SI-LIST] HFSS Issue Zpi Zpv (continued..)

From: Bi Han <mike_bihan@xxxxxxxxxxxx>
To: List` Si <si-list@xxxxxxxxxxxxx>
Date: Sun, 16 Feb 2003 23:03:55 +0800 (CST)
Hi, all:

After some experiments, I now have some new questions about Ans0ft HF-SS and 
Maxwe11 2D solver.

As stated in the previous discussion, HF-SS failed to give me satisfying 
results. The simulated result Zpi!=Zpv (Zpi ~ 200 and Zpv ~76) @2GHz. 


I will give the geometric information for information: 

0.18um Digital Cmos process, top Al metal thickness is 0.88u, the thickness of 
the between top meal and substrate is about 7.45um/K=4.2. The thickness of 
PASS1VATION (above bottom plane of top metal ) is about 2.5um/k=4.5. The 
thickness of the Si substrate is about 700um/k=11.9/10ohm-cm.


Since Ans0ft manual does not help a lot in this field, I consulted agilent HFSS 
manual, it tells that the CPW structure should use Zpv for usage. However, 
acording to my personal experience, the CPW tructure of such low frequency(2G) 
should be quasi-TEM mode, and the value of Zpi and Zpv should not differ 
greatly. Why Agilent manual gives out such info?

To test the accuracy of Zpv result, I planed to simulate the same structure 
under Maxwe11 2D and ADS linecalc.But, linecalc do not have such in-built CPW 
structure. As to Maxwe11 2D, how to attach the substrate to ground metal line 
becomes an issue. Since in HFSS, port edge will short the sub with side-ground 
of CPW(will this cause problem?), However, in 2D solver, I can only attach the 
substrte to ground metal by another metal to penetrate the SiO2 layer. This 
metal will unwillingly serve as another ground line and form a strucutre, 
somewhat like half rectangular waveguide, which does not exist in the real 
world. Is there any better way?

In short, there is still a lot remaining unclear in my mind. Any people can 
give out their valuable idea? Such as why Zpi should be different from Zpv in 
CPW structure? Is that brought by FEM method naturally or is simply wrong 
software setup by me?

Thanks!
B.H.

 

 



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[SI-LIST] HFSS Issue Zpi Zpv (continued..)

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