[SI-LIST] small device de-embedding & modeling
- From: Brecht Machiels <brecht.machiels@xxxxxxxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Tue, 13 Apr 2010 10:50:58 +0200
Hi,
I would like to obtain measurements of MOSFETs that are valid up to high
frequencies (110GHz). Unfortunately, I'm not familiar with de-embedding.
I'm currently investigating a number of de-embedding techniques:
http://ieeexplore.ieee.org/search/srchabstract.jsp?tp=&arnumber=830987&queryText%3D.QT.A+four-step+method+for+de-embedding+gigahertz.QT.%26openedRefinements%3D*%26searchField%3DSearch+All
http://ieeexplore.ieee.org/search/srchabstract.jsp?tp=&arnumber=4141067&queryText%3D.QT.Efficient+De-Embedding+Technique+for+110-GHz+Deep-Channel-MOSFET+.QT.%26openedRefinements%3D*%26searchField%3DSearch+All
I've given the first of these a quick try by emulating a measurement
using a test fixture (unlikely to be optimal) and dummy structures
simulated in ADS momentum. Afterwards, I insert a MOSFET model into the
test fixture using HSPICE. From the obtained S-parameters I can perform
de-embedding.
For large MOSFETs (W > 32 um), the de-embedded S21 and S12 are indeed
very close to the model's S21 and S12. S11 and S22 are less closely
matched to the model's, but still close. At higher frequencies (> 80
GHz), the error becomes larger.
For small MOSFETs, the de-embedded measurements only fit the model at
lower frequencies. I assume this is to be expected as the DUT's
properties become smaller compared to the test fixtures.
Also, the articles on de-embedding I have read/scrolled through always
use large MOSFETs for the DUT (W > 64 um) when verifying the presented
de-embedding technique.
This makes me wonder how typical transistor models are developed. I
assume a number of large transistors are measured to which a model is
fitted (BSIM, for example). Smaller transistors are modeled by means of
an implicit extrapolation. Could that be anywhere near how it's done?
Unfortunately, I need to use small transistors (W as small as 2 um) in
my design, so I'm not sure how to continue from here. Any suggestions?
Kind regards,
Brecht
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