Why not SiGe Microwave Schottky Diodes?

[mwman]

Can anyone explain why people use Si and Ga As for microwave/RF
Schottky diodes and not SiGe?

 

[Joerg]

mwman wrote:

Can anyone explain why people use Si and Ga As for microwave/RF
Schottky diodes and not SiGe?

For Si versus SiGe that probably boils down to one single sign: $

Regards, Joerg

 

[mwman]

Thank you, Joerg!

I'm sure cost hase something to do with it, but, if there is a
notcieable performance advantage I expect application's volume mey be a
mitigating factor.

After all, GaAs is (much) more expensive than Si, but people willingly
pay for the GaAs performance advantage!

I know SiGe is used for high microwave transistors (HBT), which are
'better' than GaAs transistors (higher ft, gain, est.). Such HBTs are
reltively new (<10years) yet many companies produce tham now as part of
RF/MW ICs.

This is why I was wondering if there are some fundamental disdvantages
for SiGe!

Regards to all readers!

 

[Joerg]

Hello mwman,


Would be nice to know the real name ;-)

I'm sure cost hase something to do with it, but, if there is a
notcieable performance advantage I expect application's volume mey be a
mitigating factor.

It's always performance per Dollar. Unless there is an application that
simply could not be done at all without SiGe it just has to make
budgetary sense.

After all, GaAs is (much) more expensive than Si, but people willingly
pay for the GaAs performance advantage!

I know SiGe is used for high microwave transistors (HBT), which are
'better' than GaAs transistors (higher ft, gain, est.). Such HBTs are
reltively new (<10years) yet many companies produce tham now as part of
RF/MW ICs.

This is why I was wondering if there are some fundamental disdvantages
for SiGe!

I am not the expert here but a few things are a bit puzzling. Research
results for SiGe diodes had been published a few years ago and IIRC
Philips was involved. However, unless I am missing something I don't see
any products to that effect on their site. Of course, their site ain't
the best so it is easy to miss something. Then they have (had?) their
SiGe wideband transistors BFU510 and BFU540. Both now carry a red
warning flag "This product has been discontinued". Hmm....

Regards, Joerg

 

[mwman]

Thank you for your reply, I found it very informative.

I'm looking for a small subcontarctor to test for us microwave diodes
and capacitors: do you 'or someone you know' knows one in the Silicon
Valley?

Regards,

Adrian

 

[Joerg]

Hello Adrian,

I'm looking for a small subcontarctor to test for us microwave diodes
and capacitors: do you 'or someone you know' knows one in the Silicon
Valley?

I had seen your other post, would have answered if I knew someone with
an impedance analyzer that can go to 35GHz. Mine is limited to 1GHz. You
might want to scope through the IEEE consultant's database and look for
microwave folks in California:

http://www.ieeeusa.org/business/consultants/cgi-bin/consultant.cgi?task=display_page/page=home.html

The other option might be to rent an analyzer from a company like Telogy
and do it in-house.

Regards, Joerg