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Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views. It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if you would like to post something on RF Cafe's Facebook page, please do.

Below are all of the forum threads, including all the responses to the original posts.


satish.1979
Post subject: current collapse Posted: Thu Oct 05, 2006 3:30 am

Captain

Joined: Tue Oct 03, 2006 3:03 am
Posts: 11
Location: India
what is current collapse phenomena in tqhbt?
How can we overcome from that?


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Stephen
Post subject: Posted: Tue Oct 10, 2006 2:56 pm

Captain

Joined: Wed Jun 21, 2006 8:33 pm
Posts: 21
Location: Queen Creek, Arizona
satish,
"Current collapse" of heterjunction bipolar transistors is an unwanted phenomena where, as a result of temperature extremes, current becomes unevenly distributed across different legs of a device (usually a single leg of a multi finger device experiences second order effects such as thermal runaway). When this happens, the total current gain of the transistor degrades and the collector current decreases, causing the "current collapse".


There are several ways to avoid it, some not as useful as others:

1. use a single legged HBT (not useful, as it can still experience problems)
2. layout is a key: proper layout can help with even temperature gradients across the device.
3. Operate the device at lower power so that you do not experience higher temperature that cause the "collapse".

This temperature operating threshold is very process specific, which addresses the other point in your question: TQHBT

If I am not mistaken, TQHBT is a Heterjunction bipolar transistor manufactured by Triquint (Google Search as I had never heard of the device). In this case, they should provide you information on temperature operating ranges for the device to avoid the "collapse" phenomena.

To be honest I am not entirely versed in the physics of the collapse, so I can not tell you exactly if the mechanism is due to beta-temperature effects of say carrier mobility effects, etc. Maybe someone else can shed light on that.

_________________
CMOS RF and Analog ESD Specialist!
www.srftechnologies.com

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satish.1979
Post subject: ThanksPosted: Wed Oct 11, 2006 8:59 am

Captain

Joined: Tue Oct 03, 2006 3:03 am
Posts: 11
Location: India
Thanks stephan for your kind and brief reply


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Jeanalmira
Post subject: Posted: Mon Oct 30, 2006 10:37 pm

General


Joined: Tue Mar 15, 2005 11:43 pm
Posts: 65
Location: Singapore
Hi :

How about GaN HEMT? I observed that it happens to GaN HEMT too. I am not sure whether it's related to surface trapping? and how this phenomenon related?

Any advice is appreciated.

Thanks and Regards,
Jean


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Stephen
Post subject: Posted: Thu Nov 09, 2006 6:48 pm

Captain

Joined: Wed Jun 21, 2006 8:33 pm
Posts: 21
Location: Queen Creek, Arizona
Jeanalmira,
I think most of my previous comments still apply. the phenomena is a temperature dependent effect and is possible among multi-legged devices. regarding any particular technology, you need to ask your foundry for detailed information on the conditions over which the collapse may occur. Overall, remember it is caused by non-uniform temperature gradients across the legs of your device.

Keep temperature low and uniform across the device, and use a very uniform layout; is the best advice I can give without specific knowledge of the process.

_________________
CMOS RF and Analog ESD Specialist!
www.srftechnologies.com



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