Gamma ray irradiation question

R

Richard Rasker

Guest
Hi all,

In the course of designing a rather simple electronic circuit for use in a
medical implant I was confronted with an unforeseen problem: the implant
must of course be sterilized, and this includes the internal electronics.

The standard sterilization procedure for this type of implants is based on
gamma ray irradiation (by a Co-60 source, if I'm not mistaken).
However, I couldn't locate much useful information with regard to the use
of gamma ray irradiation in combination with electronics; the best I could
find was the following article, which suggests the gate oxide of MOSFET's
could get permanently damaged by electron-positron-pair creation in the
presence of an electrical field:

http://www.phys.ualberta.ca/~gingrich/atlas/radiation/radiation.pdf

I surmised that the electronics wouldn't run much of a risk, since no
electrical field would be present during irradiation (i.e. the circuit was
switched off). Therefore I didn't expect too much of a problem when my
circuit (employing several FDC6327 MOSFET-pairs) was submitted for an
irradiation test.
Unfortunately afterwards, several of the FET's turned out badly damaged
(some sort of DS short circuit latch-up when a power supply was hooked up,
more or less consistent with trapped charge in the gate oxide).

My questions are the following:
- Does anyone have any quantitative information on the effects of gamma
ray irradiation for sterilization purposes on electronic components in
general and MOSFET's in particular?
- Is gamma ray sterilization at all feasible with MOSFET's?
- If not, which sterilization procedure(s) is/are commonly used for pace
makers and other electronic implants? Do these procedures have any other
possibly damaging effects on the electronics?
- Are there special 'med-spec' components for these types of circuits?

Thanks in advance for any information,

Best regards,


Richard Rasker

--
Linetec Translation and Technology Services

http://www.linetec.nl/
 
Just a thought...
it might pay you to investigate the components offered by companies to
the space programes as they have to meet stringent radiation specifications.

-=Nick



"Richard Rasker" <spamtrap@linetec.nl> wrote in message
news:pan.2004.03.15.23.18.20.556500@linetec.nl...
Hi all,

In the course of designing a rather simple electronic circuit for use in a
medical implant I was confronted with an unforeseen problem: the implant
must of course be sterilized, and this includes the internal electronics.

The standard sterilization procedure for this type of implants is based on
gamma ray irradiation (by a Co-60 source, if I'm not mistaken).
However, I couldn't locate much useful information with regard to the use
of gamma ray irradiation in combination with electronics; the best I could
find was the following article, which suggests the gate oxide of MOSFET's
could get permanently damaged by electron-positron-pair creation in the
presence of an electrical field:

http://www.phys.ualberta.ca/~gingrich/atlas/radiation/radiation.pdf

I surmised that the electronics wouldn't run much of a risk, since no
electrical field would be present during irradiation (i.e. the circuit was
switched off). Therefore I didn't expect too much of a problem when my
circuit (employing several FDC6327 MOSFET-pairs) was submitted for an
irradiation test.
Unfortunately afterwards, several of the FET's turned out badly damaged
(some sort of DS short circuit latch-up when a power supply was hooked up,
more or less consistent with trapped charge in the gate oxide).

My questions are the following:
- Does anyone have any quantitative information on the effects of gamma
ray irradiation for sterilization purposes on electronic components in
general and MOSFET's in particular?
- Is gamma ray sterilization at all feasible with MOSFET's?
- If not, which sterilization procedure(s) is/are commonly used for pace
makers and other electronic implants? Do these procedures have any other
possibly damaging effects on the electronics?
- Are there special 'med-spec' components for these types of circuits?

Thanks in advance for any information,

Best regards,


Richard Rasker

--
Linetec Translation and Technology Services

http://www.linetec.nl/
Click to expand...
 
"Richard Rasker" <spamtrap@linetec.nl> wrote in message
news:pan.2004.03.15.23.18.20.556500@linetec.nl...
Hi all,

In the course of designing a rather simple electronic circuit for use in a
medical implant I was confronted with an unforeseen problem: the implant
must of course be sterilized, and this includes the internal electronics.

The standard sterilization procedure for this type of implants is based on
gamma ray irradiation (by a Co-60 source, if I'm not mistaken).
However, I couldn't locate much useful information with regard to the use
of gamma ray irradiation in combination with electronics; the best I could
find was the following article, which suggests the gate oxide of MOSFET's
could get permanently damaged by electron-positron-pair creation in the
presence of an electrical field:

http://www.phys.ualberta.ca/~gingrich/atlas/radiation/radiation.pdf

I surmised that the electronics wouldn't run much of a risk, since no
electrical field would be present during irradiation (i.e. the circuit was
switched off). Therefore I didn't expect too much of a problem when my
circuit (employing several FDC6327 MOSFET-pairs) was submitted for an
irradiation test.
Unfortunately afterwards, several of the FET's turned out badly damaged
(some sort of DS short circuit latch-up when a power supply was hooked up,
more or less consistent with trapped charge in the gate oxide).

My questions are the following:
- Does anyone have any quantitative information on the effects of gamma
ray irradiation for sterilization purposes on electronic components in
general and MOSFET's in particular?
- Is gamma ray sterilization at all feasible with MOSFET's?
- If not, which sterilization procedure(s) is/are commonly used for pace
makers and other electronic implants? Do these procedures have any other
possibly damaging effects on the electronics?
- Are there special 'med-spec' components for these types of circuits?
Thanks in advance for any information,
Best regards,
Richard Rasker
Click to expand...
A guy I used to work with in MA designed dc-dc converters for space apps,
and we had a number of interesting chats. One of the interesting effects of
ionising radiation is it can lower the Vth of MOSFETs, sometimes even making
it negative (yes, negative). With a unipolar gate drive circuit, this of
course means the FETs all turn on - BOOM. In addition to using rad-hardened
devices ($$$) Dan also used +/-15V gate drive voltages, to ensure the darned
things stayed off.

Man, I bet that cost someone a pretty penny to figure out - can you imagine?
"lets send this one up, and see if it dies" or better yet, "bring it back
and we'll figure out what went wrong" ?!?
 
I read in sci.electronics.design that Richard Rasker
<spamtrap@linetec.nl> wrote (in <pan.2004.03.15.23.18.20.556500@linetec.
nl>) about 'Gamma ray irradiation question', on Tue, 16 Mar 2004:
In the course of designing a rather simple electronic circuit for use in
a medical implant I was confronted with an unforeseen problem: the
implant must of course be sterilized, and this includes the internal
electronics.

The standard sterilization procedure for this type of implants is based
on gamma ray irradiation
Click to expand...
Are you sure about that? If a pacemaker can be sterilized with gammas, I
don't see why your device could not be. I suspect, however, that
pacemakers are sterilized using a different method.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
 
On Tue, 16 Mar 2004 08:43:07 +0000, John Woodgate wrote:

I read in sci.electronics.design that Richard Rasker
spamtrap@linetec.nl> wrote (in <pan.2004.03.15.23.18.20.556500@linetec.
nl>) about 'Gamma ray irradiation question', on Tue, 16 Mar 2004:
In the course of designing a rather simple electronic circuit for use in
a medical implant I was confronted with an unforeseen problem: the
implant must of course be sterilized, and this includes the internal
electronics.

The standard sterilization procedure for this type of implants is based
on gamma ray irradiation

Are you sure about that? If a pacemaker can be sterilized with gammas, I
don't see why your device could not be. I suspect, however, that
pacemakers are sterilized using a different method.
Click to expand...
Sorry, I meant to say that this company (which has been making mechanical
implants up until now) uses gamma ray sterilization by default - not that
this sterilization technique is standard for electronic implants. It's a
bit confusing the way I put it.

Richard Rasker

--
Linetec Translation and Technology Services

http://www.linetec.nl/
 
On Mon, 15 Mar 2004 23:35:38 +0000, Sir Charles W. Shults III wrote:

"Richard Rasker" <spamtrap@linetec.nl> wrote in message
news:pan.2004.03.15.23.18.20.556500@linetec.nl...
Hi all,

In the course of designing a rather simple electronic circuit for use
in a medical implant I was confronted with an unforeseen problem: the
implant must of course be sterilized, and this includes the internal
electronics.
Click to expand...
[snip gamma ray trouble]

Sterilizing with gamma is all well and good, but if you are using
late generation semiconductors, you are playing with fire. Rad-hardened
chips will go a long way, but they are typically made by using larger
junction areas and sometimes shielding inside the package itself.
Expect to pay premium prices.

Cheers!

Chip Shults
Click to expand...
This information is most helpful, thanks!
I'll look into other methods of steriliation first, such as ethylene oxide
or autoclave-sterilization, and try to find the best procedure (any
information on this is, of course, still welcome :).

Richard Rasker

--
Linetec Translation and Technology Services

http://www.linetec.nl/
 
I read in sci.electronics.design that Richard Rasker
<spamtrap@linetec.nl> wrote (in <pan.2004.03.16.11.51.51.497072@linetec.
nl>) about 'Gamma ray irradiation question', on Tue, 16 Mar 2004:
This information is most helpful, thanks!
I'll look into other methods of steriliation first, such as ethylene
oxide or autoclave-sterilization, and try to find the best procedure
(any information on this is, of course, still welcome :).
Click to expand...
Can you not actually ask a pacemaker manufacturer how they sterilize?
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
 
On Tue, 16 Mar 2004 12:29:43 +0000, John Woodgate wrote:

I read in sci.electronics.design that Richard Rasker
spamtrap@linetec.nl> wrote (in <pan.2004.03.16.11.51.51.497072@linetec.
nl>) about 'Gamma ray irradiation question', on Tue, 16 Mar 2004:
This information is most helpful, thanks!
I'll look into other methods of steriliation first, such as ethylene
oxide or autoclave-sterilization, and try to find the best procedure
(any information on this is, of course, still welcome :).

Can you not actually ask a pacemaker manufacturer how they sterilize?
Click to expand...
This is indeed a planned course of action, although previous experiences
are not very encouraging: manufacturers of medical devices are as a rule
extremely secretive about even the simplest aspects of their production
process. However, information on proper sterilization of electronic
circuits is slowly accumulating, so hopefully we can make a well-informed
decision within the next week.

Richard Rasker

--
Linetec Translation and Technology Services

http://www.linetec.nl/
 
Richard Rasker <spamtrap@linetec.nl> wrote:
Hi all,

In the course of designing a rather simple electronic circuit for use in a
medical implant I was confronted with an unforeseen problem: the implant
must of course be sterilized, and this includes the internal electronics.

Gamma rays that intersect the entire outside shell need not intersect
Click to expand...
the electronics.
For example, imagine a spherical implant.
If you rotate the implant in a beam with the middle missing, all the edges
get irradiated, but not the middle.
 
On Tue, 16 Mar 2004 19:44:55 +0000, Ian Stirling wrote:

Richard Rasker <spamtrap@linetec.nl> wrote:
Hi all,

In the course of designing a rather simple electronic circuit for use in a
medical implant I was confronted with an unforeseen problem: the implant
must of course be sterilized, and this includes the internal electronics.

Gamma rays that intersect the entire outside shell need not intersect
the electronics.
For example, imagine a spherical implant.
If you rotate the implant in a beam with the middle missing, all the edges
get irradiated, but not the middle.
Click to expand...
Interesting concept (and well-proven in countless therapy cases), however
impractical in this instance; the electronics are mounted very close to
the outside housing, which has a thickness of a fraction of an inch.
Radiation levels would have to go from almost zero to full strength in the
distance of approximately 1 mm, not to mention the necessary rotational
stability and accuracy to ensure full sterilization on one hand, and avoid
damage to the circuit on the other hand. Besides, I don't think the
irradiation facility offers this sort of techniques.

I think we'll settle for autoclave sterilization at 130 degrees
centigrade (something which I can almost test in my own kitchen with my
pressure-cooker :) This means that I can't use electrolytical capacitors
- but these weren't part of the circuit in the first place. And if anyone
has some more on ethylene oxide sterilization of electronics, please let
me know as well - since that's another common alternative.

Richard Rasker

--
Linetec Translation and Technology Services

http://www.linetec.nl/
 
Richard Rasker wrote:
Hi all,

In the course of designing a rather simple electronic circuit for use in a
medical implant I was confronted with an unforeseen problem: the implant
must of course be sterilized, and this includes the internal electronics.

The standard sterilization procedure for this type of implants is based on
gamma ray irradiation (by a Co-60 source, if I'm not mistaken).
Click to expand...
I have no idea what the usual dose is to sterilise anything. It may
be far too much for any electronic device to resist. Up to a few
kGy, it should be possible to design something that survives without
using special components. Rad-hard components can stretch that by
a factor of ten to hundred, depending on the technology. Beyond
100kGy, practically nothing survives.

The main effects of radiation on transistors are a deterioration
of BJT beta and a threshold shift in FETs. The obvious message is
to design your circuits to tolerate a large change in these parameters.
I have pre-amplifiers that routinely survive doses of 3kGy before
finally breaking, designed keeping this in mind.

The trouble is that there is no way, short of testing, how a given
component will fare when irradiated. That's especially true of
ICs. An LM317 regulator will survive about 1kGy, for example, but
an LM337, its negative counterpart, dies at only 30Gy. When a
manufacturer decides to change something in his technology, a
chip that worked fine up to then may suddenly turn into a major
headache. For example, old-fashioned LSTTL would survive 10kGy,
but FAST will only take a few tens of grays.

On a sideline, avoid using any halogenated polymers. PTFE is
an absolute disaster when irradiated. HF diffuses out and
eats anything it comes into contact with. Polyimide, PEEK and
kapton are fine.

Finally, I picked a few web page addresses from the web site of
a working group that deals with these problems here:

http://www.klabs.org/DEI/index.htm
http://radnet.jpl.nasa.gov/cgi-win/1/FrontPage_CGI_Project?|main
http://flick.gsfc.nasa.gov/radhome/RadDataBase/RadDataBase.html
https://escies.org/public/radiation/esa/database.html

Regards,
Jeroen Belleman
 
On Wed, 17 Mar 2004 13:48:50 +0100, Jeroen wrote:

Richard Rasker wrote:
Hi all,

In the course of designing a rather simple electronic circuit for use in a
medical implant I was confronted with an unforeseen problem: the implant
must of course be sterilized, and this includes the internal electronics.

The standard sterilization procedure for this type of implants is based on
gamma ray irradiation (by a Co-60 source, if I'm not mistaken).
Click to expand...
[snip *lots* of ueful information]

OK, this is great stuff! Not only can I almost certainly rule out the use
of gamma irradiation with this information, I can also explain in more or
less detail to my client *why* it's not an option.
Nevertheless, I decided to put a few dozen brand new MOSFET's and several
other IC's through the gamma sterilizer, just to make certain that the
test circuit didn't die as a result of something else. For those
interested, I think I might be able to post the results here, probably
within a fortnight.

Thanks again for all your feedback, regards,


Richard Rasker

--
Linetec Translation and Technology Services

http://www.linetec.nl/
 
Richard Rasker <spamtrap@linetec.nl> wrote:
On Wed, 17 Mar 2004 13:48:50 +0100, Jeroen wrote:

Richard Rasker wrote:
Hi all,

In the course of designing a rather simple electronic circuit for use in a
medical implant I was confronted with an unforeseen problem: the implant
must of course be sterilized, and this includes the internal electronics.

The standard sterilization procedure for this type of implants is based on
gamma ray irradiation (by a Co-60 source, if I'm not mistaken).


[snip *lots* of ueful information]

OK, this is great stuff! Not only can I almost certainly rule out the use
of gamma irradiation with this information, I can also explain in more or
less detail to my client *why* it's not an option.
Nevertheless, I decided to put a few dozen brand new MOSFET's and several
other IC's through the gamma sterilizer, just to make certain that the
test circuit didn't die as a result of something else. For those
interested, I think I might be able to post the results here, probably
within a fortnight.
Click to expand...
Interested.
Thanks.
 
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