R
Richard Rasker
- Jan 1, 1970
- 0
Hi all,
Some weeks ago, I posted a few questions about gamma sterilization of
certain electronic components. From the reactions, the conclusion could be
drawn that gamma sterlization of electronics is quite a tricky business.
This also became obvious when an irradiated test circuit showed
multiple component failures.
Nevertheless, I decided to put a small batch of components through the
gamma irradiation process again, and an identical batch through steam
sterilization, for comparison purposes. Most of the selected components
are included in the design of a medical implant. Here are the results, for
those interested.
Components tested (one batch):
FDC6305N Dual N-channel MOSFET (4x)
FDC6306P Dual P-channel MOSFET (4x)
FDC6327C N- & P-channel MOSFET (4x)
TL084 quad opamp (1x)
TC1047A temperature-to-voltage converter (2x)
Sterilization procedures:
- Autoclave (steam), 134 degrees Centigrade at 2 bars of pressure
- Gamma irradiation, 1 dose of 25 kGray Co60 exposure
Steam: All components were unaffected, and behaved well within their
specifications.
Gamma: All MOSFET's were severely affected:
FDC6305N - all 8 devices exhibited short circuit from drain to source; no
response to Vgs at all.
FDC6306P - all devices exhibited dramatically lower Vgs threshold values,
with a Vgs-on between -2.1V and -2.5V (normally -1V), and a maximum drain
current Id-max (set at 0.33 A) at Vgs = approx. -3.2V (normally -1.6V).
FDC6327C - P-FET's: same as FDC6306P.
N-FET's: lower Vgs values: Vgs-on between -0.2V and -0.4V
(normally +1.1V) and Id-max at Vgs = +0.2V (normally +1.6V)
Something rather unexpected is the difference between the N-FET's in the
FDC6327C (which merely showed lower Vgs values), and the N-FET's FDC6305N,
which were completely destroyed. All P-FET's behaved in the same manner.
Apart from the changed Vgs values, other parameters seemed mostly
unaffected.
TL084 - tested in unity-gain circuit (output connected to - input, driving
voltage on + input). Two of the four opamps exhibited a massive offset
voltage of approximately +0.5V, probably as a result of damage to the
input JFET's; the other two devices in the same package seemed unaffected.
TC1047A - both devices tested seemed to operate within specifications;
however, the small number of components tested makes it difficult to say
anything definitive about the sensitivity for gamma radiation.
Conclusion: gamma sterilization of electronic circuits is quite
troublesome; especially FET's (both MOSFET's and JFET's, such as
employed in the TL084) are at risk. The most prominent effect is a
drastically lower value for Vgs, rendering the devices near useless for
most practical purposes.
If any more gamma ray testing is carried out, e.g. with bipolar
semiconductors instead of FET's, I will post the results here as well.
Richard Rasker
Some weeks ago, I posted a few questions about gamma sterilization of
certain electronic components. From the reactions, the conclusion could be
drawn that gamma sterlization of electronics is quite a tricky business.
This also became obvious when an irradiated test circuit showed
multiple component failures.
Nevertheless, I decided to put a small batch of components through the
gamma irradiation process again, and an identical batch through steam
sterilization, for comparison purposes. Most of the selected components
are included in the design of a medical implant. Here are the results, for
those interested.
Components tested (one batch):
FDC6305N Dual N-channel MOSFET (4x)
FDC6306P Dual P-channel MOSFET (4x)
FDC6327C N- & P-channel MOSFET (4x)
TL084 quad opamp (1x)
TC1047A temperature-to-voltage converter (2x)
Sterilization procedures:
- Autoclave (steam), 134 degrees Centigrade at 2 bars of pressure
- Gamma irradiation, 1 dose of 25 kGray Co60 exposure
Steam: All components were unaffected, and behaved well within their
specifications.
Gamma: All MOSFET's were severely affected:
FDC6305N - all 8 devices exhibited short circuit from drain to source; no
response to Vgs at all.
FDC6306P - all devices exhibited dramatically lower Vgs threshold values,
with a Vgs-on between -2.1V and -2.5V (normally -1V), and a maximum drain
current Id-max (set at 0.33 A) at Vgs = approx. -3.2V (normally -1.6V).
FDC6327C - P-FET's: same as FDC6306P.
N-FET's: lower Vgs values: Vgs-on between -0.2V and -0.4V
(normally +1.1V) and Id-max at Vgs = +0.2V (normally +1.6V)
Something rather unexpected is the difference between the N-FET's in the
FDC6327C (which merely showed lower Vgs values), and the N-FET's FDC6305N,
which were completely destroyed. All P-FET's behaved in the same manner.
Apart from the changed Vgs values, other parameters seemed mostly
unaffected.
TL084 - tested in unity-gain circuit (output connected to - input, driving
voltage on + input). Two of the four opamps exhibited a massive offset
voltage of approximately +0.5V, probably as a result of damage to the
input JFET's; the other two devices in the same package seemed unaffected.
TC1047A - both devices tested seemed to operate within specifications;
however, the small number of components tested makes it difficult to say
anything definitive about the sensitivity for gamma radiation.
Conclusion: gamma sterilization of electronic circuits is quite
troublesome; especially FET's (both MOSFET's and JFET's, such as
employed in the TL084) are at risk. The most prominent effect is a
drastically lower value for Vgs, rendering the devices near useless for
most practical purposes.
If any more gamma ray testing is carried out, e.g. with bipolar
semiconductors instead of FET's, I will post the results here as well.
Richard Rasker