Forum: Reliability & Maintainability Questions and Answers

Topic: Reliability & Maintainability Questions and Answers

Topic Posted by: Reliability & Maintainability Forum (src_forum@alionscience.com )
Organization: System Reliability Center
Date Posted: Mon Aug 31 12:47:36 US/Eastern 1998

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Original Message:

Posted by: Sheila Prather (sheila_s_prather@mail.northgrum.com )
Organization:Northrop Grumman Corporation
Date posted: Thu Jan 13 13:51:21 US/Eastern 2000
Subject: 217 Model for GaAs FET for high power, high frequency
Message:
MIL-HDBK-217 currently provides the high frequency GaAs FET model in section 6.8, but for that device type operating in the 1GHz range with power dissipations above 0.1W as well as for any other frequency level with high power dissipations, the model renders unrealistic results. As well, the piT factor for the devices addressed in section 6.8 have a great impact on the resulting failure rate, even for those items operating at a power level within the range of the model. These results are unrealistic since these devices typically have rated junction/channel temperatures around 175degC. To compare, the piT values for both the low noise/high frequency (section 6.6) and high power/high frequency (section 6.7) bipolar transistors are extremely smaller in comparison; despite comparable maximum junction/channel ratings. Using these models, as is, the high power/high frequency GaAs FET f.r. is unusable and obviously worst than that of the RF microwave bipolar devices. I furthered reviewed the results published in EPRD97 for the following device types. The published f.r.s for the GaAs devices were lower than those for the bipolar RF transistors for comparable packaging and type; which is totally contradictory to the results if using the model. So, my questions follow; a) what is the recommended model for the high power + high frequency GaAs devices (vs. just high frequency GaAs), and b) what, if any, modifications should be made to the piT values when using the model in section 6.8 where the frequency and power level is within the acceptable range as dictated. Thanks for your response.

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