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Be it an airplane, drone, jet, satellite, or spacecraft, aerospace platforms put their solid-state electronic components through an extreme range of temperatures and G-forces. Combine those factors with shock, Fig. 1vibration, and pressure changes, and the resulting environment makes it challenging for highly sophisticated RF/microwave devices to perform reliably. Future aerospace platforms will rely even more on RF/microwave telecommunications, geolocation, imaging, and electronic-warfare (EW) technologies. Fortunately, a wealth of ruggedization standards and qualifications have been developed since radios first took to the air. Now, new methods of employing analysis tools in conjunction with accelerated tests could take RF/microwave aerospace systems to the next level of reliability.

Breakdown Constraints

RF/microwave components in the aerospace channel must be able to withstand extreme conditions, of course, but beyond simply functioning in survival mode, these components must continue to satisfy stringent performance criteria. RF/microwave components tend to be mission-critical. It is therefore necessary to design these components with breakdown constraints in mind.

1. Space-Breakdown Mechanisms. For RF/microwave technology designers who are familiar with space applications, the enormous differences in temperature and pressure are a given. Temperature operation ranges have been designed for, simulated, and predicted with a good level of accuracy. Though they are challenging, it also is possible to account for temperature extremes. Physical stressors, such as vibration, shock, and pressure differentials, are familiar enemies as well. A greater challenge is predicting unique material, radiation, and electrical phenomena, which can lead to component degradation and, later, system failure.

2. Outgassing. Many materials developed in a pressurized atmosphere trap various liquids and gases in their structure. When encountering a high-vacuum environment, these gases and liquids may begin to creep out of the material. Occasionally, this significantly changes the material properties. The level of outgassing exhibited by a material and its effects are difficult to model or simulate. Therefore, NASA has developed a database of materials and their estimated outgassing behavior through batteries of experiments.

Fig. 23. Multipaction. Hazardous-free electrons can become trapped in metallic structures under high-vacuum conditions—especially when these devices are open to radiation and electromagnetic field emission from celestial bodies. If they develop a resonant cascade with the RF signal, these free electrons are particularly troublesome for RF/microwave electronics. This effect occurs when high-energy electrons impact metallic structures with enough deposited energy to induce secondary electron emissions.

When resonant, these electrons can quickly cascade due to self-amplification. They will then create significant, and potentially damaging, electric discharge. The wall material can be characterized for its potential to induce secondary electron emission yield (SEY), which defines its potential as a space-grade material.

4. Corona. Free electron emissions in space can also wreak havoc when interacting with the ionized atmospheric gas trapped with RF/microwave devices. If the energy of these electrons increases because of a spacecraft’s RF/microwave electronics, the electrons can excite the gaseous molecules within the devices. If the energy of the excitation is high enough, additional electrons may be released. This local electron population growth could exceed the diffusion rate and cause coronal discharge of radiation.

Fig. 3

Additionally, the high concentration of electrons could lead to RF reflections—potentially damaging the sensitive RF devices. Increased power density and component integration also make RF/microwave assemblies more susceptible to corona effects.

5. Solid-State-Transistor Breakdown Mechanisms. Because many RF parts are now solid-state, these systems are subject to the breakdown mechanisms that are inherent to semiconductor technology. In most aerospace applications, RF/microwave devices need to be rated for survivability under all environmental conditions spanning several years and up to decades. Each solid-state failure mechanism must therefore be identified, designed against, and verified under the strictest standards.

Fig. 36. Stress Migration. Hydrostatic stress gradients can drive electromigration, thus inducing voids in integrated-circuit (IC) metallization. This stress-induced-voiding (SIV) phenomenon can lead to cracks, fractures, and warping of the metallization layers, corrupting performance. Mechanical stresses, which arise from coefficient-of-thermal-expansion (CTE) mismatches, can add further stress to IC metallization. The result is increased metallization failures.

7. Electromigration. Under high-current conditions, ions within a conductor can gradually travel in response to momentum transfer by electrons and diffusing metal atoms. Higher current density increases the likelihood of electromigration. Like stress migration, electromigration can induce voiding-related failures.

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