Thermomechanical Fatigue in Sub-THz Vacuum Electron Devices

The transient temperature and stress distributions during the turn-on cycle of sub-THz vacuum electron devices (VEDs) are evaluated, thereby providing an explanation for the high stress environment created at the material surface causing fatigue failure. Furthermore, it is shown that there are transient tensile stresses that occur beneath the material surface out of phase from compressive stresses that can be the cause of the cracks observed in previously reported experimental data. High-frequency VEDs provide millimeter-wave radiation sources for many applications from space communication and medical imaging to remote chemical, biological, and weapon's detection. Lifetime estimates are presented using stress-based and strain-based approaches for such devices based on their peak operating surface temperature for low as well as high stress operating conditions.

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