Frequently Asked Questions
Q: How does Nitronex determine reliability of its parts?
A: Nitronex performs extensive reliability testing on all products prior to production release. A cross-functional team meets to outline the qualification plan for a product and then the reliability engineers execute to the plan. Long-term drift is characterized through 3-temp DC life-testing, DC-HTOL, and RF-HTOL testing. To date ~500,000 hours of DC-HTOL have been collected on Nitronex devices. Furthermore the robustness of the technology is examined through such tests as ESD and VSWR mismatch tests. Finally, mechanical aspects of a product are tested via autoclave, temperature cycling, and bond pull to name a few. Complete details of our NRF1 process qualification can be found here.
Q: How good is Nitronex’s reliability?
A: While different test methodologies and forms of reporting data make direct comparisons difficult, Nitronex believes its reliability is on par with existing technologies such as Si-LDMOS and GaAs pHEMTs. Some common metrics are MTTF (mean-time-to-failure). In this case Nitronex shows a MTTF >10 million hours at an operating temperature of 150°C and a drain voltage of 28V. Another metric is drift over 20 years of operating life. Here Nitronex has demonstrated <6% drift in Imax when operated at 200°C and 28V. Finally the robustness has been demonstrated with ESD results showing HBM ratings >1000V for the NPT35050 device and the ability to survive VSWR mismatches as high as 20:1.
Q: What makes Nitronex’s GaN-on-Si so reliable?
A: Nitronex’s GaN process has several components that make it inherently reliable. Nitronex uses a robust Au metallization scheme which is much less susceptible to eletromigration than the Al used in Si devices. GaN devices make use of a Schottky gate structure which eliminates the gate oxide that commonly plagues Si devices. Nitronex’s GaN process is able to leverage several aspects from mature GaAs fabrication procedures. Finally, Nitronex’s extensive development of optimized expitaxial structures with emphasis on reducing stress and producing intrinsic buffers mitigates many of the problems seen by GaN-on-SiC competitors.
Q: What is the activation energy for Nitronex’s NRF1 process and is it valid
at lower temperatures?
A: A 3-tempature DC life-test is used to determine the activation energy for the process. In this test, devices were stressed at junction temperatures of 260, 285, and 310°C. A failure criteria of 15% drift in in-situ drain current was applied. Data was fit to a cumulative failure plot showing a lognormal distribution. Finally the MTTFs (mean-time-to-failures) for each group were plotted on an Arrhenius plot and revealed activation energy of 2.0eV. For more details...
While the fit is excellent in the 260-310°C range, Nitronex is aware that another activation energy can exist at lower temperatures. In order to determine if this is the case, acceleration equations have been applied using 2.0eV to predict drift at temperature of 215, 200, and 150°C and show accurate ability to predict drift with this constant activation energy
Q: How does Nitronex determine junction temperature and thermal resistance?
A: Nitronex uses a Quantum Focus InfraScopeII to perform infrared thermal imaging. This tool uses pixel-by-pixel emissivity compensation to accurately measure temperature with a ~2.5µm spatial resolution. In addition to these measurements Nitronex performs full 3D FEM (finite element modeling) on all its devices and compares these results with the simulations. The combination of these two tools allows for accurate junction temperature determination.
Q: Is there an inherent disadvantage of Si compared to SiC substrates?
A: SiC is a better thermally conductive substrate but due to substrate cost and yields, SiC based GaN vendors typically use smaller devices that offset the substrate advantages.