How is GaN reliability being measured for application relevance?

A customer recently asked me a question about gallium nitride (GaN) reliability: “It seems that JEDEC (the Joint Electron Device Engineering Council) does not cover application conditions in the switching power world. Any GaN device we would use in an end product should go through such testing. In my opinion, JEDEC should incorporate these kinds of tests. What do you think?”

Our customer is asking the right question. In order for GaN to be widely adopted, it needs to be proven reliable in the intended applications, rather than merely passing the silicon qualification recipe. Due to longstanding industry experience and validation of reliability models, standards-based testing is now accepted for silicon, but that was not always the case. The power metal-oxide semiconductor field-effect transistor (MOSFET) was developed in the late 1970s, but it was not until the early 1990s that JEDEC developed a standard. It is not clear, however, what JEDEC silicon qualification means for GaN transistors.

Standards lag behind technology introductions, but a standard is not needed to make technology reliable. It is a deep understanding of the technology; its failure modes; and knowledge of testing, qualification and product operation. At TI, we are going back to the fundamentals and creating a methodology to qualify GaN. JEDEC will eventually incorporate these kinds of tests, but in the meantime please see our white paper, “A comprehensive methodology to qualify the reliability of GaN products.”

Application-relevant qualification is particularly important. Although JEDEC specifies the need for dynamic testing, it does not prescribe conditions, citing the ever-evolving applications and material sets in our industry. Most of our customers will use GaN for power conversion, for which the hard-switching transition is a basic application-relevant occurrence. This introduces very different stress than burn-in board qualification, as illustrated in Figures 3 and 4 of the white paper. We have therefore developed a JEDEC-compliant test vehicle, shown in Figure 1, to qualify GaN for hard switching. We are also running parts under actual operating conditions in order to identify and fix newly discovered field-failure mechanisms. This allows us to show that GaN will be reliable in power-conversion applications.

Figure 1: JEDEC-compliant test vehicle for inductive switching application test

It will take time for standards-based tests to be developed for GaN; however, we are proactively developing the kinds of tests needed to show that GaN will be reliable in power-conversion applications. TI tests GaN in the way the customer thinks it should be, even before the standards bodies get to it.

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