Is bulk GaN Really There Yet?
Chipworks, a Canadian firm that provides reverse engineering services to companies looking to grow their intellectual property, has discovered that the Avogy Zolt Laptop Charger, a device sold on the basis that it uses bulk GaN technology, contains no such thing.
GaN has been the holy grail of power electronics for a number of years, This is due to physical properties that theoretically allow a GaN transistor to exceed the performance spec of a silicon power MOSFET in breakdown voltage and on-state resistance. The challenge, however, has always been obtaining high quality GaN substrates at a reasonable price, writes Chipworks' St.J. Dixon-Warren in a recent blog.
Bulk GaN wafers are expensive and obtaining good crystallographic quality is challenging. Higher quality GaN epitaxial layers can be grown on SiC and silicon substrates, which allows for the formation of lateral transistor structures, but not for vertical ones.
The availability of GaN-on-silicon at reasonable cost was a particularly disruptive event, since it allowed conventional silicon processing tools to be used for processing the GaN-on-Si wafers.
Avogy claims to be a market leader in bulk GaN device technology. The Knowledge Center section of Avogy's website includes links to papers on bulk GaN p-n diodes and vertical power transistors on bulk GaN substrates. The website also lists various GaN-based diodes and JFETs, as well as the Zolt laptop charger.
Chipworks' teardown of a Zolt Laptop Charger Plus, Graphite (a new small-format, lightweight charger designed to fit easily into a briefcase or pocket) revealed that the one component deemed likely to contain the bulk vertical GaN power transistors has a substrate made of SiC and not GaN.
Chipworks now believes that the die inside the Avogy 150-00028 chip was likely fabricated by Cree, although it is also possible that it was sourced from another SiC foundry. Chipworks says it consider this to be a very curious finding.
As Dixon-Warren writes in his blog: "Avogy very publicly claims to be focused on bulk GaN power transistor and diode technology. They have announced the Zolt product with great fanfare and were given an 'Innovation Award' at the 2015 Consumer Electronics Show. Of course, whether the internal power switching transistor is GaN or SiC is immaterial to most users of the Zolt charger, but this information will be of interest to the power market in general as it provides a benchmark of what is really in production products."
