Improving the Yield of SiC High-Efficiency Power Switches

S2489 — SiC High-Efficiency Power Switches Wafer Process Improvement

Objective

Navy platforms continue to improve their performance and capabilities by insertion of
new technologies, which ultimately require additional energy. High-efficiency power
switching devices provide higher energy densities, thereby providing additional power
without requiring ever larger footprints. Under this five-year effort, the production
yield of 6.5kV and 10kV silicon carbide (SiC) metal-oxide-semiconductor field-effect
transistors (MOSFET) was increased by transitioning from production on 100mm
SiC wafers to 150mm wafers and optimizing the design. Eight design iterations were
completed under this effort to optimize doping levels and dimensions of critical
features of the device. Device yield has improved from 20 percent to greater than 50
percent, and the acceptable amount of power that can be switched is doubled.

Payoff

There are many current and future Navy platforms that will be able to take advantage
of this technology. At the start of this project, switching costs were in the range
of $100 per amp. Costs have been reduced to approximately $20 per amp. Navy
personnel are engaged to estimate the number of switching devices the Navy will
consume in the near future once this technology is transitioned to a commercial
product and to identify platforms that will be first users of this technology.

Implementation

Wolfspeed, a Cree company, has demonstrated the ability to implement its technology
into a commercial device by commercializing 1.2kV SiC metal-oxide-semiconductor
field-effect transistors (MOSFETs). Wolfspeed continually performs market research
to determine the power needs of both the commercial and Department of Defense
sectors. Using previous trends in power requirements, Wolfspeed believes the market
will require a commercial product in 18-36 months after project completion. At that
time, Wolfspeed will lock down a design with specific power ratings and begin the
transition from prototypes to commercial products. In preparation for that transition,
Wolfspeed has successfully completed JEDEC Solid State Technology Association
qualification testing of 10kV SiC MOSFETs on 100mm 4HN-SiC wafers and
is currently carrying out JEDEC qualification testing of 6.5kV SiC MOSFETs
on 150mm 4HN-SiC wafers under the Department of Energy PowerAmerica
manufacturing program.