On-wafer test aids SiC production switch
In the week that the new US president passed the $787 billion economic stimulus package, two of the compound semiconductor industry s leading SiC component makers revealed significant developments that relate directly to the new legislation.
Obama s initiative includes $16.8 billion earmarked for "energy efficiency and renewable energy", and $2 billion is available in grants to US manufacturers of advanced batteries and hybrid electrical systems. It also sets aside $4.5 billion to modernize the country's ageing electric grid.
Coincidentally or otherwise, Cree announced the same day that it was nearing volume production of an all-SiC dual-switch module based around a MOSFET and Schottky diode (see our magazine feature article for more details).
John Palmour, the North Carolina company's CTO for power components and RF devices, said of the development: "These 1200 V, 100 A modules represent the next level of integration for SiC power devices."
"The component-efficiency advantage of this technology could translate to significant energy savings for hybrid and electric vehicles, solar power inverters, and industrial motor drive systems."
A day before Cree s announcement, Germany-based Infineon Technologies said that it had just introduced the third - generation of its "thinQ" SiC Schottky devices "“ eight years after the pioneering first generation.
Compared with the second generation of thinQ devices, the latest Schottkys demonstrate an overall efficiency improvement of 0.4% for a 1 kW power-factor correction stage operating at 250 kHz.
That might not sound like much, but the reduced need for heat sinks and fans, coupled with improved reliability, can cut the cost of switched-mode power supplies by up to 20%, claims the firm.
Testing, testing
With Infineon already in the fab and Cree s latest development "offering a clear path to volume production" "“ according to the official release "“ it is clear that the manufacture of SiC power semiconductors is moving up a gear.
Assisting that shift is the US-based test and measurement company Reedholm Instruments, which has just launched the industry's first wafer-level DC test system for these types of high-power devices.
The Texan company, which already sells similar equipment for testing GaAs circuits, has had to develop the technology to handle much higher voltages.
"SiC s requirement for breakdown measurements of 2 kV or more for vertical transistors is what changes the game," said Jim Reedholm from the company. "Typical parametric probers can handle only a few hundred volts."
As a result, Reedholm s latest tool offers automated 5 A and 2 kV testing via a backside connection to vertical devices fabricated on wafers up to 150 mm in diameter. Test time per site is around 600 ms, including the time that the probe needs to move between sites.
The prober is suited to Schottky diodes, as well as power amplifiers, switches, FETs and bipolar transistors, while LED testing is also possible.
In fact, says Reedholm, the equipment is already in use at some of the leading SiC device fabs, with multiple tools per fab likely to be required as demand for the wide-bandgap semiconductor increases.
"Our customers certainly see the need for testing in volume now for power requirements, and downstream for automotive [applications]," he added.
Once Obama s stimulus package gets into full swing, that need could grow quickly.
