Your daily dose of Photovoltaic Technology Developments and Solar News

When I read the brief report about Micrel's contract manufacturing of solar cells in its San Jose semiconductor facility, I did a double take: "They're running PV wafers and semi wafers in the same fab?" I thought. "That doesn't happen too often." As it turns out, Micrel may be the only place where there's simultaneous volume processing of chips and photovoltaic solar cells, according to company VP of worldwide operations, Guy Gandenberger.

"I don't know of any other fab in the world that is integrating solar cell manufacturing with IC manufacturing," he told me in a phone interview earlier today. "Others have tried.... but no one's taken it to a large-scale production level, except Micrel." Although Guy wouldn't dilvulge the identity of the "fabless" solar customer, the devices moving through his company's 150-mm line are die-level, concentrator-type silicon cells made on SEMI standard-grade wafers, with what foundry manager Jim Crow (yes, that's really his name) characterizes as "400 suns per die" conversion capability.

After Micrel "founders the wafers," Guy explains, the customer tests the validity of the die, then creates a megamodule plate, where they take the cells, put a (concentrator) lens on top of them, package them with the die, and then build the plates. Each megamodule contains several dozen plates, and a tower utilizes five megamodules. We "are foundering the most efficient, most concentrated solar cell in the industry for our customers...where a normal solar cell on a wafer might get 10x efficiency, these are at least 100 times more efficient."

Micrel's not exactly a newbie in the solar industry, having worked on an R&D level with a customer for at least 15 years, relates Guy. But cell production has been progressively ramping for about a year and a half, becoming "a steady fab filler on a day-to-day basis." About 20% of the current 70% total capacity utilization has been offset by solar-cell wafers, a number Guy would like to see in the 30-40% range in 2008, possibly through the signing of additional foundry customers. (Note that the company's own products account for more than two-thirds of its capacity utilization at this point.)



Micrel's Gandenberger has reason to smile.

The optimization of the cell-manufacturing process has involved a long learning curve, he says. "We have had to be extremely creative to make the process work." About 95% of the equipment used for the semiconductor products were suitable for solar, with the remaining tools customized and adapted, but they "didn't have to buy any new tools." Micrel's materials suppliers had to meet specific requirements for the solar processes, and the equipment companies were consulted to help make certain modifications to the toolsets.

The process is "very controlled, with the same type of quality standards as the semiconductor industry," including stringent controls of oxide integrity and particle cleanliness, Guy insists. "We hold the production of solar cells at the same levels as chips, including die and fab yields (as in better than 95%), wafer breakage, throughput, and cycle times." Micrel does all of its own characterization and analysis work, which helps ensure that the lifetime of the solar cells it fabs "are far above any other cells on the market."

"It's not uncommon for a solar wafer to follow right after a semiconductor wafer," notes Guy, sometimes in a merged lot. (That's right, the solar and semi wafers might be in the same boat!) The various wafers can run alongside each other in an oxide furnace, with no loss in efficiencies, he claims.

Although the solar-cell business has definitely helped Micrel's margins, it's not the only nontraditional product running in the fab, mentions Guy, with a little pride in his voice. Examples of other components integrated (or at least integrating) into the process flows include MEMS, surge protection devices, near-eye vision technologies, and biometrics/biogenetics chips, with customers ranging from tiny start-ups to more mature concerns. "We offer very unique processes, that no one else will do" (and the higher margins that come with that service), and have the capability to integrate a wide range of technologies into the existing processes in the fab.

Guy and Micrel's position is do whatever it takes to "keep it at the lowest cost structure possible," in order to compete successfully at both the domestic and global levels: "I will offload costs onto anything I can."

With the surge in new application-related foundry business, might there be a need for, dare I say, added capacity in Micrel's future? "That's something I pray for every day," quips Guy.