Startup builds MEMS in standard CMOS processes

BEOL challenges
Doyle said Baolab plans to make a range of discrete MEMS including RF switches, digital compasses and accelerometers, along with solutions that combine several functions in one chip. The prototype stage has already proved the NanoEMS technology and evaluation samples will be available later this year. These are aimed at handset designers and manufacturers, and power amplifier and RF front-end module markets.

Building mechanical structures in metal does provide a number of challenges. For example, vHF is quite selective with respect to AlCu compared with the silicon dioxide dielectric. However, despite being a good etchant to free the BEOL it is not easy to control the zone that it etches. Baolab claimed to have solved this by a combination of design rules and a process tweak to change the refractive index of the silicon-nitride passivation layer.

Another challenge is that the metal layers are thin and not optimized for MEMS design. This could be addressed by adjustments to the CMOS process but Baolab wanted to have solutions that are foundry independent so the company has created designs that anticipate and allow for these issues. Similarly, sophisticated design work overcame the problems of metal creep by the aluminium along with limited voltage and current carrying capabilities.

Doyle said that larger Asian foundries tend to insist on allowing no changes to their processes, at least initially, while smaller specialist foundries that are looking for differentiation were prepared to consider allowing for thicker metal layers to support mechanical design.

Doyle declined to name Baolab's foundry partners. "We are working with two of the largest foundries in the world. We've gone out of our way to make sure we are not impacting the CMOS process. We wanted something that was transferrable between foundries," Doyle said. "We are also working with some smaller foundries, who can offer process flexibility," he added. "By the end of 2010 we expect to be delivering engineering samples of a switch and control chip pair, and an integrated chip."

Baolab was founded in 2003 by Josep Montanya i Silvestre, who serves the company as chief technology officer. The company has raised 6.5 million euro (about $10 million) including a 3 million euro Series A round from a Spanish venture capital fund nearly two years ago.

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