Electronic Design
The MEMS Wrinkle

The MEMS Wrinkle

One RFIC maker with an interesting set of EDA challenges is WiSpry, which relies on RF-MEMS (microelectromechanical systems) technology to create its chips, components, and modules. The issues a design house faces in incorporating MEMS technology is one that more companies will face as MEMS make their way into a growing array of consumer electronics. There would be no Nintendo Wii game system without them.

“We have the classic problem of having two separate tool chains to integrate,” says Jeff Hilbert, president and COO of WiSpry. “We’re fundamentally a Cadence house that uses the Coventor tools on the MEMS side.”

WiSpry uses Coventor’s tools for MEMS design and then treats the resulting MEMS devices like a design library, importing those library elements into the Cadence custom design environment. “Integration isn’t as seamless as it sounds, though,” says Hilbert. “It’s two tool chains from two vendors having to interact with each other with a least-common denominator of GDSII. A lot of our challenges are in trying to effectively exchange information between these disparate design environments.

According to Hilbert, Coventor is pursuing tighter links with mainstream EDA vendors. Hilbert hopes that WiSpry will eventually be able to move to a master design database that resides within the Cadence environment. “We would still export into Coventor to work on the MEMS devices,” he says. Integration is improving but Hilbert finds that bringing in a new technology like MEMS, with its different physics and a custom simulation environment, harkens back to EDA of a couple of decades ago. “It’s a little like the early 1980s, with custom methodologies and point tools strung together,” Hilbert says.

That notion is illustrated by the fact that WiSpry runs a chain of RF and electromechanical tools in parallel, including AWR’s Microwave Office design suite. A problem in MEMS, says Hilbert, is using 3D finite-element solvers to extract out higher-level models. WiSpry’s approach is to use Ansoft’s HFSS 3D solver to simulate capacitor structures and then use the results of those simulations to build black-box models of the MEMS devices that are imported into Microwave Office or Cadence’s Spectre RF environment.

Coventor’s tools support several levels of abstraction, Hilbert says. “The tools support a behavioral model construct,” he says. “You can effectively synthesize out of that model into a 3D electromechanical model that can be simulated. We abstract up to the equivalent of a gate-level model, and can get almost circuit-level simulation results in the MEMS environment. In doing so, we’re looking at things like the voltage required to move a mechanical structure, or modeling changes in material stress profiles.”

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