Turnkey environment allows MEMS/IC co-design, co-verification

Two-team effort
Two engineering teams traditionally collaborate to create a MEMS-based IC: one using 3-D CAD to create the MEMS mechanical sensor (or actuator) model, and the other using an EDA tool to create the IC that realizes the MEMS design and adds the necessary electronics to amplify and condition the signals going to and from the MEMS mechanical element.

The MEMS team conventionally relies on physical design and simulation CAD tools such as SolidWorks to create the 3-D geometric model for the mechanical parts of the device, then uses a CAE tool like Ansys or the CoventorWare suite's Analyzer to represent the behavior of the device with a finite-element model. Tools such as Sugar or CoventorWare Architect are used for system-level design and simulation, making use of a preexisting library of components.

The IC team, meanwhile, conventionally uses an EDA tool from such companies as Cadence or Mentor Graphics to create a schematic of the electronics, then simulates performance with a circuit simulator.

The behavioral model of the MEMS device then would have to be translated into a hardware description language such as Verilog-A or VHDL-AMS, using a hand-crafted model, lookup table or finite element analysis that only approximates the MEMS device's behavior. Those methods do not result in reusable MEMS behavioral models with a complete set of parameters for the IC tools that could reliably estimate yields.

MEMS+IC, by contrast, lets the MEMS designers work in the 3-D CAD environment with which they are familiar, then automatically transfers a fully parameterized behavioral model of the design into the IC design and simulation environment offered by Cadence's Virtuoso tool.

"We see the MEMS trend going the same way we saw analog and digital going. They used to be fairly decoupled, then you started to see digital methods distinctly built into analog functions," said Randolph Fish, director of product marketing for Virtuoso. "Now we are seeing the same thing in the MEMS world. At first the MEMS element was fairly decoupled from its electronics, but that's no longer true; the functionality of a MEMS component itself is now dependent upon the [electronic] component."

The Cadence Connections program already supports a MEMS add-on for Virtuoso from SoftMEMS LLC (Los Gatos, Calif.), but that solution does not let the MEMS design team use the 3-D modeling tools with which they are already familiar. MEMS+, on the other hand, uses traditional 3-D modeling views to create MEMS models that automatically translate to the Virtuoso EDA environment.

"We wanted to partner with somebody who was committed to MEMS and [was] considered a leader there," said Fish. "That's how we got to Coventor."

IC designers can work in Virtuoso with the MEMS device using the same methods used for any other digital, analog or mixed-signal device, including all manufacturing variables describing material properties, dimensional parameters and geometric properties of the combined design that allow accurate estimations of performance and yield.

The MEMS engineering team automatically generates a netlist for its completed design, which appears as a MEMS symbol in the Virtuoso Schematic Editor. The IC designer can then add the electronic elements to the design and run co-simulations of the MEMS and IC elements at the same time using the same simulator (either Spectre or UltraSim), which is connected to the MEMS+ component library. After co-simulation, the MEMS engineers can also review the results in MEMS+, including complete 3-D animation of the MEMS device's mechanical behaviors. When both teams are happy with the design, a parameterized layout cell can be exported to generate the final layout of the completed device for the foundry.

The Coventor design team is working to integrate the MEMS+ tool with other design environments besides Cadence's Virtuoso. The next implementation will offer integration with Matlab's Simulink, Coventor said.