Zooming in on MEMS designs with EDA

IES: IntelliSense is filling a unique niche - CAD/EDA for MEMS devices. What makes the MEMS EDA problem challenging and different from traditional semiconductor EDA tools?

Akkaraju: EDA tools usually deal with one physical domain - electrical signals. Designing MEMS devices requires handling multiple physical domains simultaneously. Typical MEMS designs involve coupling of multiple physics, such as thermomechanics, electrostatics, electromagnetics, fluidics, and optics.

In addition, the range of materials used in MEMS is much larger than what is used in electronics. MEMS devices use highly engineered materials, which take advantage of material responses. For instance, piezoelectric, piezoresistive, magnetorestrictive, and magnetic materials, which respond to applied external fields, are increasingly being used in sensors and actuators. Material physics is a significant consideration in MEMS design.

The MEMS and microfluidics fields are becoming highly interdisciplinary. Consider a typical BioMEMS device vis-a-vis an RF MEMS device. Both require very different skills sets: whereas the BioMEMS device requires expertise in biochemistry, electrokinetics, and microfluidics, the RF MEMS device requires knowledge of thermomechanics, electrostatics, electromagnetics, fluidics, and electronics. Having engineers and scientists with diverse skill sets work together demands a deep understanding of the mindset and vocabulary used in each of these disciplines. From a software perspective, this is a difficult balancing act between being easy to use and powerful enough to tackle complex interdisciplinary problems.

IES: Tell us about the 3D visualization capability.

Akkaraju: Unlike the semiconductor industry, where CMOS [Complementary Metal Oxide Semiconductor] is the dominant process flow, most MEMS devices do not use a standard process flow. The dictum seems to be one device, one process. Process flow modeling is an important aspect of MEMS design. IntelliSense provides tools to conceptualize, visualize, and analyze the manufacturing process flow. Figure 1 shows the fabrication of a MEMS rotary vibrational drive manufactured in a five-level polysilicon process.

Figure 1: (click graphic to zoom by 2.2x)

Another important aspect is individual process simulation. Etch simulation is critical to making MEMS work. The industry has developed a unique set of anisotropic wet and dry etching techniques that are highly design and process dependent. IntelliSense provides TCAD tools for process simulation of anisotropic and isotropic wet etching and RIE [Reactive Ion Etching] and ICP [Inductive Coupled Plasma Etching], allowing process and device engineers to optimize their layouts and process recipes.

IES: What are the different types of modeling and simulation capabilities in the tools, and why are they important?

Akkaraju: IntelliSense provides MEMS CAD/EDA tools for process, device, package, and system design. IntelliSuite specializes in coupled-physics modeling - users can combine device physics ranging from thermomechanics, electrostatics, piezoelectric, piezoresistive, magnetostatics, electromagnetics, microfluidics, electrokinetics, and biochemistry in an integrated environment.

As MEMS become increasingly integrated with electronics, MEMS CAD tools need to seamlessly communicate with tools from different EDA vendors. IntelliSuite provides a compatibility layer that allows the MEMS CAD and popular EDA tools from Cadence Design Systems, Mentor Graphics, and Synopsys to work together in a MEMS-electronics codesign workflow.

IES: What's one of the most difficult MEMS layout projects you've seen recently, and what were the keys to making it work?

Akkaraju: As the MEMS industry matures, the number of electromechanical components per chip is increasing. In cases of electromechanical arrays, RF MEMS and optical MEMS chip designers are looking at hundreds to thousands of moving components per chip. From a design perspective, the interaction between the various components is challenging.

In a recent design, an RF company wanted to integrate arrays of resonators on a chip. While the individual resonator design shown in Figure 2 was straightforward, the interaction between the resonators in terms of losses and performance was a challenge to optimize. To draw a parallel, the MEMS industry is where the semiconductor industry was in the early 1970s, with large-scale integration becoming practical.

Figure 2: Resonator bank layout screenshot (click graphic to zoom by 2.2x)

As the number of components grows, it becomes impractical to tune layouts by hand. Designers are now turning to schematic-driven design techniques similar to the analog design world.

Another design involved an array of 4,000 fully controllable micromirrors on a chip. The difficult part of the layout was integrating the MEMS with a bank of control ASICs. This posed design and layout challenges at the package and system levels. Chip designers often approach these issues as an afterthought. This is one of the biggest pitfalls in MEMS, which require an integrated approach to device, package, and system design.

IES: You mentioned you're working on a new release of IntelliSuite. What new capabilities will it address?

Akkaraju: IntelliSuite v8.5 is now in advanced beta testing at selected sites. We will be releasing the new version this June. The tool features a number of new capabilities, including:

• Integrated electromechanical and electromagnetic analysis for RF MEMS cosimulation


• A new multiprocessor piezoacoustic simulator for fast BAW/SAW [Bulk and Surface Acoustic Wave] simulations


• Layout and 3D model extraction from the schematic


• An advanced hexahedral mesh engine (example in Figure 3) that allows users to go directly from layout to mesh

Figure 3: Mesh engine (click graphic to zoom by 2.2x)

In addition to the latest version of IntelliSuite, we are launching Clean Room, a new product line focused on process simulation and optimization. Clean Room provides an architecture to integrate process-specific simulators into a detailed process flow. We are also introducing two new process simulators: a DRIE/ICP etch simulator to simulate deep silicon etching, a key enabling technology for MEMS, and an atomistic simulation-based anisotropic etch simulator for accurately simulating wet etches. As part of our roadmap, we plan to introduce detailed lithography and deposition simulators in the coming months.

Sandeep Akkaraju is CEO of IntelliSense Corporation, a Woburn, Massachusetts-based provider of MEMS and nanotechnology software and tools. His roles include strategic marketing and sales of software and IP solutions, channel development, and general management. Sandeep holds a B.Tech from the Indian Institute of Technology, an MS from Louisiana State University, and an MBA from INSEAD, France.

IntelliSense Corporation
781-933-8098
sakkaraju@intellisense.com
www.intellisense.com