While attending the latest Globalpress event, I met with a company I did not know before: Coventor. The meeting, as well as a panel discussion during the Globalpress event, gave me the opportunity to learn more about a segment of the semiconductor industry that is not well known in EDA: MEMS. These devices are actually quite interesting and the technology involved as challenging as a new process technology.

Coventor was founded in 1996 and is headquartered in Cary, North Carolina. It has
development and sales offices in Cambridge, Mass, (due to its roots at MIT), Silicon Valley, Ca, Paris, France and Tokyo, Japan.

Coventor’s software suite and supporting content allow engineers to efficiently simulate and analyze MEMS designs before they are committed to manufacturing, saving time, money and development resources. Its sophisticated 3D design tools support a wide range of the physics required in advanced MEMS, including the mechanical, electrical, piezo-electrical, optical, fluidic and electromagnetic domains, as well as package analysis.

What's a MEMS?
MEMS stands for Micro Electro Mechanical Systems. MEMS are micro-scale or nano-scale devices typically fabricated in a similar manner to integrated circuits (ICs) to exploit the miniaturization, integration, and batch processing benefits of semiconductor manufacturing. Unlike ICs, which consist solely of electrical components, MEMS devices combine technologies from multiple physical domains and may contain electrical, mechanical, optical, magnetic or fluidic components.

MEMS may be invisible to the naked eye, but they’ve become ubiquitous in everyday life. Automobiles now contain numerous MEMS devices, including pressure sensors for engine control, accelerometers for crash sensing, and gyroscopes for stability control. Some consumer electronics products such as inkjet printers and digital light projectors (DLPs) have depended on MEMS for years, and recent years have seen an explosion in the integration of MEMS with electronics in mobile phones, cameras and gaming controllers. The market for MEMS in mobile phones, for example, is expected to grow by more than four times from 2009 to 2012, to over $2 billion. MEMS are now found in such popular products as the Apple iPhone and iPad, and Nintendo Wii, delivering new levels of interactivity for consumers.

As you can see from the picture, a watch may contain a number of MEMS.

Challenges Facing Broader Proliferation Of MEMS

As promising as these forecasts sound, only a few large IDMs are well positioned to benefit from this rapidly growing market. This is due to the specialized expertise, long development time, and high costs of bringing MEMS devices to market. Although almost all MEMS devices are tightly integrated with electronics, either on a common silicon substrate or in the same package, MEMS design has traditionally been separated from IC design and verification.

Specific challenges include:

• MEMS design proceeds hand-in-hand with refinements to the fabrication process, unlike IC design which relies on standardized CMOS processes;

• MEMS, in contrast to ICs, are fundamentally three dimensional (3D), allowing an extra
degree of freedom in design that translates into a much larger available design space.

• MEMS rely on coupled multi-physics effects to function. In particular, many MEMS designs rely on complex coupling between highly non-linear electrostatic forces and mechanical structures. Or, for instance, high-frequency MEMS resonators for RF applications rely on complicated high-frequency resonances in piezo-electric materials.

• MEMS devices are almost always tightly integrated with analog/mixed-signal ICs, either on a common silicon substrate or in the same package.

MEMS devices are typically designed by PhD-level experts in such fields as mechanical, optical, and fluidic engineering. They use their own 2D and 3D mechanical CAD tools for design entry and finiteelement analysis (FEA) tools for simulation. Eventually the MEMS design must be handed off to an IC design team in order to design and verify the complete system prior to fabrication, but the handoff typically follows an ad-hoc approach that requires a lot of design re-entry and expert handcrafting of behavioral models for functional verification.

Moreover, MEMS historically requires specialized process development for each design, resulting in a situation often described as “one process, one product.” While there are a number of specialized MEMS foundries, support from pure-play foundries has been very limited. Thus, most successful MEMS products on the market today were designed by teams of experts inside IDMs who have their own process technology.

Coventor's MEMS Products

Coventor, Inc. has focused since its founding in 1996 on providing software tools that address the unique challenges of MEMS design automation. Coventor is now by far the leading supplier of tools for designing and simulating micro- and nano-scale MEMS. Hundreds of leading MEMS companies, R&D centers and universities around the world use Coventor’s products to research, develop, and commercialize a wide range of devices, including motion sensors, pressure sensors, optical displays, RF switches and resonators and energy harvesters. Coventor's products give these organizations an advantage in bringing MEMS-based products to market more quickly while reducing costs and controlling risk.

Because MEMS are almost always tightly integrated with electronics, the MEMS and accompanying IC must be designed and optimized together. Therefore the MEMS tools must be compatible with widely used IC design and verification tools. To address this challenge, Coventor recently introduced MEMS+, a MEMS design platform that is fully compatible Cadence Virtuoso® which is the leading platform for analog/mixed-signal IC design and verification. Rather than hand crafting over simplified behavioral models of MEMS as has been the case until now, MEMS engineers can now enter their designs in a natural 3D environment and automatically generate simulation models and layout for
their counterparts in IC design. Automatic hand-off from MEMS engineers to IC engineers working in the Cadence environment not only reduces interface errors, but provides more accurate models that allow greater optimization of MEMS+IC products.

Coventor’s flagship product, CoventorWare® was first released in 2001 and addresses the first three challenges mentioned above. CoventorWare is a suite comprised of three sub-products: Architect3D, Designer and Analyzer. Architect3D provides a unique library of MEMS building blocks that allows users to quickly assemble and simulate a MEMS design in a multi-physics circuit simulator.

Architect3D excels at simulating complex coupled electro-mechanical designs such as those relying on electrostatic comb drives. Designer includes an all-angle layout tool with MEMS-specific features including design rule checks, and makes it easy to go from a 2D layout to a 3D solid model. The 3D solid model can serve as input for the field solvers in Analyzer, or it can be exported to third-party field solvers. Analyzer provides a comprehensive suite of finite element solvers that handle the mechanical, electrical, optical, fluidic and electromagnetic domains, as well as package analysis. In addition to addressing MEMS-specific physics, and especially coupled electro-mechanics, all three
sub-products are “process flexible”. That is, the definition of the MEMS process, both the steps and material properties, is shared by all and readily modified by the users, thus addressing the challenge posed by process modifications made during the course of a design.

Recognizing that MEMS design usually proceeds hand-in-hand with process development, Coventor introduced SEMulator3D®, a novel and unique tool for MEMS process engineering and process integration. SEMulator3D uses patented voxel modeling algorithms to emulate MEMS and semiconductor fabrication steps. Voxels can be regarded as 3D pixels. Both captive and independent MEMS fabs use SEMulator3D to perform virtual fabrication of MEMS before running actual silicon through their MEMS process. The tool creates highly realistic, 3D virtual prototypes of microfabricated
devices. Examination of these virtual prototypes can reveal design errors as well as the
impact of design changes and process variations before each mask tape out and fab run, potentially reducing or eliminating design-fabricate-test cycles. In contrast to time-consuming process simulation, SEMulator3D’s voxel modeling approach is efficient enough to capture a complete MEMS die processed through its entire fabrication sequence, not just an isolated region of the die processed for one or two steps.