What are the components of MEMS devices?

The uses for microelectromechanical systems (MEMS) devices have grown exponentially. Applications for MEMS technology include actuators, sensors, inertial measurement units (IMUs), energy harvesters, pumps, motors, oscillators, resonators, and more. They are used in all areas, from consumer to medical, military, and space. Two keys to the expansive uses of MEMS devices include the ability to quickly design them and new fabrication techniques to produce them. This FAQ explores four examples of how MEMS design tools have evolved.

Initially, MEMS was designed with already available IC design and layout tools. However, MEMS devices are significantly different from conventional CMOS ICs. MEMS devices require a greater range of geometries and curves while conventional CMOS IC layouts tend to be basic Manhattan style with rectangles, rectilinear polygons, or polygons with 45-degree edges. The need to support irregular shapes has resulted in the development of MEMS-specific electronic design automation (EDA) tools (Figure 1).

Figure 1. MEMS devices like magnetic actuators, accelerometers, and rotary side drive motors require specialized EDA tools (Image: *Siemens*).

With traditional CMOS IC tools, designers needed to write C code to produce the irregular shapes needed for MEMS devices. That’s no longer necessary. For example, Siemens’ Tanner L-Edit MEMS layout editor includes toolbars for quickly drawing circles, pie wedges, tori, and other curved objects. They start as ideal arcs and have sweep angle and radius parameters that are user-editable to produce precise results. Individual curved objects can be stitched together into more complex structures as needed. More advanced editing tools are available for fine-tuning the results. The design suite includes simulation tools and more.

Adding simulation
Accurate simulation of MEMS devices can speed up arrival at the final design. For example, EDASIM offers its ConventorMP MEMS development environment that combines the company’s MEMS+ design environment with the ConventorWare simulation package. Design entry begins with the parametric definition of the fabrication technology. The MEMS+ tool set includes a library of parametric MEMS building blocks like flexible and rigid shapes, electrodes, electrostatic combs, and so on. Custom shapes can also be created. The individual components can be assembled into larger devices and the package features integration with MathWorks to speed the development of automated simulation using MATLAB scripts.

ConventorWare takes the process to the next level with MEMS-specific tools for simulating common devices like IMUs, microphones, resonators, actuators, and so on. Field solvers are available that can model multi-physics interactions like coupled electro-mechanics, piezoelectric, piezoresistive and dampening effects and electrostatics (Figure 2).

Figure 2. This MEMS design and simulation package starts with material, process, and layout tools at the device level and extends to the MEMS circuit and system levels (Image: *EDASIM*).

MEMS and mixed-signal codesign
As MEMS are adapted to a wider range of applications, the need for a MEMS and mixed-signal design flow has increased. The SIMPLE Mixed-Signal/MEMS Co-design Methodology from Cadence is designed to handle the needs of the system-on-chip (SoC) and system-in-package (SiP) MEMS plus mixed-signal design flow. The package provides efficient concurrent design and optimization of the MEMS and mixed-signal electronics. It also handles engineering change orders (ECOs) between the two domains to ensure a unified and efficient design effort (Figure 3).

Figure 3. Coordinated codesign of combined MEMS and mixed-signal solutions is required to ensure that resulting SiP or SoC devices (upper right-hand corner) meet all design goals (Image: *Cadence*).

Multiphysics for MEMS
Instead of starting with a traditional CMOS IC design approach and adding MEMS-specific functions like multi-physics simulations, COMSOL Multiphysics offers add-on modules for specific activities like MEMS and AC-DC development. The MEMS module can be used for a wide variety of modeling activities like modeling the effects of thermal expansion on the operation of MEMS devices. The module can also model complex effects like squeeze-film damping, bidirectional fluid-structure interaction, hydroscope swelling, ferroelectrostatic effects including hysteresis, and other interactions. The MEMS module can be combined with the AC-DC module to analyze magnetostrictive devices. Add-on modules are also available for microfluidics, structural mechanics, and other specialized development needs.

Summary
MEMS are complex devices that require extensive EDA tool support, including the ability to quickly develop irregular shapes, assemble multiple sub-elements into completed assemblies, and the need for accurate simulation of the resulting device. In addition, MEMS devices are often integrated into SiPs and SoCs together with mixed signal devices. And multi-physics development and simulation tools can further speed up the development of MEMS solutions.

References
Meeting MEMS design challenges with unique layout editing features – Part 1, Siemens
MEMS Module, Comsol
Mixed-Signal/MEMS Co-design Methodology, Cadence
Predicting actual from virtual, EDASIM