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MEMS design, manufacturing on the microscale

Posted: 05 Oct 2015 ?? ?Print Version ?Bookmark and Share

Keywords:Microelectromechanical systems? MEMS? surface micro-machining? moulding? LVS?

When you turn your tablet sideways, and the display automatically repositions itself, do you ever stop to think about what made that happen? Microelectromechanical systems (MEMS) are micro-scaled mechanisms designed for two primary applications:

Sensing: changes in sound, motion, pressure, and temperature. Sensing can include not just physical movement, but also vibration, acoustic waves, fluid waves, light waves, heat, and air pressure.

Actuating: conversion and management of light projection/reception, radio frequency signal processing, and fluid management. Actuation can include detection, filtering, conversion, and modulation.

The size of a MEMS device typically ranges from 20?ms?m to a millimeter, while the size of MEMS sub-components is in the range of 1 to 100?ms?m. MEMS functionality has been incorporated across a wide range of industrial and consumer markets, such as automobile safety and control systems, smartphones, tablets, video game controllers, drug delivery, microphones, gas and chemical sensors, and much, much more. These markets are continuing to grow as new innovations and applications emerge.

In place of traditional integrated circuit (IC) components like transistors, resistors, and diodes, MEMS mechanisms contain highly calibrated physical structures such as springs, screws, gears, and plates (figure). MEMS devices also use different types of processing. To achieve the physical dimensions, techniques such as surface micro-machining, bulk micro-machining, deep reactive ion etching (DRIE), and moulding are required.

Figure: MEMS devices.

Historically, MEMS devices have been manufactured using highly-specialised processes that are customised for each device type. This wide assortment of MEMS fabrication processes results in higher market production costs and a longer time to market schedule. As the market moves towards the integration of MEMS devices into high-volume CMOS IC manufacturing, the MEMS technology faces the challenge of shortening development time, reducing costs, and meeting increasingly complex performance and reliability requirements. Incorporating MEMS design directly into the CMOS design flow offers the best chance to achieve these goals, but what elements are needed to make this integration happen?

Component library. A MEMS component library contains proven physical parameterized primitives that are fabrication-ready. Designers can select primitives and define parameters (length, radius, thickness, etc.) to instantiate a component in the layout. The library is also used to supply these material properties to subsequent simulations.

Design tool. An effective MEMS design tool must provide a graphical user interface to enable designers to initiate instantiation, create new blocks, connect components, and add application-specific structures and modifications. This same tool should also provide a layout view to display the MEMS design and generate 3D views.

Process simulation tool. This tool models the results of the actual process flow based upon process settings and physical simulation of the process, such as diffusion, growth, or etching, all of which are unique to the target foundry and manufacturing line. It is similar in nature to IC lithography simulation tools. Designers use this tool to conduct simulations using multi-physics simulators, which conduct simultaneous simulations of the device in different domains (e.g., mechanical and electrical). They can also refine device behavioural models, and identify and correct design errors before test fabrication. These simulations help designers understand the effect of the process on the final physical geometry of the MEMS device. However, since they are based on actual physical models, they are often very time-consuming.

Productivity tools. This category includes automatic layout generation tools that take abstract MEMS system descriptions as input and generate detailed multi-component physical layouts, as well as macro model generators, which convert detailed physical verification results into compact models for analysis and system-level verification.

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