Given the complexities of both the product and its development sequence, MEMS organizations need facilities specially tailored to research, configuration and cleanroom production
By David Reese
Whoever coined the phrase “good things come in small packages” would be amazed to learn about the evolution of MicroElectroMechanical Systems, or MEMS.
The microminiaturization of electronic components and devices has truly revolutionized our world, putting far more computing power in the palm of our hands than the Apollo astronauts had in the spacecraft that carried them to the moon.
Combining electronic logic with physical action, MEMS can direct thousands of voice and data streams and even be equipped with artificial intelligence. MEMS have already been successfully adopted for auto airbags and precision controls in guided missiles.
And as with any burgeoning technology, the MEMS prototype must undergo rigorous analysis, simulations and laboratory tests of materials and performance before it can be considered viable for production. Once deemed ready for production, MEMS are manufactured using processes and environments similar to those that produce semiconductors and microchips.
Given the complexities of both the product and its development sequence, organizations need facilities specially tailored to MEMS research, configuration and production; yet, they must maintain the flexibility to support the technology's continued evolution.
MEMS organizations need laboratories, production cleanrooms and support areas that meet exacting standards for cleanliness and security, and with reliable, energy-efficient building systems that can continuously support a full-range of diverse operations and equipment. The overall program requirements for MEMS facilities go well beyond the normal architectural requirements for spatial sizes and relationships. Mechanical, electrical and utility systems must also be designed and configured to meet specific needs for all phases of development.
Perhaps the most important ingredient in any facility designed for MEMS research and development is the human factor—the synergy of collaboration that allows new ideas and discoveries to flourish. MEMS, like other scientific and technological ventures, illustrate how the whole is truly greater than the sum of its parts. The systems are so complicated and the technology that supports them sufficiently advanced, that it requires multidisciplinary teams of specialists to bring about their full development.
And because MEMS research and development facilities must house a wide range of interrelated activities, the overall design must be distinct in function and seamless in process. Often, the most productive R&D environments are those that reflect an understanding of why the requirements are necessary, not just why they are requirements.
MEMS facility fundamentals
There are many parallels between the stages of MEMS development and the design of facilities that house their research and fabrication. Both must be carefully planned with an eye toward how the various elements and functions interact and contribute to the desired result.
For example, a microchip fabrication specialist could walk into a MEMS fabrication area and feel right at home. It uses the same types of tools, ovens and equipment. The key is that these available, well-tested technologies are being adapted to make a new kind of product.
Still, MEMS facilities have enough distinct characteristics and specialized requirements that make careful planning a must. Experience is essential for developing any MEMS facility, whether it's new construction or adapting an existing microelectronics research or production building. It is important to incorporate long-term value and flexibility into a MEMS facility, ensuring that the systems and spaces can evolve in step with both the technology and the owner's long-term business needs.
With production cleanrooms, for example, at the current state of microminiaturization and function, most MEMS can be produced in ISO Class 4 to 6 spaces with no risk of contamination. While there is no need to “over design” for unnecessary requirements, many cleanrooms can be subsequently adapted for higher class ratings through relatively simple, inexpensive changes to the ventilation system and access controls.
As noted earlier, MEMS are produced using the same types of lithographic and micromachining techniques used for microelectronics. Likewise, HVAC, water, electrical, and networking are an integral part of prototyping and manufacturing MEMS. The cleanroom HVAC system is actually considered part of the process, as cleanroom air often comes in direct contact with the production tools.
The process varies, however, depending on the range and type of components being produced. Some facilities use what is called a “farm and field” concept, where like equipment types (steppers, coaters, etchers and washers) are located in separate rooms in “fields.”
Others have adopted the “work cell” approach, where the entire production process takes place in the same space. Some wafers may have to go through as few as five production steps, while others go through as many as 27. The space, therefore, may have redundant equipment for processes that aren't needed for another particular product.
Most MEMS production formats mirror the cell approach, in which the availability of consolidated equipment is more than a trade-off for redundancy. Experts have found that smaller bay and chase configurations promote a wider degree of flexibility in development of multiple products.
Another factor for developing a MEMS facility is the distribution systems for specialized utilities, such as compressed dry air, processed chilled water and special gases—all of which have specialized formulation and safety requirements. Facilities that use the “farm and field” concept may have a number of distribution outlets for a single type of gas, such as liquid nitrogen.
Work cells, on the other hand, require that numerous utilities be distributed throughout the facility. The distribution networks for these utilities have to be carefully developed during the programming stage, ensuring that they will be accessible for current and future needs. It is also important that sensitive utilities be properly isolated from other lines where necessary.
Microelectronics companies with operational production cleanroom facilities are well positioned to capitalize on continuing advances in MEMS technology. These organizations already have the infrastructure and equipment in place to adapt their microchip processes to MEMS. Likewise, their facilities may require relatively minor changes or upgrades to be MEMS-ready.
These facilities, however, cannot make an “overnight” switch to MEMS fabrication and production. Most likely, they already have dense configurations of utilities and services in dense space. A high level of sophistication and experience is necessary to properly integrate new utility lines, reorient others within those constraints, and maintain safety tolerances.
That same level of knowledge is also essential for designing the basic building systems that support MEMS processes and operations.
HVAC systems have higher cooling loads to accommodate the large number of machine tools, computers and telecommunications systems, as well as sophisticated control systems to optimize their environments for performance and energy efficiency. Sensors tied into the various building systems automatically adjust temperature, humidity and air pressure to within narrow tolerances.
Similarly, facility-wide electrical systems must be designed to ensure continuous operation and protect sensitive equipment, including redundant clean-power generators and localized battery uninterruptible power supplies (UPS) to support 24/7 operation and prevent spikes or other service anomalies. Strategically placed stubs for electricity, data and processed water will also help expedite equipment and process changes, which may be needed on short notice.
While structural soundness is essential for any type of science and technology facility, MEMS have requirements that may exceed those for microelectronics production, particularly if the facility also supports research activities.
Vibration control is among the most essential requirement for MEMS research and development, particularly for areas where the devices are manufactured. Depending on the components' minimum critical feature size, the acceleration limit can be as low as 250 to 500 microinches (6.25 to 12.5 µm) per second.
As such, a MEMS research and development facility would likely have to be spread out, with a maximum height of two or three stories. The building would also have a heavy, incredibly stiff structural frame, with a greater number of closely connected columns. The structural design must also isolate laboratories and other areas from internal vibrations, such as footsteps, equipment operation, supply transfers and mechanical systems.
Comprehensive vibration analysis, conducted during the site selection process, will provide the design team with valuable information about the effects of adjacent roadways, rail lines, airports, industries and other site uses. Seismic activity must also be considered, even if the proposed site is located in an area not prone to earthquake activity. Many communities have adopted international building codes that base seismic design criteria by soil type. For example, many parts of the United States have soil characteristics similar to those found in Southern California. Though these areas are relatively calm from a seismic perspective, new buildings must meet the design criteria for high-risk areas.
Even the most avid proponents of MEMS technology cannot predict how these devices will evolve. What is certain, however, is that organizations will be making tremendous investments in the facilities necessary to support MEMS research and development (Figure 1).
As with any scientific endeavor, designing facilities to support the advancement of MEMS technology begins by taking whatever experience is available and asking the right questions, then using what is discovered to learn more.
David Reese is a principal and vice president of Carter & Burgess, an architectural, engineering and construction management firm. He can be reached at [email protected]
Small, revolutionary wonders
Although revolutionary in design and function, MEMS are actually the latest milestone in a continuum of microminiaturization that began in the 1940s, with the introduction of the first transistor.
Since then, scientists and researchers have developed ways to shrink these components and, at the same time, increase their performance, memory size and capabilities. By the late 1960s, transistors could be consolidated into tiny integrated circuits, which in turn were multiplied and miniaturized to fit onto a single silicon chip. Each innovation made these chips more powerful, creating previously unimaginable new applications in the process.
MEMS takes this microtechnology a step further by turning “thinking” chips into complex machines—in other words, MEMS can sense, make decisions, perform functions and communicate directly with other machines and humans. This capability opens the door to a number of applications, particularly in the area of national defense, as well as a number of everyday uses.
For example, basic MEMS are already found in many automobiles to automatically deploy airbags in the event of crashes. Further advancements to MEMS devices will enhance the life-saving capabilities of airbags and other automobile safety systems. MEMS are also proving to be invaluable tools for the fast-growing world of DNA research, and for exploring the functions and mysteries of the central nervous system.
Skeptics often contend that a magician's feats are simply the work of “mirrors.” In describing the magic of some types of MEMS, that perception is quite accurate. A MEMS fitted with hundreds or even thousands of individually steerable mirrors can vastly enhance the efficiency of fiber-optic transmissions. This opens the door to unprecedented bandwidth capabilities, making functions like videoconferencing, on-demand video and super-fast Internet access available to a wider range of users.
Along with supplanting many existing types of fiber-optic components, switches, and filters, MEMS will also make wireless networks faster and more flexible. This capability may make MEMS essential to the next generation of home entertainment systems. Research indicates that these devices may outperform conventional LCD technology for standard and high-definition projection televisions.
How big—or small—can the world of MEMS grow? The answer lies in the imagination of researchers and scientists who will be investigating the possibilities of these miniature marvels in the coming years. Before any MEMS product reaches the marketplace, it must undergo rigorous analysis and testing to prove that the concepts can be used with complete confidence and reliability, and that full-scale production is practical.
But there's little doubt that the market is out there. Some industry observers estimate that the entire market for MEMS—including manufacturing, marketing, research and development, and joint ventures—could be worth as much as $14 billion by 2010.