MEMS infrastructure advancements drive services shift
Improvements in the assortment and depth of MEMS manufacturing services is propelling a business-model shift. It is also enabling faster, less-costly market introduction
By Roger Allan
The MEMS sector is maturing. Today, each of the steps needed to take a MEMS product from lab to market is available as a contract service from a growing number of qualified vendors, some of which specialize in certain aspects of production and some of which offer a full array of services. As a result, MEMS designers can bring their products to market faster and at a lower cost.
In his annual report card on the MEMS sector, market consultant Roger Grace has raised his grade on MEMS “infrastructure” from C+ in 1998 to A- for 2006-and notes that it continues to improve. “It is no longer necessary for companies to spend tens or hundreds of millions of dollars to create a MEMS manufacturing facility,” says Grace. “Today, many excellent MEMS foundries are available for this purpose. This has resulted in companies investing their resources in intellectual property development-and hopefully marketing-rather than in stainless steel, bricks, and mortar.”
According to the German firm Wicht Technologie Consulting (WTC), revenue from the top-10 independent contract MEMS manufacturers reached $131 million last year-a 30% expansion over the previous year. See the graphic (right) showing WTC’s list of the top-10 MEMS foundries (also known as fabrication facilities, or fabs).
The services and their vendors
WTC reports that the top revenue-generating contract foundry, Innovative Micro Technology (IMT), grew 50% from 2005 to 2006. IMT pioneered wafer-level MEMS packaging and has extensive experience in the design, prototyping, process development, and high-volume manufacturing of a wide range of products and applications such as biometrics, biotechnology, imaging, metrology, inertial measurement, optoelectronics, sensing, microfluidics, RF switching, and switch arrays. “Our strength is in our ability to handle a variety of materials like metals, magnetics, polymers, etc. “We can deposit and selectively etch 20% of the elements in the periodic table,” explains Monteith G. Heaton, vice president of sales and marketing.
Further, WTC predicts continued brisk business for contract MEMS manufacturers. The French fab Tronics Microsystems SA is ready. Tronics recently made its second expansion in the past year, adding new space and tools to improve its characterization, assembly, packaging, and testing capabilities. The expansion aims to strengthen design-to-manufacture services and to support the supply chain for customers’ unique MEMS devices. Last spring, the company added competencies for MEMS design and electronic interfacing of MEMS components and upgraded its production facility to 150mm wafer technology.
Rankings of the top-10 independent contract MEMS foundries by revenue, according to Wicht Technologie Consulting.
Micralyne, which came in fourth in WTC’s ranking, recently partnered with Polychromix, developer of inspection and analysis tools, to manufacture MEMS near-IR devices. And fifth-ranked Silex Microsystems says it can reformulate a customer’s product concept to incorporate MEMS technology with product development. Silex promises prototypes for testing within six to eight weeks.
Bennington Microtechnology Center, together with the University of Texas at Arlington, is advocating a radically different approach to MEMS manufacturing. The not-for-profit organization argues that for its MEMS manufacturing to be globally competitive and successful, the U.S. must use a knowledge-intensive methodology instead of a labor-intensive approach (see “Knowledge-based manufacturing,” next page).
Choosing the right partner
The relationship between a fabless MEMS company and its manufacturing contractor(s) can be a complex. The developer may parcel out manufacturing tasks to different partners-or a contractor may sub-contract some services to others. As an example, fabless MEMS developer SiTime uses Jazz Semiconductor to fabricate its MEMS silicon oscillator. But it works with SVTC Technologies, a development foundry, to transfer its 4-in. and 6-in. wafer designs to 8-in. wafers for manufacturing. Taiwan Semiconductor Manufacturing Co. (TSMC) makes the oscillator’s resonator component and its signal-conditioning ASIC.
InvenSense, another fabless MEMS producer, prefers to develop its own packaging and process technologies and design tools and then turn them over to a fab to manufacture the company’s MEMS gyroscopes. This allows the manufacture of virtually any bulk-silicon MEMS device and signal-conditioning electronics on nearly any CMOS platform.
From a MEMS designer’s perspective, a fabrication partner must be able to accommodate design tweaks, use new materials, and handle specialized process equipment and/or steps if needed. Another important issue is the amount of foundry time availability in the event of the need for additional design iterations-which is often tied to the size of the order. A designer must be sure that the contract foundry will not prioritize customers that have larger orders.
An example of specialized capabilities is LIGA (see “LIGA moves into the mainstream,” p. 24), which produces high aspect ratio MEMS (HARM) structures with etched walls as much as 50:1 over base, at 90° angles. Companies such as Axsun Technologies offer LIGA processing on a contract basis. Similarly, Tronics, mentioned earlier, is a leader in deep reactive ion etching (DRIE) processing on thick silicon-on-insulator (SOI) substrate. It recently joined Alcatel Micro Machining Systems to jointly develop advanced MEMS DRIE technology.
Another service some foundries offer is computer-based simulation. MEMS-specific analysis, modeling, and simulation applications are available from companies such as Coventor and IntelliSense Software. Recently, both firms have worked with a new vendor, SoftMEMS, to develop add-on MEMS capabilities for standard electronics-design automation (EDA) software; and SoftMEMS has unveiled MEMS Xplorer (for Unix and HP platforms) and MEMS Pro (for Linux PC platforms).
IMT provides simulation services using Ansys software, while some of the software providers themselves, including ESI Group, offer simulation services (see “Simulation software speeds microfluidics development,” p. 26).
In the manufacture of Akustica’s MEMS microphone, X-FAB produces the starting wafer (a). Dalsa next performs the etching and mesh-releases processes (b through e).
“A MEMS designer needs to look at how easily a particular foundry is able to make adjustments and ‘tweaks’ that come up in a design,” explains Bert Bruggeman, vice president of operations and general manager for SVTC Technologies. “These are the kinds of adjustments you normally don’t need to worry about for conventional CMOS ICs,” he adds. “We can provide a number of services like failure analysis and reliability testing,” says Scott Marquardt, SVTC’s vice president of marketing and business development. SVTC Technologies, a spin-off of Cypress Semiconductor, recently introduced a full suite of commercialization services known as FastXfer. The suite promises an easier transfer of a design to the foundry.
SVTC also offers new services as a result of its new partnership with the giant CMOS foundry, TSMC. TSMC does not produce MEMS, but because CMOS is necessary to make supporting MEMS electronic circuitry, MEMS fabs that do not provide CMOS services directly sometimes partner with CMOS foundries. The fact that SVTC, a MEMS development foundry, joined up with a major CMOS foundry may have implications for the future. For example, TSMC could incorporate some MEMS manufacturing ideas from SVTC into an inline CMOS process (as opposed to the standard MEMS batch process) when making the entire MEMS circuit, which includes the MEMS structure and the electronics (usually an ASIC).
The integration of the MEMS structure with the supporting electronics depends on how it interfaces with the circuitry. Presently, most companies use an ASIC that is then wire- or wafer-plane bonded to the MEMS device. However, one company has achieved monolithic integration. MEMS developer Akustica works with two companies to manufacture its digital microphone chips. Dalsa and X-FAB collaborate on manufacturing the MEMS structure: Dalsa performs the back-side cavity, front-side oxide, and vent-hole etching, as well as the membrane mesh release, while X-FAB creates the CMOS wafer with supporting electronics.
Is the future monolithic?
Whether that will make MEMS “manufacturable” on a fully monolithic process like a CMOS one is a matter of debate. The vast majority of MEMS experts believe this will not be cost-effective. They correctly point out that a MEMS device is a different structure than a CMOS signal-processing circuit and requires different processing methods.
Kevin A. Shaw, director of business development for Sensor Platforms, believes the difference in scalability between MEMS and CMOS is an important issue. “It is not cost-effective to process a MEMS structure on the same 8-in. wafer that holds the signal circuitry that’s designed with 0.25μm and 0.18μm line widths. It is best to let the MEMS foundry process the MEMS device and leave the signal-conditioning ASIC to a standard CMOS process, where regular process shrinks can be enjoyed at little cost to the MEMS foundry,” he explains. Moreover, placing both a MEMS and an ASIC on a single die can be challenging in terms of capital costs (more-complicated processing) and yields (a fault on either part means that both devices are lost).
Sensor Platforms designs signal-conditioning ASICs that can be joined and packaged with a MEMS structure, each on its own die, in a number of ways. Each of these methods can satisfy different requirements and lets designers test dies and use the latest and smallest ASICs from large CMOS foundries.
A MEMS manufacturing model that runs the entire gamut from concept to pilot line production is the goal of the Bennington Microtechnology Center (BMC). The idea is to provide process development for packaging and assembly (including precision robotics and automation), testing and evaluation, pilot and small batch production, user training, and microtechnology incubation-all under one roof. BMC is so convinced of its strategy that it is willing to take an equity interest in a start-up if the company cannot afford to pay for BMC’s services.
BMC is building on advanced packaging and assembly processes pioneered by researchers at the University of Texas at Arlington in the areas of microsystems, joining, sealing, interconnects, and robotic assembly. It was founded by Henry Klim, formerly president of MEMS test pioneer company Etec, and Harry Stephanou, the founding chairman and director of the Automation and Robotics Institute at the University of Texas at Arlington. It emphasizes “knowledge-based MEMS manufacturing, not labor-intensive manufacturing” for MEMS to be successful in the long run.
“Our approach is not only a matter of national economy, but also one of national security,” says Stephanou. “I’m more convinced that MEMS will become successful in specific niche markets than in mass-market applications like the consumer sector,” says Klim. “This makes it imperative that we develop and keep IP in the U.S. instead of losing it to overseas firms,” he adds. “We realized a few years ago that much of the MEMS R&D was in design; however, assembly, packaging, and testing, which take up 70% to 80% of MEMS production costs, were being neglected,” says Klim.