MEMS Foundries Play Waiting Game

By Mark LaPedus
For years, the foundries in the microelectromechanical systems (MEMS) business have been patiently waiting for the MEMS integrated device manufacturers (IDMs) to outsource some or all of their production.

The MEMS foundries are still waiting for that development. Because MEMS are custom devices tuned to a proprietary process and toolset, IDMs still prefer to use their own fabs and are generally reluctant to outsource their production to the foundries.

Over the years, however, the MEMS foundries have experienced sizeable growth from the first wave of fabless and fab-lite MEMS vendors in the market, such as ADI, InvenSense and Knowles. Now, a new crop of fabless MEMS vendors is emerging.

The fabless players, and perhaps the IDMs one day, will require a reliable MEMS foundry partner to help develop devices that are smaller, faster and cheaper. But finding the right MEMS foundry partner is easier said than done. In fact, the MEMS foundry business is like the Wild West. There are a plethora of MEMS foundries of all shapes and sizes, but not all vendors will survive. Some MEMS foundries already have disappeared, while others are struggling and may go under.

“There will continue to be a shakeout,” said Peter Himes, vice president of marketing and strategic alliances for Sweden’s Silex Microsystems, the world’s largest pure-play MEMS foundry vendor. “There is a long tail of small foundries. We think you really need to be at the high end of the scale in order to survive. The MEMS foundry business is capital-intensive. You need to reach a certain level of revenue to survive in this game.”

Over time, it’s unclear which MEMS foundries will become the winners or losers. All MEMS foundries boast an impressive array of technologies, although not all vendors are created equal. For example, some, but not all, MEMS foundries have state-of-the-art 200mm fabs. In addition, a few MEMS foundries offer turnkey services. Not all provide MEMS-on-CMOS platforms, silicon interposers, 3D through-silicon vias (TSVs) capabilities, wafer-level-packaging, and other technologies.

MEMS mania
Used in consumer, industrial and mobile applications, MEMS devices include accelerometers, compasses, gyroscopes, microphones and sensors. In total, the MEMS market is projected to reach $9.09 billion in 2013, up 8.1% from $8.41 billion last year, according to IHS. In 2012, two IDMs, Bosch and STMicroelectronics, were tied for first place in terms of worldwide MEMS sales of around $793 million.

STMicroelectronics is also the world’s largest MEMS foundry vendor, with $203 million in sales in 2012, according to Yole Développement. Sony was a distant second with $65 million in MEMS foundry sales. Meanwhile, after garnering some sizable MEMS business from ADI and InvenSense, TSMC jumped from 7th place in terms of MEMS foundry sales in 2011, to the No. 3 spot in 2012 with $42 million in sales, according to Yole.

In the MEMS foundry rankings, Silex slipped from third place in 2011 to fifth last year. Teledyne/Dalsa remained in fourth place. And GlobalFoundries cracked the top 20 rankings, according to Yole.

In total, some 20% of the world’s MEMS production is outsourced to the foundries, said Jérémie Bouchaud, an analyst with IHS. But that figure is only expected to climb to 25% within the next several years. “These are not standard processes,” Bouchaud said. “To transfer (a MEMS process) to a foundry takes a lot of energy.”

MEMS manufacturing is sometimes a slow and cumbersome process. Generally, the IDMs have it down to a fine art, while the foundries are still working on becoming more efficient. “In the past, MEMS manufacturing has been hampered by long development cycles required for a diverse set of products having their own unique processes,” said Rakesh Kumar, senior director of the MEMS program at GlobalFoundries. “MEMS tools for volume manufacturing are still not as mature as CMOS tools, and very low throughput of MEMS processes is a key manufacturing concern.”

In response, many MEMS foundries have taken steps to help speed up the manufacturing process. “Realizing the growth potential of fabless companies, MEMS foundries are focusing on offering reusable process modules that can reduce the development time and shorten the time to commercialization,” Kumar said.

Indeed, most of the growth in foundry outsourcing will come from the fabless vendors, not the IDMs. The IDMs, which dominate MEMS, already have the in-house expertise and generally do not require foundries. “The key reason for IDMs’ dominance has been their ability to provide a complete MEMS solution, starting from MEMS design to fabrication, packaging, testing and application support,” he said.

Over time, Kumar predicts the IDMs will embrace foundries to one degree or another. “Many of the IDMs have been using six-inch facilities for MEMS fabrication, and these facilities are becoming less competitive against eight-inch MEMS fabrication. So in order to be cost competitive, such IDMs will either have to invest more to upgrade their facilities or consider outsourcing the manufacturing to eight-inch foundries,” he said.

Not created equal
To attract customers, MEMS foundries are taking different approaches. In general, there are four basic types of MEMS foundries—MEMS IDMs that have a foundry component; OEMs that have a MEMS foundry; silicon foundries that offer MEMS services; and pure-play MEMs foundries.

Silex’ Himes said there are some advantages and disadvantages when going with an IDM or OEM. “The (IDMs) have been developing MEMS processes for over 20 or 30 years,” he said. “From a foundry perspective, (IDMs) may scare away customers. Customers want to make sure their IP is secure so that their foundry choice is not going to compete with them in the future.”

The silicon foundries are coming on strong, but they tend to focus on select processes and customers. On the other hand, a pure-play MEMS foundry may be able to handle a multitude of processes and customers at the same time. “Our expertise is the ability to manage this diversity in a MEMS foundry,” Himes said.

On the technology front, there are other key differences between foundries. Generally, the MEMS device sits on a CMOS-based ASIC. In many cases, the MEMS device and ASIC are processed separately and integrated through a packaging or bonding step. “Package-level integration offers greater flexibility to designers,” said GlobalFoundries’ Kumar.

Some, but not all, are offering or developing MEMS-on-CMOS processes, where the two pieces are integrated together in the fab. “The benefits of monolithic integration of MEMS with CMOS are increased levels of integration, low power, high speed and reduction of parasitics,” Kumar said. “The tradeoffs are the increased complexity of fabrication and reduced thermal budget.”

There are other considerations. At one time, MEMS were expensive devices aimed at the industrial markets. Now, MEMS are found in high-volume markets like smartphones and tablets. “A lot of MEMS ASPs are eroding by 3% to 5% a quarter,” said Mike Rosa, a MEMS expert and strategic marketing manager for 200mm Emerging Technology Products at Applied Materials. “Because of the economics, there is continued pressure to make the MEMS devices smaller, thinner and cheaper.”

To accomplish that feat, many MEMS foundries offer various stacking technologies, such as 2.5D interposers, 3D TSVs and wafer-level packaging. In one flow to reduce the form-factor, for example, Silex’ 3D TSV process can enable sub-50μm pitches for through wafer connections in up to 600μm substrates. It can be incorporated into the handle side of an SOI wafer, allowing the combination of a highly doped handle wafer and a low-doped device layer.

To reduce signal contamination and crosstalk, Silex also has developed a technology called Through Silicon Insulator (TSI). Sometimes called vertical SOI, TSI creates dielectrically isolated areas within the device.

No flow
Assembling these technologies in a MEMS fab is like putting the pieces of a jigsaw puzzle together. Generally, there is no standard tool flow for MEMS. Lithography plays a role in MEMS, but it is not the key enabler. “In the typical process flow, the MEMS device itself will have anywhere from five to 10 lithography steps. The ASIC can have many more,” said Applied’s Rosa. “When you talk about the resolution of the CD or line/space width of the lithography, MEMS is currently around one micron, with devices hitting the market at a half-micron CD.”

In MEMS, the key tools are deposition, etch and PVD. “What is critical for the fabrication of MEMS devices today is deep reactive ion etch. That process is used to carve out the caps in silicon, which are then used to encapsulate the devices. It’s being used in many devices like accelerometers, gyroscopes, and to package the microphones,” Rosa said. “For digital compasses, it’s going to be the physical vapor deposition of magnetically aligned metals. For microphones, it’s going to be thick oxides, amorphous silicon, low stress materials, conformal nitrides and things of this nature.”

In addition, MEMS often requires a “release etch” step to remove a sacrificial layer of the structure. In this market, SPTS Technologies recently acquired Xactix, a provider of xenon difluoride (XeF2)-based release etch technology. SPTS now supports release technologies for silicon/molybdenum/germanium and silicon oxide sacrificial layers, said William Johnson, president and chief executive at SPTS.

So, in other words, finding the right recipe of tools and materials remains a challenge for MEMS. “In the traditional semiconductor space, you have an ITRS roadmap or SEMI standard. That roadmap spells out to the letter what everything looks like. In the MEMS world, that doesn’t exist,” added Applied’s Rosa.