The microelectromechanical systems (MEMS) market has been plagued by two key challenges for several years: the lack of high-volume manufacturing and the absence of low-cost packaging.
Due to those challenges, MEMS technology has remained in the labs, keeping developers from advancing beyond the prototype stage. Moving MEMS technology into production volumes and developing a low-cost structure are vital goals, said Ben Naskar, president and CEO of Magfusion Inc. (Chandler, Ariz.).
Those goals are about to be met, as both pure-play MEMS companies and semiconductor foundries overcome some of the other hurdles, like yield and reliability issues, that have kept many MEMS devices from volume production.
MEMS foundry houses say they've solved these problems with manufacturing process improvements in such areas as bulk micromachining, surface micromachining and metal-type processes, and by adapting standard IC packaging technologies to the production of MEMS devices.
While many MEMS suppliers are in the prototype stage, generating 10 to 20 units at a time for evaluation, the real challenge is in finding the appropriate high-volume manufacturing platform, said Gerry Fortin, managing director of worldwide foundry management for Fairchild Semiconductor Corp. (South Portland, Maine.). One of the important improvements is the ability to provide prototype and high-volume MEMS devices in lead times consistent with IC wafers, Fortin said.
Because Fairchild is an IC manufacturing company, it has been able to refine Sandia National Lab's Summit processes for high-volume manufacturing by applying IC manufacturing techniques such as defect management and process control. Fairchild says it has reduced its MEMS production manufacturing cycle time to four weeks, which is consistent with standard IC manufacturing cycle times. This also helps to shorten the design cycle.
Fairchild already offered Sandia National Lab's Summit IV, four-layer poly process, and has just added the Summit V five-layer poly surface micromachining process. Fairchild claims to be the only volume-production foundry to offer the Summit technology, which is used for sensors, telecommunication photonic-switch applications, accelerometers, gyros, gears and RF switches. The 6-inch wafer fab has a capacity of 250,000 IC wafers per year.
Foundry MEMGen Corp.'s proprietary EFAB 3-D micromanufacturing technology can also reduce a design engineer's development time and cost, the company said. Chris Bang, MEMGen's vice president of design and applications engineering, said the process is simpler and faster than silicon micromachining as well as cost competitive with the silicon technology.
The flexible manufacturing process allows customers to make a wide range of devices as well as make changes to their design with little or no impact on the fabrication process, Bang said.
For example, the EFAB process can offer a 4x reduction in manufacturing time, from 16 weeks to four weeks, and can be used to produce just about any MEMS device, including RF MEMS, inertial devices such as accelerometers and gyros, and optical devices, Bang said. The company has a 22,000-square-foot facility in Burbank, Calif., where it's currently ramping up to production capabilities.
Motorola Inc. is also leveraging its IC expertise in the MEMS arena. The company's Sensor Products Division (Austin, Texas) has launched a new MEMS package for inertial sensors (also called accelerometers) that is about 70 percent smaller than a standard SOIC-16 package. The quad flat no-lead package will be available in 6 x 6 x 1.98-mm and 5 x 5 x 1.98-mm dimensions. The product is scheduled to be available in late 2003.
Motorola started work on the new package a couple of years ago to reduce the overall board space requirements for its inertial products. The standard IC plastic-type packaging the company uses makes it possible to take advantage of standard IC manufacturing processes to keep overall costs down, Motorola said. Initial parts have passed many of the automotive board reliability requirements, such as temperature cycling from -40 degrees C to 125 degrees C, and have survived greater than 2,000 cycles, according to the company. The primary market for Motorola's inertial sensors is in automotive applications for occupant safety crash detection.
Motorola recently expanded its accelerometer family to include a low-gravity version that allows it to offer inertial sensors with a low 1.5-G to 8-G range for applications that include automotive, consumer, health care and industrial products.
Similarly, Analog Devices Inc. (Norwood, Mass.) says it has been able to leverage its high-volume production capability and iMEMS (integrated microelectromechanical-systems) technology to develop one of its newest and lowest-cost accelerometers.
Available now, Analog Devices' dual-axis, plus/minus 2-G ADXL311 is priced at $2.50 each in quantities of 10,000. The company claims the device is the lowest-priced integrated, low-G accelerometer available. Packaged in a 5 x 5 x 2-mm eight-lead hermetic LCC, the ADXL311 can be used in such applications as personal-computing devices, sports and health-related devices, portable blood pressure-monitoring devices, and new input devices and electronic toys. Exhibiting high quality-and-reliability performance, the device offers less than one failure per billion hours of operation, the company said.
Analog Devices has also redesigned its ADSL202 dual-axis accelerometer to improve the product's accuracy over temperature for vehicular dynamic-stability control systems. The dual-axis ADXL203 and the single-axis ADXL103, both single-chip devices, feature a new microelectromechanical-system design with thicker beams and improved bonding agents to minimize the transfer of tilt, temperature and other stresses from the package to the chip, said the company.
Analog Devices' dual-axis accelerometers operate over the -40 degrees C to 125 degrees C range with typical stability performance of plus/minus 0.3 percent. That stability over temperature is more than eight times higher than competing products offer, said the company. Available in 5 x 5 x 2-mm eight-pad hermetic LCC packages, the ADXL203 and ADXL103 are priced at $7.50 and $4.95, respectively, in quantities of 10,000. Samples are available now, with volume production planned for the third quarter.
Foundry service and turnkey MEMS manufacturer PHS MEMS (Grenoble, France) uses a similar approach to MEMS manufacturing. The company's goals are to use low-cost wafer-level packaging; to bring packaging issues from the back end to the front end of the design cycle; and to provide first-level protection for MEMS devices. The company achieves this by using a proprietary process that allows it to package devices at the wafer level. The company's 3,000-square-foot foundry facility in France has the capacity to produce 12,000 wafers per month.
PHS MEMS also offers custom MEMS-based integrated passive device manufacturing, which integrates an IPD and RF switch in the same process flow, for wireless and mobile-communication applications. The devices can be integrated onto a chip or module to eliminate the requirement for discrete devices. Samples are available for evaluation.
Providing wafer-level packaging protection for the MEMS devices before dicing is also key to taking cost out of the manufacturing process, say some MEMS developers. A few suppliers, including PHS MEMS and fabless semiconductor company IC Mechanics Inc. (ICM; Pittsburgh), use a capping process or protective cap, which protects the MEMS device during dicing, die attach and packaging.
ICM's MEMS structure and MEMS sensor manufacturing process produce micromechanical structures that are hermetically sealed to the silicon IC. Such a process results in low-cost manufacturing and low-cost electrical testing of the final product. The company claims it can reduce the cost of a smart-MEMS device by more than 75 percent as compared with comparable existing MEMS devices. Samples of ICM's inertia sensors for hard-disk drives, cell phones and automotive applications are available.
Wafer-level packaging is the answer for some devices, but for others like RF MEMS components, which don't have any moving parts, it's probably not as critical, said Marlene Bourne, senior analyst for MEMS markets and technologies at research firm In-Stat/MDR (Scottsdale, Ariz.).
A few companies are moving toward a CMOS integrated process where a few additional steps are added to a standard CMOS wafer. It's a step in the right direction, but whether it will be embraced is really anyone's guess, Bourne said. In some instances it will be appropriate but in others it won't be feasible, she said.
Improvements such as those undertaken by Fairchild, Motorola and PHS MEMS are making it possible for MEMS developers to ramp their products to volume production. For instance, Magfusion plans to launch today the patented MagLatch RF switch that the company says can replace electromechanical switches and relays. Magfusion claims that it has been able to develop the industry's first magnetic switch by using a patented magnetic-based latching technology, which has allowed it to build RF switches with very high frequencies, high levels of electrical isolation and low-level insertion loss.
The initial product in Magfusion's MEMS-based magnetic-latching product family will be a single-pole, double-throw device that operates from dc to 6 GHz, offers an isolation of 40 dB or higher and a low insertion loss of less than 0.5 dB in a 5 x 5-mm surface-mount package.
Magfusion has worked very closely with its fab partner, PHS MEMS, to develop very complex magnetic-based processes to deliver the die. Meanwhile, since the product is very sensitive to contamination and any variation of temperature and humidity, Naskar said, Magfusion also developed its own hermetically sealed package.
Magfusion's RF switch offers initial contact life in excess of 10 million cycles. By using electromagnetic technology instead of electrostatic technology, the company said the device only requires voltages of less than 5 V to operate. The devices are suitable for automatic test equipment, modems, routers, radar devices, automotive electronics and power-management applications as replacements for switches. But applications are emerging in wireless markets that will require multimode, multiband switching for high performance, high isolation and increased battery life, Naskar said.
Magfusion is producing samples on its own pilot fab line and has partnered with PHS MEMS to act as its production foundry. Limited production volume will be available in the third quarter.
Similarly, MEMS developer Discera Inc. (Campbell, Calif.) is concentrating on using standard semiconductor processes that will enable it to offer low-cost MEMS devices that can replace traditional passive RF components. Discera is currently building samples of its micro resonators and micro oscillators to qualify its process and product. The company can package several multifrequency resonators on the same die, an approach it claims is not currently offered by anyone else. Samples will be available by the end of June, with volume production in the second half of 2004.
- Motorola's MEMS accelerometer line now includes a low-gravity version.
- Fairchild has reduced the MEMS production manufacturing cycle time to four weeks.
- Discera is building micro resonators to qualify its processes.
Analog Devices Inc.
Fairchild Semiconductor Corp.
IC Mechanics Inc. (ICM)
Sensor Products Division