MEMS In the Making

Nov. 30, 2011

Fluid Handling Applications of MicroElectroMechanical Systems

The MicroElectroMechanical System, or MEMS, is a device characterized by its small form factor (typically 1-100 micrometers), mechanical operating principle, and electric-based power source. While the roots of MEMS technology can be traced back to semiconductor manufacturing, these devices have been expanding into such general fluid handling applications as pressure sensing and flow measurement, particularly in the area of medical and diagnostic systems. MEMS have also found widespread acceptance for metering in inkjet printer cartridges. And while MEMS remains a relatively nascent technology, it figures to evolve significantly in the years to come.

Performance & Capability

Micro Coriolis mass flow sensors with submillimeter to millimeter diameter tubes are now being positioned for use in a variety of industrial applications.Photo courtesy of ISSYS The performance and capability of MEMS technology is improving as new packaging methods become available for enabling a higher level of reliability in micro devices. For example, much progress has been made in using vertical electrical connections (vias) to join MEMS with application-specific integrated circuits (ASICs), which are chips designed for a particular use. “Stacking the MEMS, such as an accelerometer or a gyro, with the ASIC with vertical vias as the interconnect is now an industrial reality,” says Dr. Eric Mounier, project manager of MEMS Devices & Technologies for Yole Développement, a market research and business development firm focused on a range of high-tech market segments.

“[STMicroelectronics] has just announced new MEMS chips with TSV (Through-Silicone Vias),” says Dr. Mounier. “The TSV replaces traditional wiring with short vertical interconnects in STM’s multi-chip MEMS devices, such as smart sensors and multi-axis inertial modules, enabling a higher level of functional integration and performance in a smaller form factor.” TSV, also referred to as TSS (Through-Silicon Stacking), is a high-performance technique to create 3D packages and 3D-integrated circuits, compared to alternatives, such as package-on-package, because the density of the vias is substantially higher.

According to Doug Sparks, executive vice president for MEMS manufacturer Integrated Sensing Systems (ISSYS), mass-produced MEMS have seen growth and adoption in the consumer product segment. Cellphones, gyroscopes, microphones, and low-g accelerometers have led the way in this area. In microfluidics, Sparks says plastic-based diagnostic MEMS are also gaining traction, primarily in biological systems.

In consumer electronics applications, MEMS devices are relatively low-cost, but they aren’t all that robust, says Sparks. For industrial fluidic applications, which are generally characterized by harsher environments and require higher reliability than consumer applications, Sparks says the durability of the MEMS device is important. And with a more robust solution comes a higher price-point.

Obstacles to Widespread Adoption
Dr. Mounier says cost is a key obstacle that needs to be overcome if MEMS technologies are to achieve more widespread use in the industrial segment. Sparks agrees that cost is an issue when considering high-reliability MEMS systems, but he believes as more applications come online and production volumes rise, the price-point for industrial-type MEMS systems will naturally fall.

Beyond cost, the packaging of MEMS systems is an important consideration for employing such devices in industrial applications. “Packaging for fluidic systems is critical, and we’re seeing this improve as MEMS [technology] evolves,” says Sparks. “[We’re] trying to make MEMS devices more compatible with more harsh environments.”

The durable packaging required for MEMS devices in industrial environments means they are somewhat larger than such devices used in the consumer electronics segment, for example. Also, perhaps the most troublesome aspect of packaging MEMS devices for industrial applications is figuring out how to connect them to other parts of the micro-fluidic system in a way that will stand up to the application environment. “Interconnection between the MEMS chip and a stainless or plastic manifold/piping system can be a challenge from a chemical compatibility standpoint,” says Sparks. “Do you use o-rings, epoxy, or solder? What do you use? How robust [is the interconnection] for the application, for the temperature range, and chemical compatibility over the long-term?”

Applications Now & Going Forward
Probably the most common and widespread use of MEMS technology from an industrial fluid handling perspective is for pressure sensing in differential-pressure flowmeters. On the consumer side, MEMS technologies are also widely employed for fluid handling in inkjet printer nozzles.

Other popular applications of MEMS include fluidic chemical and biological analyzers based on plastic fluidic channels, resonant density and binary concentration sensors, and thin-film, hot-wire anemometers. Sparks says MEMS-based disposable medical devices, which can be used to test for HIV and TB, have been gaining popularity, and he expects use of such systems to continue to rise in the years to come. He says MEMS devices have also found use in density-measurement systems for testing jet fuel quality and blending as part of bypass systems at many airports.

Going forward, Sparks is hopeful that valves and micropumps will see wider use, perhaps as part of drug-infusion systems for insulin and pain medications. Currently, Sparks says micropumps can be used for low flows, but the valves need to be designed so there is no leakage in the systems. If this issue is solved, Sparks says micro pump and valve systems could be an important enabling technology for the next generation of drug-infusion and dosing systems for medical applications.

Matt Migliore is the executive director of content for Flow Control magazine. He can be reached at 610 828-1711 or [email protected].

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