Memscap MEMS Wafer Fab, Bernin, France
Memscap is shipping products from its volume MEMS (micro-electromechanical systems) wafer fab in Bernin, France. The 5,900m² foundry processes 6in and 8in wafers and cost $55 million to build. It uses automated batch manufacturing processes, with an eventual capacity of above 4000 wafers/month.
Production at the plant began with low-port-count photonic switches and variable optical attenuators aimed at metro- and access-levels of telecommunications networks. The 1 x 2 and 2 x 2 port switches have embedded electronics. They are used for variety of fibre-optic applications including network and equipment protection, bypassing in FDDI and SONET, network reconfiguration and monitoring, and redundancy for optical cross-connects. Depending on the application, insertion loss ranges from 0.5dB to 1.0dB and the devices switch within a millisecond. Samples withstand >100 million operating cycles.
Memscap's devices are integrated into silicon and can combine mechanical, optical, fluid and electronics elements. Like ICs, they are built using thin material films. Thin metal or crystalline films are deposited on a substrate, imaged and etched. A sacrificial layer can be introduced to separate layers as the structure is being constructed, but is dissolved in the last step to allow moving parts. Features can range in size from a dozen microns to a dozen millimetres.
THREE MAJOR MEMS PROCESSES
Memscap is involved with the three general approaches to MEMS fabrication: bulk micromachining, surface micromachining and LIGA (lithography, plating, moulding).
Bulk silicon micromachining forms mechanical microstructures by etching directly into the wafer. The process entails etching from the backside of the wafer to form through holes and cavities for microfluidic chambers, trenches for optical alignment and suspended beams for thermomechanical sensing, among others. Deep Reactive Ion Etching (DRIE) allows for geometric freedom, including 90º sidewall profiles through the wafer and control over the etch. It etches only the layers intended on the wafer and does not restrict the shape of the feature.
Surface micromachining evolved from IC fabrication, but thicker films are required for mechanical behaviour. As some of the layers are sacrificially released to allow for free-moving parts, layers must be resistant to sacrificial etchants such as hydrofluoric acid. Photolithography is relied upon for accurate placement and definition as MEMS die have much more topography than IC die. These thicker layers also challenge etch technology, though Deep RIE is the etching method of choice.
Memscap can perform deep-Si RIE etching (to 500µm deep) of silicon, quartz, polysilicon, silicon nitride, silicon dioxide and polyimides. Frontside to backside pattern alignment can be within 1µm, and the process uses anisotropic (KOH and EDP) or isotropic chemical etching.
LIGA combines IC lithography, electroplating and moulding, with the electroplated moulds either forming the final product or having materials injected into them. LIGA can use materials like metal and plastic, and can build devices with very high aspect ratios. LIGA now dominates High Aspect Ratio Micromachining (HARM). HARM devices can have stiffer structures, increased mass, larger actuation forces and an easier "fit" with the macro-world. Memscap specializes in Optical LIGA processing.
Memscap combines these methods with proprietary foundry processes. The company's Multi-User MEMS Processes (MUMPs®) provides access to MEMS prototyping and a seamless transition into volume manufacturing. The company has PolyMUMPs for surface micromachining, SOIMUMPs for silicon-on-insulator processing, and the MetalMUMPs electroplated nickel surface micromachining for the fabrication of MEMS micro-relay devices based on a thermal actuator technology.
VOA FOR GAIN EQUALIZATION
MEMS-based products are now in development for a range of optical telecom applications, from variable optical attenuators (VOAs) to tunable filters, gain equalizers, dispersion compensation components and tunable sources.
The company's VOAs provide gain equalization of optical input or output. These are suitable for dynamic channel balancing for DWDM systems, power management in multi-stage optical amplifiers, and as building blocks for multi-function integration. They are available as dice or as fully packaged devices, with or without electronics.
The VOAs use the company's proprietary MEMS switch technology. A miniaturized shutter mechanism is located between optical waveguides or fibres. The shutter mechanically blocks the light path to reduce the amplitude of the signal without distorting the waveform. These VOAs can be deployed with erbium-doped fibre amplifiers to manage the optical power sent to receivers, protecting the receivers from too strong a signal that can increase bit-error rates.
Rugged, circuit board mountable packages can have integrated drive electronics, with a standard logic interface simplifying connection to other components.
COMMUNICATIONS AND SENSOR APPLICATIONS
Memscap MEMS aim at three major markets: next-generation wireless communications, optical communications, and sensors for aerospace, biomedical and other applications. It also offers Computer-Aided Design (CAD) solutions, offering MEMS design software tools and services to the semiconductor market.
The company supplies discrete passives for wireless, like RF-switches, varicaps, high-Q resonators and filters. MEMS-based micromirrors can form optical cross-connect switches: applying a voltage to an actuator causes the mirror to move and direct the light to a specific output port. Two-dimensional mirrors move up/down or left/right, while three-dimensional mirrors have a wide movement range.
In medicine, Memscap offers components, sensor subsystems and modules based on pressure sensors and dermatological sensors. The company's devices are commonly used in disposable blood pressure transducers, skin analysis, and weighing scales. Future applications will include tiny surgical "scrapers" injected into arteries to clean out plaque.
COMPLETE MEMS DESIGN AND PRODUCTION SERVICE
Memscap designs and produces MEMS including components, component designs (IP), CAD design tools, manufacturing and related services. The company has developed proprietary technology that can deposit RF MEMS directly on top of a mobile device's integrated circuit board.