Emerging technologies often have a gradual but long-term effect on how high-frequency design engineers work. For example, when gallium-arsenide (GaAs) transistors and integrated circuits became commercially viable in the mid-1980s, amplifier designers shifted their focus from bipolar devices to the new semiconductors. In the current decade, several emerging technologies threaten to disturb the status quo for high-frequency designers, including microelectromechanical systems (MEMS) and nanotechnology, ultrawideband (UWB) communications, multilayer circuits, and wide-bandgap semiconductors.

MEMS technology applies silicon semiconductor fabrication processes to the creation of mechanical devices, such as variable capacitors, electromechanical switches, optical lenses, and miniature motors. Early RF MEMS designs have focused on simple structures, including variable capacitors, microwave switches, and relays. Because packaging is critical to isolating MEMS devices from the operating environment, critics of initial MEMS devices cautioned that reliability would be a problem with these miniature components. But several companies have delivered reliable commercial products that dispel these complaints.

RadantMEMS (www.radantmems.com), for example, has developed the model RMSW100 single-pole, single-throw (SPST) switch for use from DC to 12 GHz, as well as the model RMSW200 SPST switch for use from DC to 40 GHz (the highest-frequency commercial MEMS switch currently available). The lower-frequency device has been performance tested at 10 GHz for high reliability at more than 100 billion switching cycles (see Microwaves & RF, July 2004, p. 102). It features less than 0.27 dB insertion loss and more than 25 dB isolation at 2 GHz.

Similarly, the model MICO6-CDK2 single-pole, double-throw (SPDT) switch from Dow-Key Microwave Corp. (www.dowkey.com) has been rated for 100 million switching cycles at frequencies from DC to 6 GHz. The high-isolation (45 dB isolation to 3 GHz and 40 dB isolation to 6 GHz) component minimizes insertion loss to 0.2 dB at 3 GHz and 0.5 dB at 6 GHz.

Of course, not all MEMS devices are switches. Discera (www.discera.com) has focused on the MEMS fabrication of microminiature oscillators. The company's first product, the model MRO 100, is the world's smallest multifrequency oscillator at one millimeter on a side (see Microwaves & RF, August 2003, p. 84). Supplied in wafer-level vacuum packaging, the 19.2-MHz oscillator is a miniature replacement for quartz-crystal oscillators in low-power circuits, such as Bluetooth wireless devices and cellular telephones. The source draws just 2.7 mA current from a +3-VDC supply.

For companies interested in exploring the boundaries of MEMS technology, MEMSCAP (www.memscap.com) features a wide range of standard MEMS devices, including high-Q inductors, variable capacitors, and RF switches. The firm also offers its customizable "Above-IC Technology," which allows the placement of RF MEMS devices directly on top of a silicon IC.

MEMS technology is also well suited for optical applications, such as movable mirrors for tunable lasers. MEMS Optical, Inc. (www.memsoptical.com), for example, is a leading supplier of refractive and diffractive microminiature optics and MEMS devices for optical applications. The company offers lines of standard devices such as scanning two-axis tilt mirrors and moving mirrors for tunable lasers as well as a complete array of optical MEMS foundry services.

With the aid of many well-known corporate sponsors, the Carnegie Mellon University Microelectromechanical Systems Laboratory (www.ece.cmu.edu) is pursing the design and development of MEMS devices using batch-fabrication processes, particularly IC fabrication processes. Jointly associated with the university's Department of Electrical and Computer Engineering and the School of Computer Science's Robotics Institute, as well as the school's Institute for Complex Engineering Systems the MEMS Lab is investigating nanometer-scale data storage, microsensors and microactuators, embedded microinstruments, microrobots, and modeling and design tools for simulating these devices. Industrial Affiliates include ADtranz, Benchmark Photonics, Coventor, DARPA, Intel Corp., the National Science Foundation, STMicroelectronics, and XACTIX. The MEMS Lab includes a 4000-sq.-ft. Class 100 clean room for fabrication, an advanced wafer-probe system for testing, and a long list of computer-aided-engineering (CAE) tools for modeling, including software from Ansoft, Cadence Design Systems, Coventor, and The MathWorks. Also, Sandia Laboratories (www.sandia.com) offers a comprehensive lineup of MEMS fabrication, modeling, and testing services for those interested in creating their own MEMS devices.

Modeling a technology like MEMS poses a challenge for software developers since both electrical and mechanical characteristics must be represented. Coventor (www.coventor.com) offers one of the most widely used design tools with their CoventorWare software suite. The integrated set of tools offers a comprehensive methodology for the design, optimization, and analysis of microminiature devices, including MEMS and fluidic components and subsystems. Individual software engines handle schematic entry, two-dimensional layout, three-dimensional model generation, and model synthesis. The tools are available separately or bundled in any combination. The firm, which recently launched an updated version of its website, offers a free (30-day) software evaluation of the 3D analyzer EM3DS on its website.

Advances in MEMS technology will aid both commercial and military systems. Both commercial and military interests are also pursuing UWB technology for its elegance in handling high date rates at low power levels and sort distances. In essence, a UWB transmitter sends billions of pulses occupying a fairly wide bandwidth. The pulses are arranged according to a temporal sequence known to the receiver, which can then extract the voice, data, or video content carried by the pulse train.

Two years ago, the Federal Communications Commission (FCC) mandated the use of the spectrum from 3.1 to 10.6 GHz for UWB transmissions in the United States at a limited transmit power of ­41 dBm/MHz. The FCC had grappled with concerns over UWB interference with existing applications, such as the Global Positioning System (GPS), C-and satellite communications, and the Microwave Landing System (MLS) before finally agreeing to the 7.5-GHz slice of bandwidth for UWB use.

In order for UWB technology to earn widespread acceptance for applications such as short-range data and video transfer, a universal transmission standard must be adopted by product designers. So far, UWB supports have divided into two camps.

This past September, the MultiBand OFDM Alliance (MBOA) announced the formation of the MBOA Special Interest Group (MBOA-SIG) to support standard specifications for short-range UWB technology. MBOA-SIG promoter companies include Alereon, Hewlett Packard, Intel Corp., Nokia, Philips Electronics, Samsung Electronics (SAIT), Staccato Communications, Sony, Texas Instruments, and Wisair. According to UWB strategist at Intel and MBOA co-founder Stephen Wood, "Our membership of more than 170 companies includes the leading semiconductor, personal-computing, mobile-phone, and consumer-electronics companies." The organization (www.multibandofdm.org) has developed specifications based on orthogonal-frequency-division-multiplex (OFDM) UWB for a physical layer (PHY) and progress is being made on specifications for the UWB Media Access Control (MAC) protocol layer.