RF MEMS Devices Posed to Revolutionise Communication

Technical Insights Microelectromechanical system (MEMS) technology is attracting tremendous interest across the world and research efforts are constantly growing. This technology has made exceptional advances in recent years and is now poised to transform radio frequency (RF). RF MEMS devices have a huge number of potential applications including wireless communications, military, space and instrumentation.

The interest in MEMS technology for RF and wireless applications can be attributed to its flexibility, which can be exploited to overcome the limitations exhibited by integrated RF devices and enable circuits with new levels of performance not achievable otherwise Thus, the ultimate goal in applying RF MEMS is to propagate the device-level benefits all the way up to the system level.

Components based on MEMS technology not only deliver superior RF performance and tunability, but do so over a much broader range of operating frequencies. For instance, an RF MEMS switch concurrently provides improved insertion loss, isolation and linearity.

RF MEMS devices can potentially be used as microswitches to build impedance networks in front of power amplifiers and to decrease the number of components in multistandard mobile phones. They can also be used as MEMS inductors and tunable capacitors for integrated voltage-controlled oscillators (VCOs) in global positioning systems (GPSs).

Since this technology enables superior passive devices, it is ideally suited for numerous wireless appliances operating in the home/ground, mobile, and space spheres such as handsets, base stations, and satellites. In fact, with RF MEMS’ characteristic properties of low power consumption and reconfigurability, ubiquitous wireless connectivity may no longer be a distant possibility.

Current research efforts are aimed at developing a single-chip RF circuit in response to wireless system manufacturers’ need for lower weight, volume, cost and increased functionality. With companies looking to integrate MEMS devices directly on the RF chip, numerous discrete components could be replaced, thereby offering enhanced performance and reliability along with significant cost savings.

The industry is only now beginning to see the advantages of such integrated devices. Over time, this integration can lead to the replacement of all passive RF chips with on-chip devices, offering considerable benefits such as smaller form factors for cell phones and added functionalities including Internet connectivity.

As telecom systems grow increasingly sophisticated, researchers continuously attempt to improve RF MEMS devices in terms of size and performance. An interesting way of achieving this is to introduce new materials in their fabrication. However, such materials will not only have to possess advanced electrical and mechanical properties, their elaboration process must also be fully compatible with all other steps involved in microfabrication.

The pulsed laser deposition (PLD) method has shown significant potential in depositing thin-films with different properties of various materials even at room temperature. Researchers at the University of Limoges in France are now exploring the electro-mechanical properties of aluminium oxide and tetrahedral amorphous carbon (ta-C) thin-films deposited at room temperature using PLD. Their research has yielded several examples illustrating the integration of such materials in RF MEMS device fabrication.

Researchers believe that such devices have numerous promising applications. Aluminium oxide as dielectric in MEMS capacitive switches is one such application. They are also exploring the possibility of small-sized MEMS switches that could reduce switching time and ease the integration of this component above complementary metal-oxide semiconductor (CMOS) circuitry.

In other interesting developments, a research team at the University of Dortmund has developed a concept for a completely CMOS-compatible integrated surface RF MEMS switch using the electrostatic actuating principle. Typically, MEMS integration in the CMOS process takes place pre-CMOS, intermediate-CMOS or post-CMOS.

This concept is based on the monolithic integration of a microelectromechanical switch by method of the intermediate-CMOS fabrication. Researchers say that only minor modifications of the CMOS process are required to integrate the MEMS switch in the process flow. Since all additional process steps are taken from the CMOS technology, the entire process remains CMOS-compatible.

Since almost exclusively CMOS-process steps are deployed and no additional equipment is needed for the fabrication, this makes it easy to transfer the process to every other CMOS-technology-line Researchers hope that further integration with already published integrated optical and mechanical processes will allow the realisation of very complex systems.

Title: Advances in RF MEMS Technology

Publ 20060209