Philips pushes out RF MEMS for wireless
The new MEMS devices are fabricated by under-etching an area of the silicon chip’s top metal layer to create a microscopic metal beam that moves up and down through electrostatic attraction in response to an applied voltage. In the case of the switched MEMS capacitor it moves until it contacts a dielectric layer situated underneath the beam. The variable MEMS capacitor employs a region of the switched capacitor’s characteristic where small deflections of the beam result in a continuously variable capacitance vs. voltage characteristic.
Philips Research has achieved tuning ranges for these variable MEMS capacitors (the ratio between maximum and minimum capacitance) as high as 17 with Q-factors (quality factors) as high as 500, outperforming virtually all other types so far reported. High "Q" means little energy lost through device operation. Equally important, these MEMS devices can be integrated alongside high-Q inductors and fixed value MIM (Metal-Insulator-Metal) capacitors using Philips’ PASSI process technology.
High-performance RF circuits can be created such as adaptive impedance matching networks and voltage controlled oscillators. These will be far superior to discrete component solutions in terms of size and performance, it is claimed. Furthermore, use of the industrialised PASSI process will enable a straightforward transfer of RF MEMS technology to production.
A PASSI/MEMS impedance matching network between a mobile phone’s power amplifier and its antenna will require less than half the printed circuit board area needed to accommodate discrete components. In addition, the matching can be made dynamically adaptive accurately matching the amplifier to the antenna at all RF power levels. In GSM systems, for example, where the RF power transmitted by a handset varies according to local signal conditions and the distance to the nearest basestation, this will significantly increase the power amplifier’s efficiency and hence conserve battery power.
Philips Research is also employing its MEMS capacitor technology to produce highly linear RF MEMS switches. These switched capacitors will be used to replace the power consuming PIN-diode switches currently used in mobile phones to prevent high RF power levels from reaching the handset’s sensitive RF receiver circuitry while the phone is transmitting.
The MEMS capacitor technology has been developed as a result of Philips’ participation in the MEMS2TUNE project within the Fifth European Community Framework programme on Information Society Technologies.
Philips thinks that although mobile phones themselves are unlikely to get smaller, circuitry miniaturisation is still required to pack more functionality into the same size package. Performance improvements are still required to enhance call quality and extend standby and talk times.
