Scientists at Philips Research claim to have made a significant step towards perfecting new MEMS (Micro Electro-Mechanical System) devices that will enhance the performance and minimise the size of RF circuits in mobile phones.
Although mobile phones themselves are unlikely to get smaller, its it still important to miniaturise the circuits within them to pack more functionality into the same size package to allow for the production of multi-band, multi-mode phones that can be used in many different parts of the world.
Philips Research’s new MEMS devices, which are the microscopic equivalent of air-spaced variable/switchable capacitors, can be integrated into silicon chips using conventional wafer fabrication processes.
These 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. In the variable MEMS capacitor, small deflections of the beam result in a continuously variable capacitance-versus-voltage characteristic.
Philips Research has achieved tuning ranges for these variable MEMS capacitors (the ratio between maximum and minimum capacitance) as high as 17, and Q-factors as high as 500, outperforming virtually all other types so far reported.
Equally important, Philips can integrate these MEMS devices alongside high Q-factor inductors and fixed value MIM (Metal-Insulator-Metal) capacitors using its process technology. This will allow the production of high-performance RF circuits such as adaptive impedance matching networks and voltage controlled oscillators that are superior to discrete component solutions in terms of size and performance.
By using the new MEMS devices, the impedance matching network that sits between a mobile phone’s power amplifier and its antenna will require less than half the printed circuit board area needed to accommodate today’s discrete component networks. In addition, the matching can be made dynamically adaptive to accurately match 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 increase the power amplifier’s efficiency and hence conserve battery power.
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.