Researchers at Philips have extended micro-electromechanical systems (MEMS) technology to variable capacitors. Thus, Philips' researchers have demonstrated micromachined electrically variable RF capacitors. The devices, which are the microscopic equivalent of air-spaced variable and switchable capacitors, can be integrated into silicon chips using conventional wafer fabrication processes, according to the company. The capacitors are made by under-etching an area of the chip's top metal layer to create a beam that moves up and down through electrostatic attraction when a voltage is applied. So it can be used as a variable capacitor. It can also be used as a switched MEMS capacitor, wherein it moves until it contacts a dielectric layer situated underneath the beam. In the variable capacitor case, the researchers claim to achieve a tuning range of 17 and Q-factor as high as 500.

According to Philips, it can integrate its MEMS capacitors alongside high-Q inductors and fixed value metal-insulator-metal (MIM) capacitors using its PASSI 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, said the developer.

Consequently, the impedance matching network that sits between a mobile phone's power amplifier and its antenna will require less than half the PC board area needed to accommodate traditional networks using discrete components. In addition, matching can be dynamically varied to obtain high accuracy. The researchers are also employing 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.