Swiss researchers to describe energy-efficient devices at IEDM

The first contribution concerns an active microelectromechanical (MEMS) resonator based on a vibrating-body field effect transistor (VB-FET). This is a hybrid device that exploits the modulation of channel charge and piezoresistivity in the body of an active FET integrated on a resonant MEM structure.

The VB-FET is implemented as a n-channel silicon resonator, on a silicon-on-insulator (SOI) substrate, which is more appropriate for the fabrication of a suspended-body transistor and for a lateral device with vertical isolation. The VB-FET always uses a combination modulation of the output: the FET channel charge modulation that is dominant at the micrometer scale, and the piezoresitivity modulation that is comparable or larger than charge modulation in smaller devices.

The EPFL VB-FET vibrates laterally rather than vertically. Like most MEMS structures the fabricated VB-FET is of micrometer scale with gaps of the order of 150-nm between the vibrating body and the lateral fixed gates.

According to EPFL, VB-FETs with double-gate and four-gate VB-FETs with resonance frequencies of 2MHz and 71MHz, respectively, exhibit built-in amplification, ultra low motional resistances and frequency tuning DC bias. This active MEMS resonator concept, with built-in amplification can achieve a negative resistance of -30 ohms, enabling the possibility of building an oscillator without any sustaining amplifier, thus reducing the power consumption and oscillator size.

The paper also demonstrates a VB-FET mixer-filter based on a single-device operating at 9.84-MHz and a VB-FET oscillator at 2.6-MHz. The VB-FET device is expected to contribute to the miniaturization and the reduction of power consumption in oscillators, mixers and filters for communications circuits.