47 research outputs found
Design, fabrication and characterisation of silicon carbide resonators
Micro-electro-mechanical systems (MEMS) are integrated mechanical and electrical
elements realised with micro-fabrication technology and employed as sensors and actuators. The integration of reliable MEMS switches and resonators into transceiver
devices is a challenging and attractive solution to increase the efficiency and reduce the
power consumption. Silicon carbide (SiC) is an excellent candidate for developing robust and reliable high frequency MEMS for transceivers applications due to its unique
mechanical properties.This thesis presents the design, fabrication and characterisation of 3C-SiC micromechanical vertical resonators. New device architectures have been developed for the
study of the electro-mechanical behaviour of the devices with the aim of optimising
the actuation efficiency, increasing the resonant frequency and obtaining new device
functions.A process for the fabrication of single or poly-crystalline 3C-SiC cantilevers, bridges
and rings has been developed with the option of integrating top electrodes made of
aluminium (Al) or lead zirconium titanate (PZT). The crystal structure and quality
of the SiC layers have been evaluated with X-ray diffraction and Raman spectroscopy.
A Young's Modulus of ~ 440 GPa has been calculated for the single crystalline SiC
from the mechanical resonant frequency of the fabricated single material cantilevers.
The fabricated Al/SiC bridges and rings have been actuated and driven into resonance electro-thermally. It has been found that wide Al electrodes applied close to the
beams' anchor can maximise the induced displacement and vibration amplitude thus
improving the actuation efficiency. Resonant frequencies in the MHz range have been
obtained with the ring architectures therefore achieving higher frequencies compared
to beam architectures. In addition, electro-thermal mixing of two input frequencies has
been demonstrated and performed with the fabricated Al/SiC structures. Furthermore,
piezo-electric transduction has been used for actuating the PZT/SiC cantilevers and
for sensing the devices' resonance electrically. The design of the PZT piezo-electric
active layer has been shown to influence strongly the devices' resonant frequency and
has been optimised to enhance the electrical output by decreasing the electrodes length
thus decreasing the feedthrough capacitance.The results obtained in this work can be used for the implementation of SiC MEMS
mixer-filters with electro-thermal actuation and piezo-electric sensing for transceiver
applications
A MEMS Filter Based on Ring Resonator with Electrothermal Actuation and Piezoelectric Sensing
AbstractWe report on the design of a two-port ring microelectromechanical (MEMS) resonator with electrothermal actuation and piezoelectric sensing for filtering applications. The ring resonator has been fabricated in silicon carbide with top platinum electrothermal actuator and lead zirconium titanate piezoelectric sensor. The transmission frequency response measurements have shown that the device with a ring radius of 200Ī¼m resonate in the frequency range 0.4MHz ā 0.6MHz, in the presence of tuning. By applying DC bias voltage in the range 4V ā 10V, a frequency tuning range of 330,000ppm has been achieved
PDMS-ZnO Piezoelectric Nanocomposites for Pressure Sensors
The addition of piezoelectric zinc oxide (ZnO) fillers into a flexible polymer matrix has emerged as potential piezocomposite materials that can be used for applications such as energy harvesters and pressure sensors. A simple approach for the fabrication of PDMS-ZnO piezoelectric nanocomposites based on two ZnO fillers: nanoparticles (NP) and nanoflowers (NF) is presented in this paper. The effect of the ZnO fillersā geometry and size on the thermal, mechanical and piezoelectric properties is discussed. The sensors were fabricated in a sandwich-like structure using aluminium (Al) thin films as top and bottom electrodes. Piezocomposites at a concentration of 10% w/w showed good flexibility, generating a piezoelectric response under compression force. The NF piezocomposites showed the highest piezoelectric response compared to the NP piezocomposites due to their geometric connectivity. The piezoelectric compound NF generated 4.2 V while the NP generated 1.86 V under around 36 kPa pressure. The data also show that the generated voltage increases with increasing applied force regardless of the type of filler
Zinc oxide nanowires-based flexible pressure sensor
Abstract Embedding piezoelectric nanowires within a soft elastomer material should provide a superior pressure sensing transducer, exploiting the piezoelectric properties of the nanowire material while maintaining flexibility. Here, a flexible sensor has been fabricated on a Kapton substrate and has incorporated a layer of polydimethylsiloxane with embedded zinc oxide nanowires as the pressure sensing mechanism. In response to applied compressive pressure up to 127Ā kPa, the device has generated a voltage, between electrodes on either side of the nanowire/polydimethylsiloxane layer, with a sensitivity of 23.6Ā mV/kPa, which is 100 times greater than previously reported zinc oxide nanostructureābased flexible sensors