Boris Sviličić

Electrothermally Actuated and Piezoelectrically Sensed Silicon Carbide Tunable MEMS Resonator

In this letter, we present the design, fabrication, and electrical testing of a silicon carbide microelectromechanical (MEMS) resonant device with electrothermal actuation and piezoelectric sensing. A doubly clamped flexural-mode beam resonator made of cubic silicon carbide has been fabricated with a top platinum electrothermal actuator and a top lead zirconium titanate piezoelectric sensor. Electrothermal transduction has been used to drive the device into resonance and tune its frequency. Piezoelectric transduction has been used as resonance sensing technique. Electrical measurements have shown that, by increasing the dc bias of the actuating voltage from 1 to 7 V, a tuning range of 171 kHz can be achieved with a device resonating at 1.766 MHz.

Piezoelectrically transduced silicon carbide MEMS double-clamped beam resonators

Silicon carbide (SiC) double-clamped beam (bridge) microelectromechanical system flexural vertical resonant devices actuated piezoelectrically and sensed piezoelectrically have been fabricated and tested. Lead zirconium titanate has been used as active material to implement the piezoelectric actuator and sensor. The transmission frequency response measurements have shown that the devices with the SiC beam length between 100 μm and 200 μm resonate in the frequency range of 0.8–1.9 MHz. The tuning of the resonant frequency has been demonstrated by applying DC bias voltage in the range of 0–5 V and frequency tuning range of 2500 ppm has been achieved. The resonant frequency tuning range has been shown to increase when the lengths of the actuating electrode and the beam are increased. The untuned devices have been shown to possess good linear behavior, while the presence of a tuning DC bias voltage can exceed the maximum power handling capabilities of a device.

3C-Silicon Carbide Microresonators for Timing and Frequency Reference

In the drive to miniaturise and integrate reference oscillator components, microelectromechanical systems (MEMS) resonators are excellent candidates to replace quartz crystals. Silicon is the most utilised resonator structural material due to its associated well-established fabrication processes. However, when operation in harsh environments is required, cubic silicon carbide (3C-SiC) is an excellent candidate for use as a structural material, due to its robustness, chemical inertness and high temperature stability. In order to actuate 3C-SiC resonators, electrostatic, electrothermal and piezoelectric methods have been explored. Both electrothermal and piezoelectric actuation can be accomplished with simpler fabrication and lower driving voltages, down to 0.5 V, compared to electrostatic actuation. The vibration amplitude at resonance can be maximised by optimising the design and location of the electrodes. Electrical read out of the resonator can be performed with electrostatic or piezoelectric transduction. Finally, a great deal of research has focused on tuning the resonant frequency of a 3C-SiC resonator by adjusting the DC bias applied to the electrodes, with a higher (up to 160-times) tuning range for electrothermal tuning compared to piezoelectric tuning. Electrothermal tuning lowers the frequency, while piezoelectric tuning can be used to raise the frequency.

Thermal- and Piezo-Tunable Flexural-Mode Resonator with Piezoelectric Actuation and Sensing

This paper reports on a piezoelectrically actuated and sensed flexural-mode microelectromechanical resonant device with electrothermally and piezoelectrically tunable resonant frequency. The device is designed as a multilayer circular membrane (diaphragm) resonator with a lead–zirconium-titanate piezoelectric actuator and a sensor, as well as platinum electrothermal tuning electrodes placed on the top of a silicon-carbide diaphragm. The design enables active electrothermal frequency tuning independent of the piezoelectric input/output operation of the device. The performance of the fabricated device has been tested using two-port transmission frequency response measurements that are performed at atmospheric conditions. Electrothermal tuning and piezoelectric tuning introduce the unique feature of shifting the resonant frequency downward and upward, respectively. The resonant frequency has been tuned by applying dc voltages in the range 0–5 V. The measurements have shown that an 886 kHz device exhibits a frequency tuning range of about −8400 ppm when tuned electrothermally and a tuning range of about +2400 ppm when tuned piezoelectrically. Simulated results have shown that the wider frequency range for electrothermal tuning is a result of a larger change in induced stress in the diaphragm for a given dc voltage, as well as the fact that the electrothermal tuning mechanism effectively serves to relax the residual tensile stress in the diaphragm. [2016-0161]

Electrothermal actuation of mems resonator based filters with piezoelectric sensing

Summary form only given: Microelectromechanical systems (MEMS) resonators have been intensively investigated as an alternative for electronic filter components currently used in communication systems because of their small size and low operating voltages [1]. Electrothermal actuation, compared to other transduction techniques for electrical induction of mechanical vibrations, brings benefits in terms of simple fabrication, impedance matching and low actuation voltages. Electrothermally actuated resonators provide high resonant frequencies, high Q-factors and wide frequency tuning range [2, 3]. Recently, we have demonstrated the piezoelectric sensing of electrothermally actuated double-clamped beam MEMS resonators [3, 4]. Piezoelectric sensing technique, compared to the alternative electrostatic transduction, offers stronger electromechanical coupling, better impedance matching and simpler fabrication process. In addition, it allows active generation of electrical potential under applied mechanical stress, without need for external bias supply. In this work, we investigate on electrothermal actuator design solutions for optimizing frequency tuning range and Q-factor of the devices. Devices of two types were fabricated, with the only difference in the electrothermal actuator layout design, slab and u-shape layout, while other technological parameters and dimensions are the same (Fig. 1). Tested devices were taken from the same die and tested by performing two-port transmission frequency response measurements. The devices operate between 0.75 and 1.2MHz for tuning voltages of 1 to 7 V, and Q-factors up to ~ 400 have been measured in atmospheric conditions. Experimental results have shown that the device actuated with u-shape electrode resonates at lower frequencies with higher Q-factor, and that wider frequency tuning has been obtained under the same actuating conditions. Design, fabrication and measurement setup details will be presented. Moreover, the influence of the electrothermal actuator design on the resonant behavior will be discussed.

Tuning performance of silicon carbide micro-resonators

Silicon carbide microresonators have been designed, fabricated and tested. Three designs have been studied: cantilever, bridge and ring resonators. The devices have been actuated electrothermally and sensed piezoelectrically. The resonant frequency as well as the amount of frequency shift as a function of DC bias voltage for the three designs have been characterized electrically using two-port measurements. It has been found that the DC tuning sensitivities of the ring and bridge resonators (between 58,000 ppm/V and 62,000 ppm/V) are significantly higher than for the cantilever (240 ppm/V). Simulations have shown that a larger temperature change, hence a larger compressive stress induced in the SiC layer exists in the bridge design compared to the cantilever design as the DC bias voltage is increased. The higher DC tuning sensitivity for the bridge design could be a result of the combination of the location of the electrode thus causing higher thermally induced compressive stress as well as the clamped-clamped beam configuration.