Maryam Ziaei-Moayyed

Silicon carbide phononic crystal cavities for micromechanical resonators

This paper demonstrates silicon carbide phononic crystal cavities for RF and microwave micromechanical resonators. We demonstrate design, fabrication, and characterization of Silicon Carbide/air phononic crystals used as Bragg acoustic mirrors to confine energy in a lateral SiC cavity. Aluminum nitride transducers drive and sense SiC overtone cavities in the 2–3GHz range with ƒxQ products exceeding 3×1013 in air. This approach enables decoupling of the piezoelectric AlN material from the SiC cavity, resulting in high Q resonators at microwave frequencies. The SiC cavities are fabricated in a CMOS-compatible process, enabling integration with wirelesss communication systems.

Silicon carbide lateral overtone bulk acoustic resonator with ultrahigh quality factor

This work demonstrates a lateral overtone bulk acoustic resonator (LOBAR), which consists of an aluminum nitride (AlN) transducer coupled to a suspended thin silicon carbide (SiC) film fabricated using standard CMOS-compatible processes. The LOBAR design allows for high transduction efficiency and quality factors, by decoupling the transduction and energy storage schemes in the resonator. The frequency and bandwidth of the resonator were lithographically defined and controlled. A LOBAR operating at 2.93GHz with a Q greater than 100,000 in air was fabricated and characterized, having the highest reported ƒ×Q product of any acoustic resonator to date.

Micro and nano fabricated phononic crystals: technology and applications

With the application of microfabrication techniques, phononic crystals have been transformed over the past decade: from hand assembled millimeter-to-meter scale crystals consisting of metal balls in water or epoxy, to precisely machined crystals with sub-micron features operating at frequencies in excess of 1 GHz. This paper reviews the contributions of Sandia National Laboratories to micro and nano scale phononic crystal devices including: the integration of piezoelectric transducers, the choice of phononic crystal materials, phononic crystal design, and the application of phononic crystals to radio frequency and thermal management applications.

Silicon carbide phononic crystals for high f.Q micromechanical resonators

This paper demonstrates silicon carbide phononic crystal cavities for RF and microwave micromechanical resonators. We demonstrate design and simulation of silicon carbide/air phononic crystals used as Bragg acoustic mirrors to confine energy in a silicon carbide cavity. Aluminum nitride piezoelectric transducers are used for drive and sense of silicon carbide overtone cavities at 2.3GHz with quality factors exceeding 3,500 in air. This approach enables decoupling of the piezoelectric material from the cavity quality factor, resulting in high f.Q products at microwave frequencies. The silicon carbide phononic crystal cavities are fabricated in a CMOS-compatible process, for integration in wireless communication systems.

Investigation of full bandgaps in silicon phononic crystal membranes with tungsten and air inclusions

It has been observed experimentally that solid-solid PnCs have larger bandgaps for a wide range of hole radii and slab thicknesses than their solid-air counterparts. Here, we theoretically investigate the optimal hole radius and thickness parameters for full bandgap formation (accounting for all transverse and longitudinal modes) in PnCs formed from a Si matrix with a square-lattice of W inclusions. The plane-wave expansion technique was used to calculate the dispersion behavior for in-plane and out-of-plane transverse and longitudinal (flexural) modes, implementing a supercell method to account for the finite third dimension. The results are compared with those for a PnC composed of air holes in a Si matrix.

Radial bulk-mode vibrations in a gate-all-around silicon nanowire transistor

This paper reports the radial bulk-mode vibrations in a gate-all-around (GAA) silicon nanowire (SiNW) transistor at 25.3GHz, with a quality factor of ~850 measured in air. The radial bulk-mode resonance is excited capacitively in the SiNW using the surrounding gate and gate dielectric as the transducer; the output is sensed piezoresistively by modulating the drain current in SiNW. The SiNWs are defined using standard lithography in a top-down front-end CMOS process, which allows for resonators with different frequencies to be fabricated on the same chip.

CMOS-compatible gate-all-around silicon nanowire detector

In this paper, we demonstrate gate-all-around (GAA) single crystalline nanowires (SiNWs) that are fabricated using top-down standard CMOS front-end processes. The GAA silicon nanowires are fabricated in well-defined locations with high-quality electrical contacts, and controlled geometry and alignment. These SiNW FETs fabricated in this process have demonstrated repeatable electrical performance with threshold voltages of ∼0.2V and subthreshold slopes of ∼80mV/dec. The p-i-n silicon nanowires are highly sensitive to the intensity and polarization of the incident light. The results in this work demonstrate that individual SiNWs are good candidates for high resolution optical sensing and allow for tuning of the optical properties of the nanoscale devices by precise control of the nanowire geometry and orientation of the incident light. These top-down fabricated SiNWs can be easily integrated in high density arrays for enhanced light absorption, resulting in imaging sensors with nanoscale spatial resolution.