Biosensors are a large and growing subgroup of MEMS. There are many current applications and interests in biosensors and our group has begun research to meet these demands. Novel technologies have been developed using piezoelectric resonator to determine biofluidic properties. Work has also begun to use lateral mode resonators for biomolecule detection in liquid media.
As mobile electronics industry pushes forward, their products demand lower power,smaller components, and greater integration. To help achieve these goals, high-Q micromachined resonators provide an avenue to bring low-power oscillators, sensors, and multi-modal filters onchip. Recently, thin-film piezoelectric-onsubstrate(TPoS) resonators have proved to offer low motional impedances with high Q in air and excellent linearity (high power handling). In these resonators, the piezoelectric layer drives and senses the vibration of a resonant body formed from the substrate (Figure 1). For the lateral-mode resonator lateral dimensions of the device (defined by lithography) determine theresonant frequency. At higher frequencies, the acoustic wavelength decreases; forcing the device features (width) to become excessively small, and consequently causing the motional impedance to rise. To compensate for the scaled transduction area, larger device lengths or higher order modes can be utilized. This will increase the overall resonant structure size allowing for a greater transduction area and electromechanical coupling.
"3D schematic of a 3rd order TPoS resonator"
"Mode shape of the 3rd order TPoS resonator"
"SEM of a typical 3rd order TPoS resonator with acoustic reflectors"
TPoD stands for Thin-film Piezoelectric-on-Diamond. TPoD resonators are lateral-extensional resonators that incorporate a piezoelectric layer. By applying an electric field through the top and bottom electrodes, a stress field is generated in the bulk of the resonator causing it to vibrate laterally. The frequency of vibrations depends on the geometry of the resonator, as well as the elastic properties of the structure.
The superior adventage of diamond is the highest Young's modulus among all materials, so higher frequencies can be achieved without having to reduce the feature sizes. This project focuses on design and optimization of such high frequency resonators.
Structure of a 5th order TPoD resonator
5th over-tone of the strain filed in a TPoD resonator
TPoS (Thin-Film Piezoelectric-on-Substrate) oscillators incorporate a TPoS resonator. This project focuses on assembling different configuration of TPoS oscillators and charactrizing them. Below you can see one such design and its phase noise plot. It has been shown that such oscillators perform very well in the nonlinear operation range of the resonator and very low phase noise values have been reported (refer to conference papers 30 and 47).
TPoD stands for Thin-Film Piezoelectric-on-Diamond. This project focuses on design and fabrication of high frequency filters with low insertion loss and large bandwidth. The filters are fabricated on a stack of aluminum nitride (AlN) on ultrananocrystalline diamond. Why Ultrananocrystalline?! Because in order to get a high quality piezoelctric film with high piezoelectric coefficient, the grains of the film should be aligned in certain directions. This would require a very smooth surface.
In the monolithic filters of this work two different lateral-extensional modes of a single resonant structure are coupled together to make a second order filter.
3D structure of a 5th order TPoD filter
Frequency response of a TPoD monolithic filter at
900MHz, showing a very low insertion loss
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