Research Areas 

A. RF Piezoelectric MEMS Systems

• MEMS Filters

We explore various MEMS resonators with different architectures and vastly different device configurations to achieve functionality in the RF and microwave frequency regimes. The field of RF MEMS resonators has found wide success both commercially and in scientific endeavors. SAW and BAW resonators are mass-produced (Qualcomm, Murata, Texas Instruments, Akoustis Technologies, etc) as filters and duplexer circuits to integrate modern communications devices like smartphones. Check out our recent work was presented in IEEE IFCS 2024 where we successfully demonstrated the implementations of SAW resonator-based lattice filter.

• Oscillators

A local oscillator (LO) unit used in radio frequency communication serves as a frequency reference element for a large spectrum of linked devices. Such oscillators demand usage of resonators with high Q for a better phase noise performance. PiezoMEMS resonators when implemented suffer from low Q due to the piezoelectric layer. In our group, we explore unique architectures where TPoS (Thin piezoelectric film on substrate) resonators are used to couple a high Q silicon. Check out our recent work 

• Extremely High-Q Resonators

The field of quantum acoustodynamics is an emerging new front where RF MEMS resonators has found its place due to its ability to couple with both mechanical and EM waves. High overtone bulk acoustic resonator (HBAR) amongst the BAW resonator fits well into this niche domain due to its ability to exhibit high frequency and high Q multi-mode across a wide band of frequency (L to X band). We explore the use of induced piezoelectricity in ferroelectric material mounted on a low acoustic sapphire substrate to achieve exceptionally high fQ in the order of 10 15 Hz at cryogenic temperatures. Check out our recent work here

B. Physical Sensors

• Pressure Sensors

MEMS pressure sensors are widely used in the biomedical, aerospace, petrochemical, and automotive industries, where there is a strong demand for miniaturized, low-power devices with high sensitivity and stability in extreme temperature and pressure conditions. In our lab, we have demonstrated an integrated circular piezoelectric MEMS resonator and diaphragm-based resonant pressure sensor that offers high sensitivity, wide bandwidth, and minimal hysteresis with low power consumption. Check out our recent works (https://doi.org/10.1109/LSENS.2023.3326127 https://doi.org/10.1109/MEMS58180.2024.10439301 ) 

• Ultrasound Transducers

Piezoelectric materials vary in their inherent properties, with some excelling at transmitting signals and others better suited for receiving. Achieving a good Figure of Merit in resonators requires balancing a large piezoelectric coefficient and low permittivity, and it is a challenge for single-material piezoelectric MEMS designs. In our group we demonstrate a novel fabrication framework for the lateral stacking of two distinct piezo/ferroelectric materials for the first time by keeping both thin film properties intact. This improves transceiver performance by laterally stacking a ferroelectric material with a high piezoelectric coefficient alongside a non-ferroelectric material with lower permittivity. The experimental results validate the proof of concept by demonstrating that the output electrical voltage is higher for PZT drive/ AlN sense compared to AlN drive/ PZT sense. Through this fabrication scheme, along with harnessing the advantages of multiple piezo/ferro thin-film materials at the same time on a single device, we are able to use the DC tuning capability of ferroelectric materials like PZT while still benefiting from the low capacitive feedthrough offered by piezoelectric materials like AlN.

C. Biomedical Devices

MEMS-based viscosity sensing is crucial for biomedical and industrial applications. Our recent work explores PZT-based microcantilever sensors for dynamic viscosity measurement. Using multi-mode operation, we achieve high responsivity and a broad sensing range through optical and electrical characterization. We further introduce a dummy device-based feedthrough cancellation technique, significantly improving signal clarity and sensitivity. Experimental results demonstrate accurate viscosity tracking across a range of glycerol-water solutions, with Q-factor variation following a power law relation. By enhancing electrical readout and eliminating parasitic signals, our study advances MEMS viscosity sensors for real-time diagnostics and fluid monitoring. Check out our findings at IEEE EFTF/IFCS 2023 ( 10.1109/EFTF/IFCS57587.2023.10272199) and IEEE EDTM 2024 (10.1109/EDTM58488.2024.10511369)

D. Nonlinear MEMS

Nonlinearity in MEMS resonators can either be mitigated or leveraged depending on the application. In many cases, nonlinear behavior is intentionally utilized to unlock new functionalities, enhance performance, or investigate fundamental physics in MEMS resonators, such as wave mixing, phonon lasing, and phononic frequency combs. In our group, we explore phononic frequency combs using internal resonance (nonlinear phenomena) coupling in curved piezoelectric micromachined ultrasonic transducers (PMUTs). Check out our recent work presented at IEEE UFFC-JS 2024 (DOI: 10.1109/UFFC-JS60046.2024.10793956), where we successfully demonstrated phononic frequency combs via 2:1 internal resonance between the first asymmetric and second symmetric modes of a curved PMUT.

E. Waferscale packaging of MEMS devices

Our group also works on wafer-scale packaging of MEMS devices such as accelerometers. We have developed a novel three-wafer stack packaging technique to protect the device from external environmental factors. The middle wafer houses the released accelerometer, while the top and bottom wafers encapsulate it. Each wafer is microfabricated using photolithography, RIE, and DRIE processes and bonded through fusion.