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Acoustic MEMS

The Acoustic MEMS research group harnesses acoustic waves manipulated on a microfabricated chips for a broad range of applications that include next-generation fast computation, ultrasound imaging and non-destructive testing, gesture recognition, sound generation and perception, wireless power delivery, cell & particle manipulation on lab-on-chips, ultra-low power wake-up sensors for Internet-of-things (IoTs), wireless passive sensors for environmental monitoring, high frequency piezoelectric resonators for ultra-low power wireless communications for IoT.


Piezoelectric Micromachined Ultrasonic Transducers (PMUT)

The use of ultrasound is familiar to all, especially in a medical context as well as structural health monitoring. Existing ultrasound applications are enabled by traditional bulk transducers. IME is working on creating the next generation of ultrasound transducers that can be fabricated at large scale using semiconductor wafer technology. Known as PMUTs, these devices are based on flexible membranes that are driven electrically by piezoelectric action to generate ultrasound as well as to sense ultrasonic echos. Benefits of PMUTs for ultrasonic sensing include power reduction, miniaturization, and the possibility of tighter integration with interface electronics to ride on benefits of digitalization and AI. IME has capabilities to process AlN, Sc-doped AlN (15% and 20% demonstrated to date) as well as PZT to address a broad range of needs. Applications of PMUTs include non-destructive testing, proximity sensing, imaging, remote environment sensing, as well as power delivery. 

 

Ultra-Low Power Wake-up Sensor Switch

With the growth of interest in IoTs, there has been extensive research on IoT sensor nodes for monitoring abnormal changes in urban environments. Most IoT sensor nodes to date depend on always-on sensors, which consume µW of stand-by power. This amount of power is a significant portion of the total power budget of an IoT sensor node. Therefore, even if an IoT node uses existing low power IC components to build the hardware, it is very difficult to extend the lifetime of the IoT node over one year due to the stand-by power consumption. To address this issue, IME has developed MEMS contact switches that can extend the battery lifetime of IoT sensor nodes to over 10 years. These switches have an almost zero-power consumption in the off-state, but they can sense environmental vibrations, sounds, temperatures, or pressures and wake up the entire IoT node if the signal exceeds a predefined threshold. In this way, the standby power consumption of a IoT node can be cut down to nW levels, and the lifetime is elongated to more than 10 years.


Piezoelectric Over Silicon-On-Nothing (PSON) Platform

Suspended form of piezoelectric MEMS devices has been realized as frequency references for wireless communication, piezoelectric micromachined ultrasonic transducers (pMUTs) for gesture recognition, ultrasonic imaging, fingerprint scanning and acoustofluidic sensors for biological cell manipulation. Conventional methods to fabricate such suspended structures include etching a port on the backside of a silicon-on-insulator (SOI) wafer and cavity-SOI wafers, where a cavity is etched into a substrate wafer and thereafter bonded to another wafer to form a sealed cavity. While backport etching on SOI wafers are generally limited to larger cavities with low densities, cavity-SOI comes at a higher cost with lower yield.

IME has developed a novel platform to fabricate piezoelectric devices on pre-released silicon membranes over embedded cavities which are formed using a silicon-on-nothing (SON) process within relatively low-cost bulk silicon wafers. This piezoelectric over silicon-on-nothing (PSON) platform has been adopted to successfully fabricate high fill-factor pMUT arrays, multi-frequency temperature compensated MEMS resonators (from few MHz to few GHz) and acoustofluidic devices.

MEMS Piezoelectric Resonators

Wireless communication demands for GHz/sub-GHz temperature compensated resonators. In the past decade, MEMS resonators have been dominating the market for timing and frequency reference devices as compared to traditional quartz-based resonators which are bulky and incompatible with conventional CMOS fabrication processing. Temperature coefficient of frequency (TCf) is higher for conventional piezoelectric-on-silicon resonators (~30ppm/°C) as compared to traditional quartz-based resonators (~1-2ppm/°C). Doped silicon has been proven to reduce TCf among MEMS resonators. 
MEMS Acustics

IME has developed a novel fabrication platform to fabricate temperature compensated piezoelectric MEMS resonators on degenerately doped silicon. Temperature compensated surface acoustic wave resonators (fabricated on unreleased doped silicon) and contour mode resonators (fabricated on pre-released doped silicon membranes with embedded cavities using PSON process) have already been successfully designed, fabricated, and characterized within our in-house facilities.

Ultrasonic Wavefront Computing Accelerator for Hybrid Computing

With ever-growing demands for greater computation power, emerging research areas such as analog computing accelerators have been growing for the past decade. An analog approach for computing 2D Fast Fourier Transform (FFT) was introduced by leveraging the principles of ultrasonic wavefront propagation and Fresnel diffraction. Such a system requires a flat acoustic lens, acoustic mediums, and transmit/receive CMOS-MEMS modules. The acoustic method which also uses the principles of wave mechanics, when operated at compatible CMOS frequencies (in GHz) can acquire the phase information required for complex FT. 

IME has developed a post-CMOS platform with via first approach to integrate AlN and ScAlN transducers on CMOS. This platform also allows the implementation of GHz imagers and fingerprint sensors with high resolution at a fast rate. Our capability also extends to the design and fabrication of GHz acoustic lenses.

Piezo MEMS Multi-Project Wafer (MPW)

Aluminium nitride (AlN) is a piezoelectric material that can readily be deposited as thin films on the wafer level. These piezoelectric properties are valuable for MEMS devices as they convert mechanical energy into electrical energy and vice versa. This enables mechanical stresses to directly generate electrical signals (for sensors) or mechanical movements to be achieved with electrical stimuli (for actuators). IME has developed numerous wafer fabrication technology platforms based on AlN, ScAlN (15% and 20% Sc doped) for MEMS devices, such as for resonators, energy harvesters, ultrasonic transducers, and other sensors. IME is also currently developing the MEMS platform for 30% Sc doped AlN.

 

Acoustic Imaging and Algorithms

IME can provide solutions and services in acoustic imaging and algorithm development. The configurable Verasonics Vantage 64 system can provide up to 64 independent driving channels (up to 50 MHz) to provide high-resolution image capability for all ultrasound applications.

Infrastructure

IME can provide services in acoustic testing and characterization ranging from kHz to MHz. We have developed a fully automated acoustic mapping setup for characterizing immersion and air-coupled ultrasonic transducers.

MEMS Infrastructure
 

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