Piezoelectric Micromachined Ultrasonic Transducers Based on Lithium Niobate

Northeastern University Background
Piezoelectric micromachined ultrasound transducers (PMUTs) will be dominating the ultrasound sensing module market due to their extensive applications in endoscopic imaging devices, medical wearables, automotive gesture recognition, industrial machinery, underwater communication, fingerprint sensors, and VR headsets. In recent years, PMUTs have been experiencing renewed interest since ultrasound is being explored as an alternative to radiofrequency waves to enable communication between small and low-power internet of things (IoT) tags. PMUTs are MEMS-based piezoelectric ultrasonic transducers that work with the bending motion of a thin membrane coupled with a thin piezoelectric film. The most investigated piezoelectric materials for PMUTs are Aluminum Nitride (AlN), Lead-Zirconate-Titanate (PZT), and Scandium-doped AlN (Sc-AlN). Since the desired operation frequency for PMUTs is in the low-frequency ultrasound range (< 1MHz to avoid attenuation), there is a need for larger communication bandwidth (for underwater and intrabody applications) and stronger electro-mechanical coupling to increase the output pressure of the device, thus increasing the communication range distance and signal-to-noise ratio. Therefore, the challenge is to design new PMUT devices with new piezoelectric materials that harness these strong piezoelectric properties.  Technology Overview Researchers at Northeastern invented a new class of PMUT based on a new piezoelectric layer, the X-cut Lithium Niobate (LN), which has never been employed before to develop PMUTs. Thin-film X-cut LN is an ideal candidate for PMUTs given its record performance in electromechanical coupling as well as its quality factor for laterally vibrating resonators in radiofrequency applications. The properties of the X-cut LN and PMUT configuration allow stronger, multiple piezoelectric coefficients of the thin film and permit the activation of a flexural mode of vibration with only top electrodes, thus reducing the fabrication cost, complexity, and reliability issues. The PMUT can be fabricated in arrays and INV‑22040 is specifically micro-fabricated in 8-inch industrial foundries. Each wafer can contain hundreds to thousands of these devices, making the cost of a single bare chip in the order of dollar cents. This PMUT offers a performance advantage in terms of energy efficiency and 4x larger bandwidth than currently established PMUT technologies. Benefits Large bandwidth  Simple fabrication  Highly efficient energy transformation High transmitting and receiving sensitivity Applications Intrabody communication with Implanted Medical Devices (IMDs) Time-of-Flight (ToF) measurements Fingerprint sensors Power transfer Range finding COVID social distancing sensor Underwater communication Opportunity Licensing Commercial Partnership  Research Collaboration

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