How MEMS Ultrasound Imaging became Ultra Small

Recommendable! Nice overview article!

"... Exo Imaging’s September 2023 launch of its handheld probe, the Exo Iris, marked the commercial debut of PMUTs for medical ultrasound. Developed by a team with experience in semiconductor electronics and integration, the Exo Iris is about the same size and weight as Butterfly’s IQ Probe. Its $3,500 price is comparable to Butterfly’s latest model, the IQ+, priced at $2,999.

The ultrasound MEMS chips in these probes, at 2 by 3 cm, are some of the largest silicon chips with combined electromechanical and electronic functionality. The size and complexity impose production challenges in terms of the uniformity of the devices and the yield.

These handheld devices operate at low power, so the probe’s battery is lightweight, lasts for several hours of continuous use while the device is connected to a cellphone or tablet, and has a short charging time. To make the output data compatible with cellphones and tablets, the probe’s main chip performs digitization and some signal processing and encoding. ...

This is only the beginning for miniaturized ultrasound. Several of the world’s largest semiconductor foundries, including TSMC and ST Microelectronics, now do MEMS ultrasound chip production on 300 and 200 mm wafers, respectively.

In fact, ST Microelectronics recently formed a dedicated “Lab-in-Fab” in Singapore for thin-film piezoelectric MEMS, to accelerate the transition from proofs of concept to volume production. Philips Engineering Solutions offers CMUT fabrication for CMUT-on-CMOS integration, and Vermon in Tours, France, offers commercial CMUT design and fabrication. That means startups and academic groups now have access to the base technologies that will make a new level of innovation possible at a much lower cost than 10 years ago. ..."

How MEMS Ultrasound Imaging became Ultra Small - IEEE Spectrum With MEMS technology, all you need is one probe and a smartphone

Two MEMS ultrasound architectures have emerged. In the capacitive micromachined ultrasonic transducer (CMUT) design, attractive forces pull and flex the membrane toward the substrate. When an oscillating voltage is added, the membrane vibrates like a struck drumhead. Increasing the voltage causes the electrostatic forces to overcome the restoring forces of the membrane, causing the membrane to collapse onto the substrate. In the piezoelectric micromachined ultrasonic transducer (PMUT) architecture, voltages applied to the piezoelectric material cause it to expand and contract in thickness and from side to side. Because the lateral dimension is much larger, the piezo disk diameter changes significantly, bending the whole structure.