Imec Unveils Ultrasound Sensor Using Optomechanical Silicon Photonic Waveguide

Article By : Anne-Françoise Pelé

Imec has demonstrated an ultrasound sensor with an ultra-sensitivity that is achieved with an optomechanical silicon photonic waveguide in an acoustical membrane.

R&D organization Imec announced it has demonstrated an ultrasound sensor with an ultra-sensitivity that is achieved with an optomechanical silicon photonic waveguide in an acoustical membrane. The 20 μm sensor is targeted at clinical and biomedical applications of ultrasonic and photoacoustic imaging such as deep-tissue mammography and the study of vascularization or innervation of potential tumorous tissue.

Piezoelectric ultrasound sensors are widely used for health monitoring, but there are some technical limitations. As Imec explains, the detection limit depends inversely on the size of the sensors which is problematic for high-resolution imaging with small acoustic wavelengths. High-resolution images require small piezoelectric sensors which intrinsically have a higher detection limit resulting in a noisy image. Also, piezoelectric sensors rely on their mechanical resonance to enhance signal amplitude. They operate in a small range around the resonance frequency to avoid high detection limits. Finally, matrices of piezoelectric sensors require one wire for each sensor element, hampering e.g., catheter applications.

Imec's optomechanical ultrasound sensor in silicon photonics
Imec’s optomechanical ultrasound sensor in silicon photonics

Imec has presented an ultrasound sensor in silicon photonic technology with ultra-sensitivity owing to an optomechanical waveguide. In a recent paper published on Nature Photonics, Imec claimed this waveguide has “a tiny 15 nm air gap between two movable parts” which are fabricated using new CMOS-compatible processing. The 20 μm small sensor has a noise equivalent pressure below 1.3 mPa Hz−1/2 in the measured range of 3–30 MHz, dominated by acoustomechanical noise. The sensitivity is two orders of magnitude larger than for piezoelectric elements of an identical size, Imec said.

The low detection limit can improve the trade-off between imaging resolution and depth for ultrasound applications. It is essential for photoacoustic imaging, where pressures are up to three orders of magnitude lower than in conventional ultrasound imaging techniques. It can also enable low-pressure applications like through-skull functional brain imaging.

“The sensor we have demonstrated will be a gamechanger for deep tissue imaging in otherwise non-transparent tissues such as skin or brain,” said Xavier Rottenberg, fellow wave-based sensors and actuators at Imec, in a statement. “For applications such as sub-cutaneous melanoma imaging and mammography, it enables a more detailed view of the tumor and vascularization around, aiding in a more detailed diagnosis.”

The sensor is undergoing further tests at selected partners sites, Imec said.

This article was originally published on EE Times Europe.

Anne-Françoise Pelé is editor-in-chief of eetimes.eu and EE Times Europe.

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