Digital microbubble array creates ultrasound holograms: Page 3 of 3

September 14, 2020 // By Nick Flaherty
Digital microbubble array creates ultrasound holograms
A team at the Max Planck Institute for Intelligent Systems has developed a chip that can produce a series of ultrasound holograms that can be used to build microparticles

chip surface is estimated to be 20 μm. A 2-μL electrolyte droplet is squeezed between the conveyor film and the chip surface under the experimental conditions, whose spread area is measured as 1 cm2.

The chip was produced by a classical 0.8µm channel length CMOS technology. This p-well technology incorporates local oxidation of silicon device isolation, a single polysilicon layer as the gate electrode, and two aluminium layers for interconnects with a total of 15 optical lithography steps. In addition, two lithography steps specialized post-processing was used for the gold electrodes.

The elements of the chip are currently sequentially addressed, which leads to relatively slow update cycle of 12s, but parallel pixel addressing is expected to drastically increase the refresh rate. To meet the requirements of portable biomedical devices, the bubble removal method can be implemented by other means such as forced fluid flow of the electrolyte or on-chip reversal of the electrolysis.

Future work could explore multilevel amplitude or phase control of sound waves exploiting the resonant behaviour of the microbubbles at specifically controlled sizes. These could be used for medical imaging, nondestructive testing, holographic acoustic tweezers and acoustic fabrication.

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