Tuesday, October 25, 2016

Ultrathin thermoacoustic Nano Loud Speakers by Tungsten ALD

Woah! This is pretty cool technology and by ALD for sure. University of Colorado, Boulder and  Structured Nanosystems LLC has demonstrated ultrathin thermoacoustic nanobridge loudspeakers from Tungesten ALD on polyimide. Previously I´ve seen same type with Single Wall CNT film by Alto University in Finland (check out Youtube movie below)

All details in the article below (Abstract and link given) and also in a news article here by Nanotechweb, which have detailed pictures and also sound test including some famous German classical music tunes. I assume that there will be a chance to listen live at ALD2017 in Denver!
The CU Boulder MEMS group utilizes ALD to advance nano-fabrication such as the deposition of specialized nano coatings and functional layers. Their current research projects can be found here.

Ultrathin thermoacoustic nanobridge loudspeakers from ALD on polyimide

J J Brown, N C Moore, O D Supekar, J C Gertsch and V M Bright 
2016 IOP Publishing Ltd
Nanotechnology, Volume 27, Number 47

Abstract: The recent development of low-temperature (<200 °C) atomic layer deposition (ALD) for fabrication of freestanding nanostructures has enabled consideration of active device design based on engineered ultrathin films. This paper explores audible sound production from thermoacoustic loudspeakers fabricated from suspended tungsten nanobridges formed by ALD. Additionally, this paper develops an approach to lumped-element modeling for design of thermoacoustic nanodevices and relates the near-field plane wave model of individual transducer beams to the far-field spherical wave sound pressure that can be measured with standard experimental techniques. Arrays of suspended nanobridges with 25.8 nm thickness and sizes as small as 17 μm × 2 μm have been fabricated and demonstrated to produce audible sound using the thermoacoustic effect. The nanobridges were fabricated by ALD of 6.5 nm Al2O3 and 19.3 nm tungsten on sacrificial polyimide, with ALD performed at 130 °C and patterned by standard photolithography. The maximum observed loudspeaker sound pressure level (SPL) is 104 dB, measured at 20 kHz, 9.71 W input power, and 1 cm measurement distance, providing a loudspeaker sensitivity value of ~64.6 dB SPL/1 mW. Sound production efficiency was measured to vary proportional to frequency f 3 and was directly proportional to input power. The devices in this paper demonstrate industrially feasible nanofabrication of thermoacoustic transducers and a sound production mechanism pertinent to submicron-scale device engineering.

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