Su-8-based nanocomposites for acoustical matching layer

Abstract

SU-8, an epoxy-based photoresist, was introduced as the acoustical matching layer between silicon and water for lab-on-chip applications integrating acoustic characterization. Acoustical performances, including the acoustic longitudinal wave velocity and attenuation of the SU-8-based matching layer, were characterized at a frequency of 1 GHz at room temperature. The gain in echo characterization with a SU-8/SiO2 bilayer and with different nanocomposite monolayers made of SU-8 and TiO2 nanoparticles (size around 35 nm) between silicon and water was characterized as being above 10 dB in each case. With the increase of concentration of TiO2 in SU-8 based composites from 0 to 30 wt%, acoustical impedance of the nanocomposites increased from about 3 to 6 MRayls, respectively. The acoustical attenuation in the nanocomposites is between 0.5 and 0.6 dB/microm. The most efficient matching was obtained with the nanocomposite integrating 30 wt% TiO2 nanoparticles, with which the enhanced loss is about 0.34 dB as the attenuation is about 0.5 dB/microm. This type of matching layer has potential applications in lab-on-chip technology for high frequency transducers or in the fabrication of high frequency piezocomposites.

Simple sacrificial-layer-free microfabrication processes for air-cavity Fresnel acoustic lenses (ACFALs) with improved focusing performance

“…The PTE values of the ACFAL-based SFATs estimated by a 1D acoustic transmission line model are close to the measured values except for S284, in which case the measured value is much lower, possibly due to (1) the tensile stress (stemming from the large thermal expansion coefficient 37 ) of the thick SU-8 bending the PZT, (2) the surface roughness of the top SU-8 layer (the black “speckles” in Fig. 2i ), shaped by the nonsmooth polyester (PET) film, and/or (3) the inaccuracy of the acoustic attenuation coefficient used in the calculation, as it is the value extracted from measurements at 1 GHz 38 . In the future, a more realistic multiphysics FEM simulation model of ACFAL in 2D or 3D, which considers the interaction between the lens material and the piezoelectric substrate, can be used to accurately predict the output pressure and PTE.…”

“…To further improve the performance of the devices, the substrate material can be changed to a piezoelectric composite, such as a 1–3 composite consisting of a lead magnesium niobate-lead titanate (PMN-PT) single crystal and epoxy, which has a lower loss, lower acoustic impedance, and higher electromechanical coupling coefficient 39 , 40 . Additionally, the acoustic impedance of the lens materials could be increased by adding titanium oxide (TiO 2 ) nanoparticles 38 , 41 , which will bring the acoustic impedance of the lens material closer to the square root of the product of the acoustic impedances of PZT and water (7.32 MRayl) for better acoustic matching 31 . These two improvements can easily be incorporated into the processes described in this paper.…”

A Review of Acoustic Impedance Matching Techniques for Piezoelectric Sensors and Transducers

“…The 0–3 nanocomposites based on Al 2 O 3 [ 237 ], CeO 2 [ 238 ], SiO 2 [ 239 ], TiO 2 [ 240 ], and Ag [ 212 ] at high frequencies 10–100 MHz have nonuniformity and high attenuation (>20 dB/mm at center frequency) caused by particle scattering. A large volume fraction (>40%) of particles is difficult to be embedded in the matrix due to the wetting problem.…”

Improving acoustic streaming effects in fluidic systems by matching SU-8 and polydimethylsiloxane layers

“…SU-8 is commonly used as a mold for microstructures fabrication, since it is compatible with ultraviolet (UV) photolithography and does not imply expensive masks. It is typically processed through spin coating techniques, and presents good mechanical properties, good chemical resistance and a very good biocompatibility [39][40][41]. PDMS is a polymer widely used in microstructures due, mainly, to its low cost processing techniques [29].…”