ACOUSTOFLUIDIC COMPONENTS AND PROCESS FOR THEIR PREPARATION

Abstract

Acoustofluidic components in which at least one microfluidic element and at least one acoustic transducer element are arranged on a piezoelectric substrate and/or on a piezoelectric layer on a non-piezoelectric substrate and/or on a non-piezoelectric substrate on a piezoelectric layer. The at least one microfluidic element is arranged in at least one propagation direction of an acoustic wave excited by the acoustic transducer element and the at least one microfluidic element prepared at least partially by lamination and photolithographic structuring comprises a base, walls and a top. At least the top is prepared by lamination and photolithographic structuring, and the microfluidic element has top thicknesses of 0.01 to 10 times the wavelength of the acoustic wave excited by the acoustic transducer element.

Claims

1. Acoustofluidic components in which at least one microfluidic element and at least one acoustic transducer element are arranged on a piezoelectric substrate and/or on a piezoelectric layer on a non-piezoelectric substrate and/or on a non-piezoelectric substrate on a piezoelectric layer, wherein the at least one microfluidic element is arranged in at least one propagation direction of an acoustic wave excited by the acoustic transducer element and the at least one microfluidic element prepared at least partially by lamination and photolithographic structuring comprises a base, walls and a top, wherein at least the top is prepared by lamination and photolithographic structuring, and the microfluidic element has top thicknesses of 0.01 to 10 times the wavelength of the acoustic wave excited by the acoustic transducer element.

2. The acoustofluidic components according to claim 1 in which a plate or a film or a microchip made of glass/glasses/ceramic/ceramics (for example, SiO2, Al2O3, Si3N4, SiN, borosilicate glass), piezoelectric materials (for example, quartz, LiNbO3, black LiNbO3, yellow-black LiNbO3, LiTaO3, AlN, Sc-AlN, ZnO, CTGS, langasite, gallium orthophosphate, PZT, PMN-PT, PVDF), metals/metal alloys (for example, Al, Cu, Ti, Ta, TiAl, CuTi) or polymers (PMMA, PTFE, PEEK, polyimide, PET, COP, PDMS, PC, COC, polycaprolactone, PS) or photoresists (for example, SUEX, ADEX, TMMF S2045, Ordyl, SU-8), of semiconductors (Si, GaAs, InAs, GaN) or of combinations of these materials is present as substrate, and/or in which as substrate a layer of the noted materials is present on a non-piezoelectric substrate.

3. The acoustofluidic components according to claim 1 in which acoustic transducer elements are present for exciting surface waves, Lamb waves and/or bulk waves.

4. The acoustofluidic components according to claim 1 in which acoustic transducer elements are present with which wavelengths of less than 1 mm, advantageously between 1 m and 500 m, are excited.

5. The acoustofluidic components according to claim 1 in which microfluidic elements are present which have been prepared by a lamination of at least two photolithographically structurable planar elements and subsequent photolithographic structuring on one or more fluidic planes.

6. The acoustofluidic components according to claim 5 in which films, film photoresists, glass plates, glass films, or polymer films are present as photolithographically structurable planar elements.

7. The acoustofluidic components according to claim 1 in which the walls of the microfluidic elements have a thickness that is smaller than the wavelength of the acoustic wave excited by the acoustic transducer element, and/or in which the walls of the microfluidic elements have a height that is 0.1 to 10 times the wavelength of the acoustic wave excited by the acoustic transducer element.

8. The acoustofluidic components according to claim 1 in which the base of the microfluidic elements is formed by the substrate and/or the coated substrate and/or by the top of a microfluidic element.

9. The acoustofluidic components according to claim 1 in which the microfluidic element has top thicknesses of 0.05 to 1 times the wavelength of the acoustic wave excited by the acoustic transducer element.

10. The acoustofluidic components according to claim 1 in which an acoustic transducer element is present by which effects such as attenuation, amplification, interference, diffraction, refraction and/or reflection of the excited wave are used in a targeted manner to excite a wave field within the fluid inside of the microfluidic element on at least one plane as a function of the excited acoustic wave and as a function of the geometric dimensions of the microfluidic elements and as a function of the position of the microfluidic element in a propagation direction of an acoustic wave excited by the acoustic transducer element.

11. The acoustofluidic components according to claim 1 in which microfluidic elements and transducer elements are arranged adjacent to and on top of one another on multiple fluidic planes.

12. The acoustofluidic components according to claim 1 in which the walls and/or the base of the microfluidic elements are surface-coated and/or surface-structured and/or deformed.

13. A process for preparing acoustofluidic components in Which on a piezoelectric substrate and/or on a piezoelectric layer on a non-piezoelectric substrate and/or on a non-piezoelectric substrate on a piezoelectric layer, either at least one microfluidic element is created at least partially a lamination of photolithographically structurable planar elements and subsequent photolithographic structuring on one or more fluidic planes, or at least one microfluidic element is applied that has already been prepared at least partially by a lamination of photolithographically structurable planar elements and subsequent photolithographic structuring on one or more fluidic planes, and furthermore at least one acoustic transducer element is applied on the substrate and/or the layer, wherein the at least one microfluidic element is arranged in at least one propagation direction of an acoustic wave excited by the acoustic transducer element, and wherein the microfluidic elements are prepared with top thicknesses that are equal to 0.01 to 10 times the wavelength of the acoustic wave excited by the acoustic transducer element.

14. The process according to claim 13 in which films, film photoresists, glass plates, glass films, or polymer films are used as photolithographically structurable planar elements.

15. The process according to claim 13 in which the microfluidic elements are prepared in that at least one photolithographically structurable planar element is laminated with a temperature increase and application of pressure on a piezoelectric substrate and/or on a piezoelectric layer on a non-piezoelectric substrate and/or on a non-piezoelectric substrate on a piezoelectric layer, and subsequently walls of the microfluidic element are structured photolithographically, and subsequently at least one additional photolithographically structurable planar element is laminated at least partially onto the walls with a temperature increase and an application of pressure and is photolithographically structured to form a top.

16. The process according to claim 13 in which the microfluidic elements with the walls and top are arranged once or multiple times simultaneously or consecutively adjacent to and/or on top of one another.

Description

EXAMPLE 1

[0093] On a 4-inch wafer of piezoelectric yellow-black 128 YX lithium niobate (LiNbO.sub.3) as substrate, chips having respectively two interdigital transducer pairs (IDT pairs for short) and peripheral structures such as dicing marks, electrical feed electrodes with contact structures and alignment marks for the lamination are created as acoustic transducer elements by means of lift-off structuring. The metallization is applied on the photolithographically structured coating layer by means of electron beam evaporation and is composed of 5 nm of titanium (as an adhesive layer) with an overlying 295 nm of aluminum.

[0094] Of the two interdigital transducer pairs, the first pair is composed of two interdigital transducers of the quarter-wave (lambda-quarter) type with widths of the finger electrodes or the empty spaces between of respectively 75 m (the SAW wavelength is therefore 300 m), an aperture of 3 mm, and 20 pairs of fingers, wherein the interdigital transducers have a distance from one another of 900 m in a propagation direction of the excited surface wave, and the second pair is composed of two interdigital transducers of the quarter-wave type with widths of the finger electrodes and the empty spaces therebetween of respectively 50 m (the SAW wavelength is therefore 200 m), an aperture of 2 mm, and 32 pairs of fingers, wherein the interdigital transducers have a distance from one another, that is, perpendicular to the finger electrodes, of 800 m. The propagation direction of both IDT pairs is the crystallographic X direction (perpendicular to the wafer flat and perpendicular to the finger electrodes of the IDTs) and the lateral distance between the IDT pairs is 1.5 mm. All four IDTs have electrical feeds (bus bars) arranged laterally on the finger electrodes with a 200 m width over the entire IDT length and end at 1 mm1 mm contact points at a distance of 500 m from the chip edge. Spring contact pins for coupling the high-frequency signal from an external electrical peripheral are attached to these electrical contact points during use.

[0095] After the lift-off of the metallization, a 100-nm thick SiO.sub.2 layer is applied as a biocompatible functional layer by means of sputtering. The SiO.sub.2 layer is then etched off at the electrical contact points using physical dry etching.

[0096] On the substrate, a 20-nm thick Ti layer is then structured as an adhesive layer by means of lift-off technology. The geometry and position of the Ti layer corresponds to that of the walls of the microfluidic element created in the subsequent step. Then, a 100-m thick film of ADEX dry film photoresist is laminated onto the substrate with the Ti layer according to the instructions of the film manufacturer with the aid of a film laminator, and is subsequently structured to form the walls of the microfluidic element by means of photolithography. Two parallel walls thereby form an open channel with a wall thickness of 25 m and a distance of 150 m, whereby the channel is located parallel to the finger electrodes in a centered manner between the IDTs of both IDT pairs. In both directions (parallel to the finger electrodes), the channel ends at a distance of 5 mm from the center between the IDT pairs in T-shaped junctions, each having three channels with a respective 35 m wall width and 50 m channel width. These end in one fluidic contact point each, with a circular, centrally arranged opening with an 800 m diameter and a 2.5 mm outer diameter. During use, sealing rings are attached to these fluidic contact points, which rings are connected to an external fluidic peripheral.

[0097] A 10-m thick film (for a top thickness of 10 m, or 0.033 times the 300 m SAW wavelengths used for the first transducer pair and 0.05 times the 200 m SAW wavelengths used for the second transducer pair) of ADEX dry photoresist is subsequently laminated onto the walls of the microfluidic element according to the instructions of the film manufacturer with the aid of a film laminator, and is then structured to form the tops of the microfluidic elements by means of photolithography. The area of the top is thereby bounded between the outer structures of the walls of the microfluidic element and the circular openings of the fluidic contact points.

[0098] At the present time, these two-layer, partially closed microfluidic elements according to the invention can only be prepared with the aid of laminating technology. Furthermore, the thickness of the top can thus be configured to be 0.033 times or 0.05 times the wavelengths used for the acoustic wave, whereby compared to the standard element with a PDMS microfluidic element, a wave-field resonance that is increased by a factor of 5 can be achieved simultaneously with an acoustic flow that is increased by a factor of 4. Furthermore, in this manner all elements necessary for the microfluidic manipulation of fluids with or without cells or particles can be prepared on a chip or wafer substrate in cleanroom technology/photolithographic technology. As a result, the handling and preparation costs decrease by 50%.

[0099] The photolithographic exposure of the laminated films takes place by means of photolithography with a wavelength of 365 nm in a mask aligner with the aid of structured quartz/chromium lithography masks.

[0100] To electrically activate the interdigital transducer, a sine wave generator is used which is operated at the resonant frequency of the interdigital transducers (approx. 13 MHz and approx. 20 MHz, respectively) and to the output of which a 2 W high-frequency amplifier is connected. The interdigital transducers are connected to the output via spring contact pins and SMA connecting cables.

[0101] The fluidic contact points are directly connected via a rubber ring to a pressure plate with a liquid reservoir. When liquid is added to the reservoir with the aid of a pump, it fills the channel from one side to the other. The outer channel access points are thereby used for the hydrodynamic pre-focusing of the liquid in the inner channel access point. The inner channel access point contains differently sized cells with a diameter of 2-20 m.

[0102] During operation, sinusoidal signals are applied to both IDT pairs at the resonance frequency of the IDTs and 200 mW of electrical power, whereby the interdigital transducers emit Rayleigh-type surface acoustic waves that form standing SAWs in the center of the IDTs of the IDT pairs. The first IDT pair (300 SAW wavelength) is thereby used to focus the cells in the center of the channel. The second IDT pair (200 m SAW wavelength) is used to split the focused cell flow into two fractions. One fraction thereby remains in the center of the channel and is transported to the centrally arranged channel outflow, and the second fraction is transported in the direction of the channel walls and to the outer channel outflows.