Method for fabricating microfluidic devices in fused silica by picosecond laser irradiation

Abstract

Method of fabricating a microfluidic device by means of inducing internal cracks in fused silica employing a picosecond laser beam, firstly utilizing irradiation of a focused temporally controlled picosecond laser beam in fused silica to generate a spatially selective modification region including randomly oriented nanocracks, then employing chemical etching to remove the irradiated area and obtain a hollow and connected three-dimensional microstructure, thereby achieving three-dimensional fabrication of microchannel structures inside the fused silica. The method can realize polarization insensitive three-dimensional uniform etching by regulating the pulse width of the picosecond laser beam, and has high chemical etch rate and selectivity, applicable for fabrication of large-sized three-dimensional microfluidic systems, high-precision 3D glass printing, etc.

Claims

1. A method for fabricating a microfluidic device, comprising: (1) fixing a glass sample of fused silica on a programmable three-dimensional positioning stage, focusing a laser beam on the glass sample via a microscope objective, wherein the laser beam is in a polarization state that is linearly polarized or circular polarized, driving the programmable three-dimensional positioning stage and starting irradiation with the linearly polarized or circular polarized laser beam simultaneously, and directly writing a pattern for forming a three-dimensional microchannel by inducing randomly oriented nanocracks within the three-dimensional microchannel pattern inside the fused silica, wherein the laser beam is temporally controlled and has a pulse width of 8 to 20 picoseconds; and (2) placing the glass sample irradiated by the laser beam in a chemical etching solution, and performing spatial selective etching removal to obtain a microchannel inside the fused silica sample possessing a three-dimensional geometric configuration, wherein rate of etching is insensitive to the polarization state and orientation of the laser beam.

2. The method of claim 1, wherein the laser beam has a repetition rate of 1-1000 kHz, and the microscope objective has a numerical aperture of 0.1-1.4.

3. The method of claim 1, wherein the chemical etching solution is a potassium hydroxide solution at a concentration of 5 mol/L to 20 mol/L at 80-95° C.

4. The method of claim 1, wherein the chemical etching solution is a hydrofluoric acid solution at a concentration of 1% to 20% (volume percentage).

5. The method of claim 1, wherein the laser beam is linearly polarized, circularly polarized, or both, before being focused and irradiating on the glass sample.

6. The method of claim 1, wherein the three-dimensional microchannel pattern inside the fused silica is a three-dimensional multi-layer network microchannel structure.

7. The method of claim 1, wherein the three-dimensional microchannel pattern inside the fused silica is a three-dimensional microcoil channel structure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic flow chart showing the method for fabricating a microfluidic device by inducing randomly oriented nanocracks in fused silica employing a picosecond laser beam in the present invention.

(2) FIG. 2 is an optical microscope image showing the 1 h chemical etching results of laser modified tracks using 8 ps laser irradiation with two different polarization states in the present invention. In FIG. 2, reference letter “a” indicates linear polarization with orientation perpendicular to the direct writing, and reference letter “b” indicates circular polarization which is produced by employing a quarter-wave plate prior to the objective.

(3) FIG. 3 is scanning electron microscope images of generated nanocracks in laser-modified regions using 8 ps laser irradiation with two different polarization states in the present invention. In FIG. 3, reference letter “a” indicates linear polarization with orientation perpendicular to the direct writing, and reference letter “b” indicates circular polarization which is produced by employing a quarter-wave plate prior to the objective.

(4) FIG. 4 is a front-view optical micrograph of a three-dimensional multi-layer network microchannel structure fabricated by 8 ps laser irradiation followed by chemical etching in the present invention.

(5) FIG. 5 is a side-view optical micrograph of the three-dimensional multi-layer network microchannel structure fabricated by 8 ps laser irradiation followed by chemical etching in the present invention.

(6) FIG. 6 is a side-view optical micrograph of a three-dimensional microcoil channel structure fabricated by 10 ps laser irradiation followed by chemical etching in the present invention.

DETAILED DESCRIPTION OF INVENTION AND EMBODIMENTS

(7) The present invention is expounded in more details with the figures and embodiments hereunder provided, which by no means serve to limit the scope of the present invention.

Embodiment 1

(8) In the first embodiment of the present invention, the method comprises the following steps:

(9) Step 1: Picosecond Laser Beam Irradiation

(10) As shown in FIG. 1, fixing a clean glass sample of fused silica with a size of 20 mm×10 mm×2 mm and polished on six sides on a three-dimensional positioning stage; the laser operating at a center wavelength of 1026 nm, with a repetition rate of 50 kHz and a pulse width of 8 ps; focusing the laser beam at a depth of 300 μm below the surface of the glass substrate using a microscope objective with a numerical aperture of 0.45 (transmission rate is ˜30% for the beam). To evaluate the effect of polarization on the etch rate, two different polarization states of the output laser beam are used to directly write the patterns: linear polarization with orientation perpendicular to the direct writing direction (marked with “a” in FIG. 2 and FIG. 3), circular polarization which is produced by employing a quarter-wave plate prior to the objective (marked with “b” in FIG. 2 and FIG. 3); the pulse energy prior to the objective and the scanning speed are 8 μJ and 0.5 mm/s, respectively. Randomly oriented nanocracks in laser-modified regions with two different polarization states can be both identified from scanning electron microscope images shown in FIG. 3.

(11) Step 2: Selective Chemical Etching

(12) Placing the glass sample irradiated by the picosecond laser beam in a 10 mol/L potassium hydroxide solution (85° C.) for ultrasonic assisted etching for 1 h, and then taking the sample out for observation. It can be seen from the comparison of etching states shown in FIG. 2 (arrows show the etched terminals of laser-modified traces, indicating the etched lengths along the horizontal and vertical segments in the regions of the triangle loops) that under the same condition, there is little difference among the etch rates of the samples irradiated by the 8 ps laser beam with different polarization states and orientations of segments (i.e. polarization insensitive). Moreover, all etch rates along the segments are higher than 500 μm/h.

Embodiment 2

(13) In the second embodiment of the present invention, the method comprises the following steps:

(14) Step 1: Picosecond Laser Beam Irradiation

(15) As shown in FIG. 1, fixing a clean glass sample of fused silica with a size of 5 mm×5 mm×5 mm and polished on six sides on a three-dimensional positioning stage; the laser operating at a center wavelength of 1026 nm, with a repetition rate of 50 kHz and a pulse width of 8 ps; focusing the light beam via a microscope objective with a numerical aperture of 0.30 (transmission rate is ˜50% for the beam), placing a quarter-wave plate before the microscope objective to generate a circularly polarized beam, writing a six-sided microchannel multilayer grid pattern inside the glass sample. The pulse energy prior to the objective and the scanning speed are 9 μJ and 0.5 mm/s, respectively.

(16) Step 2: Selective Chemical Etching

(17) Placing the glass sample irradiated by picosecond laser beam in a 10 mol/L potassium hydroxide solution (85° C.) for ultrasonic assisted etching until the laser beam irradiated region is completely removed, forming a three-dimensional hollow multi-layer network microchannel structure (as shown in the front view in FIG. 3 and the side view in FIG. 4) inside the glass sample. The etching of the channels is uniform without obvious tapered structure.

Embodiment 3

(18) In the third embodiment of the present invention, the method comprises the following steps:

(19) Step 1: Picosecond Laser Beam Irradiation

(20) Fixing a clean glass sample of fused silica with a size of 5 mm×5 mm×1 mm and polished on six sides on a three-dimensional positioning stage; the laser operating at a center wavelength of 1026 nm, with a repetition rate of 50 kHz and a pulse width of 10 ps; focusing the light beam via a microscope objective with a numerical aperture of 0.45 (transmission rate is ˜30% for the beam), placing a quarter-wave plate before the microscope objective to generate a circularly polarized beam, writing a three-dimensional microcoil pattern with a coil diameter of 200 μm and a period of 150 μm inside the glass sample. The pulse energy prior to the objective and the scanning speed are 4 μJ and 0.5 mm/s, respectively.

(21) Step 2: Selective Chemical Etching

(22) Placing the glass sample irradiated by picosecond laser beam in a 10 mol/L potassium hydroxide solution (85° C.) for ultrasonic assisted etching until the laser beam irradiated region is completely removed, forming a three-dimensional microcoil channel structure (as shown in FIG. 5) inside the glass sample. The etching of the channels is uniform without obvious tapered structure.