WO2012050420A1

WO2012050420A1 - Multilayer microfluidic filter and the method of fabricating thereof

Info

Publication number: WO2012050420A1
Application number: PCT/MY2010/000274
Authority: WO
Inventors: Bien Chia Sheng Daniel; Hing Wah Lee; Ismahadi Syono Mohd; Zaini Abdullah Ali; Rofei Mat Hussin Mohd
Original assignee: Mimos Bhd.
Priority date: 2010-10-11
Filing date: 2010-11-12
Publication date: 2012-04-19
Also published as: MY159287A

Abstract

A multilayer microfluidic filter (100) for filtering unwanted particles in sample molecules or fluid, comprising a substrate (110), such as a silicon wafer having a layer of boron (120) doped on the uppermost portion of said substrate (110), a plurality of funnel-shaped pores (130), each randomly disposed on the substrate (110) with different arrangement of sizes and positions, an adhesive layer (140), such as an adhesion, resist, or wax coated onto the sidewall of each of the plurality of pores (130), and additional layer of thin film (150) coated onto the bottom surface of the substrate (110) to improve the filtering capability.

Description

MULTILAYER MICROFLUIDIC FILTER AND THE METHOD OF

FABRICATING THEREOF

TECHNICAL FIELD

The present invention relates to a semiconductor apparatus for filtering micro particles, and more particularly, to a multilayer microfluidic silicon filter for filtering micro particles in sample molecules or fluid.

BACKGROUND OF INVENTION

The handling and dosing of small amounts of liquids or gases with microfluidic actuators (micro pumps, micro valves, etc.) has been established as a key technology for many emerging industrial applications especially in lab on chip, point of care, or chemical analysis systems. Recent advancement in technologies generates a strong trend towards miniaturized fluid handling especially for portable applications.

However, removal of macro particles is essential in some miniaturized analysis system to ensure that only the required sample molecules are supplied into the analysis region without obstruction from other impurities, particulates, or unrelated specimens such as dust, sands, and etc.

Presently, removal of micron and submicron sized particles is impossible with conventional macro-sized clarifiers or filters as the filtration gap size itself is large and bulky rendering it unsuitable for micro-applications. This is due to the fact that the impurities itself could be of micron or submicron-sized at a particular known sizes and should be discarded in order for them not to affect the sensitivity of the sensing devices.

In the case of microfluidic filters, most of the fabricated filters use a layer of specialty membrane with micro-scale / nano-scale pores present within the layer to act as the filtering element. The problem with existing solution is that the manufacturing process for the filtering membrane is incompatible with micro fabrication process while the quality of the membrane is inconsistent as the number, densities, location, or distribution of the filtering elements (pores) are difficult to be controlled and reproduced consistently.

Hence, in order to address these issues, a microfluidic filter with filtration size, depth, and shapes (pores, holes, round, square, and etc) that can be easily realized using existing micromachining process should be developed.

SUMMARY OF INVENTION

The object of the present invention is to provide a multilevel microfluidic filter on a single silicon substrate, which consists of a secondary filter with smaller cross- sectional area of holes developed using anisotropic etching of silicon and the primary filtering element of holes etched using reactive-ion etching (REE). This multilevel microfluidic filter acts as a filtering element for biomedical, aquaculture, environmental monitoring, or precision agricultural applications. The proposed invention filters impurities or unwanted particles by permitting only the required samples/agents to pass through the microfluidic filter. This is performed by taking advantage of the size variations of impurities present in the fluid flow where impurities if bigger sizes will get stuck at the larger opening of the filtration gap as it will be obstructed through the reducing filtration gap, allowing only smaller-sized particles to flow continuously in subsequent flow movement.

In one embodiment of the present invention, the multilayer microfluidic filter comprises of a substrate, such as a silicon wafer having boron doped in one side of the substrate, a plurality of pores randomly disposed on the substrate, and an adhesive layer coated onto the sidewall of the plurality of substrate.

In another embodiment of the present invention, the multilayer microfluidic filter comprises of a substrate, such as a silicon wafer having boron doped in one side of the substrate, a plurality of pores randomly disposed on the substrate, an adhesive layer coated onto the sidewall of the plurality of substrate, and additional layer of thin film coated onto the substrate for additional filtering capability. In still another embodiment of the present invention, a method of fabricating the multilayer microfluidic filter has been disclosed. This method comprises of preparing a substrate, such as a silicon wafer, doping of boron into the uppermost portion of the substrate, depositing silicon nitride on both top and bottom surface of the substrate, defining the position of the plurality of pores on the bottom surface of the substrate, etching the substrate and stopping at the boron layer, adding an adhesion layer to the side wall of the plurality of pores, eliminate the boron section covering the plurality of pores, and removing both layers of silicon nitride.

In still yet another embodiment of the present invention, a further method of fabricating the multilayer microfluidic filter has been disclosed. This method comprises of preparing a substrate, such as a silicon wafer, doping of boron into the uppermost portion of the substrate, depositing silicon nitride on both top and bottom surface of the substrate, defining the position of the plurality of pores on the bottom surface of the substrate, etching the substrate and stopping at the boron layer, adding an adhesion layer to the side wall of the plurality of pores, eliminate the boron section covering the plurality of pores, removing both layers of silicon nitride, and coating a layer of thin film onto the bottom surface of the substrate for additional filtering capability. In these embodiments, the adhesion layer comprises of adhesives, resist, or wax and the thin film comprises of polyimide.

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 is a side view of a multilayer microfluidic filter in accordance with one embodiment of the present invention; Figure 2 is a side view of a multilayer microfluidic filter in accordance with another embodiment of the present invention;

Figure 3 is a top view of a multilayer microfluidic filter in accordance with the present invention;

Figure 4 is a flow diagram illustrating a method for fabricating the multilayer microfluidic filter in accordance with one embodiment of the present invention; Figure 4a is a flow chart of the method for fabricating the multilayer microfluidic filter in accordnce with the flow diagram illustrated in figure 4;

Figure 5 is a flow diagram illustrating a method for fabricating the multilayer microfluidic filter in accordance with another embodiment of the present invention; and

Figure 5a is a flow chart of the method for fabricating the multilayer microfluidic filter in accordance with the flow diagram illustrated in figure 5.

DETAILED DESCRIPTION OF EMBODIMENTS

Described below are preferred embodiments of the present invention with reference to the accompanying drawings. Each of the following preferred embodiments describes an example in which the apparatus improves over existing prior art.

The substrate (110) described below is refering to any type of materials, which is suitable to be fabricated using micromachining technique. The details of said micromachining will not be further explained in this specification, as it is a common knowledge for a person having ordinary skill in the art of nano-technology.

The configuration of the invention is not limited to the modules mentioned in the following description. Referring to figure 1, a multilayer microfluidic filter (100) for filtering micro particles in sample molecules comprises of a substrate (110), a layer of boron (120) doped on the uppermost layer of the substrate (1 10), a plurality of pores (130), randomly disposed on the substrate (110), and an adhesive layer (140) coated on the sidewall of the substrate (110). The substrate (110) is made of preferably but not limited to silicon, which is a material suitable to be fabricated using the micromachining technique. The plurality of pores (130), randomly disposed on the substrate (110) are etched using potassium hydroxide (KOH) or tetramethylammonium hydroxide (TMAH) to create funnel-shaped pores with slanted sidewalls. The adhesion layer (140) comprises of preferably but not limited to adhesives, resist, or wax.

Referring to figure 2, a further embodiment of the multilayer microfluidic filter (100) for filtering micro particles in sample molecules comprises of a substrate (110), a layer of boron (120) doped on the uppermost layer of the substrate (110), a plurality of pores (130), randomly disposed on the substrate (110), an adhesive layer (140) coated on the sidewall of the substrate (110), and at least a first thin film (150) coated onto the bottom surface of the substrate (110) to increase the filtering capability of the multilayer microfluidic filter (100). The first thin film (150) comprises of a plurality of holes (160) having a diameter smaller than the plurality of pores (130). In this embodiment, additional thin film (not shown) having a plurality of holes aligned with the pores (130) can also be coated onto the first thin film (150) to define subsequent filtering element and further improving the filtering capability of the multilayer microfluidic filter (100). Also, the first layer of thin film (150) and its subsequent layers of thin film are preferably but not limited to polyimide.

The plurality of pores (130) of the present invention with slanted sidewall comprises of a large opening at the top surface of the substrate (110) and a smaller opening at the bottom surface of said substrate (110). The advantage of such shape is that it will easily guide fluid into the filtration area due to its natural-formed slanting sidewalls. Also, this funnel-shaped configuration provides the advantage of pre-filtering, where the large opening filters out larger particles while the smaller opening controls the size of particles, which can pass through the substrate (110). Furthermore, additional adhesion layer (140) is coated onto the sidewall of the pores (130) to increase the filtering capability of the multilayer microfluidic filter (100).

Initially, sample molecules or fluid will be directed towards the filtering area, which is the plurality of pores (130) through internal/external pumping (not shown). Upon arrival of the sample molecules or fluid at the pores (130), the samples will naturally be sucked and directed into the pores (130) due to the effects of the funnel shape of the pores (130). The multilayer microfluidic filter (100) having the funnel-shaped pores (130) has an advantage in that the samples will be steered through the pores (130) easier due to pressure gradient provided by the slanting sidewall of the pores (130). When samples with impurities passes through the plurality of pores (130), the impurities will be blocked by the pores (130) and prevented from continuously flowing through the filter (100). Referring to figure 3, it is shown that the plurality of pores (130) are randomly disposed on the substrate with different position arrangements and sizes.

Referring to figures 4 and 4a, one method (200) for fabricating the multilayer microfluidic filter (100) is illustrated. This method (200) comprises of preparing a substrate (step 1), preferably a silicon wafer; subsequently, doping a layer of boron (120) into the uppermost portion of the substrate (110) (step 2). The layer of doped boron (120) is used as etch-stop for potassium hydroxide etchant to enable subsequent filtration layers through formation of filtration holes of smaller sizes than the small opening of the plurality of pores (130). This fabricating method (200) further comprises of flipping the substrate (110) and depositing silicon nitride on both top and bottom surface of the substrate (110) (step 3); subsequently, defining the positions of the plurality of pores (130) on the bottom surface of the substrate (110) by cutting out the uriwantecT silicon nitride (step 4), and etching the substrate using potassium hydroxide and stopping at the boron layer (120) (step 5); subsequently, coating an adhesion layer (140) to the sidewalls of the plurality of pores (130) through sputtering or spin coating (step 6). Furthermore, flipping over the substrate (110), defining the positions of the smaller opening of the plurality of pores (130) (step 7), and etching the unwanted sections of the boron layer (120) to create the smaller opening of the plurality of pores (130) (step 8), and lastly, removing both layers of the silicon nitride (step 9).

Referring to figures 4, 4a, 5, and 5a, another method (300) for fabricating the multilayer microfluidic filter (100) is illustrated. This method (300) comprises of preparing a substrate (110) (step 1), preferably a silicon wafer; subsequently, doping a layer of boron (120) into the uppermost portion of the substrate (110) (step 2). The layer of doped boron (120) is used as etch-stop for potassium hydroxide etchant to enable subsequent filtration layers through formation of filtration holes of smaller sizes than the small opening of the plurality of pores (130). This fabricating method (300) further comprises of flipping the substrate (110) and depositing silicon nitride on both top and bottom surfaces of the substrate (110) (step 3); subsequently, defining the positions of the plurality of pores (130) on the bottom surface of the substrate (110) by cutting out the unwanted silicon nitride (step 4); subsequently, etching the substrate (110) using potassium hydroxide and stopping at the boron layer (120) (step 5); subsequently, coating an adhesive layer (140) to the sidewalls of the plurality of pores (130) (step 6) through sputtering or spin coating. Furthermore, flipping over the substrate (110) and defining the positions of the small opening of the pores (130) (step 7), and etching the unwanted sections of the boron layer (120) to create the smaller opening of the plurality of pores (130) (step 8); subsequently, removing both layers of the silicon nitride (step 9), and lastly, coating a first layer of thin film (150) onto the bottom surface of the substrate (110) to improve the capability of filtering (step 10). The thin film (150) is preferably a layer of polyimide. In this method, additional layer of thin film (not shown) having a plurality of holes aligned with the pores (130) can also be coated onto the first layer of thin film (150) to define subsequent filtering element and further improving the filtering capability of the multilayer microfluidic filter (100).

A summary then of what has been hereinbefore described by way of example of the present invention is a multilayer microfluidic filter (100) for filtering unwanted particles in sample molecules or fluid, comprising a substrate (110), such as a silicon wafer having boron (120) doped on the uppermost portion of said substrate (110), a plurality of pores (130), each randomly disposed on the substrate (110) with different arrangement of sizes and positions, an adhesive layer (140), such as an adhesion, resist, or wax coated onto the sidewall of each of the plurality of pores (130), and additional layer of thin film (150) coated onto the bottom surface of the substrate (110) to improve the filtering capability.

In as much as the present invention is subject to many variations, modifications and changes in detail, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Claims

1. A multilayer microfluidic filter (100) for filtering micro particles in sample molecules or fluid, comprising:

a substrate (110) having boron (120) doped on the uppermost portion of said substrate (110);

a plurality of pores (130), each randomly disposed on the substrate (110); and

an adhesive layer (140) coated to the side wall of each of the plurality of pores (130).

2. The multilayer microfluidic filter (100) as claimed in claim 1 further comprising:

at least a first layer of thin film (150) is coated onto the substrate (110); and

a plurality of holes (160) disposed on the layer of thin film (150) aligned with the plurality of pores (130).

3. The multilayer microfluidic filter (100) in accordance with claim 2, wherein additional layer of thin film is coated onto the first layer of thin film (150).

4. The multilayer microfluidic filter (100) in accordance with claim 1, wherein each of the plurality of pores (130) are in funnel shape.

5. The multilayer microfluidic filter (100) in accordance with claim 2, wherein the diameter of said holes (160) is smaller than the diameter of said pores (130).

6; The multilayer microfluidic filter (100) in accordance with claim 1, wherein the substrate (110) is made of silicon.

7. A method (200, 300) of fabricating the multilayer microfluidic filter (100) of claim 1, comprising of the following sequence of steps: preparing a substrate (110) (step 1);

doping of boron (120) into the uppermost portion of the substrate (110) (step 2);

flipping the substrate (110) and depositing silicon nitride on both top and bottom surfaces of the substrate (110) (step 3);

defining the positions of the plurality of pores (130) on the bottom surface of the substrate (1 10) (step 4);

etching the substrate (110) and stopping at the boron layer (120) (step

5);

adding an adhesion layer (140) to the side wall of the plurality of pores (130) (step 6);

flipping over the substrate (110) and defining the smaller opening of the pores (130) (step 7);

etching the substrate (110) to eliminate the unwanted sections of the layer of boron (120) covering the plurality of pores (130) (step 8); and

removing both layers of silicon nitride (step 9).

8. The method (200, 300) of fabricating the multilayer microfluidic filter (100) in accordance with claim 7 further comprising coating a layer of thin film (150) onto the bottom surface of the substrate (110) after step 9 (step 10).

9. The methods (200, 300) in accordance with claim 7, wherein adding an adhesion layer (140) to the sidewall of the plurality of pores (130) comprises of using the method of sputtering or spin coating.

10. The methods (200, 300) in accordance with claim 7, wherein the adhesion layer (140) comprises of adhesives, resist, or wax.

11. The methods (200, 300) in accordance with claims 7, wherein the plurality of pores are etched using potassium hydroxide (KOH) or tetramethylammonium hydroxide (TMAH).

12. The method (300) in accordance with claim 8, wherein the layer of thin film (150) comprises of polyimide.

13. The methods (200, 300) in accordance with claims 7, wherein the substrate is preferably a silicon wafer.