THEREOF

FIELD OF THE INVENTION

The present invention generally relates to a mixing device and particularly to a micromixing device and method of fabrication device for use in microfluidic applications.

BACKGROUND OF THE INVENTION

The current trend in miniaturization with respect to analytical and various experimental aspects of life sciences results to advancements in microfluidic based systems and applications. According to research, miniaturization of microfluidic or fluidic systems offers several advantages including, low sample volumes, low chemical consumption, fast response time, multiple simultaneous assays and portability. One of the prominent components or devices used for microfluidic systems is the micromixer.

Δ micromixer is essential for rapid mixing, a significant step in many of microfluidic systems used in a wide variety of biochemistry analysis, among others include drug delivery, agriculture, environmental monitoring and sequencing or synthesis of nucleic acids. Being a part of miniaturization, micromixers can be considered as the important elements required to ensure effectual operations . Typically, there are two main categories of micromixers, these are passive micromixers and active micromixers. A passive micromixer does not necessitate external energy, as the mixing process relies significantly on diffusion, while an active micromixer is normally built with a structure suitable to allow external powers to control its operation. Moreover, active micromixers operate based on external disturbance effects which increase the level of difficulty in obtaining accurate results. In comparison, passive micromixers are often selected over active micromixers owing to their less challenging and cost effective characteristics.

In many cases, the efficiency and effectiveness of micromixers are dependent on the structures or construction of micromixers as well as surface conditions. For passive micromixers, mixing is configured to be automated therefore there is no direct control with respect to the mixing action or other parameters such as percentage of mixing, change in location of mixing, and the likes. Consequently, there is lack of control in mixing, which at times leads to slow mixing capacity in the event that a large sample is used.

US Patent Number 7160025 discloses an apparatus for use as a micromixer . and methods of using the same. For this apparatus, there is no moving structures provided and thus there is no direct control of mixing. Apart from these drawbacks, mixing of flow is restricted to along channel in plane and the apparatus is not configured for sequential mixing on the same mixing chamber. In light of the above, it has been difficult to develop an apparatus or device which has direct control of the mixing action or moving structures, that could be actuated for mixing purposes when and as required, as well as cost effective.

The present invention is provided against the technical background. Therefore, one of the objectives of this invention is to provide a micromixer with integrated active cantilever structures and method of fabrication thereof.

In a further object of the present invention, there is provided a device for use in microfluidic applications, whereby the micromixer built in accordance with the preferred embodiments of the present invention can be microfabricated for miniaturization purposes.

In another object of the present invention, there is provided a device for micromixing whereby the mixing of fluid flowing along or through (perpendicular) the micromixer and further allows fluid mixing of conductive or non-conductive fluid.

Further purposes of the present invention will become evident from review of the following specification.

SUMMARY OF THE INVENTION

There is disclosed a micromixing device (20) for microfluidic applications comprising a substrate, an actuating cantilever unit (100) , a plurality of fluid channels, at least one encapsulation substrate (110), inlet and exit channels (13,14, 15) and a plurality of inlet (11, 12) and outlet (16) ports; wherein the cantilever unit (100) is positioned on said substrate, in a manner such that it is able to actuate during mixing, said cantilever unit (100) comprising a plurality of cantilever structures, each being arranged within the device (20) in a manner at variable angles with respect to the walls of the device (20) .

In another aspect of the present invention there is provided a method for fabricating a micromixer device for miniaturization purposes; said method comprising the steps of: providing the silicon wafer (51) , depositing and patterning a layer of silicon nitride (Si ₃ N ₄ ) (52), depositing and planarizing a layer of sacrificial oxide layer (53), depositing and pattern doped polysilicon, removing the sacrificial oxide is then removed with hydrofluoric acid based solution, depositing and etching doped polysilicon, wet etching of glass substrate, removing the polysilicon mask therefrom; and bonding of silicon or glass encapsulation for the device.

In yet another aspect of the present invention there is provided amethod for mixing fluids in microfluidic applications ^' ; said method comprising the steps of: channeling fluids to flow within a cantilever unit; said cantilever unit comprising a plurality of cantilever structures. BRIEF DESCRIPTION OF THE DRAWINGS

This invention will be described by way of non-limiting embodiments of the present invention, with reference to the accompanying drawings, in which:

FIG 1 (a) and FIG 1 (b) show the elevated top view of the device and cross sectional view of the device;

FIG 2 shows the overall view of the device in accordance with a preferred embodiment of the present invention;

FIG 3 shows the types of cantilever standards for single and group structure in accordance with a preferred embodiment of the present invention;

FIG 4 shows the examples of various arrangements of standard cells and examples of- different sequence of actuations in accordance with a preferred embodiment of the present invention;

FIG 5 shows the fabrication for miniaturization of the device in accordance with a preferred embodiment of the present invention;

FIG 6(a) shows the mixing of fluid flowing along the cantilever unit (100) ;

FIG 6(b) shows the mixing of fluid flowing through the cantilever unit (100) . BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, an embodied example of the present invention will be explained in detail with reference to the attached drawings. However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these figures is for explanatory purposes as the invention extends beyond these limited embodiments.

FIG 1 (a) and FIG 1(b) show a top elevated and cross sectional views of the micromixing device (20) with integrated actuating cantilever unit (100) . FIG 2 shows the elements within the device (20) in accordance with a preferred embodiment of the present invention. In this embodiment, the device (20) comprises at least one substrate (5), at least one portion having an active or actuating cantilever unit (100), a plurality of fluid channels (not shown), at least one encapsulation substrate (110) , inlet and exit channels (13, 14, 15) and a plurality of inlet (11, 12) and outlet (16) ports. FIG 3 shows the typical types of cantilever standards for a standard cell, particularly for a group and single structure, n being the number of cantilevers. The cantilever unit (100) which is positioned on the substrate such that it is allowed to actuate during mixing operation, comprises a plurality of cantilever structures, each being of said structures arranged within the device (20) in a manner at variable angles with respect to the walls of the device (20) such that they form a zigzag pattern therein. Each of said cantilever structures are configured to actuate on the substrate and preferably formed from conductive materials, such as, but not limiting to, doped polysilicon, metals or conductive polymers. The examples for various arrangements of standard cells and examples on different sequence of actuations are shown in FIG 4.

As discussed briefly in the preceding paragraphs and shown in FIG 3, he two typical types of cantilever standard cell (group and single) and how these standard cells could be arranged/combined in different configurations. It should be noted that each of these standard cells arrangement could be actuated independently and in any sequence but passivation layer must be included between the cells for separate actuation. The subscript numbering for the voltage (V) denotes different actuation voltage which can be applied on the contact pad connecting the cantilever standard cells and in different sequence as required.

Further, the cantilever unit (100) can be configured to actuate in different sequence to generate different waves, flow pattern or fluid for sequential mixing applications.

In one embodiment of the present invention, the substrates are formed from materials such as, but not limiting to, silicon, glass or polymers including polydimethylsiloxane (PDMS), and poly-methyl- metha-crylate (PMMA) .

The microfluidic mixers can be microfabricated for mminiaturization purposes where the proposed general fabrication process flow is presented in FIG 5. FIG 5 shows an example of the fabrication process based on an embodiment of the present invention. First there is provided a layer of silicon wafer whereby the construction or fabrication of said said layer comprising the steps of providing the silicon wafer (51) , depositing and patterning a layer of silicon nitride (Si ₃ N ₄ ) (52), depositing and planarizing a layer of sacrificial oxide layer (53) , depositing and pattern doped polysilicon (54) . The sacrificial oxide is then removed with hydrofluoric acid based solution. The second main layer is the glass wafer layer whereby the creation of the glass wafer comprises the steps of depositing and etching doped polysilicon (55), wet etching of glass substrate (56), and removing the polysilicon mask therefrom (57) . The final step is wafer bonding whereby there is bonding of silicon or glass encapsulation (58) for the device of the present invention in accordance with a preferred embodiment.

The microfluidic mixers typically reside within a microfluidic system which includes microchannel and inlet/outlet passage for fluid entry/exit as described earlier and shown in FIG 2.

In principle, after injection of different types of fluids for mixing purposes at the sample inlets (11, 12), the fluid will be directed towards the microfluidic mixers. The fluids will be channelled by means of the inlet channels (13, 14) to the mixing area, where the fluids will be mixed at which the cantilever unit (100) of the microfluidic mixers will be actuated. The actuation principle of the proposed invention is of an electrostatic-type and the displacement of the cantilever is governed by Equation 1 described below:

£ £ A

Capacitance, C= ° ^r (1)

d

Where,

ε ₀ = permittivity of free space (8.854xlCT ¹² F/m) s _r = relative static permittivity

A= overlap area between cantilever structure and bottom metallic layer

d = separation between the cantilever structure and bottom metallic layer

Upon application of voltage on the cantilever unit (100), the cantilever structures will be displaced towards the bottom metallic layer (or silicon wafer) which is grounded (0V) . The movement of the cantilever structure therefore interferes with the fluid causing disturbance in the fluid flow. As the cantilever structure is displaced more rapidly, the fluid flow inside the mixing chamber became more chaotic and high turbulence of flow will be introduced. Such condition therefore promotes mixing of fluids with greater efficiency .

In one embodiment of the present invention, the operation of the device (20) requires application of voltage for actuation; therefore it is classified as an active micromixer utilizing the disturbance generated by the movement of the cantilever structure for mixing process . In another embodiment of the present invention, the device (20) can be configured in different construction for different applications as the cantilever structures can be actuated; as and when is required; for better control of fluid mixing.

In another preferred embodiment of the present invention, the device (20) can be configured to allow mixing of fluid flowing along the cantilever unit (100) of the mixer (20) . In this arrangement, the cantilever structure will be displaced downwards towards the substrate against the flow of the fluid, as shown in FIG 6(a) .

In another preferred embodiment of the present invention, the device (20) can be configured to allow through, from top to bottom or perpendicular to the cantilever unit (100) of the mixer (20) . In this arrangement, the cantilever structures will be displaced sideways where an array of cantilevers will be applied with an actuation voltage while the other array of cantilevers will be grounded (0V) as shown in FIG 6(b) .

It is noted that for both of the alternate configurations or arrangements above, the bottom silicon substrate can be replaced by a glass substrate. In the event that the cantilever structure is preferred to be displaced vertically downwards, another metallic layer on the bottom substrate is required.

In another preferred embodiment of the present invention, the device (20) can be configured to allow fluid mixing for either conductive or non-conductive fluids. For conductive fluid, this could be achieved by simply depositing another passivation layer of silicon nitride or oxide on the microfluidic mixer structures in contact with the fluid for insulation. This would therefore aid to prevent problems of the cantilever structures being shorted during actuation .

It should noted that the device (20) of the present invention based on the preferred embodiments may be operated as a stand-alone device, or integrated into a system with other microfluidic type devices such as, but not limiting to, pumps, valves and dispensers.

The invention has been described above by way of illustration, and the specific embodiments disclosed are not intended to limit the invention to the particular forms disclosed. The invention is thus to cover all modifications, equivalents, and alternatives falling with the spirit and scope of the following claims.