MEMS device comprising a microfluidic channel for liquid or gas to be investigated

Abstract

MEMS device (1) comprising a microfluidic channel (2) for liquid or gas to be investigated, which microfluidic channel (2) is at least in part transparent for an electron- beam (6) which is used to image samples of liquid or gas in the microfluidic channel (2), wherein the microfluidic channel (2) is part of a monolithic die wherein the microfluidic channel (2) has a controlled and ensured height by application of reinforcement pillars (7) inside the microfluidic channel (2) that connect top (2') and bottom (2'') of the microfluidic channel (2), wherein in an area (5) of the microfluidic channel (2) which is at least in part transparent, the microfluidic channel (2) is provided with a reduced height in comparison with a neighboring area or areas so as to reduce the fluidic resistance and the thermal mass of the microfluidic channel (2) and improve its electron transparency for imaging.

Description

[0001] MEMS device comprising a microfluidic channel for liquid or gas to be investigated

[0002] The invention relates to MEMS device comprising a microfluidic channel for liquid or gas to be investigated, which microfluidic channel is at least in part transparent for an electron-beam which is used to image samples of liquid or gas in the microfluidic channel, wherein the microfluidic channel is part of a monolithic die wherein the microfluidic channel has a controlled and ensured height by application of reinforcement pillars inside the microfluidic channel that connect top and bottom of the microfluidic channel.

[0003] Such a MEMS device is disclosed by the article "An all- in-one nanoreactor for high-resolution microscopy on nanomaterials at high pressures. Creemer, J. F. , et al. Cancun: IEEE Xplore, 2011. DOI: 10.1109 / MEMSYS .2011.5734622. The article discloses a MEMS nanoreactor fully integrated on a single die, enabling atomic-scale imaging of nanostructured materials under high pressure and temperature (14 bar and 660 °C) . The reactor can therefore be used to study the behavior of e.g. catalysts in a transmission electron microscope (TEM) . It has a shallow channel (0.5 pm) , which is made with surface micromachining techniques and contains pillars that prevent bulging. Integrated with the channel are very thin windows (15 nm) and a resistive heater. The reactor is transparent, enabling the imaging of atomic lattice fringes with a spacing down to at least 0.15 nm.

[0004] Despite allowing for high resolution in-situ imaging, the monolithic MEMS technology as known from the above-mentioned article suffers from the following limitations.

[0005] Firstly, the known device disclosed by the article includes a resistive heater patterned on top of the channel. The nature of the channel design and architecture prevents the heater from operating above 660 °C without damaging the channel.

[0006] Secondly, the known device comprises a single height 0.5 pm channel which extends over a length of millimeters. This results in both high fluidic resistance -which limits achievable liquid flow speeds- and also results in lower resolution -since higher liquid layers will result in more electron scattering events .

[0007] Thirdly, the known device disclosed by the article does not enable the possibility of having integrated electrodes within the microfluidic channel, which would enable sensing capabilities or applications like electrochemistry.

[0008] To address at least part of these limitations and according to the invention a MEMS device is proposed having the features of one or more of the appended claims.

[0009] According to a first aspect of the invention in an area of the microfluidic channel which is at least in part transparent, the microfluidic channel is provided with a reduced height in comparison with a neighboring area or areas so as to reduce the thermal mass of the microfluidic channel and improve its electron transparency for imaging, which is particularly crucial with flowing liquids. This reduced height allows to apply higher flow rates than possible in prior art devices.

[0010] The possibility to apply high flow rates without sacrificing resolution is further enhanced by the feature that the microfluidic channel has two parts, a first and thinner part having a dimension measured in a plane orthogonal to the pillars and in a width direction of the microfluidic channel, which dimension of the thinner part is smaller than a dimension of a second and thicker part in said plane orthogonal to the pillars and in said width direction of the microfluidic channel, wherein the thinner part is in the area of the microfluidic channel which is provided with electron-beam transparency and equipped for imaging.

[0011] Preferably the device is equipped with at least one heater element that is embodied in the form of multiple heater resistive elements that are patterned in the vicinity around the microfluidic channel. This allows heating of samples to temperatures above 660 °C without damaging the channel, thus appropriately enabling in situ heating. The feature also provides that high fidelity temperature cycling is possible without damaging the structure of the microfluidic channel.

[0012] It is preferable that the multiple heater resistive elements are provided in a split heater configuration, so as to enable homogeneous heat distribution by enabling that the multiple resistive elements are individually controllable. Accurate and very precise heater control is therewith enabled. Further it enables in-situ nano-calorimetry (both in liquid and in gas conditions) within a monolithic chip.

[0013] In still another aspect of the invention the MEMS device is provided with at least one biasing electrode that reaches into the microfluidic channel. This enables the performance of electrochemical studies with the MEMS device of the invention. Furthermore this enables electrowetting and different types of bio-sensing.

[0014] Suitably the microfluidic channel comprises a top membrane and a bottom membrane opposite to the top membrane, wherein the at least one biasing electrode reaches into the microfluidic channel between the top membrane and the bottom membrane. Particularly this feature supports the versatility of using the at least one biasing electrode for electrochemical studies.

[0015] It is to be noted that there may be plural electrodes, for instance four electrodes, which may be very diversely placed to reach into the microfluidic channel.

[0016] Preferably the MEMS device is provided with two biasing electrodes which reach into the microfluidic channel, particularly between the top membrane and the bottom membrane.

[0017] Depending on the type of studies to be performed the two biasing electrodes may occupy different orientations with respect to each other. In one embodiment the two biasing electrodes reach into the microfluidic channel and are directly opposite to each other in different planes as seen in the viewing direction perpendicular to the top membrane and bottom membrane.

[0018] In another embodiment the two biasing electrodes reach into the microfluidic channel and occupy a staggered position with respect to each other in different planes as seen in the viewing direction perpendicular to the top membrane and bottom membrane.

[0019] In still another embodiment the two biasing electrodes reach into the microfluidic channel and are in a same plane as seen in the viewing direction perpendicular to the top membrane and bottom membrane.

[0020] Suitably the biasing electrode or electrodes are electron transparent.

[0021] The accompanying drawing, which is incorporated into and forms a part of the specification, illustrates one or more embodiments of the present invention and, together with the description, serves to explain the principles of the invention. The drawing is only for the purpose of illustrating one or more embodiments of the invention and is not to be construed as limiting the invention.

[0022] In the drawing:

[0023] -figure 1 depicts the MEMS device according to a first embodiment of the invention in a top view;

[0024] -figure 2 provides a cross-sectional view along the line A-A' in figure 1;

[0025] -figure 3 shows a detail of the cross-sectional section A-A' shown in figure 2;

[0026] -figure 4 provides an isometric view at the MEMS device according to the first embodiment at the location where the microfluidic channel is transparent for imaging;

[0027] -figures 5a - 5e show a second embodiment of the MEMS device according to the invention in different views; and

[0028] -figures 6a - 6e show a third embodiment of the MEMS device according to the invention in different views.

[0029] Whenever in the figures the same reference numerals are applied, these numerals refer to the same parts.

[0030] With reference to figure 1, the MEMS device 1 of the invention is shown, said device 1 comprising a microfluidic channel 2 for liquid or gas to be investigated. This microfluidic channel 2 can be more clearly seen in figure 2, wherein also the inlet 3 and the outlet 4 of the channel 2 are depicted.

[0031] At a location which is indicated with reference 5 the microfluidic channel 2 is transparent for an electron-beam 6 which is used to image samples of liquid or gas in the microfluidic channel 2.

[0032] Further it can be remarked with reference to figure 3 that the microfluidic channel 2 is part of a monolithic die wherein the microfluidic channel 2 has a controlled and ensured height by application of reinforcement pillars 7 inside the microfluidic channel 2 that connect top 12' and bottom 12' ' of the microfluidic channel 2. The top 12' layer is preferably a silicon nitride layer, but Graphene and / or Amorphous Carbon are also possibilities.

[0033] With reference again to figure 1, it is shown that the device 1 is equipped with multiple heater resistive elements 8, 9, 10, that are patterned around the microfluidic channel 2.

[0034] The multiple resistive elements 8, 9, 10 are provided in a split heater configuration, so as to arrange that the multiple resistive elements 8, 9, 10 provide homogenous heat distribution. The resistive elements are powered through the electrical terminals 9' and 9' ' for resistive element 9, and through the electrical terminals 10' and 10' ' for resistive element 10.

[0035] Figure 3 depicts that in the area 5 of the microfluidic channel 2 which is transparent for the imaging electron-beam, the microfluidic channel 2 is provided with a reduced height in comparison with a neighboring area or areas so as to reduce the thermal mass of the microfluidic channel 2 and improve its transparency for imaging. This feature can be applied independent from the other features noted herein or in combination .

[0036] Figure 4 depicts that the microfluidic channel 2 has two parts, a first and thinner part 2' having a first crosssection in a plane orthogonal to the pillars in the microfluidic channel 7, which first cross-section measures less than a second cross-section of a second and thicker part 2' ' of the microfluidic channel 2, wherein the thinner part 2' is in a center of the microfluidic channel 2 which is provided with electron-beam transparency and equipped for imaging.

[0037] In other words figure 4 shows that the microfluidic channel 2 has two parts, a first and thinner part 2' having a dimension measured in a plane orthogonal to the pillars 7 and in a width direction of the microfluidic channel 2, which dimension of the thinner part 2' is smaller than a dimension of a second and thicker part 2' ' in said plane orthogonal to the pillars 7 and in said width direction of the microfluidic channel 2, wherein the thinner part is in the area 5 of the microfluidic channel 2 which is provided with electron-beam transparency and equipped for imaging. This feature can be applied independent from the other features noted herein or in combination.

[0038] Figures 5a - 5e and figures 6a - 6e relate to a second and third embodiment of the MEMS device according to the invention, wherein the microfluidic channel 2, having an inlet 3a and an outlet 3b, comprises at least one biasing electrode la, lb in order to support electrochemical experiments. For clarity the features of the second and third embodiment are shown in figures 5a - 5e and figures 6a - 6e respectively, without the features discussed herein above with reference to figures 1 - 4. It will however be clear for the skilled person that the concerning features discussed with reference to figures 5a - 5e and with reference to figures 6a - 6e, can also be used in combination with the features discussed herein above with reference to figures 1 - 4.

[0039] The figures 5a - 5e and the figures 6a - 6e depict that the microfluidic channel comprises a top membrane 2a and a bottom membrane 2b opposite to the top membrane 2a, wherein the biasing electrode or biasing electrodes la, lb reach into the microfluidic channel between the top membrane 2a and the bottom membrane 2b. When applying two electrodes la, lb there is a large variability in possible placements of the electrodes la, lb. It is for instance possible that the two biasing electrodes la, lb reach into the microfluidic channel and are directly opposite to each other in different planes as seen in the viewing direction perpendicular to the top membrane 2a, 2b and bottom membrane .

[0040] Figures 5a - 5e show another variant wherein the two biasing electrodes la, lb reach into the microfluidic channel and occupy a staggered position with respect to each other in different planes as seen in the viewing direction perpendicular to the top membrane 2a, 2b and bottom membrane.

[0041] Figures 6a - 6e show yet another variant wherein the two biasing electrodes la, lb reach into the microfluidic channel and are in a same plane as seen in the viewing direction perpendicular to the top membrane 2a, 2b and bottom membrane. In this variant the two biasing electrodes la, lb are supported by the bottom membrane 2b.

[0042] In all embodiments it is possible that the biasing electrode or electrodes la, lb are electron transparent.

[0043] Embodiments of the present invention can include every combination of features that are disclosed herein independently from each other. Although the invention has been discussed in the foregoing with reference to an exemplary embodiment of the invention, the invention is not restricted to this particular embodiment which can be varied in many ways without departing from the invention. The discussed exemplary embodiment shall therefore not be used to construe the append-ed claims strictly in accordance therewith. On the contrary the embodiment is merely intended to explain the wording of the appended claims without intent to limit the claims to this exemplary embodiment. The scope of protection of the invention shall therefore be construed in accordance with the appended claims only, wherein a possible ambiguity in the wording of the claims shall be resolved using this exemplary embodiment.

[0044] Variations and modifications of the present invention will be obvious to those skilled in the art and it is intended to cover in the appended claims all such modifications and equivalents. The entire disclosures of all references, applications, patents, and publications cited above are hereby incorporated by reference. Unless specifically stated as being "essential" above, none of the various components or the interrelationship thereof are essential to the operation of the invention. Rather, desirable results can be achieved by substituting various components and / or reconfiguration of their relationships with one another.

Claims

CLAIMS1. MEMS device (1) comprising a microfluidic channel (2) for liquid or gas to be investigated, which microfluidic channel (2) is at least in part transparent for an electronbeam (6) which is used to image samples of liquid or gas in the microfluidic channel (2) , wherein the microfluidic channel (2) is part of a monolithic die wherein the microfluidic channel (2) has a controlled and ensured height by application of reinforcement pillars (7) inside the microfluidic channel (2) that connect top (2' ) and bottom (2' ' ) of the microfluidic channel (2) , characterized in that in an area (5) of the microfluidic channel (2) which is at least in part transparent, the microfluidic channel (2) is provided with a reduced height in comparison with a neighboring area or areas so as to reduce the fluidic resistance and the thermal mass of the microfluidic channel (2) and improve its electron transparency for imaging.

2. MEMS device according to claim 1, characterized in that the microfluidic channel (2) has two parts, a first and thinner part (2' ) having a dimension measured in a plane orthogonal to the pillars (7) and in a width direction of the microfluidic channel (2) , which dimension of the thinner part (2' ) is smaller than a dimension of a second and thicker part (2, f) in said plane orthogonal to the pillars (7) and in said width direction of the microfluidic channel (2) , wherein the thinner part is in the area (5) of the microfluidic channel (2) which is provided with electron-beam transparency and equipped for imaging.

3. MEMS device according to the preamble of claim 1 or according to any one of claims 1 - 2, characterized in that the device (1) is equipped with at least one heater element that is embodied in the form of multiple heater resistiveelements (8, 9, 10) that are patterned in the vicinity around the microfluidic channel (2) .

4. MEMS device according to claim 3, characterized in that the multiple heater resistive elements (8, 9, 10) are provided in a split heater configuration, so as to enable homogeneous heat distribution.

5. MEMS device according to the preamble of claim 1 or according to any one of claims 1 - 4, characterized in that the MEMS device is provided with at least one biasing electrode (la, lb) that reaches into the microfluidic channel (2) .

6. MEMS device according to claim 5, characterized in that the microfluidic channel comprises a top membrane (2a) and a bottom membrane (2b) opposite to the top membrane (2a) , wherein the at least one biasing electrode (la, lb) reaches into the microfluidic channel between the top membrane (2a) and the bottom membrane (2b) .

7. MEMS device according to claim 5 or 6, characterized in that the mems device is provided with two biasing electrodes (2a, 2b) which reach into the microfluidic channel, preferably between the top membrane (2a) and the bottom membrane (2b) .

8. MEMS device according to claim 7, characterized in that the two biasing electrodes (la, lb) reach into the microfluidic channel and are directly opposite to each other in different planes as seen in the viewing direction perpendicular to the top membrane (2a) and bottom membrane (2b) .

9. MEMS device according to claim 7, characterized in that the two biasing electrodes (la, lb) reach into themicrofluidic channel and occupy a staggered position with respect to each other in different planes as seen in the viewing direction perpendicular to the top membrane (2a) and bottom membrane (2b) .

10. MEMS device according to claim 7, characterized in that the two biasing electrodes (la, lb) reach into the microfluidic channel and are in a same plane as seen in the viewing direction perpendicular to the top membrane (2a) and bottom membrane (2b) .

11. MEMS device according to any one of claims 6 -10, characterized in that the biasing electrode or electrodes (la, lb) are electron transparent.

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