WO2021054830A1

WO2021054830A1 - Parallel free-hanging micro machined channels and method for the manufacturing thereof

Info

Publication number: WO2021054830A1
Application number: PCT/NL2020/050579
Authority: WO
Inventors: Yiyuan ZHAO; Henk-Willem VELTKAMP; Thomas Victor Paul SCHUT; Meint Jelle De Boer; Remco John Wiegerink; Jarno GROENESTEIJN; Joost Conrad Lötters
Original assignee: Berkin B.V.; Stichting Voor De Technische Wetenschappen; Universiteit Twente
Priority date: 2019-09-20
Filing date: 2020-09-18
Publication date: 2021-03-25
Also published as: NL2023869B1

Abstract

A method for manufacturing a pair of parallel micro machined channels, using a substrate of a first material and comprising the steps of: - forming two primary perforations in said substrate, spaced apart from each other by a distance that is larger than a width of the channels to be formed; - forming two channel outlines in said substrate, the two channel outlines being spaced apart from each other; - filling the outer circumferential surface of the two channel outlines with a second material, to form said first micro machined channel and said second micro machined channel; - forming two secondary perforations in said substrate, at positions radially outside of the micro machined channels formed in the previous step; - forming two ducts in said substrate, while ensuring that some of the substrate-forming first material remains present between the channels.

Description

Title: Parallel free-hanging micro machined channels and method for the manufacturing thereof.

Description

The present invention relates to a free-hanging MEMS component, a method for manufacturing a first micro machined channel and at least a second micro machined channel substantially parallel to said first micro machined channel, as well as a sensor and a microreactor comprising said MEMS component.

US 6,180,536 B1 discloses a microfabrication process for making enclosed, subsurface microfluidic tunnels, cavities, channels, and the like within suspended beams. The method includes as a first step etching a single crystal silicon wafer to produce trenches defining a beam. As a second step the method includes oxidizing the trench walls. Then the oxide is removed from all the horizontal surfaces on which it was just deposited, leaving only the vertical surfaces covered with the oxide layer. The next step is another vertical silicon etch, extending the depth of the trenches to below the bottom of the oxide layer and forming two interconnected channels. Between the channels, a silicon plug remains. Finally another oxidization step is performed.

A first disadvantage of the method disclosed in US 6,180,536 B1 is that it is relatively complicated. First an etching step is performed, then an oxidization step is performed, then a part of the oxidizing material is removed again, and then a second etching step is performed, after which yet another oxidization step is performed. This results in five steps: two etching steps, two oxidizing steps, and one partial oxidization removal step. The method is therefore found to be relatively complex.

A second disadvantage of the method disclosed in US 6,180,536 B1 is that the channels are interconnected. For some applications, this is undesired.

A third disadvantage of the method disclosed in US 6,180,536 B1 is that the walls of the formed channels, at the radially outer side thereof, are in contact with the silicon material. For some applications it is however desired that the formed channels are “free-hanging”, i.e. that the radially outer sides of the channels are surrounded by air, vacuum, or another non-solid material. Further disadvantageously, it was found that the flat (straight) surface walls of US 6,180,536 B1 , and the channels formed thereby are undesirable for various applications. Such walls e.g. lack robustness, e.g. when the channels are to be heated.

It is an object of the present invention to overcome at least one of the disadvantages of the method of US 6,180,536 B1. More specifically, it is an object of the present invention to provide a simpler method to form at least two micro machined channels. It is a further object of the present invention to overcome at least one of the disadvantages of the formed channels of US 6,180,536 B1. More specifically, it is an object of the present invention to provide more robust channels, and/or channels with different shapes, and/or channels provided with electrodes.

Accordingly, a first aspect of the present invention relates to a method for manufacturing a first micro machined channel and at least a second micro machined channel substantially parallel to said first micro machined channel, the method making use of a substrate of a first material and comprising the steps of: forming two primary perforations in said substrate, substantially parallel to each other, the perforations being spaced apart from each other by a distance that is larger than a width of the channels to be formed; forming two channel outlines in said substrate by removing a part of said substrate via said perforations, the two channel outlines being spaced apart from each other; filling the outer circumferential surface of the two channel outlines with a second material that is different from the first material, to form said first micro machined channel and said second micro machined channel; forming two secondary perforations in said substrate substantially parallel to each other, at positions radially outside of the micro machined channels formed in the previous step; forming two ducts in said substrate by removing a part of said substrate via said secondary perforations, while ensuring that some of the substrate forming first material remains present between the channels.

With the method according to the invention spaced apart, un connected channels advantageously result as the two primary perforations are spaced apart from each other by a distance that is larger than a (maximum) width of the channels to be formed. On top of that, due to the forming of two primary perforations and two secondary perforations, the secondary perforations being provided at positions radially outside of the formed channels, compared to US 6,180,536 B1 the need for an “intermediate” oxidization or filling step and an “intermediate” partial oxidization removing step is omitted and the micro machined channels can be formed in less process steps. Hence, compared to US 6,180,536 B1 (in the wording of that document) only three method steps are needed: two etching steps and one oxidization step. This results in faster production and a cheaper product.

Yet further, when the secondary perforations are positioned at the “right” place radially outside of the formed channels (to be discussed in more detail below), the material around the radial outer side of the channels may be removed and free-hanging channels result.

Accordingly, the object of the invention is achieved.

Advantageously, the first material remaining present in between the channels makes a vast wealth of new applications possible. Said remaining first material may also be known as an embedded silicon strip or an embedded Si strip or an embedded strip. In embodiments said first material may be heated to very high temperatures (up to 1000 °C when it is e.g. a doped silicon material). This may be beneficial if e.g. one of the channels or both channels are to be used as a combustion chamber. Further advantageously, when the first material contains silicon, said material may be used as an integrated and highly sensitive strain gauge, due to the piezo-resistivity of silicon. The first material may in other embodiments be used as an integrated capacitive sensor when the channels are used for Coriolis applications. The material remaining present between the first channel and the second channel further results in a more robust, i.e. a “stronger” assembly. This increased robustness is useful in any application where the channels are vibrated or moved in another way. Further advantageously, the first material remaining present in between the channels leads to a relatively high mechanical strength of the channels, which allows the channels e.g. to be used in skin-penetrating needles.

Although the method is for manufacturing a first micro machined channel and a second micro machined channel, it is to be understood that also a third micro machined channel or even more micro machined channels may be manufactured with the method as described herein. The manufacturing of three micro machined channels will be explained in detail with reference to the figures, but it is to be understood that the method is not limited to only manufacturing two or three channels.

In embodiments, the channels may be the same size or they may have different sizes. For example, the first and the second channels (and optionally also the third channel, when present) may have the same sizes. Alternatively, one of the first and second (and, when present, third) channels may be larger than the other(s) of the first and the second (third) channels. For example, the third channel, arranged in between the first and the second channel, may be larger or smaller than the first and the second channels, while the first and second channels have the same size.

The method is related to manufacturing a first micro machined channel and at least a second micro machined channel which are substantially parallel to each other. The channels need not be parallel to each other along their entire length. They may depart from each other at some point along their length. However, in at least one cross-sectional plane taken perpendicular to the longitudinal axis of the channels, said channels should be parallel. The at least two channels can be substantially parallel to each other along their entire length.

Seen in a cross-sectional plane perpendicular to a length direction of the channels (to be formed), the two primary perforations are spaced apart from each other by a distance that is larger than a (maximum) width of the channels to be formed. When the channels have a non-uniform cross section, preferably the distance between the primary perforations is larger than the maximum width of the channels. In an embodiment, the channels have the same cross section (and thus the same width), such that it is very clear what the “a width” of the channels means. In embodiments where the widths of the channels are not the same, the perforations should be spaced apart more than the average width of the two channels to be formed. As the two primary perforations are spaced apart from each other by a distance which is larger than a width of the channels to be formed, this ensures that some of the substrate forming first material remains present between the channel outlines when these channel outlines are formed. In other words, due to the spacing of the primary perforations, which is sized according to the desired width / shape of the channels to be formed, two separate, non-connected channels result. For example, if channels with a width of 50 pm are desired, the two primary perforations may be spaced apart by 60 pm. For example, if channels with a width of 60 pm are desired, the two primary perforations may be spaced apart by 70 pm. A person skilled in the art will usually determine in advance, i.e. before performing the method, which width the channels to be formed should have. Said person skilled in the art will then form the perforations with an appropriate spacing.

Seen in a top view of the substrate, the primary perforations may define a continuous line. However, the primary perforations may also be formed along a non-continuous, interrupted line along the length of the channel to be formed.

The primary perforations may extend only through the top layer of the substrate. However, analogous to the method explained in a co-pending application filed on the same day be the same applicant, the perforations may also be deeper, and define trenches extending into the substrate such that ultimately (round) channels may be formed below the surface level of the substrate.

After forming the two primary perforations, two channel outlines are formed in the substrate, by removing a part of the material forming the substrate via the perforations. Many methods are known in the prior art to form channel outlines in a substrate. For example, one may use a technique known as “etching” (see also US 6,180,536 B1). After the step of forming the two channel outlines, channel outlines result which are spaced apart from each other, i.e. which are separated from each other. Substrate-forming first material remains present between the channel outlines.

In a further method step the first micro machined channel and the second micro machined channel are formed by filling the outer circumferential surface of the channel outlines with a second material. This second material has material properties that allow it to withstand the duct-forming step. In other words, the second material should not be affected (disintegrated) when the ducts are formed, as the second material in the end defines the circumferential wall of the micro machined channels. Also after this step of forming the channels, substrate-forming material remains present in between the micro machined channels.

The secondary perforations are formed at positions in the substrate radially outside of the micro machined channels, allowing substrate-forming material to be removed around the formed channels in a later method step while the substrate forming material in between the formed channels is unaffected. A distance between the secondary perforations is preferably larger than the sum of the width of the first micro machined channel and the width of the second micro machined channel.

By forming the ducts, the substrate-forming first material that surrounds the first and second micro machined channels at the outer side thereof can be removed, such that free-hanging channels, i.e. channels not surrounded by substrate-forming first material / channels surrounded by air, a vacuum or other non solid material result, while the channels are connected to each other via the substrate forming first material that remains present in between them. Hence, not all of the first material around the micro machined channels is removed. Some of the first material advantageously remains present in between the channels. As stated, when this first material is e.g. a doped silicon material, it may be heated to a very high temperature (up to 1000°C or more) which is beneficial if one of the channels or both channels need to be heated / used as a combustion chamber. However, many other applications are foreseen for the thus formed channels, as will be described in the below. The skilled person can adapt the method if more than two channels are desired, e.g. by adding additional outlines, adapting the placement of the secondary perforations and forming the duct in such a way that the substrate-forming first material that surrounds all micro machined channels may be removed from the outer side thereof, while the channels are connected to each other via the substrate-forming first material that remains present in between them.

In an embodiment, at least one of the formed micro machined channels has a semi-circular shape. The “width” of the channels is then defined as the “diameter” thereof. For example in comparison to rectangular channels, a semi-circular channel may allow a more uniform flow for gasses and/or liquids flowing through the channel and/or provide more robustness. In a preferred embodiment at least one of the formed micro machined channels has a circular shape, e.g. when the mentioned trenches are first formed and the channels are formed below the surface of the substrate.

In an embodiment, a width of the formed micro machined channels is between 20 pm and 80 pm, such as between 40 and 60 pm, e.g. about 40 pm, about 50 pm or about 60 pm. Preferably, the width of the first micro machined channels is equal or substantially equal to the width of the second micro machined channel. Preferably the cross-sectional shape of the first micro machined channel is equal to the cross-sectional shape of the second micro machined channel.

In an embodiment, a distance between the two primary perforations is between 50 pm and 100 pm, such as between 55 pm and 75 pm, preferably between 60 pm and 65 pm. As stated, the distance between the two primary perforations is larger than a width (or, in case the width of the channels is to be different: the average width) of the channels to be formed. In an embodiment, a distance between the two secondary perforations is between 90 pm and 300 pm, e.g. between 100 pm and 250 pm. In general, the minimum distance between the two secondary perforations will be larger than the sum of the width of the first channel and the width of the second channel. If three channels are formed, the minimum distance between the two secondary perforations will be larger than the sum of the width of the first channel, the width of the second channel, and the width of the third channel. If the distance between the two secondary perforations is too large, not all material surrounding the micro machined channels (at the outside thereof) may be removed during the step of forming the ducts. If the distance between the two secondary perforations is too small however, also the material in between the channels may be removed. The description of the figures will provide some detailed examples in this respect. Provided that one works in the correct range, e.g. the range as indicated here, the larger the distance between the two secondary perforations, the more first material remains present in between the micro machined channels.

In an embodiment, the first material comprises highly doped Si, e.g. Boron-doped Si (also named B-doped Si).

In an embodiment, the second material comprises low-stress silicon rich silicon nitride, e.g. LPCVD SiRN. As indicated, the second material should have properties that allow it to remain intact when the first material is removed in the duct forming step. Depending on the method used to form the ducts, different second materials may be used.

In an embodiment, an area of the first material remaining between the two micro machined, spaced apart channels, seen in a cross-sectional plane perpendicular to a longitudinal direction of the channels, equals at least 25 pm² and at most 1000 pm². When the first material is e.g. used as an integrated heater, more material allows a higher temperature to be reached in the channel or channels, and/or a specified temperature in the channel(s) to be reached faster.

In an embodiment, a metal film is further provided on the substrate, at a position between the two micro machined, spaced apart, channels after the channels are formed and before the ducts are formed, preferably before the secondary perforations are formed. This allows an ohmic contact to be made between the outside world and the first material. According to a second aspect the invention relates to a free-hanging microelectromechanical system (also named MEMS) component comprising at least two substantially parallel micro machined channels that are spaced apart from each other and a silicon electrode in between said channels, the silicon electrode contacting at least a part of a circumferential wall of each of said channels. Said channels are suitable to receive a fluid, for example a gas, a liquid or a plasma.

For example, the MEMS component may be part of a sensor, such as a flow sensor. Examples of flow sensors include a thermal sensor (Wobbe meter), a Coriolis flow sensor, a relative permittivity sensor, and a calorimetric flow sensor.

For example, the MEMS component may be part of a pressure sensor.

For example, the MEMS component may be part of a fluid sensor.

For example, the MEMS component may be part of a microheater such as an evaporated, e.g. a Controlled Evaporation Mixer (CEM), wherein electrode between the channels acts either as heat source or as heat sink. More in particular, the microheater may be suited to heat, burn or evaporate a fluid inside the channels.

For example, the electrode of the MEMS component may be suitable for capacitive measurements and/or resistive measurements.

For example, the MEMS component may be made via the method according to the first aspect of the invention.

A further possible use of the MEMS component includes the measurement of dielectric properties of the fluid in the channel, e.g. to concentrate electric fields inside the channels. A further possible use of the MEMS component includes the use of one of the channels as reference channel. For example, one of the at least two channels may contain a fluid of which the properties are to be measured, while the other (another) of the at least two channels may not contain said fluid, but may e.g. be filled with air.

Advantages to be achieved with the MEMS component according to the second aspect of the invention are the same as the advantages to be achieved with the method according to the first aspect of the invention.

More in particular, the resulting component comprising two parallel channels and an electrode arranged in between the channels results in a robust, strong component that, compared to known micro machined channels, is well capable of handling vibrations, impact forces, and heat. On top of that, the component has more structural integrity. It is expected that the component therefore has a longer lifespan and suffers less from fatigue.

As it is possible to tailor the size of the electrode between the channels, the mass and stiffness of the MEMS component can be tailored as well. This is advantageous as it allows to decouple the mechanical and fluidic properties of the channels. This may be useful when optimizing for the pressure sensitivity of the MEMS component, the pressure drop inside the channels, and/or the existence of fluid waves inside the channel.

It is furthermore expected that the presence of an electrode in between the channels allows for in-depth measurements of the fluid in the channels using sound waves.

The same will now be elucidated further in the below with reference to the attached figure. In the figures:

Figures 1a - 1e schematically illustrate a first possible embodiment of the method according to the invention;

Figures 2a - 2d schematically illustrate a second possible embodiment of the method according to the invention;

Figures 3a - 3d schematically illustrate a third possible embodiment of the method according to the invention;

Figures 4a - 4e schematically illustrate a fourth possible embodiment of the method according to the invention; and

Figures 5a - 5e schematically illustrate a fifth possible embodiment of the method according to the invention.

Figures 1a - 1e depict a first possible method for the manufacturing of a pair of substantially parallel, spaced apart channels 1 , 2. The method starts with a substantially solid piece of substrate material 3, see Figure 1a. Here arranged on top of the substrate is an oxide layer 34, which may e.g. be arranged to protect the substrate from outside influences while it is being stored and which initially completely covers the first material 31. The substrate material 3 may e.g. comprise a highly doped silicon material, such as a Boron-doped silicon material. The substrate material 3 may e.g. consist entirely of Boron-doped silicon material (e.g. a wafer), possibly with trace amounts of other materials. With reference to Figure 1a, in a first method step two primary perforations 4, 5 are formed. The perforations 4, 5 here extend only through the protective layer 34, but may also extend into the substrate-forming first material 31 to form a trench in said substrate-forming first material 31. Figure 1a shows the perforations 4, 5 in a cross-sectional plane perpendicular to a longitudinal direction of the channels to be formed. In a (non-depicted) top view of the substrate 3, the perforations 4, 5 could e.g. have the shape of a straight line or the shape of an interrupted line. The perforations 4, 5 are substantially parallel to each other, and are spaced apart from each other by a distance ds1. This distance ds1 by which the perforations 4, 5 are spaced apart is larger than the width W of the channels to be formed (width W indicated in figure 1e). In the shown embodiment, the distance ds1 is about 60 pm. This distance ds1 may however e.g. be between 50 pm and 100 pm, such as between 55 pm and 75 pm, in particular between 60 pm and 65 pm.

In embodiments where there is no protective layer 34, the first method step may be omitted.

In a second method step, illustrated in Figure 1b, the formed primary perforations 4, 5 are expanded to channel outlines 6, 7 by removing a part 3’ of the substrate-forming first material 31 through the perforations 4, 5. For example the material 31 may be etched through the perforations 4, 5. Substrate-forming first material 31 remains present between the channel outlines 6, 7 such that the channel outlines 6, 7 are spaced apart from each other.

Turning to Figure 1c, the result of the third method step of forming a first micro machined channel 1 and a second micro machined channel 2 is shown. In this step, at least the outer circumferential surface of the two formed channel outlines 6, 7 are filled with a second material 32. Here also the top layer of the substrate 3 is covered with said second material 32. The result, as shown, is a first micro machined channel 1 and a second micro machined channel 2 that is substantially parallel to the first micro machined channel 1.

The second material 32 is different from the first material 31 , and preferably also different from the material which forms the oxide layer 34. For example, the second material 32 comprises a low-stress silicon rich silicon nitride or consists substantially entirely of a low-stress silicon rich silicon nitride (possible comprising also trace amounts of other materials). The thus formed channels 1 , 2 are here semi-circular in shape and are spaced apart from each other. That is, inner volumes of the channels are not in contact with each other and substrate-forming first material 31 is present between the outer walls of the channels 1 , 2 at the position where these outer walls face each other. After the third method step, substrate-forming first material 31 is also still present at positions around the channels 1 , 2.

Figure 1d displays the result of an optional intermediate method step, wherein a metal film 33, e.g. of a fourth material different than the first material 31, the second material 32, and the protective layer 34, is provided on the substrate 3 at a position between the two micro machined channels 1 , 2. In order to do so, first a part of the second material 32 may need to be removed by a process which e.g. affects the second material 32 but not the first material 31.

In figure 1e the result of the fourth and the fifth method step is displayed. At first, in the fourth method step, two secondary perforations 8, 9 are formed in the substrate 3. Similar to forming the primary perforations 4, 5 (illustrated in figure 1a), the secondary perforations 8, 9 may only “open up” the second material 32. However, the secondary perforations 8, 9 may also extend into the substrate 3 to form trenches. The formed secondary perforations 8, 9 are substantially parallel to each other, just like the primary perforations 4, 5 were. Seen from the center of the micro machined channels 1, 2 the secondary perforations 8, 9 are provided in the substrate 3 at positions beyond where the channels 1 , 2 are provided. That is, the secondary perforations 8, 9 are positioned radially outside of the micro machined channels 1 , 2.

The distance ds2 between the secondary perforations 8, 9 is here about 140 pm, but may e.g. be between 90 pm and 300 pm (as also follows from the figures 2 and 3). The width of the secondary perforations 8, 9 themselves may be about 200 pm.

It is noted that, if the first material 31 is directly exposed after the step of forming the channels 1 , 2, the step of forming secondary perforations may be optional.

After forming the secondary perforations 8, 9, ducts 10, 11 are formed by removing a part 3” of the substrate-forming first material 31 through said perforations 8, 9, e.g. by etching said material 31 away. According to the invention, this removal of a part 3” of the substrate-forming first material 31 around the channels 1 , 2 is done while it is ensured that at least some of the substrate-forming first material 31 remains present between the channels 1, 2. The remaining material is here indicated with reference 25 and may e.g. define an electrode between the channels 1 , 2 and contacting the circumferential wall 26, 27 of said channels 1 , 2.

The ducts 10, 11 are in contact with each other, freeing the assembly 100 of first micro machined channel 1 , second micro machined channel 2, and remaining electrode 25 in between the channels 1 , 2 with respect to the remainder of the substrate. In other words, the formed micro machined channels 1, 2 are free- hanging.

The formed channels 1 , 2 each have a width W, as indicated in Figure 1e. As the channels 1 , 2 are semi-circular, the width W here corresponds to the diameter D of the channels. The diameters D of the first micro machined channel 1 and the second micro machined channel 2 are about equal, and may e.g. be in the range of 20 pm to 80 pm.

An area A of the electrode 25 formed in between the channels 1, 2, seen in the cross-sectional plane as shown in Figure 1e (i.e. perpendicular to the longitudinal direction of the channels) may e.g. equal between 25 pm² and 1000 pm². In the embodiment of Figure 1e, the area equals about 230 pm² (as approximated based on figures taken by an scanning electron microscope).

The formed assembly 100 of two substantially parallel micro machined channels 1 , 2 and silicon electrode 25 in between the channels 1 , 2 may e.g. define a MEMS component as described elaborately in the above.

Now turning to Figures 2a - 2d, the method steps illustrated in figures 2a - 2c may substantially correspond to the method steps illustrated in figures la id. The situation depicted in Figure 2a corresponds to the situation depicted in figure 1b (i.e. after performing both the first and the second method step). Similarly, the situation depicted in figure 2b corresponds to the situation depicted in figure 1c (i.e. after performing the third method step) and the situation depicted in figure 2c corresponds to the situation depicted in figure 1d (after performing the optional intermediate method step). These will therefore not be discussed anymore.

In figure 2d, compared to figure 1e, the distance ds2 between the two secondary perforations 8, 9 is smaller than in figure 1e. The distance ds2 between the secondary perforations 8, 9 is here about 100 pm. As a result, less of the substrate forming first material 31 is removed in the fifth method step, although the resulting ducts 10, 11 are still in contact with each other such that free-hanging channels 1 , 2 result. Further, although material 31 still remains between the channels 1 , 2, the area of electrode 25 is smaller and here equals about 35 pm².

Now turning to Figures 3a - 3d, the method steps illustrated in figures 3a - 3c may substantially correspond to the method steps illustrated in figures 2a - 2c. These will therefore not be discussed anymore.

In figure 3d, compared to figure 1e, the distance ds2 between the two secondary perforations 8, 9 is larger than in figure 1e. The distance ds2 between the secondary perforations 8, 9 is here about 250 pm. As a result, more of the substrate forming first material 31 is removed around the channels 1, 2 in the fifth method step, resulting in larger ducts 10, 11, but also in a larger electrode 25. The area of the electrode 25 is here about 720 pm².

It is noted that if the distance ds2 between the secondary perforations 8, 9 is increased even further, e.g. beyond 300 pm (in the case of two channels of the same width W as used here), the ducts 10, 11 may no longer be in contact with each other.

With reference to Figures 4a - 4e a method for manufacturing three parallel micro machined channels 1 , 2, 12 is displayed. With reference to Figures 5a - 5e a method for manufacturing three parallel micro machined channels 1 , 2, 12 is displayed. The difference between figures 4a - 4e and figures 5a - 5e is that the third channel 12 is larger than the other two channels 1 , 2 in figures 5a - 5e while all channels 1 , 2, 12 have substantially the same size in figures 4a - 4e. As a result, figures 4a - 4e and 5a - 5e are described simultaneously.

Shown in figures 4a and 5a is a substrate 3 of a first material 31. The first material 31 is covered by a protective oxide layer 34. In a first method step, three primary perforations 4, 5, 14 are formed in said substrate 3. The three primary perforations are substantially parallel to each other. Each of the perforations 4, 5, 14 are spaced apart from each other by a distance (not indicated) that is larger than a width of the channels to be formed, in a way that is the same as described extensively in relation to figure 1a. That is to say, the distance between the first perforation 4 and the third perforation 14 is larger than a width of the channels to be formed, the distance between the second perforation 5 and the third perforation 14 is larger than a width of the channels to be formed, and (obviously) also the distance between the first perforation 4 and the second perforation 5 is larger than a width of the channels to be formed.

With reference to Figures 4b and 5b, the method step of forming three channel outlines 6, 7, 16 in the substrate 3 is indicated. This is done by removing a part of said substrate 3 via said perforations 4, 5, 14, the channel outlines 6, 7, 16 all being spaced apart from each other (as indicated).

In the third method step, shown in Figures 4c and 5c, the outer circumferential surface of the channel outlines 6, 7, 16 is filled with a second material 32 that is different from the first material 31, to form a first micro machined channel 1 , a second micro machined channel 2, and a third micro machined channel 12.

In the next, optional, step, shown in Figures 4d and 5d, metal films 33 are further provided on the substrate 3, at positions between the first micro machined channel 1 and the third micro machined channel 12 and between the second micro machined channel 2 and the third micro machined channel 12 after said channels 1 , 2, 12 are formed.

In the next method step, shown in Figures 4e and 5e, two secondary perforations 8, 9 are formed in said substrate 3, the secondary perforations 8, 9 being substantially parallel to each other, and arranged at positions radially outside of the micro machined channels 1 , 2, 12 formed in Figures 4c and 5c. next, two ducts 10, 11 are formed in said substrate 3 by removing a part of said substrate 3 via said secondary perforations 8, 9, while ensuring that some of the substrate-forming first material 31 remains present between the channels 1 , 2, 12.

This results in a free-hanging microelectromechanical system component 100 comprising three (i.e. at least two) substantially parallel micro machined channels 1 , 2, 12 that are spaced apart from each other, as well as two silicon electrodes 25 arranged in between said channels 1 , 2, 12. One silicon electrode 25 is arranged between the first channel 1 and the third channel 12, contacting a part of a circumferential wall 26, 28 of each of the first and third channels 1, 12 and another silicon electrode 25 is arranged between the second channel 2 and the third channel 12, contacting a part of a circumferential wall 27, 28 of each of the second and third channels 2, 12.

It goes without saying that options described for the method of manufacturing of two parallel channels are equally (or in an equivalent way) applicable to the method of manufacturing three parallel channels, even when this is not described explicitly.

LIST OF REFERENCE NUMERALS

1 first micro machined channel

2 second micro machined channel

3 substrate

31 first material

32 second material

33 metal film

34 third material

3’ removed part of substrate

3” removed part of substrate

4 primary perforation

5 primary perforation

6 channel outline

7 channel outline

8 secondary perforation

9 secondary perforation

10 duct

11 duct

12 third micro machined channel

14 primary perforation

16 channel outline

25 silicon electrode

26 circumferential wall of the first channel

27 circumferential wall of the second channel

28 circumferential wall of the third channel

100 free-hanging microelectromechanical system component A area of first material remaining between channels ds1 distance between the primary perforations ds2 distance between the secondary perforations

Claims

1. A method for manufacturing a first micro machined channel (1) and at least a second micro machined channel (2) substantially parallel to said first micro machined channel (1), the method making use of a substrate (3) of a first material (31) and comprising the steps of: forming two primary perforations (4, 5, 14) in said substrate (3), substantially parallel to each other, the perforations (4, 5, 14) being spaced apart from each other by a distance (ds1) that is larger than a width (W) of the channels (1, 2, 12) to be formed; forming two channel outlines (6, 7, 16) in said substrate (3) by removing a part (3’) of said substrate (3) via said perforations (4, 5, 14), the two channel outlines (6, 7, 16) being spaced apart from each other; filling the outer circumferential surface of the two channel outlines (6, 7, 16) with a second material (32) that is different from the first material (31), to form said first micro machined channel (1) and said second micro machined channel (2); forming two secondary perforations (8, 9) in said substrate (3) substantially parallel to each other, at positions radially outside of the micro machined channels (1 , 2, 12) formed in the previous step; forming two ducts (10, 11) in said substrate (3) by removing a part (3”) of said substrate (3) via said secondary perforations (8, 9), while ensuring that some of the substrate-forming first material (31) remains present between the channels (1 , 2, 12).

2. The method according to claim 1 , wherein the formed channels (1 , 2, 12) have a semi-circular shape.

3. The method according to any one of the preceding claims, wherein the first micro machined channel (1) and the second micro machined channel (2) have a substantially equal width (W).

4. The method according to any one of the preceding claims, wherein a width (W) of the channels (1 , 2, 12) is between 20 pm and 80 pm.

5. The method according to any one of the preceding claims, wherein a distance (ds1) between the two primary perforations (4, 5) is between 50 pm and 100 pm, such as between 55 pm and 75 pm, preferably between 60 pm and 65 pm.

6. The method according to any one of the preceding claims, wherein a distance (ds2) between the two secondary perforations (8, 9) is between 90 pm and 300 pm, e.g. between 100 pm and 250 pm.

7. The method according to any one of the preceding claims, wherein the first material (31) comprises highly doped Si.

8. The method according to any one of the preceding claims, wherein the second material (32) comprises low-stress silicon rich silicon nitride.

9. The method according to any one of the preceding claims, wherein an area (A) of the first material (31) remaining between the at least two micro machined channels (1 , 2, 12), seen in a cross-sectional plane perpendicular to a longitudinal direction of the channels (1 , 2, 12), equals at least 25 pm² and at most 1000 pm².

10. The method according to any one of the preceding claims, wherein the formed micro machined channels (1 , 2, 12) are free-hanging channels.

11. The method according to any one of the preceding claims, wherein a metal film (33) is further provided on the substrate (3), at a position between the at least two micro machined channels (1 , 2, 12), after the channels (1 , 2, 12) are formed and before the ducts (10, 11) are formed, preferably before the secondary perforations (8, 9) are formed.

12. Free-hanging microelectromechanical system component (100) comprising at least two substantially parallel micro machined channels (1 , 2, 12) that are spaced apart from each other and a silicon electrode (25) arranged in between said channels (1 , 2, 12), the silicon electrode (25) contacting a part of a circumferential wall (26, 27, 28) of each of said channels (1 , 2, 12).

13. Free-hanging microelectromechanical system component (100) according to claim 12, wherein the silicon electrode (25) is a microheater, a sensor for capacitive readout, or a sensor for resistive readout.

14. Sensor, e.g. a flow sensor such as a thermal sensor, a Coriolis flow sensor, or a relative permittivity sensor, a pressure sensor or a fluid sensor, comprising the free-hanging microelectromechanical system component (100) according to claim 12 or 13.

15. Microreactor comprising the free-hanging microelectromechanical system component (100) according to claim 12 or 13.