CONDUCTIVE AND TRANSPARENT INTERCONNECTION STRUCTURE, MANUFACTURING METHOD AND ASSOCIATED SYSTEM

Abstract

CONDUCTIVE AND TRANSPARENT INTERCONNECTION STRUCTURE, MANUFACTURING METHOD AND ASSOCIATED SYSTEM One aspect of the invention relates to an interconnection structure (1) comprising: a substrate (10) formed of a first electrically insulating and optically transparent material, the substrate (10) comprising a first face (11) and a second opposite face (12), the first face (11) defining a plane of the substrate; a plurality of transparent electrodes (20); said interconnection structure (1) being notable in that the transparent electrodes (20) pass through the substrate (10) from the first face (11) to the second face (12) of the substrate (10) parallel to each other, and are electrically insulated from each other by the first electrically insulating and optically transparent material. Figure to be published with the abstract: Figure 2

Description

Title of the invention: CONDUCTIVE AND TRANSPARENT INTERCONNECTION STRUCTURE, MANUFACTURING METHOD AND ASSOCIATED SYSTEM TECHNICAL FIELD OF THE INVENTION

[0001] The technical field of the invention is that of the electrical, optical and mechanical interconnection between an electronic component and a sample to be analyzed, for example a biological sample such as neuronal cells in culture in a microfluidic cell.

[0002] The invention finds application in the fields of biology and health, particularly in the field of organs-on-chips. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] Organs-on-a-chip are miniaturized technological platforms in which cells are cultured in vitro and combined with microfluidic and microelectronic technologies, as well as sensors, which may be electronic and / or optical. Organs-on-a-chip make it possible to reproduce and study the functioning of organs as closely as possible to their function in the human body.

[0004] Applied to neuronal cells (or “neurons”), organs-on-a-chip offer the possibility of understanding certain neurodegenerative diseases, such as Parkinson’s disease or Alzheimer’s disease, and of testing in-vitro treatments introduced via the microfluidic circuit.

[0005] Real-time measurement of the electrical activity of neuronal cells is one of the ways to understand these diseases. The electrical activity of neuronal cells results in the emission of action potentials on the order of tens of millivolts, for example, 70 mV. These action potentials can be received either directly by an electronic sensor on which the neuronal cells are deposited, or via an interface device placed between the neuronal cells and an electronic sensor.

[0006] To directly measure the action potentials of a neuronal cell, it is known to bring a neuronal cell into contact with a surface coated with a thin dielectric and connected to the gate of a MOS transistor (Metal Oxide Semiconductor). When the neuronal cell is electrically stimulated, it emits action potentials that are capacitively coupled to the transistor. In other words, the transistor acts as a capacitive voltage sensor capable of recording the electrical activity of an individual cell.

[0007] An electronic sensor called a "Multi Transistor Array" in English has been designed on this basis. It comprises a plurality of MOS transistors connected in series, thus forming a network or matrix of transistors.

[0008] The size of the transistors and the spacing of the transistor array ensure that each neuronal cell is electrically measured individually, regardless of its position on the matrix surface. The array records the electrical activity of the cells in parallel. Such a sensor therefore functions as an electrophysiological imaging device with spatial resolution at the neuronal cell scale.

[0009] For example, such a MOS transistor array comprising 16,384 transistors arranged in series to form an analysis surface of 1 mm² has been developed. Such a device makes it possible to grow or culture neuronal cells on the transistors and to measure the electrical activity of these cells.

[0010] The drawback of this type of sensor is that it comprises transistors formed on silicon substrates, which are therefore opaque to visible light. This is a significant limitation when one wishes to observe or measure the activity of neuronal cells optically, i.e., by microscopy or any other imaging method using visible light, in order to benefit from the complementarity between optical and electrical characterization methods. More specifically, because of the opacity of the transistors, the only possible optical imaging modality is the reflection (or "epi") modality, which consists of measuring the signal reflected by the sample. This modality limits the type of optical signals that can be measured on the cells.

[0011] To overcome this, it is possible to use an interconnection device that is completely transparent to visible light. Generally, such a device does not include transistors but conductive areas—called electrodes—that electrically and passively connect input contact points and output contact points. Thus, when neuronal cells are placed on the input contact points, their electrical activity can be collected and transmitted to the output contacts, and then processed by external sensors connected to the output contacts.

[0012] Such a device is described in patent EP2245454B1 for measuring the electrical activity of a biological sample. It consists of an array of passive microelectrodes exhibiting characteristics of transparency and biocompatibility.

[0013] The microelectrode array is said to be passive in the sense that it comprises arrangements of microelectrode circuits used solely for the transduction of bioelectrical signals, i.e., without any other pretreatment. The materials used for the substrate and the microelectrode array are transparent polymers, which allows optical observation of the sample through said array.

[0014] However, such a network does not allow the transmission of an image of the activity The electrical activity produced by the sample is measured directly and simply. Indeed, it is difficult to correlate an output signal from an output contact with the electrically active part of the sample. To achieve this, the output contacts must be connected by a wire (or similar) and a routing plan must be developed to map each output contact to the position of the measuring electrode within the network.

[0015] There is therefore a need for a transparent interconnection device allowing simple and direct imaging of the electrical activity of the sample.

[0016] This need exists for the study of a sample of neuronal cells, and more broadly for the study of samples comprising at least one source capable of generating an electrical signal. Summary of the invention

[0017] The invention offers a solution to the problem mentioned above by proposing a transparent interconnection structure with a through-electrode structure allowing an output contact to be electrically connected to a single input contact while preserving the spatial information of the input contact, in particular its position relative to the other contacts.

[0018] A first aspect of the invention relates to an interconnection structure comprising: • a substrate formed of a first electrically insulating and optically transparent material, the substrate comprising a first face and a second opposite face, the first face defining a plane of the substrate; • a plurality of transparent electrodes; said interconnection structure being remarkable in that the transparent electrodes pass through the substrate from the first face to the second face of the substrate parallel to each other, and are electrically insulated from each other by the first electrically insulating and optically transparent material.

[0019] Thus, a plurality of transparent electrodes, called through-hole electrodes, pass through the substrate between the first and second faces, that is to say in the direction of its thickness, while being electrically insulated from each other by the substrate.

[0020] The ends of the through-hole electrodes form electrical contacts on or in the first and second faces of the substrate, capable of receiving or delivering a voltage. Each electrical contact on the first face is connected to a single electrical contact on the second face, while preserving the spatial information related to the electrical contact on the first face. Spatial information refers to the position of the contact relative to the other contacts on the face. In other words, two connected electrical contacts each occupy approximately the same area on their respective faces. same position relative to the other contacts. There is therefore a spatial correspondence between the electrical contacts of the first face and the electrical contacts of the second face of the substrate, which allows to transmit faithfully and directly, i.e. without resorting to processing, an external electronic device or a wired connection, an electrical image formed on the first face to the second face.

[0021] Furthermore, when the first face of the substrate is illuminated by an incident light wave in the visible range, it is possible to detect a transmitted light wave directly opposite the electrical contacts of the second face, without the structure of the electrodes or the substrate significantly interfering with the detection. Indeed, the electrodes and the substrate are optically transparent, that is to say, they have an optical transmission coefficient greater than 85% for at least one wavelength in the 400-800 nm spectral band.

[0022] The interconnection structure thus allows the simultaneous and superimposed transmission of an electrical image and a light wave transmitted through the substrate. In other words, the interconnection structure according to the invention makes it possible to combine optical and electrical imaging and, therefore, to benefit from their complementarity.

[0023] Advantageously, each transparent electrode comprises a first portion disposed on the first surface of the substrate.

[0024] The first portion makes it possible to obtain a compact electrode end, free from any cavity, void or hollow, these irregularities being able to degrade both the conductivity of the electrode and the quality of the electrical coupling of said electrode with a voltage source, typically a biological sample.

[0025] Thus, the first portion allows better electrical contact between the electrode and the voltage source.

[0026] Finally, the first portion allows the dimensions of the electrode to be extended laterally, so as to increase the electrical contact area and / or to adapt the electrical spatial resolution.

[0027] Advantageously, the first portion has dimensions between 6 pm and 55 pm in the plane of the substrate, and a thickness between 5 nm and 100 nm.

[0028] Thus, the spatial resolution is micrometric, for example on the order of 10 pm.

[0029] Advantageously, each transparent electrode further comprises a second portion disposed on the second face of the substrate opposite the first portion.

[0030] The second portion improves the conductivity of the electrode by providing a compact second electrode end, free of any cavities, voids, or hollows. The second portion also improves the electrical contact between the electrode and a voltage receiver, typically an electronic sensor or an electro-optical device.

[0031] Advantageously, the second portion has dimensions between 6 pm and 55 pm in a plane parallel to the plane of the substrate, and a thickness between 5 nm and 100 nm.

[0032] Advantageously, the transparent electrodes are symmetrical with respect to a plane parallel to the plane of the substrate.

[0033] This improves the fidelity of the electrical image transmitted by the interconnection structure. When the interconnection structure comprises a first and a second portion, these portions have identical cross-sections (in a plane parallel to the substrate). By identical cross-sections, we mean that the cross-section of the first portion and the cross-section of the second portion are of the same shape (circular, square, rectangular, hexagonal, etc.) and the same dimensions. Thus, there is a spatial correspondence, both in position and dimensions, between the electrical contacts of the first face and the electrical contacts of the second face.

[0034] Preferably, each transparent electrode comprises a hollow cylindrical portion extending from the first face to the second face of the substrate, the interconnection structure further comprising a transparent core disposed inside the hollow cylindrical portion of each transparent electrode.

[0035] Preferably, the hollow cylindrical portion has external dimensions in a plane parallel to the plane of the substrate between 5 pm and 50 pm, and comprises a wall of thickness between 5 nm and 100 nm.

[0036] In a first embodiment, the transparent core is formed of an electrically conductive and optically transparent material.

[0037] This feature optimizes the conductivity of the electrode while ensuring its transparency. In this first embodiment, the transparent core is part of the electrode.

[0038] In a second embodiment, the transparent core is formed of a second electrically insulating and optically transparent material.

[0039] This feature optimizes the transparency of the electrode while ensuring satisfactory conductivity. In this second embodiment, the transparent core is not part of the electrode.

[0040] The interconnection structure according to the first aspect of the invention may also have one or more of the following characteristics, considered individually or according to all technically possible combinations.

[0041] The first electrically insulating and optically transparent material can be a glass, a resin, an organo-mineral polymer or an expanded polystyrene.

[0042] The substrate may have a thickness between the first face and the second face of the substrate of between 50 pm and 300 pm.

[0043] The interconnection structure can thus exhibit sufficient mechanical rigidity to receive a biological sample encapsulated in a fluidic or micro-fluidic chamber.

[0044] The substrate may have dimensions between 2.5 cm and 10 cm in a plane parallel to the plane of the substrate.

[0045] Such a substrate makes it possible to obtain one or more large active surfaces, i.e. on the order of cm2. By active surface, we mean the surface covered by several transparent electrodes that pass through the surface of the substrate.

[0046] The transparent electrodes can be spaced from each other inside the substrate by an edge-to-edge distance of between 5 pm and 30 pm.

[0047] Thus the spatial resolution is micrometric.

[0048] Advantageously, the transparent electrodes are identical in size and shape and have in the plane of the substrate a first step of repetition in a first direction and a second step of repetition in a second direction secant to the first direction.

[0049] The first repetition step and the second repetition step may or may not be identical.

[0050] The transparent, through-hole electrodes thus form a matrix network, which facilitates the fabrication and use of the interconnection structure. For example, the interconnection structure is made directly compatible with matrix sensors.

[0051] The transparent electrodes can be formed from a transparent conductive polymer or a transparent conductive metal oxide such as tin dioxide.

[0052] Tin dioxide (SnO2) has a particular advantage in manufacturing because it is compatible with a conformal deposition method, which is not the case with a conductive and transparent material such as indium tin oxide (ITO).

[0053] A second aspect of the invention relates to a method for manufacturing an interconnection structure, comprising the following steps: • Provide a substrate formed of a first electrically insulating and optically transparent material, the substrate comprising a first face and a second opposite face, the first face defining a plane of the substrate; • Create a plurality of cavities in the substrate, called through cavities, passing through the substrate between the first and second faces of the substrate parallel to each other, and spaced apart from each other, • Form in the through cavities a plurality of transparent electrodes, said transparent electrodes passing through the substrate from the first face to the second face of the substrate parallel to each other, and being electrically insulated from each other by the first electrically insulating and optically transparent material.

[0054] Preferably, the step of forming the plurality of transparent electrodes comprises the following steps: • Deposit a first layer of electrically conductive and optically transparent material onto: • the internal surface of each of the through cavities, • the first face of the substrate, and • the second side of the substrate; • Fill the through cavities with a transparent material and form an excess of the transparent material on the first and second face of the substrate; • Remove the excess thickness of the transparent material as well as portions of the first layer of electrically conductive and optically transparent material deposited on the first and second faces of the substrate.

[0055] Preferably, the step of depositing the first layer of electrically conductive and optically transparent material is carried out using a conformal deposition method such as the atomic layer deposition (ALD) method.

[0056] Preferably, the transparent electrode formation step includes an additional step of forming, for each of the through-hole electrodes formed, a first portion of transparent electrode on the first face of the substrate and a second portion of transparent electrode on the second face of the substrate, said additional step comprising the following substeps: • deposit a second layer of electrically conductive and optically transparent material on the first and second faces of the substrate, • etch the second layer of electrically conductive and optically transparent material into regions of the first and second faces of the substrate, the regions being located around the transparent electrodes formed.

[0057] Advantageously, the step of deposition of the second layer of conductive and optically transparent material is carried out with a deposition method compatible with a transparent conductive oxide (TCO).

[0058] A third aspect of the invention is a sample analysis system comprising: • a light source producing a light wave, called the incident light wave, • an interconnection structure according to the first aspect of the invention, the first face of the substrate being disposed opposite the light source and being intended to receive a sample comprising at least one suitable source to produce an electrical signal, called the sample electrical signal, the sample electrical signal being transmitted from the first face of the substrate to the second face of the substrate by the through-hole electrode located opposite said source, • an electro-optical device positioned opposite the second face of the substrate, the electro-optical device having a plurality of control electrodes arranged opposite the plurality of through electrodes of the interconnection structure, each control electrode of the plurality of control electrodes being connected to a through electrode of the plurality of through electrodes, so that the electro-optical device modulates the light wave transmitted by the sample under the effect of the electrical signal of the sample.

[0059] According to a preferred embodiment of the third aspect of the invention, the electro-optical device is a liquid crystal cell.

[0060] It is thus possible to characterize the electrical activity of the sample indirectly by using the complementarity of optical and electrical imaging modes. This aspect of the invention is particularly advantageous for studying the electrical activity of cultured neuronal cells, and more generally for the development of organs-on-chips.

[0061] The invention and its various applications will be better understood by reading the following description and examining the accompanying figures. BRIEF DESCRIPTION OF THE FIGURES

[0062] The figures are presented for illustrative purposes only and are in no way limiting of the invention. • Fig. 1 schematically represents, in top view, a first embodiment of the interconnection structure; • Fig. 2 is a cross-sectional view of the interconnection structure according to the first embodiment; • Fig. 3 is a cross-sectional view of the interconnection structure according to a second embodiment; • Fig. 4 is a synoptic diagram illustrating the sequence of steps in the manufacturing process of the interconnection structure; • Fig. 5 is a synoptic diagram illustrating a preferred implementation method for the third step of the manufacturing process; • Fig. 6 is a synoptic diagram illustrating a preferred implementation method for the fourth sub-step of the third step of the manufacturing process; • Figures 7A to 7G show cross-sectional views of steps or sub-steps manufacturing of the interconnection structure; • Fig. 8 schematically represents a sample analysis system, including the interconnection structure; • Fig. 9 is an enlarged view of Fig. 8 centered on the interconnection structure in the analysis system and on a sample placed on the interconnection structure. DETAILED DESCRIPTION

[0063] The figures are presented for illustrative purposes only and are in no way limiting of the invention.

[0064] Unless otherwise specified, the same element appearing on different figures has a unique reference.

[0065] In the description, the term "optically transparent", or "transparent", refers to any material or element that has an optical transmission coefficient greater than 85% for at least one wavelength within the spectral band extending in the visible range, i.e. between 400 nm and 800 nm.

[0066] A first aspect of the invention relates to an optically transparent interconnection structure 1 comprising a plurality of through electrodes 20.

[0067] The interconnection structure 1 is for example intended to interface between a biological sample and an electronic or electro-optical device to image the electrical and / or optical activity of said sample.

[0068] The interconnection structure 1 is described with reference to Figures 1 to 3, which schematically represent, in top view and in section view, two embodiments of the interconnection structure 1. The top view ([Fig.1]) is common to both embodiments.

[0069] With reference to figures 1, 2 and 3, the interconnection structure 1 comprises an insulating and transparent substrate 10 having a first face 11 and a second face 12 opposite to the first face 11 and a plurality of transparent and through electrodes 20. The plane defined by the first face 11 of the substrate 10 shall be designated as the plane of the substrate.

[0070] The first and second faces 11, 12 of the substrate 10 are, in these particular embodiments, interchangeable because the interconnection structure 1 is symmetrical along a plane parallel to the plane of the substrate.

[0071] In the following description, these two faces will be distinguished solely by the fact that the first face 11 of the substrate 10 is intended to receive the sample, the second face 12 being intended to be connected to an electronic device or an electro-optical device.

[0072] The terms "lateral" or "laterally" refer to the X and Y axes as shown [Fig. 1], these X and Y axes defining the plane of the substrate. Furthermore, one The term "electrode cover area" or "active area" will refer to the area covered by the electrodes in the plane of the substrate.

[0073] Finally, the transparent and through electrodes 20 will be referred to more simply as through electrodes 20 or electrodes 20.

[0074] The substrate 10 has a thickness E between the first face 11 and the second face 12, and lateral dimensions L1 and L2. The lateral dimensions L1 and L2 can be between 2.5 cm and 10 cm, in order to obtain one or more active surfaces (corresponding to one or more groups of electrodes) on the order of cm². The thickness E of the substrate 10 (and the thickness of any other element of the interconnection structure, unless otherwise specified) is measured perpendicular to the plane of the substrate, along an axis Z shown in [Fig. 2] and 3.

[0075] The substrate 10 is formed of a first insulating and optically transparent material.

[0076] The substrate 10 is thus advantageously formed of a glass, a resin, a organo-mineral polymer such as polydimethylsiloxane (or PDMS), expanded polystyrene or any other material that is both insulating, optically transparent and offers sufficient mechanical rigidity to receive on the first face 11 a fluidic chamber allowing the sample to be kept in a liquid medium.

[0077] The thickness E of the substrate 10 is chosen to give the substrate 10 good mechanical rigidity. Good mechanical rigidity means that the substrate 10 does not deform when interacting with the sample. Depending on the material used, the thickness E of the substrate 10 can be between 50 µm and 300 µm.

[0078] For example, the substrate 10 is a glass of thickness E of 300 pm and of lateral dimensions L1 = L2 = 2.4 cm offering an active surface of up to 5.76 cm2.

[0079] The through-hole electrodes 20 are conductive and optically transparent areas. By conductive area, we mean an area formed of a conductive material capable of conducting, substantially without loss, voltages ranging from a few millivolts to a few microvolts. These orders of magnitude are typical of the voltages, known as evoked potentials, produced by biological samples such as neuronal cells. The through-hole electrodes 20 are formed of a material, polymer or oxide, that is both conductive and optically transparent, for example Poly(3,4-ethylenedioxythiophene) (or PEDOT), indium tin oxide (or ITO), tin dioxide (SnO2), zinc oxide (ZnO), or aluminum-doped zinc oxide (or AZO).

[0080] The through electrodes 20 pass through the substrate over its entire thickness E, from the first face 11 to the second face 12 of the substrate 10 and are separated from each other by the first insulating and optically transparent material of the substrate 10. The first insulating and optically transparent material of the substrate 10 coats (laterally) the through electrodes 20.

[0081] The through electrodes 20 extend parallel to each other, preferably in a direction substantially perpendicular to the plane of the substrate, and even more preferably along the Z axis. By substantially perpendicular direction, we mean perpendicular to a tolerance of a few degrees, for example 5 degrees (90° ±5°).

[0082] Inside the substrate 10, the distance D3 between two adjacent transparent electrodes 20, measured edge-to-edge, is preferably between 5 pm and 30 pm. In Figures 2 and 3, the distance D3 is measured along the X direction.

[0083] Figures 2 and 3 also show in schematic cross-sectional view an enlargement of a through electrode 20 according respectively to a first embodiment and a second embodiment of the interconnection structure 1.

[0084] Common to both of these embodiments, the through electrode 20 preferably comprises, in addition to an inner portion 23 extending from the first face 11 to the second face 12 of the substrate 10, a first portion 21 disposed on the first face 11 of the substrate 10.

[0085] The through electrode 20 can also include a second portion 22 disposed on the second face 12 of the substrate 10 opposite the first portion 21. In this case, the first portion 21 and the second portion 22 extend the inner portion 23 and form the ends of the electrode 20. The first portion 21 and the second portion 22 are in direct contact with the inner portion so as to ensure the electrical continuity of the electrode 20 from one face to the other of the substrate 10.

[0086] The first portion 21 is a thin layer of an electrically conductive and optically transparent material selected from among the electrically conductive and optically transparent materials mentioned above. It may be the same material or a different material from that forming the inner portion 23 of the through-hole electrode 20.

[0087] A thin film here refers to a layer with a thickness between 5 nm and 100 nm. Thus, the thickness el of the first portion 21 is between 5 nm and 100 nm.

[0088] Laterally, the first portion 21 advantageously extends beyond the inner portion 23 of the electrode 20 (inside the substrate 10), thus increasing the contact area of ​​the electrode 20 compared to an inner portion 23 alone. Preferably, the first portion 21 has lateral dimensions strictly greater than the lateral dimensions of the inner portion 23. Thus, the first portion 21 can have lateral dimensions ranging from 6 pm to 55 pm, while the lateral dimensions of the inner portion 23 can range from 5 pm to 50 pm. For example, in Figures 2 and 3, the first portion 21 occupies a circular area with a diameter e2 ranging from 6 pm to 55 pm, while the inner portion 23 of the electrode 20 has a diameter e3 ranging from 5 pm to 50 pm.

[0089] The first portion 21 may have, in the plane of the substrate 11, a circular or other shape section, for example a square, rectangular, hexagonal, etc.

[0090] By conforming to the inner portion 23, the first portion 21 fills any hollows, holes, or voids left on the surface of the inner portion 23 during electrode manufacturing. In this way, the first portion 21 contributes to creating a hollow-free through-hole electrode 20, thus offering improved electrical conductivity. Furthermore, the first portion 21 extends the electrical contact area while reducing surface irregularities. Electrical coupling with the sample is thereby improved.

[0091] The second portion 22 is similar to the first portion 21; the description, effects and advantages given for the first portion 21 therefore apply to the second portion 22. The conductive and optically transparent material chosen to form the second portion 22 may be the same or different from the material chosen to form the first portion 21.

[0092] The first portion 21 and the second portion 22 may have, in planes parallel to the plane of the substrate, identical or, on the contrary, different sections, for example circular, square, rectangular, hexagonal, etc.

[0093] Preferably, the electrode 20 is symmetrical with respect to a plane parallel to the plane of the substrate. The first portion 21 and the second portion 22 then have identical cross-sectional shapes and dimensions. Thus, the second portion 22 has the effect of making the electrical contacts (input and output) of the through-hole electrode 20 symmetrical. The advantage is that the interconnection structure 1 can thus transmit an electrical image applied to the first face 11 of the substrate to the second face 12 of the substrate 10 with improved spatial and electrical fidelity.

[0094] Preferably, the inner portion 23 of the through electrode 20 is a hollow cylindrical portion 231 and the interconnection structure 1 further comprises a transparent core 232 disposed inside the hollow cylindrical portion 231 of each through electrode 20.

[0095] The hollow cylindrical portion 231 comprises a wall made of a thin layer of an optically transparent and electrically conductive material, preferably selected from the optically transparent and electrically conductive materials mentioned above. Even more advantageously, the optically transparent and electrically conductive material forming the hollow cylindrical portion 231 is a transparent metal oxide such as SnO2. This material is advantageously the same as that used to make the first portion 21 and / or the second portion 22. The thickness e4 of the wall of the hollow cylindrical portion 232, measured in a plane parallel to the plane of the substrate, can be between 5 nm and 100 nm. The wall is connected to the first portion 21 and the second portion 22 so that the electrode is conductive. The cylindrical portion 231 can have a circular, hexagonal, rectangular, etc. cross-section.

[0096] In the first embodiment (see [Fig. 2]), the transparent core 232 is made of an electrically conductive and optically transparent material. Preferably, the transparent core 232 is made of a transparent polymer material, for example, PEDOT. Indeed, PEDOT is among the optically transparent materials exhibiting the best ionic and electronic conductivities. The conductivity of the through-hole electrode 20 is thus enhanced while preserving its transparency. This embodiment is particularly advantageous when the voltages involved are on the order of pV. In this first embodiment, the transparent core 232 is considered to be part of the through-hole electrode 20, which then consists of a maximum of four elements, these four elements being the first portion 21, the second portion 22, the hollow cylindrical portion 231, and the transparent core 232.

[0097] In the second embodiment (see [Fig. 3]), the transparent core 232 is formed of a second electrically insulating and optically transparent material. Preferably, the transparent core 232 is made of an optical-grade adhesive, for example Vitralit™ 6127, 6128 or equivalent, or an epoxy resin. These types of materials have a higher transmission coefficient than conductive polymer materials such as PEDOT. The transparency of the through-hole electrode 20 is thus enhanced while maintaining acceptable conductivity. This embodiment is particularly advantageous when the light waves transmitted through the interconnecting structure 1 have low luminance (less than 50 cd / m²).In this second embodiment, the transparent core 232 is considered not to be part of the through electrode 20, which then consists of a maximum of three elements, these three elements being the first portion 21, the second portion 22, and the hollow cylindrical portion 231.

[0098] According to alternative embodiments not shown, the electrode 20 comprises only the inner portion 23, or only the inner portion 23 and the first portion 21, or only the inner portion 23 and the second portion 22.

[0099] With reference to [Fig.1], the transparent electrodes 20 are advantageously distributed along the two directions of the plane of the substrate.

[0100] On the first face 11 and the second face 12 of the substrate 10, the transparent electrodes 20 are spaced in pairs by a distance Dl, measured edge-to-edge, of between 1 pm and 28 pm along the X direction, and by a distance D2, measured edge-to-edge, of between 1 pm and 28 pm along the Y direction. The distances Dl and D2 may be identical or different. The distances Dl and D2 are less than the distance D3 described previously because the first and second portions 21-22 have lateral dimensions greater than the lateral dimensions of the inner portion 23.

[0101] Advantageously the through electrodes 20 are all of identical shape and dimensions and have a first repetition step PI in the first direction (here along the X axis) and a second repetition step P2 in a second direction secant to the first direction (here along the Y axis perpendicular to the X axis).

[0102] Preferably, the repetition pitches PI and P2 are micrometer-sized, more precisely PI and P2 are between 7 pm and 83 pm. The through-hole electrodes 20 are thus preferably spaced regularly and arranged in rows and columns so as to form a high-density electrical matrix (> 400 electrodes per mm2) with micrometer-sized spatial resolution. Even more advantageously, the repetition pitches PI and P2 are identical, avoiding spatial distortion of the transmitted voltages.

[0103] The through electrodes 20 may not cover the entire surface of the substrate 10, and may be arranged in groups separated by portions of substrate 10, or may be arranged more or less densely depending on the regions of the substrate 10 (not shown).

[0104] A second aspect of the invention relates to a manufacturing method 400 of the interconnection structure 1.

[0105] Fig. 4 is a synoptic diagram illustrating the sequence of steps 401 to 403 of the manufacturing process 400 of the interconnection structure 1. These same steps 401 to 403 are illustrated by figures 7A to 7C, by means of schematic cross-sectional views of the interconnection structure 1.

[0106] With reference to [Fig.7A], the first step 401 consists of providing the substrate 10 formed from the first electrically insulating and optically transparent material.

[0107] The second step 402 is illustrated in [Fig.7B] and consists of providing in the substrate a plurality of cavities 30, called through cavities 30, passing through the substrate 10 between the first face 11 and the second face 12 of the substrate 10, the through cavities 30 being spaced from each other by a portion of the substrate 10.

[0108] The cavities are formed, for example, by mechanical action (drilling) with a high-pressure water jet, or by photolithography followed by etching (chemical or dry). The cavities can also be formed by molding, particularly when the substrate 10 is a polydimethylsiloxane (or PDMS) substrate.

[0109] The third step 403 consists of forming in the through cavities 30 the transparent electrodes 20, said transparent electrodes 20 passing through the substrate 10 from the first face 11 to the second face 12 of the substrate 10, and being electrically insulated from each other by the first electrically insulating and optically transparent material, precisely by the portion 14 of the substrate 10.

[0110] Preferably, the third step 403 comprises substeps 4031 to 4033. The sequence of these sub-steps is represented [Fig.5].

[0111] Figures 7C to 7E represent in schematic cross-sectional view these substeps 4031 to 4033.

[0112] With reference to [Fig.7C], the first substep 4031 of step 403 consists of depositing a first layer 40 of electrically conductive and optically transparent material onto: • the internal surface 31 of each of the through cavities 30, • the first face 11 of substrate 10, and • the second face 12 of substrate 10.

[0113] Preferably, the deposition is carried out using a conformal deposition technique such as atomic layer deposition (ALD). SnO2, ZnO, or AZO are examples of materials compatible with this type of deposition. Preferably, the electrically conductive and optically transparent material is therefore SnO2, ZnO, or AZO.

[0114] With reference to [Fig.7D], the second substep 4032 of step 403 consists of filling the through cavities 30 with a transparent material 50 and forming an overthickness 51 of the transparent material 50 on the first 11 and the second face 12 of the substrate.

[0115] The transparent material can be conductive or insulating. Examples of materials have been given previously in relation to Figures 1 and 2.

[0116] The filling of the cavities 30 with the transparent material 50 can be achieved by capillary action or by suction. For example, the material 50 is dispensed onto the substrate 10, and a static pressure difference, due to the capillarity of the material 50 in the cavities 30 or to pumping (using a pump), allows the cavities 30 to be filled. Another filling method consists of depositing the substrate 10 onto a bath of transparent material 50 in an oven, and then placing the oven under vacuum and subsequently at atmospheric pressure. The filling of the cavities 30 with the transparent material 50 can also be achieved by screen printing or by localized deposition of droplets of the transparent material 50 onto the cavities 30 using inkjet or spray technology.

[0117] With reference to [Fig.7E], the third substep 4033 of step 403 consists of removing the excess thickness 51 of the transparent material 50 as well as the first layer 40 of electrically conductive and optically transparent material deposited on the first and second face 11-12 of the substrate 10.

[0118] This removal can be accomplished by etching, for example by reactive ion etching (RIE) or by ion beam etching (IBE), or by chemical mechanical polishing (or CMP).

[0119] At the end of substep 4033, a plurality of transparent and tra- electrodes slopes 20 were made in the transparent and insulating substrate 10. Each electrode 20 comprises, inside the substrate, the hollow cylindrical portion 231 (formed by the remaining portion of the first layer 40) and the transparent core 232 disposed inside the hollow cylindrical portion 231 (formed by the material 50).

[0120] With reference to [Fig.4], step 403 of forming the transparent through-hole electrodes 20 may also include an additional substep 4034, or fourth substep 4034, of forming, for each of the through-hole electrodes 20 formed, a first portion of transparent electrode 21 on the first face 11 of the substrate 10 and a second portion of transparent electrode 22 on the second face 12 of the substrate 10.

[0121] Substep 4034 comprises operations 4034a and 4034b, the sequence of which is shown [Fig.6].

[0122] The first operation 4034a, illustrated by [Fig.7F], consists of depositing a second layer 41 of electrically conductive and optically transparent material on the first face 11 and the second face 12 of the substrate 10. The electrically conductive and optically transparent material forming the second layer 41 is advantageously SnO2, but can be any type of conductive and optically transparent material (ITO, SnO2, ZnO, AZO, etc.).

[0123] The second sub-substep 4034b is shown [Fig.7G].

[0124] The second operation 4034b of substep 4034, represented by [Fig.7G], consists of etching the second layer 41 of electrically conductive and optically transparent material into regions 60 of the first and second faces 11-12 of the substrate, the regions 60 being located around the transparent electrodes 20.

[0125] At the end of substep 4034, the through electrodes 20 comprise, in addition to the inner portion 23 produced in the preceding substeps 4031 and 4032, the first portion 21 and the second portion 22.

[0126] These two portions allow for the filling of surface irregularities after the deposition substep 1032 and / or the removal substep 4033, such as hollows or voids forming on the first and second faces 11, 12 of the substrate 10. These irregularities are due to a capillary effect and are observed in particular when the cavities have a high aspect ratio. This is notably the case when the substrate has a thickness E of 300 pm and the cavities have micrometric lateral dimensions.

[0127] A third aspect of the invention relates to a sample analysis system, this system comprising the interconnection structure 1 described above. Figure 8 schematically represents an embodiment of this analysis system 8, ready to analyze a sample 82.

[0128] Sample 82 may be a biological sample that one wishes to characterize. It may consist of biological particles in a culture medium or in a liquid bodily. By biological particle, we mean a cell, a bacterium or other microorganism with a size between 1 pm and 500 pm.

[0129] Sample 82 is, for example, neuronal cells 821, or neurons, in a culture medium 822. Such cells are generally between 15 µm and 120 µm in size. They behave as electrical sources capable of producing an electrical signal, called the evoked potential or electrical signal Vin of sample 82. The electrical signal Vin of sample 82 is on the order of mV or pV.

[0130] System 8 is thus intended to perform imaging of the electrical activity of neurons with a spatial resolution at the scale of a neuron and a field of view on the order of cm². System 8 can therefore be used to understand certain neurodegenerative diseases such as Parkinson's or Alzheimer's by allowing real-time visualization of neuronal electrical activity and by allowing the parallel monitoring of the effect of several treatments on this electrical activity.

[0131] The system 8 comprises a light source 80, the interconnection structure 1, and an electro-optical device 81.

[0132] Fig. 9 schematically represents an enlarged view of the interconnection structure 1 in the system 8 and the sample 82 arranged on the interconnection structure 1.

[0133] The light source 80 is capable of producing a light wave 01, called incident light wave 01, in the direction of the sample 82, along a propagation direction Zo.

[0134] The light source 80 emits in the spectral band extending between 400 nm and 800 nm, known as the visible band. In the case where the light source comprises several elementary sources of the light-emitting diode (LED) or laser diode type, the elementary sources emit preferentially in the same visible band.

[0135] The light source 82 may include a diaphragm, a filter, or a diffuser (not shown).

[0136] The light source 82 may include a polarizer (not shown).

[0137] The interconnection structure 1 is arranged opposite the light source 80.

[0138] The sample 82 is disposed on the first face 11 of the substrate 10 of the structure interconnection 1.

[0139] With reference to [Fig. 8], the sample 82 is more particularly arranged in a 2D layer of neurons 821 on the first face 11 of the substrate 10. The neurons 821 are further arranged in the volume 823 of a fluidic chamber 824, the volume 823 of the fluidic chamber 824 being filled with a liquid, or culture medium 822, circulating or not, which allows the neurons 821 to be cultured. The fluidic chamber 824 is made of an optically transparent material, for example, polydimethyl- siloxane or PDMS. It preferably has micrometric dimensions so that the interconnection structure 1 can accommodate several fluidic chambers.

[0140] The interconnection structure 1 is sufficiently rigid to receive the sample 82.

[0141] The electro-optical device 81 is arranged opposite the second face 12 of the substrate 10 of the interconnection structure 1.

[0142] By electro-optical device is meant an optical device comprising at least one signal-controlled element having an electro-optical effect, this signal-controlled element being used to modulate a beam of light passing through the device 81.

[0143] With reference to [Fig.9], the electro-optical device 81 may include an interface film 811, for example a layer of polyamide, disposed between the interconnection structure 1 and the signal-controlled element 813 exhibiting an electro-optical effect.

[0144] The signal-controlled element 813 exhibiting an electro-optical effect is preferably a liquid crystal. A liquid crystal has the property of modulating the polarization of the light passing through it under the effect of an electrical signal applied to it via a control electrode.

[0145] In the embodiment shown in Figures 8 and 9, the electro-optical device 81 is a liquid crystal cell 812 whose control electrodes 814 are arranged opposite the through-hole electrodes 20 of the interconnection structure 1. Each liquid crystal 813 of the liquid crystal cell 812 is controlled by the electrical signal Vin emitted by a cell 821 of the sample 82 and transmitted by the interconnection structure 1. Under the effect of this electrical signal Vin, the liquid crystal 813 locally modulates the light wave transmitted O2 by the sample and by the interconnection structure 1. The locally modulated light wave O3 contains the information of the electrical activity of the sample 82.

[0146] A light analyzer comprising an image sensor and a polarizer (not shown) can be used to record the image of the light wave transmitted and modulated O3 by the system 8.

[0147] The electrical signal Vin of the sample is transmitted directly and faithfully, that is to say respecting the spatial distribution of said electrical signal, through the interconnection structure 1, thanks to the through electrodes 20 of the interconnection structure 1.

Claims

Demands

1. Interconnection structure (1) comprising: - a substrate (10) formed of a first electrically insulating and optically transparent material, the substrate (10) comprising a first face (11) and a second opposite face (12), the first face (11) defining a plane of the substrate; - a plurality of transparent electrodes (20); said interconnection structure (1) being characterized in that the transparent electrodes (20) pass through the substrate (10) from the first face (11) to the second face (12) of the substrate (10) parallel to each other, and are electrically insulated from each other by the first electrically insulating and optically transparent material.

2. Interconnection structure (1) according to claim 1, wherein each transparent electrode (20) comprises a first portion (21) disposed on the first face (11) of the substrate (10).

3. Interconnection structure (1) according to claim 2, wherein each transparent electrode (20) further comprises a second portion (22) disposed on the second face (12) of the substrate (10) opposite the first portion (21).

4. Interconnection structure (1) according to claim 3, wherein the transparent electrodes (20) are symmetrical with respect to a plane parallel to the plane of the substrate.

5. Interconnection structure (1) according to any one of claims 1 to 4, wherein each transparent electrode (20) comprises a hollow cylindrical portion (231) extending from the first face (11) to the second face (12) of the substrate (10), the interconnection structure (1) further comprising a transparent core (232) disposed inside the hollow cylindrical portion (231) of each transparent electrode (20).

6. Interconnection structure (1) according to claim 5, wherein the transparent core (232) is formed of an electrically conductive and optically transparent material.

7. Interconnection structure (1) according to claim 5, wherein the transparent core (232) is formed of a second electrically insulating and optically transparent material.

8. Interconnection structure (1) according to any one of claims 5 to 7, wherein the hollow cylindrical portion (231) has external dimensions in a plane parallel to the plane of the substrate between 5 pm and 50 pm, and comprises a wall of thickness (e4) between 5 nm and 100 nm.

9. Interconnection structure (1) according to any one of claims 1 to 8, wherein the substrate (10) has between the first face (11) and the second face (12) of the substrate (10) a thickness (E) of between 50 pm and 300 pm.

10. Interconnection structure (1) according to any one of claims 1 to 9, wherein the transparent electrodes (20) are spaced apart from each other inside the substrate (10) by an edge-to-edge distance (D3) of between 5 pm and 30 pm.

11. Interconnection structure (1) according to any one of claims 1 to 10, wherein the transparent electrodes (20) are identical in size and shape and have in the plane of the substrate a first repeating step (PI) in a first direction (X) and a second repeating step (P2) in a second direction (Y) secant to the first direction (X).

12. Interconnection structure (1) according to any one of claims 1 to 11, wherein the transparent electrodes (20) are formed of a transparent conductive polymer or a transparent conductive metal oxide such as tin dioxide.

13. A method (400) for manufacturing an interconnect structure (1) comprising the following steps: - Providing (401) a substrate (10) formed of a first electrically insulating and optically transparent material, the substrate (10) comprising a first face (11) and a second opposite face (12), the first face (11) defining a plane of the substrate; - Providing (402) in the substrate (10) a plurality of cavities (30), called through-holes, passing through the substrate (10) between the first face (11) and the second face (12) of the substrate (10) parallel to each other, and being spaced apart from each other; - Forming (403) in the through-holes (30) a plurality of transparent electrodes (20), said trans- parent (20) passing through the substrate (10) from the first face (11) to the second face (12) of the substrate (10) parallel to each other, and being electrically insulated from each other by the first electrically insulating and optically transparent material.

14. A method (400) for manufacturing an interconnection structure (1) according to claim 13, wherein the step of forming (403) the plurality of transparent electrodes (20) comprises the following steps: - Deposit (4031) a first layer (40) of electrically conductive and optically transparent material on: • the internal surface (31) of each of the through cavities (30), • the first face (11) of the substrate (10), and • the second face (12) of the substrate (10); - Fill (4032) the through cavities (30) with a transparent material (50) and form an overthickness (51) of the transparent material (50) on the first (11) and second face (12) of the substrate (10); - Remove (4033) the excess thickness (51) of the transparent material (50) as well as portions of the first layer (40) of electrically conductive and optically transparent material deposited on the first face (11) and the second face (12) of the substrate (10).

15. A method (400) for manufacturing an interconnection structure (1) according to claim 14, wherein the step of forming (403) the transparent electrodes (20) comprises an additional step (4034) of forming, for each of the through-hole electrodes (20) formed, a first portion (21) of transparent electrode on the first face (11) of the substrate (12) and a second portion (22) of transparent electrode on the second face (12) of the substrate (10), said additional step (4034) comprising the following substeps: - deposit (4034a) a second layer (41) of electrically conductive and optically transparent material on the first face (11) and the second face (12) of the substrate (10), - etch (4034b) the second layer (41) of electrically conductive and optically transparent material in regions (60) of the first (11) and second face (12) of the substrate (10), the regions (60) being located around the transparent electrodes (20) formed.

16. A sample analysis system (8) comprising: - a light source (80) producing a light wave (01), referred to as the incident light wave (01), - an interconnection structure (1) according to any one of claims 1 to 12, the first face (11) of the substrate (10) being disposed opposite the light source (80) and being intended to receive a sample (82) comprising at least one source (821) capable of producing an electrical signal (Vin), referred to as the sample electrical signal (Vin), the sample electrical signal (Vin) (82) being transmitted from the first face (11) of the substrate (10) to the second face (12) of the substrate (10) by the through-hole electrode (20) located opposite said source (821), - an electro-optical device (81) disposed opposite the second face (12) of the substrate (10),the electro-optical device (81) having a plurality of control electrodes (814) arranged opposite the plurality of through electrodes (20) of the interconnection structure (1), each control electrode (814) of the plurality of control electrodes (814) being connected to a through electrode (20) of the plurality of through electrodes (20), so that the electro-optical device (81) modulates the light wave transmitted (02) by the sample (82) under the effect of the electrical signal of the sample (Vin).

17. Analysis system according to claim 16, wherein the electro-optical device (81) is a liquid crystal cell (812).

Images