Tunable unit cell array for reconfigurable antenna and associated manufacturing method

Abstract

Title: Tunable unit cell array for reconfigurable antenna and associated manufacturing method The invention relates to a reconfigurable phased array antenna, intended to operate in sub-terahertz frequency bands, and more particularly to a tunable unit cell array for a reconfigurable antenna and its manufacturing method. The array of radiating elements excited by signals with controllable phase shift (in a set of discrete values) 1 comprises: • a first substrate 11 based on fused silica or quartz, • at least one tile 12 resulting from a cut in a second substrate 21 based on fused silica or quartz, each tile being fixed to the first substrate to form a tunable unit cell 10 of the array, each cell comprising at least one phase change material switch 101.The invention finds application in medical and industrial control imaging, Earth and deep space observation, and for radars and broadband telecommunications systems. Figure for abstract: Fig. 1.

Description

Title of the invention: Tunable unit cell array for reconfigurable antenna and associated manufacturing method Technical field

[0001] The present invention relates to an antenna array intended to operate in sub-terahertz frequency bands, for example of the order of one or several hundred gigahertz. The present invention relates more particularly to a reconfigurable antenna array and its manufacturing method. The invention finds application, for example, in medical and industrial control imaging, Earth and deep space observation, as well as for radars and broadband telecommunications systems. STATE OF THE ART

[0002] A reconfigurable antenna is an antenna capable of changing its frequency and radiation properties dynamically, in a controlled and reversible manner. In order to provide a dynamic response, reconfigurable antennas may incorporate actuators (such as phase-change material-based radio frequency (RF) switches, varactors, mechanical actuators or tunable materials) that allow the intentional redistribution of RF currents over the surface of the antenna and produce reversible changes in its properties; these are sometimes referred to as phased array antennas. The reconfigurability of reconfigurable antennas, including antenna arrays, is used to maximize antenna performance in a changing scenario or to meet changing operating requirements.

[0003] A reconfigurable antenna array is made up of the association of a set of reconfigurable unit radiating elements which correspond to an array of tunable unit cells arranged according to a particular geometry, in the same frequency band in order to produce a reconfigurable radiation pattern. A unit cell may be made up of a substrate with low RF losses. A metal ground plane is deposited on one side of this substrate and a radiating metal patch or element is deposited on the other side. A second substrate may be assembled on the radiating metal element in order to improve its performance. A third metal layer may also be deposited on this second substrate in order to further improve the performance of the radiating element. This metal layer may itself comprise one or more secondary radiating elements excited by coupling by the first radiating element and behaves as a structure with superimposed patch antennas and allows to improve the frequency band and the scanning range of the beam radiated by the array.

[0004] Most reconfigurable antennas are obtained today by implementing manufacturing processes which consist of transferring a first wafer comprising actuators onto at least a second wafer or wafer comprising cells based on a low RF loss material. This type of reconfigurable antenna is obtained today by implementing manufacturing processes which consist of manufacturing unitary tunable radiating elements with RF switches on a first wafer and transferring a second entire substrate with elements allowing the improvement of the overall performance of the antenna. The unitary tunable element is thus made up of the stack of 2 substrates made of low RF loss material with three metallization levels (one on each side of the stack and one between the two substrates).

[0005] For example, the scientific paper by P. Pahlavan et al., titled "Metamaterial Based Compact Patch Antenna Array for Antenna-in-Package Solutions in Frequency Handover Applications," and published in 2023 IEEE 73rd Electronic Components and Technology Conference (ECTC), Orlando, FL, USA, 2023, pp. 475-480 (doi: 10.1109 / ECTC51909.2023.00085) discloses an antenna cell array of dimensions 2x2: a. made from: i. a first slice (or wafer) based on fused silica, having a thickness of 330 microns and ii. a second wafer based on fused silica, having a thickness of 180 microns assembled to the first wafer, and b. further comprising three levels of metallization, one to constitute a power supply line, one to constitute a connection plug, or patch, per cell and one to constitute a ground plane, the latter serving as an interface between the two wafers.

[0006] The antenna proposed in this scientific document has the advantages of: a. avoiding problems linked to different thermal expansion coefficients between the slices to be assembled, due to the fact that they have the same basic composition, namely fused silica, b. avoiding having to form interconnection vias through the fused silica of each of the two slices, which again could have posed manufacturing problems, particularly in terms of thermal balance.

[0007] On the other hand, the solution proposed in this scientific document presents, like many other manufacturing methods, the disadvantage of involving the handling of two relatively thin slices, for slice diameters of 100 mm, of which result from assembly difficulties and the risk of damaging at least one of the two slices.

[0008] An objective of the present invention is to overcome at least one of the drawbacks of the prior art, preferably while retaining the advantages that it presents. SUMMARY

[0009] To achieve this objective, according to a first aspect of the invention, there is provided a tunable unit cell array for a reconfigurable antenna, comprising: a. a first substrate based on one or other of fused silica, quartz and a glass having a loss tangent of less than 0.005 at frequencies above 100 GHz, b.at least two tiles cut from at least one second substrate based on one or other of fused silica, quartz and a glass having a loss tangent of less than 0.005 at frequencies above 100 GHz, said at least two tiles being fixed to the first substrate to form at least two unit cells of the tunable unit cell array, each tunable unit cell comprising at least one phase change material switch comprised by, or formed in, or located in, the first substrate or at least one of said at least two tiles and each tile may have a different thickness.

[0010] According to a second aspect of the invention, a method of manufacturing a tunable unit cell array for a reconfigurable antenna is provided, comprising: a. providing a first substrate based on one of fused silica, quartz and a glass having a loss tangent of less than 0.005 at frequencies above 100 GHz, and comprising an array of phase change material switches, b. providing a second substrate based on one of fused silica, quartz and a glass having a loss tangent of less than 0.005 at frequencies above 100 GHz, c. cutting at least two first tiles from one of the first substrate and the second substrate, d. transferring said at least two first blocks onto the other of the first substrate and the second substrate, such that each first tile forms with the part of the substrate on which it is transferred at least one tunable unit cell of the network of tunable unit cells.

[0011] The invention according to each of its different aspects can thus consist of a first substrate on which is fixed in pieces, or equivalently in blocks, a second substrate from which the pieces or blocks have been cut. This advantageously avoids having to transfer a large substrate (larger than 50 mm) onto another substrate of equivalent dimensions, thus relaxing the flatness constraints of the assembly surfaces and / or reducing the risk of breakage of the substrates during their handling and / or their manufacture when they are subjected to thermomechanical constraints. BRIEF DESCRIPTION OF THE FIGURES

[0012] The aims, objects, as well as the characteristics and advantages of the invention will emerge more clearly from the detailed description of an embodiment thereof which is illustrated by the following accompanying drawings in which:

[0013] [Fig.l] [Fig.l] schematically represents a partial sectional view of an array of tunable unit cells according to a first embodiment of the first aspect of the invention.

[0014] [Fig.2] [Fig.2] schematically represents a perspective view of a network of tunable unit cells according to the first aspect of the invention.

[0015] [Fig.3] Figures 3 to 10 schematically represent partial sectional views illustrating a first mode of implementation of the second aspect of the invention.

[0016] [Fig.4]

[0017] [Fig.5]

[0018] [Fig.6]

[0019] [Fig.7]

[0020] [Fig.8]

[0021] [Fig.9]

[0022] [Fig. 10]

[0023] [Fig. 11] Figures 11, 12 and 13, 14 and 15 schematically represent partial sectional views illustrating, respectively, three alternative embodiments of the first aspect of the invention and of implementation of the second aspect of the invention relative to those illustrated in [Fig. 10].

[0024] [Fig. 12]

[0025] [Fig.13]

[0026] [Fig. 14]

[0027] [Fig.15]

[0028] [Fig. 16] Figures 16 to 19 schematically represent partial sectional views illustrating a second embodiment of the second aspect of the invention.

[0029] [Fig. 17]

[0030] [Fig. 18]

[0031] [Fig. 19]

[0032] [Fig.20] Figures 20 and 21 schematically represent partial sectional views illustrating, respectively, another alternative embodiment of the first aspect of the invention and implementation of the second aspect of the invention.

[0033] [Fig.21]

[0034] [Fig.22] Figures 22 and 23 schematically represent partial sectional views illustrating, respectively, a first variant relative to that illustrated in Figures 20 and 21.

[0035] [Fig.23]

[0036] [Fig.24] Figures 24 and 25 schematically represent partial sectional views illustrating, respectively, a second variant relative to that illustrated in Figures 20 and 21.

[0037] [Fig.25]

[0038] The drawings are given as examples and are not limiting of the invention. They constitute schematic representations of principle intended to facilitate the understanding of the invention and are not necessarily on the scale of practical applications. In particular, the relative thicknesses of different layers illustrated are not necessarily representative of reality. DETAILED DESCRIPTION

[0039] Before beginning a detailed review of embodiments of the invention, optional features which may possibly be used in combination or alternatively are set out below:

[0040] According to an example of the first aspect of the invention, the first substrate has a characteristic transverse dimension greater than or equal to 100 mm, or even greater than or equal to 200 mm, and / or said at least two blocks cut from the second substrate each have a characteristic transverse dimension greater than or equal to 200 μm and strictly less than 50 mm, preferably less than 5 mm.

[0041] According to an example of the first aspect of the invention, the cutting of said at least two first blocks comprises a cutting, for example by laser or by saw, in the thickness of the substrate concerned.

[0042] According to an example of the first aspect of the invention, the phase change material switch is at least partly encapsulated in silicon oxide.

[0043] According to an example of the first aspect of the invention, at least four, preferably at least sixteen, tiles are attached to the first substrate so as to give the array of tunable unit cells the shape of a two-dimensional matrix of tunable unit cells.

[0044] According to an example of the first aspect of the invention, at least one pad comprises a primary layer based on one or other of fused silica, quartz and a glass having a loss tangent of less than 0.005 at frequencies above 100 GHz, and a pattern or structuring of a metallic layer and / or a radiating element (for example a patch antenna) on the face of the primary layer which is opposite that by which said primary layer is fixed to the first substrate.

[0045] According to an example of the first aspect of the invention, at least one tile is fixed to the first substrate by means of a layer of glue.

[0046] According to an example of the first aspect of the invention, at least one pad is fixed to the first substrate by thermocompression of a metal layer deposited on said at least one pad with metal layer deposited on the first substrate.

[0047] According to an example of the first aspect of the invention, at least one pad is fixed to the first substrate by reflowing metal balls, for example gold-based, deposited beforehand on at least one of a metal layer deposited on said at least one pad and a metal layer deposited on the first substrate.

[0048] According to any one of the three preceding examples of the first aspect of the invention, the phase change material switch is comprised by, or formed in, or located in, the first substrate.

[0049] According to an example of the first aspect of the invention, at least one block is fixed to the first substrate by hybrid bonding, said at least one block and the first substrate having, at the level of the fixing of said at least one block on the first substrate, surface structures substantially overlapping each other.

[0050] According to an alternative example to the previous one, at least one block is fixed to the first substrate by reflowing metal balls, for example gold-based, deposited beforehand on at least one of a metallization layer deposited on said at least one block and a metallization layer deposited on the first substrate, said at least one block and the first substrate having, at the level of the fixing of said at least one block on the first substrate, surface structures substantially overlapping each other.

[0051] According to either of the two preceding examples, the phase change material switch is comprised by, or located in, or formed in said at least one pad.

[0052] According to the seven examples above, the network of tunable unit cells according to the first aspect of the invention can advantageously take as many configurations as there are ways of fixing each tile to the first substrate. These ways being at least four in number, these are four fixing configurations, and therefore four embodiments of each tunable unit cell, which are conceivable for each of the tiles fixed to the first substrate. This makes it possible to choose the fixing configuration most compatible with the thermal budget that the pavers and the first substrate can support.

[0053] According to an example of the first aspect of the invention, the network of tunable unit cells comprises tiles of different thicknesses. It is thus possible to advantageously modulate the focusing of the beam transmitted or reflected by the network of tunable unit cells.

[0054] According to an example of the first aspect of the invention, the tunable unit cell array further comprises, connected to each phase change material switch, a thermal actuation guide, for example of an optical or electrical nature. According to an example, the manufacturing of the thermal actuation guide may be carried out during the manufacturing of the one of said at least one pad and the first substrate comprising the phase change material switch.

[0055] According to an example of the first aspect of the invention, the thermal actuation guide, like the phase change material switch, is at least partly encapsulated in silicon oxide.

[0056] According to an example of the first aspect of the invention, the tunable unit cell array further comprises, for each phase change material switch, a metallization level forming an interconnection RF line and / or a radiating element (e.g. a patch antenna), of the phase change material switch. According to this example, the tunable unit cell array does not require an additional level of interconnections, which makes it possible to save at least one metal level.

[0057] According to an example of the first aspect of the invention, the metallization level, like the phase change material switch, is at least partly encapsulated in silicon oxide.

[0058] According to an example of the first aspect of the invention, the tunable unit cell array is silicon-free. This limits radiofrequency radiation losses.

[0059] According to another example of the first aspect of the invention, the tunable unit cell array may comprise at least one level of metal interconnections between said at least two tiles and the first substrate, which is accessible without etching the material constituting said at least two tiles and / or the first substrate to ensure an electrical connection between said at least two tiles and the first substrate at their fixing interface. In other words, the tunable unit cell array is advantageously free of vias through the material from which said at least two tiles and / or the first substrate are made. This avoids difficulties in respecting the thermal budget during manufacturing, low temperature processes being less good, and / or this avoids bonding with metallic continuity on several levels which requires additional steps and increases the cost, while increasing the risk of breakage.

[0060] According to another example of the first aspect of the invention, said at least two blocks and the first substrate are made from the same material chosen from fused silica, quartz and a glass having a loss tangent of less than 0.005 at frequencies above 100 GHz. According to this example, the thermal expansion coefficients of said at least one block and the first substrate are of the same value, which advantageously limits the thermomechanical constraints during the manufacture of the tunable unit cell array.

[0061] According to an example of the second aspect of the invention, the cutting of said at least two first blocks comprises a cutting, for example by laser or by saw, in the thickness of the substrate concerned.

[0062] According to an example of the second aspect of the invention, each first tile forms with the part of the substrate on which it is transferred a single tunable unit cell of the network of tunable unit cells.

[0063] According to an example of the second aspect of the invention, each of the first substrate and the second substrate has a characteristic transverse dimension greater than or equal to 100 mm, or even greater than or equal to 200 mm, and / or said at least two blocks each have a characteristic transverse dimension greater than or equal to 200 μm and strictly less than 50 mm, preferably less than 5 mm.

[0064] According to an example of the second aspect of the invention, each phase change material switch is intended to form in part a tunable unit cell.

[0065] According to an example of the second aspect of the invention, the first substrate and the second substrate are based on the same material.

[0066] According to an example of the second aspect of the invention, at least four, preferably at least sixteen, tiles are cut and then transferred, so that the tiles form, with the parts of the substrate on which they are transferred, an array of tunable unit cells taking the form of a matrix of tunable unit cells.

[0067] According to an example of the second aspect of the invention, the method comprises providing at least one third substrate, cutting at least one third tile from the third substrate and transferring said at least one third tile onto the substrate onto which said at least two first tiles have been transferred, the third substrate preferably having a thickness different from the substrate from which said at least two first tiles have been cut. Thus, the tiles may come from different substrates, and the latter may for example have thicknesses different from each other, so that the tiles cut from them can be transferred onto the same substrate to form tunable unit cells of different thicknesses in the same network of tunable unit cells.

[0068] According to an example of the second aspect of the invention, the provision of the first substrate comprises: a. the provision of a silicon-based growth substrate, b. the formation of phase change material switches on the growth substrate, c. the formation of thermal actuation guides of phase change material switches, d. the formation of a metallization level intended to form interconnection lines and / or radiating elements (for example patch antennas) of each phase change material switch, and e. the transfer of a first layer based on one or other of fused silica, quartz and a glass having a loss tangent of less than 0.005 at frequencies above 100 GHz, f. where appropriate, the formation of a ground plane on said layer based on one or other of fused silica, quartz and a glass having a loss tangent of less than 0.005 at frequencies above 100 GHz, then, g. removing the growth substrate by grinding, each phase change material switch, each thermal actuation guide and each interconnection line or radiating element being at least partly encapsulated in silicon oxide. It is thus possible to provide the first substrate using conventional manufacturing processes in microelectronics, and in particular in CMOS (Complementary Metal Oxide Semiconductor) foundries.

[0069] According to an example of the second aspect of the invention, the transfer of said first layer is carried out by means of a layer of silicon oxide.

[0070] According to an example of the second aspect of the invention, the method further comprises, after grinding the growth substrate, at least one step of opening, for example by etching, a layer of silicon oxide at right angles to an interconnection line of the radiating metal element.

[0071] According to an example of the second aspect of the invention, the provision of the second substrate comprises: a. providing a support substrate based on any of fused silica, quartz and glass having a loss tangent of less than 0.005 at frequencies above 100 GHz, and b. the formation, on the support substrate, of a metallic layer, and c. etching the metal layer to form patterns or structures for each tunable unit cell to be formed, and wherein the cutting step relates to the second substrate and consists of cutting tiles from the second substrate by rotating around each pattern or structure.

[0072] According to an example of the second aspect of the invention, the transfer of at least one first block is carried out by means of a layer of glue.

[0073] According to an example of the second aspect of the invention, the transfer of at least one first block is carried out by thermocompression of a metal layer of said at least one block with a metal layer of the first substrate.

[0074] According to an example of the second aspect of the invention, the transfer of at least one first block is carried out by remelting metal balls, for example based on gold, deposited beforehand on at least one of a metal layer of said at least one block and a metal layer of the first substrate.

[0075] According to any one of the three preceding examples, the cutting of said at least two first blocks is carried out in the second substrate.

[0076] According to an example of the second aspect of the invention, the transfer of at least one first block is carried out by hybrid bonding, said at least one block and the first substrate having, at the level of the fixing of said at least one first block on the first substrate, surface structures substantially superimposing each other.

[0077] According to an example of the second aspect of the invention, the transfer of at least one first block is carried out by remelting metal balls, for example based on gold, deposited beforehand on at least one of a metal layer of said at least one block and a metal layer of the first substrate, said at least one block and the first substrate having, at the level of the fixing of said at least one block on the first substrate, surface structures substantially superimposing themselves on each other.

[0078] According to any one of the two preceding examples, the cutting of said at least two first blocks is carried out in the first substrate.

[0079] A film or layer based on a material A is understood to mean a film or layer comprising this material A and possibly other materials.

[0080] A parameter "substantially equal / greater / less than" a given value means that this parameter is equal / greater / less than the given value, plus or minus 20%, or even 10%, of this value. A parameter "substantially between" two given values means that this parameter is at least equal to the smallest given value, plus or minus 20%, or even 10%, near this value, and at most equal to the largest given value, plus or minus 20%, or even 10%, near this value.

[0081] It is specified that, in the context of the present invention, the terms "on", "surmounts", "overhangs", "covers", "underlies" and their equivalents do not necessarily mean "in contact with". Thus, for example, the transfer, application or deposition of a first layer on a second layer does not necessarily mean that the two layers are directly in contact with each other, but means that the first layer at least partially covers the second layer by being either directly in contact with it, or by being separated from it by at least one other layer or at least one other element.

[0082] Unless otherwise specified, when referring to two elements connected to each other, this means directly connected without intermediate elements other than conductors, and when referring to two elements connected (in English "coupled") to each other, this means that these two elements can be connected or be linked by means of one or more other elements or by electromagnetic coupling without being directly connected.

[0083] Generally speaking, phase change materials are materials capable of alternating, under the effect of a temperature variation, between a crystalline phase and an amorphous phase, the amorphous phase having an electrical resistance greater than that of the crystalline phase.

[0084] In the following description, the thicknesses of substrate, film or layer are generally measured in directions perpendicular to the main extension plane of the substrate, film or layer.

[0085] A first embodiment of the tunable unit cell array 1 according to the first aspect of the invention is described below with reference to [Fig.l].

[0086] The tunable unit cell array 1 for reconfigurable antenna, as illustrated in [Fig.l], comprises: a. a first substrate 11 based on one or other of fused silica, quartz and a glass having a loss tangent of less than 0.005 at frequencies above 100 GHz, and b. at least one block 12 resulting from a cut in a second substrate 20 based on one or other of fused silica, quartz and a glass having a loss tangent of less than 0.005 at frequencies above 100 GHz.

[0087] Each pad 12 is fixed to the first substrate 11, here by means of a layer of glue 13, to form a tunable unit cell 10 of the network of tunable unit cells 1. Each tunable unit cell 10 comprises at least one phase change material switch 101 comprised by, or formed in, or located in, the first substrate 11.

[0088] The schematic representation provided in [Fig.l] is only partial. The entire network of tunable unit cells 1 is illustrated in [Fig.2] which shows an organization in matrix form of 4x4 tunable unit cells 10. The square nature of the two-dimensional matrix, as well as the number of tunable unit cells 10 that it can comprise, are however not limited to the example illustrated in [Fig.2]. Also, there could be several phase-change material switches 101 and / or several radiating elements in the same block 12, unlike the representation provided in [Fig.2].

[0089] The embodiment illustrated in [Fig.l] is relatively equivalent to that illustrated in [Fig.10]. Figures 3 to 9 thus illustrate both an implementation mode of the manufacturing method of the embodiment of the network which is illustrated in [Fig.l], and an implementation mode of the manufacturing method of the embodiment which is illustrated in [Fig. 10]. This implementation mode illustrated in Figures 3 to 9 is described below with reference to said figures.

[0090] As illustrated in [Fig. 3], the mode of implementation of the manufacturing method according to the second aspect of the invention firstly comprises the provision of a silicon-based growth substrate 30 on which phase change material switches 101 are formed, thermal actuation guides 102 of said switches, as well as a metallization level 103 intended to form an interconnection line and / or a radiating element 1031 per cell 10, as it appears in [Fig. 6].

[0091] The implementation steps described above are the first steps of a whole which makes it possible to obtain the supply of the aforementioned first substrate 11. Said supply continues with the following steps.

[0092] A first layer 31 based on one or other of fused silica, quartz and a glass having a loss tangent of less than 0.005 at frequencies above 100 GHz is transferred onto a silicon oxide layer 104 encapsulating, above the growth substrate 30, the phase change material switches 101, the thermal actuation guides 102 and the metallization level 103. This transfer can be carried out by means of a silicon oxide layer 33 deposited on the face of the first layer 31 by which the transfer is intended to be carried out. The transfer is therefore carried out between two silicon oxide layers 33 and 104. This produces a stack as illustrated in FIGS. 4 and 5.

[0093] Where appropriate, the provision of the first substrate 11 may comprise the formation of a ground plane 32 on the face of the layer 31 which is opposite that by which the transfer is intended to be carried out.

[0094] Once the transfer has been carried out, the provision of the first substrate 11 comprises the grinding of the growth substrate 30, until reaching the silicon oxide encapsulating the phase change material switches 101, the thermal actuation guides 102 and the metallization level 103.

[0095] Once the growth substrate 30 has been ground, an opening step 105 is provided, for example by etching, of the silicon oxide layer 104 at the level of a part of the metallization level 103 to form the interconnection line and / or the radiating metallic element 1031, and thus arrive at a first substrate 11 as illustrated in [Fig.6].

[0096] The presently detailed implementation method then comprises, with reference to [Fig. 7], providing a second substrate 20 based on one or other of fused silica, quartz and a glass having a loss tangent of less than 0.005 at frequencies above 100 GHz. More particularly, the second substrate 20 comprises a layer 201 based on one or other of fused silica, quartz and a glass having a loss tangent of less than 0.005 at frequencies above 100 GHz, on which a metallization level 202 can be deposited, which, as illustrated in [Fig. 8], can be etched so as to form a plurality of connection plugs 122.

[0097] With reference to [Fig.9], the second substrate 20 is then cut into blocks 12. Preferably, each block 12 can be topped with at least one structuring in the aforementioned metal layer 122. If [Fig.9] illustrates a cutting of the second substrate 20 into two blocks 12, it is understood that the cutting of the second substrate 20 can lead to the manufacture of a plurality of at least four blocks 12, preferably at least sixteen blocks 12, or even more.

[0098] Note here that the first and second substrates 11 and 12 preferably have a characteristic transverse dimension greater than or equal to 100 mm, while each block 12 may have a characteristic transverse dimension greater than or equal to 200 μm, but strictly less than 50 mm and preferably less than or equal to 35 mm. There is therefore sufficient space on the first substrate 11 to transfer there a plurality of blocks 12 going beyond four, or even beyond sixteen. This will be even more verified when the characteristic transverse dimension of the first substrate 11 is substantially equal to 200 mm, or even 300 mm, as is the case for most existing first substrates 11. However, each tunable unit cell is intended to comprise at least one phase change material switch 101, accompanied by its thermal actuation guide 102.

[0099] Preferably, the first substrate 11 and the second substrate 12 are made from the same material. Thus, the thermal expansion coefficients of said at least one block 12 and of the first substrate 11 are of the same value, which advantageously limits the thermomechanical constraints during the manufacture of the network of tunable unit cells 1.

[0100] It is possible to consider that the cutting of the blocks 12, for example using a laser, is carried out around each pattern or structuring of the metal layer 122 in the thickness of the second substrate 20, and that each pattern or structuring of the metal layer 122 is intended to form in part a tunable unit cell 10. It is furthermore possible to consider that the cutting of the blocks 12 is carried out so that the pattern or structuring of the metal layer 122 gives rise to a block 12 and that the patterns or structuring of the metal layer 122 etched in the metallization level 202 are distributed over the entire surface of the second substrate 20.Therefore, the cutting in the second substrate 20 of the plurality of blocks 12 which is defined there by the patterns or structures of the metal layer and the transfer of the blocks 12 thus obtained onto the first substrate 11 amounts, in a way, to recreating by blocks the second substrate 20 on the first substrate 11, a distance, at least equal to the width of the material of the second substrate destroyed during its cutting into blocks 12, being provided between the first blocks 12 neighboring each other which have been transferred.

[0101] The transfer of each block 12 is carried out so that each block 12 forms, with the part of the first substrate 11 on which it is transferred, a tunable unit cell 10 of the network of tunable unit cells 1. It should be noted that the transfer of each block 12 could lead to the production of a plurality of tunable unit cells 10, due for example to the fact that the cutting of the second substrate 20 into blocks 12 would be done so as to obtain, on each block 12, a matrix of 2x2, or even 4x4, or even more, patterns or structuring of the metal layer 122.

[0102] As already mentioned above, said transfer can be carried out by means of a simple layer of glue 13, to achieve a network of tunable unit cells 1 as partially illustrated in [Fig. 10] (or equivalently in [Fig.l]) is as represented in its entirety in [Fig.2].

[0103] The embodiment of the tunable unit cell array 1 according to the first aspect of the invention which is illustrated in [Fig. 11] is a variant of that illustrated in [Fig. 10]; it shows that the metallic pattern (or structuring) 122 which runs over or overhangs each block 12 is optional.

[0104] In a manner not illustrated in the figures, the person skilled in the art will understand that it is possible that certain blocks 12 to be transferred onto the first substrate 11 do not come from the second substrate 20, but from a third substrate having for example a thickness different from that of the second substrate 20, and more particularly a layer based on one of fused silica, quartz and a glass having a loss tangent of less than 0.005 at frequencies above 100 GHz having a thickness different from that of the layer 201 of the second substrate 20. Thus, the tiles 12 can come from different substrates, and the latter can for example have different thicknesses between them, so that the tiles 12 which are cut there can be transferred onto the same first substrate 11 for an array of tunable unit cells 1 whose tunable unit cells 10 have different thicknesses between them.

[0105] The embodiment illustrated in [Fig. 12] can be considered as a variant of the embodiment illustrated in [Fig. 10]. To obtain the embodiment of the tunable unit cell array 1 which is illustrated in [Fig. 12], a second opening step 105, for example by etching, of the silicon oxide layer 104 may be provided in line with a portion of the metal layer 1031 on the other side of the phase change material switch 101 relative to the aforementioned first opening 105, and each pad 12 may comprise a metal layer 123 by which it is intended to be transferred, on the first substrate 11, in line with the second opening 105, for example by thermocompression between the connection plug 123 and the portion of the metal layer 1031 which is exposed via the second opening 105. Note that here again, the connection plug 122 illustrated in [Fig. 12] is optional.Once the transfer is carried out, a network of tunable unit cells 1 as partially illustrated in [Fig. 13] is obtained.

[0106] According to a variant of the embodiment illustrated in [Fig. 12], this variant being illustrated in figures 14 and 15, the transfer of each block 12 may further involve the fusion of metal balls 124, for example gold-based, deposited, before the transfer, on the connection plug 123 or in the second opening 105. According to this variant, the embodiments of the network of tunable unit cells 1 which is illustrated in [Fig. 15] are achieved.

[0107] Another embodiment of the first aspect of the invention and of implementing the second aspect of the invention is illustrated in Figures 16 to 19.

[0108] According to this other embodiment, and with reference to [Fig.16], the provision of the first substrate 11 comprises: a. providing a silicon-based growth substrate 30, b. forming the phase change material switches 101 on the growth substrate 30, c. forming the thermal actuation guides 102 of the phase change material switches 101, and d. forming a metallization level 103 flush in places to form at least one metal layer 1031 of each phase change material switch 101, then e. the transfer of a substrate comprising a first layer 31 based on one or other of fused silica, quartz and a glass having a loss tangent of less than 0.005 at frequencies above 100 GHz, where appropriate a ground plane 32 on said layer 31 extending on the face of this layer which is opposite the growth substrate 30, and a surface structuring on the face of the layer 31 which is intended to be connected to said at least one metal layer 1031 of each phase change material switch 101.

[0109] [Fig. 16] clearly shows that the two assembled elements have surface structures on their assembly face that correspond to each other.

[0110] Once the assembly has been carried out, as illustrated in [Fig. 17], the silicon can be ground, to obtain a first substrate 11 as illustrated in [Fig. 18], free of silicon.

[0111] Starting from the substrate illustrated in [Fig. 18], it is possible to transfer there, as illustrated in [Fig. 19], a block 12 as described above, and, in the example illustrated, by a layer of glue 13. The other transfer methods described above obviously remain portable to the embodiment described with reference to [Fig. 19].

[0112] The embodiments previously described have as a common factor that the substrate cut is not the one comprising the active elements of the tunable unit cells 10, namely the phase change material switches 101 and their thermal actuation guide 102. On the contrary, in the embodiments of the invention which are illustrated in FIGS. 20 to 25, it is the substrate in which the active elements of the tunable unit cells 10 are located which is cut.

[0113] Thus, the pad 12 as illustrated in [Fig.20] comprises a phase change material switch 101 and its thermal actuation guide 102, and this pad 12 is intended to be transferred onto a first substrate 11 which is free of the active elements of the tunable unit cell 10 to be formed. The first substrate 11 here comprises a first layer 31 based on one or other of fused silica, quartz and a glass having a loss tangent of less than 0.005 at frequencies above 100 GHz, where appropriate a ground plane 32 extending on the face of this layer which is opposite the block 12, and a surface structuring on the face of the layer 31 which is intended to be connected to the block 12. The block 12 comprises, on its face by which it is intended to be connected to the first substrate 11, a surface structuring corresponding substantially to that of the first substrate 11. Once the assembly carried out, for example by hybrid bonding, we obtain the network of tunable unit cells 1 as partially illustrated in [Fig.21].

[0114] As an alternative to the embodiment illustrated in [Fig.21], it is possible to insert at the assembly interface metal balls 125, for example gold-based, as illustrated in [Fig.22] to produce the welding between the metal layers of the pad 12 and the metal layers of the substrate 11. The assembly then leads to a network of tunable unit cells 1 as partially illustrated in [Fig.23].

[0115] The embodiment illustrated in [Fig.25] is identical to that illustrated in [Fig.21], except that the first substrate 11 does not have a structuring of its assembly surface with the illustrated pad 12. On the contrary, according to the embodiment illustrated in [Fig.24], only a layer of silicon oxide 34 is provided to allow the assembly of the pad 12. There is therefore no connection between the pad 12 and the first substrate 11 by any metal layers. This is why, according to this embodiment, a thermal actuation guide will preferably be used which operates by capturing optical radiation, rather than by ohmic conduction. Once the assembly has been carried out, a network of tunable unit cells 1 is obtained as partially illustrated in [Fig.25].

[0116] The various embodiments of the tunable unit cell array 1 which are described above advantageously make it possible to avoid having to transfer an entire substrate of large dimension (>50 mm transverse dimension) onto another entire substrate, thus relaxing the flatness constraints of the assembly surfaces and / or reducing the risk of breakage of the substrates during their handling and / or their manufacture when they are subjected to thermomechanical constraints. Another advantage consists in the fact that it is therefore possible to fix to the first substrate 11 blocks 12 of different thicknesses.

[0117] Let us recall here that the present invention relates to a reconfigurable phase-shifted array antenna, intended to operate in millimeter and sub-terahertz frequency bands, for example between 100 GHz and 500 GHz.

[0118] The invention is not limited to the embodiments previously described and extends to all embodiments covered by the invention.

Claims

Claims

1. A tunable unit cell array (1) for a reconfigurable antenna, comprising: • a first substrate (11) based on one of fused silica, quartz and a glass having a loss tangent of less than 0.005 at frequencies above 100 GHz, • at least two tiles (12) resulting from a cut in at least one second substrate (20) based on one of fused silica, quartz and a glass having a loss tangent of less than 0.005 at frequencies above 100 GHz, said at least two tiles (12) being fixed to the first substrate (11) to form at least two tunable unit cells (10) of the tunable unit cell array (1), each tunable unit cell (10) comprising at least one phase change material switch (101) comprised by the first substrate (11) or at least one of said at least two paving stones (12) and each paving stone may have a different thickness.

2. A tunable unit cell array (1) according to the preceding claim, wherein at least four, preferably at least sixteen, tiles are attached to the first substrate (11) so as to give the tunable unit cell array (1) the shape of a two-dimensional matrix of tunable unit cells (10).

3. A tunable unit cell array (1) according to any preceding claim, wherein at least one tile (12) comprises a primary layer (121) based on any of fused silica, quartz and glass having a loss tangent of less than 0.005 at frequencies above 100 GHz, and a pattern or structuring of a metal layer and / or a radiation element (122) on the face of the primary layer (121) which is opposite that by which said primary layer (121) is attached to the first substrate (11).

4. A tunable unit cell array (1) according to any preceding claim, wherein at least one tile (12) is fixed to the first substrate (11) by means of a layer of glue (13).

5. A tunable unit cell array (1) according to any preceding claim, wherein at least 2 tiles (12) are attached to the first substrate (11) by thermocompression of a metal layer (123) deposited on said at least one tile (12) with a metal layer (111) deposited on the first substrate (H).

6. A tunable unit cell array (1) according to any preceding claim, wherein at least one pad (12) is attached to the first substrate (11) by reflowing metal balls (124), for example gold-based, previously deposited on at least one of a metal layer (123) deposited on said at least one pad (12) and a metal layer (111) deposited on the first substrate (11).

7. A tunable unit cell array (1) according to one of the three preceding claims, wherein the phase change material switch (101) is comprised in the first substrate (11).

8. Tunable unit cell array (1) according to one of claims 1 to 6, wherein at least one tile (12) is fixed to the first substrate (11) by hybrid bonding, said at least one tile (12) and the first substrate (11) having, at the level of the fixing of said at least one tile (12) on the first substrate (11), surface structures substantially overlapping each other.

9. A tunable unit cell array (1) according to any one of claims 1 to 6, wherein at least one pad (12) is attached to the first substrate (11) by reflowing metal balls (125), for example gold-based, previously deposited on at least one of a metal layer (126) deposited on said at least one pad (12) and a metallization layer (111) deposited on the first substrate (11), said at least one pad (12) and the first substrate (11) having, at the attachment of said at least one pad (12) to the first substrate (11), surface structures substantially overlapping each other.

10. A tunable unit cell array (1) according to any one of the two preceding claims, wherein the phase change material switch (101) is comprised in said at least one tile (12).

11. A tunable unit cell array (1) according to any preceding claim, comprising tiles (12) of different thicknesses from each other.

12. A tunable unit cell array (1) according to any preceding claim, further comprising, connected to each phase change material switch (101), a thermal actuation guide (102), for example of an optical or electrical nature.

13. A tunable unit cell array (1) according to any preceding claim, further comprising, for each phase change material switch (101), a metallization level (103) forming an interconnecting RF line (1031) and / or a radiating metallic element of the phase change material switch (101).

14. A tunable unit cell array (1) according to any one of the preceding thirteen claims, wherein said at least two tiles (12) and the first substrate (11) are made from the same material selected from fused silica, quartz and a glass having a loss tangent of less than 0.005 at frequencies above 100 GHz.

15. A method of manufacturing a tunable unit cell array (1) for a reconfigurable antenna, comprising: • providing a first substrate (11) based on one of fused silica, quartz and a glass having a loss tangent of less than 0.005 at frequencies above 100 GHz, and comprising a matrix of phase change material switches (101), • providing a second substrate (20) based on one of fused silica, quartz and a glass having a loss tangent of less than 0.005 at frequencies above 100 GHz, • cutting at least two first tiles (12) from one of the first substrate (11) and the second substrate (20), • transferring said at least two first tiles (12) onto the other of the first substrate (11) and the second substrate (20), so that each first tile (12) forms with the part of the substrate (11 or 20) on which it is transferred at least one tunable unit cell (10) of the network of tunable unit cells (1).

16. Manufacturing method according to the preceding claim, in which at least four, preferably at least sixteen, blocks (12) are cut out and then transferred, so that the blocks (12) form, with the parts of the substrate (11 or 20) on which they are transferred, a network of tunable unit cells (1) taking the form of a matrix of tunable unit cells (10).

17. Manufacturing method according to any one of the two preceding claims, comprising providing at least one third substrate, cutting at least one third block from the third substrate and transferring said at least one third block onto the substrate (11 or 20) onto which said at least two first blocks (12) have been transferred, the third substrate preferably having a thickness different from the substrate from which said at least two first blocks (12) have been cut.

18. A manufacturing method according to any one of the three preceding claims, wherein providing the first substrate (11) comprises: • providing a silicon-based growth substrate (30), • forming the phase change material switches (101) on the growth substrate (30), • forming thermal actuation guides (102) of the phase change material switches (101), • forming a metallization level (103) for forming interconnection lines (1031) and / or radiating metallic elements of each phase change material switch (101), and • transferring a first layer (31) based on one or other of fused silica, quartz and a glass having a loss tangent of less than 0.005 at frequencies above 100 GHz,• where appropriate the formation of a ground plane (32) on said layer (31) based on one or the other of, fused silica, quartz and a glass having a loss tangent of less than 0.005 at frequencies above 100 GHz, then, • removing by grinding the growth substrate (30), each phase change material switch (101), each thermal actuation guide (102) and each interconnection line or radiating metallic element (1031) being at least partly encapsulated in silicon oxide (104).

19. Manufacturing method according to the preceding claim, further comprising, after grinding the growth substrate (30), at least one step of opening (105), for example by etching, a layer of silicon oxide (104) at the level of an interconnection line, (1031) of the radiating metallic element.

20. A method according to any one of the preceding five claims, wherein providing the second substrate (20) comprises: • providing a support substrate (201) based on any one of fused silica, quartz and a glass having a loss tangent of less than 0.005 at frequencies above 100 GHz, and • forming, on the support substrate (201), a metal layer (202), and • etching the metal layer (202) to form patterns or structurings (122) for each tunable unit cell (10) to be formed, and wherein the cutting step relates to the second substrate (20) and comprises cutting tiles (12) in the second substrate (20) by rotating around each pattern or structuring (122).

21. Method according to any one of the six preceding claims, in which the transfer of at least one first block (12) is carried out by means of a layer of glue (13).

22. Method according to any one of the seven preceding claims, in which the transfer of at least one first block (12) is carried out by thermocompression of a metallic layer (123) of said at least one first block (12) with a metallic layer (111) of the first substrate (11).

23. Method according to any one of the eight preceding claims, in which the transfer of at least one first block (12) is carried out by remelting metal balls (124), for example gold-based, previously deposited on at least one of a metal layer (123) of said at least one first block (12) and a metal layer (111) of the first substrate (11).

24. Method according to any one of the three preceding claims, in which the cutting of said at least two first blocks (12) is carried out in the second substrate (20).

25. Method according to any one of claims 15 to 23, in which the transfer of at least one first block (12) is carried out by hybrid bonding, said at least one first block (12) and the first substrate (11) having, at the level of the fixing of said at least one first block (12) on the first substrate (11), surface structures substantially superimposing each other.

26. Method according to any one of claims 15 to 23, in which the transfer of at least one first block (12) is carried out by remelting metal balls (125), for example based on gold, deposited beforehand on at least one of a metal layer (126) of said at least one first block (12) and a metal layer (111) of the first substrate (11), said at least one first block (12) and the first substrate (11) having, at the level of the fixing of said at least one first block (12) on the first substrate (11), surface structures substantially overlapping each other.

27. Method according to any one of the two preceding claims, in which the cutting of said at least two first blocks (12) is carried out in the first substrate (11).

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