Mechanical or optomechanical resonator device

Abstract

The present invention relates to a device (2) comprising a first layer (202) having a first portion (202A) attached to a front face (204) of a substrate (200) and a second portion (202B) suspended above a plane comprising the front face (204). The device (2) comprises a resonator (212) attached to the second portion (202B) of the first layer (202) and suspended below the second portion (202B) of the first layer (202) and above the plane comprising the front face (204) of the substrate (200). Only a first portion of the resonator (212) faces the substrate (200) and / or the first layer (202) in a direction orthogonal to the front face (204).

Description

DESCRIPTION Mechanical or opto-mechanical resonator device

[0001] This application claims priority from French patent application FR 22 / 12956 filed on December 8, 2022 and entitled "Device with optical, mechanical or opto-mechanical resonator", which is considered to be an integral part of this description within the limits provided by law. Technical field

[0002] This description relates generally to integrated circuits, and more particularly to photonic integrated circuits. Prior art

[0003] Known photonic circuits comprise an optical or optomechanical resonator comprising, for example, a disc, a circular ring or a closed loop in the shape of an athletics track ("racetrack" in English), and having a portion which projects beyond an edge of the substrate on which the circuit is formed. The portion of the resonator which projects beyond the edge of the substrate is configured to interact with a surface, for example a surface to be imaged, which modifies the resonance wavelength of the optical resonator, for example following a modification of the effective optical index of the optical resonator resulting from the material placed opposite the projecting portion of the resonator and the distance between this material and the projecting portion of the resonator, and / or for example following a deformation of the resonator resulting from a force exerted on the optomechanical resonator by the surface.Such photonic circuits serve, for example, as force probes for atomic force microscopes (AFM).

[0004] Figure 1 illustrates, by a schematic top view, a theoretical, or ideal, example of such a photonic circuit 1, Figure 2 being a schematic sectional view of this circuit 1 taken in plane AA of Figure 1.

[0005] The circuit 1 comprises a substrate 100, for example made of silicon, only part of which is shown in figures 1 and 2.

[0006] An optical or optomechanical resonator 102, for example made of silicon, is fixed to the substrate 100 by an anchoring pad 104, for example made of silicon nitride, silicon oxide or polycrystalline silicon, so that the resonator is suspended above the substrate 100 and a portion of the resonator 102 projects beyond an edge or flank 110 of the substrate, or, more generally, an edge 110 of the circuit 1. In this example, the resonator 102 comprises a disk 106 and a tip 108 fixed to the periphery of the disk 106. The tip 108 is oriented in a direction parallel to the face of the substrate 100, called the front face of the substrate 100, to which the anchoring pad 104 is fixed, and orthogonal to the intersection of the edge 110 of the substrate 100 with this front face, a portion of the resonator 102 extending beyond the intersection of edge 110 with the front face of the substrate. In the example of Figures 1 and 2, edge 110 is orthogonal to the front face of substrate 100.

[0007] The representation of Figures 1 and 2 is ideal in that the intersection of the flank 110 with the front surface of the substrate 100 beyond which a portion of the resonator 102 protrudes is arranged between the pad 104 and the portion of the resonator 102 which protrudes beyond the substrate 100, for example between the pad 104 and the tip 108.

[0008] Figure 3 is a schematic sectional view taken in a section plane similar to plane AA of Figure 1, illustrating circuit 1 at a manufacturing stage.

[0009] At this stage, the resonator 102 and the pad 104 are embedded in a material 300 that can be selectively etched relative to the resonator 102 and the substrate 100. The material 300 can also be selectively etched relative to the material of the pad 104. The assembly of the material 300, the resonator 102 and the pad 104 forms a layer resting on and in contact with the front face of the substrate 100.

[0010] At this stage, the entire resonator 102 is, in a direction orthogonal to the front face of the substrate 100, facing the substrate 100, or, in other words, the substrate 100 still extends under the entire resonator 102 and beyond.

[0011] At this step, an etching, for example a deep reactive ion etching (DRIE) is carried out from the rear face of the substrate 100 to the front face of the substrate 100, to remove a portion of the substrate 100 not coated with an etching mask 301 and form the flank 110 of the substrate 100 (FIGS. 1 and 2). In FIG. 3, the desired position of the flank 110 is represented by a dotted line 302.

[0012] More particularly, the mask 301 covers the part of the substrate 100 which must be left in place (to the left of the line 302 in FIG. 3) and does not cover the part of the substrate 100 which it is desired to remove by etching (to the right of the line 302 in FIG. 3).

[0013] Next, although not illustrated here, the material 300 is removed by selective etching relative to the material(s) of the substrate 100, the resonator 102 and, by way of example, the pad 104 when the material 300 is selectively etchable relative to the material of the pad 104. In another example where the material 300 is not selectively etchable relative to the material of the pad 104, the time of selective etching of the material 300 relative to the material(s) of the substrate 100 and the resonator 102 is limited. so as to leave the pad 104 in place. In the latter case, the accesses of the etching solution to the pad 104 are configured to allow the pad 104 to be left in place while controlling the etching time.

[0014] However, the etching through the substrate 100 has an angle 0 relative to the ideal cutting plane 302, and, in addition, a dispersion d0 on the value of this angle 0.

[0015] Due to the angle 0, the dispersion d0 and the thickness E of the substrate 100 which is several hundred micrometers, the etching emerges on the side of the front face of the substrate 100 with a misalignment of more or less A relative to the ideal cutting plane 302. For example, for an angle 0 equal to 1°, a dispersion d0 equal to 1° and a thickness E equal to 400 pm, A is equal to 7 pm.

[0016] Furthermore, as represented in FIG. 3 by a double arrow 304, the alignment of the mask 301 with the targeted cutting line 302 has an error of plus or minus d, with d for example equal to 500 nm, which further adds to the uncertainty about the location where the etching opens on the side of the front face of the substrate 100.

[0017] However, the maximum dimensions that the suspended part of the resonator 102 can have, that is to say the entire part of the resonator 102 which is not directly in contact with the pad 104 in figures 1 and 2, are limited by the position of the pad 104. Due to the uncertainty about the place where the etching opens on the side of the front face of the substrate 100, the part of the resonator 102 which protrudes beyond the substrate 100 may not protrude far enough beyond the substrate 100, or the substrate 100 may be etched under the pad 104, which renders the circuit 1 inoperative.

[0018] Although the problem related to the uncertainty about where the etching of the substrate 100 ends on its front face has been presented in the case where one seeks to obtain a flank 110 orthogonal to the front face of the substrate 100, this problem also arises when one wishes to obtain a flank 110 on a slope to facilitate access of the probe (resonator 102) to a surface to be studied. When the flank 110 is on a slope, the intersection of the flank 110 with the front face of the substrate 100 is closer to the part of the resonator 102 projecting beyond the substrate 100 than the intersection of the flank 110 with the rear face of the substrate 100 which is opposite the front face.For example, such a sloping flank 110 can be obtained with a substrate 100 made of monocrystalline silicon using anisotropic etching, for example anisotropic wet etching, for example using an etching solution comprising potassium hydroxide (KOH), tetramethylammonium hydroxide (TMAH) or ethylenediamine pyrocatechol (EDP), making it possible to discover planes oriented along a given crystallographic direction. In the case of a sloping flank 110, the uncertainty on the location where the etching of the substrate 100 opens onto its front face is then at least partly determined by the uncertainty on the thickness of the substrate 100. Summary of the invention

[0019] There is a need for a photonic circuit in which an optical or optomechanical resonator extends beyond the circuit substrate, overcoming all or part of the disadvantages of known photonic circuits in which an optical or optomechanical resonator extends beyond the circuit substrate, for example all or part of the disadvantages associated with the manufacture of these known circuits.

[0020] An embodiment overcomes all or part of the drawbacks of known photonic circuits in which an optical or optomechanical resonator extends beyond the circuit substrate, for example all or part of the disadvantages associated with the manufacture of these known circuits.

[0021] One embodiment provides a device comprising: a substrate; a first layer having a first portion attached to a front face of the substrate and a second portion suspended above a plane comprising the front face of the substrate; and an optical, optomechanical or mechanical resonator attached to the second portion (202B) of the first layer and suspended under said second portion of the first layer and above the plane comprising the front face of the substrate, only a first portion of the resonator being, in a direction orthogonal to the front face of the substrate, facing the substrate and / or the first layer.

[0022] According to one embodiment, the resonator comprises a second part which, in a direction orthogonal to the front face of the substrate, is not opposite either the first layer or the substrate.

[0023] According to one embodiment, in a direction parallel to the front face of the substrate, the second part of the resonator is arranged beyond an edge of the substrate and beyond an edge of the first layer.

[0024] According to one embodiment, in a direction parallel to the front face of the substrate and orthogonal to the intersection of said edge of the substrate with the front face of the substrate, a dimension of the second part of the resonator is less than 50 pm.

[0025] According to one embodiment: the device comprises a second layer; the second layer is arranged between the first layer and the front face of the substrate; and the resonator is defined in the second layer.

[0026] According to one embodiment, the device further comprises at least one third layer disposed between the front face of the substrate and the second layer, and at least one fourth layer disposed between the second layer and the first layer.

[0027] According to one embodiment, the first part of the first layer rests on a stack of layers, the stack preferably comprising the second layer.

[0028] According to one embodiment, the resonator comprises a circular ring, an athletics track-shaped loop, or a disc.

[0029] According to one embodiment, the resonator is fixed to the second part of the first layer by at least one anchoring pad.

[0030] According to one embodiment, said at least one anchoring pad extends in height from the second layer to the second part of the first layer.

[0031] According to one embodiment, said at least one anchoring pad is in contact with the disc; or said at least one anchoring pad is arranged inside a region delimited laterally by the ring and the device comprises holding arms each extending from an internal edge of the ring to said at least one anchoring pad; or said at least one anchoring pad is arranged inside a region delimited laterally by the closed loop, preferably in the center of this region, and the device comprises holding arms each extending from an internal edge of the closed loop to said at least one anchoring pad.

[0032] According to one embodiment, the resonator further comprises a tip attached to the outer periphery of the disk, ring or closed loop.

[0033] According to one embodiment, the second part of the resonator comprises the tip, the tip extending lengthwise in a direction parallel to the front face of the substrate and, preferably, orthogonal to the intersection of said edge of the substrate with the front face of the substrate.

[0034] According to one embodiment, the resonator is an optical or opto-mechanical resonator and the device further comprises a waveguide defined in the same layer as the resonator, a portion of the waveguide being optically coupled to the resonator.

[0035] According to one embodiment, the portion of the waveguide is suspended between the second part of the first layer and a plane comprising the front face of the substrate, preferably by holding arms defined in the same layer as the optical resonator and each extending from said portion of the waveguide to an anchoring pad fixed to the substrate or to the second part of the first layer. Brief description of the drawings

[0036] These and other features and advantages will be set forth in detail in the following description of particular embodiments given without limitation in relation to the attached figures, among which:

[0037] Figure 1, described previously, represents, in a top view, an ideal example of a photonic circuit;

[0038] Figure 2, previously described, represents a schematic sectional view taken in a plane AA of Figure 1;

[0039] Figure 3, described previously, represents a schematic sectional view illustrating a manufacturing step of the circuit of Figures 1 and 2;

[0040] Figure 4 represents, by a schematic top view, an embodiment of a photonic circuit;

[0041] Figure 5 represents a schematic sectional view taken in plane AA of Figure 4;

[0042] Figure 6 represents a schematic sectional view taken in plane BB of Figure 4;

[0043] Figure 7 represents a schematic sectional view taken in plane BB of Figure 4 according to an alternative embodiment;

[0044] Figure 8 represents, by a schematic top view, another variant embodiment of the photonic circuit of Figures 4 to 7;

[0045] Figure 9 represents a schematic sectional view taken in plane AA of Figure 8;

[0046] Figure 10 represents, by a schematic top view, yet another variant embodiment of the photonic circuit of Figures 4 to 7;

[0047] Figure 11 represents, by a schematic top view, yet another variant embodiment of the photonic circuit of Figures 4 to 7; and

[0048] Figure 12 represents, by a schematic top view, yet another variant embodiment of the photonic circuit of Figures 4 to 7. Description of the embodiments

[0049] The same elements have been designated by the same references in the different figures. In particular, the structural and / or functional elements common to the different embodiments may have the same references and may have identical structural, dimensional and material properties.

[0050] For the sake of clarity, only the steps and elements useful for understanding the embodiments described have been shown and are detailed. In particular, the methods for manufacturing the photonic circuits described here have not been detailed, the manufacturing of the embodiments and variants of these photonic circuits from usual steps of manufacturing known photonic circuits being within the reach of the person skilled in the art from the description below.

[0051] Unless otherwise specified, when referring to two elements mechanically connected to each other, this means directly in contact without intermediate elements, and when referring to two elements mechanically connected or coupled to each other, this means that these two elements can be connected or linked by means of one or more other elements.

[0052] In the following description, when reference is made to absolute position qualifiers, such as the terms "front", "back", "top", "bottom", "left", "right", etc., or relative position qualifiers, such as the terms "above", "below", "upper", "lower", etc., or to orientation qualifiers, such as the terms "horizontal", "vertical", etc., reference is made unless otherwise specified to the orientation of the figures.

[0053] Unless otherwise specified, the expressions "about", "approximately", "substantially", and "of the order of" mean to within 10%, preferably to within 5%.

[0054] In order to overcome the drawbacks of the known photonic circuits described previously, a photonic circuit is proposed here comprising a layer, called a support layer, having a part fixed to a front face of the circuit substrate, and a part suspended above a plane of the front face of the substrate. The optical resonator or opto- mechanical is attached to the suspended portion of the support layer, the resonator then being suspended under the suspended portion of the support layer, i.e. under a plane comprising a lower face of the support layer which is turned towards the front face of the substrate. The attachment of the resonator to the lower face of the suspended portion of the support layer allows that, in a direction orthogonal to the front face of the substrate, only a first part of the resonator is opposite the front face of the substrate and / or the lower face of the support layer. Thus, in a direction orthogonal to the front face of the substrate, a second part of the resonator is opposite neither the substrate nor the support layer, and therefore projects beyond the substrate and the support layer.

[0055] The support layer is thinner than the substrate, its thickness being for example at most 100 μm, preferably at most 10 μm. Thus, when a portion of the support layer is removed by etching from its upper face to its lower face so that a part of the resonator protrudes beyond the part of the support layer left in place, the uncertainty on the place where this etching opens on the lower face of the support layer is much lower than that on the place where, on the front face of the substrate, an etching made from the rear face of the substrate to the front face of the substrate opens. This makes it possible to relax the constraints on the positioning of the anchor pad to which the resonator is fixed. This also makes it possible to relax the constraints on etching through the substrate, for example the constraints on controlling the etching slope through the substrate.

[0056] Unless otherwise stated, when referring to an element that is anchored, fixed, attached, or hooked, the English "hooked") to the support layer, this means that this element is mechanically coupled to the support layer, itself comprising a part fixed to the substrate. For example, put another way, this means that this element is mechanically coupled to the substrate via the support layer. For example, put another way, this means that the mechanical connection between this element and the support layer is shorter (or more direct) than each mechanical connection that this element has with the substrate.

[0057] Symmetrically, unless otherwise stated, when referring to an element anchored, fixed, attached or hooked to the substrate, this means that this element is mechanically coupled to the substrate, itself being coupled to the support layer. For example, said another way, this means that this element is coupled to the support layer via the substrate. For example, said again another way, this means that the mechanical connection between this element and the substrate is shorter (or more direct) than each mechanical connection that this element has with the support layer.

[0058] Examples of embodiments and alternative embodiments of such a photonic circuit will now be described in relation to Figures 4 to 12.

[0059] Figure 4 represents, by a schematic top view, an embodiment of a photonic circuit 2, Figure 5 being a schematic sectional view taken in the plane AA of Figure 4 and Figure 6 being a schematic sectional view taken in the plane BB of Figure 4. In these figures, only a part of the circuit 2 and its substrate 200 is represented.

[0060] The photonic circuit 2, or device 2, comprises a substrate 200, for example a semiconductor substrate, for example made of silicon. In other words, the circuit 2 is formed on the substrate 200. For example, the substrate 200 has a thickness of several hundred micrometers, for example a thickness of at least 200 μm.

[0061] The circuit 2 comprises a layer 202, called the support layer 202. For example, the thickness of the layer 202 is less than 100 pm, for example substantially equal to 10 pm, although this thickness may be, for example, less than 10 pm, or even less than 1 pm.

[0062] The layer 202 comprises a first portion 202A fixed to the substrate 200, and, more particularly to a front face 204 of the substrate 200 (upper face in FIGS. 4 and 5). The portion 202A of the layer 200 is fixed to the substrate 200, for example, by a stack 203 of layers, the stack 203 having a surface connected to a lower face 206 of the layer 202 and a surface connected to the front face of the substrate 200. As an alternative example, the portion 202A of the layer 200 is fixed by a pad made of the same material as that of the layer 202 and / or the substrate 200, this pad replacing the stack 203 and having a surface connected to the layer 202 and a surface connected to the front face of the substrate 200.

[0063] The layer 202 further comprises a second portion 202B suspended above the substrate 200, i.e. above a plane comprising the face 204 of the substrate 200.

[0064] The two portions 202A and 202B of the layer 202 are connected to each other. In other words, the portion 202B of the layer 200 is in the extension of the portion 202A of the layer 200, or, in another word, the layer 200 is continuous at the boundary between its portions 202A and 202B. The boundary between the portions 202A and 202B of the layer 200 is indicated by a double dotted line 208 in FIG. 4, and by a single dotted line also referenced 208 in FIGS. 5 and 6.

[0065] The suspended portion 202B of the layer 202 projects at least partially beyond an edge, or flank, 210 of the substrate 200 in a direction parallel to the plane of the face 204 and orthogonal to the intersection, or junction, of the flank 210 with the face 204 of the substrate 200. In FIG. 4, the position of the flank 204 under the layer 202 is indicated by a double dotted line also referenced 210.

[0066] In the example of Figures 4 to 6, the flank 210 is shown as being orthogonal to the face 204 of the substrate 200 although, in practice, this flank 210 may be inclined relative to the normal to the face 204, either deliberately so that the flank 210 is sloping as described previously in relation to Figures 1 to 3, or due to the etching slope of the substrate 200.

[0067] In the example of Figures 4-6, the suspended portion 202B of the layer 202 includes a region disposed facing the substrate 200 in a direction orthogonal to the face 204, although, in other examples not shown, the portion 202B of the layer 200 does not include any region disposed facing the substrate in a direction orthogonal to the face 204.

[0068] The circuit 2 comprises an optical or optomechanical resonator 212. The resonator 212 is formed in, or defined in, a layer 214. The layer 214 is made of a material suitable for guiding light at the operating wavelengths of the circuit 2. For example, the layer 214 is made of silicon, silicon nitride, arsenic gallium or germanium.

[0069] Layer 214 is disposed between substrate 200 and layer 202. For example, layer stack 203 comprises a portion of layer 214.

[0070] According to one embodiment, as is the case in Figures 4 to 6, the resonator 212 comprises a disk 212A. Optionally, the resonator 212 comprises a tip 212B fixed to the periphery of the disc 212A. Preferably, the tip 212B extends lengthwise in a direction parallel to the face 204 and orthogonal to the intersection of the flank 210 with the face 204 of the substrate 200.

[0071] The resonator 212, and more particularly the disk 212A of the resonator 212 in the example of FIGS. 4 to 6, is fixed to the suspended part 202B of the support layer 202. The resonator 212 is suspended under the layer 202, and more precisely, under the suspended part 202B of this layer 202. The resonator 212 is also suspended above a plane comprising the face 204 of the substrate.

[0072] More precisely, the resonator 212 is fixed to the suspended part 202B of the layer 202 by at least one anchoring pad 216. Each pad 216 extends in height from the layer 214 to the layer 202, and, more particularly, to the face 206 of the layer 202.

[0073] Preferably, when the resonator 212 comprises a disk 212A, each pad 216 extends between the disk 212A and the layer 202 and is arranged sufficiently far from the edge of the disk 212A, for example more than 1 pm from the edge of the disk 212A, so as not to disturb the optical modes which are propagated in the disk 212A and are offset towards the periphery of the disk 212A. The attachment of each pad 216 directly to the disk 212A but sufficiently far from the edge of the disk 212A makes it possible to limit the optical losses because the optical modes propagated in the disk 212A are offset towards the periphery of the disk 212A, and therefore to increase the optical quality factor.

[0074] Preferably, a single pad 216 fixes the resonator 212 to the layer 202, this pad 216 then preferably being arranged in the center of the disk 212A to limit as much as possible the optical losses resulting from the pad 216.

[0075] In figures 4 to 6, plot 216 is indicated by a cross.

[0076] Only a first part of the resonator 212 (the part delimited by a dotted line in FIG. 4) is, in a direction orthogonal to the face 204, arranged opposite the substrate 200 and / or the suspended part 202B of the layer 200. Thus, the resonator 212 comprises a second part which, in a direction orthogonal to the face 204, is not arranged opposite the substrate 200 or the layer 202. This second part of the resonator 212 therefore projects beyond the flank 210 of the substrate 200 and also beyond the layer 202, for example in a direction parallel to the face 204 and orthogonal to the intersection of the flank 210 with the face 204 of the substrate 200. When the resonator 212 comprises the tip 212B, the latter is part of the second part of the resonator 212, i.e., no portion of the tip 212B faces the substrate 200 or the layer 202 in a direction orthogonal to the face 204 of the substrate 200.

[0077] According to one embodiment, the second part of the resonator 212 has, in a direction parallel to the face 204 and orthogonal to the intersection of the flank 210 with the face 204 of the substrate 200, a dimension or length less than 50 pm.

[0078] For example, during the manufacture of the circuit 2, the layer 214 initially rests on a layer 218, itself resting on the substrate 200. Then different elements, including the resonator 212, are defined by etching in the layer 214. At this step of etching the layer 214, a portion of the layer 214 can be left in place at the location of the stack 203, so that the stack 203 comprises this portion of the layer 214. Then, at least one layer 220 is formed on the assembly and then the layer 202 is formed, by deposition or by transfer, on the layer 220. The anchor pad 216 may be made of the same material as the layer 202 by providing an opening in the layer 220 up to the resonator 212 which will be filled by the material of the layer 202 during its deposition, or else made of another material by filling the opening in the layer 220 with this material before forming the layer 202. The layers 218 and 220 are made of materials that can be selectively etched relative to the materials of the layers 214 and 202 and of the substrate 200. Portions of the layer 202 and of the substrate 200 are then removed during two respective etching steps, then portions of the layers 218 and 220 are removed by selective sacrificial etching relative to the layers 202 and 214 and to the substrate 200 to obtain the circuit 2. For example, the etching(s) of the layers 218 and 220 are selective by relative to the material of the plot 216.As another example, the pad 216 is made of the same material as that of the layer 220 and the person skilled in the art will then be able to provide openings in the layer 202 and / or in the layer 214 so that by controlling the etching time of the layer 220, the pad 216 is left in place at the end of the etching.

[0079] In the above manufacturing method example, when layer 214 is a semiconductor layer, for example made of silicon, and layer 218 is an insulating layer, for example made of silicon oxide, layer 214 may correspond to the semiconductor layer of a semiconductor on insulator (SOI) type structure formed on substrate 200.

[0080] Still in the manufacturing method example above, in circuit 2, stack 203 includes a left-in-place portion of layer 218, and may or may not include a left-in-place portion of layer 220. Indeed, it is possible for stack 203 not to include a left-in-place portion of layer 220 by providing that, after the formation of layer 220 on layer 214, an opening is etched in layer 220 up to layer 214 at the location of stack 203. Thus, when layer 202 is then formed by deposition on layer 220, at the location of the stack, the material of layer 202 comes directly into contact with layer 214 due to the through opening in layer 220. Layer 202 can then be planarized. In yet another example, the stack is replaced by a pad made of a material identical to that of layer 202. For this, at the location of this pad, before the deposition of layer 202, an opening is etched through layers 220, 214 and 218 to substrate 200, so that, during the formation of layer 202 by deposition of the material of this layer on layer 220, this material fills the opening and forms the pad there.

[0081] In another example, the layer 202 corresponds to a portion of a first substrate, for example a semiconductor, for example silicon, the layer 220 then resting on this first substrate and the layer 214 then resting on the layer 220. In the same way as previously, elements, including the resonator 212, are formed in the layer 214. A filling material, for example identical to the material of the layer 218, is deposited then planarized by stopping before or on the layer 214. The substrate 200 coated with the layer 218 is then transferred onto the structure before thinning the first substrate so as to leave only the layer 202. The following steps for obtaining the circuit 2 are then similar to what was described for the other example above.

[0082] In this other example of a manufacturing method, when transferring the substrate 200 onto the structure comprising the first substrate, the layer 218 may already be part of the structure and then rest on the layer 214 rather than coating the substrate 200, and the substrate 200 is then brought into contact with the layer 218 during the transfer step.

[0083] In this other example of a manufacturing method, when layer 214 is a semiconductor layer, for example made of silicon, and layer 220 is an insulating layer, for example made of silicon oxide, layer 214 may correspond to the semiconductor layer of a semiconductor on insulator (SOI) type structure formed on the first substrate.

[0084] Of course, the two ways of manufacturing the circuit 2 which are described above are only examples, and the person skilled in the art is able, from the present description, to provide other methods of manufacturing the circuit 2 using steps which are each usual in the manufacturing of photonic circuits. In particular, the person skilled in the art will be able to adapt the examples of manufacturing methods described above to obtain a stack 203 comprising a portion of each of the layers 220, 214 and 218, or a stack 203 comprising only a portion of each of the layers 220 and 214, or a stack 203 comprising only a portion of each of the layers 218 and 214, or a stack 203 comprising only a portion of the layer 214, or even to obtain a pad made of the material of the layer 202 and / or of the substrate 200 in place of the stack 203.

[0085] Preferably, the circuit 2 comprises only one layer 220 and one layer 218. However, the layer 220 may correspond to a plurality of layers stacked on top of each other and / or the layer 218 may correspond to a plurality of layers stacked on top of each other.

[0086] For example, the two sacrificial layers 218 and 220 are made of the same material, selectively etchable relative to the material(s) of the layers 214 and 202 of the substrate. 200, and, for example, of the pad 216. However, in another example, the layers 218 and 220 may be made of different materials, each selectively etchable relative to the material(s) of the layers 214 and 202, of the substrate 200 and, for example, of the pad 216.

[0087] For example, the substrate 200 is made of silicon or arsenic-gallium.

[0088] For example, layer 218 is a layer of silicon oxide or a photonic polymer such as, for example, BCB benzocyclobutene.

[0089] For example, layer 220 is a layer of silicon oxide or a photonic polymer such as, for example, BCB benzocyclobutene.

[0090] For example, pad 216 is made of silicon, silicon nitride or silicon oxide.

[0091] For example, the thickness of the layer 214 is between 40 and 1000 nm, for example between 50 and 500 nm.

[0092] For example, the thickness of the layer 220 is greater than 500 nm, so that the portion of the layer 202 arranged above the resonator 212 does not modify the optical properties of the resonator 212.

[0093] For example, the thickness of the layer 218 is greater than 500 nm so that the substrate 200 is sufficiently far from the resonator 212 so as not to modify its optical properties.

[0094] As previously indicated, under the non-suspended portion 202A of the layer 202, the layer 218 is, for example, arranged between the face 204 of the substrate 200 and the layer 214, and the layer 220 is, for example, arranged between the layer 214 and the face 206 of the layer 202. Preferably, the circuit 2 does not comprise any other layer than the layer 218 between the face 204 of the substrate 200 and the layer 214, and does not does not include any layer other than layer 220 between layer 214 and face 206 of layer 202.

[0095] Of course, the person skilled in the art is able to adapt the materials of the layers 202, 214, 218 and 220, of the substrate 200 and, for example, of the pad 216 while retaining the etching selectivities indicated previously between the substrate 200 and the layer 218, the layers 218 and 220 with respect to the layers 214 and 202 and to the substrate 200, for example when the layer 214 is made of a material other than silicon.

[0096] In practice, although not indicated heretofore, circuit 2 comprises a waveguide 222 formed in, or defined in, layer 214. This waveguide 222 comprises a portion 224 optically coupled to resonator 212.

[0097] The portion 224 of the waveguide 222 is, like the resonator 212, suspended under a plane comprising the face 206 of the layer 202 and above a plane comprising the face 204 of the substrate 200.

[0098] According to one embodiment, as is the case in the example of FIGS. 4 to 6, the portion 224 of the waveguide 222 is suspended above the substrate 200 and under the layer 202.

[0099] According to one embodiment, the portion 224 of the waveguide 222 is fixed to the substrate 200, and more particularly to the face 204 of the substrate 200. For this, the circuit 2 comprises holding arms 226 each having one end connected to the portion 224 of the waveguide 222, and an opposite end connected to an anchoring pad 228, itself connected to the face 204 of the substrate 200. In FIGS. 4 to 6, the pads 228 are each marked with a cross. Each pad 228 is, for example, made of a material allowing the etching of the sacrificial layers 218 and 220 to be selective with respect to this material. As an alternative example, each pad 228 is made of the same material as that of the layer 220 and / or 218, the removal of the layers 218 and 220 by selective etching relative to the material(s) of the layer 214, the layer 220 and the substrate 200 then being implemented by controlling the etching time so as to leave the pads 228 in place at the end of this etching. In this alternative example, the accesses of the etching solution to the pads 228 are configured to allow the pads 228 to be left in place by controlling the etching time. As an example, each holding arm 226 corresponds to a beam or to one or more beams placed end to end to form at least one meander.

[0100] In the example of Figures 4 to 6, the portion 224 of the waveguide 222 is arranged between the resonator 212 and the stack 203 of layers 218, 214, 220 on which the part 202A of the layer 202 rests.

[0101] Alternative embodiments of circuit 2 will now be described in relation to figures 7 to 12. Unless otherwise indicated, everything described for circuit 2 of figures 4 to 6 applies to circuits 2 according to these alternative embodiments.

[0102] Figure 7 represents a schematic sectional view taken in plane BB of figure 4 according to an alternative embodiment of circuit 2.

[0103] The circuit 2 of Figure 7 differs from that of Figures 4 to 6 only in that the portion 224 of the waveguide 222 is, in the alternative embodiment of Figure 7, fixed to the suspended part 202B of the layer 202 rather than to the substrate 200. In this case, the anchoring pads 228 are no longer connected to the substrate 200 but to the part 202B of the layer 202, and, more particularly, to the face 206 of the layer 202. For example, the pads 228 are then similar or identical to the pads 216 (Figures 4 and 5).

[0104] Because the resonator 212 and the portion 224 of the waveguide 22 are both attached to the suspended portion 202B of the layer 202, the dimensions of the gap between the portion 224 of the waveguide 222 and the resonator where the waveguide 222 is optically coupled to the resonator 212 are independent of any deformations that the substrate 200 might undergo.

[0105] Furthermore, in the same way that connecting the pad 216 to the suspended portion 202B of the layer 202 rather than to the substrate 200 allows for the relaxation of constraints on the positioning of the pad 216 that result from etching the substrate 200 from its backside to its frontside to define the flank 210 there, connecting the pads 228 to the suspended portion 202B of the layer 202 rather than to the substrate 200 allows for the relaxation of constraints on the positioning of the pads 228.

[0106] Figure 8 represents, by a schematic top view, another variant embodiment of the photonic circuit 2 of figures 4 to 6, figure 9 being a schematic sectional view taken in plane AA of figure 8.

[0107] In this variant, the circuit 2 differs from what has been described in relation to FIG. 7 in that the resonator 212 does not comprise any part which, in a direction orthogonal to the face 204 of the substrate 200, is facing the substrate 200. However, the resonator 212 comprises a first part which, in a direction orthogonal to the face 204, is facing the suspended part 202B of the layer 202, and a second part which, in this direction, is facing neither the substrate 200 nor the layer 202.

[0108] Furthermore, in the example of Figures 8 and 9, the portion 224 of the waveguide 222 is fixed to the suspended part 202B of the layer 202. In this case, as illustrated by Figures 8 and 9, this portion 224 of the guide waveform 222 may also not include any portion which, in a direction orthogonal to the face 204, is disposed opposite the substrate 200.

[0109] In another example not illustrated, the portion 224 of the waveguide 222 is, in a direction orthogonal to the face 204, arranged at least partly opposite the substrate 200, the pads 228 then being able to be connected either to the substrate 200, or to the suspended part 202B of the layer 202.

[0110] Figure 10 represents, by a schematic top view, yet another variant embodiment of the photonic circuit 2 of figures 4 to 9.

[0111] The circuit 2 according to this variant embodiment differs from the circuits 2 described previously in relation to figures 4 to 9 by the shape of the suspended part 202B of the layer 202.

[0112] Indeed, in the exemplary embodiments and variant embodiments of figures 4 to 9, this suspended part 202B has a substantially rectangular shape, and therefore has a straight edge 1000 (see figures 4 to 9) beyond which the resonator 212 projects in a direction parallel to the face 204 of the substrate 200 and orthogonal to the intersection of the flank 210 with the front face 204 of the substrate 200.

[0113] In this variant, the suspended portion 202B of the layer 202 has a different shape, an example of which is illustrated in FIG. 10. However, as in the embodiments and alternative embodiments described previously, the resonator 212 comprises a second portion which, in a direction orthogonal to the face 204 of the substrate 200, is neither opposite the substrate 200 nor opposite the suspended portion 202B of the layer 202, and which, in a direction parallel to the face 204 of the substrate 200 and orthogonal to the intersection of the flank 210 with the front face 204 of the substrate 200, protrudes beyond the suspended portion 202B of the layer 202.

[0114] The person skilled in the art is able to provide other shapes of the suspended portion 202B of the layer 202 than those illustrated, by way of example, in relation to FIGS. 4 to 10.

[0115] Although, in the example of FIG. 10, the portion 224 of the waveguide 222 does not include any part arranged facing the substrate 200 in a direction orthogonal to the face 204 of the substrate 200 and the pads 228 are then connected to the portion 202B of the layer 202, in other examples not illustrated, this portion 224 of the waveguide 222 is arranged facing the substrate 200 in a direction orthogonal to the face 204 of the substrate 200, the pads 228 then being able to be connected either to the substrate 200 or to the suspended portion 202B of the layer 202.

[0116] Furthermore, in the example of Figure 10, the resonator 212 does not include any portion that is disposed facing the substrate 200 in a direction orthogonal to the face 204 of the substrate 200. However, in other examples not shown, the resonator 212 may include, as in the example of Figures 4 to 6, only a portion that is disposed facing the substrate 200 in a direction orthogonal to the face 204 of the substrate 200.

[0117] Figure 11 represents, by a schematic top view, yet another variant embodiment of the photonic circuit 2 of figures 4 to 10.

[0118] In this variant, the circuit 2 differs from the circuits 2 according to the embodiments and variant embodiments described previously in relation to figures 4 to 10 by the fact that it does not comprise a disc 212A, but a circular ring 212C. The ring 212C is attached to the suspended portion 202B of the layer 202.

[0119] For example, the ring 212C is attached to the suspended portion 202B of the layer 202 by at least one anchoring pad 216 and at least one holding arm 1100, for example three arms 1100 in the example of Figure 11 although in other examples not shown the circuit 2 comprises only a single arm 1100, two arms 1100 or more than three arms 1100. Each pad 216 extends in height from the layer 202 to a plane comprising the face of the layer 214 facing the layer 202. Each arm 1100 is similar to the arms 226 and is therefore defined in the layer 214 (not referenced in Figure 11). Each arm 1100 extends from an edge of the ring 212C to a pad 216. In other words, each arm 1100 has one end connected to the ring 212C and an opposite end connected to a pad 216.

[0120] Preferably, when the resonator 212 comprises a ring 212C, each pad 216 is arranged inside the ring 212C, that is to say that each pad 216 is arranged in a region delimited laterally by the internal edge of the ring 212C, and is arranged sufficiently far from the internal edge of the ring, for example more than 1 pm from the edge of the ring 212C, so as not to disturb the optical modes which are propagated in the ring 212C. In this case, each arm 1100 extends from an internal edge of the ring 212C to a corresponding pad 216. The arrangement of each pad 216 inside the ring 212C and sufficiently far from the inner edge of the ring 212C makes it possible to limit optical losses because the optical modes propagated in the ring 212C are shifted towards the outer edge of the ring 212C, and therefore to increase the optical quality factor.

[0121] Preferably, a single pad 216 fixes the resonator 212 to the layer 202, this pad 216 then preferably being arranged in the center of the ring 212C to limit as much as possible the optical losses resulting from the pad 216.

[0122] As an alternative example, a single pad 216 fixes the resonator 212 to the layer 202, this pad being disposed inside the resonator 212 but offset from the center of the ring. Each holding arm 1100 may then comprise a first portion extending from the inner edge of the ring 212C to the center of the ring 212C and a second portion, common to all the holding arms 1100, extending from the center of the ring 212C to the single pad 216.

[0123] Multiple sets of an arm 1100 and a pad 216 could be arranged such that the pads 216 are outside the ring 212C and each arm 1100 then extends from an outer edge of the ring 212C to a corresponding pad 216. However, compared to the case where the arms 1100 are connected to the inner edge of the ring 212C as described above, this alternative configuration would have had greater optical losses.

[0124] In the example of Figure 11, resonator 212 includes optional tip 212B.

[0125] Figure 12 represents, by a schematic top view, yet another variant embodiment of the photonic circuit 2 of figures 5 to 11.

[0126] In this variant, the circuit 2 differs from the circuits 2 according to the embodiments and variant embodiments described previously in relation to figures 4 to 11 by the fact that it does not comprise a disc 212A or a circular ring 212C, but a closed loop 212D for example in the shape of an athletics track ("racetrack" in English), or, in other words, for example in the shape of an oblong ring. For example, the ring 212D comprises two parallel rectilinear portions connecting together two portions in semicircle. As an alternative example, the two semicircle portions are connected to each other by two non-parallel rectilinear portions when the two semicircle portions do not have the same radius, or, more generally, by two portions which may be rectilinear or have meanders. The loop 212D is attached to the suspended portion 202B of the layer 202.

[0127] For example, the loop 212D is attached to the suspended portion 202B of the layer 202 by at least one anchoring pad 216 and at least one holding arm 1100. Each pad 216 extends vertically from the layer 202 to a plane comprising the face of the layer 214 facing the layer 202. Each arm 1100 is similar to the arms 226 and is therefore defined in the layer 214 (not referenced in FIG. 12). Each arm 1100 extends from an edge of the loop 212D to a pad 216. In other words, each arm 1100 has one end connected to the loop 212D and an opposite end connected to a pad 216.

[0128] Preferably, when the resonator 212 comprises a loop 212D, each pad 216 is arranged inside the ring 212D, that is to say that each pad 216 is arranged in a region delimited laterally by the internal edge of the loop 212D, and is arranged sufficiently far from the internal edge of the loop 212D, for example more than 1 pm from the edge of the loop 212D, so as not to disturb the optical modes which are propagated in the loop 212D. In this case, each arm 1100 extends from an internal edge of the loop 212D to a corresponding pad 216. The arrangement of each pad 216 inside the loop 212D and sufficiently far from the inner edge of the loop 212D makes it possible to limit optical losses because the optical modes propagated in the ring 212C are shifted towards the outer edge of the loop 212D, and therefore to increase the optical quality factor.

[0129] In the example of Figure 12, the loop 212D is attached to the layer 202 by two pads 216 disposed inside the loop 212D and four arms 1100. Each arm 1100 extends from an inner edge of the loop 212D to a pad 216. In other words, each arm 1100 has one end connected to the inner edge of the loop 212D and an opposite end connected to a pad 216. For example, in Figure 12 where the circuit 2 comprises two pads 216, two of the four arms 1100 each extend from the inner edge of the loop 212D to a first of the two pads 216, the other two arms 1100 each extending from the inner edge of the loop 212D to the second pad 216. For example, as illustrated in Figure 12, when the circuit 2 comprises at least two pads 216 arranged inside the loop 212D, these pads can be mechanically coupled to each other by mechanical reinforcement arms 1200 similar to the arms 1100 and 226.In this case, each arm 1200 has one end connected to one pad 216 and an opposite end connected to another pad 216. In the particular example of Figure 12, a single arm 1200 connects the two pads 216.

[0130] As an alternative example not shown, a single pad 216 fixes the resonator 212 to the layer 202, this pad 216 then preferably being arranged in the center of the loop 212D to limit as much as possible the optical losses resulting from the pad 216. However, this single pad 216 can be arranged inside the resonator 212 but offset relative to the center of the loop 212D, each holding arm 1100 then being able to comprise a first portion going from the internal edge of the loop 212D to the center of the loop 212D and a second portion, common to all the holding arms 1100, going from the center of the loop 212D to the single pad 216.

[0131] Multiple sets of an arm 1100 and a pad 216 could be arranged such that the pads 216 are outside the loop 212D and each arm 1100 then extends from an outer edge of the loop 212d to a corresponding pad 216. However, compared to the case where the arms 1100 are connected to the inner edge of the loop 212D as described above, this alternative configuration would have had greater optical losses.

[0132] In the example of Figure 12, resonator 212 includes optional tip 212B.

[0133] In the exemplary embodiments and alternative embodiments described above, the flank 210 may correspond to an outer lateral edge of the substrate 200 or to an edge of the substrate 200 corresponding to the edge of a through-opening etched through the substrate 200.

[0134] Furthermore, although embodiments and alternative embodiments have been described previously in which the structure 212 is an optical or opto-mechanical resonator defined in the layer 214, in other embodiments not illustrated, the structure 212 comprising the disk 212A, the circular ring 212C or the closed loop 212D has no optical function and is used as a mechanical resonator 212. This mechanical resonator 212 is attached to the layer 202 in the same manner as previously described, for example by at least one pad 216 and at least one arm 1100. Preferably, the pads 216 are arranged between the disk 212A and the layer 202 or inside the ring 212C or the loop 212D. Indeed, anchoring from the inside allows higher mechanical quality factors thanks to reduced mechanical coupling of the resonator 212 with the acoustic modes of the substrate 200.

[0135] Preferably, the mechanical resonator 212 is fixed to the layer 212 by a single pad 216 disposed in the center of the disc 212A or at the center of the ring 212C or center of the loop 212D, where the amplitude of the mechanical mode used is the lowest, which makes it possible to further reduce the mechanical coupling of the resonator 212 with the acoustic modes of the substrate 200. However, as an alternative example, a single pad 216 fixes the resonator 212 to the layer 202, this pad being disposed inside the resonator 212 but offset from the center of the disc 212A, the ring 212C or the loop 212D. In the case of the ring 212C or the loop 212D, each holding arm 1100 can then comprise a first portion going from the internal edge of the ring 212C to the center of the ring 212C and a second portion, common to all the holding arms 1100, going from the center of the ring 212C to the single stud 216.

[0136] The reading of the movement of the mechanical resonator 212 can then be done by non-optical transduction techniques (capacitive for example) or even optical by using an optical resonator separated from the mechanical resonator 212 by a space varying with the movements of the mechanical resonator, and by measuring variations in the resonance wavelength of the optical resonator resulting from these variations in the space between the mechanical resonator 212 and the optical resonator.

[0137] Various embodiments and variations have been described. Those skilled in the art will understand that certain features of these various embodiments and variations could be combined, and other variations will occur to those skilled in the art.

[0138] Finally, the practical implementation of the embodiments and variants described is within the reach of the person skilled in the art from the functional indications given above. In particular, from the description given above of circuit 2, the person skilled in the art is able to implement the manufacturing method of this circuit 2, using steps each being customary in the manufacturing processes of photonic circuits.

Claims

CLAIMS Device (2) comprising: a substrate (200); a first layer (202) comprising a first portion (202A) fixed to a front face (204) of the substrate (200) and a second portion (202B) suspended above a plane comprising the front face (204) of the substrate (200); and an optomechanical or mechanical resonator (212) fixed to the second portion (202B) of the first layer (202) and suspended under said second portion (202B) of the first layer (202) and above the plane comprising the front face (204) of the substrate (200), only a first portion of the resonator (212) being, in a direction orthogonal to the front face (204) of the substrate (200), facing the substrate (200) and / or the first layer (202). Device according to claim 1, in which the resonator (212) comprises a second part which, in a direction orthogonal to the front face (204) of the substrate, is not opposite either the first layer (202) or the substrate (200).Device according to claim 2, wherein, in a direction parallel to the front face (204) of the substrate (200), the second part of the resonator is disposed beyond an edge (210) of the substrate (200) and beyond an edge of the first layer (202). Device according to claim 2 or 3, wherein, in a direction parallel to the front face (204) of the substrate (200) and orthogonal to the intersection of said edge (210) of the substrate (200) with the front face (204) of the substrate (200), a dimension of the second part of the resonator (212) is less than 50 μm. The device of any one of claims 1 to 4, wherein: the device comprises a second layer (214); the second layer (214) is disposed between the first layer (202) and the front face (204) of the substrate (200); and the resonator (212) is defined in the second layer (214). The device of claim 5, wherein the device further comprises at least one third layer (218) disposed between the front face (204) of the substrate (200) and the second layer (214), and at least one fourth layer (220) disposed between the second layer (214) and the first layer (202). Device according to claim 5 or 6, wherein the first part (202A) of the first layer (202) rests on a stack (203) of layers (218, 214, 220), the stack preferably comprising the second layer (214).Device according to any one of claims 1 to 7, wherein the resonator (212) comprises a circular ring (212C), a loop in the shape of an athletics track (212D) or a disc (212A). Device according to claim 8, wherein the resonator (212) is fixed to the second part (202B) of the first layer (202) by at least one anchoring pad (216). Device according to claim 9 in its dependency on claim 5, wherein said at least one anchoring pad (216) extends in height from the second layer (214) to the second part (202B) of the first layer (202). . Device according to claim 9 or 10, wherein said at least one anchoring stud (216) is in contact with the disc (212A); or said at least one anchoring stud (216) is arranged inside a region delimited laterally by the ring (212C) and the device (2) comprises holding arms (1100) each extending from an internal edge of the ring (212C) to said at least one anchoring stud (216); or said at least one anchoring stud (216) is arranged inside a region delimited laterally by the closed loop (212D), preferably in the center of this region, and the device (2) comprises holding arms (1100) each extending from an internal edge of the closed loop (212D) to said at least one anchoring stud (216). .A device according to any one of claims 9 to 11, wherein the resonator (212) further comprises a tip (212B) attached to the outer periphery of the disc (212A), ring (212C) or closed loop (212D). . A device according to claim 12 taken in its dependence on claim 3, wherein the second portion of the resonator (212) comprises the tip (212B), the tip (212B) extending lengthwise in a direction parallel to the front face (204) of the substrate (200) and, preferably, orthogonal to the intersection of said edge (210) of the substrate (200) with the front face (204) of the substrate (200). . A device according to any one of claims 1 to 13, wherein the resonator (112) is an opto-mechanical resonator and the device further comprises a waveguide (222) defined in the same layer (214) as the. resonator (212), a portion (224) of the waveguide (222) being optically coupled to the resonator (212). . Device according to claim 14, in which the portion (224) of the waveguide (222) is suspended between the second part (202B) of the first layer (202) and a plane comprising the front face (204) of the substrate (200), preferably by holding arms (226) defined in the same layer (214) as the optical resonator (212) and each extending from said portion (224) of the waveguide (222) to an anchoring pad (228) fixed to the substrate (200) or to the second part (202B) of the first layer (202).

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