Phase change material switch

Abstract

The invention discloses a phase change material switch. The present disclosure relates to a switch (100) based on a phase change material formed on a support substrate (101) and comprises:-a zone (107) made of said phase change material coupling a first and a second conductive electrode (105A, 105B) of the switch; and-a waveguide (111) interposed between the support substrate and the section made of the phase change material and comprising a central region (111C) made of a first material having a first optical index, the central region (111C) being surrounded by a peripheral region (103) made of a second material having a second optical index less than the first optical index.

Description

Technical Field

[0001] The present invention relates generally to electronic devices and more particularly to switches. The present invention relates more particularly to switches based on phase change materials. Background Art

[0002] Various applications use switches to block or allow the flow of electrical signals between different parts of an electronic circuit, depending on the state of the signal used to control the switch. In the field of telecommunications, switches for radio frequency signals (also called radiofrequency (RF) switches) are integrated in various types of devices, such as reconfigurable filters, phase shifters, transmit array or reflectarray reconfigurable antennas, etc. These switches allow in particular the implementation of various functions: RF signal routing, switching of antennas between transmit and receive modes, activation of filters corresponding to a given frequency band, etc. RF switches are particularly used to design and implement reconfigurable radiating surfaces in the sub-THz frequency band, for example in the order of one or several hundred gigahertz, for applications in medical imaging and industrial monitoring, earth and deep space observation, as well as broadband telecommunication systems and radars.

[0003] RF switches are usually implemented based on field effect transistors, PIN diodes, electromechanical relays or MEMS (MicroElectroMechanical System) components, depending on the desired performance level. However, these switches are not completely satisfactory, especially for high-frequency applications, such as around 100 GHz. The performance of an RF switch depends on a parameter called the Figure of Merit (Fom), which is equal to the ON state resistance R of the RF switch. ON and the OFF state capacitor C OFF The product of resistance R ON and capacitor C OFF They reflect the insertion loss of the switch in the ON state and the isolation of the switch in the OFF state, respectively, both of which are quantities that need to be minimized for RF applications.

[0004] In order to surpass the limitations of the above-mentioned RF switches, switches based on phase change materials that are capable of switching between a conductive crystalline phase and an electrically insulating amorphous phase are proposed. Compared with the usual transistor- and PIN diode-based RF switches, switches based on phase change materials have a quality factor that is about ten times lower. For example, the quality factor of a transistor- and PIN diode-based RF switch is about 100 fs, compared with a quality factor of about 10 fs for a phase change material-based RF switch. The latter also has the following advantages: having non-volatile ON and OFF states, the switch does not require energy consumption to remain in either state. MEMS-based RF switches can achieve relatively low quality factors, but have various disadvantages, especially precision and high fingerprint, and have volatile states.

[0005] Among switches based on phase change materials, direct heating switches controlled by passing an electric current through the phase change material, or indirect heating switches controlled by, for example, passing an electric current pulse through a heating element electrically insulated from the phase change material, have been proposed. However, these switches have various disadvantages. In a direct heating switch, the control signal disturbs the RF signal transmitted between the conducting electrodes of the switch. In an indirect heating switch, the heating element generates parasitic capacitance and parasitic resistance. In addition, the indirect heating switch includes metal conducting tracks for transmitting the control signal from the current source to the heating element. In the case where the RF switch is part of a reconfigurable antenna, providing these tracks can highly disturb the field radiated by the antenna.

[0006] To overcome these drawbacks, switches based on RF phase change materials and optical actuation have been proposed. Optical actuation is implemented in these switches by direct laser irradiation of the phase change material. However, this requires precise alignment of the laser beam with the phase change material, making the integration of such switches highly complicated, especially in reconfigurable antenna applications that may include hundreds of switches. Summary of the invention

[0007] There is a need to overcome some or some of the disadvantages of existing switches. In particular, it is desirable to optimize the implementation of optically actuated phase change material switches.

[0008] To this end, one embodiment provides an optically actuated phase change material based switch formed on a supporting substrate and comprising:

[0009] a portion made of a phase change material coupling the first conductive electrode and the second conductive electrode of the switch; and

[0010] - a waveguide inserted between the supporting substrate and the portion made of said phase change material and comprising a central region made of a first material having a first optical index surrounded by a peripheral region made of a second material having a second optical index lower than the first optical index.

[0011] According to one embodiment, the central area of ​​the waveguide is separated from the portion made of said phase change material by a distance less than or equal to 100 nm, preferably less than or equal to 50 nm, more preferably equal to about 20 nm.

[0012] According to one embodiment, the waveguide further comprises an input coupling element having a Bragg structure, the input coupling element comprising evenly spaced sections of concentric rings.

[0013] According to one embodiment, the switch further comprises a laser source intended to illuminate the coupling element with laser radiation having a central wavelength equal to approximately 915 nm.

[0014] According to one embodiment, the input coupling element is separated from the supporting substrate by a distance within plus or minus 100 nm equal to about 1,500 nm.

[0015] According to one embodiment, the central region of the waveguide is separated from the supporting substrate by a distance within plus or minus 100 nm equal to about 1,500 nm.

[0016] According to one embodiment, the switch further comprises a first conductive via and a second conductive via extending between the portion made of the phase change material and the first conductive electrode and the second conductive electrode, respectively.

[0017] According to one embodiment, the central region of the waveguide is separated from the first conducting via and the second conducting via by a distance higher than or equal to 0.3 μm.

[0018] According to one embodiment, the section made of phase change material is coated with a passivation layer.

[0019] According to one embodiment, the central region and the peripheral region of the waveguide are made of silicon nitride and silicon oxide, respectively.

[0020] According to one embodiment, the central region of the waveguide is about 300 nm high and about 600 nm wide.

[0021] Another embodiment provides a method for manufacturing an optically actuated phase change material based switch comprising the following steps in succession:

[0022] a) forming a first conductive electrode and a second conductive electrode of a switch on a supporting substrate;

[0023] b) forming a waveguide on a supporting substrate including a central region made of a first material having a first optical index, the central region being surrounded by a peripheral region made of a second material having a second optical index less than the first optical index; and

[0024] c) forming a section made of the phase change material coupling the first conductive electrode and the second conductive electrode of the switch on the support substrate, the waveguide being interposed between the support substrate and the section made of the phase change material. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The foregoing features and advantages, as well as others, will be described in detail in the following description of specific embodiments given by way of illustration and not limitation with reference to the accompanying drawings, in which:

[0026] Figure 1A is a schematic partial top view of an example phase change material based switch according to one embodiment;

[0027] Figure 1B and Figure 1C yes Figure 1A The switches based on phase change materials are shown along Figure 1A A schematic partial cross-sectional view of planes BB and CC as shown; and

[0028] Figure 2A , Figure 2B , Figure 2C , Figure 2D and Figure 2E is along Figure 1A A schematic partial cross-sectional view of plane CC is shown, showing a method for manufacturing a Figure 1A , Figure 1B and Figure 1C Successive steps of an example method of a phase change material based switch are shown. DETAILED DESCRIPTION

[0029] Similar features have been designated by similar reference numerals in the various figures. In particular, common structural and / or functional features in the various embodiments may have the same reference numerals and may be provided with the same structure, dimensions, and material properties.

[0030] For clarity, only the operation and elements that are useful for understanding the embodiments described herein are illustrated and described in detail. In particular, applications in which phase change material based switches may be provided are not described in detail, and the described embodiments and alternatives are compatible with conventional applications implementing switches.

[0031] Unless otherwise specified, when referring to two elements being connected together, this means a direct connection without any intermediate elements except conductors, and when referring to two elements being coupled together, this means the two elements may be connected or they may be coupled via one or more other elements.

[0032] In the following disclosure, unless otherwise stated, when referring to absolute position qualifiers, such as terms "front", "back", "top", "bottom", "left", "right", etc., or when referring to relative position qualifiers, such as terms "above", "below", "higher than", "lower than", etc., or when referring to orientation qualifiers, such as "horizontal", "vertical", etc., reference is made to the orientation shown in the figure.

[0033] Unless otherwise indicated, the expressions "about," "approximately," "substantially," and "approximately" mean within 10%, and preferably within 5%.

[0034] In the following disclosure, unless otherwise specified, the "insulating" and "conductive" qualifiers mean electrical insulation and electrical conductivity, respectively.

[0035] Figure 1Ais a schematic partial top view of an example phase change material based switch 100 according to one embodiment. Figure 1B and Figure 1C yes Figure 1A The switches based on phase change materials are shown along Figure 1A Schematic partial cross-sectional view of planes BB and CC shown. In the example shown, plane BB is orthogonal to the conduction direction of the switch 100 and plane CC is parallel to the conduction direction of the switch 100 .

[0036] In the example shown, the switch 100 is formed on a support substrate 101. The support substrate 101 is, for example, a wafer or a piece of wafer made of a semiconductor material (e.g., silicon). Alternatively, the support substrate 101 may be made of an insulating material, such as glass, quartz, etc. Figure 1A , Figure 1B and Figure 1C In the orientation shown, planes BB and CC are orthogonal to the top surface of the support substrate 101 .

[0037] In the example shown, the support substrate 101 is coated with an insulating layer 103. Figure 1A , Figure 1B and Figure 1C In the orientation shown, the insulating layer 103 is located on the top surface of the support substrate 101 and is in contact with it. As an example, the layer 103 is an oxide layer, such as silicon oxide (SiO 2 ). The insulating layer 103 is Figure 1A Not shown in order not to overload the drawing.

[0038] In the example shown, the switch 100 also includes conductive electrodes 105A and 105B, which are separated from the support substrate 101 by a portion of the insulating layer 103. The portion of the insulating layer 103 is therefore vertically inserted between the top surface of the support substrate 101 and the conductive electrodes 105A and 105B. In the example shown, the conductive electrodes 105A and 105B are separated from each other by a portion of the insulating layer 103 extending laterally therebetween. The conductive electrodes 105A and 105B are intended, for example, to be connected to an RF communication circuit, which is not shown in detail in the drawings. The conductive electrodes 105A and 105B are made of a conductive material. As an example, the conductive electrodes 105A and 105B are made of a metal (e.g., copper or aluminum oxide) or of a metal alloy. In addition, the conductive electrodes 105A and 105B can have a single-layer or multi-layer structure. In the case of a multi-layer structure, the conductive electrodes 105A and 105B are formed, for example, by a stack, which is formed in Figure 1B and Figure 1C The orientation shown below includes, from bottom to top:

[0039] - a layer made of titanium having a thickness equal to, for example, about 10 nm;

[0040] a layer made of a copper and aluminum oxide alloy having a thickness equal to, for example, about 440 nm;

[0041] - a layer made of titanium having a thickness equal to, for example, about 10 nm;

[0042] - A layer made of titanium nitride having a thickness equal to, for example, approximately 100 nm.

[0043] In the example shown, the switch 100 also includes a section 107 made of phase change material that couples the conductive electrodes 105A and 105B. In this example, the section 107 made of phase change material extends vertically to align with a portion of each conductive electrode 105A, 105B. A first end of the section 107 made of phase change material is located in alignment with the conductive electrode 105A, and a second end of the section 107 opposite the first end is located in alignment with the conductive electrode 105B. As an example, the section 107 made of phase change material has a thickness of about 100 nm.

[0044] In the example shown, conductive vias 109A and 109B extend vertically from the bottom surface of the portion 107 made of phase change material through a portion of the insulating layer 103 to the top surface of the conductive electrodes 105A and 105B, respectively. The conductive vias 109A and 109B are located near the first end and the second end of the portion 107 made of phase change material, respectively, and allow the portion 107 to be electrically connected to the conductive electrodes 105A and 105B, respectively. As an example, the conductive vias 109A and 109B are made of metal (e.g., copper, aluminum oxide, or tungsten) or made of a metal alloy.

[0045] In the example shown, the sides of the conductive vias 109A and 109B are bounded or coated by the insulating layer 103. In addition, the sides and bottom of the phase change material portion 107 that are not in contact with the top surfaces of the conductive vias 109A and 109B are bounded or coated by the insulating layer 103.

[0046] For example, the portion 107 made of phase change material is made of a chalcogenide, i.e. a material or alloy comprising at least one chalcogenide element, such as a material from the group consisting of germanium telluride (GeTe), antimony telluride (SbTe) or germanium antimony telluride (GeSbTe, conventionally designated as “GST”). Alternatively, the portion 107 is made of vanadium dioxide (VO 2 ) is made.

[0047] Generally, phase change materials are able to switch between a crystalline phase and an amorphous phase under temperature changes, the amorphous phase having a higher resistance than the crystalline phase. In the case of switch 100, this phenomenon is utilized to obtain an OFF state that prevents current from flowing between conductive electrodes 105A and 105B when the material of section 107 is in the amorphous phase, and an ON state that allows current to flow between conductive electrodes 105A and 105B when the material of section 107 is in the crystalline phase.

[0048] In the example shown, the switch 100 further comprises a waveguide 111 interposed between the support substrate 101 and the section 107 made of phase change material. In this example, the waveguide 111 extends laterally along a main direction visibly orthogonal to the conduction direction of the switch 100. In the example shown, the waveguide 111 comprises a central region 111C or core surrounded by an insulating peripheral region made of a portion of the insulating layer 103. The central region 111C and the peripheral region of the waveguide 111 are made of a material selected so as to obtain a contrast in optical index, allowing the optical mode of interest emitted from the laser source LS to be confined and guided within the central region 111A. As an example, the laser source LS comprises a laser diode or a pulsed diode.

[0049] The central region 111C of the waveguide 111 has an optical index higher than that of the peripheral regions. As an example, the central region 111C of the waveguide 111 is made of silicon nitride (SiN) and the peripheral regions are made of silicon oxide. The use of silicon nitride for implementing the central region 111C is advantageously compatible with CMOS (Complementary Metal Oxide Semiconductor) manufacturing methods. In addition, silicon nitride allows obtaining a large uniformity in thickness, a correct light wave confinement during propagation in the waveguide 111, and low propagation losses. For example, except for the portion aligned with the section 107 made of phase change material, the central region 111C of the waveguide 111 is surrounded by the material of the insulating layer 103, for example, with a thickness higher than 1.5 μm, so as to limit the propagation losses in the waveguide 111.

[0050] Figure 1C The plane CC shown in FIG. 1 is substantially orthogonal to the propagation direction of the laser radiation in the waveguide 111. In the example shown, the peripheral region of the waveguide 111 (in this example, the insulating layer 103) coats or defines a face of the central region 111C parallel to the propagation direction of the laser radiation (the side faces, bottom face and top face of the central region 111C are parallel to the axis orthogonal to the plane CC). In this example, a portion of the insulating layer 103 is formed from a face of the central region 111C that is aligned with the portion 107 made of phase change material (in this example, the insulating layer 103) and is disposed on the surface of the central region 111C. Figure 1CThe orientation shown is the top surface of the central region 111C) and extends vertically to the opposite side (with the region 107 made of phase change material) where the region 107 is located. Figure 1C The orientation shown is the bottom surface of section 107).

[0051] In the example shown, in a cross-sectional view along a plane CC orthogonal to the propagation direction of the laser radiation in the waveguide 111, the central region 111C is clearly rectangular in section. As an example, the cross section of the central region 111C has a width equal to about 600 nm and a height or thickness equal to about 300 nm. In addition, the central region 111C is separated from the portion 107 made of phase change material by a distance less than or equal to 100 nm, for example less than or equal to 50 nm, for example equal to about 20 nm. In this example, the distance separating the central region 111C from the portion 107 made of phase change material corresponds to the thickness of a portion of the insulating layer 103 interposed between the central region 111C and the portion 107 made of phase change material. As an alternative, the portion 107 made of phase change material can be located on the central region 111C of the waveguide 111 and in contact therewith.

[0052] The coupling of the optical power of the radiation emitted in the central region 111C of the waveguide 111 with the phase change material of the section 107 is performed via the evanescent field. The inventors have observed that the closer the central region 111C is to the section 107, the higher the optical coupling and the higher the reflection due to the index change. On the contrary, the farther the central region 111C is from the section 107, the lower the reflection and the lower the coupling ratio. For example, the distance separating the section 107 made of phase change material from the central region 111C of the waveguide 111 is selected so that the optical wave is absorbed by the phase change material of the section 107 and at the input face of the section 107 made of phase change material (at Figure 1B and Figure 1C The orientation shown is a compromise between reflecting optical waves on the bottom surface of section 107).

[0053] As an example, the central region 111C of the waveguide 111 is laterally separated from the conducting vias 109A and 109B by a distance higher than or equal to 0.3 μm in case the conducting vias 109A and 109B have a lateral dimension lower than 10 μm and a distance higher than or equal to 0.5 μm, for example higher than or equal to 1 μm, along the propagation axis of the radiation in the central region 111C of the waveguide 111, in case the conducting vias 109A and 109B have a lateral dimension higher than or equal to 10 μm along the propagation axis of the radiation in the central region 111C of the waveguide 111. It allows avoiding or limiting absorption of the radiation transmitted from the waveguide 111 by the material of the conducting vias 109A and 109B.

[0054] For example, the waveguide 111 is of the single-mode type, i.e. it is suitable for limiting and guiding a single optical mode for each polarization type. For example, the waveguide 111 is more particularly suitable for limiting and guiding a single optical mode selected among the zero-order electric transverse mode (TE0) and the zero-order magnetic transverse mode (TM0). Since the TE0 and TM0 modes are orthogonal to each other, they cannot couple to each other within the waveguide 111. The selection of the mode limited and guided between the TE0 mode and the TM0 mode by the waveguide 111 is determined by the polarization of the laser source LS. In the case where the laser source LS emits radiation with electric transverse polarization TE, the waveguide 111 is therefore suitable for limiting and guiding only the zero-order electric transverse mode TE0.

[0055] As an example, the radiation emitted by the laser source LS has a central wavelength of around 915 nm. It allows obtaining a compromise between the absorption of the radiation by the phase-change material of the sector 107, which is more important because the wavelength of the emission of the laser source LS is low, and the decay of the radiation transmitted from the waveguide 111, the former being more important because the wavelength of the emission of the laser source LS is low, and the latter being lower because the wavelength of the emission of the laser source LS is high. As an example, the absorption of the radiation by the phase-change material of the sector 107 is twice as great when the wavelength of the radiation is equal to about 915 nm than when it is equal to about 1,550 nm. Moreover, in the case where the region 111C is made of silicon nitride, the decay of the radiation transmitted by the waveguide 111 is too high at wavelengths less than 500 nm to allow obtaining a phase change of the material of the sector 107.

[0056] For example, on the side of its end intended to be illuminated by the laser source LS, the waveguide 111 comprises an input coupling element 113, also called input surface of the waveguide 111. In the example shown, the input coupling element 113 is a diffraction grating with a Bragg structure allowing to capture the radiation emitted by the laser source LS, and this radiation will propagate along the waveguide 111 until opposite to the section made of phase change material. In the example shown, the input coupling element 113 comprises uniformly spaced portions of concentric rings, for example spaced by a distance equal to about 340 nm, and each having the same width, for example approximately 340 nm, for example when viewed from above. It advantageously allows the input coupling element 113 to be implemented by means of a lithographic equipment with a resolution of approximately 300 nm, the width and spacing of the ring portions of the input coupling element 113 being even lower, since the central wavelength of the laser radiation emitted from the source LS is small.

[0057] The ring portions of the input coupling element 113 are laterally separated from each other by portions of the insulating layer 103. As an example, the concentric ring portions of the input coupling element 113 are made of the same material as the central region 111C of the waveguide 111. The central region 111C of the waveguide 111 and the rings of the input coupling element 113 are, for example, formed in the same insulating layer 115. The insulating layer 115 extends, for example, over a majority of the top surface of the holding support 101. In the example shown, portions of the insulating layer 115 are located on and in contact with portions of the top surfaces of the conducting electrodes 105A and 105B.

[0058] For example, the input coupling element 113 is separated from the support substrate 101 by a distance within 100 nm up and down equal to about 1,500 nm. It advantageously allows to exploit the structured reflection of the light waves transmitted by the waveguide 111 on the top surface of the holding support 101, in particular in the case where the support substrate 101 is made of silicon, and to optimize the coupling between the laser source LS and the waveguide 111 by means of the input coupling element 113.

[0059] For example, the central region 111C of the waveguide 111 is separated from the supporting substrate 1001 by a distance higher than 1 μm. This advantageously allows to avoid or limit the phenomenon of optical absorption of the radiation transmitted by the waveguide 111 by the holding support 101. In the example shown, the central region 111C of the waveguide 111 is separated from the supporting substrate 101 by the same distance as the input coupling element 113. In this case, the central region 111C is separated from the supporting substrate 101 by a distance within 100 nm above and below equal to about 1,500 nm. The conducting electrodes 105A and 105B and the portion of the insulating layer 103 inserted between the supporting substrate 101 and the conducting electrodes 105A and 105B have, for example, a cumulative thickness within 100 nm above and below equal to 1,500 nm. As an example, the conductive electrodes 105A and 105B each have a thickness equal to about 560 nm, and the portion of the insulating layer 103 interposed between the support substrate 101 and the conductive electrodes 105A and 105B has a thickness equal to about 940 nm.

[0060] As an alternative, an insulating layer (e.g., a layer made of silicon oxide) having a thickness of, for example, equal to about 20 nm may be inserted between the support substrate 101 and the conductive electrodes 105A and 105B. In such a case, the thickness of the conductive electrodes 105A and 105B and / or the thickness of the portion of the insulating layer 103 inserted between the support substrate 101 and the conductive electrodes 105A and 105B is suitable to achieve a distance within a range of 100 nm above and below equal to about 1,500 nm between the top surface of the region 107 made of the phase change material and the top surface of the support substrate 101. As an example, in the case of providing an insulating layer of about 20 nm thick between the insulating layer 115 and the conductive electrodes 105A and 105B, the conductive electrodes 105A and 105B each have a thickness equal to about 560 nm, and the portion of the insulating layer 103 inserted between the support substrate 101 and the conductive electrodes 105A and 105B has a thickness equal to about 920 nm.

[0061] In the example shown, the side of the portion 107 made of phase change material opposite to the support substrate 101 (at Figure 1B and Figure 1C The top surface of the region 107 in the orientation shown is coated with a passivation layer 117. In this example, the passivation layer 117 is located on and in contact with the top surface of the region 107 made of phase change material. The passivation layer 117 allows the phase change material of the region 107 to be protected from oxidation. In the example shown, the sides and top surface of the passivation layer 117 are coated by the insulating layer 103. In the example shown, a portion of the insulating layer 103 extends over the top surface of the passivation layer 117. For example, the passivation layer 117 has a thickness equal to about 20 nm. As an example, the passivation layer 117 is made of silicon nitride or germanium nitride. Figure 1A The passivation layer 117 is not shown in the drawing in order not to overload the drawing sheet. As an alternative, the passivation layer 117 can be omitted.

[0062] Although not yet Figure 1A , Figure 1B and Figure 1C As shown in FIG. 1 , the switch 100 may further include a contact element and / or a conductive track, such as a metal track, which is located on the top surface of the insulating layer 103 and in contact therewith. The contact element and / or the conductive track are, for example, connected to the conductive electrodes 105A and 105B of the switch 100 and provide, for example, a function of routing RF signals. The contact element and / or the conductive track are, for example, separated from the central area 111C of the waveguide 111 by a distance higher than 1 μm, for example higher than 1.5 μm. It allows to avoid or limit the absorption of the radiation transmitted by the waveguide 111 by the material of the contact element and / or the conductive track.

[0063] To trigger the switch 100 from the OFF state to the ON state, the portion 107 is heated at a temperature T1 and for a duration d1, for example using a laser source LS, via the waveguide 111. The temperature T1 and the duration d1 are selected so as to induce a phase change of the material of the portion 107 from the amorphous phase to the crystalline phase. As an example, the temperature T1 is above the crystallization temperature and below the melting temperature of the phase change material, and the duration d1 ranges from 100 ns to 1 μs.

[0064] Conversely, to trigger the switch 100 from the ON state to the OFF state, the portion 107 is heated at a temperature T2 higher than the temperature T1 and for a duration d2, which is less than the duration d1, via the waveguide 111, for example using a laser source LS. The temperature T2 and the duration d2 are selected so as to induce a phase change of the material of the portion 107 from the crystalline phase to the amorphous phase. As an example, the temperature T2 is higher than the melting temperature of the phase change material and the duration d2 ranges from 10 ns to 100 ns.

[0065] One advantage of the switch 100 is the location of the waveguide 111 below the section 107 made of phase change material, i.e. between the supporting substrate 101 and the section 107 made of phase change material. It allows a passivation layer 117 to be provided on the section 107 made of phase change material in order to protect this material from oxidation during the steps of manufacturing and using the switch 100. If the waveguide 111 were placed above the section 107 made of phase change material, for example if the central region 111C of the waveguide was located on and in contact with the passivation layer 117, the confinement of the optical waves within the waveguide would be reduced and it would reduce the coupling with the phase change material of the section 107. Furthermore, providing the central region 111C of the waveguide 111 above the section 107 made of phase change material would require etching of the material of the central region 111C to stop on the phase change material of the section 107, which would have the chance to degrade the latter. This would highly complicate the implementation of the switch 100.

[0066] Figure 2A , Figure 2B , Figure 2C , Figure 2D and Figure 2E is along Figure 1A A schematic partial cross-sectional view of plane CC is shown, showing a method for manufacturing a Figure 1A , Figure 1B and Figure 1C Successive steps of an example method of a phase change material based switch 100 are shown.

[0067] More specifically, Figure 2AThe structure obtained at the end of the step of forming a portion 103-1 of the insulating layer 103 on one side of the top surface of the supporting substrate 101 is shown. For example, the portion 103-1 of the insulating layer 103 is a thermal oxide layer located on the top surface of the supporting substrate 101 and in contact therewith.

[0068] More specifically, Figure 2B The structure obtained at the end of the step of forming the conductive electrodes 105A and 105B and the other portion 103 - 2 of the insulating layer 103 on one side of the top surface of the supporting substrate 101 is shown.

[0069] As an example, one or more conductive layers, for example made of metal or of a metal alloy, are first deposited successively on all top surfaces of the portion 103-1 of the insulating layer 103. During this step, the one or more conductive layers are formed, for example, by PVD (physical vapor deposition). The conductive electrodes 105A and 105B are then formed, for example, by photolithography and then etching of the one or more conductive layers.

[0070] A portion 103-2 of the insulating layer 103 is then deposited on one side of the top surface of the supporting substrate 101. The portion 103-2 of the insulating layer 103 thus coats the portion of the top surface of the portion 103-1 that is not coated by the conductive electrodes 105A and 105B, and also coats the side and top surfaces of the conductive electrodes 105A and 105B. The portion 103-2 of the insulating layer 103 is formed, for example, by PECVD (Plasma-Enhanced Chemical Vapor Deposition), for example by HDPCVD (High-Density Plasma Chemical Vapor Deposition). As an example, the portion 103-2 of the insulating layer 103 has a thickness of about 700 nm after deposition. For example, the thickness is then reduced by chemical and mechanical polishing (CMP) stopping on the conductive electrodes 105A and 105B so that the portion 103 - 2 of the insulating layer 103 is flush with the top surfaces of the conductive electrodes 105A and 105B.

[0071] More specifically, Figure 2C The structure obtained at the end of the following steps is shown:

[0072] a) depositing an insulating layer 115 on one side of the top surface of the support substrate 101;

[0073] b) a structured insulating layer 115; and

[0074] c) Depositing another portion 103 - 3 of the insulating layer 103 on one side of the top surface of the support substrate 101 .

[0075] As an example, the deposition of the insulating layer 115 is performed by PECVD. The insulating layer 115 has a thickness equal to about 300 nm, for example. The central region 111C of the waveguide 111 and the input coupling element 113 ( Figure 2C 1 (not shown) is formed at the end of the step of structuring (for example by photolithography and then etching) the insulating layer 115.

[0076] By way of example, the deposition of the portion 103-3 of the insulating layer 103 is performed by HPCVD. After deposition, the portion 103-3 of the insulating layer 103 has, for example, a thickness equal to about 500 nm. The portion 103-3 of the insulating layer 103 is then planarized, for example by an operation of chemical and mechanical polishing, wherein the portion 103-3 of the insulating layer 103 is stopped on the portion of the insulating layer 115 remaining after structuring, so that the portion 103-3 of the insulating layer 103 is flush with the top surface of the insulating layer 115.

[0077] When viewed from above, insulating layer 115 has, for example, a surface equal to at least 35%, for example at least 75% and it may reach 90% of the surface of support substrate 101 . This advantageously allows facilitating the stopping of the step of chemically and mechanically polishing portion 103 - 3 of insulating layer 103 .

[0078] More specifically, Figure 2D The structure obtained at the end of the step of depositing another portion 103 - 4 of the insulating layer 103 on one side of the top surface of the support substrate 101 and forming the conductive vias 109A and 109B is shown.

[0079] As an example, depositing the portion 103-4 of the insulating layer 103 is performed by PECVD. For example, the portion 103-4 of the insulating layer 103 has a thickness less than or equal to 100 nm, such as less than or equal to 50 nm, such as equal to about 20 nm after deposition.

[0080] As an alternative, depositing portion 103 - 4 of insulating layer 103 may be omitted.

[0081] The conductive vias 109A and 109B are formed, for example, by photolithography followed by etching, such as reactive ion etching (RIE), and then one or more conductive layers, for example made of metal or metal alloy, are deposited on one side of the top surface of the support substrate 101 .

[0082] In the example shown, the conductive vias 109A and 109B extend vertically from the top surface of the portion 103-4 of the insulating layer 103 to the top surface of the conductive electrodes 105A and 105B, respectively. As an example, each conductive via 109A, 109B is made of a stack comprising a titanium nitride layer, for example having a thickness equal to about 30 nm and formed by PVD, which is coated by a tungsten layer formed by CVD (Chemical Vapor Deposition). The stack is then planarized, for example, by chemical and mechanical polishing, stopping on the portion 103-4 of the insulating layer 103, or, in a variant in which the portion 103-4 of the insulating layer 103 is omitted, stopping on the insulating layer 115.

[0083] More specifically, Figure 2E The structure obtained at the end of the following consecutive steps is shown:

[0084] a) depositing a layer 207 made of a phase change material on one side of the top surface of the support substrate 101;

[0085] b) depositing an insulating layer 217 on one side of the top surface of the support substrate 101;

[0086] c) depositing another portion 103 - 5 of the insulating layer 103 on one side of the top surface of the support substrate 101 ; and

[0087] d) The structured layers 207 and 217 and the portion 103 - 5 of the insulating layer 103 .

[0088] As an example, the layer 207 made of phase change material is deposited by PVD.

[0089] For example, the portion 103-5 of the insulating layer 103 is structured by photolithography followed by etching (e.g. RIE etching) so that only the region of the portion 103-5 that is located at a position aligned with the future portion 107 made of phase change material remains. The portion 103-5 of the insulating layer 103 is then used, for example, as a hard mask to structure the passivation layer 217 and the layer 207 made of phase change material. The layers 217 and 207 are structured simultaneously, for example, in the same step of photolithography followed by etching (e.g. RIE etching). The previously referenced Figure 1A , Figure 1B and Figure 1C A portion 107 and a passivation layer 117 made of a phase change material are depicted.

[0090] from Figure 2EStarting from the structure shown in , a further step may be performed, which is to deposit another portion of the insulating layer 103 (having a thickness of, for example, about 2 μm) and then polish this portion of the insulating layer 103, for example by CMP, in order to obtain a thickness of, for example, about 1.5 μm over the central region 111C of the waveguide 111. For example, the above reference Figure 1A , Figure 1B and Figure 1C The structure described is obtained from this. For simplicity, Figure 1A , Figure 1B and Figure 1C An example is shown in which the portions 103-1, 103-2, 103-3, 103-4, and 103-5 of the insulating layer 103 are made of the same material. However, this example is not limiting, and the above reference Figure 2A-2E The different portions of the described insulating layer 103 may alternatively be made of different materials.

[0091] Furthermore, although not shown in detail in the drawings, a step of forming conductive vias is then performed, which extend vertically from the top surface of the insulating layer 103 to the top surfaces of the conductive electrodes 105A and 105B, passing through the insulating layer 115, and then a step of forming contact elements and / or conductive tracks, which are located on and in contact with the top surfaces of these vias, may be performed. As an example, the conductive vias are formed by performing openings in the insulating layers 103 and 115 by photolithography and then etching (e.g., RIE etching), which are then filled, for example, with a metal or a metal alloy.

[0092] As an example, each contact element is made of a stack of Figure 1B and Figure 1C The orientation shown below includes, from bottom to top:

[0093] - a titanium layer having a thickness equal to, for example, about 10 nm;

[0094] - a copper and aluminum oxide alloy having a thickness equal to, for example, about 1 μm;

[0095] a titanium layer having a thickness equal to, for example, about 10 nm; and

[0096] - a titanium nitride titanium layer having a thickness equal to, for example, approximately 100 nm.

[0097] The contact elements and / or the conducting tracks are obtained, for example, by successive deposition (for example by PVD) of layers made of the abovementioned materials, these depositions being followed by a structuring step, for example by photolithography and then etching.

[0098] Reference above FIG. 2A to FIG. 2EOne advantage of the described method lies in the fact that it allows the central region 111C of the waveguide 111 to be formed on a planar surface. In particular, in reference Figure 2B During the steps described, a planarization step, for example by CMP, is performed before depositing the insulating layer 115. In particular, the portion 103-2 of the insulating layer 103 is planarized, for example by CMP, with a stop on the layer forming the conductive electrodes 105A and 105B, or on the top surface of the stack forming the conductive electrodes 105A and 105B, for example a layer made of titanium nitride. The stop surface during this step is, for example, higher than 35%, for example about 50%, of the surface of the supporting substrate 101. It makes the stop planarization operation easier.

[0099] A person skilled in the art may have considered that forming the central region 111C of the waveguide 111 on the portion 107 made of phase change material would be complicated to perform, because the phase change material of the portion 107 would be likely to be damaged by the compound used during the planarization operation. A solution to overcome this problem may include providing an etch stop layer on the top surface of the portion 107 made of phase change material, and the etch stop layer is in contact with the top surface, which etch stop layer will be removed later or taken into account in the operation of the switch 100. However, this will complicate the implementation of the switch 100. In addition, the surface of the portion 107 made of phase change material is, for example, less than 1% of the surface of the supporting substrate 101, and the planarization operation cannot be accurately controlled. A dummy element made of phase change material, such as a pad, may be provided in order to increase the surface of the phase change material, for example to obtain a portion made of phase change material having a cumulative surface higher than 35% of the surface of the supporting substrate 101. However, this will make the design and implementation of the switch 100 highly more complicated.

[0100] Although not described in detail, switch 100 may be integrated into any type of device including at least one switch that optionally averages adjustments within the capabilities of a person skilled in the art based on reading this specification. In particular, a person skilled in the art will be able to integrate switches of the type of switch 100 in RF applications, such as in a reconfigurable antenna with a transmitter array or a reflector network, based on the teachings of this specification.

[0101] Various embodiments and variations have been described. Those skilled in the art will appreciate that certain features of these embodiments may be combined and that those skilled in the art will readily conceive of other variations. Finally, the actual implementation of the embodiments and variations described herein is within the capabilities of those skilled in the art based on the functional descriptions provided herein. In particular, the described embodiments are not limited to the specific examples of materials and dimensions indicated in this specification.

Claims

1. An optically actuated phase change material based switch (100) formed on a supporting substrate (101) and comprising: - a portion (107) made of the phase change material, coupling the first conductive electrode and the second conductive electrode (105A, 105B) of the switch; and - a waveguide (111) inserted between the support substrate and the portion made of the phase change material and comprising a central region (111C) made of a first material having a first optical index, the central region (111C) being surrounded by a peripheral region (103) made of a second material having a second optical index less than the first optical index.

2. The switch (100) according to claim 1, wherein: The central region (111C) of the waveguide (111) is separated from the portion (107) made of the phase change material by a distance less than or equal to 100 nm, preferably less than or equal to 50 nm, more preferably equal to about 20 nm.

3. The switch (100) according to claim 1 or 2, wherein: The waveguide (111) also includes an input coupling element (113) having a Bragg structure, the input coupling element (113) comprising evenly spaced portions of concentric rings.

4. The switch (100) according to claim 3, further comprising a laser source (LS) intended to illuminate the coupling element (113) with laser radiation having a central wavelength equal to about 915 nm.

5. The switch (100) according to claim 3 or 4, wherein: The input coupling element (113) is separated from the support substrate (101) by a distance within a range of plus or minus 100 nm equal to about 1,500 nm.

6. The switch (100) according to any one of claims 1 to 5, wherein: The central region (111C) of the waveguide (111) is separated from the support substrate (101) by a distance within a range of plus or minus 100 nm equal to about 1,500 nm.

7. The switch (100) according to any one of claims 1 to 6, further comprising a first conductive via and a second conductive via (109A, 109B) extending between the portion (107) made of the phase change material and the first conductive electrode and the second conductive electrode (105A, 105B), respectively.

8. The switch (100) according to claim 7, wherein: The central region (111C) of the waveguide (111) is separated from the first conductive via and the second conductive via (109A, 109B) by a distance greater than or equal to 0.3 μm.

9. The switch (100) according to any one of claims 1 to 8, wherein: The portion (107) made of the phase change material is coated with a passivation layer (117).

10. The switch (100) according to any one of claims 1 to 9, wherein: The central region (111C) and the peripheral region (103) of the waveguide (111) are made of silicon nitride and silicon oxide, respectively.

11. The switch (100) according to any one of claims 1 to 10, wherein: The central region (111C) of the waveguide (111) is about 300 nm high and about 600 nm wide.

12. A method for manufacturing an optically actuated phase change material based switch (100), comprising the following steps in succession: a) forming a first conductive electrode and a second conductive electrode (105A, 105B) of the switch on a supporting substrate (101); b) forming a waveguide (111) on the support substrate including a central region (111C) made of a first material having a first optical index, the central region (111C) being surrounded by a peripheral region (103) made of a second material having a second optical index smaller than the first optical index; and c) forming a section (107) made of the phase change material on the support substrate, coupling the first conductive electrode and the second conductive electrode of the switch, the waveguide being interposed between the support substrate and the section made of the phase change material.

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