High critical temperature metal nitride layer with oxide or oxynitride seed layer

Abstract

A superconducting device includes a substrate, a metal oxide or metal oxynitride seed layer on the substrate, and a metal nitride superconducting layer directly disposed on the seed layer. The seed layer is an oxide or oxynitride of a first metal, and the superconducting layer is a nitride of a different second metal.

Description

Technical Field

[0001] The present disclosure relates to using a seed layer to increase the superconducting critical temperature of a metal nitride layer. Prior Art

[0002] In the context of superconductivity, the critical temperature (T) represents the temperature at which a material becomes superconducting. Niobium nitride (NbN) is a material that can be used in superconducting applications, such as superconducting nanowire single photon detectors (SNSPDs) for quantum information processing, defect analysis in CMOS and LIDAR. The critical temperature of NbN depends on the material's crystal structure and atomic ratio. For example, referring to Figure 1, cubic delta-phase NbN offers advantages due to its relatively high critical temperature, e.g., 9.7 K to 16.5 K. (The indicated process temperatures are specific to a particular manufacturing process and may not be applicable to other processes and deposition chamber designs.)

[0003] Niobium nitride can be deposited onto a workpiece by physical vapor deposition (PVD). For example, sputtering can be performed using a niobium target in the presence of nitrogen. Sputtering is performed by inducing a plasma in a reactor chamber containing the target and workpiece. Summary of the Invention

[0004] In one embodiment, a superconducting device includes a substrate, a metal oxide or metal oxynitride seed layer on the substrate, and a metal nitride superconducting layer disposed directly on the seed layer. The seed layer is an oxide or oxynitride of a first metal, and the superconducting layer is a nitride of a second, different metal.

[0005] In another aspect, a superconducting device includes a substrate, a lower seed layer on the substrate, an upper seed layer disposed directly on the lower seed layer, and a superconducting layer disposed directly on the upper seed layer. The lower seed layer is a nitride of a first metal, the upper seed layer is an oxide or oxynitride of the first metal, and the superconducting layer is a nitride of a second, different metal.

[0006] Features may include one or more of the following.

[0007] The metal oxide or metal oxynitride seed layer may have a thickness of 0.1 nm to 1 nm. The metal oxide or metal oxynitride seed layer may be one to five atomic layers thick. The metal oxide or metal oxynitride seed layer may have a thickness of approximately 5 nm. The metal nitride seed layer may have a thickness of 3 nm to 5 nm. The superconducting layer may include at least one superconducting wire. The device may be a superconducting nanowire single photon detector (SNSPD). The metal nitride superconducting layer may have a thickness of 4 nm to 50 nm.

[0008] Implementations may provide, but are not limited to, one or more of the following advantages. The critical temperature of a metal nitride layer (e.g., a NbN layer) can be increased. This allows for the fabrication of devices, such as SNSPDs, using superconducting wires with higher critical temperatures. The larger difference between the operating temperature (2 K to 3 K) and the critical temperature provides superior detection efficiency, lower dark counts, and potentially faster time response.

[0009] It should be noted that "superconducting" indicates that the material becomes superconducting at the operating temperature of the device (e.g., 2 K to 3 K). During device fabrication at or above room temperature, or when the device is not cooled for operation, the material is not actually superconducting.

[0010] The details of one or more implementations are described in the accompanying drawings and the following description. Other possible aspects, features, and advantages will become apparent from the detailed description, drawings, and claims. Simple diagram description

[0011] FIG. 1 is a graph showing the phase of niobium nitride as a function of processing temperature and nitrogen atomic percentage.

[0012] FIG. 2A is a schematic cross-sectional view of a device including a metal nitride lower seed layer, a metal oxide or oxynitride upper seed layer, and a superconducting metal nitride layer.

[0013] FIG. 2B is a schematic cross-sectional view of the element of FIG. 2A , wherein the superconducting layer has been etched to form a superconducting wire.

[0014] 3A to 3C are flow charts of a method for manufacturing the device of FIG. 2A or FIG. 2B.

[0015] FIG. 4A is a schematic cross-sectional view of a device including a metal oxide or oxynitride seed layer and a superconducting metal nitride layer.

[0016] FIG. 4B is a schematic cross-sectional view of the element of FIG. 4A , wherein the superconducting layer has been etched to form a superconducting wire.

[0017] FIG. 5 is a flow chart of a method for manufacturing the device of FIG. 4A or FIG. 4B .

[0018] FIG. 6A is a schematic cross-sectional view of a device including a metal nitride seed layer and a superconducting metal nitride layer.

[0019] FIG. 6B is a schematic cross-sectional view of the element of FIG. 6A , wherein the superconducting layer has been etched to form a superconducting wire.

[0020] FIG. 7 is a flow chart of a method for manufacturing the device of FIG. 6A or FIG. 6B.

[0021] FIG. 8A is a schematic top view of a SNSPD including distributed Bragg reflectors.

[0022] FIG. 8B is a schematic cross-sectional side view of the element of FIG. 8A .

[0023] FIG. 9A is a schematic top view of a SNSPD including a waveguide.

[0024] FIG. 9B is a schematic cross-sectional side view of the element of FIG. 9A .

[0025] FIG. 9C is a schematic cross-sectional side view of another implementation of the element of FIG. 9A .

[0026] Like reference numbers and names in the various drawings indicate like elements. Implementation Method

[0027] As mentioned above, niobium nitride (particularly delta-phase NbN) offers several advantages as a superconducting material. However, delta-phase NbN can be difficult to deposit with satisfactory quality. Furthermore, the greater the difference between the operating temperature (2 to 3 K) and the critical temperature, the better the device performance. An aluminum nitride (AlN) layer can be used as a seed layer to increase the critical temperature of the NbN layer. Without being bound by any particular theory, the AlN seed layer can induce a crystalline structure in the NbN layer, which increases the critical temperature.

[0028] However, it has surprisingly been discovered that exposing the AlN seed layer to the atmosphere and maintaining it at room temperature before depositing the NbN layer can actually provide a higher critical temperature than depositing the NbN layer on the AlN seed layer—for example, by approximately 0.5 K—without breaking vacuum and reducing the substrate temperature. Again, without being bound by any particular theory, two non-exclusive possibilities have been proposed. First, exposing the AlN to the atmosphere may cause a thin layer of aluminum oxide or aluminum oxynitride to form on the surface of the AlN layer, which induces a superior crystalline structure in the NbN layer. Second, thermal cycling the AlN seed layer by lowering the substrate temperature from a first deposition temperature for AlN (for example, 400°C) to room temperature (i.e., 20°C to 22°C) and then returning the substrate temperature to a second deposition temperature for NbN (for example, 400°C) may affect the stress in the AlN seed layer, which may affect its crystalline structure, and in turn, the crystalline structure of the NbN layer.

[0029] FIG2A is a schematic diagram of some layers of a device 100 including a metal nitride layer 108 serving as a superconducting material. FIG2B is a schematic diagram of a device 100 in which the metal nitride layer has been formed into a feature, such as a superconducting wire 108′. Device 100 may be a superconducting nanowire single-photon detector (SNSPD), a superconducting quantum interference device (SQUID), a circuit in a quantum computer (e.g., an RF line), etc. FIG3A through FIG3C are flow charts of a manufacturing method 200.

[0030] Metal nitride layer 108 is disposed on support structure 102. Support structure 102 may include a substrate, such as a silicon wafer. The substrate may be a dielectric material, such as sapphire, SiO2, fused silica, or quartz, or a semiconductor material, such as silicon, gallium nitride (GaN), or gallium arsenide (GaAs). Although depicted as a single block, support structure 102 may include multiple underlying layers. For example, support structure 102 may include a distributed Bragg reflector (DBR), which includes multiple pairs of layers formed from high- and low-refractive-index materials deposited on a substrate, or a waveguide formed on the substrate.

[0031] The seed layer structure 103 is formed on the support structure 102 . The seed layer structure 103 includes a lower seed layer 104 and an upper seed layer 106 .

[0032] Lower seed layer 104 covers the top of support structure 102, for example, in direct contact with the top surface of support structure 102. Lower seed layer 104 is a metal nitride layer. Specifically, lower seed layer 104 and superconducting layer 108 are nitrides of different metals. Lower seed layer 104 may be aluminum nitride (AlN). However, hafnium nitride (HfN), chromium nitride (CrN), or nitrides of alloys of aluminum and hafnium or scandium may also be suitable.

[0033] Lower seed layer 104 may have a thickness of about 3 nm to 50 nm, for example, about 5 nm, about 10 nm, or about 20 nm. Lower seed layer 104 may have a (002) c-axis crystal orientation. Lower seed layer 104 need not be superconducting at the operating temperature of device 100. Lower seed layer 104 may be deposited (step 202) by a standard chemical vapor deposition or physical vapor deposition process. The deposition process may be performed with the substrate at a temperature of 200° C. to 500° C. (e.g., 400° C.).

[0034] Exemplary processing parameters for the lower seed layer are 1 kW to 5 kW of power applied to the sputtering target, a total pressure (nitrogen and inert gas) of 2 mTorr to 20 mTorr with nitrogen and inert gas supplied in a ratio between 3:100 and 6:1 (e.g., approximately 3:1), a wafer temperature of 200° C. to 500° C., and no bias voltage applied to the wafer.

[0035] An upper seed layer 106 is formed on top of the lower seed layer 104, e.g., in direct contact with the top surface of the lower seed layer 104 (step 204). The upper seed layer 106 is a metal oxide or metal oxynitride layer. Specifically, the upper seed layer 106 is an oxide or oxynitride of the same metal as the metal nitride in the lower seed layer 104. The upper seed layer 106 may be aluminum oxide or aluminum oxynitride, as this appears to raise the critical temperature of NbN, e.g., by approximately 0.5 K compared to aluminum nitride as a seed layer. However, hafnium oxide or oxynitride, chromium oxide or oxynitride, or alloys of aluminum with hafnium or scandium may also be suitable.

[0036] The upper seed layer 106 can be thinner than the lower seed layer 104. Depending on the fabrication method, the upper seed layer 106 can be approximately 0.1 nm to 3 nm thick. In some implementations, the upper seed layer 106 is only one to five atomic layers thick, for example, two to three atomic layers thick. The upper seed layer 106 can have a (002) c-axis crystal orientation. The upper seed layer 106 need not be superconducting at the operating temperature of the device 100.

[0037] Referring to FIG. 3A , one technique for forming the metal oxide or metal oxynitride of the upper seed layer 106 is to expose the lower seed layer 104 to a gas containing oxygen and / or water (step 204a). For example, the lower seed layer 104 can be exposed to air. As another example, the lower seed layer 104 can be exposed to pure oxygen. As another example, the lower seed layer 104 can be exposed to a gas mixture containing 20% to 90% oxygen by volume and one or more other gases, such as nitrogen and / or a noble gas (e.g., argon). In some implementations, the gas mixture includes water, such as water vapor or steam. The pressure can be from 1 Torr to 1 atmosphere, for example, from 0.8 to 1 atmosphere.

[0038] Referring to FIG. 3B , another technique for forming the metal oxide or metal oxynitride of the upper seed layer 106 is to expose the lower seed layer 104 to a gas containing an oxygen (O 2 ) plasma (step 204 b). For example, the lower seed layer 104 can be exposed to a pure oxygen plasma. For example, oxygen gas can be introduced into the plasma treatment chamber, and the oxygen plasma can be formed at a power of approximately 100 W. The pressure can be between 2 mTorr and 500 mTorr. Generally, a dedicated chamber for oxygen plasma treatment can use a relatively high pressure, e.g., 100 mTorr to 500 mTorr, while a relatively low pressure, e.g., 2 mTorr to 15 mTorr, can be used if the oxygen plasma treatment is performed in the same chamber used to deposit the lower seed layer.

[0039] Without being bound by any particular theory, exposing AlN to oxygen may result in the formation of a thermal oxide or thermal oxynitride layer (ie, an aluminum oxide or aluminum oxynitride layer) on the surface of the AlN layer.

[0040] In some implementations, the substrate with the lower seed layer is lowered from a first temperature (e.g., 300°C to 500°C) for depositing the lower seed layer to a lower second temperature (e.g., 20°C to 300°C). The lower seed layer is exposed to an oxygen-containing gas or plasma at the lower second temperature. The second temperature can be at least 200°C lower than the first temperature. For example, the second temperature can be room temperature, i.e., 20°C to 22°C. The substrate is then raised to an elevated third temperature for depositing the metal nitride of the superconducting layer.

[0041] In some implementations, the substrate with the lower seed layer is maintained at an elevated temperature, e.g., at or above 300° C., e.g., at the same temperature at which the lower seed layer is deposited (e.g., 400° C.), and the substrate is exposed to an oxygen-containing gas or plasma at the elevated temperature.

[0042] In some implementations, the substrate with the lower seed layer is lowered from a first temperature to a second temperature and then raised to an elevated third temperature (e.g., at or above 300° C., e.g., 300° C. to 500° C.), and the lower seed layer is exposed to an oxygen-containing gas or plasma at the elevated third temperature.

[0043] The exposure time may depend on the pressure and temperature and may range from 1 second to 120 minutes. For example, the exposure time to air at room temperature may be about 45 minutes. As another example, the exposure time to oxygen plasma (where the substrate is at the same temperature as the lower seed layer (e.g., about 400° C.)) may be about 30 seconds.

[0044] In the techniques of Figures 3A and 3B, the upper seed layer 106 is actually a native oxide or native oxynitride formed on the underlying metal nitride layer and is therefore expected to be two to four atomic layers thick. For example, the upper seed layer 106 can be up to about 1 nm thick.

[0045] Referring to FIG. 3C , another technique that can be used to form the metal oxide or metal oxynitride of the upper seed layer 106 is to deposit the upper seed layer 106 by physical vapor deposition. Exemplary processing parameters for the upper seed layer include a power of 1 kW to 5 kW applied to the sputtering target, a total pressure (oxygen and inert gas) of 2 mTorr to 20 mTorr with oxygen and inert gas supplied in a ratio between 3:100 and 6:1, and a wafer temperature of 200° C. to 500° C. CVD and ALD techniques also exist for depositing aluminum oxide or aluminum oxynitride.

[0046] In the technique of FIG3C , the thickness of the upper seed layer 106 depends on the processing time or the number of iterations of the deposition process. For example, the thickness of the upper seed layer 106 can be 1 nm to 2 nm.

[0047] 2A and 2B , a superconducting metal nitride layer 108 is deposited on the upper seed layer 106, for example, in direct contact with the upper seed layer 106. The metal nitride layer 108 is formed of niobium nitride (NbN), titanium nitride (TiN), or niobium titanium nitride (NbxTi1-xN). The superconducting layer 108 may have a thickness of 4 nm to 50 nm, for example, about 5 nm, about 10 nm, or about 20 nm.

[0048] Metal nitride layer 108 can be deposited using standard chemical vapor deposition or physical vapor deposition processes. Exemplary process parameters include a base pressure of 1e-8 Torr, a power applied to the target of 1 kW to 3 kW, a total pressure of 5 mTorr to 7 mTorr during processing, a wafer temperature of 400°C, no bias applied to the wafer, and a percentage of gas (e.g., N₂) sufficient to obtain cubic delta-phase NbN. In some implementations, metal nitride layer 108 is deposited in the same processing chamber used to deposit lower seed layer 104 and upper seed layer 106, for example by switching to a new target. This allows for higher throughput manufacturing. Alternatively, the substrate can be transferred to a different deposition chamber without breaking vacuum. This allows the metal nitride layer to be deposited without exposing the seed layer to the atmosphere and with reduced risk of contamination.

[0049] After depositing the metal nitride layer 108, a capping layer 110 may be deposited on the metal nitride layer 108 (step 208). The capping layer 110 serves as a protective layer, for example, to prevent oxidation or other types of contamination or damage to the metal nitride layer 108. The capping layer 110 may be a dielectric, but need not be superconducting at the operating temperature of the device 100. The capping layer 110 may be amorphous silicon (a-Si). In some implementations, the capping layer 110 is a nitride of a different material than the metal used for the metal nitride of the superconducting layer 108. Examples of materials for the capping layer 110 include AlN, Al2O3, SiO2, and SiN. The capping layer 110 may be deposited by standard chemical vapor deposition or physical vapor deposition processes.

[0050] Etching can be used to form trenches 112 through at least the metal nitride layer 108 to form superconducting wire 108' or other structures desired for device 100 (step 210). Wire 108' can have a width of approximately 25 nm to 250 nm, for example, approximately 60 nm. Although FIG. 2B depicts trenches 112 as extending through metal nitride layer 108 and capping layer 110 and not into upper seed layer 106, other configurations are possible. By way of example, trenches 112 can extend partially into upper seed layer 106 or completely through upper seed layer 106, or completely through upper seed layer 106 and partially into lower seed layer 104 or completely through lower seed layer 104.

[0051] Air may contain contaminants, so for any of the above processes, the upper seed layer 106 can be formed on the lower seed layer 104 without breaking vacuum, for example, without removing the substrate from the deposition chamber in which the lower seed layer is deposited, or without breaking vacuum during the transfer of the substrate from the deposition chamber in which the lower seed layer is deposited to the chamber in which the upper seed layer is formed. Similarly, the metal nitride superconducting layer 108 can be formed on the upper seed layer 106 without breaking vacuum.

[0052] When forming the upper seed layer 106 by oxygen plasma treatment (see FIG. 3B ) or by PVD (see FIG. 3C ), Applied Materials Endura® with pulsed PVD can be used. Deposition of the lower seed layer and the oxygen plasma treatment or PVD of the oxide or oxynitride can be performed in the same chamber. NbN deposition can be performed in a different chamber within the same Endura tool without breaking vacuum.

[0053] FIG4A is a schematic diagram of some layers in device 100' including a metal nitride layer 108 serving as a superconducting material. FIG4B is a schematic diagram of device 100' in which the metal nitride layer has been formed into a feature, such as a superconducting wire 108'. Device 100' is similar to device 100, but the seed layer structure 103 of device 100' comprises a single metal oxide or metal oxynitride seed layer 106', rather than a lower seed layer and an upper seed layer. Device 100' can be configured and manufactured as described for device 100, except as discussed below. FIG5 is a flow chart of a method 200' of manufacturing.

[0054] A seed layer 106' is disposed on top of support structure 102. Seed layer 106' is a metal oxide or metal oxynitride. Specifically, seed layer 106' is an oxide or oxynitride of a different metal than the metal nitride in superconducting layer 108. Seed layer 106' may be aluminum oxide or aluminum oxynitride (AlN), as this appears to raise the critical temperature of NbN, for example, by approximately 0.5 K compared to aluminum nitride as a seed layer. However, hafnium oxide, hafnium oxynitride, gallium oxide, or gallium oxynitride may also be suitable. Unlike device 100, there is no metal nitride layer of the same metal directly contacting the bottom of metal oxide or oxynitride seed layer 106'.

[0055] Seed layer 106' may have a thickness of about 3 nm to 50 nm, for example, about 5 nm, about 10 nm, or about 20 nm. Seed layer 106' may have a (002) c-axis crystal orientation. Seed layer 106' need not be superconducting at the operating temperature of device 100. Seed layer 106' may be deposited (step 204') by a standard chemical vapor deposition or physical vapor deposition process. The deposition process may be performed with the substrate at a temperature of 200°C to 500°C (e.g., 400°C).

[0056] Exemplary processing parameters are a power of 1 kW to 5 kW applied to the sputtering target, a total pressure (nitrogen and inert gas) of 2 mTorr to 20 mTorr with nitrogen and inert gas supplied in a ratio between 3:100 and 1:6, a wafer temperature of 200°C to 500°C, and no bias voltage applied to the wafer.

[0057] Applied Materials Endura® with pulsed PVD can be used for the deposition of both the seed layer and the superconducting layer. For example, aluminum oxide can be deposited in one chamber and NbN can be deposited in a different chamber within the same tool without breaking vacuum.

[0058] A thermal cycle may be applied between the deposition of the seed layer 106′ and the superconducting layer 108. For example, the substrate with the seed layer 106′ is lowered from a first temperature to a second temperature, and then raised to an elevated third temperature, e.g., at or above 300° C., e.g., 300° C. to 500° C., for depositing the metal nitride superconducting layer 108. Alternatively, the substrate with the seed layer 106′ may be maintained at an elevated temperature, e.g., at or above 300° C., e.g., at the same temperature at which the seed layer 106′ is deposited, until the metal nitride superconducting layer 108 is deposited.

[0059] FIG. 6A is a schematic diagram of some layers in a device 100″ including a metal nitride layer 108 serving as a superconducting material. FIG. 6B is a schematic diagram of a device 100″ in which the metal nitride layer has been formed into a feature, such as a superconducting wire 108′. Device 100″ is similar to device 100′, but rather than a seed layer comprising a metal oxide or metal oxynitride, the seed layer structure 103 of device 100″ comprises a single layer of metal nitride that has undergone thermal cycling. Except as discussed below, device 100″ may be configured and manufactured as discussed with respect to devices 100 and 100′. FIG. 7 is a flow diagram of a method 200″ of manufacturing.

[0060] A seed layer 104' is disposed on top of the support structure 102. The seed layer 104' is a metal nitride. Specifically, the seed layer 104' and the superconducting layer 108 are nitrides of different metals. The seed layer 104' can be aluminum nitride. However, hafnium nitride or gallium nitride are also suitable. Unlike the device 100, there is no metal oxide or metal oxynitride between the seed layer 104' and the superconducting layer 108.

[0061] The seed layer 104' may be deposited (step 204') directly on the support structure 102 by a standard chemical vapor deposition or physical vapor deposition process. The deposition process may be performed with the substrate at a first temperature of 200°C to 500°C (eg, 400°C).

[0062] After deposition, the substrate with the metal nitride seed layer undergoes a thermal cycle (step 205). Specifically, the substrate with the seed layer is cooled from a first temperature (e.g., 200°C to 500°C) at which the seed layer was deposited to a lower second temperature. For example, the substrate with the seed layer 104′ is cooled from a first temperature (e.g., 300°C to 500°C) at which the seed layer was deposited to a lower second temperature (e.g., 20°C to 300°C). The second temperature may be at least 200°C lower than the first temperature. For example, the second temperature may be room temperature, i.e., 20°C to 22°C. The seed layer may be thermally cycled while in a vacuum or while exposed to nitrogen and / or an inert gas (e.g., argon). The substrate is then raised to an elevated third temperature, e.g., 300°C to 500°C, for depositing the metal nitride superconducting layer. The thermal cycle may alter the crystalline structure of the seed layer 104′.

[0063] After thermal cycling, a metal nitride superconducting layer 108 may be deposited on the seed layer 104'. The superconducting layer 108 is deposited without breaking vacuum or otherwise exposing the seed layer to oxygen or an oxygen-containing vapor (eg, H2O).

[0064] 8A and 8B illustrate a top view and a side view, respectively, of a device 100a configured as a superconducting nanowire single photon detector (SNSPD). The device 100a can use any of the configurations of the seed layer 103 described above.

[0065] The SNSPD element 100a can include at least one superconducting wire 108' disposed on a support structure 102. The superconducting wire 108' can be connected between conductive electrodes 120. The superconducting wire 108' can be arranged on the support structure 102 in a zigzag pattern (e.g., parallel lines running back and forth). In some implementations, multiple wires 108' are connected in parallel between the electrodes 120, with each wire 108' covering a separate area 152. However, there may be only a single wire 108' covering the entire detection area of the element 100a. Additionally, many other patterns are possible, such as a zigzag pattern or a double helix.

[0066] The support structure 102 includes a substrate 124 and a distributed Bragg reflector (DBR) 126 comprising pairs of layers formed of high-refractive-index and low-refractive-index materials.

[0067] SNSPD element 100a operates by directing photons (illustrated as beam 10) from the top of element 100a close to the surface (e.g., perpendicularly relative to substrate 124). The SNSPD element operates by allowing photons to enter from the top and impinge on the SNSPD. Upon initial impact or after reflection from the DBR, the absorption of the photons creates a hotspot on the NbN nanowire. This hotspot raises the temperature of the NbN nanowire above its critical temperature, causing a portion of the wire to cease to be superconducting. Current crowding may occur in the area surrounding the hotspot, resulting in current densities exceeding the critical current density, potentially destroying the superconducting state of the entire wire. The transition from the superconducting state to the normal resistive state of the NbN wire can be detected electrically by passing a current through the element and monitoring the voltage difference between the electrodes.

[0068] Another form of a superconducting nanowire single-photon detector (SNSPD) device includes a waveguide for inputting photons into the detector along an axis generally parallel to the substrate surface. Figures 9A and 9B illustrate a device 100b configured as a superconducting nanowire single-photon detector (SNSPD) and having a waveguide 138. Device 100b can use any of the configurations described above for the seed layer 103.

[0069] SNSPD element 100b may include at least one superconducting wire 108' disposed on support structure 102. The superconducting wire(s) 108' may be arranged to form a plurality of parallel wires, with adjacent wires connected at alternating ends. Although FIG. 9A illustrates four parallel wires, the element may have only two parallel wires (e.g., a U-shaped wire) or a greater number of wires. Superconducting wire 108' may be connected between conductive electrodes.

[0070] The support structure 102 may include a substrate 134, a dielectric layer 136 on the substrate 134, and a waveguide 138 disposed on the dielectric layer 136. The dielectric layer 136 is a first material having a first refractive index, and the waveguide 138 is a second material having a second refractive index higher than the first refractive index.

[0071] Photons, shown by beam 10b, are injected into the device from the side (e.g., generally parallel to the top surface of substrate 134) via waveguide 138. Specifically, the photons may enter along an axis generally parallel to the parallel lines of conductive line 108' (shown by arrow A).

[0072] Additionally, along an axis transverse to the direction of light propagation, the conductive line 108' can be located near the center of the waveguide 138. For example, on each side of the element, a gap 130 can exist between the outer edge of the conductive line 108' and the outer edge of the waveguide 138. This gap 130 can have a width of approximately 25% to 30% of the total width of the waveguide.

[0073] Generally speaking, because the dielectric layer 136 below the waveguide 138 and the empty space or air above the waveguide 138 both have a lower refractive index than the waveguide 138, photons in the waveguide 138 are trapped by total internal reflection. However, due to the optical coupling between the waveguide 138 and the nanowire 108', the photons can escape into the nanowire 108' and be absorbed by the nanowire 108'. In this type of device, the optical coupling efficiency can be very high.

[0074] 9C , if the waveguide 138 is formed of a suitable metal nitride (e.g., aluminum nitride), the top surface of the waveguide 138 may provide a lower seed layer and may be processed to form the upper seed layer 106, or the upper seed layer 106 may be formed directly on the waveguide 138, i.e., without depositing a separate lower seed layer.

[0075] Although specific implementations have been described, other and further implementations may be devised without departing from the basic scope of this disclosure. It is contemplated that elements and features of one embodiment may be beneficially incorporated into other embodiments without further recitation. However, it should be noted that the drawings depict only illustrative embodiments. The scope of the present invention is determined by the following claims.

[0076] 10a: Beam 10b: Beam 100: Component 100': Component 100":Component 100a: Component 100b: Component 102: Support structure 103: Seed layer structure 103 / 104': Seed layer 103 / 106': Seed layer 104: lower seed layer 104': seed layer 106: Upper seed layer 106': seed layer 108: Metal nitride layer 108':Superconducting wire 110: Covering layer 112: Groove 120: conductive electrode 124:Substrate 126: Distributed Bragg Reflector (DBR) 130: Gap 134:Substrate 136: dielectric layer 138: Waveguide 200:Method 200': Method 200":Method 202: Steps 204': Steps 204a: Step 204b: Step 204c: Steps 205: Steps 206: Steps 208: Steps 210: Steps A: Arrow

Claims

1. A superconducting device, comprising: A substrate that is dielectric or semiconductor; On the substrate, there is a metal nitride seed layer, which is a nitride of a first metal, such as aluminum, hafnium, chromium, an alloy of aluminum and hafnium, or an alloy of aluminum and scandium; and a metal nitride superconducting layer directly disposed on the seed layer, which is a nitride of a different second metal and is patterned to form a wire.

2. The element as claimed in claim 1, wherein the seed layer provides the metal nitride superconducting layer with a critical temperature higher than that of the first metal nitride layer.

3. The element as claimed in claim 1, wherein the metal nitride seed layer is directly disposed on the substrate.

4. The element as claimed in claim 1, comprising a distributed Bragg reflector between the substrate and the metal nitride seed layer.

5. The element as claimed in claim 1, comprising an optical waveguide between the substrate and the metal nitride seed layer for receiving light propagating substantially parallel to one of the top surfaces of the substrate.

6. The element as claimed in claim 1, wherein the second metal is niobium nitride, titanium nitride, or niobium titanium nitride.

7. The element as claimed in claim 6, wherein the metal nitride superconducting layer comprises a δ-phase NbN.

8. The element as claimed in claim 1, wherein the metal nitride seed layer has a thickness of less than 2 nm.

9. The element as claimed in claim 1, wherein the metal nitride seed layer has a thickness of 3 nm to 50 nm.

10. The element as claimed in claim 1, comprising a metal nitride seed layer between the substrate and the metal nitride seed layer.

11. The element as claimed in claim 10, wherein the metal nitride seed layer is a nitride of the first metal.

12. The element as claimed in claim 10, wherein the metal oxide seed layer has a thickness of 3 nm to 50 nm.

13. The element as described in claim 1, further comprising a capping layer on the superconducting layer.

14. The element as claimed in claim 1, comprising a single metal nitride superconducting layer.

15. The element as claimed in claim 1, wherein the metal nitride superconducting layer has a thickness of 4 nm to 50 nm.

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