High critical temperature metal nitride layer with oxide or oxynitride seed layer - Patents.com

Abstract

To provide a super-conductive device which uses a seed layer to improve a super-conductive critical temperature of a metal nitride layer.SOLUTION: A super-conductive device 100' includes: a substrate 102; an upper part seed layer 106' for forming one of a metal oxide and a metal oxynitride on the substrate; and a metal nitride super-conductive layer 108' and a capping layer 110' directly arranged on the upper seed layer. The upper seed layer is formed of a first metal, one of oxide and oxynitride, and the super-conductive layer is formed of a second metal, nitride. The first metal is aluminum and the second metal, nitride is one of niobium nitride, titanium nitride, and niobium titanium nitride.SELECTED DRAWING: Figure 4B

Description

[Technical Field]

[0001] The present disclosure relates to the use of a seed layer to improve the superconducting critical temperature of a metal nitride layer. [Background technology]

[0002] In the context of superconductivity, the critical temperature (T C ) refers to the temperature below which a material becomes superconducting. Niobium nitride (NbN) is a material that can be used in superconducting applications (e.g., superconducting nanowire single-photon detectors (SNSPDs) used in quantum information processing, defect analysis in CMOS, LIDAR, etc.). The critical temperature of niobium nitride depends on the crystalline structure and atomic ratio of the material. For example, referring to Figure 1, cubic δ-phase NbN has several advantages due to its relatively "high" critical temperature, e.g., 9.7-16.5 K (the processing temperatures shown are for a specific manufacturing process and may not necessarily be applicable to other processes and deposition chamber designs).

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

[0004] In one aspect, 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, wherein 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, wherein 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] Embodiments may provide one or more of the following advantages, but are not limited to: The critical temperature of metal nitride layers, such as NbN layers, can be increased, allowing for the fabrication of devices, such as SNSPDs, having superconducting wires with higher critical temperatures. A larger difference between the operating temperature (2-3 K) and the critical temperature provides superior detection efficiency, lower dark counts, and possibly faster temporal response.

[0007] Note that "superconducting" indicates that the material becomes superconducting at the operating temperature of the device, e.g., 2-3 K. The material is not actually superconducting during device fabrication at temperatures above room temperature or when the device is not cooled for operation.

[0008] The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other potential aspects, features, and advantages will become apparent from the description, drawings, and claims. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 illustrates the phases of niobium nitride as a function of processing temperature and atomic percentage of nitrogen. [Figure 2A] 1 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. [Figure 2B] FIG. 2B is a schematic cross-sectional view of the device of FIG. 2A after etching the superconducting layer to form superconducting wires. [Figure 3A] 3A-3C are a flowchart of a method for fabricating the device of FIG. 2A or 2B. [Figure 3B] 3A-3C are a flowchart of a method for fabricating the device of FIG. 2A or 2B. [Figure 3C] 3A-3C are a flowchart of a method for fabricating the device of FIG. 2A or 2B. [Figure 4A] 1 is a schematic cross-sectional view of a device including a metal oxide or oxynitride seed layer and a superconducting metal nitride layer. [Figure 4B] FIG. 4B is a schematic cross-sectional view of the device of FIG. 4A after etching the superconducting layer to form superconducting wires. [Figure 5] 4C is a flowchart of a method for manufacturing the device of FIG. 4A or 4B. [Figure 6A] 1 is a schematic cross-sectional view of a device including a metal nitride seed layer and a superconducting metal nitride layer. [Figure 6B] FIG. 6B is a schematic cross-sectional view of the device of FIG. 6A after etching the superconducting layer to form superconducting wires. [Figure 7] 6C is a flowchart of a method for manufacturing the device of FIG. 6A or 6B. [Figure 8A] FIG. 1 is a schematic top view of an SNSPD including a distributed Bragg reflector. [Figure 8B] FIG. 8B is a schematic cross-sectional side view of the device of FIG. 8A. [Figure 9A] FIG. 1 is a schematic top view of an SNSPD including a waveguide. [Figure 9B] FIG. 9B is a schematic cross-sectional side view of the device of FIG. 9A. [Figure 9C] FIG. 9B is a schematic cross-sectional side view of another embodiment of the device of FIG. 9A. DETAILED DESCRIPTION OF THE INVENTION

[0010] Like reference numbers and designations in the various drawings indicate like elements.

[0011] As mentioned above, niobium nitride, especially δ-phase NbN, has several advantages as a superconducting material. However, δ-phase NbN can be difficult to deposit with satisfactory quality. Furthermore, the greater the difference between the operating temperature (2-3 K) and the critical temperature, the better the device performance. An aluminum nitride (AlN) layer can be used as a seed layer to improve the critical temperature of the NbN layer. Without being limited to any particular theory, the AlN seed layer may induce a crystalline structure in the NbN layer that results in an increase in the critical temperature.

[0012] Surprisingly, however, it has been discovered that exposing the AlN seed layer to air and room temperature prior to deposition of the NbN layer can actually provide a higher critical temperature, e.g., about 0.5 K higher, than depositing an NbN layer on an AlN seed layer without breaking vacuum and lowering the substrate temperature. Again, without being limited to any particular theory, two non-exclusive possibilities have been proposed. First, exposing the AlN to air may result in the formation of a thin aluminum oxide or aluminum oxynitride layer on the surface of the AlN layer, which may induce a superior crystalline structure in the NbN layer. Second, thermally cycling the AlN seed layer by lowering its temperature from the first deposition temperature for AlN, e.g., 400 °C, to room temperature, i.e., 20–22 °C, and then raising the substrate temperature to the second deposition temperature for NbN, e.g., 400 °C, may affect the stress in the AlN seed layer, which may affect its crystalline structure, which in turn may affect the crystalline structure of the NbN layer.

[0013] Figure 2A is a schematic diagram of several layers in device 100, including a metal nitride layer 108 used as a superconducting material. Figure 2B is a schematic diagram of device 100 in which the metal nitride layer is 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 (e.g., an RF line) in a quantum computer, or the like. Figures 3A-3C are a flowchart of a method 200 of fabrication.

[0014] The metal nitride layer 108 is disposed on the support structure 102. The 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 illustrated as a single block, the support structure 102 may include multiple underlying layers. For example, the support structure 102 may include a distributed Bragg reflector (DBR) including multiple pairs of layers formed of high and low refractive index materials deposited on a substrate, or a waveguide formed on a substrate.

[0015] A 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.

[0016] The lower seed layer 104 covers the top surface of the support structure 102, e.g., is in direct contact with the top surface of the support structure 102. The lower seed layer 104 is a metal nitride layer. In particular, the lower seed layer 104 and the superconducting layer 108 are nitrides of different metals. The lower seed layer 104 may be aluminum nitride (AlN). However, hafnium nitride (HfN), chromium nitride (CrN), or nitrides of alloys of aluminum with either hafnium or scandium may also be suitable.

[0017] The lower seed layer 104 may have a thickness of about 3 to 50 nm, for example, about 5 nm, about 10 nm, or about 20 nm. The lower seed layer 104 may have a (002) c-axis crystallographic orientation. The lower seed layer 104 need not be superconducting at the operating temperature of the device 100. The lower seed layer 104 may be deposited by a standard chemical vapor deposition or physical vapor deposition process (step 202). The deposition process may be performed with the substrate at a temperature of 200-500°C (e.g., 400°C).

[0018] Exemplary process parameters for the bottom seed layer are a power applied to the sputtering target of 1-5 kW, a total pressure (nitrogen and inert gas) of 2-20 mTorr with nitrogen gas and inert gas supplied in a ratio of between 3:100 and 6:1 (e.g., 3:1), a wafer temperature of 200-500°C, and no bias voltage applied to the wafer.

[0019] An upper seed layer 106 is formed on the upper surface of the lower seed layer 104, for example, in direct contact with the upper surface of the lower seed layer 104 (step 204). The upper seed layer 106 is a metal oxide or metal oxynitride layer. In particular, the upper seed layer 106 is an oxide or oxynitride of the same metal as the metal of the metal nitride in the lower seed layer 104. The upper seed layer 106 may be aluminum oxide or aluminum oxynitride, which appears to improve the critical temperature of NbN by, for example, about 0.5 K over aluminum nitride as a seed layer. However, hafnium oxide or oxynitride, chromium oxide or oxynitride, or an oxide or oxynitride of an alloy of aluminum with either hafnium or scandium may also be suitable.

[0020] The upper seed layer 106 can be thinner than the lower seed layer 104. The upper seed layer 106 can be approximately 0.1 to 3 nm thick, depending on the method of fabrication. In some embodiments, the upper seed layer 106 is only 1 to 5 atomic layers thick, for example, 2 or 3 atomic layers thick. The upper seed layer 106 can have a (002) c-axis crystallographic orientation. The upper seed layer 106 need not be superconducting at the operating temperature of the device 100.

[0021] Referring to FIG. 3A, one technique that can be used to form 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 20-90% by volume oxygen and one or more other gases, such as nitrogen and / or a noble gas (e.g., argon). In some embodiments, the gas mixture includes water (e.g., water vapor or mist). The pressure can be from 1 Torr to 1 atmosphere, e.g., from 0.8 to 1 atmosphere.

[0022] Referring to FIG. 3B, another technique that can be used to form 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 (O) plasma (step 204b). For example, the lower seed layer 104 can be exposed to pure oxygen plasma. For example, oxygen gas can be introduced into a plasma treatment chamber, and the oxygen plasma can be generated at a power of about 100 W. The pressure can be 2 to 500 mTorr. Generally, a dedicated chamber for oxygen plasma treatment can use a relatively high pressure, for example, 100 to 500 mTorr, while if the oxygen plasma treatment is performed in the same chamber used to deposit the lower seed layer, a relatively low pressure, for example, 2 to 15 mTorr, can be used.

[0023] Without being limited to any particular theory, exposure of 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.

[0024] In some embodiments, a substrate having a lower seed layer is cooled from a first temperature, e.g., 300-500°C, at which the lower seed layer is deposited, to a second, lower temperature, e.g., 20-300°C. The lower seed layer is exposed to an oxygen-containing gas or plasma at the second, lower 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., 20-22°C. The substrate is then heated to a third temperature for deposition of the metal nitride of the superconducting layer.

[0025] In some embodiments, the substrate with the lower seed layer is maintained at an elevated temperature, e.g., 300°C or higher, e.g., 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.

[0026] In some embodiments, the substrate with the lower seed layer is cooled from a first temperature to a second temperature and then heated to a higher third temperature, e.g., 300°C or higher, e.g., 300-500°C, and the lower seed layer is exposed to an oxygen-containing gas or plasma at the higher third temperature.

[0027] The exposure time can be from 1 second to 120 minutes, depending on the pressure and temperature. For example, the exposure time for air at room temperature can be about 45 minutes. As another example, the exposure time for oxygen plasma with the substrate at the same temperature at which the lower seed layer is deposited, e.g., about 400°C, can be about 30 seconds.

[0028] 3A and 3B, the upper seed layer 106 is effectively a native oxide or oxynitride formed on the underlying metal nitride layer, and is therefore expected to be 2 to 4 atomic layers thick. For example, the upper seed layer 106 may be up to about 1 nm thick.

[0029] 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 process parameters for the upper seed layer are a power applied to the sputtering target of 1-5 kW, a total pressure (oxygen and inert gas) of 2 to 20 mTorr with oxygen gas and inert gas supplied in a ratio between 3:100 and 6:1, and a wafer temperature of 200-500° C. CVD and ALD techniques also exist for depositing aluminum oxide or oxynitride.

[0030] 3C, the thickness of the upper seed layer 106 depends on the processing time or number of iterations of the deposition process. For example, the thickness of the upper seed layer 106 can be 1-2 nm.

[0031] 2A and 2B, a superconducting metal nitride layer 108 is deposited on, for example, directly contacting, the upper seed layer 106 (step 206). 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 to 50 nm, for example, about 5 nm, about 10 nm, or about 20 nm.

[0032] The 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 1-8 Torr, a power applied to the target of 1-3 kW, a total pressure during processing of 5-7 mTorr, a wafer temperature of 400°C, no bias voltage applied to the wafer, and a gas ratio of N2 sufficient to achieve cubic δ-phase NbN. In some embodiments, the metal nitride layer 108 is deposited in the same process chamber used to deposit the lower seed layer 104 and the 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.

[0033] After the metal nitride layer 108 is deposited, a capping layer 110 may be deposited on the metal nitride layer 108 (step 208). The capping layer 110 functions, for example, as a protective layer to prevent oxidation or other types of contamination or damage to the metal nitride layer 108. The capping layer 108 may be a dielectric, but need not be superconducting at the operating temperatures of the device 100. The capping layer 108 may be amorphous silicon (a-Si). In some embodiments, the capping layer 108 is a nitride of a material different from the metal of the metal nitride used in the superconducting layer 108. Examples of materials for the capping layer 108 include AlN, Al2O3, SiO2, and SiN. The capping layer 108 may be deposited by standard chemical vapor deposition or physical vapor deposition.

[0034] Etching can be used to form trenches 112 at least through the metal nitride layer 108 to form superconducting wires 108′ or other structures required for device 100 (step 210). The wires 108′ can have a width of about 25 to 250 nm, for example, about 60 nm. While FIG. 2B shows the trenches 112 extending through the metal nitride layer 108 and the capping layer 110 and not into the upper seed layer 106, other configurations are possible. As an example, the trenches 112 can extend partially into or completely through the upper seed layer 106, or can extend completely through the upper seed layer 106 and partially into or completely through the lower seed layer 104.

[0035] Because air may contain contaminants, for any of the above processes, the upper seed layer 106 may be formed on the lower seed layer 104 without breaking vacuum, such as removing the substrate from the deposition chamber in which the lower seed layer is deposited, or without breaking vacuum during 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 may be formed on the upper seed layer 106 without breaking vacuum.

[0036] If the upper seed layer 106 is formed by oxygen plasma treatment (see FIG. 3B) or by PVD (see FIG. 3C), an Applied Materials Endura® tool using impulse PVD can be used. The deposition of the lower seed layer and either the oxygen plasma treatment or the PVD of the oxide or oxynitride can be performed in the same chamber. The NbN deposition can be performed in a different chamber in the same Endura tool without breaking vacuum.

[0037] FIG. 4A is a schematic diagram of several layers in device 100′, including a metal nitride layer 108 used as the superconducting material. FIG. 4B is a schematic diagram of device 100′ in which the metal nitride layer has been formed into features, such as superconducting wires 108′. Device 100′ is similar to device 100, except that instead of having both a bottom seed layer and a top seed layer, the seed layer structure 103 of device 100′ has a single metal oxide or metal oxynitride seed layer 106′. Except as described below, device 100′ can be configured and fabricated as described for device 100. FIG. 5 is a flowchart of a method of fabrication 200′.

[0038] A seed layer 106' is disposed on the support structure 102. The seed layer 106' is a metal oxide or metal oxynitride. In particular, the seed layer 106' is an oxide or oxynitride of a metal different from the metal of the metal nitride in the superconducting layer 108. The seed layer 106' may be aluminum oxide or aluminum oxynitride (AlN), which appears to improve the critical temperature of NbN by, for example, about 0.5 K over 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 in direct contact with the bottom of the metal oxide or oxynitride seed layer 106'.

[0039] The lower seed layer 106 may have a thickness of about 3 to 50 nm, for example, about 5 nm, about 10 nm, or about 20 nm. The seed layer 106' may have a (002) c-axis crystallographic orientation. The seed layer 106' need not be superconducting at the operating temperature of the device 100. The seed layer 106' may be deposited by a standard chemical vapor deposition or physical vapor deposition process (step 204'). The deposition process may be performed with the substrate at a temperature between 200 and 500°C, for example, 400°C.

[0040] Exemplary process parameters are a power applied to the sputtering target of 1-5 kW, a total pressure (nitrogen and inert gas) of 2 to 20 mTorr with nitrogen gas and inert gas supplied in a ratio between 3:100 and 1:6, a wafer temperature of 200-500°C, and no bias voltage applied to the wafer.

[0041] An Applied Materials Endura® using impulse PVD can be used to deposit the seed layer and the superconducting layer. For example, aluminum oxide deposition can be done in a first chamber, and NbN deposition can be done in a different chamber in the same tool, but without breaking vacuum.

[0042] A thermal cycle can be applied between the deposition of the seed layer 106′ and the deposition of the superconducting layer 108. For example, the substrate with the seed layer 106′ can be ramped down from a first temperature to a second temperature and then ramped up to a higher third temperature, e.g., above 300° C., e.g., 300-500° C., for the deposition of the metal nitride superconducting layer 108. Alternatively, the substrate with the seed layer 106′ can be maintained at an elevated temperature, e.g., above 300° C., e.g., the same temperature at which the seed layer 106′ is deposited, e.g., 400° C., until the deposition of the metal nitride superconducting layer 108.

[0043] FIG. 6A is a schematic diagram of several layers in device 100″, including a metal nitride layer 108 used as the superconducting material. FIG. 6B is a schematic diagram of device 100″ in which a metal nitride layer has been formed into features, such as superconducting wires 108′. Device 100″ is similar to device 100′, except that instead of having a metal oxide or metal oxynitride seed layer, the seed layer structure 103 of device 100″ comprises a single layer of metal nitride that has been subjected to a thermal cycle. Except as described below, device 100″ can be configured and fabricated as described for devices 100 and 100′. FIG. 7 is a flowchart of a method of fabrication 200″.

[0044] A seed layer 104' is disposed on the support structure 102. The seed layer 104' is a metal nitride. In particular, the seed layer 104' and the superconducting layer 108 are nitrides of different metals. The seed layer 104' may be aluminum nitride. However, hafnium nitride or gallium nitride may also be suitable. Unlike the device 100, no metal oxide or metal oxynitride is present between the seed layer 104' and the superconducting layer 108.

[0045] The seed layer 104' may be deposited (step 204') directly onto 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 between 200 and 500°C, for example, 400°C.

[0046] After deposition, the substrate with the metal nitride seed layer undergoes a thermal cycle (step 205). Specifically, the substrate with the seed layer is ramped down from a first temperature at which the seed layer is deposited, e.g., 200-500°C, to a lower second temperature. For example, the substrate with the seed layer 104′ is ramped down from a first temperature at which the seed layer is deposited, e.g., 300-500°C, to a lower second temperature, e.g., 20-300°C. 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., 20-22°C. The seed layer can undergo the thermal cycle while under reduced pressure or while exposed to nitrogen and / or an inert gas (e.g., argon). The substrate is then ramped up to a higher third temperature, e.g., 300-500°C, for deposition of the metal nitride superconducting layer. The thermal cycle can change the crystalline structure of the seed layer 104′.

[0047] After thermal cycling, a metal nitride of superconducting layer 108 may be deposited on seed layer 104'. Superconducting layer 108 is deposited without breaking vacuum or otherwise exposing the seed layer to oxygen or oxygen-containing vapors (e.g., HO).

[0048] 8A and 8B show top and side views, respectively, of a device 100a configured as a superconducting nanowire single photon detector (SNSPD). The device 100a may use any of the seed layer 103 configurations described above.

[0049] The SNSPD device 100a may include at least one superconducting wire 108′ disposed on the support structure 102. The superconducting wire 108′ may be connected between the conductive electrodes 120. The superconducting wire 108′ may be arranged in a serpentine pattern (e.g., a front-to-back parallel line) on the support structure 102. In some embodiments, multiple wires 108′ are connected in parallel between the electrodes 120, with each wire 108′ covering a distinct area 152, although there may be only a single wire 108′ that covers the entire detection area of ​​the device 100a. Additionally, many other patterns are possible, such as a zigzag or double helix.

[0050] The support structure 102 includes a substrate 124 and a distributed Bragg reflector (DBR) 126 that includes pairs of layers formed of high and low refractive index materials.

[0051] The SNSPD device 100a is operated by photons (represented by light beam 10a) approaching it from above, e.g., at normal incidence to the substrate 124. The operating principle of an SNSPD device is that photons to be detected originate from above the SNPSD and shine on it. Absorption of the photon, either upon initial impact or upon reflection from the DBR, creates a hot spot on the NbN nanowire, which raises the temperature of the NbN above its critical temperature, causing a portion of the wire to no longer be superconducting. The region around the hot spot can experience current crowding, resulting in a current density higher than the critical current density and disrupting the superconducting state of the entire wire. The change of the NbN wire from its superconducting state to its normal-resistive state can be detected electrically by passing a current through the device and monitoring the voltage difference between the electrodes.

[0052] Another form of superconducting nanowire single photon detector (SNSPD) device includes a waveguide that inputs photons to the detector along an axis generally parallel to the surface of the substrate. Figures 9A and 9B show a device 100b configured as a superconducting nanowire single photon detector (SNSPD) and having a waveguide 138. Device 100b can use any of the seed layer 103 configurations described above.

[0053] The SNSPD device 100b may include at least one superconducting wire 108′ disposed on the support structure 102. The superconducting wire(s) 108′ may be arranged to form multiple parallel wires with adjacent wires connected at alternating ends. While FIG. 9A shows four parallel wires, the device may have only two parallel wires, e.g., U-shaped wires, or a larger number of wires. The superconducting wire 108′ may be connected between conductive electrodes.

[0054] 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 102c is a first material having a first refractive index, and the waveguide 102d is a second material having a second refractive index higher than the first refractive index.

[0055] Photons, represented by light beam 10b, are injected into the device laterally through waveguide 138, e.g., approximately parallel to the top surface of substrate 132. In particular, the photons may be incident along an axis (indicated by arrow A) that is generally parallel to the parallel lines of wire 108'.

[0056] Additionally, along an axis transverse to the direction of light propagation, the wire 108' may be positioned near the center of the waveguide 138. For example, on either side of the device, there may be a gap 130 between the outer edge of the wire 108' and the outer edge of the waveguide 138. This gap 130 may have a width of approximately 25-30% of the overall width of the waveguide.

[0057] Generally, the dielectric layer 136 below the waveguide 138 and the free space or air above the waveguide 138 both have a lower refractive index than the waveguide 138, so photons in the waveguide 138 are trapped by total internal reflection. However, because of the optical coupling between the waveguide 138 and the nanowire 108′, photons can escape into the nanowire 108′ and thus be absorbed by the nanowire 108′. In this type of device, the optical coupling efficiency can be very high.

[0058] Referring to FIG. 9C, if the waveguide 138 is formed of a suitable metal nitride, such as aluminum nitride, the top surface of the waveguide 138 can be provided with a lower seed layer and processed to form the upper seed layer 106, or the upper seed layer 106 can be formed directly on the waveguide 108, i.e., without the need to deposit a separate lower seed layer.

[0059] List of Embodiments Embodiment 1. 1. A superconducting device comprising: a substrate; a metal oxide or metal oxynitride seed layer on the substrate, the seed layer being an oxide or oxynitride of a first metal; and a metal nitride superconducting layer disposed directly on the seed layer, the metal nitride superconducting layer being a nitride of a second metal different from the first metal. Embodiment 2. 2. The device of embodiment 1, wherein the nitride of the second metal is niobium nitride, titanium nitride, or niobium titanium nitride. Embodiment 3. 3. The device of embodiment 2, wherein the metal nitride superconducting layer comprises δ-phase NbN. Embodiment 4. 3. The device of embodiment 1 or 2, wherein the first metal is aluminum. Embodiment 5. 5. The device of any one of embodiments 1 to 4, wherein the metal oxide or metal oxynitride seed layer has a thickness of less than 2 nm. Embodiment 6. 6. The device of embodiment 5, wherein the metal oxide or metal oxynitride seed layer has a thickness of 0.1 to 1 nm. Embodiment 7. 6. The device of embodiment 5, wherein the metal oxide or metal oxynitride seed layer is 1 to 5 atomic layers thick. Embodiment 8. 5. The device of any one of embodiments 1 to 4, wherein the metal oxide or metal oxynitride seed layer has a thickness of 3 to 50 nm. Embodiment 9. 9. The device of any one of the preceding embodiments, wherein the metal oxide or metal oxynitride seed layer has a thickness of about 5 nm. Embodiment 10. 10. The device of any one of embodiments 1 to 9, wherein the metal oxide or metal oxynitride seed layer is an oxide of the first metal. Embodiment 11. 10. The device of any one of embodiments 1 to 9, wherein the metal oxide or metal oxynitride seed layer is an oxynitride of the first metal. Embodiment 12. 12. The device of any one of the preceding embodiments, comprising a metal nitride seed layer between the metal oxide or metal oxynitride seed layer and the substrate. Embodiment 13. 13. The device of embodiment 12, wherein the metal nitride seed layer is a nitride of the first metal. Embodiment 14. 14. The device of embodiment 12 or 13, wherein the metal nitride seed layer has a thickness of 3 to 50 nm. Embodiment 15. 15. The device of embodiment 14, wherein the metal nitride seed layer has a thickness of 3 to 5 nm. Embodiment 16. 16. The device of any one of embodiments 1 to 15, further comprising a capping layer on the superconducting layer. Embodiment 17. 17. The device of any one of claims 1 to 16, wherein the superconducting layer comprises at least one superconducting wire. Embodiment 18. 18. The device of embodiment 17, wherein the device comprises a superconducting nanowire single photon detector (SNSPD). Embodiment 19. 19. The device of any one of the preceding embodiments, comprising a distributed Bragg reflector between the substrate and the metal oxide or metal oxynitride seed layer. Embodiment 20. 19. The device of any one of the preceding embodiments, comprising an optical waveguide between the substrate and the metal oxide or metal oxynitride seed layer for receiving light propagating substantially parallel to a top surface of the substrate. Embodiment 21. 21. The device of any one of claims 1 to 20, wherein the metal nitride superconducting layer has a thickness of 4 to 50 nm. Embodiment 22. 1. A superconducting device comprising: a substrate; a lower seed layer on the substrate, the lower seed layer being a nitride of a first metal; an upper seed layer disposed directly on the lower seed layer, the upper seed layer being an oxide or oxynitride of the first metal; and a superconducting layer disposed directly on the upper seed layer, the superconducting layer being a nitride of a second metal different from the first metal. Embodiment 23. 23. The device of embodiment 22, wherein the top seed layer has a thickness of 0.1 to 1 nm. Embodiment 24. 24. The device of embodiment 22 or 23, wherein the lower seed layer has a thickness of 3 to 50 nm. Embodiment 25. 25. The device of any one of embodiments 22 to 24, wherein the nitride of the second metal is niobium nitride, titanium nitride, or niobium titanium nitride. Embodiment 26. 26. The device of any one of embodiments 22 to 25, wherein the first metal is aluminum. Embodiment 27. 27. The device of claim 22, wherein the metal nitride superconducting layer has a thickness of 4 to 50 nm. Embodiment 28. 1. A superconducting device comprising: a substrate; an aluminum nitride seed layer on the substrate; an aluminum oxide or aluminum oxynitride seed layer disposed directly on the aluminum nitride seed layer; and a superconducting layer, the superconducting layer being niobium nitride, titanium nitride, or niobium titanium nitride, disposed directly on the upper seed layer.

[0060] While particular embodiments have been described, other and further implementations may be devised without departing from the basic scope of the present disclosure. It is believed that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation. It should be noted, however, that the drawings depict only exemplary embodiments. The scope of the invention is determined by the claims that follow.

Claims

1. A superconducting device, a dielectric or semiconducting substrate; a metal oxynitride seed layer on the substrate, the seed layer being an oxynitride of a first metal; and a metal nitride superconducting layer, the metal nitride being a nitride of a second metal different from the first metal, disposed directly on the seed layer and patterned to form a wire; SUPERCONDUCTING DEVICES

2. The device of claim 1 , wherein the seed layer provides the metal nitride superconducting layer with a higher critical temperature than a metal nitride layer of the first metal.

3. The device described in claim 1, wherein the metal oxynitride seed layer is disposed directly on the substrate.

4. The device of claim 1 , further comprising a distributed Bragg reflector between the substrate and the metal oxynitride seed layer.

5. The device of claim 1 including an optical waveguide between the substrate and the metal oxynitride seed layer for receiving light propagating substantially parallel to a top surface of the substrate.

6. The device of claim 1 , wherein the nitride of the second metal is niobium nitride, titanium nitride, or niobium titanium nitride.

7. The device of claim 6 , wherein the metal nitride superconducting layer comprises δ-phase NbN.

8. The device of claim 6 , wherein the first metal is aluminum.

9. The device of claim 1, wherein the metal oxynitride seed layer has a thickness of less than 2 nm.

10. The device of claim 1, wherein the metal oxynitride seed layer has a thickness of 3 to 50 nm.

11. The device of claim 1, wherein the metal oxynitride seed layer is an oxynitride of the first metal.

12. The device of claim 1, having a metal nitride seed layer between the metal oxynitride seed layer and the substrate.

13. The device of claim 12 , wherein the metal oxynitride seed layer is a nitride of the first metal.

14. The device of claim 12, wherein the metal nitride seed layer has a thickness of 3 to 50 nm.

15. The device of claim 1 further comprising a capping layer on the metal nitride superconducting layer.

16. The device of claim 1 comprising a single metal nitride superconducting layer.

17. The device of claim 1, wherein the metal nitride superconducting layer has a thickness of 4 to 50 nm.

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