DESC:

FORM 2
The Patents Act 1970 (39 of 1970)
&
The Patent Rules 2003
NON-PROVISIONAL SPECIFICATION
(See Section 10 and rule 13)

TITLE
“A METHOD FOR FABRICATION OF SUPERCONDUCTING NANOWIRE SINGLE PHOTON DETECTORS”

APPLICANT:
SUPERQ TECHNOLOGIES INDIA PVT LTD
No 18, Gayatri Krupa, Somanna Gardens, Vidyaranyapura Bangalore Karnataka India 560097

PREAMBLE OF THE DESCRIPTION:
THE FOLLOWING NON-PROVISIONAL SPECIFICATION PARTICULARLY DESCRIBES THE NATURE OF THIS INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED:

A) CROSS- REFERENCE TO RELATED APPLICATION

This application claims the priority of the provisional application with serial number 202341000614 filed on 4th January 2023 (further post-dated for “2” months and new priority date is 4th March 2023) with the title, “A METHOD FOR FABRICATION OF SUPERCONDUCTING NANOWIRE SINGLE PHOTON DETECTORS” and the contents of which is incorporated in entirety.

B) TECHNICAL FIELD

[0001] The present invention is generally related to a field of material science. The present invention is particularly related to High Temperature Superconductors (HTS) having critical temperature Tc > 77K. The present invention is more particularly related to a superconducting nanowire single photon detector device system and method of fabrication thereof in an efficient manner to yield high quality nanowires suitable for detecting single photons with improved performance.

C) BACKGROUND OF THE INVENTION

[0002] The energy of a single photon in the visible or near-infrared range is around 10-19 J. A Single-photon detector is an extremely sensitive device capable of registering these quantum objects. A Single-photon detector is an optical detector that provides an electrical signal (voltage pulse) as an output upon detection of a single photon of incident light. Superconducting Nanowire Single Photon Detectors (SNSPDs), also known just as Superconducting Single Photon Detectors (SSPDs), have developed into some of the most advanced superconducting photodetectors, and are key enabling technologies in the development of quantum communication protocols. SNSPDs have the potential to detect single photons and particularly stand out in terms of broadband operation with high detection efficiency (>90%), exceptional signal-to-noise ratio, ultra-high temporal resolution and fast recovery time.
[0003] SNSPD operates at a current close to the critical current and a temperature below the critical temperature. In the region of photon absorption, local suppression of superconductivity occurs, and a “hotspot” is formed. If at this time a current close to the critical current is passed through the strip, then it redistributes over the part of the film remaining in the superconducting state. If the critical current density begins to exceed a threshold value (threshold current), then a vortex penetrates the nanowire or a vortex–antivortex pair is generated inside the hotspot. Due to the destruction of superconductivity, a resistive region
(also known as a phase slip Centre) is created. Under the influence of the Lorentz force, the vortices begin to move and heat up the nanowire. As a result, the entire cross-section of the strip goes into a normal, that is a non-superconducting state, the current is displaced into the high-frequency line and is detected by the pulsed output voltage signal through electronic hardware. To observe the single- photon detection effect in the visible and infrared wavelength ranges, the active element of the detector is a nanowire made of a thin superconducting film. The nanowire thickness should be of the order of the coherence length of the superconducting material, and the strip width should be less than the penetration depth of the magnetic field.
[0004] Currently, SNSPDs based on Low-Temperature Superconductors (LTS) have several drawbacks, mainly associated to the type of superconducting material used for forming the superconducting nanowire or nano-strip which make them operable only under ultra-low operation temperatures. Presently, the demonstrated SNSPDs perform the function at extremely low temperature, less than the liquid helium temperature (< 4.2 K). This summons the setting up of bulky and costly cooling systems, which results in not only high initial investment but also high maintenance costs. This makes the packaging of SNSPDs extremely impractical and expensive, and their application is limited to academic research.
[0005] Evidently the choice of a HTS is practical and economical choice for large scale deployment of SNSPDs. The operation temperature of the SNSPDs is mainly decided by the two factors i.e., selection of the functional materials having high transition temperature and the way of fabricating the array of nanowires as this ultimately affects the superconducting properties of the material. The steps involved in the fabrication of nanowire/nanostrips of the existing SNSPDs are deposition of the superconducting thin films on the substrate followed by etching to obtain the required nano-patterns. However, in HTS films, degradation of the superconducting properties occurs when the thickness approaches the nanometer scale.
[0006] Therefore, the fabrication of such thin and narrow high critical temperature nanowires with homogeneous superconducting properties is challenging, both given the material’s growth mode and given the limitations of current patterning technology. The etching techniques which are employed to fabricate the nanowires/nanostrip deteriorates the properties of the superconducting material. Moreover, the use of a protective layer usually degrades the superconducting properties due to the chemical interaction and surface chemistry of the compound. Atomic diffusion with another material can degrade the transition temperature drastically. It can be concluded that the post processing of the deposited superconducting thin films deteriorates the indispensable properties and causes not only decline in the system efficiency but also lowers the temperature at which the detection of photons is to be performed.
[0007] FIG. 1 illustrates the fabrication process of a conventional SNSPD. The conventional SNSPD 100 comprises substrate 101 suitable for fabricating a SNSPD 100. A suitable buffer layer 102 is deposited on the substrate (101) using a deposition technique. Further, a superconducting thin film 103 is deposited on the buffer layer 102 using a suitable deposition technique. The deposited superconducting film 103 is then encapsulated using a Gold (Au) layer 104, to protect the superconducting thin film from any kind of damage during patterning. Furthermore, the stack of films are patterned to an array of nanowires 105 using lithography and etching processes. Lastly, the Au encapsulation layer 104 is removed using an etching process to form a superconducting nano-strip 106 prior to the photo response measurements. Hence, the etching process potentially affects the quality of the superconducting
thin film.
[0008] Hence, in the view of this, there is a need for an improved superconducting nanowire single photon detector device system made up of a HTS material having a superconducting critical temperature above 77K. Moreover, there is a need for fabrication of a SNSPD, that preserves the quality of the superconducting material thereby solving the problem relating to the fabrication process and allowing for high quality films to be deposited and used for superconducting applications.
[0009] The above-mentioned shortcomings, disadvantages and problems are addressed herein, and which will be understood by reading and studying the following specification.

D) OBJECTS OF THE INVENTION:

[0010] The primary object of the present invention is to provide a superconducting nanowire single photon detector and method for fabrication thereof.
[0011] Another object of the present invention is to provide a superconducting nanowire single photon detector (SNSPD) device system made up of a HTS material having a superconducting critical temperature above 77K.
[0012] Yet another object of the present invention is to provide a method for fabrication of SNSPD that preserves the quality of the superconducting material thereby solving the problem relating to the fabrication process and allowing for high quality films to be deposited and used for superconducting applications.
[0013] Yet another object of the present invention is to provide a SNSPD made up of HTS material such as Rare-earth Barium Copper Oxide (ReBCO) having a critical temperature above 77K.
[0014] Yet another object of the present invention is to provide a SNSPD fabricated on a silicon substrate patterned and isotropically etched.
[0015] Yet another object of the present invention is to provide a SNSPD with STO (Strontium Titanate) as a buffer layer.
[0016] Yet another object of the present invention is to provide a SNSPD supported by a system.
[0017] Yet another object of the present invention is to provide a system supporting the SNSPD comprising a light source, cryo-packaging, amplifier, and a data acquisition system.
[0018] Yet another object of the present invention is to provide a method for fabrication of a SNSPD, by patterning of silicon substrate followed by deposition of a suitable buffer layer and the superconducting material.
[0019] Another object of the present invention is to provide a method for fabricating a SNSPD, that eliminates any further post-processing which adversely affects the quality of the superconducting material, specifically, surface quality which degrades the critical temperature considerably and affects the efficiency of the SNSPD.
[0020] Yet another object of the present invention is to provide a method for fabricating a SNSPD, capable of sensitive detection of light down to single-photon level.
[0021] These and other objects and advantages of the embodiments herein will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings.

E) SUMMARY OF THE INVENTION

[0022] The following details present a simplified summary of the embodiments herein to provide a basic understanding of the several aspects of the embodiments herein. This summary is not an extensive overview of the embodiments herein. It is not intended to identify key/critical elements of the embodiments herein or to delineate the scope of the embodiments herein. Its sole purpose is to present the concepts of the embodiments herein in a simplified form as a prelude to the more detailed description that is presented later.
[0023] The other objects and advantages of the embodiments herein will become readily apparent from the following description taken in conjunction with the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.
[0024] The various embodiments of the present invention provide a superconducting nanowire single photon detector device, system, and method for fabrication thereof. A High Temperature Superconductivity (HTS) Superconducting nanowire single photon detector (SNSPD) device and system is described. The SNSPD device comprises a substrate such as silicon. The substrate functions as a base. A lithography technique is carried out on the substrate to define nano lithographic patterns. The lithography technique helps to replicate patterns (positive or negative masks) into the underlying substrate. The various lithography techniques that can be implemented includes photolithography, electron beam lithography, X-ray and extreme UV lithography, focused ion beam and neutral atomic beam lithography, soft lithography, colloidal lithography, nano-imprint lithography, scanning probe lithography, atomic force microscope nano-lithography, and others. The said nano lithographic patterns are etched into silicon isotropically, to modify its side-wall profile using a suitable dry etching method such as plasma etching. The device further comprises a suitable buffer layer such as Strontium Titanate STO, which is deposited on top of the patterned substrate using a suitable deposition method such as Radio Frequency (RF) Magnetron Sputtering. The thickness of the buffer layer deposited on the patterned substrate is less than 100 nm. On deposition of the suitable buffer layer, a lift-off process of STO buffer layer is carried out to achieve patterned STO buffer layer on the substrate. The lift-off process involves creating a pattern by depositing a thin film over the patterned photoresist with a specific lift-off profile and removing the resist with a solvent to leave behind the thin film only in the patterned area, directly on the substrate, and is carried out post the buffer layer deposition. The photoresist is also known as a resist, is a light-sensitive material used in lithography process, to form a patterned coating on a surface. The device further comprises a HTS material such as Rare-earth Barium Copper Oxide (ReBCO) for example Yttrium Barium Copper Oxide (YBCO) or Bismuth Strontium Calcium Copper Oxide (BSCCO). Further, the HTS material is deposited on the buffer layer using deposition techniques such as sputtering or pulsed laser deposition. The HTS material utilized is made up of a cuprate based superconductor material having a critical temperature (Tc) greater than 77K, which is above the temperature corresponding to the boiling point of liquid nitrogen. Finally, the device comprises a gold (Au) contact pad deposited using a suitable deposition method such as sputtering or evaporation, using a shadow mask, which is fabricated ex-situ using Deep- Reactive Ion Etching (DRIE).
[0025] According to one embodiment of the present invention, the superconducting nanowire single photon detector (SNSPD) device is further supported by a system. The system comprises a light source consisting of suitable optics such as attenuated laser source or a single photon source. The light source is placed optionally as a part of the system supporting SNSPD device. Further, the ReBCO chip or the HTS material consisting of a meandered nanowire, is attached to a fibre-optic ferrule followed by an appropriate cryo-packaging such as liquid nitrogen cryostat, in a modular form. The function of the SNSPD device supported by the system includes generating an electrical pulse signal upon absorption of an incident photon, which is then amplified by a suitable amplifier such as low-noise amplifiers (LNA). Further, each output signal is recorded and counted by a data acquisition system (DAQ) consisting of a high-bandwidth oscilloscope or time correlation counter.
[0026] According to one embodiment of the present invention, the method for fabrication of SNSPD is provided. The method comprises procuring a suitable substrate such as silicon. The substrate acts as a base. The method further involves cleaning the substrate using piranha solution to remove organic residues from the substrate. The piranha solution, also known as piranha etch, is a mixture of sulfuric acid and hydrogen peroxide, used to clean organic residues off substrates. Post cleaning the substrate, the method involves defining patterns on the substrate using lithographic techniques. The lithography helps to replicate patterns both positive and negative masks into the underlying substrate. The lithographic techniques include photolithography, electron beam lithography, X-ray and extreme UV lithography, focused ion beam and neutral atomic beam lithography, soft lithography, colloidal lithography, nano-imprint lithography, scanning probe lithography, atomic force microscope nanolithography, and others. Further, the method involves etching the lithographic patterns into silicon isotropically, to modify its side-wall profile using a suitable dry etching method such as plasma etching. Furthermore, the method involves depositing a suitable buffer layer such as strontium titanate (STO) on top of the patterned substrate using suitable deposition techniques such as Radio Frequency (RF) Magnetron Sputtering. The thickness of the buffer layer deposited on the patterned substrate is less than 100 nm. The method further involves employing lift-off process, which involves creating a pattern by depositing a thin film over the patterned photoresist with a specific lift-off profile and removing the resist with a solvent to leave behind the thin film only in the patterned area, directly on the substrate. The lift-off process is carried out post the buffer layer deposition. The photoresist is a light-sensitive material used in lithography process, to form a patterned coating on a surface. Furthermore, the method involves annealing STO thin film buffer layer, to remove the chemical residuals and to improve the surface quality, resulting in crystalline STO film. The method further involves depositing a suitable HTS material such as ReBCO (Rare-earth Barium Copper Oxide), Yttrium Barium Copper Oxide (YBCO) or Bismuth Strontium Calcium Copper Oxide (BSCCO) on the crystalline STO film using deposition techniques such as sputtering or pulsed laser deposition. The method further involves annealing of the HTS material such as ReBCO film to obtain a crystalline ReBCO thin film. Finally, the method involves fabricating gold (Au) contact pads using a shadow mask, fabricated using the Deep Reactive-ion etching (DRIE) process.
[0027] From the foregoing discussion, it is apparent that the present invention makes use of High Temperature Superconductors, also referred to as HTS materials having critical temperature, Tc > 77K which operate above the temperature corresponding to the boiling point of liquid nitrogen for the fabrication of superconducting nanowires. Therefore, the fabrication of the HTS nanowires of the present invention on the patterned substrates in an efficient manner helps to yield high quality nanowires suitable for detecting single photons with improved noise performance. In addition, the key aspect of the present invention is the fabrication of nanowires without post processing of the superconducting thin films. The present invention involves firstly, the use of HTS materials having critical temperature >77K and secondly efficient fabrication method would increase the operation efficiency of such detectors. Therefore, the embodiments of the present invention prevent the deterioration of properties of the ReBCO superconducting materials and also makes the production process considerably faster and cost-effective for industrial applications. In addition, the method of fabrication of SNSPD yields high-quality superconducting devices capable of sensitive detection of light down to single- photon level. Subsequently, the use of a high-temperature superconductor warrants overall lower power consumption and the device cost as the operating temperature is higher (>10K) compared to other superconducting single photon detectors in the market.
[0028] It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiments may be combined to form a further embodiment of the disclosure.
[0029] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent in reference to the drawings and the following detailed description.

F) BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The other objects, features and advantages will occur to those skilled in the art from the following description of the preferred embodiment and the accompanying drawings in which:
[0031] FIG. 1 illustrates the fabrication method of a Superconducting Nanowire Single Photon Detector (SNSPD) [Pior-art], according to the conventional method existing in the literature.
[0032] FIG. 2. Illustrates a fabrication method of a HTS (High- Temperature Superconductivity) based SNSPD, according to an embodiment of the present invention.
[0033] FIG. 3 is a flowchart illustrating the method for fabrication of SNSPD, according to an embodiment of the present invention.
[0034] FIG. 4 is a flowchart illustrating the method for integrating the SNSPD to a system for detecting photons, according to an embodiment of the present invention.
[0035] Although the specific features of the present invention are shown in some drawings and not in others. This is done for convenience only as each feature may be combined with any or all of the other features in accordance with the present invention.

G) DETAILED DESCRIPTION OF THE DRAWINGS:

[0036] In the following detailed description, a reference is made to the accompanying drawings that form a part hereof, and in which the specific embodiments that may be practiced is shown by way of illustration. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments and it is to be understood that other changes may be made without departing from the scope of the embodiments. The following detailed description is therefore not to be taken in a limiting sense.
[0037] In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. It will be apparent, however, to one skilled in the art that the present disclosure can be practiced without these specific details.
[0038] The detailed description of various exemplary embodiments of the disclosure is described herein with reference to the accompanying drawings. It should be noted that the embodiments are described herein in such details as to clearly communicate the disclosure. However, the amount of details provided herein is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[0039] It is also to be understood that various arrangements may be devised that, although not explicitly described or shown herein, embody the principles of the present disclosure. Moreover, all statements herein reciting principles, aspects, and embodiments of the present disclosure, as well as specific examples, are intended to encompass equivalents thereof.
[0040] While the disclosure is susceptible to various modifications and alternative forms, specific embodiment thereof has been shown by way of example in the drawings and will be described in detail below. It should be understood, however, that it is not intended to limit the disclosure to the forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternatives falling within the scope of the disclosure.
[0041] The various embodiments of the present invention provide a superconducting nanowire single photon detector device, system, and method for fabrication thereof. A High Temperature Superconductivity (HTS) based superconducting nanowire single photon detector device and system is described.
[0043] According to one embodiment of the present invention, the method for fabrication of SNSPD is provided. The method comprises procuring a suitable substrate such as silicon. The substrate acts as a base. The method further involves cleaning the substrate using piranha solution to remove organic residues from the substrate. The piranha solution, also known as piranha etch, is a mixture of sulfuric acid and hydrogen peroxide, used to clean organic residues off substrates. Post cleaning the substrate, the method involves defining patterns on the substrate using lithographic techniques. The lithography helps to replicate patterns of both positive and negative masks into the underlying substrate. The lithographic techniques include photolithography, electron beam lithography, X-ray and extreme UV lithography, focused ion beam and neutral atomic beam lithography, soft lithography, colloidal lithography, nano-imprint lithography, scanning probe lithography, atomic force microscope nanolithography, and others. The method involves etching the lithographic patterns into silicon isotropically, to modify its side-wall profile by dry etching using a suitable dry etching method such as plasma etching. Furthermore, the method involves depositing a suitable buffer layer such as strontium titanate (STO) on top of the patterned substrate using suitable deposition techniques such as Radio Frequency (RF) Magnetron Sputtering. The thickness of the buffer layer deposited on the patterned substrate is less than 100 nm. The method further involves employing lift-off process, which involves creating a pattern by depositing a thin metal film over the patterned photoresist with a specific lift-off profile and removing the resist with a solvent to leave behind the metal only in the patterned area, directly on the substrate. The lift-off process is carried out post the buffer layer deposition. The photoresist is also known as a resist, is a light-sensitive material used in lithography process, to form a patterned coating on a surface. Furthermore, the method involves annealing STO thin film buffer layer, to remove the chemical residuals and to improve the surface quality, resulting in crystalline STO film. The method further involves depositing a suitable HTS material such as Rare-earth Barium Copper Oxide (ReBCO), Yttrium Barium Copper Oxide (YBCO) or Bismuth Strontium Calcium Copper Oxide (BSCCO) on the crystalline STO film using deposition techniques such as sputtering or pulsed laser deposition. The method further involves annealing of the HTS material such as ReBCO film to obtain a crystalline ReBCO thin film. Finally, the method involves fabricating gold (Au) contact pads using a silicon shadow mask fabricated ex-situ using Deep Reactive-Ion Etching (DRIE) technique.
[0044] According to an embodiment of the present invention, a method for integrating the SNSPD obtained to a system for detecting photons is provided. The method involves providing a light source consisting of suitable optics such as attenuated laser source or a single photon source. The light source is placed optionally as a part of the system supporting superconducting nanowire single photon detector device. Further the method involves, coupling a ReBCO chip or the HTS material consisting of a meandered nanowire, to a fibre-optic ferrule, then followed by cryo-packaging such as liquid nitrogen cryostat, in a modular form. The function of the SNSPD device supported by the system includes generating an electrical pulse signal upon absorption of an incident photon, which is then amplified by a suitable amplifier such as low-noise amplifiers (LNA). The method further involves amplifying the electric pulse signal generated by the SNSPD. Further the method involves counting and recording each output signal by a data acquisition system comprising a high-bandwidth oscilloscope or time correlation counter.
[0045] FIG. 2 illustrates the fabrication flow of a HTS (High- Temperature Superconductivity) based superconducting single photon detector, according to an embodiment of the present invention. With respect to FIG. 2, 200 illustrates the superconducting nanowire single photon detector device. The device 200 comprises a substrate 201 such as silicon. The substrate 201 functions as a base. A lithography technique is carried out on the substrate 201 to define nano-patterns. The lithography technique helps to replicate patterns (positive or negative masks) into the underlying substrate. The various lithography techniques that can be implemented includes photolithography, electron beam lithography, X-ray and extreme UV lithography, focused ion beam and neutral atomic beam lithography, soft lithography, colloidal lithography, nano-imprint lithography, scanning probe lithography, atomic force microscope nanolithography, and others. The device 200 further comprises a suitable buffer layer such as Strontium Titanate STO 202, which is deposited on top of the patterned substrate 201 using a suitable deposition method such as Radio Frequency (RF) Magnetron Sputtering. The thickness of the buffer layer deposited on the patterned substrate is less than 100nm. On deposition of the suitable buffer layer 202, a lift-off process of STO buffer layer 202 is carried out to achieve patterned STO buffer layer 203 on the substrate 201. The lift-off process involves creating a pattern by depositing a thin metal film over the patterned photoresist with a specific lift-off profile and removing the resist with a solvent to leave behind the metal only in the patterned area, directly on the substrate 201, and is carried out post the buffer layer deposition. The photoresist is also known as a resist, is a light-sensitive material used in lithography process, to form a patterned coating on a surface. The device 200 further comprises a superconducting HTS material 204 such as Rare-earth Barium Copper Oxide (ReBCO), Yttrium Barium Copper Oxide (YBCO) or Bismuth Strontium Calcium Copper Oxide (BSCCO). Further, the HTS material is deposited on the buffer layer 203 using deposition techniques such as sputtering or pulsed laser deposition. The HTS material 204 utilised is made up of a cuprate based superconductor material having a critical temperature (Tc) greater than 77 K, which is above the temperature corresponding to the boiling point of liquid nitrogen. FIG. 2 further illustrates the SNSPD fabrication process. 201 shows the Silicon substrate suitable for fabricating a SNSPD. The second step involves lithography patterning on the substrate and isotropic modification of the side wall profile of defined lithography patterns by plasma etching process (202). A suitable buffer layer (203) is deposited on the substrates (201) using a deposition technique as a part of the next step involves the deposition of a superconducting thin film (204) using a suitable deposition technique. The deposited superconducting films (204) are encapsulated using a Gold (Au) layer (205), using another silicon deep reactive ion etching (DRIE) physical shadow mask to protect the quality of superconducting thin film, so that which would avoid another lithography pattering step and further degrade the quality of superconducting thin film (204). This is performed by yet another deposition process. There are two types of isotropic sidewall profile modification possible using plasma etching process such as dumbbell shaped, or steep bottom narrow profile as shown in the FIG. 2.
[0046] FIG. 3 is a flowchart illustrating the method for fabrication of SNSPD, according to an embodiment of the present invention. The method 300 involves procuring a suitable substrate such as silicon at step 301. The substrate acts as a base. The method 300 further involves cleaning the substrate using piranha solution to remove organic residues from the substrate at step 302. The piranha solution, also known as piranha etch, is a mixture of sulfuric acid and hydrogen peroxide, used to clean organic residues off substrates. Post cleaning the substrate, the method 300 involves defining nano lithographic patterns on the substrate using lithographic techniques at step 303. The lithography helps to replicate patterns into the underlying substrate. The lithographic techniques include photolithography, electron beam lithography, X-ray and extreme UV lithography, focused ion beam and neutral atomic beam lithography, soft lithography, colloidal lithography, nano-imprint lithography, scanning probe lithography, atomic force microscope nanolithography, and others. Further the method 300 involves performing the isotropic modification of the sidewall profile of silicon by plasma etching at step 304. Furthermore, method 300 involves depositing a suitable buffer layer such as strontium titanate (STO) on top of the patterned substrate using suitable deposition techniques such as Radio Frequency (RF) Magnetron Sputtering at step 305. The thickness of the buffer layer deposited on the patterned substrate is less than 100 nm. On deposition of the buffer layer, the method 300 involves employing lift-off process, which involves creating a pattern by depositing a thin metal film over the patterned photoresist with a specific lift-off profile and removing the resist with a solvent to leave behind the metal only in the patterned area, directly on the substrate at step 306. The lift-off process is carried out, post the buffer layer deposition. The photoresist is a light-sensitive material used in lithography process, to form a patterned coating on a surface. Furthermore, method 300 involves annealing STO thin film buffer layer, to remove the chemical residuals and to improve the surface quality, resulting in a crystalline STO film at step 307. The method 300 further involves depositing a suitable HTS material such as Rare-earth Barium Copper Oxide (ReBCO) for example Yttrium Barium Copper Oxide (YBCO) or Bismuth Strontium Calcium Copper Oxide (BSCCO) on the crystalline STO film using deposition techniques such as sputtering or pulsed laser deposition at step 308. The method 300 further involves annealing of the HTS material such as ReBCO film to obtain a crystalline ReBCO thin film at step 309. The said HTS material utilized is made up of a cuprate based superconductor material having a critical temperature (Tc) greater than 77 K, which is above the temperature corresponding to the boiling point of liquid nitrogen. Finally, the method 300 involves fabricating gold (Au) contact pads using a silicon shadow mask fabricated ex-situ using Deep Reactive-Ion Etching (DRIE) technique using a shadow mask at step 310.
[0047] FIG. 4 is a flowchart illustrating the method for integrating the SNSPD to a system for detecting photons, according to an embodiment of the present invention. The method 400 involves providing a light source consisting of suitable optics such as attenuated laser source or a single photon source at step 401. The light source is placed optionally as a part of the system supporting superconducting nanowire single photon detector device. Further the method 400 involves, coupling a ReBCO chip or the HTS material consisting of a meandered nanowire, to a fibre-optic ferrule at step 402, then followed by cryo-packaging such as liquid nitrogen cryostat, in a modular form at step 403. The function of the SNSPD device supported by the system includes generating an electrical pulse signal upon absorption of an incident photon, which is then amplified by a suitable amplifier such as low-noise amplifiers (LNA). The method 400 further involves amplifying the electric pulse signal generated by the SNSPD at step 404. Further the method 400 involves counting and recording each output signal by a data acquisition system (DAQ) comprising a high-bandwidth oscilloscope or time correlation counter at step 405.
[0048] The foregoing examples and illustrative implementations of various embodiments have been provided merely for explanation and are in no way to be construed as limiting the present invention. While the present invention has been described with reference to various embodiments, illustrative implementations, drawings, and techniques, it is understood that the words, which have been used herein, are words of description and illustration, rather than words of limitation.
[0049] Further, although the present invention has been described herein with reference to particular means, materials, embodiments, techniques, and implementations, the present invention is not intended to be limited to the particulars disclosed herein; rather, the present invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims.
[0050] It will be understood by those skilled in the art, having the benefit of the teachings of this specification, that the present invention is capable of modifications and other embodiments may be affected and changes may be made thereto, without departing from the scope and spirit of the present invention.

H) ADVANTAGES OF THE INVENTION:

[0051] The present invention provides a superconducting nanowire single photon detector (SNSPD) device system and method for fabrication thereof. A SNSPD is an optoelectronic device that converts incident light or other electromagnetic radiation in the ultra-violet, visible, and infrared spectral regions into electrical signals thereon. A single-photon detector is a quantum detector that can detect one incident photon at a time. A single-photon detector comprises a Superconductor strip biased near its critical current. The Superconductor strip provides a detectable output signal upon absorption of a single incident photon. The Superconductor strip meanders to increase its probability of receiving a photon from a light source. Hence, the single-photon detector of the present invention is suitable for a multitude of applications including free-space and satellite communications, quantum communications, quantum cryptography, weak luminescence, and semiconductor device testing.
[0052] Low dark count rate, high detection efficiency and accurate timing resolution are the three most desired features of a single-photon detector. These characteristics can be equivalently described using figure-of-merit, for example the Noise Equivalent Power (NEP) or Signal to Noise Ratio (SNR). Detectors with low noise performances are increasingly sought after for applications in both quantum and classical technologies. In particular, linear optics quantum information processing crucially relies on the availability of low dark count rate single photon detectors. Most prominently, quantum key distribution implementations are currently limited in rate and range by imperfect detector characteristics. Other applications of the present invention, which would greatly benefit from improved single-photon detection systems include the characterization of quantum emitters, optical time domain reflectometry as well as picosecond imaging circuit analysis.
[0053] Furthermore, the present invention makes use of High Temperature Superconductors, also referred to as HTS materials having critical temperature, Tc > 77 K which operate above the temperature corresponding to the boiling point of liquid nitrogen for the fabrication of superconducting nanowires. Therefore, the fabrication of the HTS nanowires of the present invention on the patterned substrates in an efficient manner helps to yield high quality nanowires suitable for detecting single photons with improved noise performance. In addition, the key aspect of the present invention is the fabrication of nanowires without post processing of the superconducting thin films. The present invention involves firstly, the use of HTS materials having critical temperature >77K and secondly efficient fabrication method would increase the operation efficiency of such detectors. Therefore, the embodiments of the present invention prevent the deterioration of properties of the ReBCO like superconducting materials and also makes the production process considerably faster and cost-effective for industrial applications. In addition, the method of fabrication of SNSPD yields high-quality superconducting devices capable of sensitive detection of light down to single-photon level. Subsequently, the use of a high-temperature superconductor warrants overall lower power consumption and the device cost as the operating temperature is higher (>10K) compared to other superconducting single photon detectors in the market.
[0054] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments.
[0055] It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the appended claims.
[0056] Although the embodiments herein are described with various specific embodiments, it will be obvious for a person skilled in the art to practice the invention with modifications. However, all such modifications are deemed to be within the scope of the claims.
[0057] It is also to be understood that the following claims are intended to cover all of the generic and specific features of the embodiments described herein and all the statements of the scope of the embodiments which as a matter of language might be said to fall there between.
[0058] The scope of the embodiments of the present invention is ascertained by the claims to be submitted at the time of filing the complete specification.

,CLAIMS:WE CLAIM:

1. A superconducting nanowire single photon detector (SNSPD) device, comprising:

a. selecting a substrate typically a silicon, functioning as a base;

b. nano lithographic patterns defined on the substrate using lithography techniques, said techniques including photolithography, electron beam lithography, X-ray lithography, extreme UV lithography, focused ion beam lithography, neutral atomic beam lithography, soft lithography, colloidal lithography, nano-imprint lithography, scanning probe lithography, atomic force microscope nano-lithography;

c. isotropic etching of the nano lithographic patterns into silicon to modify its side-wall profile;

d. a buffer layer of Strontium Titanate (STO) deposited on the patterned substrate by Radio Frequency (RF) Magnetron Sputtering, wherein the thickness of the buffer layer is less than 100 nm;

e. a high temperature superconductivity (HTS) material selected from the group consisting of Rare-earth Barium Copper Oxide (ReBCO) materials, deposited on the buffer layer; and wherein the critical temperature of the HTS material is greater than 77K.

f. a gold (Au) contact pad deposited using a silicon shadow mask fabricated ex-situ using Deep-Reactive Ion Etching (DRIE) with a shadow mask.

2. The said SNSPD device of claim 1, wherein the HTS material comprises Yttrium Barium Copper Oxide (YBCO) or Bismuth Strontium Calcium Copper Oxide (BSCCO).

3. The said SNSPD device of claim 1, wherein the nano-patterns are replicated into the substrate using positive or negative masks.

4. The said SNSPD device of claim 1, wherein the isotropic modification of the side wall profile of the defined nano-lithography patterns are done by plasma etching process.

5. The said SNSPD device of claim 1, wherein the lift-off process of the STO buffer layer is carried out post the deposition of the buffer layer.

6. The said SNSPD device of claim 1, wherein the substrate is silicon.

7. The said SNSPD device of claim 1, wherein the HTS material is deposited on the buffer layer by sputtering or pulsed laser deposition.

8. The said SNSPD device of claim 1, wherein the critical temperature (Tc) of the HTS material is above the temperature corresponding to the boiling point of liquid nitrogen.

9. The said SNSPD device of claim 1, wherein the gold (Au) contact pad is deposited using a silicon shadow mask fabricated shadow mask to define its shape using Deep-Reactive Ion Etching (DRIE).

10. The said SNSPD device of claim 1, further comprising a system for supporting the SNSPD device in detecting individual low-energy photons with high quantum efficiencies, comprising:

a. a light source comprising suitable optics selected from an attenuated laser source or a single photon source, wherein the light source is optionally a part of the system supporting the SNSPD device;

b. a ReBCO chip or high-temperature superconducting (HTS) material comprising a meandered nanowire, attached to a fiber-optic ferrule;

c. an appropriate cryo-packaging, such as a liquid nitrogen cryostat, in a modular form;

d. wherein the SNSPD device, supported by the system, functions to generate an electrical pulse signal upon absorption of an incident photon, which is then amplified by a suitable amplifier, such as low-noise amplifiers (LNA); and

e. wherein each output signal is recorded and counted by a data acquisition system (DAQ) comprising a high-bandwidth oscilloscope or time correlation counter.

11. A method for the fabrication of a superconducting nanowire single photon detector (SNSPD), comprising:

a. Procuring a substrate typically a silicon, wherein the substrate acts as a base;

b. Cleaning the substrate using a piranha solution to remove organic residues from the substrate;

c. Defining patterns on the substrate using lithographic techniques;

d. Performing the isotropic modification of the sidewall profile of silicon by plasma etching;

e. Depositing a buffer layer comprising strontium titanate (STO) on the patterned substrate using Radio Frequency (RF) Magnetron Sputtering, wherein the thickness of the buffer layer is less than 100 nm;

f. Employing a lift-off process post the buffer layer deposition;

g. Annealing the STO thin film buffer layer to obtain a crystalline STO film;

h. Depositing a high-temperature superconducting (HTS) material selected from the group consisting of Rare-earth Barium Copper Oxide (ReBCO), Yttrium Barium Copper Oxide (YBCO), and Bismuth Strontium Calcium Copper Oxide (BSCCO) on the crystalline STO film using deposition techniques such as sputtering or pulsed laser deposition;

i. Annealing the HTS material to obtain a crystalline HTS thin film; and

j. Fabricating gold (Au) contact pads using a shadow mask fabricated using the Deep Reactive-ion etching (DRIE) process.

12. The method of claim 11, wherein the lithographic techniques include photolithography, electron beam lithography, X-ray lithography, extreme UV lithography, focused ion beam lithography, neutral atomic beam lithography, soft lithography, colloidal lithography, nano-imprint lithography, scanning probe lithography, or atomic force microscope nanolithography.

13. The method of claim 11, wherein the plasma etching techniques are employed for isotropically etching the sidewall of the nano-patterned silicon.

14. The method of claim 11, wherein the lift-off process involves creating a pattern by depositing a thin film over the patterned photoresist with a specific lift-off profile and removing the resist with a solvent to leave behind the thin film only in the patterned area, directly on the substrate.

15. The method of claim 11, further comprising depositing additional layers or structures on the crystalline HTS thin film for device integration or enhancement of performance.

16. The method of claim 11, wherein the substrate is cleaned using a piranha solution comprising sulfuric acid and hydrogen peroxide.

17. The method of claim 11, wherein the buffer layer is annealed to remove chemical residuals and improve surface quality, resulting in a crystalline STO film.

18. The method of claim 11, wherein the HTS material is annealed to obtain a crystalline HTS thin film with improved superconducting properties.

19. The method of claim 11, wherein the gold (Au) contact pads are fabricated using a shadow mask to define the contact regions on the crystalline HTS thin film.

Dated this 28th day of February 2024

For, SUPERQ TECHNOLOGIES PRIVATE LIMITED

BY THEIR AGENT

(DR. BABITHA THARAPPAN)
IN/PA-1614
ATV-LEGAL
A METHOD FOR FABRICATION OF SUPERCONDUCTING NANOWIRE SINGLE PHOTON DETECTORS