Superconducting qubits and method of fabrication
Offset sputtering in superconducting qubit fabrication enhances coherence times by forming components with negative stress, addressing the limitations of conventional methods and enabling more efficient quantum operations.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- IQM FINLAND OY
- Filing Date
- 2025-12-11
- Publication Date
- 2026-06-25
AI Technical Summary
Existing superconducting qubit fabrication techniques, such as concentric sputtering, fail to achieve optimal coherence times (T1 and T2) due to limitations in qubit design and fabrication processes, leading to reduced operational capabilities.
The use of offset sputtering to deposit a superconducting thin film on a substrate, where the sputtering source is offset from the substrate's normal center line by a non-zero angle and distance, results in the formation of superconducting qubit components with enhanced coherence times (T1) by creating negative stress in the thin film.
Offset sputtering significantly increases the coherence time (T1) of superconducting qubits to 0.97 ms, surpassing conventional methods by achieving a mean T1 time of 0.50 ms, thereby enabling more complex and efficient quantum operations.
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Abstract
Description
[0001] SUPERCONDUCTING QUBITS AND METHOD OF FABRICATION
[0002] Technical Field
[0003] The invention relates to the field of superconducting qubits, in particular to a method of manufacturing at least one component of a superconducting qubit and superconducting qubit produced according to said method.
[0004] Background
[0005] A qubit is a physical device that provides at least two individually addressable quantum states that can exist in superposition. The ability to maintain a superposition of quantum states over longer time periods allows for more operations to be performed on those states, enabling more complex and more useful computation to be performed on the qubits.
[0006] The coherence time of a qubit refers to the time over which a qubit can maintain a superposition of quantum states. The speed of decoherence, i.e. any process by which a superposition of quantum states collapses to a classic state, may be expressed in terms of time periods Ti and T2. T1refers to the characteristic time period over which the energy of a qubit is lost to the environment. T2refers to the characteristic time period over which the phase information of states in a superposition is lost. Longer T1and T2times lead to more useful qubits on which more operations, or gates, may be performed. T1and T2are impacted by qubit design, fabrication techniques, and other factors.
[0007] Summary of the Invention
[0008] A first aspect of the invention relates to a method for manufacturing at least one component of a superconducting qubit. The method comprises depositing a superconducting thin film on a substrate by offset sputtering of a superconducting thin film material, wherein the axis of the sputtering source is offset from the normal centre line of the substrate by a non-zero angle and by a non-zero distance measured parallel to the surface of the substrate; and forming at least one component of the superconducting qubit from the superconducting thin film.
[0009] The at least one component of the superconducting circuit may include at least one of: one or more capacitor pads, one or more resonators, one or more waveguides, and one or more ground planes. The superconducting thin film material may comprise one or more of: niobium, tantalum, aluminium, titanium nitride, and niobium nitride.
[0010] Depositing the superconducting thin film on the substrate by offset sputtering of a superconducting thin film material may be performed under suitable sputtering conditions to produce a thin film having a negative stress.
[0011] Forming at least one component of the superconducting qubit from the superconducting thin film comprises patterning and etching the superconducting thin film.
[0012] The method may further comprise forming at least one Josephson junction on the substrate such that the at least one Josephson junction is electrically connected to the superconducting thin film.
[0013] A second aspect of the invention relates to a superconducting qubit, wherein at least one of the components of the superconducting qubit was formed by offset sputtering of a superconducting material, wherein the axis of the sputtering source is offset from the normal centre line of the substrate by a non-zero angle and by a non-zero distance measured parallel to the surface of the substrate.
[0014] A third aspect of the invention relates to a superconducting qubit, wherein at least one of the components of the superconducting qubit was formed according to the method described above.
[0015] Brief Description of the Drawings
[0016] Figure 1 depicts an arrangement for offset sputtering.
[0017] Figure 2 is a flow diagram depicting a method of forming at least one component of a superconducting qubit using offset sputtering.
[0018] Detailed Description of the Invention
[0019] The present invention relates to improvements in superconducting qubit fabrication based on the use of offset sputtering to deposit a superconducting thin film on a substrate, from which one or more “large-scale” components of the superconducting qubit can be fabricated. In this context “large-scale” components refers to components of the qubit with dimensions roughly of the order of a micron or larger, for example capacitor pads, resonators, waveguides and ground planes.
[0020] In particular, the inventors have discovered that by using offset sputtering to deposit the superconducting thin film, the Ti time of the qubit may be dramatically increased.
[0021] For example, one recent academic study (Kono, S., Pan, J., Chegnizadeh, M. et
[0022] al. Mechanically induced correlated errors on superconducting qubits with relaxation times exceeding 0.4 ms. Nat Commun 15, 3950 (2024). https: / / doi.org / 10.1038 / s41467-024-48230-3; Supplementary Information) describes a process for manufacturing a transmon qubit in which, amongst other steps, a niobium thin film is deposited on a substrate using centre gun sputtering (DC sputtering using a Pfeiffer SPIDER Sputtering system). In that study, the authors were able to achieve a T1 time of 0.45 ms. The inventors of the present invention were able to achieve a comparable T1 time of 0.50 ms using a similar manufacturing technique, as discussed in more detail below. Surprisingly, the T1 time was dramatically increased to 0.97 ms by the use of offset sputtering instead of the typical top-down or bottom-up concentric sputtering. Table 1 below shows the mean and maximum T1 times for qubits formed using concentric sputtering (wafers A1-A3) and offset sputtering (wafers B1-B3), with the mean and maximum T1 times for wafers B1-B3 being generally and in some cases significantly higher than for wafers A1-A3.
[0023] Mean T1(μs) Max T1(μs)
[0024] Wafer A1 96 ± 76 346 ± 35
[0025] Wafer A2 127 ± 79 394 ± 33
[0026] Wafer A3 180 ± 79 431 ± 25
[0027] Wafer B1 297 ± 130 663 ± 72
[0028] Wafer B2 342 ± 160 964 ± 92
[0029] Wafer B3 174 ± 121 636 ± 34
[0030] Table 1 In conventional sputtering deposition, the sputtering target (i.e. the source of the material to be deposited on a substrate) is arranged concentrically and parallel to the substrate onto which target material is to be deposited. The term “offset sputtering” as used in the context of the present invention refers to a sputtering technique in which the sputtering target is arrange non-concentrically and at a non-zero angle (i.e. not parallel) with respect to the substrate. This is illustrated in Figure 1. The offset sputtering arrangement 100 includes a sputtering source 101, e.g. a magnetron sputtering source, which includes a target made of the source material, which is to be deposited on the substrate 102. The centre line 111 of the sputtering source 101, i.e. the imaginary line extending perpendicularly from the centre of the target of the sputtering source 101 towards the substrate 102, is offset from the centre line 112 of the substrate, i.e. the imaginary line extending through the centre of the substrate 102 and normal to the surface of the substrate 102, by a horizontal distance r, measured parallel to the surface of the substrate, and an angle 9, which is measured relative to the direction normal to the surface of the substrate 102, i.e. parallel to the substrate centre line 112.
[0031] The offset sputtering technique of the present invention is conceptually similar to confocal sputtering, which is a deposition technique in which multiple sputtering sources are arranged at an offset within a vacuum chamber. However, confocal sputtering is specifically used to deposit multiple materials onto a substrate, in sequence or in parallel, without breaking vacuum. In contrast, in the present invention, offset sputtering is used to deposit a single material onto the substrate.
[0032] Thus, a first aspect of the present invention relates to a method for manufacturing at least one component of a superconducting qubit. The method may be part of a longer method for forming multiple components of a superconducting qubit, including smaller-scale components such as Josephson junctions.
[0033] The method 200 is depicted in Figure 2. At step 201, a superconducting thin film is deposited on a substrate by offset sputtering of a superconducting thin film material. The superconducting thin film material may be, for example: niobium, tantalum, aluminium, titanium nitride, or niobium nitride. Step 201 may further include deposition of additional layers of different superconducting thin film material to form a multi-layer film. The substrate may be a silicon substrate, a sapphire substrate, or any other substrate suitable for use in the method 200 or a broader method for fabricating a superconducting qubit that includes the method 200. The substrate may be a wafer on which multiple superconducting qubits and / or multiple superconducting circuits each comprising multiple superconducting are formed before being diced into individual superconducting qubits / superconducting circuits.
[0034] Offset sputtering may be performed under suitable conditions to lead to negative stress in the resulting thin film. The person skilled in the art is aware of suitable mechanisms for producing thin films with negative stress, for example suitable control of the inert gas pressure as described in one academic study with respect to Niobium (C. T. Wu, Intrinsic stress of magnetron-sputtered niobium films, Thin Solid Films, Volume 64, Issue 1, 1979, Pages 103-110, ISSN 0040-6090, https: / / doi.org / 10.1016 / 0040-6090(79)90549-2) and another with respect to Tantalum (Asa’ad Al-masha’al, Andrew Bunting, Rebecca Cheung, Evaluation of residual stress in sputtered tantalum thin-film, Applied Surface Science, Volume 371, 2016, Pages 571-575, ISSN 0169-4332, https: / / doi.org / 10.1016 / j.apsusc.2016.02.236).
[0035] Step 201 may be preceding by substrate preparation steps, for example cleaning the substrate of organic contamination. Any suitable cleaning method may be used, for example cleaning by Piranha solution (a mixture of sulfuric acid and hydrogen peroxide), or HF and BHF (a mixture of a buferinq agent, such as ammonium fluoride NH4F, and hydrofluoric
[0036]
[0037] acid HF).
[0038] Following deposition of the superconducting thin film on the substrate at step 201, the superconducting thin film is formed into at least one component of a superconducting qubit at step 202. As mentioned above, the at least one component of the superconducting qubit may be a “large-scale” component of the superconducting qubit, e.g. capacitor pads, resonators, waveguides and / or ground planes. The formation of at least one component of the superconducting qubit from the superconducting film may be performed by patterning and etching the thin film, e.g. deposition of a suitable photoresist, followed by patterning and development of the photoresist by exposure to a suitable light source, e.g. by lithography or direct laser writing, and etching of the superconducting thin film via the patterned photoresist to selectively remove superconducting thin film material and produce the at least one component of the superconducting qubit. The skilled person is aware of other techniques for patterning a thin film, for example focused ion beam ablation. The present invention is not limited to any one technique for forming the at least one component of a superconducting qubit from the superconducting thin film, nor is the invention limited to patterning techniques currently known in the art.
[0039] The method 200 may include a further step 203 of forming one or more further components of the superconducting qubit, for example one of more Josephson junctions. The one or more further components of the superconducting qubit may be formed using any suitable process that is compatible with steps 201 and 202, i.e. that does expose the superconducting thin film to conditions, substances or other factors that significantly degrade its properties. One suitable method is described in Kono, S., Pan, J., Chegnizadeh, M. et al. Mechanically induced correlated errors on superconducting qubits with relaxation times exceeding 0.4 ms, referred to above. The superconducting qubits for which one or more components are formed using the above method may be double-pad type transmon qubits.
Claims
Claims1. A method for manufacturing at least one component of a superconducting qubit, the method comprising:depositing a superconducting thin film on a substrate by offset sputtering of a superconducting thin film material, wherein the axis of the sputtering source is offset from the normal centre line of the substrate by a non-zero angle and by a non-zero distance measured parallel to the surface of the substrate;forming at least one component of the superconducting qubit from the superconducting thin film.
2. The method of claim 1, wherein the at least one component of the superconducting circuit includes at least one of: one or more capacitor pads, one or more resonators, one or more waveguides, and one or more ground planes.
3. The method of any preceding claim, wherein the superconducting thin film material comprises one or more of: niobium, tantalum, aluminium, titanium nitride, and niobium nitride.
4. The method of any preceding claim, wherein depositing the superconducting thin film on the substrate by offset sputtering of a superconducting thin film material is performed under suitable sputtering conditions to produce a thin film having a negative stress.
5. The method of any preceding claim, wherein forming at least one component of the superconducting qubit from the superconducting thin film comprises patterning and etching the superconducting thin film.
6. The method of any preceding claim, wherein the method further comprises forming at least one Josephson junction on the substrate such that the at least one Josephson junction is electrically connected to the superconducting thin film.
7. A superconducting qubit, wherein at least one of the components of the superconducting qubit was formed by offset sputtering of a superconducting material,wherein the axis of the sputtering source is offset from the normal centre line of the substrate by a non-zero angle and by a non-zero distance measured parallel to the surface of the substrate.
8. A superconducting qubit, wherein at least one of the components of the superconducting qubit was formed according to the method of any of claims 1 to 6.