WO2021150101A1

WO2021150101A1 - Low-loss dielectric for high frequency cryogenic applications

Info

Publication number: WO2021150101A1
Application number: PCT/NL2021/050014
Authority: WO
Inventors: Sten VOLLEBREGT; Akira Endo; Jochem Jan Anton BASELMANS; Bruno BUIJTENDORP
Original assignee: Technische Universiteit Delft
Priority date: 2020-01-23
Filing date: 2021-01-13
Publication date: 2021-07-29
Also published as: NL2024742B1

Abstract

The present invention is in the field of an electromagnetic circuit which may be used as a detector or in a quantum computer, which may be provided in an electronic device, and in a method of operating said electromagnetic circuit. Therein a low-loss dielectric is used for high frequency typically cryogenic applications.

Description

Low-loss dielectric for high frequency cryogenic applications

FIELD OF THE INVENTION

The present invention is in the field of an electromagnetic circuit, which may be used as a detector or in a quantum computer, which may be provided in an electronic device, and in a method of operating said electromagnetic circuit. Therein a low-loss dielectric is used for high frequency typically cryogenic applications.

BACKGROUND OF THE INVENTION

The present invention is in the field of an electromagnetic circuit. An electromagnetic circuit may relate to lumped circuit elements, a transmission line, a resonator, a device, a system.

A resonator oscillates with increased amplitude at some resonant frequencies. The oscillations can be acoustic, electromagnetic, such as optical, or mechanical. Resonators may be used to generate waves of specific resonance frequencies. They may also be used to detect or filter specific arriving resonance frequencies. Resonators can therefore produce oscillations of very precise frequency, the resonance frequency, and higher order frequencies thereof. Resonators can be electromagnetic of nature, solid state, and combinations thereof, such as a cavity, and circuits, such as a circuit comprising an inductor and a capacitor.

There has been further research and development for obtaining millimeter and sub millimeter wavelength resonators. It is an advantage to provide these on a chip, such that semi conductor technology can be used to produce these resonators. Frequencies up to 1100 GHz can be obtained, with a relatively narrow bandwidth around resonance frequencies. On-chip filter bank spectrometers using superconducting resonators as narrow band-separation filters could be used as multi-object broadband spectrometers for millimeter or smaller wavelength telescopes for astronomy. Advantages thereof are a good sensitivity, a compact size, and flexibility. It is however difficult to obtain high quality factors Q with millimeter and submillimeter resonant filters.

Recently superconducting materials are used in resonators. For instance, US 6,626,995 recites use of magnesium diboride as a superconductivity thin film which can be applied to a rapid single flux quantum (RSFQ) circuit, and a method for making the same, using a template film is formed on top of the substrate, wherein the template has a hexagonal crystal structure.

The superconducting thin film is formed on top of the template film.

So far performance of the prior art resonators is hampered by losses in the (superconducting) circuits.

Some documents have superconducting materials incorporated therein. For instance, JP 2008 071908 (A) recites a superconductive photodetector which can obtain higher quantum efficiency in detecting a single photon. A fine line formed of a superconductive photo detective material is disposed closely in a surface of a crystal substrate in a meander shape. Another meander fine line is disposed in a rear surface of a crystal substrate or an upper h insulating film in a position corresponding to a clearance of the meander fine line. Thereby, a plurality of sets of meander fine lines are shifted mutually and set in piles almost without a clearance. There remains no untreated photon in a light irradiation region, thus remarkably improving quantum efficiency. US 9,653,398 (Bl) recites a method of forming a superconductor device is provided. The method includes depositing a non-oxide based dielectric layer over a substrate, depositing a photoresist material layer over the non-oxide based dielectric layer, irradiating and developing the photoresist material layer to form a via pattern in the photoresist material layer, and etching the non-oxide based dielectric layer to form openings in the non oxide based dielectric layer based on the via pattern. The method further comprises stripping the photoresist material layer, and filling the openings in the non-oxide based dielectric with a superconducting material to form a set of superconducting contacts. Cunnane et al. in “Penetration depth of MgB2 measured using Josephson junctions and SQUIDs”, Appl. Phys. Lett. 102, 072603 (2013), using two methods of different mechanisms. The first method used MgB2 Josephson junctions and the magnetic field dependence of the junction critical current.

The second method deduced the penetration depth from the inductance of a MgB2 microstrip used to modulate the voltage of a MgB2 DC SQUID. The two methods showed a consistent value of the low-temperature penetration depth for MgB2 to be about 40 nm. Both the small penetration depth value and its temperature dependence are in agreement with a microscopic theory for MgB2 in the clean limit. Endo et al. in “On-chip filter bank spectroscopy at 600- 700 GHz using NbTiN superconducting resonators”, Appl. Phys. Lett. 103, 032601 (2013), demonstrate the principle of an on-chip submillimeter wave filter bank spectrometer, using superconducting micro resonators as narrow band-separation filters. The filters are made of NbTiN/SiNx/NbTiN microstrip line resonators, which have a resonance frequency in the range of 614-685 GHz, two orders of magnitude higher in frequency than what is currently studied for use in circuit quantum electrodynamics and photodetectors. The frequency resolution of the filters decreases from 350 to 140 with increasing frequency, most likely limited by dissipation of the resonators. And Cunnane et al. in “Characterization of MgB2 Superconducting Hot Electron Bolometers“, in IEEE Transactions on Applied Superconductivity, Los Alamitos, Vol. 25, No. 3, June 302015, p. 1-6, recite Hot-Electron Bolometer (HEB) mixers having proven to be the best tool for high-resolution spectroscopy at the

Terahertz frequencies. They fabricated and characterized thin-film (~ 15 nm) MgB2-based spiral antenna-coupled HEB mixers on SiC substrate. An IF bandwidth greater than 8 GHz at 25 K and the device noise temperature < 4000 K at 9 K using a 600 GHz source was reported. Using temperature dependencies of the radiation power dissipated in the device we have identified the optical loss in the integrated micro antenna responsible as a cause of the limited sensitivity of the current mixer devices. From the analysis of the current voltage (IV) characteristics, we have derived the effective thermal conductance of the mixer device and estimated the required local oscillator power in an optimized device to be ~ 1 pW.

The present invention therefore relates to an improved circuit, which solves one or more of the above problems and drawbacks of the prior art, providing reliable results, without jeopardizing functionality and advantages.

SUMMARY OF THE INVENTION

It is an object of the invention to overcome one or more limitations of the prior art and provide an electromagnetic circuit that has low losses, in particular a low dielectric loss, typically tan d < 10³, in particular tan d < 10 ⁵, such as tan d of about 10⁷. The present invention relates to an electromagnetic circuit comprising a substrate 10, on the substrate a first layer 11 of superconducting material, on the superconducting material a dielectric layer 12, wherein the dielectric layer is a SiC layer, in particular a SiC layer with a dielectric constant of >5, more in particular >6, such as 6.8 or larger, and on the dielectric layer a second layer 13 of superconducting material or part thereof, wherein the part may be one or more of a geometrical shaped flat object, such as a line, a disc, a square, a rectangle, a multigonal object, wherein the second layer of superconducting material may comprise at least one line, such as at least two lines, preferably 3-1000 lines, wherein lines may be parallel, and at least one coupling for operating the resonator, such as capacitive or inductive couplings. The layers and substrate may be considered as a sandwich structure. In said sandwich structure in principle layers can be interchanged, such as the first and second layer of superconducting material. Suitable superconducting materials have at a given frequency, such as at a resonance frequency from 100- 1000 GHz, a superconducting gap energy which is at least larger than the photon energy, preferably >101% thereof, such as >110% thereof. The layers may be provided directly on top of one and another, with at least one intermediate layer, and combinations thereof. The SiC layer has a low mechanical stress, especially if the layer is deposited by plasma enhanced chemical vapor deposition (PECVD). The present SiC layer is typically an amorphous layer, as it is deposited, such as by chemical vapor deposition, in particular PECVD. On the contrary, SiCh and SiN_x layers showed relatively high losses being considered too high for the present application, and amorphous silicon are preferably also not been used, as high stresses in the layers were observed. The stress in the present SiC is preferably < 100 MPa, more preferably < 50 MPa, such as < 10 MPa.

In a second aspect the present invention relates to an electronic device comprising an electromagnetic circuit according to the invention, wherein the electronic device is preferably selected from a resonator, a high-frequency coupler, a signal router, a detector, such as an astronomical detector, a quantum computer, a transmission line, an electromagnetic capacitor, an electromagnetic filter, a chip, such as an integrated circuit, an amplifier, and combinations thereof.

In a third aspect the present invention relates to a method of operating an electromagnetic circuit according to the invention or an electronic device according to the invention, comprising providing the resonator or the device, cooling the electromagnetic circuit or the c temperature <200 K, and detecting a signal, such as an astronomical signal.

Advantages of the present description are detailed throughout the description.

DETAILED DESCRIPTION OF THE INVENTION

In an exemplary embodiment of the present electromagnetic circuit the resonance frequency may be from 1 MHz to 1 THz, preferably from 1-800 GHz, preferably from 3-700 GHz, such as 100-600 GHz.

In an exemplary embodiment of the present electromagnetic circuit the second layer of superconducting metal may comprise 1-100 lines, preferably 10-64 lines, such as 24-48 lines, wherein lines may be parallel to one and another or not.

In an exemplary embodiment of the present electromagnetic circuit one or at least two first lines may have an equal first length, and wherein one or at least two second lines have an equal second length, wherein the first length is different from the second length (see e.g. fig. 2j). Therewith two different resonators, with each a resonance frequency, can be provided, such as on one device.

In an exemplary embodiment of the present electromagnetic circuit a length of lines may be equal to a 1/2* a resonance frequency.

In an exemplary embodiment of the present electromagnetic circuit two lines may be connected by a bridge of second layer superconducting material and wherein a length of the two connected lines may be equal to a 1/4 * a resonance frequency.

In an exemplary embodiment of the present electromagnetic circuit two or more resonators may be provided, such as two or more resonators with a different frequency.

In an exemplary embodiment of the present electromagnetic circuit the dielectric layer may be deposited by PECVD.

In an exemplary embodiment of the present electromagnetic circuit the dielectric layer may have a low stress of < 10 MPa.

In an exemplary embodiment of the present electromagnetic circuit the substrate may be selected from a semiconductor material, such as silicon, from dielectric materials, such as sapphire, glass, silicon oxide, and silicon nitride, and may be preferably provided as a wafer.

In an exemplary embodiment of the present electromagnetic circuit it may comprise at least two couplings for connecting to an outside world.

In an exemplary embodiment of the present electromagnetic circuit a thickness of the dielectric layer may be from 1-50000 nm, preferably from 10-5000 nm, more preferably 30-1000 nm, even more preferably 50-350 nm, such as 100-200 nm.

In an exemplary embodiment of the present electromagnetic circuit a thickness of the first layer of superconducting metal may be from 5-1000 nm, preferably 10-500 nm, such as 100-300 nm.

In an exemplary embodiment of the present electromagnetic circuit a thickness of the second layer of superconducting metal may be from 5-1000 nm, preferably 10-5(

100-300 nm.

In an exemplary embodiment of the present electromagnetic circuit a width of the lines each individually may be from 1-10 pm, such as 2-5 pm.

In an exemplary embodiment of the present electromagnetic circuit a length of the lines each individually may be from 0.1-10 mm.

In an exemplary embodiment of the present electromagnetic circuit between at least two lines no solid material is present, i.e. the space in between is left open, or is etched away, or a combination thereof. Depending on further processing a gas, such as air, or virtually no gas, such as vacuum, may be present in between lines.

In an exemplary embodiment of the present electromagnetic circuit a first space in between two adjacent first lines may be 1-100 pm.

In an exemplary embodiment of the present electromagnetic circuit a second space in between two adjacent second lines may be 10-500 pm (see e.g. fig. 2c).

In an exemplary embodiment of the present electromagnetic circuit the lines each individually may be capacitively coupled to a signal line (see e.g. fig. 2b).

In an exemplary embodiment of the present electromagnetic circuit the superconducting material may be selected from NbTiN, NbSnN, Nb, NbN, Ta, Al, and combinations thereof.

In an exemplary embodiment the present electronic device may comprise at least two channels, preferably 3-100000 channels, such as 5-1000 channels, a readout line, and a wave filter.

In an exemplary embodiment of the present method the cooling of the electromagnetic circuit or the device may be to a temperature <10 K, such as < 4 K.

The invention will hereafter be further elucidated through the following examples which are exemplary and explanatory of nature and are not intended to be considered limiting of the invention. To the person skilled in the art it may be clear that many variants, being obvious or not, may be conceivable falling within the scope of protection, defined by the present claims. SUMMARY OF THE FIGURES

Figs la-b, 2a-j and 3 show details of the present invention.

DETAILED DESCRIPTION OF FIGURES The figures are detailed throughout the description, and specifically in the experimental section below.

In the figures:

100 resonator

10 substrate

11 first superconducting layer

12 dielectric layer

13 second superconducting layer 14 parallel resonator lines

Figure la shows a stack of layers suited for the present invention, comprising a substrate 10, a first superconducting layer 11, a dielectric SiC layer 12, and a second superconducting layer 13 comprising parallel lines 14. Fig. lb shows alternative shapes of the second superconducting layer 14, wherein the left most may be considered as a partial coverage of the SiC layer 12

FIG. 2 shows results of prior work of some of the present inventors, published in Applied Physics letters 103, 032601 (2013), doi: 10-1063/1.4813816, which document and its contents are incorporated by reference. In fig. 2a 3 -port network model of a single submillimeter wave filter is shown. kSM and kMW indicate the submillimeter wave and microwave wavelengths, respectively, which are reduced by the dielectric medium and also by the kinetic inductance of the superconductor. Fig. 2b shows a Network model of a single channel, which is a combination of a submillimeter wave filter and a microwave resonator (MKID). The channel is capacitively coupled to the signal line on the filter end and to the readout line on the MKID end. Fig. 2c shows a Micrograph of a small area on the filter bank chip. The image captures the antenna and 5 channels of the filter bank nearest to the antenna. Fig. 2d shows a Double-slot antenna etched into the NbTiN ground plane. The horizontal line is the signal MSL which is connected to the filter bank. Fig. 2e shows a Submillimeter wave MSL filter, shaped like the character U. Figs. 2f-2g show Sections of the MSL-MKID. Figs. 2h-2i show Microwave coupler of the MKID for reading out the response. Fig. 2j shows a Block diagram of the experimental setup.

Fig. 3 shows an example of a resonator.

EXPERIMENTS

The present SiC layer was deposited using SiC PECVD.

With respect to the SiC PECVD deposition the following parameters were used. The stress may be tuned using the gas ratios and LF/HF power ratio:

Substrate temperature: 400 °C;

RF high-frequency (13.56 MHz) power: 450 W;

RF low-frequency (240 kHz) power: 150 W;

S1H4 flow: 25 seem;

CH₄ flow: 411 seem Pressure: 0.27 kPa (2 Torr)

Deposition rate: 10 nm/sec. For 250 nm a time of 26 sec was used.

Claims

1. Electromagnetic circuit comprising a substrate (10), on the substrate a first layer (11) of superconducting material, on the superconducting material a dielectric layer (12), wherein the dielectric layer is a SiC layer, and on the dielectric layer a second layer (13) of superconducting material or part thereof, wherein the second layer of superconducting material preferably comprises at least one line, more preferably two lines (14), preferably 3-100000 lines, and at least one coupling for operating the electromagnetic circuit, wherein the at least one coupling is a capacitive coupling or an inductive coupling.

2. Electromagnetic circuit according to claim 1, wherein the lines form a resonator with a resonance frequency from 1 MHz to 1 THz, preferably from 1-800 GHz, preferably from 3-700 GHz, such as 100-600 GHz.

3. Electromagnetic circuit according to any of claims 1-2, wherein the second layer of superconducting material comprises 5-100 lines, and/or wherein at least two first lines have an equal first length, and wherein at least two second lines have an equal second length, wherein the first length is different from the second length, and/or wherein a length of lines is equal to a 1/2* a resonance frequency, and/or wherein two lines are connected by a bridge of second layer superconducting material and wherein a length of the two connected lines is equal to a 1/4 * a resonance frequency, and/or wherein two or more resonators are provided, such as two or more resonators with a different frequency.

4. Electromagnetic circuit according to any of claims 1-3, wherein the dielectric layer is deposited by PECVD, and/or wherein the dielectric layer has a low stress of < 10 MPa.

5. Electromagnetic circuit according to any of claims 1-4, wherein the substrate is selected from a semiconductor material, such as silicon, from dielectric materials, such as sapphire, glass, silicon oxide, and silicon nitride, and is preferably provided as a wafer.

6. Electromagnetic circuit according to any of claims 1-5, wherein the electromagnetic circuit comprises at least two contacts for connecting to an outside world.

7. Electromagnetic circuit according to any of claims 1-5, wherein a thickness of the dielectric layer is from 10-50000 nm, and/or, wherein a thickness of the first layer of superconducting material is from 5-1000 nm, such as 100-300 nm, and/or wherein a thickness of the second layer of superconducting material is from 5-1000 nm, and/or wherein between at least two lines no solid material is present.

8. Electromagnetic circuit according to any of claims 3-7, wherein a width of the lines each individually is from 1-10 pm, such as 2-5 pm, and/or wherein a length of the lines each individually is from 0.1-10 mm, and/or wherein a first space in between two adjacent first parallel lines is 1-100 pm, and/or wherein a first space in between two adjacent first parallel lines is 1-100 pm, wherein a second space in between two adjacent second parallel lines is 10-500 pm, and/or wherein the lines each individually are capacitively coupled to a signal line.

9. Electromagnetic circuit according to any of claims 1-8, wherein the superconducting material is selected from NbTiN, NbSnN, Nb, NbN, Ta, Al, and combinations thereof.

10. Electronic device comprising an electromagnetic circuit according to any of claims 1-9, wherein the electronic device is preferably selected from a resonator, a high-frequency coupler, a signal router, a detector, such as an astronomical detector, a quantum computer, a transmission line, an electromagnetic capacitor, an electromagnetic filter, a chip, and combinations thereof.

11. Electronic device according to claim 10, comprising at least two channels, such as 3-100000 channels, a readout line, and a wave filter.

12. Method of operating an electromagnetic circuit according to any of claims 1-9 or an electronic device of claims 10 or 11, comprising providing the electromagnetic circuit or the device, cooling the electromagnetic circuit or the device to a temperature <200 K, and detecting a signal, such as an astronomical signal.

13. Method according to claim 12, comprising cooling the electromagnetic circuit or the device to a temperature <10 K, such as < 4 K.