Fabrication of Nb/Al-Al/sub 2/O/sub 3//Nb junctions with extremely low leakage currents

Lichtenberger, Arthur W.; McClay, C.P.; Mattauch, R.J.; Feldman, M.J.; Pan, S. K.; Kerr, A. R.

doi:10.1109/20.92842

Cited by 59 publications

(15 citation statements)

References 15 publications

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“…The junction capacitance is determined from the junction size obtained by SEM-observation of the test junctions. We use a capacitance to surface ratio of 48 fF/µm 223, 24 . …”

Section: Experiments a Samplementioning

confidence: 99%

Kerr coefficients of plasma resonances in Josephson junction chains

et al. 2015

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We present an experimental and theoretical analysis of the self-and cross-Kerr effect of extended plasma resonances in Josephson junction chains. We calculate the Kerr coefficients by deriving and diagonalizing the Hamiltonian of a linear circuit model for the chain and then adding the Josephson non-linearity as a perturbation. The calculated Kerr-coefficients are compared with the measurement data of a chain of 200 junctions. The Kerr effect manifests itself as a frequency shift that depends linearly on the number of photons in a resonant mode. By changing the input power on a low signal level, we are able to measure this shift. The photon number is calibrated using the self-Kerr shift calculated from the sample parameters. We then compare the measured cross-Kerr shift with the theoretical prediction, using the calibrated photon number.

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“…The junction capacitance is determined from the junction size obtained by SEM-observation of the test junctions. We use a capacitance to surface ratio of 48 fF/µm 223, 24 . …”

Section: Experiments a Samplementioning

confidence: 99%

Kerr coefficients of plasma resonances in Josephson junction chains

et al. 2015

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“…It may be expected, that SNEP (Selective Niobium Etching Process) affects the sub-gap current to a lesser extent, which would explain the high value of V, in ref. 1.…”

Section: Discussionmentioning

confidence: 99%

Characterization of different types of Nb-AlO/sub x/ based Josephson tunnel junctions

et al. 1991

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I Junction fabricationThe Nb/Al,AlO,(/Al)/Nb trilayer is deposited in a turbo pumped vacuum system. Nb and A1 films were deposited by two DC magnetron sputter guns at a rate of 200 nm/min and 22 nm/min, respectively. During sputtering the oxygen pressure was in the low lo-' mbar range. The water pressure was 10-7-10-8 mbar. The T, of the Nb films is 9.2 K. The trilayer configuration of the junctions is listed in table 1. The thickness of the Nb base electrodes is 300 nm. The A1 overlayers were thermally oxidized in pure 0, at 10 'C, during 1 hour. The double oxide layer of the SNIIS type junction has been formed in two steps. The A1 layer was oxidized in 0.04 mbar 0, for 15 minutes. Then a second Al layer of 10 A was deposited and completely oxidized in 27 mbar 02.The junction areas (20x20, 10x10, and 5x5 pm2 on one thermally oxidized Si wafer) were defined by SNAP (Selective Niobium Anodization Process) [5]. To complete the junctions 300 nm Nb was deposited and structured by lift-off, to form contacts with the counter electrodes. Results on SNIS and SNINS iunctions I-V measurementsThe I-V characteristics of the junctions have been obtained with help of a low noise, battery powered current source. A battery powered amplifier with an input noise of 5 nV/\/Hz and a bandwidth of 80 kHz was used to amplify the voltage across the junction. The characteristic gap and sub-gap parameters of the Josephson tunnel junctions are listed in table 2. The sum-gap voltage Vg (= 2 4 e , where A is the superconducting gap of the electrodes at 4.2 K) is an average value of 10 junctions with a standard deviation of 0.01 mV. The theoretical maximum critical current density J,, is obtained from J,, = I ,,/A = n V /(4.RN.A), where A is the area of the junction, RN =' 4 mV/I(t mV), and I,, is the critical current. The sub-gap parameters are obtained by suppressing the zero voltage current by a magnetic field. This enabl&d an accurate measurement of the sub-gap current in 5x5 pm junctions. In larger junctions the magnetic field induced resonant modes causing extra currents at finite voltages below V,. This made it very difficult to measure the sub-gap current accurately With our sample holder we could measure four 5x5 pm2 junctions 0018-9464/91/0300-3153$01.00 0 1991 IEEE

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“…Our best explanation for why single resist processing worked now after being abandoned for a multi-layer resist process before can be attributed to the photoresists used in processing. The current process succeeds using a negative resist, optimized for high temperature use and liftoff, whereas the single resist used in the past was a resist modified with a chlorobenzene dip to create an overhang preferable for liftoff [7]. The question of why elements smaller than ~1.5µm have resistive or point contact electrical characteristics remains unsolved at this time.…”

Section: Chapter Two: Single Resist Processingmentioning

confidence: 99%

“…This is the most critical processing step for creating SIS devices, requiring precise definition of the junction area, but it is also demanding of the SiO2 layer. The concept of using a multi-layer resist for creating junctions started for this group with the fabrication of micron sized Nb/Al-Al2O3/Nb Junctions with a trilevel resist liftoff process [7,8]. This process replaced the previously used single resist approach that utilized a combination of anodized Nb2O5, formed from the exposed niobium, along with evaporated SiOx for the insulation layer encircling the device junctions and between the M1 base electrode and M3 wiring layers.…”

Section: Chapter One: Sis Insulation Applicationsmentioning

confidence: 99%

“…However for specific prototyping purposes, a single resist process would be a major benefit. A single resist process was previously developed before at UVA [7], but was for junctions larger than 3µm in size and used evaporated SiOx. As a testing method, and not as a means of producing SIS devices for real applications, the yield and device area are less critical so long as working junctions are created with a known diameter.…”

Section: Chapter Two: Single Resist Processingmentioning

confidence: 99%

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Improving Insulation Methods in New and Existing Fabrication Processes

Matthews

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Fabrication of Nb/Al-Al/sub 2/O/sub 3//Nb junctions with extremely low leakage currents

Cited by 59 publications

References 15 publications

Kerr coefficients of plasma resonances in Josephson junction chains

Kerr coefficients of plasma resonances in Josephson junction chains

Characterization of different types of Nb-AlO/sub x/ based Josephson tunnel junctions

Improving Insulation Methods in New and Existing Fabrication Processes

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