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Properties of Unshunted and Resistively Shunted Nb/AlOx-Al/Nb Josephson Junctions With Critical Current Densities From 0.1 to 1 mA/μm2
- Source :
- IEEE Transactions on Applied Superconductivity. 27:1-15
- Publication Year :
- 2017
- Publisher :
- Institute of Electrical and Electronics Engineers (IEEE), 2017.
-
Abstract
- We investigated current–voltage characteristics of unshunted and externally shunted Josephson junctions (JJs) with high critical current densities J c in order to extract their basic parameters and statistical characteristics for JJ modeling in superconducting integrated circuits as well as to assess their potential for future technology nodes. Nb/AlO x -Al/Nb junctions with diameters from 0.5 to 6 μm were fabricated using a fully planarized process with Mo or MoN x thin-film shunt resistors with sheet resistance R sq = 2 Ω/sq and R sq = 6 Ω/sq, respectively. We used our current standard MIT Lincoln Laboratory process node SFQ5ee to fabricate JJs with J c = 0.1 mA/μm2 and our new process node SFQ5hs (where “hs” stands for high speed) to make JJs with J c = 0.2 mA/μm 2 and higher current densities up to about 1 mA/μm2. Using LRC resonance features on the I–V characteristics of shunted JJs, we extract the inductance associated with Mo shunt resistors of 1.4 pH/sq. The main part of this inductance, about 1.1 pH/sq, is the inductance of the 40-nm Mo resistor film, while the geometrical inductance of superconducting Nb wiring contributes the rest. We attribute this large inductance to “kinetic” inductance arising from the complex conductivity of a thin normal-metal film in an electromagnetic field with angular frequency $\boldsymbol{\omega },$ ${{\mathbf \sigma }}(\boldsymbol{\omega }) = {\boldsymbol{\sigma }_0}/({1 + \boldsymbol{i\omega \tau }})$ , where ${{{\mathbf \sigma }}_0}$ is the static conductivity and $\boldsymbol{\tau }$ the electron scattering time. Using a resonance in a large-area unshunted high- J c junction excited by a resistively coupled small-area shunted JJ, we extract the Josephson plasma frequency and specific capacitance of high- J c junctions in 0.1–1 mA/μm2 J c range. We also present data on J c targeting and JJ critical current spreads. We discuss the potential of using 0.2-mA/μm2 JJs in very large scale integration single flux quantum circuits and 0.5-mA/μm2 JJs in high-density integrated circuits without shunt resistors.
- Subjects :
- 010302 applied physics
Physics
Josephson effect
Superconductivity
Condensed matter physics
Resonance
Order (ring theory)
Condensed Matter Physics
01 natural sciences
Electronic, Optical and Magnetic Materials
law.invention
Inductance
law
Magnetic flux quantum
0103 physical sciences
Electrical and Electronic Engineering
Resistor
010306 general physics
Sheet resistance
Subjects
Details
- ISSN :
- 15582515 and 10518223
- Volume :
- 27
- Database :
- OpenAIRE
- Journal :
- IEEE Transactions on Applied Superconductivity
- Accession number :
- edsair.doi...........ea97ea7670904a1cff23956376d516d4