Experimental Study of the Effect of Flux Trapping on the Operation of RSFQ Circuits

Ebert, B.; Ortlepp, T.; Uhlmann, Friedrich

doi:10.1109/tasc.2009.2018738

Cited by 7 publications

(3 citation statements)

References 12 publications

(15 reference statements)

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“…By trapping the magnetic flux quanta in moats that are distant from a critical part of the superconducting circuit, the influence of the trapped magnetic flux can be avoided. So far, the optimum shape and placement of the moats have been experimentally investigated [10], [13], [14], [15], [16], [17], [18], [19]. Material suitable for the superconducting ground plane has been investigated to efficiently trap the flux quantum in the moat [20].…”

Section: Introductionmentioning

confidence: 99%

Influence of Magnetic Flux Trapped in Moats on Superconducting Integrated Circuit Operation

Yamanashi

Imai

Yoshikawa

2018

IEEE Trans. Appl. Supercond.

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The influence of a trapped flux quantum in a superconducting ground plane hole, called a moat, on superconducting circuit operation was analyzed. We devised a calculation model to estimate the magnetic flux threading a signal line of a superconducting integrated circuit by the trapped flux quantum in a moat placed near the signal line by using a conventional inductance extraction tool. Assuming one flux quantum trapped in the moat, the dependence of the magnetic flux threading the signal line on the distance between the moat and the signal line were calculated. We measured the flux linkage by measuring the modulation of the I-V characteristic of a dc-SQUID with a moat near the SQUID implemented by using the 2.5 kA/cm 2 Nb standard process. The measured flux linkage agrees well with the analysis results using the devised calculation model. When the distance between the 1 µm × 10 µm moat and the SQUID, the signal line size of which corresponds to the typical inductance of an adiabatic flux quantum parametron (AQFP), is 1 µm and one flux quantum is trapped in the moat, the measured magnetic flux linkage threads the signal line was approximately 1.2% of the flux quantum. This flux linkage induces approximately 4% deterioration of the device margin of the AQFP. The devised calculation model and experimental results provide useful information for designing highly integrated future superconducting integrated circuits.

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Section: Introductionmentioning

confidence: 99%

Influence of Magnetic Flux Trapped in Moats on Superconducting Integrated Circuit Operation

Yamanashi

Imai

Yoshikawa

2018

IEEE Trans. Appl. Supercond.

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“…In rare cases, however, the detected BER do not fit into one of the operational modes (table 1). We do not analyze those cases in detail, but most probably these cases are malfunctions of some circuit parts due to trapped flux [13].…”

Section: Experimental Test Methodsmentioning

confidence: 99%

Controlled initialization of superconducting π-phaseshifters and possible applications

Mielke¹,

Ortlepp²,

Kunert³

et al. 2010

Supercond. Sci. Technol.

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The rapid single-flux quantum electronics (RSFQ) is a superconducting, naturally digital circuit family which is currently close to being commercially applied. RSFQ is outstanding because of its very low switching energy resulting in very low power consumption. This advantage causes, however, a significant influence of thermal noise. For industrial applications, a certain noise immunity is required which is still a challenge, especially for circuits of higher complexity.Integrating phase-shifting elements is a new concept for further improvements concerning stability against the influence of thermal noise. We have already shown that the implementation of phase-shifting elements significantly reduces the influence of thermal noise on circuit behavior by experimentally analyzing the bit-error rate (Mielke et al 2009 IEEE Trans. Appl. Supercond. 19 621-5). Concepts which are easily implementable in standard niobium technology are especially promising.The π-phaseshifter consists of a superconducting loop which is able to store a single flux quantum. The loop current related to the stored flux creates a well-defined phase shift. To achieve the correct functionality of complex circuits it is essential to store exactly one flux quantum in each π-phaseshifter during the cooling down of the chip. Thus, for studying the feasibility of this new approach, the initialization reliability of the π-phaseshifter needs to be verified.We present an experimental investigation of this reliability to obtain a general assessment for the application of the π-phaseshifter in niobium technology. Furthermore, we compare the configuration shielded by a solid ground plane with a configuration with a ground-plane hole below the π-phaseshifter.Justified by the experimental results we suggest programmable RSFQ circuits based on π-phaseshifters. The characteristics of these devices can be influenced by a controlled initialization of the π-phaseshifter.The fabrication was performed by FLUXONICS Foundry.

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“…Nevertheless, a low T-span defluxing procedure was attempted with the πChip2.25 sample in a measurement setup specialized for experiments with low-T c Nb superconducting circuits and equipped with an automatized defluxing system [46]. A short current pulse through an Au resistor structured on the sample was used to temporarily raise the temperature of the neighbouring RSFQ π-shift circuit structures above the Nb T c , while the measurement system, synchronised with the pulse, was set to automatically measure and record the I C at the output of a DC-SFQ-DC after the temperature dropped to the operating value of 4.2K at the end of each cycle (a few seconds after the end of the current pulse).…”

Section: Measurement Artifactsmentioning

confidence: 99%

Superconducting Circuits with Π-shift Elements

Andreski

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Although the two superconducting phase transitions manifest in the same manner, just one aspect of which is the abrupt disappearance of DC electrical resistance shown in Figure 1.1, scientists speculated they are probably a result of unlike physical processes. This claim is nowadays well accepted in the scientific community, there being much evidence about the different nature of the superconducting phase of high-T c and low-T c materials (even in the absence of an exact microscopic model for the former). Indeed, a few key characteristics differentiate the two groups of superconductors, the most prominent being the already mentioned unconventional order parameter symmetry. It is a feature superficially similar to anisotropy in crystals and results in a number of interesting effects distinctive to high-T c superconductors. The aspects of the unconventional order parameter symmetry relevant to superconducting circuits, which is the main focus of this thesis, are presented in Chapter 2.Chapter 4 describes the improvements to the hybrid YBCO-Nb fabrication process and discusses the results of the implemented changes that, together with the knowledge gained about particular procedures, show a positive trend in process robustness. Also presented are electromagnetic simulation techniques modelling electrical parameters of the superconducting thin films as well as comparison with experimentally obtained values. Subsequently, the same Chapter briefly addresses the experimental difficulties with magnetic shielding, where measurements were 2.2 Network aspects of current flow in superconductors

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Experimental Study of the Effect of Flux Trapping on the Operation of RSFQ Circuits

Cited by 7 publications

References 12 publications

Influence of Magnetic Flux Trapped in Moats on Superconducting Integrated Circuit Operation

Influence of Magnetic Flux Trapped in Moats on Superconducting Integrated Circuit Operation

Controlled initialization of superconducting π-phaseshifters and possible applications

Superconducting Circuits with Π-shift Elements

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