Heat transfer analysis of a programmable Josephson voltage standard chip operated with a mechanical cooler

IEICE Electron. Express

Amagai

et al. 2019

Self Cite

Reliable and easy fabricated packaging for a Josephson voltage standard circuit was proposed and the thermal stress and temperature distribution in the chip were numerically analyzed. The chip for programmable Josephson voltage standard circuits was bonded with InSn solder to a copper plate to achieve good thermal contact. Although this packaging allowed very good thermal contact, the chip sometimes broke due to thermal stress caused by a difference in the expansion coefficient between silicon and copper. Slits were thus added to the copper plate to reduce the thermal stress. The numerical analysis suggested that the slits reduce the thermal stress in the voltage standard chip, and thus reduce the risk of the chip cracking when it is cooled. The numerical analysis also suggested that the temperature increase in the chip was about 1 mK which caused a negligible reduction in the operating margin of the PJVS operation.

Section: Methodsmentioning

confidence: 51%

“…The size of the silicon chip is 15 mm Â 15 mm Â 0:6 mm. The thickness of the InSn was measured by cutting the chip and substrate [26]. Although there were variation of the thickness, typical value of 0.01 mm was used for the calculation.…”

Section: Numerical Simulation Of Thermal Stressmentioning

confidence: 99%

Reliable packaging of Josephson voltage standard circuit for cryocooler operation

IEICE Electron. Express

Amagai

et al. 2019

Self Cite

“…The bias operating points in our PJVS system may be affected by the self-heating effect of the chip with a large number of junctions. Therefore, we conducted a heat transfer analysis of the proposed chip module and obtained the optimized operating conditions [26]. Figure 1 depicts the typical measurement result of a quantized voltage step with dither currents simultaneously applied for all junctions used for generating an AC waveform.…”

Section: Ac-programmable Josephson Voltage Standardmentioning

confidence: 99%

Extending voltage range to 10 V rms in AC–DC difference measurements with AC programmable Josephson voltage standard

Amagai

et al. 2020

Meas. Sci. Technol.

Self Cite

The larger-scale programmable Josephson voltage standard (PJVS) chip composed of 524 288 niobium nitride-based overdamped Josephson junctions enables us to generate stepwise-approximated AC waveforms with a root-mean-square (rms) amplitude of up to 10 V. In this study, we have extended the voltage range of the differential sampling system based on the AC-PJVS to an rms value of 10 V with the larger-scale PJVS chip. The sampling digital voltmeter (DVM) that is employed to measure differential voltages is modified to use a 10 MHz reference clock instead of an internal clock. This modification substantially improves the uncertainty of AC-DC difference measurements at low frequencies, which is caused by the internal clock error of the sampling DVM, by preventing the incoherent sampling of the differential voltages. The expanded uncertainties (k = 2) of the AC-DC difference measurements are reduced from 7.0 µV/V to 1.8 µV/V for a frequency of 62.5 Hz and from 8.0 µV/V to 4.4 µV/V for a frequency of 1 Hz. The improvements in the uncertainty are more significant compared with a conventional method at low frequencies, where the accuracy of a thermal voltage converter is reduced.

“…The temperature increase on the chip surface is estimated to be approximately 0.1 K on the basis of the estimated bias shift (0.15 mA) and the temperature dependence of the center values of the Shapiro steps (−1.7 mA/K) in our chip. To clarify the mechanism of these phenomena, we are now conducting a heat conduction analysis, which we will report elsewhere [17].…”

Section: Heating Effect In the Pjvs Chipmentioning

confidence: 99%

Calibration System for Zener Voltage Standards Using a 10 V Programmable Josephson Voltage Standard at NMIJ

Iwasa

IEEE Trans. Instrum. Meas.

et al. 2015

Self Cite

We have developed a calibration system for the Zener voltage standards using a programmable Josephson voltage standard (PJVS) for liquid-helium consumption reduction and improvement in the calibration performance. The PJVS array is composed of 524 288 niobium nitride (NbN)-based overdamped Josephson junctions and is cooled by a 10-K compact cooler. To verify the validity of the system, indirect and direct comparisons of the PJVS system and our conventional Josephson voltage standard system have been carried out. As a result, an agreement within a relative expanded uncertainty of 8.4 × 10 −10 was obtained for a nominal voltage of 10 V. We also discuss the uncertainty sources in the calibration of the Zener voltage standards using our PJVS system.Index Terms-Calibration, dc voltage, Josephson junction array, liquid helium, mechanical cooler, programmable Josephson voltage standard (PJVS), Zener voltage standard.