This paper describes a suitable method to obtain and compare the loading effects of thermal transfer standards to obtain optimal values of input impedance and the AC-DC difference loading errors. The loading effects are evaluated with different values of source series-connected resistance and a bypass capacitance at desired frequencies and applied voltages. The results indicate that the AC-DC difference loading errors are minimized with a nominal source series-connected resistance value of 50 Omega, and a bypass capacitance value in the range of 33 pF to 68 pF.

Multijunction thermal converters are routinely used at many primary standards laboratories for ac voltage measurements and calibrations. After nearly two decades of inactivity, the Primary Standards Laboratory at Sandia National Laboratories has reestablished the process of fabricating silicon based multijunction thermal converters. Initial results indicate the devices perform similarly to devices fabricated circa 2001 with ac-dc differences of less than 2 μV/V over the frequency range of 20 Hz to 20 kHz. From 20 kHz to 1 MHz, the ac-dc difference was higher, but remained below 200 μV/V. In addition to presenting these results, new design considerations, such as high-resistivity substrates for high-frequency applications, are discussed.

We have developed a new measurement module that can be installed in existing National Institute of Standards and Technology (NIST) Programmable Josephson Voltage Standard (PJVS) systems to provide automated leakage-current measurement capability. The system utilizes several relays to switch between normal PJVS operating modes and leakage-current measurement modes without any manual operator actions. The simplicity and convenience of this automated method enables the verification of system leakage current characteristics on a frequent schedule. Full automation of these tasks provides significant advantages over traditional measurement methods performed by an operator, including reduced noise and drift, and reduced sensitivity to other activities in the nearby environment.

This paper describes the effects on device performance caused by modifications to thermocouple design and fabrication. Such modifications are intended to lower the output resistance of multijunction thermal converters (MJTCs) fabricated on fused silica substrates. Device component metals were deposited by physical vapor deposition and fabricated into device features by either wet chemical etching or metal lift-off. The low-temperature-coefficient-of-resistance Ni 75 Cr 20 Al 2.5 Cu 2.5 alloy heater is thermally isolated from the rest of the chip by a 25 μm fused silica membrane produced by bead blasting the back side of the substrate. Thermocouples were shorted along 50% and 25% of their length for a set of test devices; control devices were left unmodified. MJTC output resistances were decreased from about 13.2 kΩ for the non-shorted thermocouples to about 10.5 kΩ for the 50% shorted thermocouples. At 3 V input voltage, measured ac-dc differences of the devices for frequencies between 10 Hz and 1 MHz showed no significant impact on ac-dc difference due to thermocouple shorting. However, we observed indications that shorting the thermocouples results in a reduction in the signal-to-noise ratio of the measurement of the output voltage.

The cryocooled 10 V Programmable Josephson Voltage Standard (PJVS) system was successfully set up at Center for Measurement Standards (CMS) in Taiwan. In order to more precisely evaluate the performance of this system, we directly compared the cryocooler PJVS system and NIST's portable PJVS system. The comparison result shows excellent agreement between these two systems. The agreement between these two systems at 1.018 V was -0.10 nV with a combined standard uncertainty of 1.04 nV, and -0.07 nV at 10 V with a combined standard uncertainty of 1.22 nV or a relative standard uncertainty of 1.22×10 -10 at the 95 % level of confidence.

This paper describes the design and testing of a hybrid buffer amplifier (HBA) with a theoretical gain error of less than 1 μV/V gain error and 60 μdeg phase error up to 20 kHz. The application of this amplifier is for use in ac-dc difference measurements such as unloading low amperage ac-dc current shunts and Josephson Arbitrary Waveform Synthesizers. Preliminary experimental results show the ac-dc difference errors less than (3±2) μV/V (k=2) for 200 Ω and 400 Ω impedances at a rms amplitude of 1 V, and less than (4±2) μV/V (k=2) for 50 Ω impedance at a rms amplitude of 2 V.

Standards and Calibration Laboratory (SCL) setup in 2018 a liquid helium based programmable Josephson voltage standard (PJVS) developed by the National Institute of Standards and Technology (NIST). The system was validated by direct comparison with a NIST transportable PJVS system at 1.018 V, 4 V, 6 V, 8 V and 10 V. The difference between the systems was within 0.5 nV, with an expanded uncertainty of less than 2.2 nV ($k=2$). In this paper, the setup and the results of the direct comparison method are presented.

This paper presents precision measurements with a prototype cryogen-liquid-free DC Josephson voltage standard that produces a 1 V maximum output. Its cryostat is sufficiently compact that it can be operated on a bench close to devices under test. Compared to the National Institute of Standards and Technology (NIST) programmable Josephson voltage standard (PJVS), this bench-top Josephson voltage standard (BJVS) has a smaller cryostat (only 25 % of the volume), the Josephson junction array circuit is less complex and has only 10 % as many junctions, simpler bias electronics, and reduced mechanical cooling requirements. Direct voltage comparison between the BJVS and the PJVS achieved a relative agreement of 5×10 -10 at 1 V. With the recent redefinition of the International System of Units (SI), the BJVS becomes a primary realization the unit volt, requiring only access to a standard single-phase power outlet and a GPS signal (SI second).

This paper describes the design and fabrication of high-current multijunction thermal converters (HC-MJTCs) on Si substrates using wet chemical etching. The fabricated devices consist of a Si heat-reservoir under a heater. The low-resistive Cu 80 Au 20 alloy heater is thermally isolated from the rest of the chip by a nitride-oxide membrane, which is produced by utilizing a simple potassium hydroxide (KOH) wet chemical etching. Measurements show that the devices exceed their rated current level up to 2 A without failure. Furthermore, the ac-dc differences of the devices were below 13 μA/A over the input current levels at frequencies above 400 Hz, though large negative ac-dc differences were present below 100 Hz.

The unique properties of the quantum Hall effect allow one to revisit traditional measurement circuits with a new flavour. In this paper we present the first realization of a quantum Hall Kelvin bridge for the calibration of standard resistors directly against the quantum Hall resistance. The bridge design is particularly simple and requires a minimal number of instruments. The implementation here proposed is based on the bridge-on-a-chip, an integrated circuit composed of three graphene quantum Hall elements and superconducting wiring. The accuracy achieved in the calibration of a 12 906Ω standard resistor is of a few parts in 108, at present mainly limited by the prototype device and the interferences in the current implementation, with the potential to achieve few parts in 109, which is the level of the systematic uncertainty of the quantum Hall Kelvin bridge itself.

A single-unit thermal converter for precision ac current measurement is desirable because of its relatively small package and low power dissipation. In this article, high-current multijunction thermal converters (HC-MJTCs) on silicon (Si) substrates fabricated by wet chemical etching have been investigated at input rms currents of up to 2 A. The use of wet chemical etching aids the fabrication of a freestanding nitride- oxide membrane, maintaining the Si heat reservoir under the heater of the HC-MJTC intact. Below 10 mPa, the output voltage from the HC-MJTC and the thermal time-constant increase by approximately six times, implying improved efficiency of the thermal current converter. The absolute value of the ac-dc differences of the device was less than 17 μA/A over input current levels of up to 2 A at frequencies above 100 Hz. However, input current level-dependent ac-dc differences were observed at frequencies below 400 Hz even under vacuum. This behavior originated primarily from a change in the electrical resistance of the heater in this Si-based device. Therefore, these low-frequency ac-dc differences can be substantially compensated using the measured ac and dc electrical resistances of the heater.

This paper describes a simple model for planar multi-junction thermal converters based on physical dimensions and properties of the converter chip and all wire bonds. The model was used to explain extremely low (<; 700 μV/V) AC-DC differences at 100 MHz. Two designs of multi-junction thermal converters (MJTC) were tested against the model and the results are presented.

A comparison study between Y + 36° and 0° X-cut lithium niobate (LiNbO3) was performed to evaluate the influence of crystal cut on the acoustic propagation to realize a piezoelectric high-voltage sensor. The acoustic time-of-flight for each crystal cut was measured when applying direct current (DC), alternating current (AC), and pulsed voltages. Results show that the voltage-induced shift in the acoustic wave propagation time scaled quadratically with voltage for DC and AC voltages applied to X-cut crystals. For the Y + 36° crystal, the voltage-induced shift scales linearly with DC voltages and quadratically with AC voltages. When applying 5 μs voltage pulses to both crystals, the voltage-induced shift scaled linearly with voltage. For the Y + 36° cut, the voltage-induced shift from applying DC voltages ranged from 10 to 54 ps and 35 to 778 ps for AC voltages at 640 V over the frequency range of 100 Hz-100 kHz. Using the same conditions as the Y + 36° cut, the 0° X-cut crystal sensed a shift of 10-273 ps for DC voltages and 189-813 ps for AC voltage application. For 5 μs voltage pulses, the 0° X-cut crystal sensed a voltage induced shift of 0.250-2 ns and the Y + 36°-cut crystal sensed a time shift of 0.115-1.6 ns. This suggests a frequency sensitive response to voltage where the influence of the crystal cut was not a significant contributor under DC, AC, or pulsed voltage conditions. The measured DC data were compared to a 1-D impedance matrix model where the predicted incremental length changed as a function of voltage. When the voltage source error was eliminated through physical modeling from the uncertainty budget, the combined uncertainty of the sensor (within a 95% confidence interval) decreased to 0.0033% using a Y + 36°-cut crystal and 0.0032% using an X-cut crystal for all the voltage conditions used in this experiment.

A comparison study between Y+36° lithium niobate (LiNbO3) and 0° X-cut LiNbO3 was performed to evaluate the influence of crystal cut on the performance of a piezoelectric high-voltage (HV) sensor. The acoustic wave propagation time was monitored prior to, during, and after applying three different HV source types to the crystal. Direct current (DC), alternating current (AC), and pulsed voltages were used. Data show that the voltage-induced shift in the acoustic wave propagation time scales quadratically for DC and AC voltage for the X-cut crystal. For the Y+36° LiNbO3 crystal, the acoustic wave arrival time scales linearly with DC voltage and quadratically with AC voltage. When applying 5 μs voltage pulses to the crystal, the voltage-induced shift scales linearly with voltage for both crystal cuts. Data suggest LiNbO3 has a frequency sensitive response to voltage and the influence from the crystal cut is significant when applying AC and pulsed voltage to the crystal.

We present a method to measure high voltages using the piezoelectric crystal lithium niobate without using voltage dividers. A 36° Y-X cut lithium niobate crystal was coupled to two acoustic transducers, where direct current voltages were applied from 128–1100 V. The time-of-flight through the crystal was determined to be linearly dependent on the applied voltage. A model was developed to predict the time-delay in response to the applied voltage. The results show a sensitivity of 17 fs/V with a measurement error of 1 fs/V was achievable using this method. The sensitivity of this method can be increased by measuring the acoustic wave after multiple passes through the crystal. This method has many advantages over traditional techniques such as: favorable scalability for larger voltages, ease of use, cost effectiveness, and compactness.