Hidefumi Nishinaka

Automated measurement system for 1-/spl Omega/ standard resistors using a modified Wheatstone bridge

A modified Wheatstone bridge that has four detectors to sense the imbalances in the circuit and a digitally controlled feedback system to balance it automatically with a resolution of a few parts in 10/sup 9/ is described, and its operating principle is briefly explained. The performance of the fully automated measurement system using the bridge is examined. Data were taken with a measuring current of 50 mA through each resistor. The total integration time of 120 s for each feedback cycle corresponds to an effective noise bandwidth of 3.3 mHz, so that the estimated voltage resolution is 35 pV using the experimentally determined noise power spectrum of 0.61 nV/ square root Hz. Combining this with the voltage drop of 50 mV at each resistor, a resolution of 1.43 n Omega is expected for each feedback cycle, and 0.28 n Omega for each relative resistance ratio. The average standard deviation from the linear fits is 0.31 n Omega , which is in good agreement with the estimated value and is only a factor of four larger than the ultimate sensitivity determined by thermal noise of 1- Omega standard resistors. >

A Modified Wheatstone Bridge for High-Precision Automated Resistance Measurement

A modified Wheatstone bridge has been developed which auto-balances using a digitally controlled feedback system. The bridge has four detectors to sense the imbalance in the circuit, and a resolution of better than 0.01 ppm with nearly maintenance-free operation.

Comparison of a Multichip 10-V Programmable Josephson Voltage Standard System With a Superconductor–Insulator–Superconductor-Based Conventional System

We developed a 10-V dc programmable Josephson voltage standard (PJVS) using a multichip technique. The PJVS was based on NbN/TiNx/NbN junctions and operated using a 10-K compact cryocooler. We carried out an indirect comparison with a superconductor-insulator-superconductor-based conventional Josephson voltage standard (JVS) by measuring the voltage of a 10-V zener diode reference standard. The combined standard uncertainty of the comparison was u c = 0.03 muV(k = 1), and the relative combined standard uncertainty was 3 times10-9.

Single-Chip 10-V Programmable Josephson Voltage Standard System Based on a Refrigerator and Its Precision Evaluation

We precisely evaluated a single-chip 10-V programmable Josephson voltage standard (PJVS) system based on a closed-cycle refrigerator by directly comparing it with a conventional Josephson voltage standard system. The PJVS chip fabricated using NbN/TiNx/NbN junction technology was used. The result of the measurement showed a good agreement with a combined standard uncertainty of 3.1 parts in 1010 at 10 V.

A direct comparison of a 10 V Josephson voltage standard between a refrigerator-based multi-chip programmable system and a conventional system

A multi-chip 10 V programmable Josephson voltage standard (PJVS) system was demonstrated using a closed-cycle refrigerator. We precisely measured the PJVS by a direct comparison measurement with a conventional Josephson voltage standard. The result agreed within a combined standard uncertainty of 3.9 × 10−10 at 10 V.

Measurements of the quantized Hall resistance at the ETL

The quantized Hall resistance R/sub H/(4) of Si-MOSFETs has been measured in terms of Omega /sub ETL/ by the use of a recently constructed measurement system at the Electrotechnical Laboratory, Japan. The time variation of the 1- Omega /sub ETL/ resistance standard relative to the QHR is traced. A potentiometric method is used to compare R/sub H/(4) with a reference resistor of nominal value 6453.2- Omega . A cryogenic current comparator system is used to link the 6453.2- Omega resistor to Omega /sub ETL/. The estimated overall uncertainty is 5*10/sup -8/. The experimental equipment and procedure are described in detail. >

Determination of the quantized hall resistance value by using a calculable capacitor at ETL

We report the International System (SI) value of the quantized Hall resistance (R<inf>H</inf>) determined by using a calculable capacitor at the electrotechnical laboratory (ETL). As the result of our measurements at ETL, a most reliable value of h / e² has been estimated as 25 812.8036 Ω<inf>SI</inf> with a systematic uncertainty of 0.25 ppm root sum square (rss) and a random error of 0.20 ppm one standard deviation (1σ).

Study of the Quantized Hall Effect as a Resistance Standard at ETL

Study of the quantized Hall effect as a resistance standard at ETL is in progress. The quantized Hall resistances (QHRs) have been measured using AlGaAs/GaAs modulation doped (MD) structures, that have been made at ETL, and Si-MOSFETs. The measurements were carried out at magnetic fields of 7 T for a GaAs sample (i = 2) and 15 T for a Si sample (i = 4) at a temperature of 1.3 K. The QHR value was 25 812.8025 ¿ETL (± 0.13 ppm), determined using a Si-MOSFET. The QHR value of an AlGaAs/GaAs MD device was 0.06 ppm smaller than that of the Si-MOSFET. The difference in QHR values between Si and GaAs samples was within the total uncertainty of our measurements. An apparent difference in QHR values cannot be found between materials or between Landau numbers within our measurement uncertainty. A new AlGaAs/GaAs SIS structure, in which the density of the two-dimensional electron gas can be changed by variation of gate voltage as in a Si-MOSFET, is introduced as an excellent candidate for a future device that can realize the QHR at much lower magnetic fields.

The effects of the environmental conditions of some Zener voltage references

We measured variations of output voltages of four Zener standards (Fluke732B) with change of environmental conditions such as humidity, temperature and pressure. Four Zener standards have negligibly small humidity characteristics. The characteristic of the temperature was the order of 0.01 ppm/K. The characteristic of the pressure was approximately 0.02 ppm/10 hPa.

SI value of quantized Hall resistance based on ETL's calculable capacitor

The SI value of the quantized Hall resistance based on Electrotechnical Laboratorys (ETL) calculable capacitor is presented. Some improvements for previous measurement systems were made and some of the measurement techniques were changed. Based on measurements of ETL, the value of h/e/sup 2/ is estimated to be 25,812.8064 Omega /sub SI/ with a systematic uncertainty of 0.24-p.p.m. root-sum-square (r.s.s.) and a random error of 0.11-p.p.m. at one standard deviation (1 sigma ). >