Self-Calibration Quantum Hall Ratio/Resistance Bridge
AccuBridge® Model 6020Q
Since 1994, Measurements International’s (MI) 6010B, and 6010C technology has set the standard for DC Current Comparator (DCC) Resistance Bridge performance in calibration laboratories globally. The time has now come to advance this best-in-class series, taking advantage of twenty-first century AccuBridge® technology.
Measurements International’s major technological advantage in resistance measurements is the development of the first commercially available portable Quantum Hall system, 6800, (Figure 1) which uses AccuBridge® technology as the measurement system operated at ambient temperatures. The current range is from 1 μA to 200 mA for use as a Quantum Hall Bridge and a resistance bridge. The 6020Q features increased ampere-turn (AT) sensitivity with more turns on both the master and slave windings and a new voltage feedback circuit to improve on the linearity error of the nanovolt amplifier.
Measurements International has world-class expertise in both DC Resistance metrology at NMI’s and ISO 17025 accreditation throughout industry. As your accreditation partner and global support partner, MIL offers leading product knowledge and applications expertise through coaching, system design, implementation, calibration services, and ongoing expert support ensuring your competitive advantage.
At MI, it’s not only about the equipment and science, it’s about what you can do and the ease with which you can do it.
The AccuBridge® 6020Q (furthermore 6020Q) room temperature Quantum Hall Resistance Bridge can be used to characterize both GaAs/AlGaAs (Figure 2) or graphene samples by measuring and plotting the field sweep, the contact resistance (Vcr), the longitudinal resistance and dissipation of the I = 2 plateau (Vxx), and transferring the Hall Resistance (Vxy) to a 1 kΩ or 10 kΩ standard resistors.
Enhancements using AccuBridge® technology include a higher ampere-turn sensitivity covering a wider range of resistance ratio, a current and voltage feedback circuit for increased linearity performance and a new calibration technique with increased resolution in obtaining even tighter specifications. In addition to the updated technology, it has the 6010’s dependability, simplified calibration, ease-of-use, automation, the speed of measurement and worldwide support making the 6020Q the best and only resistance bridge that offers uncertainty specifications that rival anything available today.
The 6020Q is a fully automated bridge. Its speed, precision and measurement accuracy accounts for its preferred status as the primary resistance bridge in most NMIs throughout the world. It is designed for flexibility and ease of use and is perfectly suited for stand-alone resistor calibrations.
The 6020Q has two inputs: Rx and Rs. The number of inputs can be expanded to 40 when used in conjunction with the 4200 series Low Thermal Four Terminal Matrix Scanners, see Figure 3. It is recommended that the model 4210A 10-Channel Matrix Scanner be ordered for use in the Quantum Hall System. Measurements can then be performed automatically with software. Delayed or scheduled measurements can be performed at any time. Automatic current reversal ensures that DC offsets and thermals are cancelled out the measurement.
As a stand-alone device, the 6020Q is capable of performing the sweep check, contact resistance, longitudinal potential difference (dissipation) and hall resistance measurements on the Quantum Hall Resistance (QHR) sample. You can select menu driven functions using the front panel display or over IEEE-488. Also, you can use the 6020Q as a high accuracy DC Resistance Ratio Bridge for calibrating resistors using either an 1 Ω or 10 kΩ standard resistor. For laboratories without a QHR system, the 6020Q can be used to build up from the 1 Ω or down from the 10 kΩ.
The 6020Q performs the field sweep check measurement (see figure 4) by feeding a current, into the source and drain of the sample, and then reversing it. This enables measurement of potential differences between various points on the sample. These potential differences can be measured at hall resistances Vxy (1-2) or Vxy (3-4) and the longitudinal resistance Vxx (1-3) and Vxx (2-4) on the sample. Vxy (1-2) and Vxy (3-4) should be in close agreement with each other, as should Vxx (1-3) and Vxx (2-4).
The 6020Q’s microvolt detector makes contact resistance measurements. It is important to measure the contact resistance each time the QHR device is cycled to room temperature and re-cooled as large contact resistances can lead to errors in the QHR measurement. The 6020Q uses a three-probe measurement on each of the contacts in turn to measure the contact resistance. The contact resistance is equal to Vcr/I = resistance of wire + resistance of contact + resistance of 2-DEG.
For an accurate transfer of the QHR value, the longitudinal potential difference must be measured. You can do this by measuring between Vxx (1-3) and Vxx (2-4) using the 6020Q’s Vxx nanovolt mode. Take this measurement to verify that there is no dissipation (see Figure 5) in the 2-DEG. When the 2-DEG is quantized, Vxx should go to 0 and should be < 2 × 10-8 of Vxy.
For traceable measurements, use the keypad on the touch screen to enter the QHR value and related uncertainty in the resistor ID standards file and the 1000 Ω transfer resistor into the measurand (unknown) ID file. Enter standard resistors such as the 1 Ω or 10 kΩ into the standards file after they have been calibrated. Enter resistors to be calibrated into the measurand (Rx) or unknown file. Using the keypad, enter measurement functions such as current through the unknown resistor, settle time, number of measurements, and number of statistics into the Programs file.
Example (for stated specifications)
Maximum Current Reversal Rate = 12 seconds
Maximum Measurement Setting = 50 Measurements
Maximum Statistical Settings = 40 Measurements
The 6020Q is compatible with both the 6800A and 6800B software, as well as both the 4220 and 4210 Matrix scanners.
When performing resistance measurements, the 6020Q’s low-noise, touch screen display is interactive with the measurements. You can display data (several measurements at a time), a combination of data and a graph of the measurements, or just the graph. When a reading is complete, the average value and uncertainty (based on the number for statistics) are displayed. All uncertainty calculations are 2σ level. For resistance measurements, the Summary screen displays measurement data as well as graphical information for current measurements, which can be viewed anytime in ratio or ohms.
Windows® Based Operating Software
Measurements International’s software features an MI report generation, historical analysis and tracks and corrects for resistor drift rates. Combined with a 9400 Standard Resistor Oil Bath or 9300A Air Bath, alpha and beta calculations can be performed automatically on resistors under test. All data can be exported directly to Excel for creating various test patterns or mainframe applications. Resistor baths (oil or air), instrument controllers, printers, system software, IEEE interface, installation, and training are all available from MI.
Either Rs or Rx can be selected as the standard. 6020Q uncertainties
in the bridge and software are specified at the 2σ level (95 %) this includes all secondary specifications such as linearity and noise with a ± 2 °C temperature variance.
|0.1 Ω to 100 kΩ|
|Rx||Ratio & Accuracy (ppm)*|
|0.1 Ω||< 0.02||—||—|
|1 Ω||< 0.015||< 0.015||< 0.015|
|10 Ω||< 0.015||< 0.015||< 0.015|
|100 Ω||< 0.015||< 0.015||< 0.015|
|1 kΩ||< 0.015||< 0.015||< 0.015|
|10 kΩ||< 0.02||< 0.015||—|
|100 kΩ||—||< 0.05||—|
*As a ratio device the accuracy specifications can be improved upon based on your standards and environmental conditions.
|Linearity||< 0.005 ppm of full scale|
|Operating Conditions||10 °C to 35 °C, 10 % to 90 % RH non-condensing|
|Test Current Range||1 μA to 200 mA|
|Test Current Resolution||18-bit|
|Display||Touch Screen Display (no external keyboard), Resolution 0.001 ppm|