The two-channel Model 2182A Nanovoltmeter is optimized for making stable, low noise voltage measurements and for characterizing low resistance materials and devices reliably and repeatably. It provides higher measurement speed and significantly better noise performance than alternative low voltage measurement solutions.
The Model 2182A represents the next step forward in Keithley nanovoltmeter technology, replacing the original Model 2182 and offering enhanced capabilities including pulse capability, lower measurement noise, faster current reversals, and a simplified delta mode for making resistance measurements in combination with a reversing current source, such as the Model 6220 or 6221.
Flexible, Effective Speed/Noise Trade-offs
The Model 2182A makes it easy to choose the best speed/filter combination for a particular application’s response time and noise level requirements. The ability to select from a wide range of response times allows optimizing speed/noise trade-offs. Low noise levels are assured over a wide range of useful response times, e.g., 15nV p-p noise at 1s and 40-50nV p-p noise at 60ms are typical. Figure 1 illustrates the Model 2182A’s noise performance.
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Figure 1. Compare the Model 2182A’s DC noise performance with a nanovolt/micro-ohm-meter’s. All the data shown was taken at 10 readings per second with a low thermal short applied to the input.
Reliable Results
Power line noise can compromise measurement accuracy significantly at the nanovolt level. The Model 2182A reduces this interference by synchronizing its measurement cycle to line, which minimizes variations due to readings that begin at different phases of the line cycle. The result is exceptionally high immunity to line interference with little or no shielding and filtering required.
Optimized for Use with Model 6220/6221 Current Sources
Device test and characterization for today’s very small and power-efficient electronics requires sourcing low current levels, which demands the use of a precision, low current source. Lower stimulus currents produce lower—and harder to measure—voltages across the devices. Linking the Model 2182A Nanovoltmeter with a Model 6220 or 6221 Current Source makes it possible to address both of these challenges in one easy-to-use configuration.
When connected, the Model 2182A and Model 6220 or 6221 can be operated like a single instrument. Their simple connections eliminate the isolation and noise current problems that plague other solutions. The Model 2182A/622X combination allows making delta mode and differential conductance measurements faster and with less noise than the original Model 2182 design allowed. The Model 2182A will also work together with the Model 6221 to make pulse-mode measurements.
The 2182A/622X combination is ideal for a variety of applications, including resistance measurements, pulsed I-V measurements, and differential conductance measurements, providing significant advantages over earlier solutions like lock-in amplifiers or AC resistance bridges. The 2182A/622X combination is also well suited for many nanotechnology applications because it can measure resistance without dissipating much power into the device under test (DUT), which would otherwise invalidate results or even destroy the DUT.
An Easy-to-Use Delta Mode
Keithley originally created the delta mode method for measuring voltage and resistance for the Model 2182 and a triggerable external current source, such as the Model 2400 SourceMeter instrument. Basically, the delta mode automatically triggers the current source to alternate the signal polarity, and then triggers a nanovoltmeter reading at each polarity. This current reversal technique cancels out
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Figure 2. Results from a Model 2182A/6220 using the delta mode to measure a 10mΩ resistor with a 20µA test current. The free Model 6220/6221 instrument control example start-up software used here can be downloaded from www.keithley.com.
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Figure 3. It’s simple to connect the Model 2182A to the Model 6220 or 6221 to make a variety of measurements. The instrument control example start-up software available for the Model 622X current sources includes a step-by-step guide to setting up the instrumentation and making proper connections.
any constant thermoelectric offsets, so the results reflect the true value of the voltage being measured. The improved delta mode for the Model 2182A and the Model 622X current sources uses the same basic technique, but the way in which it’s implemented has been simplified dramatically. The new technique can cancel thermoelectric offsets that drift over time (not just static offsets), produces results in half the time of the original technique, and allows the current source to control and configure the Model 2182A. Two key presses are all that’s required to set up the measurement. The improved cancellation and higher reading rates reduce measurement noise to as little as 1nV.
Differential Conductance Measurements
Characterizing non-linear tunneling devices and low temperature devices often requires measuring differential conductance (the derivative of a device’s I-V curve). When used with a Model 622X current source, the Model 2182A is the industry’s fastest, most complete solution for differential conductance measurements, providing 10X the speed and significantly lower noise than other instrumentation options. There’s no need to average the results of multiple sweeps, because data can be obtained in a single measurement pass, reducing test time and minimizing the potential for measurement error.
Pulsed Testing with the Model 6221
When measuring small devices, introducing even tiny amounts of heat to the DUT can raise its temperature, skewing test results or even destroying the device. When used with the Model 2182A, the Model 6221’s pulse capability minimizes the amount of power dissipated into a DUT. The Model 2182A/6221 combination synchronizes the pulse and measurement. A measurement can begin as soon as 16µs after the Model 6221 applies the pulse. The entire pulse, including a complete nanovolt measurement, can be as short as 50µs.
In the delta, differential conductance, and pulse modes, The Model 2182A produces virtually no transient currents, so it’s ideal for characterizing devices that can be easily disrupted by current spikes (see Figure 4).
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Figure 4. The Model 2182A produces the lowest transient currents of any nanovoltmeter available.
Metrology Applications
The Model 2182A combines the accuracy of a digital multimeter with low noise at high speeds for high-precision metrology applications. Its low noise, high signal observation time, fast measurement rates, and 2ppm accuracy provide the most cost-effective meter available today for applications such as intercomparison of voltage standards and direct measurements of resistance standards.
Nanotechnology Applications
The Model 2182A combined with the Model 622X current source or Series 2400 SourceMeter ® instrument is a highly accurate and repeatable solution for measuring resistances on carbon nanotube based materials and silicon nanowires.
Research Applications
The Model 2182A’s 1nV sensitivity, thermoelectric EMF cancellation, direct display of “true” voltage, ability to perform calculations, and high measurement speed makes it ideal for determining the characteristics of materials such as metals, low resistance filled plastics, and high and low temperature superconductors.
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Figure 5. The Model 2182A’s delta mode provides extremely stable results, even in the presence of large ambient temperature changes. In this challenging example, the 200nV signal results from a 20µA current sourced by a Model 6221 through a 10mΩ test resistor.
Optional Accessory: Model 2187-4 Low Thermal Test Lead Kit
The standard cabling provided with the Model 2182A Nano volt meter and Model 622X Current Sources provides everything normally needed to connect the instruments to each other and to the DUT. The Model 2187-4 Low Thermal Test Lead Kit is required when the cabling provided may not be sufficient for specific applications, such as when the DUT has special connection requirements. The kit includes an input cable with banana terminations, banana extensions, sprung-hook clips, alligator clips, needle probes, and spade lugs to accommodate virtually any DUT. The Model 2187-4 is also helpful when the DUT has roughly 1GΩ impedance or higher. In this case, measuring with the Model 2182A directly across the DUT will lead to loading errors. The Model 2187-4 Low Thermal Test Lead Kit provides a banana cable and banana jack extender to allow the Model 2182A to connect easily to the Model 622X’s low impedance guard output, so the Model 2182A can measure the DUT voltage indirectly. This same configuration also removes the Model 2182A’s input capacitance from the DUT, so it improves device response time, which may be critical for pulsed measurements.
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Figure 6. Model 2187-4 Test Lead Kit
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Figure 7. Model 2182A rear panel
Applications:
- Research
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- Determining the transition temperature of superconductive materials
- I-V characterization of a material at a specific temperature
- Calorimetry
- Differential thermometry
- Superconductivity
- Nanomaterials
- Metrology
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- Intercomparisons of standard cells
- Null meter for resistance bridge measurements