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Keithley 6517A Electrometer

The Keithley 6517A is a precision electrometer and high-resistance meter designed for ultra-low-current, high-impedance, charge, resistivity, and insulation measurements. It combines a sensitive electrometer input with a programmable high-voltage source, guarded triaxial connections, automated test sequences, environmental monitoring, and computer interfaces. Its principal strength is not general semiconductor curve tracing, but accurate measurement of extremely small leakage currents and very high resistances.

Key Features and Capabilities

Ultra-Low-Current Measurement:
Provides ten current ranges from 20 pA to 20 mA. The 20 pA range has 100 aA resolution, while specified input-bias current is below 3 fA at calibration temperature. This makes the instrument suitable for leakage-current and high-impedance measurements that are beyond ordinary digital multimeters.

Precision Voltage Measurement:
Includes 2 V, 20 V, and 200 V ranges, with greater than 200 TΩ input impedance in parallel with 20 pF. Guarding reduces effective input capacitance to less than 2 pF, helping minimize loading of high-impedance sources.

High-Resistance Measurement:
Specified automatic resistance ranges extend from 2 MΩ to 200 TΩ. Manual voltage-source operation can display calculated values up to 10¹⁸ Ω, with accuracy determined from the selected current range and voltage-source accuracy.

Surface and Volume Resistivity:
Directly supports resistivity measurements using appropriate electrode fixtures. An alternating-polarity method can compensate for background and offset currents in insulating materials and test fixtures.

Charge Measurement:
Provides four charge ranges from 2 nC to 2 µC, with resolution as fine as 10 fC. An automatic-discharge function can reset the charge integrator at a selected level for repeated or continuous measurements.

Integrated High-Voltage Source:
The programmable bipolar source has 100 V and 1000 V ranges, with output capabilities of up to ±10 mA and ±1 mA, respectively. It can bias devices and insulating samples while the electrometer measures the resulting leakage current.

Guarded Triaxial Input:
A rear-panel three-lug triaxial input, switchable guard, shielding provisions, and low-leakage measurement techniques help suppress cable leakage, capacitive loading, electrostatic interference, and environmental noise.

Built-In Test Sequences:
Includes automated routines for diode leakage, capacitor leakage, cable insulation, resistor characterization, surface and volume resistivity, surface-insulation resistance, and square-wave or staircase voltage sweeps. Results are stored in the reading buffer.

Environmental Measurements:
Can include readings from a Type-K thermocouple and compatible relative-humidity probe. This is particularly valuable because humidity and temperature can strongly affect insulation resistance and material resistivity.

Filtering, Triggering, and Data Storage:
Supports selectable integration from 0.01 to 10 power-line cycles, median and averaging filters, external triggering, analog outputs, and storage of up to 15,706 readings in SCPI mode.

Programmability and Automation:
Provides IEEE-488/GPIB and RS-232 interfaces. SCPI is supported on both interfaces; the older DDC command language is available through IEEE-488.

Scientific and Engineering Applications

Leakage-Current Characterization:
Measurement of reverse-biased diodes, capacitors, cables, connectors, dielectric layers, PCB surfaces, and other devices with picoampere- or femtoampere-level leakage.

Insulation Resistance Testing:
Evaluation of cable insulation, polymers, ceramics, coatings, circuit-board materials, and electrical insulating structures.

Surface and Volume Resistivity:
Measurement of insulating sheets, films, polymers, ESD materials, and dielectric samples using suitable electrode fixtures.

Dielectric and Materials Research:
Investigation of polarization, charge accumulation, conduction, absorption, and time-dependent leakage in high-resistance materials.

Charge and Piezoelectric Measurements:
Measurement of small accumulated charges from capacitive, electrostatic, triboelectric, or piezoelectric sources.

Environmental and Aging Studies:
Long-duration recording of leakage or resistance together with temperature and humidity, allowing environmental dependence and material degradation to be studied.

The Keithley 6517A is often paired with instruments such as the Agilent/Keysight 4156C Semiconductor Parameter Analyzer or Keithley SourceMeter systems. While a parameter analyzer excels at sourcing voltage/current and performing comprehensive device I–V characterization, the 6517A specializes in the extreme low end of electrical measurement, offering significantly better sensitivity for femtoamp currents, teraohm-to-petaohm resistance measurements, and charge measurements that are beyond the practical range of most semiconductor parameter analyzers.

The most important distinction from the Agilent 4156C is that the 6517A is primarily a single-channel extreme-low-current and high-resistance instrument with a high-voltage bias source. The 4156C is a multi-channel semiconductor parameter analyzer optimized for coordinated I–V sweeps of multi-terminal devices.

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