Keithley 6517B Electrometer/High Resistance Meter
2025-09-04
In cutting-edge fields such as bulk resistivity measurement of semiconductor materials, characterization of insulating materials, weak photocurrent detection, and electrostatic discharge research, the challenges researchers face have already exceeded the limits of conventional instruments:How to stably measure faint current at the 10^-17 A level? How to accurately quantify ultra-high resistance above 10^15 Ω? Traditional picoammeters and multimeters are completely ineffective in this field. Keithley 6517B offers 0.1 fA (10^-16 A) current resolution, 10 PΩ (10^16 Ω) resistance measurement capability, and < 3.5 fA offset current with industry-leading performance, combined with Built-in voltage source and charge measurement function, it has become the undisputed industry standard in the field of high resistance and weak current measurement.
1. Core Principle: Ultimate Accuracy Based on Feedback Ammeter Technology
The core of the 6517B is a electrometer-grade operational amplifier that adopts Feedback Ammeter technology, which is the key to achieving femtoampere-level measurement accuracy.
Principle of Feedback Ammeter:
The weak current under test (I_IN) flows directly into the virtual ground inverting input terminal of the operational amplifier.
This current is forced to flow through a high-precision feedback resistor (R_F).
A voltage (V_OUT = -I_IN × R_F) is generated at the output of the operational amplifier, which is then measured by a high-precision ADC.
Advantages: Due to the extremely high input impedance of the operational amplifier (>10^15 Ω), almost all the incoming current flows through the feedback resistor, and the input terminal always maintains a virtual ground potential close to 0V, which greatly reduces errors and leakage current caused by input voltage fluctuations.
Key Technologies for Femtoampere Measurement:
guarded technology: All input connecting lines are surrounded by a Guard ring at the same potential as the input signal. The guard potential is synchronized with the input signal potential, thus eliminating leakage current between cables and fixtures.
Low-noise Design: Specially-made low-noise JFET input stage and carefully selected components are used to minimize the background noise.
Sealing and Drying: Key input components are sealed and filled with dry gas inside to prevent leakage caused by moisture.
II. Detailed Specifications (Defining the pinnacle of the industry)
Core Electrical Performance Specifications
| Parameter | 6517B Specifications | Features & Benefits |
|---|---|---|
| Current Measurement Range | 10 fA to 20 mA (8 ranges in total) | Covers a wide range from weak dark current to microampere-level photocurrent |
| Current Resolution | 0.1 fA (at 2 nA range) | Detects extremely weak current changes and provides key data for material research |
| Voltage Bias | < ± 3.5 fA (Typical) | Extremely low input bias current means that even when the input terminal is open, the instrument's own current is extremely small, ensuring the accuracy of low current measurement |
| Input Impedance | > 200 TΩ (range dependent) | Extremely high input impedance ensures negligible impact on the circuit under test |
| Resistance Measurement Range | 10 Ω to 10 PΩ (10^16 Ω) | Direct measurement of bulk resistivity of insulating materials and semiconductor wafers |
| Built-in Voltage Source | 0 to ±1000 V (Programmable, 1V step) | Provides high-stability bias voltage for resistance measurement and device testing, no external power supply required |
| Charge Measurement Range | 10 fC to 2 μC | Used for measuring physical phenomena such as capacitor charge, piezoelectric effect and triboelectric electrification |
Accuracy and Stability
| Parameter | Condition | Specification |
|---|---|---|
| Current Accuracy | (1 year, 23°C ±1°C, 2 nA range) | ±(0.3% of reading + 100 fA) |
| Voltage Source Accuracy | (1 year, 23°C ±1°C) | ±(0.05% output + 1 mV) |
General Specifications
| Specification | Description |
|---|---|
| Interface | GPIB (IEEE-488.2), RS-232, Handler (for sorter integration) |
| Display | Vacuum fluorescent display (VFD), clear and bright |
| Scanning Function | Built-in voltage scanning and delay functions for automatic I-V curve generation |
3. Key Precautions (Avoid measurement pitfalls and ensure authentic data)
Electrostatic shielding and protection (Guard) is critical:
Triaxial cable must be used: the center conductor carries the signal, and the outer guard shield must be connected to the Guard terminal of the instrument. Ordinary coaxial cables are strictly prohibited.
Guard connection: Install the DUT or fixture in a metal shield box, and connect the shield box to the Guard terminal to eliminate spatial electrostatic interference and surface leakage current.
Environmental control is critical:
Humidity control: The ambient humidity must be < 40% RH. Higher humidity leads to more severe surface leakage on insulating materials, which will make the measurement result significantly lower. It is recommended to perform measurement in a drying oven or a sealed chamber filled with dry gas.
Temperature stability: Avoid drastic temperature fluctuations, as thermal electromotive force will introduce measurement errors. Warm up the instrument for at least 1 hour to achieve thermal stability.
Electromagnetic Interference (EMI) shielding: Keep away from interference sources such as AC power lines, motors, fluorescent lamps, etc. Placing the entire test system in a Faraday cage or a metal shield box is the best practice.
Measurement tips and optimization:
Zero correction: Before performing the most precise measurement, execute the Zero Check function to measure and store the internal offset of the instrument, which will be automatically subtracted in subsequent measurements.
Select appropriate range: Try to use the smallest range to get the best resolution and accuracy, but avoid input overload.
Delay time: Set a sufficient delay between voltage application and measurement, especially for high resistance measurements, to allow the dielectric absorption effect to stabilize.
Safe operation:
High Voltage Warning: The built-in voltage source can output 1000 V DC. During operation, ensure that all high-voltage connections are secure, well-insulated, and marked with obvious warning signs.
IV. Core Application Fields
Characterization of Semiconductor Materials and Devices:
Wafer-level Leakage Current Test: Measure the gate leakage current (IGSS) of MOSFET to evaluate the quality of high-k gate dielectric.
Bulk Resistivity and Sheet Resistance: Use four-point probe method or van der Pauw method, cooperate with built-in voltage source to accurately measure the resistivity of semiconductor wafers and epitaxial wafers.
Insulation Material Evaluation:
Test the bulk resistivity and surface resistivity of polymer materials, ceramics and glass, to evaluate whether their insulation performance meets national standards (such as GB/T 1410).
Optoelectronics and Sensor Research:
Photodiode Dark Current: Accurately measure the background noise current of photodetectors under no-light conditions.
Dark current and charge conversion efficiency characterization for image sensors (CCD/CMOS).
Electrostatic Research:
Accurate measurement of Triboelectric charge.
Weak current monitoring for Electrostatic Discharge (ESD) events.
5. Efficient Operation Guide (Take ultra-high resistance measurement as an example)
Step 1: System Setup and Connection
Make sure all connections are done in a dry, shielded environment.
Step 2: Instrument Setup
Press 【POWER】 to turn on the instrument, and warm it up for 1 hour.
Press 【ZERO CHECK】 to perform zero calibration.
Select the resistance measurement mode 【RESISTANCE】.
Set the built-in voltage source: press 【SOURCE】, and set an appropriate test voltage (e.g. 100 V or 500 V).
Set the delay time: set a sufficient stabilization time (e.g. 30 - 60 seconds) in the menu.
Step 3: Perform measurement and read the result
Press the 【OPERATE】 key to start the measurement.
The instrument will automatically calculate and display the resistance value directly (units can be Ω, kΩ, MΩ, GΩ, TΩ).
Record the stable reading.
Step 4: Calculate Resistivity (if required)
For bulk resistivity ρ, the calculation formula is: ρ = R x (A / t)
R: Measured resistance value (Ω)
A: Electrode area (m²)
t: Sample thickness (m)
Why Do Top-Tier Laboratories Choose 6517B?
Unmatched Precision Authority: With 0.1 fA resolution and < 3.5 fA bias current, it delivers the most reliable low-level current measurement data.
Highly Integrated Functionality: A single unit integrates an electrometer, high resistance meter, voltage source, and charge meter, eliminating the need for complex system integration.
Keithley Quality and Reliability: As an industry benchmark for electrical measurement, its stability and repeatability have stood the test of time.
Powerful Automation Capability: The GPIB interface enables easy integration into automated test systems for long-duration, high-repeatability precision measurement.