研究目的
To develop a programmable ultra low DC current source (ULCS) capable of generating currents from 1 fA up to 100 pA with 100 aA resolution for calibration of DC low current meters.
研究成果
The developed ULCS is suitable for low current measurement applications such as optical detector characterizations, night vision systems, and medical instrumentation systems. Further evaluations will be performed on the uncertainty budget.
研究不足
The loss factor for the 1 pF capacitor is 10 times worse when used with the relay card, affecting current values lower than 10 fA. Further investigations are needed for stability of ramp voltage generation and loss factor improvement.
1：Experimental Design and Method Selection:
The ULCS is based on applying a ramp voltage on standard capacitors. The device is fully automated with computer control.
2：Sample Selection and Data Sources:
Standard capacitors with values between 1 pF and 1000 pF are used.
3：List of Experimental Equipment and Materials:
Includes a NI-USB 4431 DAQ card, Agilent 16380 type standard air capacitors, AH2500A capacitance bridge, and Keithley 6430 electrometer.
4：Experimental Procedures and Operational Workflow:
The DAQ card generates ramp voltages with slopes between 1 mV/s and 100 mV/s. Capacitance measurements were performed at 1 kHz frequency.
5：Data Analysis Methods:
Characterization measurements of ramp voltages were performed periodically in decade steps, with linear fit equations used for non-decade values.
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