Fixed-Current Quasistatic C-V Measurement for High-Capacitance DUTs
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing quasistatic C-V measurement techniques for high power devices, such as SiC MOS devices, face instability due to high capacitance, leading to unstable results in SMU feedback ammeters, making it difficult to derive accurate capacitance values.
Innovation Solution
A quasistatic capacitance-voltage (QSCV) technique using a SMU that forces a fixed current into the gate terminal of a device under test, measures voltage over time, and derives capacitance, compensating for leakage currents and parasitic capacitances to stabilize measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a SMU feedback ammeter is used to measure current for deriving capacitance in quasistatic C-V measurements, then the measurement technique can be applied to traditional silicon MOS devices, but the results become unstable when applied to high power devices with higher capacitance
Solution Approach 1:
The patent changes the measurement parameter from current to voltage. Instead of measuring current through the DUT using the SMU ammeter (which becomes unstable with high capacitance), the method measures the voltage across a known series resistor. This parameter change allows the same SMU to accurately measure devices with capacitances ranging from small traditional MOS devices to large high power devices without stability issues.
2Reliability
If voltage is measured instead of current using a SMU, then measurement stability is improved for high capacitance devices, but additional circuit elements are required
Solution Approach 1:
The patent introduces a simple series resistor as an intermediary element between the SMU and the DUT. This resistor serves as a mediator that converts the difficult-to-measure current (which causes instability) into an easily measurable voltage drop across the resistor. The series resistor is a passive, simple component that does not significantly complicate the circuit while enabling stable voltage-based measurements.
3Productivity
If leakage current is not corrected in quasistatic C-V measurements, then the measurement process is simpler, but the accuracy of capacitance values deteriorates
Solution Approach 1:
The patent performs preliminary measurements to characterize and account for leakage currents before deriving the final capacitance values. The method measures the voltage across the series resistor during the charging process, and through mathematical analysis, separates the leakage current component from the capacitive current component. This preliminary characterization of leakage allows for accurate capacitance extraction even in the presence of significant leakage currents.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The technique provides stable and accurate capacitance measurements for high power devices, allowing for characterization of interface traps and internal charges, requiring only one SMU and avoiding noisy measurements.
Implementation Method 1
a current source configured to output a constant current to a connected device under test (DUT); a voltage sensor configured to sense a voltage to the DUT... measure a first set of voltages over time while the current source outputs a first constant current to the DUT
Data Source
AI summary
A test and measurement instrument is described, having: a current source configured to output a constant current to a device under test (DUT); a voltage sensor configured to sense a voltage to the DUT, where the voltage sensor is configured to: measure a first set of voltages over time while the current source outputs a first current the DUT; measure a second set of voltages over time while the current source outputs a second current to the DUT, the second current having a different polarity to the first current; and measure a third set of voltages over time while the current source outputs a third current to the DUT, the third current having a same polarity as the first current. Furthermore, the test and measurement instrument includes one or more processors configured to derive a capacitance of the DUT based on the second and third currents.