Three-Terminal Device Capacitance Measurement with Residual Inductance Cancellation
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Solution Overview
Problem
Existing methods for measuring inter-terminal capacitances of three-terminal semiconductor devices, such as power MOS FETs and IGBTs, face challenges due to increasing bias voltages that exceed the capabilities of conventional LCR meters, leading to inaccurate or unfeasible measurements.
Innovation Solution
A measurement apparatus and method utilizing a route selector to connect terminals of a three-terminal device to an LCR meter in various configurations, allowing for the application of higher bias voltages and cancellation of residual inductance effects, enabling precise measurement of inter-terminal capacitances by acquiring error impedances and using numerical analysis to derive accurate capacitance values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional LCR meter is used for measuring inter-terminal capacitances, then measurement simplicity is maintained, but measurement precision deteriorates due to residual inductance influences and inability to handle high bias voltages
Solution Approach 1:
The measurement system is segmented into multiple functional modules: LCR meter for impedance measurement, route selector for terminal switching, DC power supplies for bias voltage application, and cable assemblies for connections. This segmentation allows each component to be optimized independently while maintaining overall measurement precision and managing complexity through modular architecture.
Solution Approach 2:
Cable assemblies with known characteristics serve as intermediaries between the LCR meter and the device under test. These cables are carefully selected and characterized to minimize and account for their own inductance and capacitance effects, allowing accurate measurement despite their presence in the measurement path.
2Adaptability or versatility
If bias voltages are increased to match power device requirements, then adaptability to power devices is improved, but measurement capability deteriorates due to exceeding LCR meter voltage limits
Solution Approach 1:
DC power supplies act as intermediaries between the measurement system and the device under test, providing the necessary high bias voltages (e.g., 50V, 100V, 200V) that exceed LCR meter ratings. The power supplies are connected through carefully designed cable assemblies that maintain signal integrity while withstanding the high voltages, enabling reliable adaptation to power devices without compromising measurement reliability.
Solution Approach 2:
The system changes operating parameters by applying different bias voltages through DC power supplies to match various power device requirements. The LCR meter measures impedance at these elevated voltage conditions, and the route selector switches between different voltage levels and terminal configurations, allowing the system to adapt to different device specifications while maintaining measurement reliability through controlled parameter variation.
3Measurement precision
If multiple measurement terminals are connected to LCR meter terminals, then measurement completeness is improved, but residual inductance effects worsen due to longer cable routes
Solution Approach 1:
The inductance and capacitance of each cable assembly are measured and characterized before use in the actual device measurement. These pre-measured cable parameters are then used in calculations to compensate for their effects during device characterization. This preliminary characterization allows the system to account for cable effects and maintain measurement precision even with multiple connections.
Solution Approach 2:
The measurement system uses feedback by comparing expected impedance values with actual measurements, then adjusting calculations to compensate for cable effects. The route selector enables switching between different terminal configurations, allowing the system to perform multiple measurements and use the results to feedback-correct for residual inductance and capacitance effects, improving overall measurement completeness and accuracy.
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 solution allows for highly accurate and reproducible measurement of inter-terminal capacitances, effectively addressing the limitations of conventional methods by canceling residual inductance influences and enabling measurement of high-voltage terminals, thus improving the evaluation of three-terminal device performance.
Implementation Method 1
The LCR meter generally measures an AC signal between two terminals... a voltage between both ends of a capacitance Cgd is measured as a voltage Vm by a voltmeter 110, and a current flowing through the capacitance Cgd is measured as a current Im by an ammeter 114
Implementation Method 2
a guard terminal GD of the LCR meter 102 is connected to the terminal S via a cable 906... A current Ie flowing through a capacitance Cds does not flow through the ammeter 114 due to the use of the terminal GD
Data Source
AI summary
Provided are a measurement apparatus and a measurement method capable of measuring inter-terminal capacitances of a three-terminal device while reproducibility is high and influences of residual inductances are cancelled. The measurement apparatus includes: a route selector including a first terminal, a second terminal, a third terminal, a fourth terminal, a fifth terminal, and a sixth terminal, the fourth to sixth terminals being configured to connect to any of the first to third terminals; an LCR meter; a device under test, which is a three-terminal device; first, second, and third cables for respectively connecting the fourth to sixth terminals of the first route selector and first, second, and third terminals of the device under test to each other; and fourth, fifth, and sixth cables for respectively connecting the first to third terminals of the first route selector and first, second, and third terminals of the LCR meter to each other.