MOS Transistor Threshold Voltage Measurement Circuit
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Solution Overview
Problem
Existing methods for determining the threshold voltage of transistors, such as binary search and interpolation, are slow and require multiple force/measure cycles due to the need to sweep input voltages across ranges to narrow in on the threshold voltage.
Innovation Solution
Implementing an operational amplifier-based measurement circuit that sets the gate voltage to 0 V and uses a constant current source to maintain a threshold current, allowing direct measurement of the threshold voltage through feedback, reducing the need for iterative adjustments and enabling measurement in both saturation and linear modes with a single force/measure cycle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If binary search or interpolation techniques are used to determine threshold voltage, then measurement accuracy is achieved, but measurement time increases due to multiple force/measure cycles
Solution Approach 1:
The operational amplifier circuit is pre-configured with feedback connections to the transistor gate, and the constant current source is pre-established at the transistor source. This preliminary setup eliminates the need for iterative voltage sweeping, allowing direct measurement of threshold voltage in a single force/measure cycle while maintaining measurement accuracy.
Solution Approach 2:
The operational amplifier uses feedback from the transistor drain to automatically adjust the gate voltage to maintain the threshold current condition. This feedback mechanism replaces manual iterative adjustment with automated real-time control, significantly reducing measurement time while preserving measurement precision.
2Measurement precision
If iterative voltage sweeping is performed to narrow in on threshold voltage, then accurate threshold voltage determination is achieved, but productivity decreases due to slow measurement speed
Solution Approach 1:
The measurement circuit is pre-configured with the operational amplifier feedback loop and constant current source established before measurement begins. This preliminary setup enables direct threshold voltage measurement without iterative sweeping, dramatically improving wafer-level testing efficiency while maintaining accurate threshold voltage determination.
Solution Approach 2:
The manual iterative voltage sweeping process is replaced with an automated operational amplifier feedback system. This substitution eliminates the time-consuming mechanical sweeping process while maintaining measurement accuracy, thereby improving productivity in wafer-level electrical testing.
3Measurement precision
If multiple force/measure cycles are used to sweep input voltages, then threshold voltage measurement is achieved, but device complexity increases due to required circuit configurations
Solution Approach 1:
The operational amplifier-based circuit is designed to measure threshold voltage in both saturation and linear modes using the same basic configuration. This multi-functional design eliminates the need for separate circuit configurations for different operating modes, reducing device complexity while maintaining measurement precision.
Solution Approach 2:
The circuit is pre-configured with the operational amplifier feedback loop and constant current source, which can directly measure threshold voltage without requiring multiple force/measure cycles or complex switching arrangements. This preliminary configuration simplifies the overall circuit design while achieving accurate threshold voltage measurement.
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
This approach significantly reduces the time required to measure threshold voltage, improving the efficiency of wafer-level electrical testing by allowing direct and rapid determination of transistor parameters with minimal cycles, enhancing the speed and accuracy of semiconductor product evaluation.
Implementation Method 1
an operational amplifier is provided having a first input, a second input, and an output. The output of the operational amplifier is coupled to the gate of the transistor, the first input of the operational amplifier is coupled to a reference voltage, and the second input of the operational amplifier is coupled to the source of the transistor
Implementation Method 2
A constant current source is coupled to the source of the transistor. A parameter of the transistor is measured
Data Source
AI summary
A method of measuring a parameter of a device in a circuit includes providing a device under test (DUT). The DUT includes a metal oxide semiconductor (MOS) transistor having a gate, a source, and a drain coupled to a first voltage supply node. The method further includes coupling a constant current source to the source of the transistor, coupling an operational amplifier to the transistor, and measuring a parameter of the transistor.