MOS Transistor Threshold Voltage Measurement Using Constant Drain Voltage
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Solution Overview
Problem
Conventional threshold voltage measuring devices for MOS transistors face inaccuracies due to body effects caused by variations in source voltage or back gate voltage, leading to inconsistent measurements.
Innovation Solution
A threshold voltage measuring device that maintains source and drain voltages at constant levels, using a drain voltage clamping circuit and a constant current supply circuit to ensure a stable drain-source current, thereby preventing body effects and allowing accurate measurement of threshold voltages in MOS transistors, including those in arrays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional threshold voltage measuring device is used, then measurement can be performed, but measurement precision deteriorates due to body effect
Solution Approach 1:
The patent applies equipotentiality by maintaining the source voltage at a constant level (VS = constant) and the back gate voltage at a constant level (VB = constant), thereby eliminating potential differences that cause body effects. This is achieved through a constant voltage supply circuit that provides stable voltages to the source terminal and back gate terminal, ensuring that the threshold voltage measurement is not affected by body effect variations.
Solution Approach 2:
The patent employs feedback mechanisms through operational amplifiers (OP1, OP2) that continuously monitor and adjust the source voltage and back gate voltage to maintain them at constant levels. The feedback loops ensure that any deviations from the desired constant voltages are corrected, thereby preventing body effects from occurring during threshold voltage measurement.
2Measurement precision
If constant current method is used, then threshold voltage can be measured, but measurement precision deteriorates due to source voltage variation
Solution Approach 1:
The patent maintains the source voltage at a constant level (VS = constant) using a constant voltage supply circuit, thereby eliminating source voltage variations that would otherwise affect measurement precision. This equipotential approach ensures that the source terminal remains at a stable potential throughout the measurement process.
Solution Approach 2:
The patent uses feedback through operational amplifier OP1 to continuously monitor and adjust the source voltage, ensuring it remains constant despite any disturbances. This feedback mechanism compensates for voltage variations and maintains stable source voltage conditions during threshold voltage measurement.
3Productivity
If multiple transistors in array are measured, then productivity increases, but measurement precision deteriorates due to leakage current
Solution Approach 1:
The patent maintains constant back gate voltage (VB = constant) for all transistors in the array during measurement, which prevents body effect variations and reduces leakage current. This equipotential approach ensures that all transistors are measured under identical voltage conditions, improving both productivity and precision.
Solution Approach 2:
The patent changes the operating parameters by maintaining constant source and back gate voltages rather than using conventional variable voltage methods. This parameter change enables rapid sequential measurement of multiple transistors while maintaining high precision by preventing body effect-induced leakage currents.
Data Source
AI summary
A threshold voltage measuring device may include a metal-oxide-semiconductor (MOS) transistor, a drain voltage clamping circuit configured to control a drain voltage of the MOS transistor wherein the drain voltage having a substantially constant level, and a constant current supply circuit configured to cause a drain-source current to flow through the MOS transistor wherein the drain-source current having a substantially constant magnitude.