MOSFET Interface Trap Measurement via Charge Pumping Frequency Analysis
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Solution Overview
Problem
Traditional charge pumping techniques fail to accurately measure interface traps in thin gate oxide MOSFETs due to the difficulty in separating charge pumping current from tunneling current, especially when tunneling current is comparable or greater than the charge pumping current, leading to inaccuracies in determining interface trap density.
Innovation Solution
The method involves plotting charge pumping current versus frequency to determine the number of interface traps, utilizing the slope of the plot to calculate trap participation and the y-intercept to determine tunneling current, recognizing that charge pumping current occurs only during voltage transitions and tunneling current is dependent on duty cycle, not frequency, thus allowing for separation of the two currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If traditional charge pumping techniques are used to measure interface traps, then the measurement process is simple, but the measurement precision deteriorates when tunneling current is comparable to or greater than charge pumping current
Solution Approach 1:
The patent segments the total measured current into two distinct components: charge pumping current and tunneling current. By applying a periodic gate voltage and analyzing the current at the fundamental frequency and its harmonics, the method separates the charge pumping signal (which contains the interface trap information) from the tunneling current background, enabling accurate measurement even when tunneling current is comparable to or greater than charge pumping current.
Solution Approach 2:
The patent employs periodic gate voltage application with a specific frequency to activate charge pumping. By using periodic excitation and analyzing the resulting current at the fundamental frequency and harmonics, the method creates a distinguishable signal pattern that separates charge pumping effects from continuous tunneling current, improving measurement precision without complicating the overall process.
2Quantity of substance
If gate voltage amplitude is increased to enhance charge pumping current, then the charge pumping current increases, but the tunneling current increases exponentially leading to greater measurement difficulty
Solution Approach 1:
The patent uses periodic gate voltage application where the charge pumping current is activated only during the transition phases (rising and falling edges) of the periodic waveform. This creates a periodic current signal at the fundamental frequency and its harmonics, which can be easily distinguished from the continuous tunneling current background through frequency domain analysis, avoiding the exponential increase in tunneling current that would occur with DC voltage increases.
Solution Approach 2:
The patent employs dynamic gate voltage switching with controlled rise and fall times. By optimizing the transition times and frequency of the periodic voltage application, the method maximizes charge pumping current while keeping tunneling current manageable. The dynamic nature of the periodic excitation creates a time-varying signal that can be separated from the steady-state tunneling current through spectral analysis.
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 effectively separates charge pumping current from tunneling current, providing accurate measurements of interface traps, even when tunneling current exceeds charge pumping current, and validates calculations to correct for errors, enhancing the reliability of interface trap determination in thin gate oxide MOSFETs.
Implementation Method 1
Interface trap charge pumping is a well-known transient recombination effect that is activated by cycling or pumping the Si—SiO2 interface of the MOSFET between accumulation and inversion states.
Implementation Method 2
plotting charge pumping current versus frequency to determine the number of interface traps, utilizing the slope of the plot to calculate trap participation and the y-intercept to determine tunneling current, recognizing that charge pumping current occurs only during voltage transitions and tunneling current is dependent on duty cycle, not frequency
Data Source
AI summary
A method for measuring interface traps in a MOSFET, includes measuring charge pumping current of a pulse wave form for various frequencies over a predetermined frequency range, creating plotted points of the measured charge pumping current versus the predetermined frequency range, determining the total number of interface traps participating in the charge pumping current by calculating the slope of a best fit line through the plotted points.