A review of recent MOSFET threshold voltage extraction methods
In the rapidly evolving field of semiconductor technology, the accurate extraction of the threshold voltage (Vth) of Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) is crucial for optimizing device performance and ensuring reliable operation. Over the years, numerous methods have been developed to extract Vth, each with its own advantages and limitations. This article provides a comprehensive review of the recent advancements in MOSFET threshold voltage extraction methods.
One of the most widely used methods for Vth extraction is the subthreshold slope (SS) method. This method is based on the assumption that the subthreshold current (Ids) varies exponentially with Vth. By measuring the Ids at different gate voltages and fitting the data to an exponential curve, the Vth can be determined. However, the SS method is sensitive to device mismatch and temperature variations, which can lead to inaccuracies in the extracted Vth.
Another popular method is the constant-current method, which is based on the assumption that the Ids curve can be approximated by a parabolic function around the threshold region. By fitting the Ids data to this parabola, the Vth can be extracted. This method is less sensitive to device mismatch and temperature variations compared to the SS method, but it requires precise control of the gate voltage during the measurement process.
The linear method is another technique for Vth extraction that has gained attention in recent years. This method is based on the linear relationship between the gate voltage and the drain current in the subthreshold region. By fitting the Ids data to a linear function, the Vth can be determined. The linear method is relatively simple and accurate, but it requires a precise measurement of the Ids at the threshold point.
The integral method is another recently developed technique for Vth extraction. This method is based on the integral of the Ids curve in the subthreshold region. By calculating the integral and fitting the data to a model, the Vth can be extracted. The integral method is less sensitive to device mismatch and temperature variations compared to the SS method, and it is also less dependent on the specific measurement setup.
In addition to these methods, some researchers have proposed hybrid approaches that combine the strengths of multiple methods to improve the accuracy of Vth extraction. For example, a hybrid method that combines the SS method with the constant-current method has been shown to provide better accuracy in the presence of device mismatch and temperature variations.
In conclusion, the accurate extraction of MOSFET threshold voltage is essential for optimizing device performance and ensuring reliable operation. This review has discussed several recent advancements in MOSFET threshold voltage extraction methods, including the subthreshold slope, constant-current, linear, integral, and hybrid methods. Each method has its own advantages and limitations, and the choice of method depends on the specific requirements of the application. As semiconductor technology continues to advance, it is expected that new and improved methods for Vth extraction will be developed to meet the increasing demands of the industry.
