Process and Low-Frequency Noise Variability Estimation of Tunable Piezoresistive Sensing Performance in Junctionless Nanowire FETs

In this paper, a tunable piezoresistive pressure sensor is designed and developed using junctionless nanowire (JL-NW) gate-all-around (GAA) field-effect transistors (FETs) integrated into a circular diaphragm. The measured results show that piezoresistive sensitivity is improved by ~4 times in the subthreshold (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SS</i>) regime compared to the ON-state (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_ON</i>) condition. This improvement is achieved by reducing channel conductivity with a low gate bias below the threshold voltage. Piezoresistivity variability is observed to be ~20% in the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SS</i> regime and ~10% in the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_ON</i> conditions, attributed to ~±4 nm diameter variations in the nanowires during fabrication. Symmetric thin nanowire diameters yield a higher gauge factor than asymmetric ones, highlighting the importance of controlling fabrication process variations for stable nanoelectromechanical system (NEMS) sensors in advanced technology nodes. Low-frequency noise (LFN) is measured to assess the minimum detectable strain (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">MDS</i>) and signal-to-noise ratio (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SNR</i>), indicating that JL-NW GAA FET provides superior resolution and performance as a sensing element compared to the inversion-mode nanowire (NW) GAA FET. Additionally, it offers better reliability and easier integration with advanced CMOS technologies.