Negative bias temperature instability (NBTI) is an effect that causes a gradual shift in transistor threshold voltage (VT). It manifests as an absolute drain current IDsat decrease, transconductance gm decrease, and absolute VT increase. NBTI is primarily observed in p-channel MOSFETs when the gate-to-source voltage is negative.
NBTI is caused by charged defect densities in the gate oxide interface region. The VT shift is dependent on voltage stress on the gate terminal, temperature, and the duty cycle of the stressing voltage. Typical stress levels required to induce NBTI are temperatures in the 100-250 ºC range and electric field conditions across the oxide region higher than 6 MV/cm.
The NBTI prognostic cell is a part of the Sentinel Silicon™ library of prognostic (“canary”) cells.
NBTI Cell Layout – click to enlarge
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Ridgetop is certified as category 1A under the Defense Microelectronics Activity (DMEA) as part of the Trusted Supplier Program. Ridgetop has history of designing analog and mixed signal ICs for demanding applications in space satellites that are subjected to extreme temperatures and radiation. Our designs have utilized bulk CMOS, CMOS-SOI, and SiGe at process geometries down to 28 nm channel lengths. Radiation hardness is also a concern, and Ridgetop has addressed those requirements as well. A recent Ridgetop design was delivered to ON Semiconductor for the U.S. Air Force STELLAR Star Tracker.
Under contract to NASA, Ridgetop designed an effective 3-axis wireless rotational sensor. The RotoSense™ sensor has been tested on fast-spinning pinion gears on helicopter gear boxes, and also rolling stock for railroad safety improvements.