Bias Stress-Induced Threshold-Voltage Instability of SiC MOSFETs

We have observed instability in the threshold voltage, VT, of SiC metal-oxide semiconductor field-effect transistors (MOSFETs) due to gate-bias stressing. This effect has routinely been observed by us in all 4H and 6H SiC MOSFETs from three different manufacturers—even at room temperature. A positive-bias stress, applying an electric field of about 1 to 2 MV/cm across the gate oxide, for 3 minutes followed by a negative-bias stress for another 3 minutes typically results in a shift of the ID-VGS current-voltage characteristic in the range of 0.25 to 0.5 V and is repeatable. We speculate that this effect is due to the presence of a large number of near-interfacial oxide traps that presumably lie in the oxide transition region that extends several nm into the oxide from the SiC interface, caused by the presence of C and strained SiO2. This instability is consistent with charge tunneling in and out of these near-interfacial oxide traps, which in irradiated Si MOSFETs has been attributed to border traps. Also consistent with charge tunneling is the observed linear increase in the magnitude of the SiC VT instability with log (time).

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The gamma-ray irradiation sensitivity and dosimetric information instability of RADFET dosimeter

Nuclear Technology and Radiation Protection ◽

10.2298/ntrp1304415p ◽

2013 ◽

Vol 28 (4) ◽

pp. 415-421 ◽

Cited By ~ 7

Author(s):

Milic Pejovic

Keyword(s):

Threshold Voltage ◽

Field Effect ◽

Room Temperature ◽

Gamma Ray ◽

Field Effect Transistors ◽

Metal Oxide Semiconductor ◽

Oxide Semiconductor ◽

Threshold Voltage Shift ◽

Voltage Shift ◽

Gamma Ray Irradiation

The gamma-ray irradiation sensitivity to radiation dose range from 0.5 Gy to 5 Gy and post-irradiation annealing at room and elevated temperatures have been studied for p-channel metal-oxide-semiconductor field effect transistors (also known as radiation sensitive field effect transistors or pMOS dosimeters) with gate oxide thicknesses of 400 nm and 1 mm. The gate biases during the irradiation were 0 and 5 V and 5 V during the annealing. The radiation and the post-irradiation sensitivity were followed by measuring the threshold voltage shift, which was determined by using transfer characteristics in saturation and reader circuit characteristics. The dependence of threshold voltage shift DVT on absorbed radiation dose D and annealing time was assessed. The results show that there is a linear dependence between DVT and D during irradiation, so that the sensitivity can be defined as DVT/D for the investigated dose interval. The annealing of irradiated metal-oxide-semiconductor field effect transistors at different temperatures ranging from room temperature up to 150?C was performed to monitor the dosimetric information loss. The results indicated that the dosimeters information is saved up to 600 hours at room temperature, whereas the annealing at 150?C leads to the complete loss of dosimetric information in the same period of time. The mechanisms responsible for the threshold voltage shift during the irradiation and the later annealing have been discussed also.

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