EFFECTS OF TOTAL-IONIZING DOSE ON CARBON NANOTUBE FIELD-EFFECT TRANSISTORS

Abstract

Carbon nanotube field-effect transistors (CNTFETs) are an emerging alternative semiconductor technology. CNTFETs are a Schottky barrier transistor where the channel between a metal source/drain is a carbon nanotube (CNT) mesh. The CNTFETs in this research use non-stochiometric oxides for work function engineering to set the Schottky barrier height. This non-stochiometric oxide encapsulating the CNTFET is thick compared to the gate dielectric and is analogous to the buried oxide (BOX) in fully-depleted silicon-on-insulator (FDSOI) silicon transistors. To evaluate how this technology will perform in a radiation environment, total-ionizing-dose irradiation (TID) and low-frequency noise (LFN) testing was conducted on experimental CNTFETs. Three different lots of CNTFETs exhibited significant threshold voltage shift from TID irradiation up to 1 Mrad (SiO2). LFN noise testing shows that these CNTFETs exhibit higher noise levels compared to modern silicon transistors. At frequencies lower than 50 Hz the noise is dominated by random-telegraph noise. Above 50 Hz the noise is dominated by percolation switching noise from changing current paths in the CNT mesh. Additional noise comes from the higher amount of charged defects present in emerging technology oxides. Post-irradiation LFN testing shows and increased role for traps in the oxides than before irradiation.