Fig. 1. (Color online) Structure and properties of the SWCNT-film-based FET. (a) AFM morphologic image showing the SWCNT film deposited on the Si/SiO₂ substrate. The inset is the optical image of a SWCNT FET, of which the channel length is 10 μm and the width is 20 μm. (b) Typical transfer charateristics curves of the SWCNT FET before irradiation at V_DS = –10 V. (c) Schematic diagram of the low-energy charged particle irradiation simulation test device composed of an ionization chamber, accelerator and irradiation chamber. (d) Schematic showing the total ionizing dose (TID) and displacement damage effect in the SWCNT FET induced by proton irradiation.

Fig. 2. (Color online) Simulation results of (a) the distribution of protons in the source/drain region (Au/Pd/Ti/SWCNT/SiO₂/Si), (b) the number of vacancies in the source/drain region (Au/Pd/Ti/SWCNT/SiO₂/Si), (c) distribution of protons in the channel region (SWCNT/SiO₂/Si), and (d) the number of vacancies in the channel region (SWCNT/SiO₂/Si) by SRIM. The energy of the protons is 150 keV. The inset is the illustration of the simulation region, including the source/drain contact region and the SWCNT channel region.

Fig. 3. Simulation result of the energy loss in the metal/CNT contact and channel region of the CNT-layer performed by GEANT 4 with four different proton irradiation fluences of 5 × 10¹², 5 × 10¹³, 5 × 10¹⁴ and 1 × 10¹⁵ p/cm².

Fig. 4. Raman spectra of SWCNT FETs before and after proton irradiation with four different proton fluences of 5 × 10¹², 5 × 10¹³, 5 × 10¹⁴ and 1 × 10¹⁵ p/cm². (a) Single point Raman spectra of SWCNT FETs with different proton fluences, in which the G peaks are normalized. (b) Statistical study on the ratio of the D peak intensity to the G peak intensity (I_D/I_G) with different proton fluences. Each sample has 121 test points, which are obtained by Raman mapping. The test area is 5 × 5 μm² and the spacing is 0.5 μm.

Fig. 5. (Color online) (a) Typical transfer characteristics curves of the SWCNT FETs at V_DS = –10 V with different proton fluences. (b) Threshold voltage (V_th) values extracted by the Y-function method with different proton fluences. (c) Band structure of SWCNT with metal before and after proton irradiation at the on- (left) and off-state (right). (d) Hysteresis in typical transfer characteristics curves with different proton fluences at V_DS = –10 V.

Fig. 6. Statistics measurements of (a) the threshold voltage (V_th), (b) rate of on-current (I_on) change, (c) rate of off-current (I_off) change, (d) rate of on/off ratio change, (e) rate of mobility change, and (f) subthreshold swing (SS) with four different proton irradiation fluences of 5 × 10¹², 5 × 10¹³, 5 × 10¹⁴ and 1 × 10¹⁵ p/cm².

Fig. 7. (Color online) TLM measurements of SWCNT FETs before and after proton irradiation with four different proton fluences of 5 × 10¹², 5 × 10¹³, 5 × 10¹⁴ and 1 × 10¹⁵ p/cm². (a) Typical current–voltage curves of a complete SWCNT TLM test structure before proton irradiation at V_BG = –10 V. Inset is the optical image of a SWCNT TLM test structure consisting of several FETs, which have the same channel width (7 μm) and different channel length (4, 6, 10, 14, 18, 22, 28 and 35 μm, respectively). (b) Length-dependent total resistances of SWCNT FETs with different proton fluences.