Electrical Properties of Carbon-Nanotube-Network Transistors during Proton-Micro-Beam Irradiation

Carbon-Nanotube-network transistor exhibits a large radiation tolerance, and has potentials to be applied to radiation-resistance devices. In our previous work, we have reported that the CNT-network transistors are applicable in use in very high dose gamma-ray field with the total dose up to 30 kGy.[1] In this work, we extended our studies to investigate the electrical properties of CNT-network transistors against protons. For irradaition, SPICE-NIRS microbeam [2] was used to target CNT-network transistor (100 x 20 µm2) with a beam size of 200 µm2 in diameter. Protons at the CNNT layer were calculated to be 3.34 MeV with the beam intensity (protons per second) controlled to be 5.0x104, or 5.0 x105 within ± 5 % deviation. Irradiation was conducted at the drain voltage of -1 V under positive and negative gate bias in air. The drain current of the device was increased gradually for positive gate bias during the irradiation, and then decreased gradually after the irradiation stopped. In contrast, the drain current was decreased gradually for negative gate bias during the irradiation, and then increased gradually after the irradiation was stopped. These changes caused by the irradiation suggested that the irradiated proton formed the negative charges near the CNT/gate insulator interfaces.[1] Ishii S et al., Physica Section E, in press [2] Konishi T et al., J Radiat Res, 54: 736-747 (2013)International Workshop on Superconductivity and Related Functional Materials 201

Electrical responses of a carbon nanotube thin-film transistor to MeV proton irradiation in air.

We used protons with incident energy of 3.30 MeV to irradiate a carbon nanotube thin-film transistor (CNTTFT) to study its electrical response in air environment. The drain current (ID) was monitored by applying a constant gate voltage (VGS) to the CNTTFT; proton irradiation was turned on and off at a beam intensity of 50,000 cps. ID increased at a negative VGS of −20 V and decreased at a positive VGS of +10 V during proton irradiation. For both VGS values, ID began to recover after proton irradiation. According to the calculations for the energy loss of protons, the incident protons deposited their energy on the CNTTFT. Micro-Raman analysis revealed that no structural change in the CNT was caused by the incident protons. The reversible electrical responses of the CNTTFT to proton irradiation should be applicable to the detection and dosimetry of MeV incident protons in air