Elsevier

Microelectronic Engineering

Volume 85, Issues 5–6, May–June 2008, Pages 1413-1416
Microelectronic Engineering

Characterization at the nanometer scale of local electron beam irradiation of CNT based devices

https://doi.org/10.1016/j.mee.2007.12.014Get rights and content

Abstract

We report on the specialised characterization of the local electron beam irradiation of carbon nanotube (CNT) based devices motivated by previous studies on device electrical characteristics. In particular, Kelvin probe force microscopy provides surface potential description of the device under exposure. The experimental characterization is complemented with 3-dimensional electric field modelling of the devices using finite element methods. The modelling includes the effect of electron charging and AFM tip potential. Comparison of simulation and experiments shows good agreement and contributes to assess the distortion of electrical characteristics of CNT based devices under electron beam irradiation.

Introduction

Electronic structure and transport properties of carbon nanotube (CNT) based devices are interesting from both fundamental and technological point of view [1], [2]. A deep understanding of the electronic structure and transport properties of CNT based devices is of interest to improve their performance and their fabrication process. Our work contributes to this comprehension from the determination of the effect of a local low-energy electron beam exposure of carbon nanotube (CNT) based devices by the realization of specially oriented characterization. Previous studies of the effect of spatially extended electron exposure on CNT devices [3] revealed a pronounced change of their electrical conduction characteristics. Additional exposure experiments were performed in [4] where the electron exposure was spatially restricted to selected areas of the CNT devices. They showed that the change of the electrical properties of the CNT devices occurs at the CNT itself, rather than in the contacts. In the present work, we complement the previous studies using AFM-based methods of electrical characterizations. In order to fully understand the results of the characterization, the system is modelled using finite element methods.

Section snippets

Device fabrication and local e-beam irradiation

CNTs are grown by CVD on a 200 nm thick SiO2 layer thermally grown on p-type silicon substrate. Alignment marks are defined by electron beam lithography (EBL) on PMMA, which are used to determine the coordinates of the CNT by AFM inspection. A second EBL process is performed to contact the pre-selected nanotubes. Pattern is transferred again by Cr + Au thin bilayer deposition and lift off of the resist. Electrical characterization is performed in a probe station to obtain the device electrical

KPFM

To better understand the effect of the local exposure, we have used Kelvin probe force microscopy (KPFM) under clean-room conditions. KPFM is an AFM based technique that provides direct information about surface potential with nanometer spatial resolution [5]. Previous authors have shown the potential of using AFM advanced modes for the electrical characterization of CNT devices [6]. For KPFM imaging, the CNT is biased by only one electrode and a commercial Si tip coated with Pt is used. Gate

Electric field simulations

In order to explain this behaviour, we have performed 3D finite elements simulations [7] of the device including electronic charging and the presence of a polarized AFM tip. This allows us to compare the modelled electrostatic potential of the device with the registered surface potential obtained by KPFM. An overview of the simulation flow is showed in Fig. 5. The modelization includes biased contact and gate, locally delivered charge and polarized AFM tip. Fig. 6 left represents the potential

Conclusions

We have shown that KPFM is a powerful technique to determine local changes in the electrical properties of CNT. KPFM is successfully applied to characterize CNT FET devices and contacted CNT before and after electron beam irradiation. In addition, the system has been modelled using finite elements simulations to determine the electrical field distribution. The simulations reflect well the effect of the electron beam exposure. Information from both KPFM images and simulations reveals the strong

Acknowledgement

This work is partially funded by projects Charpan (FP6-MNP-IP 515803-2) and Sensonat (NAN2004-09306-C05).

References (7)

  • G. Rius et al.

    Microelectron. Eng.

    (2007)
  • A.V. Krasheninnikov et al.

    Nature Mater.

    (2007)
  • Ph. Avouris et al.

    Nature Nanotechnol.

    (2007)
There are more references available in the full text version of this article.

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