Field Emission of ITO-Coated Vertically Aligned Nanowire Array
© The Author(s) 2010
Received: 25 January 2010
Accepted: 13 April 2010
Published: 29 April 2010
An indium tin oxide (ITO)-coated vertically aligned nanowire array is fabricated, and the field emission characteristics of the nanowire array are investigated. An array of vertically aligned nanowires is considered an ideal structure for a field emitter because of its parallel orientation to the applied electric field. In this letter, a vertically aligned nanowire array is fabricated by modified conventional UV lithography and coated with 0.1-μm-thick ITO. The turn-on electric field intensity is about 2.0 V/μm, and the field enhancement factor, β, is approximately 3,078 when the gap for field emission is 0.6 μm, as measured with a nanomanipulator in a scanning electron microscope.
Field emission is quantum mechanical tunneling of electrons through the surface potential barrier into vacuum , which has been widely exploited in vacuum electronic applications including electron guns, microwave tubes, and flat panel displays . Vertically aligned nanowire array (VANA) shows excellent field emission properties owing to a strong local electric field due to their parallel orientation to the applied electric field . Numerous studies have been carried out on the fabrication of VANAs as field emitters using bottom-up synthesis approaches [4–6]. However, these bottom-up methods have drawbacks such as an expensive process and relatively low fabrication reliability, thus making them unsuitable for mass production.
In this letter, a top–down method of modified conventional UV lithography is suggested for the fabrication of a VANA, thereby resolving the problems of bottom-up methods while allowing control over the VANA’s position and shape. In the lithography process, a photoresist VANA is fabricated with a UV exposure dose control. After the lithography, a carbonization process (pyrolysis process) is followed to provide volume contraction of the array’s structure. The pyrolyzed carbon VANA is coated with a 0.1-μm-thick ITO layer in order to realize a durable field emitter and to provide low turn-on voltage [7, 8]. ITO has good transparence characteristics in the visible region of the electromagnetic spectrum while maintaining high electrical conductivity, thermal stability, and oxidation resistance [4, 9]. In a field emission experiment, a nanomanipulator in a scanning electron microscope (SEM) is used in order to measure field emission while precisely controlling the distance between the anode and cathode (field emitter).
Note that −21.18 is the slope of the red line and −5.76 is the y-intercept of the red line in Fig. 4b. The estimated field enhancement factor of the ITO-coated VANA, β, is 3,078 when the work function of ITO is 4.5 eV . The measured value of the field enhancement factor is comparable with previous research results of field emitters [4, 14, 15].
In summary, an ITO-coated VANA was fabricated by a top–down method using modified conventional UV lithography, and the field emission characteristics were evaluated using a Zyvex nanomanipulator. The top–down method offers many advantages including an economical process, good fabrication reliability, and suitability for mass production. The turn-on electric field intensity of the ITO-coated VANA is about 2.0 V/μm, and the estimated field enhancement factor β is 3,078. These results show that the ITO-coated VANA is a very promising candidate for vacuum electron field emission applications.
This work was partly supported by Brain Korea 21 and Award No KUK-F1-038-02, made by King Abdullah University of Science and Technology (KAUST).
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