Design of a multi-walled carbon nanotube field emitter with micro vacuum gauge
© Dong et al.; licensee Springer. 2013
Received: 21 January 2013
Accepted: 21 February 2013
Published: 28 March 2013
The variation of vacuum level inside a field emission device when electron is emitted from multi-walled carbon nanotubes (MWCNTs) by electric field was measured where MWCNT gauge packaged with a vacuum device was used to measure the degree of a vacuum until the end of the vacuum device life. It was found that the electrical properties of MWCNTs altered with the degree of a vacuum. We fabricated MWCNT gauge which were printed and pasted by the screen printer. In this paper, we report the successful detection of the ionization of gases in vacuum state.
KeywordsMulti-walled carbon nanotubes Field emitter Vacuum gauge Outgassing
Carbon nanotube (CNT) is one of the most promising materials for a field emitter due to its remarkable electrical conductivity, chemical and mechanical stability, and characteristics having unique structures such as high aspect ratio [1–5]. Many researches have been highly devoted to developing a practical application for the commercialization of field emitter, but there are still some problems to be solved such as the lifetime of the emitter [6–10]. There are many factors that affect the emitter lifetime working in a state of vacuum. Among them, outgassing generated during emission is inarguably one of the most critical factors [11–13]. Especially, some organic binders can still remain after firing when the multi-walled carbon nanotube (MWCNT) emitter is made in paste and be the source to release gas in the vacuum panel. The outgassing can give a severe damage to the vacuum microelectronic device by electrical arcing and ion bombardment onto a cathode or an anode. In addition to the physical damages, some gases can cause chemical etching to the MWCNT emitter. These highlight that controlling the outgassing is a key issue for emission devices prepared from the paste.
Therefore, it is very important to monitor the vacuum level in a vacuum device in order to maintain satisfying field emission properties. To measure the inner vacuum of the device, the vacuum gauge should be integrated to the vacuum device without affecting the device. MWCNTs were used to fabricate the real time-monitoring vacuum gauge that satisfies these conditions. MWCNTs facilitate the fabrication of a microstructure and this microstructure was used to build the micro vacuum gauge that could be set up in the device. Here, we demonstrate a simple screen-printed MWCNT device that combines the MWCNT field emission and MWCNT-based vacuum gauge for the measurement of the vacuum level. Also, the MWCNT vacuum gauge packaged with a vacuum device is used to measure the lifetime of the vacuum device.
The weight ratio of MWCNT/glass frit/indium tin oxide (ITO) powder/Ethyl cellulose/α-terpineol was 1:10:2:9:100. MWCNT powder grown by chemical vapor deposition was used as an electron emission source and glass frit as an inorganic binder to enhance the adhesion between MWCNT and the substrate after firing. MWCNT field emitters and the vacuum gauge were fabricated by the screen-printing process, where the field emitters were used as electron source. In the mixture of MWCNTs, the organic binder was premixed through an ultra-sonication for 30 min. Then, a three-roll milling process was carried out for mixing and dispersion of MWCNTs in the organic binder to form a polymer matrix. Mechanically well-dispersed MWCNT paste was printed onto an ITO glass. The residue of organic binder leads to problems such as outgassing and arcing during a field emission measurement. Therefore, organic materials in paste were removed by drying the printed MWCNT paste in the furnace for 30 min at 400°C to obtain stable emission characteristics.
The gas sensing and field emission areas were printed in cathode plate. The MWCNT paste film was fired at 350°C in nitrogen (N2) ambient in a furnace. Finally, the MWCNTs in printed cathode layer are randomly distributed in a matrix material. Therefore, their emission characteristics are poor compared to, for instance, highly ordered arrays of vertically aligned MWCNTs. The surface treatment of printed MWCNTs was performed for vertical alignment as well as protrusion of MWCNTs from the surface to increase of field emission current and to improve the sensitivity of the vacuum gauge.
Results and discussion
In this work, the change in inner vacuum of the vacuum-packaged emitter device and the current of printed MWCNT ionization vacuum gauge by field emission were explored. The MWCNT emitter showed excellent emission characteristics under vacuum pressure below 10-6 Torr. The MWCNT source vacuum gauge presented good measurement linearity from 10-7 to 1 Torr for air. This MWCNT-based gauge is expected to find several applications such as ultrahigh vacuum systems, vacuum inside sealed devices, and field emission devices.
This work was supported by the World Class University (WCU, R32-2009-000-10082-0) Project of the Ministry of Education, Science and Technology (Korea Science and Engineering Foundation) and supported by the Industrial Core Technology Development Program funded by the Ministry of Knowledge Economy (no. 10037394).
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