Preparation of a Low Cost Carbon Nanotubes Field Electron Emission Thin Film and its Initial Application Research

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1 Solid State Phenomena Online: ISSN: , Vols , pp doi: / Trans Tech Publications, Switzerland Preparation of a Low Cost Carbon Nanotubes Field Electron Emission Thin Film and its Initial Application Research G.Y.Liu 1,a,, C.Y.Zhi 2,b, S.H.Xia 1-1,c, J.G.Zhang 1-1,d, H.Y.Li 3,e,J.X.Yang 3,f, S.Liu 2, E.G.Wang 2,g, 1 Inst. of Elec., Chi. Acad. of Sci., 1 Microwave Co., 1-1 State key lab. of Trans. Tech., Beijing State key Lab. of Surf. Phys., Inst. of phys. Chi. Acad. of Sci., Beijing BOE Electron Materials Institution, Beijing a b c liugy123@126.com, chunyiz@sohu.com, shxia@mail.ie.ac.cn, d jgzhanghli@yahoo.com.cn, e lihongyan@boe.com.cn, f jiuxiayang@boe.com.cn, g egwang@aphy.iphy.ac,cn Key words: Carbon nanotubes (CNT s). Multiwall carbon nanometer tubes (MCNT s). Field emission array (FEA). Field (or Bias) assistant hot filament chemical vapor deposition (FA HF-CVD). Gated CNT s/fea. Flat panel character display tube ( FCT). Abstract A large area perfect aligned carbon nanotubes (CNTs) thin film was grown directly on a stainless steel substrates by a low cost bias-assisted hot-filament chemical-vapor deposition (BA HF-CVD) technology. The CNT s / stainless steel field emission array (FEA) cathode (CNT s/fea) has been fabricated. The field electron emission behavior of the CNT s/fea cathode was characterized in a vacuum condition, a high electron emission of about 10mA/cm 2 at a low electric field of 4V/μm implies the promising the application as a cathode of the flat panel display device, so further assembled this cathode in a kind of vacuum device, and the possibility of the operation from a flat panel character (Pictures) display tube FCT has been tested initially. 1. Introduction Carbon nanotubes (CNT s) is a new substitute of field electron emission material in the field of vacuum microelectronics which has been attracted much attention in the last decade. Up to now, as a bright star in the field of the field emission array (FEA), the CNT s have already been able to synthesize by various techniques, but if for low cost purpose, means for industry and for a real-life device, or consider its application, we need to try to find out still, especially about its technologies first. In order to seek a low cost, being suitable for industry produce s fabrication method of CNT s thin film, meanwhile to solve a problem of controllable growth at certain parts of a substrate without using the large scale integrate (LSI) process, a matchable with glass metal electrode material type stainless steel has been choose and treated as the substrate [1] of growing directly CNT s, a modified version of the HF-CVD - bias assisted hot filament chemical vapor deposition (BA HF-CVD) method [2] has been chosen for growing directly CNT s thin film on certain parts of the stainless steel sheet electrode. A structure of non-gated carbon nanotubes field emission array CNT s/fea electron source has been performed after several special steps of growing CNT s inside the reaction chamber of BA HF-CVD. A perfect aligned CNT s thin film has been synthesized on the requisite parts of stainless steel electrodes. The electron emission characteristics in vacuum has been investigated and the typical morphologies of obtained CNT s / FEA samples has been determined. Finally we assembled the CNT s / FEA into a fully sealed glass vacuum flat panel character (picture) display tube (FPC), further tried the CNT s/fea s application in the industry. 2. Experimental 2-1. Preparation for the substrate All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-09/05/16,06:55:52)

2 1042 Nanoscience and Technology The structure of a whole glass device demands a matchable sealing between the glass envelopes and the metal electrode, it means that two materials should have basically near expansion coefficient, so that to guarantee to a sealed whole glass tube. As revealed by our works on the preceding years [1], the CNT s were able to be grown successfully on the surface of the 309 type stainless steel plate in no catalyst condition by microwave plasma chemical vapor deposition (MP-CVD), now what we need to try, just to change the MP-CVD method into a low cost BA HF-CVD method, but we must to keep the situation in no catalyst, means growing directly. Finally, the surface of the original 304-type stainless steel sheet don t need to polish, its surface was with high smooth finish, just need to cut into a suitable size and shape of the cathode according to the structure of the character tube and the demand of device s processes. Our design is : rectangle of mm 2. All its edges and angles need to smooth. Make a thorough cleaning before using Growth directly of the CNTs on the substrate of cathode Gas mixer H 2 O Gas Sources G as inlet 2 C ham ber 3 A node 4 F ilam ent 5 View window 6 S am ple 17 Drain valve 7 C athode 8 Insolate plate 9 H older 10 V acuum gauges 11 H igh vacuum valve 12 DC Power supply 13 DC Power supply 14 Therm ocouple 15 M illivoltm eter 16 M echanical pump 18 Flange plate 19 B ell jar 20 Flow meter 21 Valve 22 Gas mixer Fig.1 Schematic diagram of a low cost BA HF-CVD equipment A simple and low cost field (bias) assisted hot-filament chemical vapor deposition (BA HF-CVD) technology was employed to grow a high aligned multiwall carbon nanotubes field emission array thin film. Fig.1 depicts an approximately diagram of our apparatus. In the reaction chamber an metal molybdenum (Mo) anode plate was installed above the filament, the filament is made by a tungsten filament of diagramφ=0.3mm. The N 2 was used as the work matter, its purity is %, and the CH 4 was used as reactive gas, its purity is 99.9%. The plasma is generated through the direct current discharge. The characteristic of the discharge is with a low electric field intensity in plasma (~ 10V/cm), the electric field intensity rate of the gas pressure in the reaction chamber is in low, the thermal ionization is the key in the ionization mechanism, it means the collision process of the particle take a main effect, and the electron temperature is close to the ion temperature and the atom temperature.. Tab.1 the growth conditions of the CNTs/ FEA Background pressure (Pa) Reactive pressure (KPa) Gas flow rates of N 2 :CH 4 (sccm) Time for surface etch (min.) Bias on Cathode & anode (V) Temp. of filament ( 0 C) Growth time (min.) / The growth condition of the CNT s/ FEA is shown on Tab.1 Its process is: after the reactive chamber was pumped to 1Pa, vacuum system was backfilled to 1.9 kpa from the N 2 gas source first, raised up the temperature of the filament to C, bias

3 Solid State Phenomena Vols on the cathode and the anode through a DC power supply (500V 1A) into generating a direct current plasma discharge inside the reactive chamber, kept the plasma to etch the surface of the stainless steel for 5 minutes first, so that we can get a thorough clean, then filled a mixture of CH 4 and N 2 according to the flow rates of 100:5, kept the plasma to grow the CNTs for 30 minutes, went out, finally drew the cathode after cooling thoroughly Investigation of the structure and the field electron emission behavior of CNT s-fea We have examined the morphologies of obtained the MCNT s / stainless steel cathode samples by a Hitachi S-4000 scanning electron microscope (SEM) at 20KV. The typical morphology of MCNT s nanotube is shown in Fig.2. As showing, the morphology of the MCNT s nanotube grew by the BA HF-CVD method is no obvious difference with the morphology of the MCNT s nanotube grew by the MP-CVD method [1]. A high aligned and vertical to the substrate, the tube diameters of nm MCNT s thin film was synthesized with more uniform diameter, it is suitable to fabricate the MCNT s/fea cathode, moreover the sample was clearer, a few of the noncrystalline carbon and nanometer carbon particle, no need the purification treatment, but some caps covered on the CNT was discovered, we considered it was Fe nano-particle, and it was formed in initial stage of CNT growing. Fig.2 Scanning electon micrographs of a CNT s/fea cathode made of MCNT s which are grew directly on a stainless steel plate electrode For several CNT s/fea cathodes, we investigated its field emission properties. The experiments were performed at room temperature in a high vacuum of 10-3 Pa, test diode operated at an electrode structure of plane parallel, the diameter of the anode is 1.5mm, put it at a distance of 0.5 mm from the cathode, applied the DC voltage on between the anode and the cathode, the I-V properties for the MCNT s/fea cathode is shown in Fig.3. Low threshold electric field and fairly high electron emission current were obtained The stainless steer electrode coating with CNT s was suitable for the field emitter of vacuum devices, the threshold electric field for the CNT s /FEA grew in a temperature of C is 2.5 V/μm,and under the electric field intensity of 4 V/μ m, the electron emission current density is 10mA/cm Application research of CNT s/fea By using of a basic method the same with ref.[3], a new structure of a small fully sealed glass flat panel character tube FPC with the cathode of CNT s/fea has been manufactured. On the screen of the FPC, the character is in blue color, the background is the white color. A photograph of finished FPC tube has been shown in Fig.4. Its size is cm 3, details in ref.[4]. All the vacuum operating for total about 15 FPC glass tubes have been done in batchs during [3]. Two kinds of characters including the English, the Chinese and a kind of picture have been displayed in two colors. The possibility of operating CNT s / FEA for a flat panel character display tube FCT has been tested initially.

4 1044 Nanoscience and Technology Current(nA) Ln ( l 2 / V ) /V Electric field (V/µm) Fig.3 Emission current vs. applied electrical field for the CNT s/fea and the corresponding FN plot Fig.4 Photographs of fully sealed glass flat panel character(picture) tubes 3. Summary 1.This novel method of creating carbon nanotubes field emission array CNT s / FEA on certain parts of the substrate electrode has been proved, this CNT s / FEA was able to produce a vacuum electron emission with the turn on electric intensity of 2.5V/μm and the emission current density of 10mA/cm 2 under the electric intensity of 4V/μm without any further processing beyond growing of BA HF-CVD. The emission level is enough to operate the flat panel character display tube FPC, meanwhile this method is in low cost. 2.The structure of the CNT s / FEA sample is able to provide the FPC with its assembling, based on the CNT s / FEA, all the fully sealed glass FPC tubes has been assembled successfully. 3. Three kinds of character (picture) have been displayed under static state work condition. Acknowledgements The research is sponsored by the NSFC (Project No , No: ). We thank G.Y.Yin, C.Z.Fan, B.R.Shun from Tsinghua Univ.at Beijing100084, Y.G.Ding,R.Q.Zhao, X.H.Liao,Y.Q.Zhen from IECAS at Beijing , Z.X.Shen, J.X.Ye from BOE at Beijing , Y.J.Lu from PRIABS at Beijing for technical assistance. References [1] G.Y.Liu, D.Y.Zhong, S.H.Xia, et al., Applied Surface Science, 2003, 215: [2] X.D.Bai, Q.L.Guo, E.G.Wang, et al., Appl. Phys. Lett.,2000,76(18): [3] G.Y.Liu, S.H.Xia, Y.J.Lu et al., Chinese Journal of Liquid Crystals and displays,2001,16(4): [4] H.Y.Lee,G.Y.Liu,J.S.Wu et al., Proc. of international new display technique conference, one of 7th Beijing science & technology exchange activities, Beijing electron society, Beijing, China, 9-10,Octuber,2004 :

5 Nanoscience and Technology / Preparation of a Low Cost Carbon Nanotubes Field Electron Emission Thin Film and its Initial Application Research /