Effects of applying stress on the electron field emission properties in amorphous carbon thin films

Abstract

Diamond-like carbon ͑DLC͒ films have always had high intrinsic stress due to their metastable structure and the fine balance between film density and bond stability. We show the effects of high intrinsic stress on the electron field emission performance, where a lower electric field for emission is recorded with increasing stress in the DLC films. In addition to examining "as deposited" films with different magnitudes of intrinsic stress, we subject the DLC films to external pressure by physically bending the a-C / silicon substrates. The result is a phenomenon where electrons are "squeezed" out of the films, and can be applied to the fabrication of stress sensors. © 2005 American Institute of Physics. ͓DOI: 10.1063/1.1940129͔Amorphous carbon ͑a-C͒ thin film research has attracted enormous interest for the last two decades due to its unique properties 1 and possible application as cold cathodes for electron field emission. 2 However, the ability of a-C thin films to possess high intrinsic stress has been undesirable, particularly in view of microelectromechanical system applications. In fact, a-C films with intrinsic stress values ͑ϳ12 GPa͒ of almost one order of magnitude higher than those found in other amorphous materials ͑Ͻ1 GPa͒ such as a-Si, a-Ge, or metals have been reported. Excessive stress on thin films can cause adhesion problems where the film delaminates from the substrate. The presence of high stress on a-C has been reported to have induced changes in the electronic properties such as electrical conductivity. 3 The a-C films with high sp 2 concentrations ͑ϳ90% ͒ can have high intrinsic stress and a local density close to those found in tetrahedral amorphous carbon ͑TAC͒ thin films. 1 The high compressive stress in these graphite-like a-C ͑GAC͒ films is a result of the ion bombardment during the deposition process that "knock-on" carbon which subimplant into the films and thus create regions of high stress. 4 This results in the densification of the films which increase the local density. It is known from theoretical studies that by applying pressure ͑stress͒ to a material one can modify its electronics properties, e.g., band structure, resistivity, position of Fermi level. 5,6 The influence of internal pressure on the electron emission properties of nanocomposite thin films which contain nano-graphite has been reported by Poa et al. 7 in which by varying the deposition conditions, the properties of the nano-graphite as a function of stress were studied. The observed low threshold field was explained by the amount of intrinsic stress induced within the carbon matrix. Basically, the variation in field emission characteristics with intrinsic stress can be driven by two effects: ͑1͒ band structure modifications in the film and ͑2͒ increases in local density within the film. In both cases, the beneficial effect is the lowering of field emission threshold fields and/or increasing the electric field enhancement factor. Due to the dielectric mismatch within the carbon films, electric field lines terminat...

Influence on the Proprieties of PET Coated Diamond-Like Carbon Film for Different Preparing Condition by PECVD

“…Diamond-like carbon (DLC) has been used in a number of application such as hard coating for tools, cold cathode electron emitters, micro-electro-mechanical systems (MEMS), car parts and protective coating in hard disk drives. These applications are mainly associated with the high hardness and low friction coefficient of DLC [1][2] . One of the attractive properties of the DLC film is their gas barrier property.…”