ICMCTF1998 Session G8: Flat Panel Display Technologies

Field emission displays have emerged as a leading contender of low-power flat panel applications. As one of the promising field emission cathodes (FECs), diamond thin film has unique advantages over its conventional micro-tip counterpart because of the superlative physical and chemical properties of diamond and the simplicity of cathode manufacturing. Over the last year, FEPET Inc., one of the leading organizations in developing diamond RECs, has made tremendous progresses in its cathode emission performance, film processing, and understanding of the emision mechanisms. Currently, an emission site density (ESD) of 2 x 10^-5 sites / cm² and current density of 100 mA / cm² have been achieved at an extraction field of about 10 V / micron. We also developed a novel patterning process that allows emission patterning without applying any post - deposition processing to the film to degrade its emission properties. The improvement in film emission properties is found closely related to a diminished diamond peek and a strongly accentruated graphitic or amorphous carbon shift in the UV - Raman spectra. High resolution atomic force microscopy (AFM) analysis also showed an association of the emission sites with insulating - conductive - insulting regions of the surface.

With the achievable ESD today, diamond film FEC can already find many practical applications such as low to medium resolution displays and backlights for LCDs. For high resolution color displays, significant improvement in emission site density is still necessary and a substrate with high quality surface becomes indispensable. The use of high-temperature glass applied for polysilicon AMLCDs or a low-temperature diamond thin film deposition process needs, therefore, to be developed.

Amorphous carbon (a-C) thin films with its large area deposition capabilities and low threshold voltages for electron emission holds great promise as a future flat cathode material.

We have deposited hydrogenated a-C (a-C:H) and nitrogenated a-C (a-C:H:N) thin films at different self bias voltages, pressures and gas compositions using a capacitively coupled radio frequency plasma enhanced chemical vapour deposition system. The samples were annealed at various temperatures and their electrical conductivity and electron emission properties measured. The field emission properties of the samples are used to ascertain whether or not there is a correlation between the emission characteristics and the heat treatments performed. It is hoped that the heat treatment will help in conditioning cathodes without the need for current or voltage stressing.

Electron emission is observed at fields as low as 10 V/um. Lifetime tests show that the current turns off after a while, which is in keeping with the space charge interlayer model proposed for these films.

Diamond-like carbonfilms 5 - 15 nm thick were deposited onconductive n-Si and metal substrates using highly reproducible direct ion beam deposition from a RF ICP source ¹. Combinations of gases such as Ch ₄, CH ₄ -N₂, CH2 ₄ -N₂ -He we used to form plasma. The field electron emission of the films were examined as a function of deposition conditions and post-deposition surface modification by Ni ultrathin coatings. A specially designed high vacuum scanning tunneling-field emission microscope was employed for simultaneous mapping of the topography, work function and local field electron emission intensity. It was shown that the deposited DLC films demonstrated efficient field emission, and long-term stability. The results are interpreted based on band bending (built-in electrical field), and reduced electrical resistivity of namometer scale thick films along with the deviation of the resistivity over the surface

¹B. Druz et al., Surface and Coatings Technology 86-87 (1996) 708-714