Developments in Ceramic Materials Research

Field Emission Display on Ceramic 243
the phosphors of a pixel to create an image, as a result the panel thickness can be reduced
down to several millimetres [4]. Another advantage of a FED structure over a CRT is the
reduction in the number of drivers by a factor of three (one single emitter sends electrons
towards a sub-pixel which is successively red, green and blue).
Field Emission Display Technology and Advanced Ceramics Technology
For an electron to leave a material, the electron must gain energy to exceed the work
function, which is a potential barrier at the surface of a metallic conductor that binds electrons
to the material. This can be accomplished in a variety of ways, including thermal excitation in
the case of thermionic emission, electron and ionic bombardment in the case of secondary
electron emission, and the absorption of photons in the case of photoelectric emission. Field
emission differs from all these forms of electron emission in that the emitted electrons do not
gain an energy which exceeds the material’s work function.
Field emission phenomenon results from the tunnelling of electrons from a metal or a
semiconductor into the vacuum under an application of a strong electric field. The high
electric field applied to the vicinity of the surface of a substance to low and thin the potential
barrier on the surface, so that free electrons with high potential energy inside the substance
can have possibility to tunnel through the thinned potential barrier and leave the surface.
Since there is no heat transfer involved in the electron emission, field emitters are called cold
cathode electron source [5]. To achieve a low operating voltage of a cold field emitter, in the
case of a micro tips based FED, the tips are manufactured into very sharp form so that the
local electric field strengths become high enough for even a moderately low voltage applied
to the adjacent gate electrode [6]. Using a low work function material could also significantly
reduce the turn on gate voltage for a field emitter. The most popular low work function
material for forming a micro tip is molybdenum [7]. The micro tip field emitter fabrication
technique was initially invented by Dr. Charles A. “Capp” Spindt at the Stanford Research
Institute (now called SRI International) in 1968 [8]. The principal component of a Spindt
cathode comprise a basic triode structure: a bottom cathode conducting layer, on which
molybdenum micro tips in conical shape reside; a top gate conducting electrode layer, and an
insulating oxide layer in between [9]. In the fabrication process, molybdenum cones with tip
radii less than 30 nm are deposited by electron beam evaporation into the emitter wells. The
cone forming process is self aligned. The advantages of such a structure include the high
electron drawing efficiency since the electron emission portion is arranged in the vicinity of
the centre of gate electrode where the electric field is most concentrated, the in-plane
uniformity of drawn current is high, and the directivity of electron emission is regular,
compared to the other field emission device.
Spindt’s development stimulated the technology further into a concept to use field emitter
arrays in a matrix addressed display (FED) conceived by the SRI team of which Spindt was a
member, and patented by M. E. Crost, K. R. Shoulders and M. H. Zinn in 1970 [10]. By
1972, the SRI group had overcome more engineering problems to demonstrate to their
satisfaction that it was feasible to manufacture FEDs [11]. Their new fabrication methods
were patented by C. A. Spindt, K. R. Shoulders, and L. N. Heynick in 1973 and 1974 [12, 13,
14]. However SRI was unable to obtain funding to develop the FED concept in the decades of
the seventies and early eighties. The idea was picked up and the initiative to develop the