Developments in Ceramic Materials Research

Field Emission Display on Ceramic 255
In this figure, the curve shows a gate potential voltage ramped from 80 V up to 150 V,
with increment of 1 V in step. The leakage current value was far below 1% of the emission
current value for the whole course, indicating a good quality of the dielectric insulating layer.
Field emission can be described in physics by the Fowler-Nordheim equation [37], which
can be written in a simple form as:
I = aV
b
−
2 V
e
(1.1)
where I – emission current
V – applied electric field potential voltage
a and b are treated as constants that are related with the emitting area and geometric
factor of the emitter.
Equation (1.1) can be rewritten in another mathematics function as the following:
⎛
I ⎞ b
ln⎜ = − ln a
2 ⎟
⎝V
⎠ V
(1.2)
Ideally plotting ln(I/V 2 ) versus 1/V should yield a straight line. In fact, this linear form of
Fowler-Nordheim plot is widely used in practice to distinguish field emission mechanism
from other electron emission mechanisms. Converting the I-V curve into the function ln(I/V 2 )
versus 1/V gives Fowler-Nordheim plot. Figure 8 (b) shows the Fowler-Nordheim plot
version of the I-V curve in Figure 8 (a). The linear curve proves the nature of field emission
mechanism from the micro field emitters.
To use the micro field emitters for display application, it is important to study the
emission stability and life time characteristics. In the stability test, individual pixel of the
micro field emitters was randomly chosen and was applied to a fixed gate potential voltage
while the emission current was monitored over a period of time. A LabView test graph
showing an emission current trace for a length of 17.5 hours from a pixel is illustrated in
Figure 9. The data were acquired after a preliminary tip cleaning process at a high emission
current of ~8×10 -5 A by keeping the gate voltage at 155 V for 30 seconds, followed by
reducing the gate potential down to a lower value of 150 V for this life time test. The
emission current and the leakage current data were collected, averaged and stored in memory
every minute under the control of the automatic data acquisition system. The leakage current
value is well below 1% of the emission current over the entire test period, indicating a high
quality SiO2 insulating layer.
In order to investigate the uniformity of emission current from the micro field emitters on
ceramic substrate, a comparison study with micro field emitters on silicon wafer was
performed. To do this, an identical fabrication procedure to produce micro field emitters on
ceramic substrate was applied to silicon wafers. The wafers were diced into the same
dimension as the ceramic substrate. After a surface cleaning treatment, a thin dielectric layer
of SiO2 was deposited using PECVD onto the silicon substrates to insulate the surface. Then
the silicon substrates went through the same batch process along with the ceramic substrates
for micro field emitters’ fabrication.