Developments in Ceramic Materials Research

252
Li Chen
Figure 6. Molybdenum micro tips with gate structure.
Electrical Characteristic Study: Electrical Set up
Molybdenum micro field emitters belong to the vacuum microelectronics devices,
therefore it is vital to create a clean ultra high vacuum condition for these devices to work.
The electrical characterisation of the micro field emitters on ceramic was performed inside a
turbo molecular pump based ultra high vacuum system. A special designed mechanical jig
was built to mount the ceramic sample, and make the associated electrical connections to the
gate electrode and back contact electrode. A low voltage phosphor screen with a dimension of
2×2 inches was electrically insulated and physically separated from the micro field emitters
with a small spatial gap of approximately 2 mm. The phosphor screen is made of a piece of
glass, coated with a conducting layer of indium tin oxide, on which a thin layer of phosphor
power was coated. When the phosphor screen is powered up with positive high voltage
potential, it accelerates the negatively charged electrons towards it if electrons are emitted
from the micro field emitters. A schematic diagram showing the experimental set up is
illustrated in Figure 7. The back contact cathode electrode of micro field emitters was
electrically grounded to a common earth. The gate electrode and the back contact cathode
electrode were connected to a Keithley source meter model 2400, which provides a voltage
source supply to the device under test, and acts as a micro ampere current meter for the close
loop electrical circuit. In this case, any leakage current passing through the gate electrode and
the micro field emitter cathode electrode was monitored by the source meter 2400. To prevent
the source meter from short circuit in case of an un-predicted discharging event between the
gate electrode and cathode electrode, an external resistor was loaded in series between the
Keithley source meter 2400 and the gate electrode.