Y. Taniyasu, M Kasu, and T. Makimoto
Materials Science Laboratory
Aluminum nitride (AlN) is a wide-band-gap (6.2 eV) semiconductor.
Its electron affinity is nearly zero. Therefore, AlN is a promising material
for field emitters because electrons in materials with nearly zero electron
affinity can be easily extracted from the surface to vacuum. However, for
AlN, the reported field emission current is too low and the turn-on electric
field too high for device application. The reason is that the electron concentration
in the AlN samples is so low that the electrons necessary for field emission
can not be efficiently supplied to the surface.
Recently, we have achieved n-type conductive Si-doped AlN [1]. In addition,
we found that heavy Si doping is very effective in improving the field emission
properties of AlN [2]. This study demonstrates a triode-type field emission
display (FED) and presents the field emission properties of the heavily Si-doped
AlN in an actual device structure [3].
The display has a vertical triode structure consisting of the heavily Si-doped
AlN cathode, mesh grid, and phosphor coated anode screen as shown in Fig.
1. The electrons are emitted by applying grid voltage and then accelerated
by the anode voltage. The phosphor is excited by the electrons and emits luminescence.
The cathode current (field emission current), I, was detected at an electric
field strength of EG = 11 V/μm. Above this turn-on
electric field, the IC increased exponentially
with increasing electric field strength and reached 16 μA at EG
= 23 V/μm. We measured the stability of the cathode current against time
under the DC mode without a feedback circuit. The display showed a low current
fluctuation of 5.5 %. The high stability originates from the strong Al-N bond
strength.
Figure 2 shows photographs of the display during operation. The luminescence
area is almost the same as the opening area of the mesh grid. We observed
uniform luminescence with the brightness of 300 cd/m2, which is intense
enough for display application. During operation, the uniform and bright luminescence
was maintained over the entire field emission area. These results prove that
the heavily Si-doped AlN field emitter is very promising for vacuum microelectronic
devices.
[1] Y. Taniyasu, M. Kasu, and T. Makimoto, Appl. Phys. Lett. 85
(2004) 4672.
[2] M. Kasu and N. Kobayashi, Appl. Phys. Lett. 79 (2001)
3642.
[3] Y. Taniyasu, M. Kasu, and T. Makimoto, Appl. Phys. Lett. 84
(2004) 2115.
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Fig. 1.
Schematic diagram of display structure using heavily Si-doped AlN. |
Fig. 2. The photograph of the display during operation. | |