AlN field emission display

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.

Fig. 1. Schematic diagram of display structure using heavily Si-doped AlN.
Fig. 2. The photograph of the display during operation.

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