Improvement of electron emission efficiency for MIS type tunnel emitter using crystalline insulator film.

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Tunnel emitter is expected as a miniature cold cathode in a micron scale vacuum tube integrated circuit. Then, many researchers have been studied the fabrication and operation of MIM or MIS tunnel emitter so far. But in these cases, amorphous oxide insulator films have been commonly used as the tunnel barrier layr. On the other hand, alkaline-earth fluoride films can be hetero-epitaxially grown on Si substrate and they have superior electrical properties as insulator film. In this experiment, in order to improve the efficiency of MIS tunnel emitter, BaF_2 film on a n-type Si (111) substrate was used as a crystalline tunnel barrier insulator. The experimental results of this study are as follows,(1) The BaF_2 films were deposited on the chemically cleaned n-type Si (111) substrates for various substrate temperature by vacuum evaporation technique. The crystallographic quality and surface morphology of the films were investigated by X-ray diffractometer (XRD) and scanning electron microscope (SEM), respectively. The crystallinity of the BaF_2 film improed as a increase of deposition temperature T_S in the range from room temperature tp 700ﾟC.The (111) oriented crystal growth were observed above 400ﾟC by XRD measurement.(2) A 10nm thick and 1mm width Au counter electrode was deposited across the 1mm width BaF_2 insulator strip which was trimmed by SiO_2 insulator, and hence a cross type MIS diode which have 1mm*1mm emission area was fabricated. The I-V characteristics of MIS diodes for various BaF_2 deposition temperature were measured. Diode current break voltage increased with increasing BaF_2 deposition temperature T_S.(3) The electron emission of the tunnel emitter which was fabricated on the smooth and having good crystallinity BaF_2 film deposited at T_S=700ﾟC was measured. Pico-Ampere/mm^2 order electron emission current density into the vacuum (where, BaF_2 thickness was 120nm and diode voltage V_d=5V) was obtained.