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

隧道发射极有望作为微米级真空管集成电路中的微型冷阴极。因此，到目前为止，许多研究人员都在研究MIM或MIS隧道发射极的制备和操作。但是在这些情况下，非晶氧化物绝缘体膜通常用作隧道势垒层。另一方面，碱土氟化物薄膜可以异质外延生长在Si衬底上，作为绝缘膜具有上级电学性能。为了提高MIS隧道发射极的效率，在n型Si（111）衬底上用BaF_2薄膜作为晶体隧道势垒绝缘层。实验结果如下：（1）采用真空蒸发技术，在化学清洗后的n型Si（111）衬底上，在不同的衬底温度下沉积了BaF_2薄膜。利用X射线衍射仪（XRD）和扫描电子显微镜（SEM）分别对薄膜的结晶质量和表面形貌进行了表征。在室温至700 ℃范围内，随着沉积温度T_S的升高，BaF_2薄膜的结晶度提高，XRD测量表明，在400 ℃以上，BaF_2薄膜的晶体生长为（111）取向。(2)在宽度为1 mm的BaF_2绝缘带上淀积厚10 nm、宽1 mm的Au对电极，并用SiO_2绝缘层修整，制成发射面积为1 mm × 1 mm的十字型MIS二极管。测量了不同BaF_2沉积温度下MIS二极管的I-V特性。二极管电流击穿电压随BaF_2沉积温度T_S的升高而增大。(3)测量了在T_S=700 ℃下淀积的平整、结晶性好的BaF_2薄膜上制作的隧道发射极的电子发射。在BaF_2厚度为120 nm，二极管电压Vd =5V的条件下，获得了皮安/mm^2量级的电子发射电流密度。

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.