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

隧道发射极有望成为微米级真空管集成电路中的微型冷阴极。到目前为止，已经有很多研究者对MIM或MIS隧道发射体的制作和运行进行了研究。但在这些情况下，非晶态氧化物绝缘膜通常被用作隧道阻挡层。另一方面，碱土氟化物薄膜可以在硅衬底上异质外延生长，具有优异的绝缘膜电学性能。本实验采用n型Si(111)衬底上的BaF_2薄膜作为晶体隧道势垒绝缘体，以提高MIS隧道发射极的效率。本研究的实验结果如下：(1)采用真空蒸发技术在经过化学清洗的n型Si(111)衬底上沉积了不同衬底温度的BaF_2薄膜。用X射线衍射仪(X射线衍射仪)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分析。在室温tp 700ﾟC范围内，随着沉积温度T_S的升高，BaF_2薄膜的结晶度提高，在400ﾟC以上观察到(111)择优取向生长.(2)在经过SiO_2绝缘层修整的1 mm宽BaF_2绝缘带上沉积10 nm厚、1 mm宽的Au对电极，从而制作出发射面积为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着BaF_2沉积温度TS的升高而增大。(3)测量了在T_S=700ﾟC的BaF_2薄膜上制备的具有良好结晶性的平整BaF_2隧道发射体的电子发射。在真空(BaF_2厚度为120 nm，二极管电压V_d=5V)中获得了皮安培/mm^2级电子发射电流密度。

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.