Development of Nitride and Carbide Cathodes for Realization of Highly Stable Vacuum Micro Electron Sources

我们研究了过渡金属氮化物和碳化物薄膜作为高稳定真空微电子源阴极材料的潜力。首先，在单晶硅衬底上沉积了HfN、VN、TaN、ZRC、HFC、Vc、NbC、TaC、Cr3C2、WC薄膜。用高灵敏度的质子和氦离子束的背散射测量了氮和碳的组成。研究了阴极的结晶度、取向、功函数、电阻率等重要参数随组成的变化规律。结果表明，除VN外，氮化物薄膜的功函数大多为4.7 eV-4.8 eV，而碳化物薄膜的功函数相对较高，为438 eV-5.2 eV。在间隙为1.5μm的超高真空中研究了平板样品的电子发射特性，获得了电流-电压特性和短期稳定性。借助于我们原来的S-K图评判法，我们判定HfN、Tan、Vc、Cr3C2的一些材料被提名为下一次考试的候选人。其次，我们研究了取向与电流稳定性的关系，发现(111)取向的薄膜具有比(100)取向更好的性能。此外，还研究了与阴极寿命密切相关的抗氧化性，发现氮化物比碳化物具有更高的抗氧化性。考虑到上述所有结果，可能的候选者之一是(111)取向的HFN薄膜。为了给出最终的判断，我们制作了硅场发射阵列，在其上沉积了(111)取向的HFN薄膜，并测试了其电子发射性能。与目前研究人员已经测试过的NBN场发射阵列相比，测试并不能显示出更好的性能。结果表明，目前最佳材料为NBN。

We have investigated the potential of transition metal nitride and carbide thin films as a cathode material for highly stable vacuum micro electron source. Firstly, thin films of HfN, VN, TaN, ZrC, HfC, VC, NbC, TaC, Cr_3C_2, WC were deposited on flat silicon substrates. Composition of nitrogen and carbon were examined using backscattering of proton and helium ion beam with high sensitivity. Properties of crystallinity, orientation, work function, electric resistivity, which are important parameters for cathodes, were investigated as a function of composition. As a result, it was found that the work function of nitride films (except VN) were mostly 4.7eV-4.8eV, while that of carbides were relatively higher 438eV-5.2eV. Electron emission properties from flat sample were investigated in ultra high vacuum with the gap spacing of 1.5μm. Current-voltage characteristics and short term stability were acquired. With an aid of our original evaluating method of S-K chart, we judged that some materials of HfN, TaN, VC, Cr_3C_2 were nominated as a candidate for the next examination. Secondly, we investigated the relationship between the orientation and the current stability, and found that (111) oriented films had the properties superior to (100) oriented ones. Also resistance against oxidation, which is closely related to the life of the cathode, was examined and it was found that nitrides are more resistive than the carbides. Taking all the results described above into consideration, one of the possible candidates was found to be (111) oriented HfN film. To give final judge, we fabricated silicon field emission array, on which we deposited the (111) oriented HfN film and examined its electron emission properties. The test could not show better performance as compared to NbN field emission array, which has already measured by the present researchers. The results showed the best material at present is NbN.