单晶LaB_6场发射阵列的电化学腐蚀工艺

Electro-chemical etching method for single crystal lanthanum hexaboride field emission arrays

六硼化镧(LaB6)场发射尖锥阵列的刻蚀工艺是制备LaB6场发射阵列阴极的关键。在(111)面单晶LaB6基片上,用等离子体增强化学气相沉积法制备氮化硅层做掩膜,光刻后采用电化学腐蚀方法对基片进行刻蚀,得到具有一定高度的LaB6尖锥场发射阵列。讨论了单晶LaB6的电化学腐蚀机理。改变各种电化学腐蚀参数,包括电解液成分、电解液浓度、阳极所加电压,用电子扫描显微镜观察样品形貌。结果发现H3PO4是刻蚀单晶LaB6的理想电解液,它克服了过去电化学实验中经常遇到的尖锥各向异性问题。随着电解液浓度或阳极电压的增大,尖锥高度增加,但是基底表面变得更为粗糙。另一方面,阳极电压太小时,有横向刻蚀现象产生,不利于提高发射体的场增强因子。此外,在二极管结构中初步测试了LaB6尖锥场发射阵列的电流发射特性,在真空度2×10-4Pa、极间距离0.1 mm、阳极电压900 V下,发射电流达到13 mA。

The fabrication of LaBS field emission arrays is the key technology for manufacturing LaB6 field emission cathodes. Silicon nitride film was deposited as mask layer on the （111） single crystal LaBs substrate by plasma-enhanced chemical vapor deposition method, and then patterned to form an array of 4μm diameter silicon nitride disks by reactive ion etching method. Using these Si3N4 disks as hard masks, the underlying LaBS was etched to form tip field emission arrays by electro-chemical etching method. The etching mechanism was discussed, and the sample morphologies were investigated by SEM as the etching conditions changed. The experimental results indicated that Ha PO4 could overcome the anisotropic phenomenon usually occurred in previous electro-chemical etching experiments. The emitters would be higher with the increment of the H3PO4 concentration or anodization voltage, while the surfaces of emitters and substrate would be rougher. On the other hand, side-etching would occur when H3PO4 concentration was too low, which was not favorable for increasing the enhancement factor of field emitters. Further more, field emission properties of the fabricated LaB6-field emission arrays were measured using diode geometry at a base pressure of 2 × 10^-4 Pa. When the anode plate was applied 900 V and placed 0.1 mm above the cathode, the emission current was 13 mA.