氧化铝表面二次电子发射抑制及其在微放电抑制中的应用

Secondary electron emission suppression on alumina surface and its application in multipactor suppression

空间大功率微波器件中的二次电子倍增现象会诱发微放电效应,使得器件性能劣化或失效.针对加载氧化铝的同轴低通滤波器进行建模,并通过微放电阈值仿真验证了降低放电敏感表面的二次电子产额(SEY)可有效提升器件微放电阈值.针对器件中易于发生微放电的氧化铝表面,应用激光刻蚀制备表面微结构,获得孔隙比例为67.24%、平均深宽比例为1.57的微孔结构,氧化铝SEY峰值(δ_(m))由2.46降低至1.10.应用磁控溅射工艺研究氮化钛(TiN)薄膜低SEY特性,当N2与Ar流量比为7.5:15时,TiN薄膜δ_(m)低至1.19.在激光刻蚀微结构氧化铝表面镀覆TiN薄膜,实现表面SEY的剧烈降低,δ_(m)降至0.79.通过仿真电子束辐照氧化铝表面带电特性,分析了表面带电水平对SEY的影响规律,以及低SEY表面抑制微放电的物理机制.选取填充了纯度为99.5%氧化铝片的同轴滤波器进行验证,结果表明:微结构氧化铝表面镀覆TiN薄膜后,器件微放电阈值由125 W增加至650 W.研究对于介质填充微波器件微放电效应抑制机理分析具有重要科学意义,对于提高微波器件微放电阈值具有工程应用价值.

For the high-power microwave(HPM)components applied to the space environment,the seed electrons in the components may resonate with the radio-frequency electrical field and may further lead the secondary electron multiplication to occur,triggering off the phenomenon of multipactor.Multipactor deteriorates the performance of the components,and in severe circumstances,it is even possible to result in the failure of the components or the spacecraft.Alumina ceramic possesses good dielectricity,high hardness,good thermal isolation,low dielectric loss,etc.,so it is widely used in HPM systems including dielectric windows,and many other microwave components.However,alumina ceramic possesses a relatively high level of secondary electron yield(SEY or d),indicating that the devastating effect of multipactor discharge is likely to be triggered off inside the alumina-filled HPM components in the space environment.In this work,the model of alumina loaded coaxil low pass fillter is simulated to verify that reducing the SEY of the alumina surface is effective and necessary to improve the multipactor threshold.After that,we use several technologies to achieve an ultralow SEY on the alumina surface.Firstly,a series of microstructures with different porosities and aspect ratios is fabricated.The results indicate that the microstructure with 67.24%porosity and 1.57 aspect ratio shows an excellent low-SEY property,which is able to suppress the SEY peak value(dm)of alumina from 2.46 to 1.10.Then,various process parameters are used to fabricate TiN films on silicon sheets.Experimental results indicate that the TiN film achieves the lowest dm of 1.19 when the gas flow ratio of N2∶Ar is 7.5∶15.Thereafter,we deposit TiN ceramic coating onto the laser-etched microstructure samples,and an ultralow dm of 0.79 is finally achieved on alumina surface.Then we implement a qualitative analysis to explore the influence of surface charge on the secondary electron emission and multipactor for the microstructured alumina surface,discuss the mechanism of low-SEY surfaces mitigating unilateral and bilateral multipactor.For verifying the actual effect of low-SEY technologies on the suppression of multipactor,we use the technologies of constructing microstructure and depositing TiN films on the alumina surface which is filled in the designed coaxial low pass filter.Finally,we obtain a significant improvement in the multipactor threshold for the filter,which increases from 125 W to 650 W,and the improvement is 7.16 dB.This work develops an effective method to reduce SEY for alumina,which is of great scientific significance in revealing the mechanism of multipactor for the dielectric-filled microwave components and also is of engineering application significance in improving the reliability of HPM components.