PTFE-SiO_(2)复合涂层电子发射特性及抑制放电

Electron Emission Characteristics and Discharge Suppression of PTFE-SiO_(2) Composite Coating

目的调控空间电子器件有机介质聚四氟乙烯(PTFE)表面的二次电子发射系数(SEY)接近1,以降低表面电荷沉积速率,减少静电放电(ESD)的发生。方法通过磁力搅拌将PTFE分散液和SiO_(2)粉末混合均匀,制备不同浓度配比的PTFE-SiO_(2)混合溶液,将混合溶液旋涂在覆铜板表面,在80℃烘箱中加热4h得到复合涂层。利用扫描电子显微镜(SEM)对涂层表面形貌进行观察,采用局域漏电流法对复合涂层的二次电子发射系数进行测试,通过MATLAB对表面电势进行仿真计算,在SEM中对复合涂层放电特性进行测试。结果从SEM图可以看出,随着SiO_(2)浓度的增大,复合涂层表面SiO_(2)颗粒变得密集。从SEY测试结果可以看出,在SEY>1的能量区间内,复合涂层的SEY随SiO_(2)浓度的增大而逐渐降低,当SiO_(2)质量分数大于15%后,涂层的SEY基本保持不变;在SEY<1的能量区间内,当SiO_(2)浓度为15%时,复合涂层的SEY达到最大值。表面电势仿真计算结果及放电测试结果显示,复合涂层能有效降低表面电荷沉积速率及增大放电阈值。结论当SiO_(2)颗粒质量分数为15%时,复合涂层SEY的调控效果最显著,SEY最大值从2.0变化到1.6,10keV能量下的SEY从0.6变化到0.8。当SiO_(2)颗粒质量分数大于15%时,复合涂层能有效降低真空器件PTFE表面电荷沉积速率,提高放电阈值,减少静电放电的发生。因此,这是一种有效提高航天器电子器件可靠性和工作时间的表面处理方法。

Polytetrafluoroethylene(PTFE)is widely used in spacecraft,but charge accumulation occurs when PTFE is irradiated by plasma because of its poor electrical conductivity,which is harmful to the device.To reduce the rate of surface charge accumulation and the occurrence of electrostatic discharge(ESD),in this paper,PTFE-SiO_(2) composite coatings were prepared by magnetic stirring,regulating the secondary electron yield(SEY)of PTFE close to 1 over a wide energy range.The PTFE dispersion and SiO_(2) powder were mixed by magnetic stirring,and the mixed solutions were spin-coated on the copper-clad plate,which was used to simulate a space electronics device environment.Then the composite coatings were obtained by heating at 80℃for 4 h,and their morphologies were studied with a scanning electron microscopy(SEM).Their secondary electron emission(SEY)properties were measured through the local leakage current method in the SEM.The surface potential was calculated by MATLAB and the discharge characteristics were tested in the SEM.The morphology of composite coatings showed that the surface roughness increased with the increase of SiO_(2) concentration,and the SiO_(2) particles were only partially exposed at low concentration.As the SiO_(2) concentration increased,the SiO_(2) particles changed from the tilt to the horizontality and then covered the PTFE.At the energy where SEY was greater than 1,the shading effect of SiO_(2) particles made the SEY of the composite coating decrease with the increase of SiO_(2) concentration when the concentration of SiO_(2) was less than 15%.When the concentration of SiO_(2) was greater than 15%,the shading effect was weakened due to the decrease of the tilt angle,which made the SEY no longer change with the concentration.At the energy where SEY was less than 1,the high SEY property of SiO_(2) made the SEY of the composite coating increase with the increase of SiO_(2) concentration when the SiO_(2) concentration was less than 15%.When the concentration of SiO_(2) was greater than 15%,the SEY decreased with the increase of concentration due to the decrease of the tilt angle and the shading effect,and finally tended to be the intrinsic SYE of flat SiO_(2).The calculation results of surface potential showed that the balance potential of negative charge was much larger than that of the positive charge,and was approximately equal to the difference between the incident electron energy and Ep2.When the SiO_(2) concentration was 15%,the equilibrium potential and the charge accumulation rate were the lowest,which were correlated with the maximum values ofσ10 and Ep2.The test of discharge showed that the composite coating could effectively reduce the surface charge deposition rate and increase the discharge threshold.In conclusion,the composite coating can regulate the SEY of PTFE close to 1 over a wide energy range and increase the Ep2 of PTFE coating.The high SEY property of SiO_(2) and the shading effect play a major role in modulating the SEY.The modulation effect of SEY is the most obvious when the concentration of SiO_(2) is 15%.The maximum SEY value changes from 2.0 to 1.6,and the SEY at 10 keV changes from 0.6 to 0.8.The composite coating can effectively improve the discharge threshold,and reduce the charge accumulation rate and the occurrence of ESD.Therefore,it is a very processing way to improve the reliability and service time of spacecraft electronic devices.