微机电系统微米间隙的预击穿和击穿特性研究

为了预测和评估微机电系统(MEMS)中微电极结构的绝缘性能,采用MEMS加工工艺,制备了电极间隙为5～40 μm的金属铝薄膜电极,研究了试样在直流电压下的预击穿过程中电流-电压关系曲线以及击穿电压随电极间隙的变化规律,并利用扫描电子显微镜(SEM)进行了微电极表面的微观分析.研究结果表明:预击穿过程的电流-电压曲线说明,在击穿之前电流的变化主要包括自由带电粒子的定向迁移阶段、电流密度达到饱和阶段以及碰撞电离持续发展形成电子雪崩阶段；场致电子发射的Fowler-Nordheim曲线表明,当微电极的间隙大于5 μm时,其击穿特性仍然符合巴申曲线,与相关文献的研究结论一致；微电极击穿阈值均大于相同间隙的宏观金属电极的击穿阈值；微电极击穿后在阳极表面有坑洞产生,而在阴极表面存在溅射沉积现象.

Prebreakdown and Breakdown Characteristics of Micrometer Gap in Micro-Electro-Mechanical System Device

To carefully predict and evaluate the insulation characteristics for providing the guidelines of insulation design in micro-electro-mechanical system(MEMS) devices,the samples were prepared by etching insulation gaps measured from 5 μm to 40 μm.The pre-breakdown current-voltage curve and relationships between breakdown voltages and electrode gaps were measured on the test samples fabricated with aluminium film electrodes in standard MEMS processes.The electrode surface after breakdown was analyzed by scanning electron microscopy(SEM).The results show that the pre-breakdown current-voltage curve can be divided into three stages: free charged particles directionally migrate along electric field;the current density gets saturated;the impact ionization develops into electron avalanche continuously.Fowler-Nordheim plot verifies that for larger scale(>5 μm),the breakdown characters agree with Paschen curve and are consistent with the previous studies.However,the breakdown thresholds between micro-electrodes are greater than those between macroscopic metal electrodes.SEM analysis shows that anode surface becomes crater-like and the cathode surface is sputtered with metal.