Novel low-temperature variable inductors using porous anodic alumina

In this study, the authors study the benefits of using porous anodic alumina (PAA) as a new material to develop tunable RF micro-electro-mechanical systems (MEMS) inductors. To the authors knowledge, this is the first time that PAA material is proposed and successfully used as a structural material for MEMS devices and for fabrication of tunable inductors. The authors explain the fabrication process for producing tri- and bi-layer of PAA/aluminium or PAA/gold. These structures are used as thermal actuators to provide tunability for the inductor. The PAA layer is fabricated using an inexpensive simple procedure at a low-temperature process of 80°C. The experimental results for a tri-layer of Al-PAA-Al inductor exhibits a measured wide tuning range of 31% with inductor variation of 6.5-8.5 nH at 3 GHz and a quality factor of 6 on low-resistivity Si substrate. To improve the quality factor, bimorph layers of gold and PAA are fabricated on alumina substrates. The quality factor has greatly improved. A peak quality factor of over 20 with a tuning range of 18% is demonstrated.