Design of silicon-based suspended inductors for UHF applications

We present technological procedures to obtain suspended inductors for UHF applications, where the dominant element is the so-called planar inductor. This element does not have, up to now, a high quality factor, Q, because, in the IC silicon approach, inductors suffer losses due to the conductive substrate. Therefore, the performance of a planar inductor is improved by eliminating the silicon substrate below the planar spiral (named bulkless inductor). Thus, in order to minimize photolithographic steps, we propose a suitable silicon etching procedure to increase the quality factor of planar inductors by using just 4 photolithographic steps. From simulation results, we obtained an inductance of 23 nH (5.85 nH per turn) that represents an augmentation of 750% when it is compared with a conventional planar inductor.