A passband-corrected high rejection channel-select micromechanical disk filter

The introduction of a 39nm-gap capacitive transducer, voltage-controlled frequency tuning, and a stress relieving coupled array design has enabled a 0.09% bandwidth 223.4-MHz channel-select filter with only 2.7dB of in-band insertion loss and 50dB of out-of-channel interferer rejection. This amount of rejection is more than 23dB better than a previous capacitive-gap transduced filter design that did not benefit from sub-50nm gaps. It also comes in tandem with a 20dB shape factor of 2.7 realized by a hierarchical mechanical circuit design utilizing 206 resonant micromechanical circuit elements, all contained in an area footprint (sans bond pads) of only 600μm×420μm. The key to such low insertion loss for this tiny percent bandwidth is Q´s >8,800 supplied by polysilicon disk resonators employing for the first time capacitive transducer gaps small enough to generate coupling strengths on the order of (Cx /Co) ~0.1%, which is a 6.1× improvement over previous efforts. Defensive strategies built into the array-composite design hierarchy counter process variations via electrical stiffness tuning, and alleviate stress by allocating displacement-buffer devices to increase filter performance and yield. This filter is the first demonstrated that truly offers low insertion loss and high rejection channel-selection for ultra-low power communication front-ends targeted for autonomous sensor networks.