Single-Chip Multi-Frequency Radio Frequency Passive Components Based on Aluminum Nitride Cross-Sectional Lamé Mode MEMS Resonators
The advent of carrier aggregation has increased the requirements on filtering in LTE-Advanced (LTE-A) handsets. In this context, the development of lithographically-defined integrated filters is essential to replace off-chip components currently adopted in commercial platforms and to enable the implementation of miniaturized adaptive RF front-ends. In addition, the development of on-chip matching networks is highly desirable in order to maximize the power-transfer, from filters to antennas and vice versa, for any possible operative scenario. This talk will discuss a new class of monolithic integrated radio-frequency (RF) passive components based on the recently developed Aluminum Nitride (AlN) MEMS Cross-Sectional Lamé-mode Resonator (CLMR) technology. Differently from any resonator technology demonstrated to date, CLMRs rely on a coherent combination of the ¬e31 and e33 piezoelectric coefficients of AlN to transduce a 2-dimensional (2D) mechanical mode of vibration, which is characterized by longitudinal vibrations along both the width and the thickness of the AlN plate. This feature enables the implementation of AlN CLMRs with high values of electromechanical coupling coefficient, kt2>7%. In addition, due to dependence of such 2D mode on the lateral dimensions of the plate, CLMRs operating at significantly different frequencies can be lithographically defined on the same substrate without requiring additional fabrication steps. The capability of achieving high FOM (kt2?Q), comparable to the ones of commercially available AlN FBAR devices, and multiple operating frequencies on the same chip without additional fabrication costs (lithographic tunability of the resonance frequency), makes this technology one of the best candidate for the implementation of monolithic integrated contiguous and not-contiguous filters for platforms adopting carrier-aggregation (CA). Our group has recently exploited these unique features for the experimental demonstrations of several prototypes with groundbreaking performance: (1) CLMRs operating between 700 MHz and 1 GHz showing kt2 and FOM in excess of 6.2% and 145, respectively, which are the highest ever demonstrated in AlN resonators operating in the same frequency range; (2) CLMR ladder filters operating around 900 MHz, fabricated on the same silicon substrate and showing a fractional bandwidth (BW3dB) as high as 4% and an insertion loss as low as 0.4 dB; (3) a Cross-Sectional Lamé-Mode Transformer (CLMT), showing a record-high open-circuit voltage-gain in excess of 39, which is suitable for the implementation of low-loss narrow-band matching networks and voltage-amplification stages in miniaturized AC-to-DC and DC-to-DC converters.