Piezoelectric Cross-Sectional Lame Mode Transformer

INV-16025

 

The growing demand of service bands in miniaturized mobile platforms is leading to an increased need for reconfigurable passive components such as antennas and filtering networks for use with static devices currently employed in Radio-Frequency (RF) front-ends. Although several approaches have been discussed to vary the operation of passive components, within a significantly wide tuning range, reconfigurable passive networks still remain unused in commercial products because of the difficulties in preserving high-performance throughout the entire tuning range. This is mainly due to the inability of preserving good power transfer between reconfigured adjacent passive stages. Such a limitation would be surpassed if reconfigurable matching networks (RMNs) were also available. Although matching networks are commonly formed by lumped components, such as inductors and capacitors, or distributed elements (transmission lines), they can also be formed by non-reciprocal devices, such as transformers (TRs). However, as TRs are generally large and lossy, their use in low-power integrated applications has not to be taken into consideration so far. 

 

In this invention, Northeastern Researchers used a novel class of MEM piezoelectric transformers capable of achieving high open-circuit voltage-gain in excess of 100 (for quality factors greater than 2000) between input and output of 2-port Aluminum Nitride (AlN) cross-sectional Lame mode resonators (CLMRs). A CLMR consists of a thin AlN film sandwiched between two interdigitated metallic layers (i.e. IDTs) where adjacent electrodes are connected to opposite voltage polarities. CLMRs can achieve kt2 in excess of 7%, thus comparable to what demonstrated by commercial AlN film-bulk-acoustic resonators (AlN FBARs). CLMTs showing a larger displacement at the input port than that at the output port. As their insertion-loss is negligible, a lower displacement value at their output port must result in a larger voltage level (Vout) than that applied at the input port (Vin). Similarly, the introduction of mechanical asymmetries, such as the use of different strip sizes for the input and output portions of the IDTs, would also produce a discrepancy in the effective sound velocity relative to input and output ports, hence producing a voltage-gain. 

 

- Cross-Sectional Lame Mode Transformers (CLMTs) use the special characteristics of two-dimensional modes of vibration to achieve much larger Gv than those based on contour-modes of vibration in piezoelectric plates. 

 

- Integrated and miniaturized on-chip transformers

- Reconfigurable matching networks

 

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