Chip-Scale Near-Field Resonant Power Transfer via Elastic Waves

This paper reports on the proof-of-concept demonstration of an approach for the synthesis of a through package charging and authenticating communication link enabled by GHz-range aluminum nitride (AlN) piezoelectric transducers. The acoustic link is formed by two thickness-mode acoustic transducers placed on the two sides of a packaging substrate. The link leverages the enhancement of energy transfer that occurs at resonance; 1-μm-thick (2.7 GHz) and 6-μm-thick (500 MHz) AlN acoustic links are demonstrated showing substantial enhancement of power transfer efficiencies (PTE) when using thicker AlN substrates. PTEs of -8 dB at 2.7 GHz and -2 dB at 500 MHz are measured for transducers' size of 1×100 × 100 μm
³
and 6×100 × 100 μm
³
through 700and 500-μm-thick silicon substrates, respectively. The experimental values are in very close agreement with the analytical model of the acoustic link. The potential misalignment between the two transducers is the main limitation of this approach. To overcome this challenge, acoustic phased arrays are devised to enable steering of the transmitted beam. Preliminary results on the steering capability demonstrate about 8 dB of improvement in PTE via a two-element array when dealing with a 100-μm misalignment. This paper is the first step toward the development of next-generation high-efficiency and micro-scale power transfer units that could energize chips through packages.