New directions in piezoelectric phononic integrated circuits: exploiting field confinement (SOUNDMASTER)

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The analogy between manipulating light and gigahertz (GHz) frequency acoustic waves in chip-scale platforms has been extensively explored, with ideas from silicon photonics, mainly strong geometric confinement and routing, being applied to acoustic waves to develop phononic integrated circuits (PnICs). It is important to note that while the light-sound analogy is generally applied to the strain field, acoustic waves in piezoelectric materials have a co-propagating electromagnetic (EM) field as well. This EM field, which oscillates at GHz frequencies, but is confined to acoustic wavelengths (~10^5 smaller), underpins the dominance of piezoelectric resonators and filters in radio frequency (RF) devices. Despite the advances made in PnICs in the past decade, the majority of piezoelectric devices, both bulk and surface wave based, still rely on weak transverse confinement and manipulation of quasi plane acoustic waves.This project seeks to answer the question: if one could actively control and manipulate these co-propagating EM fields in waveguide geometries with strong transverse confinement, what qualitatively new sensing and information processing paradigms can one enable?We show that by exploiting strong field enhancement in a PnIC platform, one can design resonant magnetic near field generators for electron spin resonance experiments that can improve the spin detection sensitivity by ~10^7, down to the thermal noise limit. In addition, by engineering acousto-electric interactions in waveguide geometries, acoustic phase shifters and mode-selective, non-reciprocal amplifiers can be realized that exert active control on acoustic wave propagation, and push active passive device integration to its limit, enabling a new class of devices for RF signal processing. To ensure these devices perform as expected, we also address the important question: can we get GHz frequency acoustic waves into and out of micrometre-scale devices with near-unity efficiency?