  We investigate the prospects for micron-scale acoustic wave components and
circuits on chip in solid planar structures that do not require suspension. We
leverage evanescent guiding of acoustic waves by high slowness contrast
materials readily available in silicon complementary metal-oxide semiconductor
(CMOS) processes. High slowness contrast provides strong confinement of GHz
frequency acoustic fields in micron-scale structures. We address the
fundamental implications of intrinsic material and radiation losses on
operating frequency, bandwidth, device size and as a result practicality of
multi-element microphononic circuits based on solid embedded waveguides. We
show that a family of acoustic components based on evanescently guided acoustic
waves, including waveguide bends, evanescent couplers, Y-splitters, and
acoustic-wave microring resonators, can be realized in compact, micron-scale
structures, and provide basic scaling and performance arguments for these
components based on material properties and simulations. We further find that
wave propagation losses are expected to permit high quality factor (Q),
narrowband resonators and propagation lengths allowing delay lines and the
coupling or cascading of multiple components to form functional circuits, of
potential utility in guided acoustic signal processing on chip. We also address
and simulate bends and radiation loss, providing insight into routing and
resonators. Such circuits could be monolithically integrated with electronic
and photonic circuits on a single chip with expanded capabilities.
