Epitaxially-grown Barium-Titanate-Silicon Heterostructures for Piezo-acoustic Quantum Devices

Piezo-acoustic cavities in quantum limits have technological advantages in processing and storage of quantum information. Coupling piezo-acoustic cavities to superconducting quantum devices can also lead to hybrid circuits that act as quantum memories or electromechanical transducers. However, this demands on chip integration of piezoelectric and superconducting materials with disparate physical and chemical properties. Here, we propose a path for on-chip integration of piezoelectric thin films via heteroepitaxy of barium titanate (BTO) on Si substrates. BTO is an ideal candidate for this application due to large piezoelectric and electro-optic coefficients that are maintained even at cryogenic temperatures. We demonstrate growth of highly crystalline BTO thin film on Si via pulsed laser deposition method. By changing the buffer layer composition we tune the crystalline orientation of the BTO thin films between (100) and (101). By performing low-temperature X-ray diffractometry, we confirm the absence phase transitions down to 12 K. We will complement these results with cryogenic dielectric constant measurements and high-resolution transmission electron microscopy.