Flip-chip design for coupling ultra-clean carbon nanotubes to surface acoustic waves

Hybrid quantum systems require the integration of multiple materials with complementary functionality into a single device. Since materials have unique fabrication constraints (deposition, lithography, thermal processing etc.), it is sometimes necessary to build components on separate chips. The components can then be coupled using a flip-chip geometry that sandwiches the two chips together. Recent success with flip-chip devices include ultra-clean gating of 2DEGs [1], generation of acoustoelectric current in graphene [2], and coupling of superconducting qubits with a bulk acoustic-wave resonator [3]. 

 

In our work, we combine ultra-clean suspended carbon nanotubes (CNTs) with surface acoustic waves (SAWs). We designed our flip-chip geometry to maintain a 250-nm air gap between the CNT and the SAW. We control the air gap distance using lithographically defined spacers and verify the air gap distance with optical interference and capacitance measurements. Our method of gluing the chips eliminates the need for mechanical clamps. Electron-beam lithography is used to fabricate interdigitated transducers for short-wavelength SAWs (240-nm wavelength) on LiNbO3. We use capacitive coupling to feed RF signals from the carbon nanotube chip to the SAW transducers. In this poster we report on the fabrication and characterization of our first devices.

[1] A. J. A. Beukman, F. Qu, K. W. West, L. N. Pfeiffer, et al., A Noninvasive Method for Nanoscale Electrostatic Gating of Pristine Materials, Nano Lett. 15, 6883 (2015).

[2] J. R. Lane, L. Zhang, M. A. Khasawneh, B. N. Zhou, et al., Flip-Chip Gate-Tunable Acoustoelectric Effect in Graphene, J. Appl. Phys. 124, 194302 (2018).

[3] Y. Chu, P. Kharel, T. Yoon, L. Frunzio, et al., Creation and Control of Multi-Phonon Fock States in a Bulk Acoustic-Wave Resonator, Nature 563, 666 (2018).