Photomask-based integration process of low-defect suspended carbon nanotubes into SOI MEMS

A fully-developed photomask-based integration process is reported. The process can integrate suspended carbon nanotubes (CNTs) into micro-structures on silicon-on-insulator chips. The process features batch-compatible fabrication and post-growth metallization of suspended CNTs, which has never been demonstrated by any other processes. The post-growth metallization avoids deterioration of the metals at the elevated CNT growth temperature and enables mechanically robust double-clamped configuration. Two key steps ensure a significant reduction of the risk for damage or contamination of the CNTs during post-growth processing. SiO2 bridges were fabricated to physically support CNTs during the wet processing, and a protective Al2O3 layer (∼40 nm) was deposited to prevent resist contamination during lithography. The combination of these two steps enables the removal of the unprotected suspended segments of unwanted CNTs by oxygen plasma ashing, improving device yield by a factor of six. The electrically interfaced suspended CNT device possessed high CNT quality (D/G(+) intensity ratio of 1/224 in Raman spectroscopy) and good electrical properties, such as low device resistances as low as 105 kΩ and reduced gate hysteresis as low as 65 mV in ambient air. Measurements of eights devices indicate that the release step did not have a systematic influence on the device resistances.