M.Sc Thesis

M.Sc StudentRabkin Tsvi
SubjectInfluence of Dielectric/Nanotube Interface on Carbon
Nanotube Field-Effect Transistors Charge Sensing
DepartmentDepartment of Nanoscience and Nanotechnology
Supervisor DR. Yuval Yaish


Carbon nanotubes and especially carbon nanotube field-effect transistors (CNTFET) are widely studied for various applications due to their sensitivity for surface conditions. One of the most promising applications of CNTFETs are sensing applications due to the remarkable sensitivity to charges. There are many examples for such applications -- gas detectors using carbon nanotubes for ammonia sensing or bio-sensors, in which biological linkers are attached to the nanotube and the recognition event between the analyte is sensed by the CNTFET.

The first challenge to overcome towards CNTFET-based sensors is to be able to fabricate these sensors in a large-scale reproducible process. Many efforts are invested in controlling carbon nanotube synthesis to produce high-quality single walled carbon nanotubes placed at a specific location, orientation and length. The following challenge is to be able to selectively sense specific charges, since CNTFETs are sensitive to all surface charges.

This work demonstrates large-scale fabrication of CNTFET devices for sensing applications and fabrication of optical sensing devices using conjugated polymers. Measurements of plain CNTFETs have shown that transfer curve shift alone is not sufficient for the sensing capabilities of CNTFET due to reversible charge injection from the CNT into the underlying dielectric layer. This charge injection can be responsible for the hysteresis phenomena widely reported in transfer curve measurements of CNTFETs, where the presence of other molecules such as water layers can modify the injection barrier. The suggested leaky-capacitor model predicts the time-dependent measurements where the effective gate potential of CNTFETs decay to zero in a time scale of hundreds of seconds.

This observation may imply that CNTFETs may not be suitable for long-duration switching purposes, due to this nanotube/oxide interface interaction. However, CNTFETs are excellent probes for understanding oxide trap generation, trap dynamics. In addition, there are other possible applications involving dielectric medium charge storage such as supercapacitors and memory devices.