PECVD grown silicon nitride ultra-thin films for CNTFETs

As-fabricated carbon nanotube field effect transistors (CNTFETs) exhibit p-type nature. In this work, silicon nitride (SiN_x) films are deposited on CNTs to realize n-type CNTFETs. This method of fabricating n-type CNTFETs is advantageous as SiN_x film serves both as a passivation layer and as a top-gate dielectric. There has been extensive work done on SiN_x passivation phenomena previously, but very few have investigated the properties of ultra-thin SiN_x films with thickness less than 20 nm. In this work, the ultra-thin SiN_x films are deposited using plasma enhanced chemical vapor deposition (PECVD) method. This paper discusses the systematic investigation of the effect of PECVD process parameters such as flow rates of precursor gasses (NH₃, SiH₄), power of electrodes and deposition temperature on the properties of SiN_x films such as refractive index, dielectric constant and stoichiometry. The quality of the SiN_x thin films obtained is comparable with several reports that have investigated thicker films. Using these ultra-thin SiN_x films, we implement a CNTFET based logic inverter. The results indicate that ultra-thin films of SiN_x have great potential in future transistor technology.