The effect of post-hydrogen annealing and multilayer channel structure on nano-crystalline silicon thin film transistor performance

The effect of multilayer channel structure and post-hydrogen annealing (PHA) on the performances of nano-Si thin film transistors (nc-Si TFTs) prepared by a hot wire chemical vapour deposition system on Si substrates was investigated. The experimental results showed that the PHA could improve (about 10%) both saturation and off currents. In particular, when a multilayer channel structure was adopted, the improvement became remarkable, because the underlying layers were used as a buffer layer, which could enhance the film's crystalline volume fraction. For example, under the condition of Vgs = 20 V and Vds = 20 V, a TFT with a 4-layer PHA treated nc-Si channel and a 5 nm n+ nc-Si source/drain layer could achieve the highest saturation current Isat of 5.8 × 10−6 A and the lowest Ioff of 4.1 × 10−11 A, respectively. The mechanisms related to the different factors were also discussed in detail.