WHY SiN_:H is the preferred gate dielectric for amorphous Si thin film transistors (TFTs) and SiO_2 the preferred gate dielectric for folycrystalline Si FTFs

摘要

Constraint theory developed for bulk glasses and recrently applied to thin films and sinle crystalline Si (C-Si) dielectric interfaces is extended in this paper to a-Si:H and polcycrystalline-Si (poly-Si) dielectric interfaces in TFTs where it provides guidelines for device optimization. The constraining effects of network bonding forces are a linar function of the average bonding coordination, N_(av). N_(av) approx 3 separates low-defect density networks as in SiO_2 (N_(av) chemical bounds 2.67), from highly-defective networks such as non-hydrogenated Si_3N_4(N_(av) approx 3 also separates device-quality from highly-defective SI-dielectric interfaces. These criteria are applied to Si-SiO_2 and Si=SiN_x:H interfaces that are integral components of TFT devies.