High-performance polycrystalline silicon ͑poly-Si͒ thin-film transistors ͑TFTs͒ with oxide/nitride/oxynitride ͑ONO͒ multilayer gate dielectrics were fabricated. The low-temperature ͑Ϲ300°C͒ ONO multilayer dielectric uses three stacked layers: the bottom layer is a very thin N 2 O-plasma oxynitride deposited by plasma-enhanced chemical vapor deposition ͑PECVD͒, the middle layer is PECVD Si 3 N 4 , and the top layer is tetraethoxysilane ͑TEOS͒ oxide. The ONO gate dielectric on poly-Si films shows a very high breakdown field of 9.4 MV/cm, a longer time-dependent dielectric breakdown lifetime and a lower charge trapping rate than single-layer PECVD TEOS oxide or nitride. The fabricated poly-Si TFTs with ONO gate dielectric exhibited excellent transfer characteristics, high field-effect mobility of 213 cm 2 /V s, and an ON/OFF current ratio of over 10 8 .In the realization of large-area active matrix liquid crystal displays ͑AMLCDs͒ with embedded peripheral poly-Si thin-film transistor ͑TFT͒ drive circuits on the panel, field-effect mobility and gate insulator quality are two of the most important determinants of the performance and reliability of low-temperature polycrystalline silicon ͑LTPS͒ TFTs. 1 It has been reported that high field-effect mobility LTPS TFTs were obtained by excimer laser annealing ͑ELA͒. 2 However, traditional LTPS TFTs use single-layer plasmaenhanced chemical vapor deposition ͑PECVD͒ SiO 2 or Si 3 N 4 as the gate insulator and so suffer from high interface trap density, low breakdown strength, and high gate leakage current. 3,4 In 1984, Watanabe et al. first reported silicon oxide-nitride-oxide ͑ONO͒ films as alternative dielectrics for dynamic random access memory ͑DRAM͒ cell capacitors. 5 In 1995, Yang et al. used ONO film as a gate insulator in high temperature TFTs. 6 In ONO multilayer structures, the bottom oxide provides a device-quality electrical SiO 2 /Si interface. The nitride layer increases the effective dielectric constant of the ONO sandwich in such a way that a film twice as thick as SiO 2 -based dielectric shows equal capacitance, and therefore decreased threshold voltage, decreased subthreshold swing, and increased drive current of the poly-Si TFTs. Finally, the top oxide provides the electrical contact to the poly-Si gate electrode. 7 Although ONO structures exploit the advantages of oxide and nitride films concomitantly, ONO films are prepared by thermal growth in a low-pressure ͑LP͒CVD reactor at high temperature ͑Ͼ750°C͒; this method is not appropriate for fabricating LTPS TFTs at a temperature much higher than a strain point of the glass substrate.This paper presents a low temperature ͑Ϲ300°C͒ PECVD oxide/ nitride/N 2 O-plasma oxynitride ͑ONO͒ multilayer gate dielectric. PECVD SiO 2 /Si 3 N 4 stack dielectric has lower leakage current and much longer ͑by two to three orders of magnitude͒ time-dependent dielectric breakdown ͑TDDB͒ lifetime than single-layer PECVD tetraethoxysilane ͑TEOS͒ oxide or Si 3 N 4 dielectrics. 8 Furthermore, N 2 O-plasma oxide has been reported to h...