120 °C fabrication technology for a-Si:H thin film transistors on flexible polyimide substrates

In this article, we report a fabrication process for hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFT) at 120 °C on flexible Kapton® substrates for large-area imaging applications. The samples are based on the bottom-gate inverted staggered TFT structure. Initially, both sides of the substrate are coated by amorphous silicon nitride (a-SiNx:H), followed by 120 nm of aluminum (Al) film for the gate. After gate patterning, a trilayer is deposited at 120 °C by plasma-enhanced chemical vapor deposition comprising of 250 nm a-SiNx:H gate dielectric, 50 nm a-Si:H, and 250 nm top (passivation) a-SiNx:H. After opening the contact windows, we deposit 35 nm of n+ a-Si:H at 120 °C. Next, a 1 μm Al top contact layer is deposited. The a-Si:H films are deposited from a gas mixture of silane (SiH4) and hydrogen. For the n+ a-Si:H layer, a hydrogen-diluted (1% PH3+99% SiH4) mixture is used. The a-SiNx:H films are deposited from a helium-diluted mixture of silane, ammonia and nitrogen. Dry etching is used except for the metal layers, where wet etching is used. The TFTs show an off-current less than 10−12 A, and an on-current of more than 10−6 A, thus giving an on/off current ratio greater than 106. The effective device mobility, μeff, is about 0.4 cm2/V s.In this article, we report a fabrication process for hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFT) at 120 °C on flexible Kapton® substrates for large-area imaging applications. The samples are based on the bottom-gate inverted staggered TFT structure. Initially, both sides of the substrate are coated by amorphous silicon nitride (a-SiNx:H), followed by 120 nm of aluminum (Al) film for the gate. After gate patterning, a trilayer is deposited at 120 °C by plasma-enhanced chemical vapor deposition comprising of 250 nm a-SiNx:H gate dielectric, 50 nm a-Si:H, and 250 nm top (passivation) a-SiNx:H. After opening the contact windows, we deposit 35 nm of n+ a-Si:H at 120 °C. Next, a 1 μm Al top contact layer is deposited. The a-Si:H films are deposited from a gas mixture of silane (SiH4) and hydrogen. For the n+ a-Si:H layer, a hydrogen-diluted (1% PH3+99% SiH4) mixture is used. The a-SiNx:H films are deposited from a helium-diluted mixture of silane, ammonia and nitrogen. Dry etching is use...