AbstractTop‐gate TFTs are fabricated at T < 200 °C using μc‐Si:H film with different thickness, 30, 100 and 200 nm as active layer. Silicon nitride deposited at 150 °C is used as gate insulator. Due to improved crystallinity, mobility increases with the μc‐Si:H thickness. However, the columnar structure of thick μc‐Si:H films induces some shift of the TFT's characteristics. The denser structure of thinnest film, constituted by nano‐grains embedded in amorphous phase, leads to highly stable TFTs. Present results show that a mean way between the needs of high crystallinity, obtained in high thick films, and stability, obtained with dense material, has to be found in μc‐Si:H low temperature technology (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)