A high-k gate insulator of HfO2 deposited by sputtering using electron cyclotron resonance (ECR) plasma was investigated. HfO2 films deposited in the metal mode, in which oxygen flow is controlled to be relatively small, provided small capacitance equivalent thickness of 1.1 nm and a gate leakage current of less than 1 mA/ cm(2) at 1 V. Fixed charges and traps were minimized by optimizing postannealing temperature and O-2 flow rate. The large amount of slow traps seen in low- frequency (1 kHz) capacitance- voltage measurements was effectively reduced by a low- temperature annealing at 400degreesC. Current- voltage measurements taken in the accumulation region suggest that Schottky emissions are dominant for the Al/ HfO2 / Si diodes. A very small barrier height was observed for the Al/ HfO2 having an ultrathin HfO2 film. (C) 2004 The Electrochemical Society.