Characteristics of SrTiO3 Field-Effect Transistors with DyScO3 Gate Insulators

We have developed a top-gate type of field-effect transistor with a single-crystal SrTiO3 channel and a DyScO3 gate insulator stack consisting of an epitaxial interface layer and an amorphous breakdown barrier layer. We show that the zero-bias conductivity of the transistor channel is strongly affected by the presence of charged traps in the amorphous gate insulator. Low off-state current could only be achieved in devices that were fabricated at an oxygen ambient pressure of 10 mTorr. At lower pressures, metallic channel interfaces were obtained, even after post-annealing in air. When both epitaxial and amorphous DyScO3 films were grown at 10 mTorr of oxygen, the on/off ratio of the field-effect transistors (FETs) reached 10(6). We argue that when designing oxide FETs, it is necessary to consider not only breakdown characteristics, but also the charged trap density in wide-gap oxide insulators. (C) 2010 The Japan Society of Applied Physics