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 postannealing 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.