Abstract: A memory element is formed of a thin film transistor. The thin film transistor has a semiconductor layer, a source electrode electrically connected to the semiconductor layer, a drain electrode electrically connected to the semiconductor layer and formed separately from the source electrode, a gate electrode for controlling formation of a channel of the semiconductor layer, and a gate insulation film for isolating the gate electrode and the semiconductor layer from each other and causing a hysteresis in the relation between the drain current and the gate circuit. The insulation film is a silicon nitride film whose composition ratio of silicon to nitrogen is in a range of approx. 0.85 to 1.1. According to this invention, the relation between the gate voltage and the drain current can be set to have a hysteresis. Therefore, the thin film transistor can be used as a memory element.

Abstract: Gd and Bi are used as sputter sources and are simultaneously sputtered, or sputtered alternately, each time in an amount for forming a layer having a thickness of 10 atoms or less, thereby forming a thin film on a substrate, in which Gd and Bi are mixed at a ratio of 4:3. The thin film is heat-treated to form a crystalline thin film having a phase represented by Gd.sub.4 Bi.sub.3.