Semiconductor devices

A semiconductor device, comprising:

• a transistor including:
• an interface insulation layer on a substrate, the interface insulation layer having a first thickness,
• a first gate insulation layer on the interface insulation layer, the first gate insulation layer having a second thickness greater than the first thickness, and including an insulation material having a hysteresis characteristic;
• a first gate electrode on the first gate insulation layer, and
• impurity regions on the substrate and adjacent to sidewalls of the first gate electrode,
• wherein the transistor has one of a first threshold voltage and a second threshold voltage different from the first threshold voltage depending on a voltage level of the first gate electrode.

A semiconductor device, comprising:

• a transistor including:
• a substrate including a recess,
• an interface insulation layer on a lower sidewall and a bottom of the recess,
• a first gate insulation layer on the interface insulation layer, the first gate insulation layer including a ferroelectric material,
• a first gate electrode on the first gate insulation layer to fill a lower portion of the recess, the first gate electrode including a metal,
• a second gate electrode contacting the first gate electrode in the recess, and the second gate electrode including a material different from a material of the first gate electrode, and
• impurity regions on the substrate and adjacent to sidewalls of the recess;
• and
• a capacitor electrically connected to one of the impurity regions of the transistor,
• wherein the transistor has one of a first threshold voltage and a second threshold voltage different from the first threshold voltage depending on a voltage level of the first gate electrode.