Memory structure in ferroelectric nonvolatile memory and readout method therefor

A storage/holding method of a ferroelectric nonvolatile memory which has memory cells each including a field effect transistor, a first ferroelectric capacitor having one of electrodes connected to a gate electrode of the field effect transistor, and a second ferroelectric capacitor in which one of electrodes is connected to the gate electrode of the field effect transistor and the remnant polarization amount is substantially equal to that of the first ferroelectric capacitor;

• comprising the steps of:
• polarizing the thin ferroelectric films of the first and second ferroelectric capacitors in opposite directions to each other with respect to the gate electrode of the field effect transistor by grounding the other electrode of the second ferroelectric capacitor and applying a voltage to the other electrode of the first ferroelectric capacitor;
• and
• setting the other electrode of the first ferroelectric capacitor to 0V.

A readout method of a ferroelectric nonvolatile memory which has memory cells each including a field effect transistor, a first ferroelectric capacitor having one of electrodes connected to a gate electrode of the field effect transistor, and a second ferroelectric capacitor in which one of electrodes is connected to the gate electrode of the field effect transistor and the remnant polarization amount is substantially equal to that of the first ferroelectric capacitor and in which information is stored by polarizing the thin ferroelectric films of the first and second ferroelectric capacitors in opposite directions to each other with respect to the gate electrode of the field effect transistor, comprising the steps of:

• setting the other electrode of the second ferroelectric capacitor into an electrically floating state;
• applying a positive voltage pulse to the other electrode of the first ferroelectric capacitor;
• and
• detecting a drain current in the field effect transistor to determine stored information.

A readout method of a ferroelectric nonvolatile memory which has memory cells each including a field effect transistor, a first ferroelectric capacitor having one of electrodes connected to a gate electrode of the field effect transistor, and a second ferroelectric capacitor in which one of electrodes is connected to the gate electrode of the field effect transistor and the remnant polarization amount is substantially equal to that of the first ferroelectric capacitor and in which information is stored by polarizing the thin ferroelectric films of the first and second ferroelectric capacitors in opposite directions to each other with respect to the gate electrode of the field effect transistor, comprising the steps of:

• setting the other electrode of the second ferroelectric capacitor into an electrically floating state;
• applying a positive voltage pulse to the other electrode of the first ferroelectric capacitors;
• and
• subsequently applying a negative voltage pulse whose absolute value is smaller than the positive voltage pulse to the other electrode of the first ferroelectric capacitor.