Method and circuit for reading data from a ferroelectric memory cell
AssigneeOki Electric Industry Co., Ltd.
InventorYasushi Igarashi
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Abstract
Data stored in a ferroelectric capacitor in a ferroelectric memory cell are read by applying a preliminary voltage to the ferroelectric capacitor to increase its polarization if a certain data value is stored, then applying a series of read voltages to produce a potential responsive to the stored data. The preliminary voltage may be applied either before or after one terminal of the ferroelectric capacitor is placed in a floating state, which is maintained while the series of read voltages is applied. Application of the preliminary voltage provides an increased reading margin if the ferroelectric capacitor has partially lost polarization while storing the certain data value, by restoring some of the lost polarization.
Claims19
A method of reading data stored in a ferroelectric capacitor in a ferroelectric memory cell, the ferroelectric capacitor having a first terminal and a second terminal, the method comprising:
- applying a reference voltage to the ferroelectric capacitor;
- then
- applying a preliminary voltage lower than the reference voltage to the ferroelectric capacitor, the preliminary voltage increasing a polarization of the ferroelectric capacitor if a certain data value is stored in the ferroelectric capacitor;
- then
- applying a series of read voltages to the ferroelectric capacitor, the series of read voltages producing a potential responsive to the data stored in the ferroelectric capacitor at the first terminal of the ferroelectric capacitor.
A circuit for reading data stored in a ferroelectric capacitor in a ferroelectric memory cell, the ferroelectric capacitor having a first terminal and a second terminal, the circuit comprising:
- a first driver for driving said first terminal to a reference potential, then placing said first terminal in an electrically floating state;
- a second driver for driving said second terminal to the reference potential, then driving said second terminal to a preliminary potential lower than the reference potential, thereby increasing a polarization of the ferroelectric capacitor if a certain data value is stored in the ferroelectric capacitor, then driving said first terminal to the reference potential again, then driving said second terminal to a series of read potentials;
- a sensing unit for sensing said data according to a potential of said first terminal;
- and
- a control unit for selecting the ferroelectric memory cell and controlling the first driver, the second driver, and the sensing unit, thereby causing the series of read potentials to be applied after said first terminal has been placed in the electrically floating state, and causing the sensing unit to sense said data after the series of read potentials has been applied.
A circuit for reading data stored in a ferroelectric capacitor in a ferroelectric memory cell, the ferroelectric capacitor having a first terminal and a second terminal, the circuit comprising:
- a first driver for driving said first terminal to a reference potential, then placing said first terminal in an electrically floating state;
- a second driver for driving said second terminal to the reference potential, then driving said second terminal to a preliminary potential lower than the reference potential, thereby increasing a polarization of the ferroelectric capacitor if a certain data value is stored in the ferroelectric capacitor, then driving said second terminal to a series of read potentials;
- a sensing unit for sensing said data according to a potential of said first terminal;
- and
- a control unit for selecting the ferroelectric memory cell and controlling the first driver, the second driver, and the sensing unit, thereby causing the preliminary potential to be applied after said first terminal has been placed in the electrically floating state, and causing the sensing unit to sense said data after the series of read potentials has been applied.
Dependencies are inferred from the claim text.