Ferroelectric semiconductor memory device and method for reading the same
A first ferroelectric memory cell and a second ferroelectric memory cell each include a ferroelectric capacitor and a transistor and each store one set of information. A word-line is shared by the first and second ferroelectric memory cells. A first plate line is connected to the first ferroelectric memory cell and a second plate line is connected to the second ferroelectric memory cell. A selection transistor has one end connected to the first and second ferroelectric memory cells and the other end connected to a bit-line.
1. A ferroelectric semiconductor memory device comprising:
a first ferroelectric memory cell and a second ferroelectric memory cell, the memory cells together storing one set of information, each memory cell comprising a ferroelectric capacitor for holding a charge and a transistor connected in parallel to the ferroelectric capacitor;
a word-line shared by the first and second ferroelectric memory cells;
a first plate line connected to the first ferroelectric memory cell;
a second plate line connected to the second ferroelectric memory cell;
a selection transistor having one end connected to both the first and second ferroelectric memory cells and another end connected to a bit-line; and
a control circuit controlling voltages applied to a gate of the selection transistor, the first plate line, the second plate line, the word-line, and the bit-line.
2. The ferroelectric semiconductor memory device according to claim 1 , wherein
a plurality of the first ferroelectric memory cells connected in series form a first block,
a plurality of the second ferroelectric memory cells connected in series form a second block, and
the first and second ferroelectric memory cells sharing the word-line together store one set of information.
3. The ferroelectric semiconductor memory device according to claim 2 , wherein
the first and second blocks each comprise a plurality of ferroelectric memory cells connected in series, each memory cell comprising the ferroelectric capacitor and the transistor that are connected in parallel.
4. The ferroelectric semiconductor memory device according to claim 1 , wherein
the control circuit reads the information by performing steps comprising the steps of:
applying a voltage of Vcc/2 [V] to the bit-line and leaving the bit-line at a floating state;
applying a voltage of Vcc [V] to the first plate line and a voltage of 0 [V] to the second plate line; and
applying a voltage of 0 [V] to the first plate line and a voltage of Vcc [V] to the second plate line.
5. The ferroelectric semiconductor memory device according to claim 3 , further comprising a sense amplifier circuit connected to the bit-line, the sense amplifier circuit differentially amplifying a voltage of the bit-line and a reference voltage, wherein
the reference voltage is set to a voltage of Vcc/2.
6. The ferroelectric semiconductor memory device according to claim 1 , wherein
the control circuit reads the information by performing steps comprising the steps of:
applying a voltage of Vcc/2 [V] to the first plate line, the second plate line, and the bit-line, and leaving the bit-line at a floating state;
applying a voltage of Vcc [V] to the first plate line and a voltage of 0 [V] to the second plate line; and
applying a voltage of 0 [V] to the first plate line and a voltage of Vcc [V] to the second plate line.
7. The ferroelectric semiconductor memory device according to claim 6 , further comprising a sense amplifier circuit connected to the bit-line, the sense amplifier circuit differentially amplifying a voltage of the bit-line and a reference voltage, wherein
the reference voltage is set to a voltage of Vcc/2.
8. A method for reading a ferroelectric semiconductor memory device comprising:
a first cell block and a second cell block, each cell block comprising a plurality of ferroelectric memory cells connected in series, each memory cell comprising a ferroelectric capacitor for holding a charge and a transistor connected in parallel to the ferroelectric capacitor;
a word-line shared by a ferroelectric memory cell in the first cell block and a ferroelectric memory cell in the second cell block, the ferroelectric memory cells together storing one set of information;
a first plate line connected to the first cell block;
a second plate line connected to the second cell block; and
a selection transistor having one end connected to both the first and second cell blocks and another end connected to a bit-line,
the method comprising the steps of:
applying a voltage of Vcc/2 [V] to the bit-line and leaving the bit-line at a floating state;
applying a voltage of 0 [V] to a word-line connected to ferroelectric memory cells from which information is to be read; and
applying a voltage of Vcc [V] to the first plate line and applying a voltage of 0 [V] to the second plate line, thereby reading information from the ferroelectric memory cells.
9. The method for reading a ferroelectric semiconductor memory device according to claim 8 , further comprising the steps of:
applying a voltage of Vcc [V] to the first plate line and applying a voltage of 0 [V] to the second plate line, thereby reading information from the ferroelectric memory cells; and
applying a voltage of 0 [V] to the first plate line and applying a voltage of Vcc [V] to the second plate line, thereby rewriting the read information to the ferroelectric memory cells.
10. A method for reading a ferroelectric semiconductor memory device comprising:
a first cell block and a second cell block, each cell block comprising a plurality of ferroelectric memory cells connected in series, each memory cell comprising a ferroelectric capacitor for holding a charge and a transistor connected in parallel to the ferroelectric capacitor;
a word-line shared by a ferroelectric memory cell in the first cell block and a ferroelectric memory cell in the second cell block, the ferroelectric memory cells together storing one set of information;
a first plate line connected to the first cell block;
a second plate line connected to the second cell block; and
a selection transistor having one end connected to both the first and second cell blocks and another end connected to a bit-line,
the method comprising the steps of:
applying a voltage of Vcc/2 [V] to the first plate line, the second plate line, and the bit-line, and leaving the bit-line at a floating state;
applying a voltage of 0 [V] to a word-line connected to ferroelectric memory cells from which information is to be read; and
applying a voltage of Vcc [V] to the first plate line and applying a voltage of 0 [V] to the second plate line, thereby reading information from the ferroelectric memory cells.
11. The method for reading a ferroelectric semiconductor memory device according to claim 10 , further comprising the steps of:
applying a voltage of Vcc [V] to the first plate line and applying a voltage of 0 [V] to the second plate line, thereby reading information from the ferroelectric memory cells; and
applying a voltage of 0 [V] to the first plate line and applying a voltage of Vcc [V] to the second plate line, thereby rewriting the read information to the ferroelectric memory cells.