Semiconductor memory
A ferroelectric memory has a plurality of memory cells respectively having a cell transistor and ferroelectric capacitor whose one terminal is connected with the cell transistor, a plurality of word lines respectively connected with said cell transistor, a plurality of plate lines connected with the other terminal of said ferroelectric capacitor and intersecting with said word lines, a plurality of local bit lines connected with said cell transistors, and a global bit line that is selectively connected with local bit lines. Furthermore, the ferroelectric memory has a sensing amplifier unit that detects the amount of charging of the local bit lines from said memory cells while maintaining the potential of the local bit lines at a potential equivalent to the non-selected plate lines, during reading.
1. A ferroelectric memory comprising:
a plurality of memory cells respectively having a cell transistor and a ferroelectric capacitor whose one terminal is connected with the cell transistor;
a plurality of word lines respectively connected with said cell transistors;
a plurality of plate lines intersecting with said word lines and connected with the other terminal of said ferroelectric capacitors;
a plurality of local bit lines connected with said cell transistors;
a global bit line selectively connected with said local bit lines; and
a sense amplifier unit that, during reading, detects amount of charge delivered to said local bit lines by said memory cells while maintaining the potential of said local bit lines at a potential equal to non-selected plate lines.
2. The ferroelectric memory according to claim 1 further comprising a plate line driver that, when a selected word line is driven, drives the plate line corresponding to said selected memory cell such that reading voltage is applied to said ferroelectric capacitor and maintains said non-selected plate lines corresponding to the non-selected memory cells at a prescribed potential.
3. The ferroelectric memory according to claim 2 wherein, when said local bit line is driven on rewriting to the selected said memory cell, said plate line driver drives the non-selected plate lines also to a potential equivalent to that of the local bit line.
4. The ferroelectric memory according to claim 1 wherein said local bit lines are connected with a plurality of memory cells; said global bit lines are respectively provided in respect of a plurality of local bit lines; and said sense amplifier unit is provided for each said global bit line.
5. The ferroelectric memory according to claim 4 comprising a write circuit provided for each said global bit line and that drives said global bit line to a rewriting level in response to the output of said sense amplifier unit.
6. The ferroelectric memory according to claim 1 wherein said local bit lines are provided parallel with said word lines and the local bit lines are constituted by diffusion regions connected in common with first source/drain regions of a plurality of cell transistors arranged in the direction of the extension of said word lines; and
said global bit lines are connected with said local bit lines through a connection circuit and the global bit lines are arranged parallel with plate lines.
7. The ferroelectric memory according to claim 6 wherein said connection circuit connects said local bit line with the global bit line in response to driving of a selected word line.
8. The ferroelectric memory according to claim 6 wherein a contact via is formed in a second source/drain region of the said cell transistor and the second source/drain region is connected with an electrode of the ferroelectric capacitor through said contact via.
9. The ferroelectric memory according to claim 8 wherein said ferroelectric capacitor is formed on the contact via formed in said second source/drain region and a conductive layer providing said plate lines is formed on said ferroelectric capacitor.
10. The ferroelectric memory according to claim 8 wherein said ferroelectric capacitor is formed in a position adjacent to said second source/drain region and said second source/drain region is connected with a top electrode of said ferroelectric capacitor through said contact via and a conductive layer connected with the contact via; and, in addition, the bottom electrode of said ferroelectric capacitor provides said plate line.
11. The ferroelectric memory according to claim 1 wherein said global bit line extends parallel with said plate lines and the global bit line and plate lines are provided by the same conductive layer.
12. The ferroelectric memory according to claim 1 wherein said global bit line extends parallel with said plate lines, said global bit line is provided by a conductive layer and said plate lines are provided by extending one electrode of said ferroelectric capacitor.
13. The ferroelectric memory according to claim 1 wherein said sense amplifier unit comprises a source follower transistor that is connected with said global bit line and whose gate/source voltage is made to be about the threshold voltage; a polarization charge detection capacitor that resets the other terminal of this source follower transistor to negative voltage; and a sense amplifier that detects a voltage change in respect of the amount of polarization charge flowing into the polarization charge detection capacitor from said selected memory cell.