Methods of reading ferroelectric memory cells

A method of reading a ferroelectric memory cell, comprising:

• coupling a reference bit line and a cell output bit line to a fixed potential, wherein the memory cell is associated with the cell output bit line and wherein the memory cell has a capacitor having a ferroelectric portion;
• connecting a first current source to the reference bit line and a second current source to the cell output bit line, wherein the second current source is matched to the first current source;
• charging each bit line with its associated current source for a predetermined period without producing a potential difference across the ferroelectric portion of the capacitor exceeding a polarization reversal threshold level of the ferroelectric portion, thereby developing a differential signal across the two bit lines;
• and
• sensing the differential signal.

A method of reading a bi-state ferroelectric memory cell, comprising:

• precharging a reference bit line to a reference potential;
• precharging a sensing bit line to a second potential higher than the first potential, wherein the memory cell is coupled to the sensing bit line;
• isolating the precharged reference and sensing bit lines;
• coupling a capacitor of the memory cell to the sensing bit line, wherein the capacitor contains a ferroelectric dielectric layer and wherein a potential difference across the capacitor after coupling is below a polarization reversal threshold level for the ferroelectric dielectric layer;
• decoupling the capacitor of the memory cell from the sensing bit line;
• and
• sensing a potential difference between the reference bit line and the sensing bit line wherein a potential of the reference bit line exceeds a potential of the sensing bit line by a difference between the second potential and the reference potential when the memory cell has the first state and wherein a potential of the sensing bit line exceeds a potential of the reference bit line by the difference between the second potential and the reference potential when the memory cell has the second state.

A method of reading a ferroelectric memory cell, comprising:

• coupling a reference bit line and a cell output bit line to a fixed potential, wherein the memory cell is associated with the cell output bit line and wherein the memory cell has a capacitor having a ferroelectric portion;
• connecting a first current source to the reference bit line and a second current source to the cell output bit line, wherein the second current source is matched to the first current source;
• charging each bit line with its associated current source for a predetermined period, thereby developing a differential signal across the two bit lines;
• and
• sensing the differential signal;
• wherein the current sources are chosen such that a potential difference across the ferroelectric portion of the capacitor of the memory cell associated with the cell output bit line and across a ferroelectric portion of a capacitor of a memory cell associated with the reference bit line are less than or equal to a polarization reversal threshold of the ferroelectric portions at the end of the predetermined period.

A method of reading a ferroelectric memory cell, comprising:

• precharging a reference bit line to a first potential;
• precharging a sensing bit line to a second potential, wherein the second potential is higher than the first potential and wherein the memory cell is coupled to the sensing bit line;
• isolating the precharged reference and sensing bit lines;
• coupling a capacitor of the memory cell to the sensing bit line, wherein the capacitor contains a ferroelectric dielectric layer and wherein a potential difference across the capacitor after coupling is below a polarization reversal threshold level for the ferroelectric dielectric layer;
• decoupling the capacitor of the memory cell from the sensing bit line;
• driving the bit line having a lower potential to a ground power rail;
• and
• driving the bit line having a higher potential to a supply potential power rail.