Systems and methods for writing and non-destructively reading ferroelectric memories
View Patent ↗Ferroelectric memory cell configurations, a system for controlling writing and reading to those configurations and a method for employing those configurations for writing and reading ferroelectric memories are provided. Ferroelectric memory cells according to the disclosed configurations are read without disturbing the stored data, i.e., not requiring any modification of the stored polarization state of the ferroelectric memory cell to read the stored data, thus providing a “non-destructive” reading process. Ferroelectric memory cells are read without requiring that a charge or sense amplifier be a part of the ferroelectric memory cell. Various transistor configurations provide a capability to read a signal effect through a transistor channel as an indication of capacitance of a ferroelectric memory cell polarization state.
1. A ferroelectric memory cell, comprising:
a ferroelectric memory capacitor that stores a polarization state of the ferroelectric memory cell;
a transistor, a gate of the transistor being connected to a first electrode of the ferroelectric memory capacitor, the ferroelectric memory capacitor being a separate electronic component from the transistor; and
an alternating current signal source that applies an alternating current signal to a channel of the transistor and that measures a magnitude of an alternating current through the channel of the transistor as an indication of a polarization state of the ferroelectric memory cell.
2. The ferroelectric memory cell of claim 1 , further comprising an additional capacitor, a first electrode of the additional capacitor being connected to the gate of the transistor.
3. The ferroelectric memory cell of claim 2 , further comprising:
a first voltage source connected to a second electrode of the ferroelectric capacitor on an opposite side of the ferroelectric memory capacitor from the gate of the transistor;
at least one second voltage source that applies a bias across a channel of the transistor; and
a third voltage source connected to a second electrode of the additional capacitor on an opposite side of the additional capacitor from the gate of the transistor.
4. The ferroelectric memory cell of claim 3 ,
the ferroelectric memory cell being written by applying a voltage between the first voltage source and the third voltage source,
the writing being irrespective of a voltage of the at least one second voltage source, and
the ferroelectric memory cell being read by setting both the first voltage source and the third voltage source to a substantially same potential, applying a bias from the at least one second voltage source across a channel of the transistor, and measuring the current through the channel of the transistor as an indication of a polarization state of the ferroelectric memory cell.
5. The ferroelectric memory cell of claim 3 , the first voltage source and the third voltage source being switchable to generate positive and negative polarization across the ferroelectric memory capacitor.
6. The ferroelectric memory cell of claim 5 , the first voltage source and the third voltage source being switchable by at least one of a first switch being interposed between the first voltage source and the second electrode of the ferroelectric memory capacitor and a second switch being interposed between the third voltage source and the second electrode of the additional capacitor.
7. The ferroelectric memory cell of claim 6 , the first switch and the second switch being open except during writing and reading operations for the ferroelectric memory cell.
8. The ferroelectric memory cell of claim 6 , at least one of the first switch and the second switch being one of a single transistor and a transmission gate.
9. The ferroelectric memory cell of claim 6 , at least one of the first switch and the second switch being multiple switches for applying differing potentials respectively to at least one of the second electrode of the ferroelectric memory cell capacitor and the second electrode of the additional capacitor from separate voltage sources of different potentials.
10. The ferroelectric memory cell of claim 3 , at least one of the first and third voltage sources being a variable voltage source.
11. The ferroelectric memory cell of claim 1 , the transistor being one of a metal-oxide-semiconductor field-effect transistor (MOSFET) and a thin-film transistor (TFT).
12. The ferroelectric memory cell of claim 1 , the transistor being one of an n-type transistor or a p-type transistor.
13. The ferroelectric memory cell of claim 1 , at least the ferroelectric memory cell capacitor and the transistor being disposed on one or more flexible substrates.
14. The ferroelectric memory cell of claim 1 , further comprising a resistor connected to the channel of the transistor for converting a current through the channel of the transistor to a voltage.
15. A write/read system for writing and reading a ferroelectric memory cell, the ferroelectric memory cell including a ferroelectric memory capacitor that stores a polarization state of the ferroelectric memory cell; and a transistor, a gate of the transistor being connected to a first electrode of the ferroelectric memory capacitor, the ferroelectric memory capacitor being a separate electronic component from the transistor, the write/read system comprising:
a first voltage source connected to a second electrode of the ferroelectric memory capacitor on an opposite side of the ferroelectric memory capacitor from the gate of the transistor;
at least one second voltage source that applies a bias across a channel of the transistor;
a measuring device for measuring a current through the channel of the transistor as an indication of a polarization state of the ferroelectric memory cell;
an additional capacitor with a first electrode connected to the gate of the transistor; and a third voltage source connected to a second electrode of the additional capacitor on an opposite side of the additional capacitor from the gate of the transistor;
a processor that is programmed to cause an alternating current signal source to apply an alternating current signal to the channel of the transistor, the measuring device measuring a magnitude of an alternating current through the channel of the transistor as an indication a polarization state of the ferroelectric memory cell; and
an output device that displays data based on a result of the measuring by the measuring device to a user as an indication of read data stored in the ferroelectric memory cell.
16. The write/read system of claim 15 , further comprising:
a processor that is programmed to cause a voltage to be applied between the first voltage source and the third voltage source to write the ferroelectric memory cell irrespective of a voltage of the at least one second voltage source, and to (1) set both the first voltage source and the third voltage source to a substantially same potential, and (2) apply a bias from the at least one second voltage source across the channel of the transistor, the measuring device measuring the current through the channel of the transistor while the bias from the at least one second voltage source is applied as an indication of the polarization state of the ferroelectric memory cell; and
an output device that displays data based on a result of the measuring by the measuring device to a user as an indication of read data stored in the ferroelectric memory cell.
17. The write/read system of claim 15 , the first voltage source and the third voltage source being switchable to generate positive and negative polarization across the ferroelectric memory capacitor.
18. The write/read system of claim 17 , the first voltage source and the third voltage source being switchable by at least one of a first switch being interposed between the first voltage source and the second electrode of the ferroelectric memory capacitor and a second switch being interposed between the third voltage source and the second electrode of the additional capacitor.
19. The write/read system of claim 18 , at least one of the first switch and the second switch being one of a single transistor and a transmission gate.
20. The write/read system of claim 18 , at least one of the first switch and the second switch being multiple switches for applying differing potentials respectively to at least one of the second electrode of the ferroelectric memory cell capacitor and the second electrode of the additional capacitor from separate voltage sources of different potentials.
21. The write/read system of claim 15 , at least one of the first voltage source and the third voltage source being a variable voltage source.
22. The write/read system of claim 15 , a plurality of circuit components of the write/read system being disposed on one or more flexible substrates.