Semiconductor memory cell and manufacturing method thereof, and semiconductor memory devices
A semiconductor memory cell includes: a memory element formed by a first field effect transistor having a gate insulating film made of a ferroelectric film; and a select switching element formed by a second field effect transistor having a gate insulating film made of a paraelectric film. The ferroelectric film and the paraelectric film are stacked together with a semiconductor film of a compound semiconductor interposed therebetween. A first gate electrode of the first field effect transistor is formed on a side of the ferroelectric film, and a second gate electrode of the second field effect transistor is formed on a side of the paraelectric film so as to face the first gate electrode. The semiconductor film forms a common channel layer of the first and second field effect transistors.
1. A semiconductor memory cell, comprising:
a memory element formed by a first field effect transistor having a gate insulating film made of a ferroelectric film; and
a select switching element formed by a second field effect transistor having a gate insulating film made of a paraelectric film, wherein
the ferroelectric film and the paraelectric film are stacked together with a semiconductor film of a compound semiconductor interposed therebetween,
a first gate electrode of the first field effect transistor is formed on a side of the ferroelectric film,
a second gate electrode of the second field effect transistor is formed on a side of the paraelectric film so as to face the first gate electrode, and
the semiconductor film forms a common channel layer of the first and second field effect transistors.
2. The semiconductor memory cell of claim 1 , wherein
a channel resistance of the semiconductor film is independently controlled by a polarization state of the ferroelectric film and a voltage that is applied to the second gate electrode.
3. The semiconductor memory cell of claim 1 , wherein
the semiconductor film is made of the compound semiconductor of a same conductivity type.
4. The semiconductor memory cell of claim 1 , wherein
the semiconductor film is made of an oxide semiconductor or a nitride semiconductor.
5. The semiconductor memory cell of claim 1 , wherein
carriers in the semiconductor film are only electrons or holes.
6. The semiconductor memory cell of claim 1 , wherein
capacitance of the ferroelectric film is substantially equal to that of the paraelectric film.
7. The semiconductor memory cell of claim 1 , wherein
read operation from the memory element is performed by applying a predetermined voltage to the second gate electrode to turn off the select switching element, and detecting a current flowing in the channel layer according to a polarization state of the ferroelectric film.
8. The semiconductor memory cell of claim 1 , wherein
common source/drain electrodes of the first and second field effect transistors are formed on the semiconductor film so as to interpose the first and second gate electrodes between the common source/drain electrodes.
9. A method for manufacturing the semiconductor memory device of claim 1 , comprising the steps of:
forming the first gate electrode on a substrate;
continuously forming the ferroelectric film and the semiconductor film of the compound semiconductor on the substrate so as to cover the first gate electrode;
forming the paraelectric film on the semiconductor film; and
forming the second gate electrode on the paraelectric film at a position facing the first gate electrode.
10. A semiconductor memory device, comprising:
multiple ones of the semiconductor memory cells of claim 1 are connected in series.
11. The semiconductor memory device of claim 10 , wherein
the second field effect transistor is of a normally-on type.
12. The semiconductor memory device of claim 11 , wherein
write operation to a selected one of the semiconductor memory cells is performed by applying a predetermined voltage to the first gate electrode of the selected semiconductor memory cell to change a polarization state of the ferroelectric film.
13. A semiconductor memory device, comprising:
a plurality of semiconductor memory cells arranged in an array, wherein
each of the semiconductor memory cells is configured so that a memory element formed by a first field effect transistor having a gate insulating film made of a ferroelectric film is connected in parallel with a select switching element formed by a second field effect transistor having a gate insulating film made of a paraelectric film,
the semiconductor memory cell located at one end of the semiconductor memory cells connected in a column direction is connected to a source line having a ground potential, and the semiconductor memory cell located at the other end thereof is connected to a bit line to which a write voltage is applied,
write operation to the semiconductor memory cells connected in a row direction is performed sequentially from a row located closer to the source line to a row located closer to the bit line, after reset operation is performed so as to orient polarization of the ferroelectric film of the memory elements in all the semiconductor memory cells in a same direction, and
when writing data to each of the semiconductor memory cells in a selected row, the select switching element is turned off, if the write operation is to be performed so as to turn a polarization state of the ferroelectric film of the memory element to an off state of the first field effect transistor.
14. The semiconductor memory device of claim 13 , wherein
the ferroelectric film and the paraelectric film are stacked together with a semiconductor film of a compound semiconductor interposed therebetween,
a first gate electrode of the first field effect transistor is formed on a side of the ferroelectric film, and a second gate electrode of the second field effect transistor is formed on a side of the paraelectric film so as to face the first gate electrode, and
the semiconductor film forms a common channel layer of the first and second field effect transistors.
15. The semiconductor memory device of claim 14 , wherein
a channel resistance of the semiconductor film is independently controlled by a voltage that is applied to the first gate electrode, and a voltage that is applied to the second gate electrode.
16. The semiconductor memory device of claim 13 , wherein
the first field effect transistors in all the semiconductor memory cells are turned off in the reset operation.
17. The semiconductor memory device of claim 15 , wherein
when writing data to each of the semiconductor memory cells in the selected row, the select switching elements of the semiconductor memory cells in every row located closer to the bit line than the selected row are turned on.
18. The semiconductor memory device of claim 16 , wherein
when writing data to each of the semiconductor memory cells in the selected row, the select switching elements of the semiconductor memory cells in every row located closer to the source line than the selected row are turned on.
19. The semiconductor memory device of claim 13 , wherein
when writing data to each of the semiconductor memory cells in the selected row, a voltage applied in the reset operation is applied the first gate electrodes of the semiconductor memory cells in every row located closer to the bit line than the selected row.
20. The semiconductor memory device of claim 13 , wherein
the second field effect transistor is of a normally-on type.
21. The semiconductor memory device of claim 13 , wherein
the reset operation is performed by turning on the select switching elements of all the semiconductor memory cells, applying a first voltage to all the bit lines, and applying a second voltage to the first gate electrodes of all the semiconductor memory cells.
22. The semiconductor memory device of claim 13 , wherein
a drive voltage of the first field effect transistor is equal to that of the second field effect transistor.