Ferroelectric memory devices employing conductivity modulation of a thin semiconductor material or a two-dimensional charge carrier gas and methods of operating the same
A ferroelectric memory device contains a two-dimensional semiconductor material layer having a band gap of at least 1.1 eV and at least one of a thickness of 1 to 5 monolayers of atoms of the semiconductor material or includes a two-dimensional charge carrier gas layer, a source contact contacting a first portion of the two-dimensional semiconductor material layer, a drain contact contacting a second portion of the two-dimensional semiconductor material layer, a ferroelectric memory element located between the source and drain contacts and adjacent to a first surface of the two-dimensional semiconductor material layer, and a conductive gate electrode located adjacent to the ferroelectric memory element.
1. A ferroelectric memory device comprising:
a two-dimensional semiconductor material layer having a band gap of at least 1.1 eV and at least one of a thickness of 1 to 5 monolayers of atoms of the semiconductor material or includes a two-dimensional charge carrier gas layer;
a source contact contacting a first portion of the two-dimensional semiconductor material layer;
a drain contact contacting a second portion of the two-dimensional semiconductor material layer;
a ferroelectric memory element located between the source and drain contacts and adjacent to a first surface of the two-dimensional semiconductor material layer; and
a conductive gate electrode located adjacent to the ferroelectric memory element.
2. The ferroelectric memory device of claim 1 , wherein:
the two-dimensional semiconductor material layer includes the two-dimensional charge carrier gas layer which comprises a two-dimensional electron gas (2DEG) layer;
the ferroelectric memory element contacts the first surface of the two-dimensional semiconductor material layer; and
the conductive gate electrode contacts the ferroelectric memory element.
3. The ferroelectric memory device of claim 2 , wherein the ferroelectric memory element comprises a ferroelectric dielectric material.
4. The ferroelectric memory device of claim 2 , wherein the ferroelectric dielectric material is selected from barium titanate, colemanite, bismuth titanate, europium barium titanate, ferroelectric polymer, germanium telluride, langbeinite, lead scandium tantalate, lead titanate, lead zirconate titanate, lithium niobate, polyvinylidene fluoride, potassium niobate, potassium sodium tartrate, potassium titanyl phosphate, sodium bismuth titanate, ammonium dihydrogen phosphate, potassium dihydrogen phosphate KH 2 PO 4 (KDP), lithium tantalate, lead lanthanum titanate, and lead lanthanum zirconate titanate.
5. The ferroelectric memory device of claim 2 , further comprising:
a backside ferroelectric memory element in contact with a second surface of the two-dimensional semiconductor material layer that is located on an opposite side of the first surface of the two-dimensional semiconductor material layer;
a conductive backside gate electrode in contact with the backside ferroelectric memory element; and
an electrically conductive path connecting the conductive backside gate electrode and the conductive gate electrode.
6. The ferroelectric memory device of claim 2 , further comprising a backside contact electrode located adjacent to a second surface of the two-dimensional semiconductor material layer that is located on an opposite side of the first surface of the two-dimensional semiconductor material layer.
7. The ferroelectric memory device of claim 1 , wherein:
the two-dimensional semiconductor material layer has a thickness in a range from 0.3 nm to 10 nm; and
the two-dimensional semiconductor material layer comprises a two-dimensional charge carrier gas layer that is located within 10 nm from a two-dimensional Euclidian plane that includes an interface between the two-dimensional semiconductor material layer and the ferroelectric memory element.
8. The ferroelectric memory device of claim 1 , wherein the two-dimensional semiconductor material layer has the thickness of 1 to 5 monolayers of atoms of the semiconductor material.
9. The ferroelectric memory device of claim 1 , wherein each of the conductive gate electrode, the source contact, and the drain contact comprise a respective metallic contact material selected from a metal-semiconductor compound, a conductive metallic nitride, an elemental metal, and an intermetallic alloy material.
10. The ferroelectric memory device of claim 1 , wherein the two-dimensional semiconductor material layer comprises fluorinated graphene.
11. The ferroelectric memory device of claim 1 , wherein the two-dimensional semiconductor material layer comprises hexagonal boron nitride.
12. The ferroelectric memory device of claim 1 , wherein the two-dimensional semiconductor material layer comprises molybdenum disulfide.
13. The ferroelectric memory device of claim 1 , wherein the two-dimensional semiconductor material layer comprises germanane.
14. A ferroelectric memory array comprising an array of the ferroelectric memory devices of claim 1 .
15. A method of operating the ferroelectric memory device of claim 1 , comprising:
programming a polarization direction of the ferroelectric memory element by applying a positive bias voltage or a negative bias voltage to the conductive gate electrode with respective to the two-dimensional semiconductor material layer; and
sensing a polarization direction of the ferroelectric memory element by measuring a magnitude of electrical current between the source contact and the drain contact under a read voltage between the source contact and the drain contact.
16. The method of claim 15 , further comprising applying a gate read voltage to the conductive gate electrode while sensing the polarization direction of the ferroelectric memory element.
17. The method of claim 15 , wherein the ferroelectric memory device further comprises:
a backside ferroelectric memory element in contact with a second surface of the two-dimensional semiconductor material layer that is located on an opposite side of the first surface of the two-dimensional semiconductor material layer; and
a conductive backside gate electrode in contact with the backside ferroelectric memory element.
18. The method of claim 17 , further comprising applying a same bias voltage to the conductive backside gate electrode as to the conductive gate electrode during programming and sensing the polarization direction of the ferroelectric memory element.
19. A method of manufacturing the ferroelectric memory device of claim 1 , comprising:
forming the two-dimensional semiconductor material layer;
forming the ferroelectric memory element directly on the first surface of the two-dimensional semiconductor material layer;
forming the conductive gate electrode on the ferroelectric memory element;
forming the source contact on the first portion of the two-dimensional semiconductor material layer; and
forming the drain contact on the second portion of the two-dimensional semiconductor material layer.
20. The method of claim 19 , further comprising:
forming a backside ferroelectric memory element on a second surface of the two-dimensional semiconductor material layer; and
forming a conductive backside gate electrode on the backside ferroelectric memory element.