Memory device using a multilayer ferroelectric stack and method of forming the same
A memory device includes a semiconductor channel, a gate electrode, and a stack located between the semiconductor channel and the gate electrode. The stack includes, from one side to another, a first ferroelectric material portion, a second ferroelectric material portion, and a gate dielectric portion that contacts the semiconductor channel.
1. A memory device, comprising:
an alternating stack of insulating layers and electrically conductive layers comprising gate electrodes and located over a substrate;
a vertical semiconductor channel vertically extending through the alternating stack; and
a stack located between the vertical semiconductor channel and the electrically conductive layers, the stack including, from one side to another, a first ferroelectric material layer comprising a first ferroelectric material, a second ferroelectric material layer comprising a second ferroelectric material, and a gate dielectric layer,
wherein the vertical semiconductor channel is in direct contact with the gate dielectric layer, the first ferroelectric material layer, and the second ferroelectric material layer; and
wherein the second ferroelectric material extends vertically from a bottommost one of the insulating layers to a topmost one of the insulating layers, and exhibits spontaneous electrical polarization in an absence of an external electric field at each level of the insulating layers.
2. The memory device of claim 1 , wherein:
a vertical stack of ferroelectric memory cells is located at each level of the electrically conductive layers; and
each of the ferroelectric memory cells comprises a respective portion of the first ferroelectric material layer, a respective portion of the second ferroelectric material layer, and a respective portion of the gate dielectric layer.
3. The memory device of claim 2 , wherein each of the gate dielectric portions comprises a respective portion of a gate dielectric layer that vertically extends from a bottommost one of the electrically conductive layers to a topmost one of the electrically conductive layers.
4. The memory device of claim 1 , further comprising:
a plurality of memory stack structures vertically extending through the alternating stack, wherein each of the memory stack structures comprises a memory film and an additional vertical semiconductor channel, and the memory film comprises the vertical stack of ferroelectric memory cells;
drain regions contacting a top end of a respective one of the vertical semiconductor channels and having a doping of an opposite conductivity type of the vertical semiconductor channels; and
a source region located in a semiconductor material layer underlying the alternating stack and located in, or on, the substrate.
5. The memory device of claim 1 , wherein:
each of the insulating layers contacts the first ferroelectric material; and
each of the insulating layers is spaced from the second ferroelectric material contained within the second ferroelectric material layer by inter-ferroelectric dielectric material portions of the memory film which are located between the first ferroelectric material layer and the second ferroelectric material layer.
6. The memory device of claim 1 , further comprising barrier dielectric portions located between the electrically conductive layers and the first ferroelectric material layer.
7. The memory device of claim 1 , further comprising an inter-ferroelectric dielectric layer located between the first ferroelectric material layer and the second ferroelectric material layer.
8. The memory device of claim 7 , wherein the inter-ferroelectric dielectric layer vertically extends from a first horizontal plane including a bottom surface of a bottommost one of the electrically conductive layers to a second horizontal plane including a top surface of a topmost one of the electrically conductive layers.
9. The memory device of claim 1 , wherein the first ferroelectric material continuously extends vertically from the bottommost one of the insulating layers to the topmost one of the insulating layers, and exhibits spontaneous electrical polarization in an absence of an external electric field at each level of the insulating layers.
10. The memory device of claim 1 , further comprising a barrier dielectric spacer in contact with a bottom surface of the first ferroelectric material layer.
11. The memory device of claim 10 , wherein:
the substrate comprises a semiconductor material layer in contact with a bottom end of the vertical semiconductor channel; and
the barrier dielectric spacer comprises an oxide of a semiconductor material of the semiconductor material layer.
12. The memory device of claim 10 , wherein:
the barrier dielectric spacer comprises an opening therethrough; and
the vertical semiconductor channel is in direct contact with a sidewall of the barrier dielectric spacer located at the opening through the barrier dielectric spacer.