Memory device and multi-level memory cell having ferroelectric storage element and magneto-resistive storage element

1. A memory device, comprising:

a plurality of word lines, a plurality of bit lines and a plurality of source lines; and

a plurality of multi-level memory cells, each of the plurality of multi-level memory cells is coupled to one of the plurality of word lines, one of the plurality of bit lines and one of the plurality of source lines, wherein each of the plurality of multi-level memory cells comprises:

a ferroelectric storage element, configured to store a first bit of a multi-bit data; and

a magneto-resistive storage element, configured to store a second bit of the multi-bit data,

wherein ferroelectric storage element is cascaded to the magneto-resistive storage element,

the ferroelectric storage element is formed in a front-end-of-line processing of a semiconductor fabrication, and

the magneto-resistive storage element is formed in a back-end-of-line processing of the semiconductor fabrication.

2. The memory device of claim 1 , wherein

a footprint area of the ferroelectric storage element is same as a footprint area of the magneto-resistive storage element.

3. The memory device of claim 1 , wherein the ferroelectric storage element comprises:

a substrate, comprising a first doped region and a second doped region;

a drain terminal, coupled to the first doped region of the substrate;

a source terminal, coupled to the second doped region of the substrate;

a gate terminal; and

a ferroelectric layer, located between the gate terminal and a region that is located between the first doped region and the second doped region of the substrate.

4. The memory device of claim 1 , wherein the magneto-resistive storage element comprises:

a magnetic layer, having a variable polarization direction;

a reference magnetic layer, having a fixed polarization direction; and

a tunnel barrier layer, sandwiched between the magnetic layer and the reference magnetic layer, wherein an electrical resistance of the magneto-resistive storage element varies according to whether the variable polarization direction of the magnetic layer is aligned with the fixed polarization direction of the reference magnetic layer.

5. The memory device of claim 1 , further comprising:

a read/write circuit, coupled to the plurality of multi-level memory cells, configured to perform a memory operation to a selected multi-level memory cell among the plurality of multi-level memory cells,

the selected multi-level memory cell is coupled to a selected word line from the plurality of word lines, a selected bit line from the plurality of bit lines and a selected source line from the plurality of source lines.

6. The memory device of claim 5 , wherein the read/write circuit is configured to:

read the first bit stored in the ferroelectric storage element; and

in response to determining that the first bit stored in the ferroelectric storage element is a first logic state, perform a write operation to change the first bit stored in the ferroelectric storage element from the first logic state to a second logic state and read the second bit stored in the magneto-resistive storage element.

7. The memory device of claim 5 , wherein the read/write circuit is configured to:

write first bit data to the ferroelectric storage element based on a voltage difference between the selected word line and the selected bit line; and

write second bit data to the magneto-resistive storage element based on a current flowing through the selected bit line and the selected source line.

8. The memory device of claim 7 , wherein the read/write circuit is configured to:

apply a first write voltage to the selected word line and apply a reference voltage to the selected bit line and the selected source line to write the first bit data to the ferroelectric storage element, and

apply an enable voltage to the selected word line, apply the reference voltage to the selected source line, and apply a second write voltage to the selected bit line to write the second bit data to the magneto-resistive storage element.

9. The memory device of claim 8 , wherein

the read/write circuit is configured to write the first bit data to the ferroelectric storage element before writing the second bit data to the magneto-resistive storage element.

10. A multi-level memory cell, comprising:

a ferroelectric memory element, configured to store a first bit of a multi-bit data;

a magneto-resistive storage element, configured to store a second bit of the multi-bit data,

wherein the ferroelectric storage element is cascaded to the magneto-resistive storage element,

the ferroelectric storage element is formed in a front-end-of-line processing of a semiconductor fabrication, and

the magneto-resistive storage element is formed in a back-end-of-line processing of the semiconductor fabrication.

11. The multi-level memory cell of claim 10 , wherein

a footprint area of the ferroelectric storage element is same as a footprint area of the magneto-resistive storage element.

12. The multi-level memory cell of claim 11 , wherein the ferroelectric storage element comprises:

a substrate, comprising a first doped region and a second doped region;

a drain terminal, coupled to the first doped region of the substrate;

a source terminal, coupled to the second doped region of the substrate;

a gate terminal; and

a ferroelectric layer, located between the gate terminal and a region between the first doped region and the second doped region of the substrate.

13. The multi-level memory cell of claim 11 , wherein the magneto-resistive storage element comprises:

a magnetic layer, having a variable polarization direction;

a reference magnetic layer, having a fixed polarization direction; and

a tunnel barrier layer, sandwiched between the magnetic layer and the reference magnetic layer, wherein an electrical resistance of the magneto-resistive storage element varies according to whether the variable polarization direction of the magnetic layer is aligned with the fixed polarization direction of the reference magnetic layer.

14. The multi-level memory cell of claim 10 , further comprising:

an access transistor, configured to enable the multi-level memory cell for a memory operation.

15. The multi-level memory cell of claim 10 , wherein

first bit data is written to the ferroelectric storage element based on a voltage difference between a word line and a bit line, and

second bit data is written to the magneto-resistive storage element based on a current flowing through the bit line and a source line.

16. A method, adapted to a memory device having a plurality of multi-level memory cells, each of the plurality of multi-level memory cells comprises a ferroelectric storage element and a magneto-resistive storage element, the method comprising:

storing a first bit of a multi-bit data to the ferroelectric storage element of a multi-level memory cell among the plurality of multi-level memory cells; and

storing second bit of the multi-bit data to the magneto-resistive storage element of the multi-level memory cell among the plurality of multi-level memory cells, wherein the ferroelectric storage element is cascaded to the magneto-resistive storage element,

wherein the ferroelectric storage element is formed in a front-end-of-line processing of a semiconductor fabrication, the magneto-resistive storage element is formed in a back-end-of-line processing of the semiconductor fabrication.

17. The method of claim 16 , further comprising:

reading the first bit stored in the ferroelectric storage element;

in response to determining that the first bit stored in the ferroelectric storage element is a first logic state, performing a write operation to change the first bit stored in the ferroelectric storage element from the first logic state to a second logic state and reading the second bit stored in the magneto-resistive storage element.

18. The method of claim 16 , further comprising:

writing first bit data to the ferroelectric storage element based on a voltage difference between a word line and a bit line coupled to the multi-level memory cell; and

writing second bit data to the magneto-resistive storage element based on a current flowing through the bit line and a source line coupled to the multi-level memory cell,

wherein writing the first bit data to the ferroelectric storage element comprises:

applying a first write voltage to the word line; and

applying a reference voltage to the bit line and the source line, and

wherein writing the second bit data to the magneto-resistive storage element comprises:

applying an enable voltage to the word line;

applying the reference voltage to the source line; and

applying a second write voltage to the bit line.