Flexible substrate for use with a perpendicular magnetic tunnel junction (PMTJ)

1. A method, comprising:

forming, at a low temperature, a thin film transistor structure above a flexible substrate in a film thickness direction, wherein the low temperature is less than about 200° C., and wherein the thin film transistor structure includes a contact pad on a lower or upper surface thereof;

forming, at a high temperature, a perpendicular magnetic tunnel junction (pMTJ) structure above a rigid substrate, wherein the high temperature is greater than about 200° C.;

removing the rigid substrate from below the pMTJ structure; and

bonding, at the low temperature, the pMTJ structure to the thin film transistor structure using an adhesion layer.

2. The method as recited in claim 1 , wherein the thin film transistor structure utilizes a bottom gate/bottom contact architecture, and wherein forming the thin film transistor structure comprises:

forming a gate layer above the flexible substrate;

forming a gate oxide layer above the gate layer and exposed portions of the flexible substrate in a film thickness direction, the gate oxide layer electrically insulating the gate layer from layers formed thereabove;

forming a source layer and a drain layer above the gate oxide layer in the film thickness direction; and

forming a channel layer above the source layer, the drain layer, and an exposed portion of the gate oxide layer that is not covered by the source layer or the drain layer in the film thickness direction,

wherein the source layer is separated from the drain layer by a portion of the channel layer.

3. The method as recited in claim 1 , wherein the thin film transistor structure utilizes a bottom gate/top contact architecture, and wherein forming the thin film transistor structure comprises:

forming a gate layer above the flexible substrate in a film thickness direction;

forming a gate oxide layer above the gate layer and exposed portions of the flexible substrate that are not covered by the gate layer in the film thickness direction, the gate oxide layer electrically insulating the gate layer from layers formed thereabove;

forming a channel layer above the gate oxide layer in the film thickness direction;

forming a source layer and a drain layer above the channel layer in the film thickness direction;

forming an insulative layer above the source layer, the drain layer, and exposed portions of the channel layer in the film thickness direction, wherein the source layer is separated from the drain layer by a portion of the insulative layer;

removing a portion of the insulative layer that is positioned above the drain layer to form a contact hole, the contact hole exposing a top edge of the drain layer; and

forming a contact pad layer in the contact hole and above a portion of the insulative layer, the contact pad comprising a low temperature bonding conductive material, wherein an upper portion of the contact pad layer extends beyond extents of the drain layer in an element thickness direction perpendicular to the film thickness direction.

4. The method as recited in claim 1 , wherein the thin film transistor structure utilizes a top gate/bottom contact architecture, and wherein forming the thin film transistor structure comprises:

forming a source layer and a drain layer above the flexible substrate in a film thickness direction;

forming a channel layer above the source layer, the drain layer, and a portion of the flexible substrate between the source layer and the drain layer in the film thickness direction, wherein the source layer is separated from the drain layer by a portion of the channel layer;

forming a gate oxide layer above the gate layer and exposed portions of the flexible substrate that are not covered by the gate layer in the film thickness direction; and

forming a gate layer above the gate oxide layer in the film thickness direction, wherein the gate layer is electrically insulated from layers formed therebelow by the gate oxide layer.

5. The method as recited in claim 1 , wherein the thin film transistor structure utilizes a top gate/top contact architecture, and wherein forming the thin film transistor structure comprises:

forming a channel layer above a portion of the flexible substrate in a film thickness direction;

forming a source layer and a drain layer above the channel layer in the film thickness direction;

forming a gate oxide layer above the source layer, the drain layer, a portion of the channel layer between the source layer and the drain layer, and exposed portions of the substrate not covered by the channel layer in the film thickness direction, wherein the source layer is separated from the drain layer by a portion of the gate oxide layer;

forming a gate layer above the gate oxide layer in the film thickness direction, wherein the gate layer is electrically insulated from layers formed therebelow by the gate oxide layer;

forming an insulative layer above the gate layer and exposed portions of the gate oxide layer in the film thickness direction;

removing portions of the insulative layer and the gate oxide layer that is positioned above the drain layer to form a contact hole, the contact hole exposing a top edge of the drain layer; and

forming a contact pad layer in the contact hole and above a portion of the insulative layer, the contact pad comprising a low temperature bonding conductive material, wherein an upper portion of the contact pad layer extends beyond extents of the drain layer in an element thickness direction perpendicular to the film thickness direction.

6. The method as recited in claim 5 ,

wherein the flexible substrate comprises at least one material selected from a group consisting of: polyimide, polyether ether ketone (PEEK), polyethylene naphthalate (PEN), and transparent conductive polyester film,

wherein the gate layer comprises at least one material selected from a group consisting of: doped polysilicon, W, TaN, TiNi, and TiN,

wherein the gate oxide layer comprises at least one material selected from a group consisting of SiO 2 , Al 2 O 3 , and HfO 2 ,

wherein the source layer comprises at least one material selected from a group consisting of: Pt, Ir, Pd, Au, Ti, Ta, Cu, Iridium Tin Oxide (ITO),

wherein the drain layer comprises at least one material selected from a group consisting of: Pt, Ir, Pd, Au, Ti, Ta, Cu, and ITO,

wherein the channel layer comprises at least one material selected from a group consisting of: ZnO 2 , InZnO, InGaZnO, pentacene, poly(3-hexylthiophene) (P3HT), and alkyl-substituted triphenylamine polymers (PTAA), and wherein the contact pad layer comprises at least one material selected from a group consisting of: Au, Ag, and Ta.

7. The method as recited in claim 1 , wherein removing the rigid substrate from below the pMTJ structure comprises:

adhering a lift layer to an upper surface of a bit line layer positioned above the pMTJ structure, the lift layer comprising polydimethylsiloxane (PDMS); and

etching, using concentrated hot phosphoric acid (H 3 PO 4 ), a sacrificial buried layer located below the pMTJ structure and above the rigid substrate to release the pMTJ structure from the rigid substrate.

8. The method as recited in claim 1 , wherein forming the pMTJ structure comprises:

forming a sacrificial buried layer above the rigid substrate in a film thickness direction;

forming the adhesion layer above the sacrificial buried layer in the film thickness direction;

forming a bottom electrode layer above the adhesion layer in the film thickness direction;

forming a pMTJ above the bottom electrode layer in the film thickness direction;

forming an upper electrode layer above the pMTJ in the film thickness direction;

patterning the adhesion layer, the bottom electrode, the pMTJ, and the upper electrode layer to form a pillar via a material removal process;

forming a second insulative layer around the pillar to an upper extent of the upper electrode layer in the film thickness direction;

forming a channel through the second insulative layer that is separated from a side of the pillar by a portion of the second insulative layer; and

forming a bit line layer above the second insulative layer, an exposed portion of the sacrificial buried layer and the upper electrode layer, and along sides of the channel.

9. The method as recited in claim 8 , wherein the sacrificial buried layer has a thickness of about 50 nm to about 100 nm and comprises at least one material selected from a group consisting of: SiN, SiGe, and amorphous silicon (α-Si), and

wherein the bit line layer comprises at least one material selected from a group consisting of: W, TaN, TiNi, TiN, and TiW.