Planar Multiferroic/Magnetostrictive Nanostructures as Memory Elements, Two-Stage Logic Gates and Four-State Logic Elements for Information Processing

A magnetostrictive nanomagnet comprising:

• a silicon base layer on which is formed a first electrical contact and an inter-digitated array at one edge of the substrate;
• and
• a magnetostrictive nanomagnetic layer formed over the silicon base layer,
• wherein magnetization of the nanomagnet is rotated by strain transferred from the substrate when a surface acoustic wave (SAW) launched by the inter-digitated array propagates in the substrate.

A method of making magnetostrictive-piezoelectric multiferroic nanomagnets comprising the steps of:

• spinning a resist on an n+ silicon (Si) substrate;
• forming a window in the resist with a lithographic technique;
• depositing an elastically soft layer within the window;
• depositing a piezoelectric (PZT) layer on top of the soft layer within the window;
• depositing a magnetostrictive layer over the PZT layer within the window;
• and
• forming electrical contacts for electrically accessing a top surface of the magnetostrictive layer in order to apply a voltage through the multiferroic structure that is mostly dropped across the PZT layer.

A method of making magnetostrictive-piezoelectric multiferroic nanomagnets comprising the steps of:

• spinning a resist on an n+ silicon (Si) substrate;
• forming a window in the resist with a lithographic technique;
• depositing an elastically soft layer;
• forming a magnetostrictive layer over the soft layer;
• depositing a piezoelectric (PZT) layer over the magnetostrictive layer;
• and
• forming electrical contacts for electrically accessing the top of the PZT layer in order to apply a voltage across the PZT layer.

A method for fabricating a cross-bar architecture with the multiferroic element at an intersection of two mutually perpendicular contact lines for addressing individual elements, comprising the steps of:

• delimiting a parallel array of gold lines on a silicon substrate to form one set of contact lines;
• spinning a first resist over the silicon substrate and gold lines;
• opening a first set of windows in the first resist by lithography, said first set of windows being aligned with the gold lines;
• sputtering a layer of silicon dioxide on the first set of windows opened by lithography;
• spinning a layer of electron-beam resist;
• opening a second set of windows in the electron-beam resist, said second set of windows being aligned in a way to be cross-wise with the first set of windows;
• sequentially depositing a hard magnet, followed by an approximate 1 nm layer of a tunnel barrier oxide deposited with atomic layer deposition, followed by a magnetostrictive layer deposited, followed by a piezoelectric layer deposited with pulsed laser deposition, followed by lift-off to produce a layered structure within each window of the second set of windows;
• and
• spinning a third resist and opening horizontal slats through which a conducting organic layer is deposited to make soft electrical contacts and complete the cross-bar architecture for addressing individual elements;
• whereby silicon dioxide pillars prevent expansion or contraction in a direction perpendicular to pillar faces to generate uniaxial strain in the piezoelectric layer when a potential difference is imposed between the gold lines and the conducting polymer lines, and the conducting polymer is a soft material that does not clamp and prevent the piezoelectric layer from expanding or contracting in a direction parallel to the pillar faces, this expansion/contraction operating to generate strain in the piezoelectric layer and rotate the magnetization of the magnetostrictive layer.

A method of making magnetostrictive nanomagnets comprising the steps of:

• spinning a resist on an n+ silicon (Si) substrate;
• forming periodic windows in the resist with a lithographic technique;
• depositing a magnetostrictive layer within the windows;
• spinning a second layer of resist and carrying out a second level of lithography to deposit a periodic arrays of masses interposed between rows of magnets;
• and
• forming interdigitated electrodes on the Si substrate for launching surface acoustic waves.

A multiferroic nanomagnetic non-volatile memory comprising:

• an array of multiferroic nanomagnets with negligible dipole interaction with binary bits encoded in a plurality of stable magnetization directions, each of said multiferroic nanomagnets comprising a piezoelectric layer and a magnetostrictive layer;
• means for applying a voltage pulse to the piezoelectric layer of each of the multiferroic nanomagnets to produce compressive/tensile stress in the magnetostrictive layer to independently switch a logic state of the multiferroic nanomagnets which act as individual memory elements;
• means for reading stored bits using a magnetic tunnel junction integrated vertically underneath each nanomagnet;
• and
• a crossbar architecture to individually address each nanomagnet for read and write operations.