Voltage controlled spintronic devices for logic applications

Static information storage and retrieval – Systems using particular element – Magnetic thin film

Reexamination Certificate

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C365S173000, C257S421000

Reexamination Certificate




This invention relates generally to voltage controlled devices for logic applications. More particularly, this invention relates to voltage controlled rotation devices coupled to tunneling magneto-resistance devices.
Logic gates incorporated into devices such as microprocessors are well known in the computer and electronics industries. Logic gates currently used in such projects have several characteristics, however, they cannot be reprogrammed to form a different type of logic gate. It is therefore desirable to construct a logic device that can be quickly reprogrammed to act as a different type of logic gate, and that would result in less power consumption and heat loss, is relatively simple to fabricate, and also would result in space and cost savings.
The term “spintronics” refers to a new generation of electronic devices that make use of the electron spin as well as its charge. It is anticipated that spintronics devices will have superior properties compared to their semiconductor counterparts based on reduced power consumption due their inherent nonvolatility, elimination of the initial booting-up of random access memory, rapid switching speed, ease of fabrication, and large number of carriers and good thermal conductivity of metals. Such devices include giant magnetoresistance (GMR) and tunneling magnetoresistance (TMR) structures that consist of ferromagnetic films separated by metallic or insulating layers, respectively. Switching of the magnetization direction of such elementary units is by means of an external magnetic field that is generated by current pulses in electrical leads that are in proximity.
A system whereby the magnetization direction is controlled by an applied voltage is discussed at length in U.S. Ser. No. 09/467,808, incorporated herein by reference. Such as system comprises a ferromagnetic device with first and second ferromagnetic layers. The ferromagnetic layers are disposed such that they combine to form an interlayer with exchange coupling. An insulating layer and a spacer layer are located between the ferromagnetic layers. When a direct bias voltage is applied to the interlayer with exchange coupling, the direction of magnetization of the second ferromagnetic layer will change. The structure of a voltage-controlled rotation (VCR) device represents a marriage of GMR and TMR in that the two ferromagnetic layers are separated by nanoscale layers of both a metallic spacer and an insulator. The behavior of the VCR structure was described in U.S. Ser. No. 09/467,808 based on a free-electron-like, one-dimensional approximation. The principle of operation is that a bias voltage modulates the spin-dependent reflectivities such that the magnetization direction of the two ferromagnetic layers can be rotated from parallel to anti-parallel alignment. With such a device element there are many possible applications, such as in magnetic sensors, microwave devices, optical switches, and logic devices.
There are several logic devices that are well-known in the art, but these have their drawbacks. In particular, it would be desirable if these logic devices could be reprogrammed in some way, so that each logic gate could be shifted from one type of device within the group of AND, OR, NAND, and NOR gates to a second part and become part of a new circuit.
It is therefore an object of this invention to provide a voltage-controlled rotation transistor for use in logic devices.
It is also an object of this invention to provide a method of constructing AND, OR, NAND, NOR and NOT gates using voltage-controlled rotation transistors.
It is yet another object of this invention to create a series of changeable logic gates wherein the character of a particular logic gate can change depending upon external controllable parameters.
It is yet another object of this invention to create a series of logic gates wherein the individual gates can be re-programmed by a user.
It is still another object of this invention to create a series of logic gates wherein the logic gates can be reprogrammed on nanosecond time scales.
The above referenced objects, advantages and features of the invention together with the organization and manner of operation thereof will become apparent from the following detailed description when taken into conjunction with the accompanying drawings wherein like elements have like numerals throughout the drawings described below.

patent: 5629549 (1997-05-01), Johnson
patent: 5654566 (1997-08-01), Johnson
patent: 5768181 (1998-06-01), Zhu et al.
patent: 5926414 (1999-07-01), McDowell et al.
patent: 6069820 (2000-05-01), Inomata et al.


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