# US 9,520,174 B2 · Method and apparatus for writing to a magnetic tunnel junction (MTJ) by applying incrementally increasing voltage level

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- Number: US 9,520,174 B2
- Document ID: US9520174B2
- Status: Granted
- Kind: B2
- Application number: 14/754,635
- Filed: 2015-06-29
- Published: 2016-04-28
- Granted: 2016-12-13
- Earliest claimed: 2010-04-07
- Assignees: Avalanche Technology, Inc.
- Applicants: Ebrahim Abedifard; Petro Estakhri
- Inventors: Ebrahim Abedifard; Petro Estakhri
- Web page: https://patentgrep.com/patent/US9520174B2

## CPC

- G11C 11/1675: {Writing or programming circuits or methods}
- G11C 11/16: using elements in which the storage effect is based on magnetic spin effect
- G11C 11/161: {details concerning the memory cell structure, e.g. the layers of the ferromagnetic memory cell}
- G11C 11/1659: {Cell access}
- G11C 11/1673: {Reading or sensing circuits or methods}
- G11C 11/1677: {Verifying circuits or methods}
- G11C 11/1693: {Timing circuits or methods}
- G11C 11/5607: {using magnetic storage elements}
- G11C: STATIC STORES (semiconductor memory devices H10B)

## Abstract

A method of writing to magnetic tunnel junctions (MTJs) of a magnetic memory array includes storing in-coming data in a cache register, reading the present logic state of a first one of a set of at least two MTJs, the set of at least two MTJs including the first MTJ and a second MTJ. The in-coming data is to be written into the second MTJ. Further steps are storing the read logic state into a data register, swapping the contents of the data register and the cache register so that the cache register stores the read logic state and the data register stores the in-coming data, applying a first predetermined voltage level to the set of MTJs thereby causing the first MTJ to be over-written, applying a second predetermined voltage level to the set of MTJs, and storing the in-coming data into the second MTJ.

## Claims

### Claim 1

A method of writing to a magnetic tunnel junction (MTJ) of a magnetic memory array comprising:
a. selecting a word line that is coupled to an MTJ to be written;
b. applying a voltage pulse with a voltage level of Vx to a source line coupled to the MTJ;
c. reading a state of the MTJ after applying the voltage pulse;
d. comparing the state of the read MTJ to a value in a write latch;
e. determining if a desired state is written to the read MTJ; and
f. if the MTJ is determined not to be written to the desired state, increasing the voltage level and re-applying the voltage pulse with the increased voltage level and repeating steps c. through f. until the MTJ is written to the desired state.

### Claim 2 (depends on 1)

The method of writing to a magnetic tunnel junction (MTJ), as recited in claim 1, wherein the desired state is same as an in-coming data.

### Claim 3 (depends on 1)

The method of writing to a magnetic tunnel junction (MTJ), as recited in claim 1, wherein an access transistor is coupled to the MTJ and the word line is coupled to the access transistor and wherein upon writing the desired state into the MTJ, de-selecting the word line.