Static information storage and retrieval – Systems using particular element – Magnetic thin film
Reexamination Certificate
2002-08-16
2004-09-21
Nguyen, Viet Q. (Department: 2818)
Static information storage and retrieval
Systems using particular element
Magnetic thin film
C365S173000, C365S097000, C365S087000, C365S074000, C365S066000, C365S048000
Reexamination Certificate
active
06795339
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thin film magnetic memory device having a magnetic film and a communication function as well as a radio chip, a distribution management system and a manufacturing process management system each using the thin film magnetic memory device.
2. Description of the Related Art
Attention has been paid to an MRAM (Magnetic Random Access Memory) device serving as a memory capable of storing nonvolatile data with lower consumption power. The MRAM device is a memory which stores data in a nonvolatile manner using a plurality of thin film magnetic elements formed on a semiconductor integrated circuit and which can randomly access the respective thin film magnetic bodies.
In recent years, it is particularly made public that the performance of the MRAM device surprisingly advances by using a thin film magnetic body utilizing a magnetic tunnel junction (MTJ) as a memory cell. The MRAM device which includes memory cells having magnetic tunnel junctions is disclosed in technical documents such as “A 10 ns Read and Write Non-Volatile Memory Array Using a Magnetic Tunnel Junction and FET Switch in each Cell”, ISSCC Digest of Technical Papers, TA7.2, February 2000 and “Nonvolatile RAM based on Magnetic Tunnel Junction Elements”, ISSCC Digest of Technical Papers, TA7.3, February 2000.
FIG. 17
is a schematic diagram showing the configuration of a memory cell having a magnetic tunnel junction (which memory cell will be also referred to simply as “MTJ” memory cell hereinafter).
Referring to
FIG. 17
, the MTJ memory cell includes a tunnel magneto-resistance element TMR having electric resistance changing according to the data level of magnetically written, stored data, and an access element ATR. Access transistor ATR is connected to tunnel magneto-resistance element TMR in series between a bit line BL and a source line SL. Access element ATR is typically formed out of a field effect transistor.
Bit line BL for carrying a data write current and a data read current during data write and data read, respectively, a write digit line WDL for carrying the data write current during data write, a word line WL for instructing data to be read, and source line SL for pulling down the voltage of tunnel magneto-resistance element TMR to a ground voltage GND during data read are arranged for the MTJ memory cell.
During data read, tunnel magneto-resistance element TMR is electrically connected between source line SL (ground voltage GND) and bit line BL when access transistor ATR is turned on.
FIG. 18
is a conceptual view for explaining a data write operation for writing data to the MTJ memory cell.
Referring to
FIG. 18
, tunnel magneto-resistance element TMR includes a magnetic body layer which has a fixed magnetization direction (which layer will be also simply referred to as “fixed magnetic layer” hereinafter) FL and a magnetic body layer which is magnetized in a direction according to a data write magnetic field generated by the data write current (which layer will be also simply referred to as “free magnetic layer” hereinafter) VL. A tunneling barrier TB formed out of an insulating film is provided between fixed magnetic layer FL and free magnetic layer VL. Free magnetic layer VL is magnetized in the same direction as or the opposite direction to the magnetization direction of fixed magnetic layer FL in accordance with the level of written, stored data.
The electric resistance of tunnel magneto-resistance element TMR changes according to the relative relationship in magnetization direction between fixed magnetic layer FL and free magnetic layer VL. Specifically, if the magnetization layer of fixed magnetic layer FL is the same as (parallel to) that of free magnetic layer VL, the electric resistance of tunnel magneto-resistance element TMR becomes lower than that of tunnel magneto-resistance element TMR if the magnetization direction of fixed magnetic layer FL is opposite (anti-parallel) to that of free magnetization direction FL.
During data write, word line WL is inactivated and access transistor ATR is turned off. In this state, data write currents for magnetizing free magnetic layer VL are applied to bit line BL and write digit line WDL, respectively in accordance with the level of written data. That is, the magnetization direction of free magnetic layer VL is determined according to the directions of the data write currents carried to write digit line WDL and bit line BL, respectively.
FIG. 19
is a conceptual view showing the relationship between the data write current and the magnetization direction of the MTJ memory cell.
Referring to
FIG. 19
, the horizontal axis Hx indicates the direction of a magnetic field H(WDL) generated by the data write current carried to write digit line WDL. The vertical axis Hy indicates a magnetic field H(BL) generated by the data write current carried to bit line BL.
The magnetization direction of free magnetic layer VL is updated only if the sum of magnetic fields H(WDL) and H(BL) reaches an external region of an asteroid characteristic line shown. That is, to execute data write, it is necessary to carry a sufficient data write current to generate a magnetic field having an intensity exceeding a predetermined intensity to both of write digit line WDL and bit line BL.
On the other hand, if a magnetic field corresponding to the inner region of the asteroid characteristic line is applied, the magnetization direction of free magnetic layer VL has no changed. Namely, if a predetermined data write current is applied only to one of write digit line WDL and bit line BL, data write is not executed. The magnetization direction which has been written to the MTJ memory cell, i.e., stored data level is held in a nonvolatile manner until new data is written. As indicated by the asteroid characteristic line, it is possible to decrease a necessary magnetization threshold to change the magnetization direction along a magnetization easy axis by applying a magnetic field in a magnetization hard axis direction to free magnetic layer VL.
FIG. 20
is a conceptual view for explaining a data read operation for reading data from the MTJ memory cell.
Referring to
FIG. 20
, during data read, access transistor ATR is turned on in response to the activation of word line WL. As a result, tunnel magneto-resistance element TMR is electrically connected to bit line BL while being pulled down to ground voltage GND. In this state, by applying a data read current Is to a current path including bit line BL and tunnel magneto-resistance element TMR, voltage change according to the electric resistance of tunnel magneto-resistance element TMR, i.e., the level of the stored data of the MTJ memory cell can be generated in bit line BL. For example, if precharging bit line BL with a predetermined voltage and then starting the supply of data read current Is, it is possible to read the data stored in the MTJ memory cell by detecting the voltage of bit line BL.
FIG. 21
is a block diagram of an MTJ memory cell formed on a semiconductor substrate.
Referring to
FIG. 21
, access transistor ATR formed on a semiconductor substrate SUB includes source/drain regions
310
and
320
which are n-type regions, and a gate
330
. Source/drain region
310
is electrically connected to source line SL through a metal film formed in a contact hole
341
.
Write digit line WDL is formed on a metal wiring layer formed on the upper layer of source line SL. Tunnel magneto-resistance element TMR is electrically connected to source/drain region
320
of access transistor ATR through a metallic film formed on a strap
345
and a contact hole
340
. Strap
345
is provided to electrically connect tunnel magneto-resistance element TMR to access transistor ATR and is formed out of a conductive material.
Bit line BL is electrically connected to tunnel magneto-resistance element TMR and provided on the upper layer of tunnel magneto-resistance element TMR. As already described, during data write, it is necessary to carry a data write current to each of bit
McDermott Will & Emery LLP
Nguyen Viet Q.
Renesas Technology Corp.
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