Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Magnetic field
Reexamination Certificate
2002-09-06
2004-03-09
Ho, Hoai (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Magnetic field
C257S295000
Reexamination Certificate
active
06703676
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic memory device being a nonvolatile solid-state memory using magnetoresistive elements, and to a manufacturing method thereof.
2. Description of Related Art
In recent years, semiconductor memory devices being solid-state memories have widely been used for information equipment and the like. The kinds of the semiconductor memory devices are various such as a dynamic random access memory (DRAM), a ferroelectric random access memory (FeRAM), and an electrically erasable programmable read-only memory (EEPROM). The characteristics of such semiconductor memory devices have both merits and demerits, and it is difficult for the conventional semiconductor memory devices to meet all of the specifications required by the present information equipment.
Accordingly, a magnetic memory device (a magnetic random access memory (MRAM)) using magnetoresistive elements has been researched and developed in recent years. Because the magnetic memory device uses magnetic films for storing information, the magnetic memory device has nonvolatility being a feature such that the stored information is not erased even if the power supply to the magnetic memory device is turned off. And the magnetic memory device is expected to meet all of the specifications required by various pieces of information equipment with respect to various characteristics such as a recording time, a readout time, a recording density, the capable number of times of rewriting, and electric power consumption.
The magnetic memory device is provided with the magnetoresistive elements as its memory cells. Spin dependent tunneling magnetoresistive elements (TMR elements) are suitably used as such magnetoresistive elements. The TMR element has the basic structure composed of two magnetic layers and a thin non-magnetic layer put between them for storing information. The magnetoresistive ratio (MR ratio) of the TMR element is larger than that of other magnetoresistive elements, and the value of resistance of the TMR element can be set at a value within a range from several k&OHgr; to several tens k&OHgr; which is the most suitable value as the value of resistance of a memory cell of the magnetic memory device. Consequently, the TMR elements are generally used as memory elements of the magnetic memory device.
The value of the resistance of the TMR element differs in the case where the pieces of magnetization of the magnetic layers with the non-magnetic layer put between them are parallel to each other (see
FIG. 14A
) and in the case where the pieces of magnetization of them are anti-parallel to each other (see FIG.
14
B). Accordingly, the two states can be stored as logical values “0” and “1”, respectively. The states of the logical values “0” and “1” can be stored by, for example, fixing the direction of the magnetization of one of the two magnetic layers and by changing the direction of the magnetization of the other of the two magnetic layers by external magnetic fields. The operation is the so-called information writing operation. The method is known which uses the magnetic fields generated by an electric current flowing through the wiring disposed in the vicinity of the TMR element for changing the direction of the magnetization.
Then, the value of the resistance of the TMR element is obtained by detecting the voltage or the current of the TMR element. The states of the logical values “0” and “1” can be distinguished on the basis of the value of the resistance. The operation is the so-called information readout operation. To put it more concretely, the following two detection methods are known: the absolute detection method distinguishing the states of the logical values “0” and “1” on the basis of the absolute value of the resistance, and the differential detection method reading the states of the logical values “0” and “1” by applying a magnetic field weaker than that at the time of writing to cause the magnetization reversal of only the magnetic layer having a smaller coercive force.
The TMR element using the so-called in-face magnetization films magnetized in the direction parallel to the surfaces of the magnetic layers as shown in
FIGS. 14A and 14B
has the following problem in the case where the size of the element is made to be small. That is, when the size of the TMR element is made to be small, demagnetizing fields (self attenuation magnetic fields) are generated in the magnetic layers and the curling of the magnetization is also generated at the end surfaces thereof. Thereby, the magnetization direction of the magnetic layer to record and hold information is not determined in a fixed direction to be instable. Consequently, it becomes impossible for the TMR element to hold the information owing to the decrease of the magnetoresistance ratio (MR ratio) thereof caused by the instability of the magnetization direction and the like. Hence, the TMR element of the type of in-face magnetization has the limitations of the miniaturization and the large scale integration of the memory device using the TMR elements owing to the impossibility of the holding of information in case of making the sizes of the TMR elements too small.
U.S. Pat. No. 6,219,275 discloses a TMR element using the so-called perpendicular magnetic anisotropy film in which magnetization is made in the direction perpendicular to the surfaces of magnetic layers (see
FIGS. 15A and 15B
) for solving the above-mentioned problem. The perpendicularly magnetized TMR element does not generate large demagnetizing fields even if the size of the TMR element is made to be small, and can hold information stably. Consequently, the perpendicularly magnetized TMR elements can constitute a magnetic memory device smaller in size and more highly integrated than that composed of the TMR elements of the type of the in-face magnetization.
In the case where a magnetic memory device is composed by the use of the above-mentioned TMR elements, it is general to adopt the structure in which the TMR elements are laminated on metal oxide semiconductor field effect transistors (MOSFET's). To put it concretely, the magnetic layers of the TMR elements are connected with the drain regions of the MOSFET's through conductive members such as metal plugs.
A conventional magnetic memory device has the problem in which it is difficult to form non-magnetic layers located between magnetic layers to be flat. In such a case, the problem may be produced in which magnetization directions of the upper and the lower magnetic layers of a memory cell in such a magnetic memory device cannot be formed in an ideally parallel state or an ideally anti-parallel state. In particular, in the case where the tunneling barrier layer of a TMR element is not flat, unevenness of film thickness is produced to generate a leakage current. The leakage current causes the decrease of the MR ratio in turn. Moreover, in the case where the magnetization directions of the upper and the lower magnetic layers is not in the ideally parallel state or the ideally anti-parallel state, the spin polarizability of the interfaces of the tunneling barrier layer decreases also to decrease the MR ratio. That is, it becomes impossible to obtain stable changes of the magnetoresistance of the TMR element.
SUMMARY OF THE INVENTION
Accordingly, the present invention aims to provide a magnetic memory device having the following characteristics, and a manufacturing method thereof. That is, the surface roughness of the magnetoresistive elements laminated on the conductive members of the magnetic memory device is small, and the magnetic layers and the non-magnetic layers of the magnetic memory device are flat. Moreover, in the magnetic memory device using TMR elements particularly, the leakage current is suppressed, and the MR ratio thereof is high.
A feature of the present invention exists in a point that in a non-volatile magnetic memory device including a magnetoresistive element composed of a first and a second magnetic layers being magnetized chiefly
Hirai Tadahiko
Nishimura Naoki
Ho Hoai
Ho Tu-Tu
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