Abstract:
The integrated memory has memory cells with a magnetoresistive memory effect connected to column lines and row lines. Each of the memory cells is respectively wired between one of the column lines and one of the row lines. They are constructed such that they can be disconnected from the respective column line and/or row line by conducting a given current through the respective memory cell. It is thus possible to achieve a relatively small outlay for repairing a memory in the event of a defect of a memory cell.

Description:
BACKGROUND OF THE INVENTION 
     FIELD OF THE INVENTION 
     The invention lies in the integrated technology field and relates, more specifically, to an integrated memory having cells with a magnetoresistive memory effect. Each of the memory cells is connected between one of several column lines and one of several row lines. 
     Memory cells with a magnetoresistive effect generally comprise ferromagnetic layers of a modifiable condition for storing data signals. This type of memory effect is generally known as the GMR (Giant Magnetoresistive) effect or the TMR (Tunneling Magnetoresistive) effect. The electrical resistance of such a memory cell depends on the magnetization in the ferromagnetic layers. 
     Integrated memories having memory cells of this type—also referred to as so-called MRAM memories—are often constructed like integrated DRAM memories. Generally, these memories comprise a cell arrangement with substantially parallel row lines and column lines, whereas the row lines customarily run transverse to the column lines. 
     International PCT publication WO 99/14760 (corresponding to commonly assigned, copending U.S. application Ser. No. 09/528,159) describes an MRAM memory of this type. There, each of the memory cells is wired between one of the row lines and one of the column lines and electrically connected to the respective column line and row line. The memory cells with a magnetoresistive effect are thus more highly resistive than the row lines and column lines. The column lines are connected to a read amplifier for reading a data signal of one of the memory cells. Reading is accomplished by measuring the detectable current on the column line. 
     In an MRAM memory of that type, there are no diodes or transistors such as are provided in a DRAM memory for connecting the memory cells to the respective column lines in dependence upon the addressing for reading purposes. This brings particular advantages given a geometric arrangement of the memory cells. In particular, it is possible to save space in the arrangement of the memory cells by using a stack arrangement of the cells. 
     Owing to influences that are conditional to production, such as processing fluctuations, or as a result of aging, it is possible that individual memory cells may exhibit an undesirable, relatively low resistance and may thus be defective. Connected column lines and row lines are substantially shorted by way of such defective cells. Such shorts influence additional memory cells along this respective column line or row line. Furthermore, as a result of a short caused by one of the memory cells, other memory cells along affected lines can no longer be tested in a functional test. When a memory with a defective cell is repaired, the problem cannot be eliminated by replacing a single affected row line or column line, since the functioning of memory cells of the other affected line is still impaired due to the short. It is therefore necessary to replace both affected lines of a defective memory cell in this case. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a integrated memory having memory cells with magnetoresistive memory effect which overcomes the above-noted deficiencies and disadvantages of the prior art devices and methods of this general kind, and with which the outlay for repairing the memory in the event of a defect of a memory cell which triggers a short between a row line and a column line can be reduced. with the above and other objects in view there is provided, in accordance with the invention, an integrated memory, comprising: 
     a plurality of column lines and a plurality of row lines; 
     a plurality of memory cells with a magnetoresisitve memory effect; and 
     electrical connections formed between and connecting the memory cells each to a respective one of the column lines and to a respective one of the row lines, and wherein at least one of the electrical connections is configured to be severed by a current flow through the memory cell, whereby the electrical connection is interrupted. 
     In other words, the object of the invention are achieved by an integrated memory with magnetoresistive memory cells that are respectively wired between one of several column lines and one of several row lines and electrically connected to the respective column line and row line. The memory cells are configured so as to be disconnectible from the respective column line and/or row line by means of a current flow through the respective memory cell, thereby interrupting the respective electrical connection. 
     In the inventive integrated memory, when defective memory cells emerge which trigger a short between the respective connected row line and column line, it is possible to disconnect these so as to interrupt the respective electrical connection. The short between the affected row line and column line is thus interrupted. The column line and row line connected to a defective memory cell, and the memory cells connected to these, are therefore no longer affected by the short. The column line and row line that are connected to a defective memory cell can continue to be used for a normal operation or a test operation of the integrated memory, for example. The outlay for disconnecting the memory cell is relatively small. On principle, no lines need to be replaced. 
     The integrated memory advantageously comprises redundant memory cells for repairing defective cells, which are combined into at least one redundant row line and/or redundant column line which can replace regular lines having defective memory cells per address. In this process, the integrated memory is tested using an external testing device, and the redundant elements are then programmed using what is known as a redundancy analysis. A redundant circuit comprises programmable elements, for instance in the form of programmable fuses, which serve for storing the address of a line that must be replaced. 
     To repair the integrated memory in the event of a defective memory cell, it suffices to replace only one of the affected lines by a redundant line. Since the short in the defective memory cell is interrupted, the other affected lines can continue operating. The repair outlay can be advantageously reduced in this way. 
     If the integrated memory comprises several redundant row lines and column lines, in the event of a defective memory cell, it is possible to proceed with a functional test of the remaining memory cells, for instance along the connected row line, if the defective memory cell is first disconnected from the affected row line. In this way, all memory cells of the integrated memory can be tested even if defective cells should meanwhile emerge. The advantage of this is that a purposeful optimized programming of the redundant lines can be carried out by means of a subsequent redundancy analysis. Since the number of redundant lines is usually limited, the production yield of integrated memories can be increased by these means. 
     In accordance with an added feature of the invention, the current flow for disconnecting one of the memory cells has a higher current intensity than a rated current flow for reading data signals from or for writing data signals into a respective one of the memory cells. The current flow for disconnecting a defective memory cell is, by way of example, generated by a current source that is connected from the outside. An overvoltage limit is thus expediently defined, so that a predetermined voltage is not exceeded when the elevated current is injected. 
     In accordance with an additional feature of the invention, electrical interconnects are respectively provided between the memory cells and each connected column line and/or between the memory cells and each connected row line. The interconnects comprise a rupture joint which can be severed by the current flow for disconnecting a defective memory cell. The rupture joint is achieved by a tapering of the width of the respective interconnect and thus forming a fuse link. The tapering is constructed such that the respective interconnect is separated by the current flow for disconnecting the defective memory cell. 
     In accordance with a concomitant feature of the invention, the memory cells comprise an electrically disconnectible material which is wired between the memory cells and the respective column line and/or row line. This material is constructed such that the current flow for disconnecting a defective memory cell interrupts the electrical connection between the memory cell and one or both of the two connected lines. The disconnectible material is expediently layered onto the memory cells. 
     Other features which are considered as characteristic for the invention are set forth in the appended claims. 
     Although the invention is illustrated and described herein as embodied in an integrated memory having memory cells with a magnetoresistive memory effect, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
    
    
     The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a circuit schematic of the integrated memory with magnetoresistive memory cells according to the invention; 
     FIG. 2 is a diagrammatic perspective view of an embodiment of a memory cell with a connected row line and column line; and 
     FIG. 3 is a diagrammatic perspective view of an additional embodiment of a memory cell, with a connected row line and column line. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there is seen an exemplary embodiment of an inventive memory having memory cells MC with a magnetoresistive memory effect. Any known GMR/TMR elements are suitable as the memory cells, provided they exhibit higher impedance than the column lines (here referenced bit lines BL 0  to BLn) and the row lines (here referenced word lines WL 0  to WLm). The memory here comprises an exemplary number of word lines and bit lines. The memory cells MC, which are arranged in a matrix-type memory cell field  1 , are each wired between one of the bit lines BL 0  to BLn and one of the word lines WL 0  to WLm. 
     For reading a data signal from one of the memory cells MC, the corresponding bit line is connected to a non-illustrated read amplifier. The relevant word line is actuated for reading information that is stored in a memory cell. To this end, it is charged with a predetermined potential, so that a current flow arises through the memory cell that is to be read out. All other word lines are set to reference potential. For reading out a data signal, the bit line connected to the memory cell being read out is connected to a corresponding read amplifier, which detects this current flow. 
     The memory cell MC 12  represented in FIG. 1 is connected to the word line WL 1  and the bit line BL 2 . It is assumed here that the memory cell MC 12  is defective. The bit line BL 2  and the word line WL 1  are shorted via the memory cell MC 12 , this being represented schematically in FIG. 1 by a short-circuit arc KS. If the short persists during a normal operation of the memory, a proper read or write operation cannot occur in select memory cells along the word line WL 1  or the bit line BL 2 . In that case, the current flow for reading or writing data signals is superimposed by the current flow that is brought about by the short in the memory cell MC 12 . 
     The memory cell MC 12  according to the invention is constructed such that it can be disconnected from the bit line BL 2  and/or the word line WL 1  by means of the current IB. The current IB is provided by an external source and is higher than a current for reading or writing a data signal. In this way, the shorted electrical connection between the bit line BL 2  and the word line WL 1  can be interrupted. The memory cell MC 12  is thus suitably addressed by the switches SB and SW. The current source for generating the current IB and the word line WL 1  are respectively connected to a reference potential GND of the memory. 
     The memory cells MC of the memory cell field  1  are operationally tested in a functional test. If a defective memory cell MC is detected, it can be disconnected as described above. The memory cell field  1  can be completely tested without an undesirable short-circuit current arising. Given the emergence of defective memory cells MC, affected word lines WL 0  to WLm or affected bit lines BL 0  to BLn can be replaced by redundant word lines RWL or redundant bit lines RBL, respectively. By virtue of the complete testing of the memory field  1 , a complete redundancy analysis can be carried out, with the aid of which a purposeful optimized programming of the redundant word lines RWL and redundant bit lines RBL can occur. 
     Of course, it is also possible to continue to operate the memory without replacement by a redundant line. But the affected memory cell is defective, which can impair operation. In a repair using a redundant line, only the affected word line or bit line (WL 1  or BL 2  in FIG. 1) must be replaced. 
     Referring now to FIG. 2, there is shown an exemplary embodiment of the memory cell MC 12 , which is connected to the word line WL 1  and the bit line BL 2 . An electrical interconnect LB 1  is provided between the memory cell MC 12  and the word line WL 1 . An interconnect LB 2  is provided between the memory cell MC 12  and the bit line BL 2 . Here, each of the two interconnects LB 1  and LB 2  expediently comprise a rupture joint, i.e., a fuse, in the form of taperings VJ 1  and VJ 2 , respectively. The widths, that is to say the diameters, of the interconnects LB 1  and LB 2  are expediently reduced at the tapers. The widths of the interconnects LB 1  and LB 2  are dimensioned such that they can be severed by the elevated current flow IB in order to disconnect the memory cell MC 12 , while they are completely functional at the current used for regular read-out and writing. The memory cell MC 12  is composed of three layers. It has a hard magnetic layer HM, a tunnel barrier TB, and a soft magnetic layer WM. 
     Referring now to FIG. 3, there is shown another embodiment of the memory cell MC 12 . In this example, a layer material SM which can be electrically disconnected or separated is disposed between the memory cell MC 12  and the word line WL 1 . Additionally or alternatively, the layer material SM can be disposed between the memory cell MC 12  and the bit line BL 2 . As in FIG. 2, the memory cell MC 12  is disconnected by means of layer SM by a current IB through the memory cell, thereby interrupting the electrical connection between the memory cell MC 12  and the word line WL 1 .