Embodiments of the invention relate to a memory circuit using magnetic storage elements and particularly relate to magnetic random access memory (MRAM) circuits.
Magnetic (or magneto-resistive) random access memory (MRAM) circuits have several desirable characteristics such as high speed, high density (i.e., small bit cell size), low power consumption, and no degradation over time, particularly over the dynamic random access memory (DRAM) circuit. MRAM circuits are integrated typically with a complementary metal-oxide semiconductor (CMOS) technology.
A first aspect of the invention provides a memory circuit. A lower metallization layer defines first conducting lines. A continuous magnetic storage element stack is over the lower metallization layer and a bottom electrode of the stack is in direct contact with the first conducting lines. An upper metallization layer is over the continuous magnetic storage element stack. The upper metallization layer defines second conducting lines, which are in direct contact with the continuous magnetic storage element stack. Localized areas of the continuous magnetic storage element stack define discrete magnetic bits, each energizable through a selected pair of the first and second conducting lines.
A second aspect of the invention provides a memory circuit. A lower metallization layer defines first conducting lines. A magnetic tunnel junction (MTJ) stack is over the patterned lower metallization layer and a bottom electrode of the stack is in direct contact with the first conducting lines. The stack has a top free layer, a middle tunnel oxide layer and a bottom fixed layer overlying the bottom electrode. The stack is patterned through a single mask, by etching the top free layer until the tunnel oxide layer, to define partially isolated individual stacks. An upper metallization layer is over the partially isolated individual stacks and defines second conducting lines, which are in direct contact with the partially isolated individual stacks. The partially isolated individual stacks are encapsulated by dielectric regions and define discrete magnetic bits, each energizable through a selected pair of the first and second conducting lines.
A third aspect of the invention provides a memory circuit. A lower metallization layer defines first conducting lines. A magnetic tunnel junction (MTJ) stack is over the patterned lower metallization layer and a bottom electrode of the stack is in direct contact with the first conducting lines. The stack has a top free layer, a middle tunnel oxide layer and a bottom fixed layer overlying the bottom electrode. The stack is patterned by etching through a single mask, to define fully isolated individual stacks. An upper metallization layer is over the fully isolated individual stacks to define second conducting lines, which are in direct contact with said fully isolated individual stacks. The fully isolated individual stacks are encapsulating by dielectric regions and define discrete magnetic bits, each energizable through a selected pair of the first and second conducting lines.
A fourth aspect of the invention provides a method for forming a memory circuit. The method includes the steps of patterning a lower metallization layer to define first conducting lines, followed by forming a continuous magnetic storage element stack over the patterned lower metallization layer, such that a bottom electrode of the stack is in direct contact with the first conducting lines. This is followed by forming an upper metallization layer over the continuous magnetic storage element stack and then by patterning the upper metallization layer to define second conducting lines, which are in direct contact with said continuous magnetic storage element stack. Localized areas of the continuous magnetic storage element stack define discrete magnetic bits, each energizable through a selected pair of the first and second conducting lines.
According to an embodiment of each of the first and the fourth aspects of the invention, the magnetic storage element stack has a magnetic tunnel junction (MTJ) stack.
A fifth aspect of the invention provides a method for forming a memory circuit. The method includes the steps of patterning a lower metallization layer to define first conducting lines, followed by forming a continuous magnetic storage element stack over said patterned lower metallization layer such that a bottom electrode of the stack is in direct contact with the first conducting lines. The stack has a top free layer, a middle tunnel oxide layer and a bottom fixed layer overlying the bottom electrode. This is followed by patterning the stack through a single mask, by etching the top free layer until the tunnel oxide layer, to define partially isolated individual stacks. This is followed by forming an upper metallization layer over the partially isolated individual stacks and then patterning the upper metallization layer to define second conducting lines, which are in direct contact with the partially isolated individual stacks. The partially isolated individual stacks are encapsulated by dielectric regions. The partially isolated individual stacks define discrete magnetic bits, each energizable through a selected pair of the first and second conducting lines.
A sixth aspect of the invention provides a method for forming a memory circuit. The method includes the steps of patterning a lower metallization layer to define first conducting lines, followed by forming a continuous magnetic storage element stack over the patterned lower metallization layer such that a bottom electrode of the stack is in direct contact with the first conducting lines. The stack has a top free layer, a middle tunnel oxide layer and a bottom fixed layer overlying the bottom electrode. This is followed by patterning the stack through a single mask, by etching to define fully isolated individual stacks, then forming an upper metallization layer over the fully isolated individual stacks, and then patterning the upper metallization layer to define second conducting lines, which are in direct contact with the fully isolated individual stacks. The fully isolated individual stacks are encapsulated by dielectric regions. The fully isolated individual stacks define discrete magnetic bits, each energizable through a selected pair of the first and second conducting lines.
According to an embodiment for each of the first to the sixth aspects of the invention, the lower metallization layer has an M2 layer and the upper metallization layer has an M3 layer.
According to another embodiment for each of the first to the sixth aspects of the invention, the first conducting lines have a plurality of word lines and the second conducting lines have a plurality of bit lines.
According to the first and fourth aspects of the invention, the four masking and etching steps as described in the foregoing ‘Background’ section can be avoided. Similarly, according to the second and fifth aspects of the invention, etching the top free layer until the tunnel oxide layer is achieved through only a single mask and a partial etch. According to the third and sixth aspects of the invention, full etching of the stack is achieved through only a single mask. All these aspects of the invention and their embodiments enable significant savings in the processing time and cost. Reduced number of processing steps also enhance yield.
In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the invention. It will be apparent, however, to one skilled in the art that the invention can be practiced without these specific details.
Reference in this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Moreover, various features are described which may be exhibited by some embodiments and not by others. Similarly, various requirements are described which may be requirements for some embodiments but not other embodiments.
According to the embodiments shown in
The embodiments as described in
In consideration with the aforesaid limitations, the aspects and embodiments of the present invention embodiments may however be useful for applications where maintaining low cost for the memory circuits 200, 300, 400 is of higher priority than the quality of performance. One such application may be for memory circuits 200, 300, 400 which are of disposable types, which are designed for short term usages and are of lower complexity. The interference effects may be reduced by increasing the distance between the magnetic bits 214, 314, 414 in the layout design for the memory circuits 200, 300, 400 which would however be at the cost of increased area. Similarly, the aspects and embodiments of the present invention embodiments may be useful for applications where only reading operation is required, and not writing operation.
All the aspects of the invention provides a memory circuit, that is compatible with any semiconductor technology such as complementary metal-oxide-semiconductor (CMOS), bipolar-junction-transistor and CMOS (BiCMOS), silicon-on-insulator (SOI) and the like. The embodiments of the invention are equally applicable when any other type of magnetic storage element stack 222, 322, 422 is used.
Although the present invention has been described with reference to specific exemplary embodiments, it will be evident that the various modification and changes can be made to these embodiments without departing from the broader spirit of the invention. Accordingly, the specification and drawings are to be regarded in an illustrative sense rather than in a restrictive sense.
This application is a continuation of U.S. patent application Ser. No. 14/264,914, filed Apr. 29, 2014, which is a divisional of U.S. patent application Ser. No. 12/960,430, filed Dec. 30, 2010, and issued as U.S. Pat. No. 8,711,612, on Apr. 29, 2014.
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