Patent Application
20070279967
The present invention relates to a magnetic memory. The following description is presented to enable one of ordinary skill in the art to make and use the invention and is provided in the context of a patent application and its requirements. Various modifications to the preferred embodiments and the generic principles and features described herein will be readily apparent to those skilled in the art. Thus, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features described herein.
The present invention provides a method and system for providing and using a magnetic storage cell and magnetic memory. The method and system comprise providing a magnetic element and providing a selection device. The magnetic element is programmable to a first state by a first write current driven through the magnetic element in a first direction and to a second state by a second write current driven through the magnetic element in a second direction. The selection device is connected with the magnetic element. The selection device includes gate which has an aperture therein. The magnetic element is configured such that the first write current and second write current are provided to the magnetic element across the aperture.
The present invention is described in the context of particular magnetic memories having certain components, such magnetic storage cells having magnetic elements and particular components. One of ordinary skill in the art will readily recognize that the present invention is consistent with the use of magnetic memories having other and/or additional components consistent with the present invention. The method and system in accordance with the present invention are also described in the context of reading from, writing to, or providing a single magnetic storage cell. However, one of ordinary skill in the art will readily recognize that the method and system can be extended to read from, write to, and/or provide multiple magnetic storage cells substantially in parallel. The present invention is described in the context of certain memories. However, one of ordinary skill in the art will readily recognize that the present invention is compatible with memories and other devices not inconsistent with the present invention. The present invention is also described in the context of particular methods. One of ordinary skill in the art will, however, readily recognize that other methods having different and/or additional steps consistent with the present invention may be used.
To more particularly describe the method and system in accordance with the present invention, refer to
The selection device 110 is a donut selection device. The donut selection device 110 is preferably a transistor, such as a CMOS transistor. The selection device 110 thus preferably includes a gate 112, a source 114, and a drain 116. The gate 112 has an aperture 113 therein. The drain 116 and, in a preferred embodiment, the conductor 104 are aligned with the aperture 113. In a preferred embodiment, the magnetic element 102 is aligned with the aperture 113. However, in other embodiments, the magnetic element 102 may not be aligned with the aperture 113. The magnetic element 102 and the donut selection device 110 are configured such that the write currents are provided across the aperture 113. Because of the presence of the aperture 113, the donut selection device 110 is termed a donut selection device 110. In addition, although the gate 112 and aperture 113 are depicted as having a square or rectangular shape perimeter in the plan view, another shape and/or an aperture of another shape may be used.
In operation, the magnetic element 102 may be programmed by connecting the source 114 to a high (e.g. supply) voltage and the magnetic element 102 to ground to write the magnetic element to one state. Thus, current is driven across the gate 112 from its outer perimeter across the inner edges gate 112 forming the aperture 116 (hereinafter simply termed “across” the aperture) and to the magnetic element 102. Stated differently, the current may flow to the drain 116, and thus the magnetic element 102, from all sides of the aperture 113. The magnetic element 102 may be programmed to another state by connecting the source 114 to a low voltage (e.g. ground) and the magnetic element 102 to a high voltage (e.g. supply voltage). Thus, current is driven from the magnetic element 102, across the aperture 113, and across the gate 112 from its inner perimeter to the source 114 at the outer perimeter. The current may flow from the drain 116, and thus the magnetic element 102, to the source 114 from all sides of the aperture 113. During reading, a lower current is driven through the magnetic element 102 either from the source 114 to the drain 116 and the magnetic element 102, or vice versa.
The donut selection device 110 is capable of supporting a larger write current than a conventional transistor of the same size. Because current is driven across the aperture 113, the effective width of the gate 112 of the transistor 110 is increased for a given cell 100 area. As stated above, the current that may be driven through a magnetic storage cell 100 varies as the gate width. Consequently, a higher driving current may be achieved for a given area of the magnetic storage cell 100. For example, due to the layout of the donut selection device 110, the size of the unit cell is believed to be approximately twenty-five F2. A magnetic storage cell 100 of this size may provide approximately 300 uA driving current for a 90 nm technology node. Thus, a reduced cell size and, therefore, increased memory density may be achieved.
In addition, the magnetic storage cell 100 may have improved signal. It is noted that when reading the state of a magnetic element 102, the output signal is closely related to the resistance of the donut selection device I 10. This is because the magnetic element 102 is connected in series with the donut selection device 110, essentially forming a voltage divider. As a result, the higher the resistance of the donut selection device 110, the lower the signal from the magnetic element 102. Because the effective gate width of the donut selection device 110 is longer than that of a conventional transistor for a given magnetic storage cell size, the resistance of the donut selection device 110 is lower. Consequently, an improved signal in the form of a higher current difference between high and low resistance states of the magnetic element 102 may be achieved. This high delta current enables high speed reading and could essentially reduce the error rate of reading. Thus, the magnetic storage cell 100 may have a more compact size, may be capable of supporting a higher write current for a given size, an enhanced read signal that allows for a higher memory speed during operation and improved data integrity.
In addition to the magnetic storage cells 100, the magnetic memory 150 includes a source line 152, global word lines 154, and bit lines 156. The source line 152 is connected with the sources of the magnetic storage cells 100. Thus, in the embodiment shown, the sources 114 of the donut selection devices 110 are connected together and share the source line 152. The ability of a group of the magnetic storage cells 100 to share the source line 152 may further increase the density of the magnetic memory 150. In addition, isolation structures, such as the structures 38/38′ in the conventional magnetic RAMs depicted in
In operation, one or more magnetic storage cells 100 may be programmed by connecting the source line 152 to a high (e.g. supply) voltage and the bit line(s) 156 to ground to write the magnetic element to one state. At the same time, the desired row(s) are enabled by connecting the desired global word line(s) 154 to a high voltage.
Thus, the magnetic memory 150 shares the benefits of the magnetic storage cell 100. In particular, the magnetic memory utilizes donut selection devices 110 having a longer gate width for a given area of the storage cell 100. Consequently, a higher density memory capable of using a higher write current as well as improved reading characteristics may be achieved. Furthermore, the isolation between unit cells 100′ is eliminated and replaced by the gates 112. Thus, memory density might be further increased. In addition, multiple storage cells 100 may share the source line 152. As a result, a further increase in memory density may be provided. The global word line 154 may, in a preferred embodiment, be made of metal. The global word line 154 may thus be used to provide a higher speed for the donut selection devices 110. The global word line 154 may also improve performance of the gate 112, which is preferably made from high resistance poly-silicon.
The donut selection device 110 is provided for each magnetic storage cell 100 in the memory, via step 202. Step 202 includes providing the sources 114 for the magnetic storage cells 100. The sources 114 may be interconnected, for example by doping interconnecting regions of a substrate. Step 202 also includes providing the drains 116 and the gates 112 having apertures 113. Other interconnects, such as the source line 152 and word line 154, may be provided, via step 204. The conductor (contact/via) 104 is provided, via step 206. In a preferred embodiment, the conductor 104 is a metal plug provided in the aperture 113 and is electrically connected to the drain 116 of each storage cell 100. The magnetic element 102 is provided, via step 208. Step 208 includes providing the magnetic element 102 that is capable of being written by driving current(s) through the magnetic element. The interconnects are provided, via step 210. Thus, step 210 may provide bit lines 156. Note that in a preferred embodiment, other interconnect layers such as word lines 154 and source line 152 were previously provided. Processing of the magnetic memory 150 may then be completed.
Thus, using the method 200, a magnetic memory 150 which includes storage cells 100 may be provided. Consequently, the benefits of the memory 150 and storage cells 10 may be achieved.
It is determined whether the magnetic element is to be programmed, via step 252. If so, then it is determined whether the magnetic element is to be programmed into a first state, via step 254. If so, then the source line 152 is connected to a high (e.g. supply) voltage and the bit line(s) 156 is to ground, via step 256. In addition, step 256 connects the desired global word line(s) 154 to a high voltage to enable the desired row(s). Because the global word line(s) 154 are driven high in step 256, the appropriate donut selection device(s) 110 may be turned on.
If it is determined in step 254 that the magnetic element is not to be programmed into the first state, then the magnetic element 102 is to be programmed into a second state. Thus, the source line 152 is connected to a low voltage (e.g. ground) and the bit line(s) 156 is connected to a high voltage (e.g. supply voltage), via step 258. Also in step 258, the desired global word line 154 is driven high. Thus, current is driven from the magnetic element 102, across the aperture 113, and across the gate 112 from its inner perimeter to the source 114 at the outer perimeter.
If it is determined in step 252 that the magnetic element 102 is not to be programmed, then a read operation ensues. Thus, a lower current is driven through the magnetic element 102, via step 260. Step 260 may either drive from the source 114 to the drain 116, or vice versa. Thus, step 260 may include connecting the source 114 to a high voltage and the magnetic element 102 to ground, or vice versa. However the voltage to which the source 114 or magnetic element 102 are connected is lower than for a write operation. Consequently, the read current that flows in step 260 is insufficient to change the state of the magnetic element 102.
Thus, magnetic storage cell 100 and magnetic memory 150 may be written using a more localize phenomenon, at a higher write current, with lower cell size and improved read characteristics. Consequently, performance of the magnetic memory 150 and storage cell 100 may be improved.
A method and system for providing and using a magnetic memory having an improved read and write margins has been disclosed. The present invention has been described in accordance with the embodiments shown, and one of ordinary skill in the art will readily recognize that there could be variations to the embodiments, and any variations would be within the spirit and scope of the present invention. Accordingly, many modifications may be made by one of ordinary skill in the art without departing from the spirit and scope of the appended claims.
