Abstract:
A partition may be made up of two planes of memory cells in a phase change memory. These planes may be configured so that they are not adjacent to one another. In some embodiments, this may mean that the adjacent planes may share sensing circuits, reducing the overall size of the memory array. In addition, by using non-adjacent planes to make up a partition, the planes may be spaced in a way which reduces resistance of power conveying lines. This may mean that smaller sized lines may be used, further reducing the size of the overall array.

Description:
BACKGROUND 
     This relates generally to bit alterable crosspoint memories. 
     Phase change memory devices are one type of bit alterable crosspoint memory. A phase change memory uses phase change materials, i.e., materials that may be electrically switched between a generally amorphous and a generally crystalline state, for electronic memory application. One type of memory element utilizes a phase change material that may be, in one application, electrically switched between a structural state of generally amorphous and generally crystalline local order or between different detectable states of local order across the entire spectrum between completely amorphous and completely crystalline states. The state of the phase change materials is also non-volatile in that, when set in either a crystalline, semi-crystalline, amorphous, or semi-amorphous state representing a resistance value, that value is retained until changed by another programming event, as that value represents a phase or physical state of the material (e.g., crystalline or amorphous). The state is unaffected by removing electrical power. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a depiction of a phase change memory plane in accordance with one embodiment of the present invention; 
         FIG. 2  is a depiction of a phase change memory interleaved architecture in accordance with one embodiment of the present invention; and 
         FIG. 3  is a system depiction in accordance with one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     A phase change memory may include an array of memory cells. Each cell may include a phase change memory element, as well as one or more other devices such as a select device. A tile may be a group of phase change memory cells on a series of adjacent word and bitlines. For example, in one embodiment, a tile may have a million cells on a thousand consecutive rowlines and a thousand consecutive bitlines. A plane is made up of eight tiles in accordance with one embodiment. However, a plane may include any number of tiles greater than one. 
     In accordance with one embodiment, each tile is capable of providing 8 inputs or outputs. Thus, in such an example, a plane is capable of 64 inputs and outputs. Each plane may have sensing circuits associated with a group of eight tiles, in one embodiment. A local input/output may be provided to the various tiles of the plane. 
     Thus, referring to  FIG. 1 , a series of tiles  13 , making up a plane  12 , may have a block of contiguous sensing circuits  14 . The tiles  13  may be coupled to an 8 bit local input/output line  16 . Thus, the eight tiles may output a total of 64 bits. 
     If it is desired to have more outputs than is possible with one plane, for example 128 bit outputs, two planes may be paired to provide the desired number of inputs and outputs. Two planes that are grouped together may be collectively known as a partition. 
     Referring to  FIG. 2 , the planes  12   a  and  12   b  together could make up a partition. Similarly, the planes  12   a  and  12   c  could make up a partition. Likewise, the planes  12   b  and  12   d  could make up a partition. Each set of adjacent planes, such as the planes  12   a  and  12   b , may share a block of physically contiguous sensing circuits  14  such as the circuit  14   a . Particularly in the case where the partition is made up of the planes  12   a  and  12   c , the sensing circuit  14   a  may be shared between the planes  12   a  and  12   b  since these two planes are never accessed at the same time. 
     In other words, by interleaving the planes in forming partitions, by taking two non-adjacent planes to make up a partition, two adjacent planes, such as the planes  12   a  and  12   b , may share their sensing circuits  14   a . Likewise, the planes  12   c  and  12   d  may share the sensing circuits  14   b . In this embodiment, the planes  12   a  and  12   c  make up a partition which is accessed at one time to, for example, provide a 128 inputs and outputs, while the planes  12   b  and  12   d  are accessed at one time to make up the desired number of inputs and outputs. 
     The effect of this interleaving of planes to form partitions is illustrated by the length dimensions indicated as P and S. The length P is a length in the direction from adjacent plant-to-adjacent plane, as indicated in  FIG. 2 . The length S is the length of the sensing circuits for those planes. Without interleaving, the total length of the two planes, together with the sensing circuits for one partition, is two times the quantity P+S. With the interleaving arrangement, the total length of the clip is reduced by S×N/2, where N is the number of planes. Thus, a considerable savings in size may be achieved. 
     In addition, in some embodiments, there are high powered signals that run up the length of the chip, parallel to the main input/output bus  18 . These high powered signals carry current to be driven into the arrays during program and also perform other functions. When simultaneously activated planes are adjacent, the voltage drops due to the routing resistance is at the worst case 2×I×R, where I is the current required by each plane and R is the resistance of the length of the line running up the height of the chip. 
     With interleaved planes, the two planes comprising a partition may be placed independently. For example, one plane may be at the top and one plane may be at the middle of the chip. In this scenario, the worst case voltage drop becomes I×R+I×R/2, which is equal to 1.5 I×R, so 25 percent of the drop may be removed. This can mean that metal lines may be made more narrow, increasing resistance and giving the same voltage drop tolerance, again reducing die size. 
     It is not necessary in all embodiments that the two interleaved planes be closely spaced. Instead, the planes making up a partition may be spaced by any distance which is advantageous, in some embodiments. 
     The present invention is not limited to phase change memories, but, rather, is applicable to any high bandwidth bit alterable crosspoint memory. 
     Programming of a chalcogenide to alter the state or phase of the material may be accomplished by applying voltage potentials to a lower address line and upper address line, thereby generating a voltage potential across the select device and memory element. When the voltage potential is greater than the threshold voltages of any select device and memory element, then an electrical current may flow through the chalcogenide in response to the applied voltage potentials, and may result in heating of the chalcogenide. 
     This heating may alter the memory state or phase of the chalcogenide. Altering the phase or state of the chalcogenide may alter the electrical characteristic of memory material, e.g., the resistance of the material may be altered by altering the phase of the memory material. Memory material may also be referred to as a programmable resistive material. 
     In the “reset” state, memory material may be in an amorphous or semi-amorphous state and in the “set” state, memory material may be in an a crystalline or semi-crystalline state. The resistance of memory material in the amorphous or semi-amorphous state may be greater than the resistance of memory material in the crystalline or semi-crystalline state. It is to be appreciated that the association of reset and set with amorphous and crystalline states, respectively, is a convention and that at least an opposite convention may be adopted. 
     Using electrical current, memory material may be heated to a relatively higher temperature to amorphosize memory material and “reset” memory material (e.g., program memory material to a logic “0” value). Heating the volume of memory material to a relatively lower crystallization temperature may crystallize memory material and “set” memory material (e.g., program memory material to a logic “1” value). Various resistances of memory material may be achieved to store information by varying the amount of current flow and duration through the volume of memory material. 
     Turning to  FIG. 3 , a portion of a system  500  in accordance with an embodiment of the present invention is described. System  500  may be used in wireless devices such as, for example, a personal digital assistant (PDA), a laptop or portable computer with wireless capability, a web tablet, a wireless telephone, a pager, an instant messaging device, a digital music player, a digital camera, or other devices that may be adapted to transmit and/or receive information wirelessly. System  500  may be used in any of the following systems: a wireless local area network (WLAN) system, a wireless personal area network (WPAN) system, a cellular network, although the scope of the present invention is not limited in this respect. 
     System  500  may include a controller  510 , an input/output (I/O) device  520  (e.g. a keypad, display), static random access memory (SRAM)  560 , a memory  530 , and a wireless interface  540  coupled to each other via a bus  550 . A battery  580  may be used in some embodiments. It should be noted that the scope of the present invention is not limited to embodiments having any or all of these components. 
     Controller  510  may comprise, for example, one or more microprocessors, digital signal processors, microcontrollers, or the like. Memory  530  may be used to store messages transmitted to or by system  500 . Memory  530  may also optionally be used to store instructions that are executed by controller  510  during the operation of system  500 , and may be used to store user data. Memory  530  may be provided by one or more different types of memory. For example, memory  530  may comprise any type of random access memory, a volatile memory, a non-volatile memory such as a flash memory and/or a memory such as memory discussed herein. 
     I/O device  520  may be used by a user to generate a message. System  500  may use wireless interface  540  to transmit and receive messages to and from a wireless communication network with a radio frequency (RF) signal. Examples of wireless interface  540  may include an antenna or a wireless transceiver, although the scope of the present invention is not limited in this respect. 
     References throughout this specification to “one embodiment” or “an embodiment” mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one implementation encompassed within the present invention. Thus, appearances of the phrase “one embodiment” or “in an embodiment” are not necessarily referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be instituted in other suitable forms other than the particular embodiment illustrated and all such forms may be encompassed within the claims of the present application. 
     While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.