Abstract:
A multi-port phase change random access memory (PRAM) cell, includes a PRAM element including a phase change material, a writing controller configured to operate in correspondence with a writing word line, the writing controller connecting a writing bit line to the PRAM element, and a reading controller configured to operate in correspondence with a reading word line, the reading controller connecting the PRAM element to a reading bit line.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   Embodiments relate to a phase change random access memory (PRAM) and, more particularly, to a multi-port phase change random access memory cell and multi-port phase change random access memory device including the same. 
   2. Description of the Related Art 
   A PRAM device may include a plurality of PRAM cells. Generally, a PRAM cell may have a writing speed that is slower than a reading speed. Accordingly, there is a need for a PRAM device that provides an improved read/write access time. 
   SUMMARY OF THE INVENTION 
   Embodiments are therefore directed to a multi-port phase change random access memory cell and multi-port phase change random access memory device including the same, which substantially overcome one or more of the problems due to the limitations and disadvantages of the related art. 
   It is therefore a feature of an embodiment to provide a multi-port phase change random access memory cell having separate reading and writing ports, and multi-port phase change random access memory device including the same. 
   It is therefore another feature of an embodiment to provide a multi-port phase change random access memory device configured to operate a multi-port phase change random access memory cell having different writing and reading speeds. 
   At least one of the above and other features and advantages may be realized by providing a multi-port phase change random access memory (PRAM) cell, including a PRAM element including a phase change material, a writing controller configured to operate in correspondence with a writing word line, the writing controller connecting a writing bit line to the PRAM element, and a reading controller configured to operate in correspondence with a reading word line, the reading controller connecting the PRAM element to a reading bit line. 
   The multi-port PRAM cell may operate in a writing mode, during which data is written to the PRAM element, and a reading mode, during which data is read from the PRAM element, the writing controller may provide a writing current to the PRAM element in the writing mode, and the reading controller may provide a reading current to the PRAM element in a reading mode. 
   The writing controller may include a writing access transistor, the writing access transistor having a gate connected to the writing word line, a first terminal connected to the writing bit line, and a second terminal connected to the PRAM element, and the reading controller may include a reading access transistor, the reading access transistor having a gate connected to the reading word line, a first terminal connected to the reading bit line, and a second terminal connected to the PRAM element. 
   At least one of the above and other features and advantages may also be realized by providing a PRAM element including a phase change material, a writing controller configured to operate in correspondence with a writing word line, the writing controller connecting a writing bit line to the PRAM element, a reading controller configured to operate in correspondence with a reading word line, the reading controller connecting the PRAM element to a reading bit line, and a developer configured to provide a developing current to the PRAM element as part of a data read operation. 
   The developer may be configured to operate in correspondence with the reading word line. 
   The developer may include a developing transistor having a gate connected to the reading word line. 
   The developing transistor may have a predetermined turn-on resistance, the predetermined turn-on resistance may be greater than the minimum resistance of the PRAM element, and the predetermined turn-on resistance may be less than the maximum resistance of the PRAM element. 
   The developer may provide a developing current that is greater than a minimum current required to read data from the PRAM element and less than a current that affects a crystallization state of the PRAM element. 
   The developer may also provide the developing current to at least one other multi-port PRAM cell. 
   The multi-port PRAM cell may include a plurality of writing controllers and a plurality of reading controllers, the writing controllers may connect respective writing bit lines to the PRAM element, the writing controllers being configured to operate in correspondence with respective writing word lines, and the reading controllers may connect the PRAM element to respective reading bit lines, the reading controllers being configured to operate in correspondence with respective reading word lines. 
   The multi-port PRAM cell may further include a plurality of developers, the developers being configured to provide a developing current to the PRAM element as part of a data read operation. 
   The developers may be configured to operate in correspondence with respective reading word lines. 
   Each developer may include a developing transistor having a gate connected to a respective reading word line. 
   Each developing transistor may have a predetermined turn-on resistance, the predetermined turn-on resistance may be greater than the minimum resistance of the PRAM element, and the predetermined turn-on resistance may be less than the maximum resistance of the PRAM element. 
   Each developer may provide a developing current that is greater than a minimum current required to read data from the PRAM element and less than a current that affects a crystallization state of the PRAM element. 
   At least one developer may also provide the developing current to an adjacent multi-port PRAM cell. 
   The multi-port PRAM cell may operate in a writing mode, during which data is written to the PRAM element, and a reading mode, during which data is read from the PRAM element, at least one writing controller may provide a writing current to the PRAM element in the writing mode, and at least one reading controller may provide a reading current to the PRAM element in a reading mode. 
   Each writing controller may include a writing access transistor, the writing access transistor having a gate connected to a respective writing word line, a first terminal connected to a respective writing bit line, and a second terminal connected to the PRAM element, and each reading controller may include a reading access transistor, the reading access transistor having a gate connected to a respective reading word line, a first terminal connected to a respective reading bit line, and a second terminal connected to the PRAM element. 
   At least one of the above and other features and advantages may also be realized by providing a phase change random access memory (PRAM) device, including a plurality of multi-port PRAM cells, a data writing unit connected to the plurality of multi-port PRAM cells and configured to write data to the multi-port PRAM cells, and a data reading unit connected to the plurality of multi-port PRAM cells and configured to read data from the multi-port PRAM cells. Each PRAM cell may include a PRAM element including a phase change material, a writing controller configured to operate in correspondence with a writing word line, the writing controller connecting a writing bit line to the PRAM element, and a reading controller configured to operate in correspondence with a reading word line, the reading controller connecting the PRAM element to a reading bit line. 
   The PRAM device may further include at least one developer configured to provide a developing current to one or more of the plurality of PRAM cells as part of a data read operation. 
   The multi-port PRAM cell may include a plurality of writing controllers and a plurality of reading controllers, the writing controllers may connect respective writing bit lines to the PRAM element, the writing controllers being configured to operate in correspondence with respective writing word lines, and the reading controllers may connect the PRAM element to respective reading bit lines, the reading controllers being configured to operate in correspondence with respective reading word lines. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other features and advantages will become more apparent to those of ordinary skill in the art by describing in detail example embodiments with reference to the attached drawings, in which: 
       FIG. 1  illustrates a schematic view of a multi-port PRAM cell according to an embodiment; 
       FIG. 2  illustrates a multi-port PRAM cell according to a first embodiment; 
       FIG. 3  illustrates a multi-port PRAM cell according to a second embodiment; 
       FIG. 4  illustrates a plurality of multi-port PRAM cells that share a developer according to a third embodiment; 
       FIG. 5  illustrates a multi-port PRAM cell according to a fourth embodiment; 
       FIG. 6  illustrates a multi-port PRAM cell according to a fifth embodiment; 
       FIG. 7A  and  FIG. 7B  illustrate schematic views of a multi-port PRAM device according to an embodiment; and 
       FIG. 8  illustrates a block diagram of a multi-port PRAM device according to an embodiment. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Korean Patent Application No. 10-2006-0097601, filed on Oct. 4, 2006, in the Korean Intellectual Property Office, and entitled: “Multi-Port Phase Random Access Memory Cell and Multi-Port Phase Random Access Memory Device Including the Same,” is incorporated by reference herein in its entirety. 
   Example embodiments will now be described more fully hereinafter with reference to the accompanying drawings; however, they may be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like reference numerals refer to like elements throughout. 
     FIG. 1  illustrates a schematic view of a multi-port PRAM cell  100  according to an embodiment. 
   Referring to  FIG. 1 , the multi-port PRAM cell  100  may include a PRAM element. The size of the multi-port PRAM cell  100  may be less than that of a similar memory cell in a Dynamic Random Access Memory (DRAM). Moreover, the operational speed of the multi-port PRAM cell  100  may be faster than that of a similar memory cell in a Static Random Access Memory (SRAM). 
   The multi-port PRAM cell  100  may be included in a phase change random access memory (PRAM) device, which may be a non-volatile memory device that stores data using materials such as a phase change material, in which the resistance depends on a crystalline state. The crystalline state may be changed by a phase transition caused by a temperature change. PRAM devices may change the crystalline state of the phase change material, e.g., from a crystallized to a non-crystallized state, and vice versa, so as to store information. For the phase change of the phase change material to occur, a high temperature of above 900° C. may be required, which may be provided by joule heating as a result of a current flowing through the phase change random access device. 
   In a writing operation, current may flow through the phase change material so that the phase change material is heated above a melting temperature, after which the phase change material may be quickly cooled, such that the phase change material stores information, e.g., a logical “1,” in an amorphous form. This state may be referred to as a reset state. Also, when the phase change material is heated above a crystallization temperature, maintained at a predetermined temperature for a certain period of time, and then cooled down, the phase change material may store information, e.g., a logical “0,” in a crystallized state. This state may be referred to as a set state. 
   In a read operation, a bit line and a word line may be selected so that a specific PRAM cell  100  is selected. A current may flow from an external source to the PRAM cell  100  so as to distinguish between “1” and “0” as a difference in a voltage according to a resistance, i.e., a crystallization state, of a phase change material in the PRAM cell  100 . 
   The multi-port PRAM cell  100  may include m data writing routes and n data reading routes. The multi-port PRAM cell  100  may be connected to m writing word lines WWL [m: 1 ], m writing bit lines RBL [m: 1 ], n reading word lines RWL [n: 1 ], and n reading bit lines RBL [n: 1 ], where m and n are natural numbers. Since a writing port and a reading port may be separately provided, even where the PRAM element has a slower writing speed than a reading speed, it can be optimally used. 
     FIG. 2  illustrates a multi-port PRAM cell  200  according to a first embodiment. 
   The multi-port PRAM cell  200  according to the first embodiment may include a data reading route and a data writing route. The multi-port PRAM cell  200  may include a PRAM element GST, which may include a phase change material such as a chalcogenide alloy, e.g. a germanium-antimony tellurium (Ge—Sb—Te (GST)) alloy, etc. The multi-port PRAM cell  200  may further include a writing controller WTR and a reading controller RTR. The writing controller WTR may respond to an activation of a writing word line WWL that is to be operated and may write data provided through a writing bit line WBL to the PRAM element GST. The reading controller RTR may respond to an activation of a reading word line RWL that is to be activated and may output data of the PRAM element GST to a reading bit line RBL. 
   In a writing mode, during which data is written to the PRAM element GST, the writing controller WTR may provide a writing current to the PRAM element GST. In a reading mode, during which data is read from the PRAM element GST, the reading controller RTR may provide a reading current to the PRAM element GST. 
   The writing controller WTR may include, e.g., a writing access transistor, in which a gate of the writing controller WTR is connected to the writing word line WWL, a first terminal of the writing controller WTR is connected to the writing bit line WBL, and a second terminal of the writing controller WTR is connected to the PRAM element GST. The reading controller RTR may include a reading access transistor, in which a gate of the reading controller RTR may be connected to the reading word line RWL, a first terminal of the reading controller RTR may be connected to the reading bit line RBL, and a second terminal of the reading controller RTR may be connected to the PRAM element GST. 
   When the writing word line WWL is activated in the writing mode, the writing controller WTR may be turned on. Then, a writing current, corresponding to a logic level of data that is to be written, may be provided to the PRAM element GST through the writing bit line WBL, and accordingly, data may be written to the PRAM element GST. 
   When the reading word line RWL is activated in the reading mode, the reading controller RTR may be turned on. Then, a reading current used to read data from the PRAM element GST may be provided to the PRAM element GST through the reading bit line RBL. Accordingly, data stored in the PRAM element GST may be read through the reading bit line RBL. 
     FIG. 3  illustrates a multi-port PRAM cell  300  according to a second embodiment. 
   The multi-port PRAM cell  300  may include a data reading route and a data writing route. The configuration and operation of the multi-port PRAM cell  300  according to the second embodiment may correspond to that of the multi-port PRAM cell  200  illustrated in  FIG. 2 , except that the multi-port PRAM cell  300  may also include a developer DEVTR. In order to avoid repetition, in the following description only the developer DEVTR will be described in detail. 
   The multi-port PRAM cell  300  according to the second embodiment may include the PRAM element GST including the phase change material, the writing controller WTR, the reading controller RTR, and the developer DEVTR. The developer DEVTR may provide a developing current IDEV to the PRAM element GST so as to read data from the PRAM element GST. 
   According to an activation or deactivation of a reading word line RWL, the developer DEVTR may apply or not apply the developing current IDEV to the PRAM element GST. The developer DEVTR may include a developing transistor, which may be turned on or turned off according to the activation or deactivation of the reading word line RWL. 
   In an implementation, the turn-on resistance of the developing transistor DEVTR may be larger than the minimum resistance of the PRAM element GST and smaller than the maximum resistance of the PRAM element GST. 
   In an implementation, the developing current IDEV may be larger than the minimum current capacity that can read data from the PRAM element GST and smaller than the current capacity that affects the state of the PRAM element GST. 
   When the reading word line RWL is activated in a reading mode, a second reading access transistor RTR 2  and the developing transistor DEVTR may be turned on. Accordingly, the developing current IDEV may be provided to the PRAM element GST and the data stored in the PRAM element GST may be read through corresponding first reading access transistor RTR 1  and a corresponding reading bit line RBL. 
   The multi-port PRAM cell  200  according to the first embodiment may apply a reading current through the reading bit line RBL to read data from the PRAM element GST. However, the reading current may generally be very small, and thus providing the reading current may be difficult. In the multi-port PRAM cell  300  according to the second embodiment, the developing current IDEV may function as the reading current to the PRAM element GST, and may be provided using the developer DEVTR. Thus, a small reading current, i.e., the developing current IDEV, may be easily provided to the PRAM element GST. 
     FIG. 4  illustrates a plurality of multi-port PRAM cells  400 _ 1  and  400 _ 2  that share a common developer DEVTR according to a third embodiment. 
   Referring to  FIG. 4 , the developer DEVTR of the multi-port PRAM cell  400 _ 1  may be shared between the multi-port PRAM cell  400 _ 2  and the multi-port PRAM cell  400 _ 1 . The multi-port PRAM cells  400 _ 1  and  400 _ 2  may be included in a same PRAM cell array. The developer DEVTR may provide the developing current IDEV to the multi-port PRAM cells  400 _ 1  and  400 _ 2 . In this embodiment, only the multi-port PRAM cell  400 _ 1  may include the developer DEVTR, and the multi-port PRAM cell  400 _ 2  may not include a separate developer, which may allow the area of the PRAM cell array to be reduced. 
     FIG. 4  illustrates two multi-port PRAM cells  400 _ 1  and  400 _ 2  sharing one developer DEVTR. However, it will be appreciated that the number of multi-port PRAM cells that share one developer DEVTR is not restricted to the illustrated implementation, and two or more multi-port PRAM cells may share one developer DEVTR. 
     FIG. 5  illustrates a multi-port PRAM cell  500  according to a fourth embodiment. 
   Referring to  FIG. 5 , the multi-port PRAM cell  500  according to the fourth embodiment may include the PRAM element GST including the phase change material, a first writing controller WRT 1  and a second writing controller WTR 2 , and a first reading controller RTR 1  and a second reading controller RTR 2 . Thus, the multi-port PRAM cell  500  may include two data reading routes and data writing routes. The configuration and operation of the multi-port PRAM cell  500  according to the fourth embodiment may otherwise correspond to that of the multi-port PRAM cell  200  according to the first embodiment described above. 
     FIG. 6  illustrates a multi-port PRAM cell  600  according to a fifth embodiment. 
   Referring to  FIG. 6 , the multi-port PRAM cell  600  according to the fifth embodiment may include the PRAM element GST including the phase change material, the first writing controller WRT 1  and the second writing controller WTR 2 , the first reading controller RTR 1  and the second reading controller RTR 2 , and a first developer DEVTR 1  and a second developer DEVTR 2 . Thus, the multi-port PRAM cell  600  may include a plurality of developers. The configuration and operation of the multi-port PRAM cell  600  according to the fifth embodiment may otherwise correspond to that of the multi-port PRAM cell  200  according to the first embodiment described above. 
     FIG. 7A  and  FIG. 7B  illustrate schematic views of a multi-port PRAM device  700  according to an embodiment. 
   Referring to  FIGS. 7A and 7B , the multi-port PRAM device  700  may include k PRAM cells  710 _ 1  through  710 _k, where k is a natural number. Each of the k PRAM cells  710 _ 1  through  710 _k may receive m writing addresses WADDR, m writing data signals WDATA, and a respective writing control signal WCTRL, where m is a natural number. Also, each of the k PRAM cells  710 _ 1  through  710 _k may receive n reading addresses RADDR, n reading data signals RDATA, and a respective reading control signal RCTRL, where n is a natural number. 
     FIG. 8  illustrates a block diagram of a multi-port PRAM device  800  according to an embodiment. 
   Referring to  FIG. 8 , the multi-port PRAM device  800  may include a multi-port PRAM cell array  810 , data writing units  820 ,  840 ,  850 ,  860 , and  870 , and data reading units  825 ,  845 ,  855 ,  865 ,  867 , and  876 . 
   The multi-port PRAM cell array  810  may include a plurality of the above-described multi-port PRAM cells according to one or more embodiments. The data writing units may include a write row decoder  820 , a write pre-decoder  840 , a write pre-decoder  850 , a DIN buffer  860 , and a write driver  870 , which may write data to the multi-port PRAM cell array  810 . The data reading units may include a read row decoder  825 , a read pre-decoder  845 , a read address buffer  855 , a Dout driver  865 , a data multiplexer  867 , and a sense amp  875 , which may read data from the multi-port PRAM cell array  810 . 
   As described above, a multi-port memory cell and a multi-port memory device according to embodiments may be formed using PRAM element, which may allow the size of the resultant multi-port PRAM cell to be smaller than that of a multi-port memory cell formed using DRAM. Also, an operational speed of the multi-port PRAM cell according to embodiments may be improved as compared to that of a multi-port memory cell formed using SRAM. 
   In addition, since the multi-port PRAM cell and the multi-port PRAM device according to the above-described embodiments may separately include a writing port and a reading port, even where the PRAM element has a slower writing speed than a reading speed, it can be optimally driven. 
   Exemplary embodiments have been disclosed herein, and although specific terms are employed, they are used and are to be interpreted in a generic and descriptive sense only and not for purpose of limitation. Accordingly, it will be understood by those of ordinary skill in the art that various changes in form and details may be made without departing from the spirit and scope of the present invention as set forth in the following claims.