Abstract:
A fusion memory device having phase change memory devices that have different resistance distributions and a corresponding data processing system is presented. The fusion memory device includes a first and a second phase change memory group arranged on the same chip. Because the second phase change memory group exhibits a resistance distribution different from that of the first phase change memory group, then the fusion memory device can be configured to simultaneously function as both a DRAM device and as a flash memory device. Because the first and second phase change memory groups can be composed of similar PRAM components, the corresponding manufacturing and driving circuitry is markedly simplified as compared to other fusion memory devices that have dissimilar DRAM and flash memory components.

Description:
CROSS-REFERENCES TO RELATED APPLICATION 
     The present application claims priority under 35 U.S.C. 119(a) to Korean application numbers 10-2009-0054891 and 10-2009-0071244, filed on Jun. 19, 2009 and Aug. 3, 2009, respectively, in the Korean Patent Office, which are incorporated by reference in its entirety as if set forth in full. 
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The embodiments described herein relate to semiconductor integrated devices and, more particularly, to a fusion memory device composed of memory devices that exhibit different functions and a data processing system using the same. 
     2. Related Art 
     Memory device can be classified into a volatile memory devices and a non-volatile memory devices. The volatile memory devices include random access memories (RAM) which data stored therein are erased when the power is off. Non-volatile memory devices include read only memories (ROM) which data stored therein is retained when power is off. Typically, a dynamic random access memory (DRAM) is regarded as the RAM and a flash memory device is regarded as the ROM. 
     DRAMs operate at relatively high speeds due to lower power consumption and simple random access. However, DRAMs require carrying out periodic refresh operations due to their volatile properties and require an increased capacitor capacity due to demand for high charge storage. 
     Meanwhile, flash memory devices readily stores data at high capacities due to a relatively high integration and flash memories do not require refresh operations due to their non-volatile properties. However, flash memories requires operation voltages that a relatively higher than the power voltage due to the two-layered stack gate structure. Accordingly, flash memories oftentimes require separate voltage boosting circuits for generating the desired program and erase voltages. Furthermore, since it is difficult to randomly access, data is programmed at a page unit, and thereby operating speeds of flash memories are often relatively slow. 
     Currently, due to market demands, semiconductor memory devices are gradually scaled down more and more. It is a market trend to embody a system on chip (SOC) that the functional blocks having various functions are integrated on one-chip. A fusion memory device is an exemplary SOC. 
     The fusion memory device is a compound memory device that may contain various different types of memory devices such as having memory chips that have different properties or have non-memory chips which are embedded into a basic memory device together with logic devices. That is, the fusion memory is regarded as a system memory that also provides software suitable to the system specification. A fusion memory device composed of a flash memory device and a static RAM (SRAM) together with a logic device may be integrated into a one-chip design depending on how complex and how high performance the digital electronic appliances needs. 
     Therefore, flash memory device may require a DRAM which is a representative volatile memory device and a flash memory device which is a non-volatile memory device to be integrated in one-chip. However, the DRAM and the flash memory device have distinctly different operation voltages and different driving operational modes such that the different driving circuits are required. Furthermore, since they have different device structures, when they are integrated on one semiconductor substrate, they necessarily must be fabricated by using separately distinct fabrication processes. 
     SUMMARY 
     A fusion memory device includes a first phase change memory group, and a second phase change memory group arranged on the same chip with the first phase change memory group and having a resistance distribution different from the first phase change memory group during phase-changing. 
     The first phase change memory device group may be a substitute device for a flash memory device and the second phase change memory device group may be a substitute device for a DRAM device. 
     The first phase change memory group may have a first sensing ratio and the second phase change memory group may be a second sensing ratio lower than the first sensing ratio. 
     The first phase change memory group may comprise a plurality of phase change memory cells which are programmed such that a phase change material layer in each of the plurality of phase change memory cells is fully phase-changed. The second phase change memory group may comprise a plurality of phase change memory cells which are programmed such that a phase change material layer in each of the plurality of phase change memory cells is partially phase-changed. 
     The plurality of phase change memory cells in the second phase change memory group may be smaller than the plurality of phase change memory cells in the first phase change memory group. 
     According another example embodiment comprises a fusion memory device that includes a first phase change memory group composed of a plurality of first phase change memory cells, each has a first set resistance and a first reset resistance and a second phase change memory group configured to be integrated on the same substrate with the first phase change memory group and being composed of a plurality of second phase change memory cells, each having a second set resistance and a second reset resistance, wherein the second reset resistance is smaller than the first reset resistance. 
     According to still another example embodiment, a data processing system includes a central processing unit (CPU), a data storage block configured to be controlled by the CPU and including memory cell arrays and a page buffer, and a work memory block configured to be controlled by the CPU and performing an address mapping operation of the data storage block. The data storage block comprises a first phase change memory group having a first set resistance and a first reset resistance. The work memory block comprises of a second phase change memory group having a second set resistance and a second reset resistance. The second reset resistance is lower than that of the first reset resistance. 
     These and other features, aspects, and embodiments are described below in the section entitled “Detailed Description.” 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features and other advantages of the subject matter of the present disclosure will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a block diagram illustrating a data processing system as an example of a fusion memory device according to the inventive concept; 
         FIG. 2  is a block diagram illustrating a data processing system according to an example embodiment; 
         FIG. 3  is a schematic circuit diagram of first and second phase change memory groups according to the example embodiment; 
         FIG. 4  is a diagram showing voltage program conditions of the first and second phase change memory groups according to the example embodiment; 
         FIG. 5  is a graph showing resistance distributions of the first and second memory groups according to the example embodiment; 
         FIG. 6  is a plan view of a fusion memory device including a first and second phase change memory groups according to another example embodiment; 
         FIG. 7  is a sectional view of the first and second phase change memory groups of  FIG. 6 ; 
         FIG. 8  is a sectional view of a first and second phase change memory groups according to another example embodiment; 
         FIG. 9  is a graph showing an energy consumed in phase-change of the first and second phase change memory groups according to the example embodiment; 
         FIG. 10  is a graph showing a operation speed and an integration degree of the first and second phase change memory groups according to the example embodiment; 
         FIG. 11  is a graph showing a life span and a non-volatile property of the first and second phase change memory groups according to the example embodiment; and 
         FIG. 12  is a diagram showing first and second phase change memory groups disposed on a semiconductor chip according to an example embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Example embodiments are described herein with reference to cross-sectional illustrations that are schematic illustrations of example embodiments (and intermediate structures). As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, example embodiments should not be construed as limited to the particular shapes of regions illustrated herein but may be to include deviations in shapes that result, for example, from manufacturing. In the drawings, lengths and sizes of layers and regions may be exaggerated for clarity. Like reference numerals in the drawings denote like elements. 
     The inventive concept can embody phase change memory devices having various performances by modifying resistance distributions of the phase memory devices such that a DRAM and a flash memory device in a fusion memory device are substituted with phase change memory devices. Hereinafter, the fusion memory device with complex function will be described in more detail. In an example embodiment, the word “fusion memory” is commonly designated as a memory device that a main memory as well as a different kind of memory such as non-memories or specific logic devices are integrated on one-chip. 
       FIG. 1  is a data processing system  100  as an example of a fusion memory device according to an example embodiment. Referring to  FIG. 1 , the data processing system  100  may include a data storage block  10 , a code storage block  20 , a work memory block  30 , a cache memory block  40 , a memory controller  50  and a central processing unit (CPU)  60 . 
     In the data processing system  100 , when the data desired by the CPU  60  does not exist in the work memory block  30 , the CPU  60  provides commands and addresses to the memory controller  50 . The memory controller  50  subsequently writes the commands and the addresses into the data storage block  10  by using the predetermined interface method. When the commands and the addresses are provided, the data storage block  10  automatically carries out the read/write operation. Furthermore, the page data read from a memory core (not shown) of the data storage block  10  is temporarily stored in a page buffer (not shown) within the data storage block  10 . The page data stored in the page buffer is transferred to the work memory block  30  by a constant unit. If a desired amount of data is transferred to the work memory block  30 , then the CPU  60  receives the data transferred in the work memory block  30 . 
     Herein, the data storage block  10  may include a plurality of memory cell arrays and the page buffer and the data storage block  10  may comprise a memory device with high data processing speed and a long life span. The work memory block  30  controls the address mapping operation of the data storage block  10  and may comprise a memory device with a simple random access and a lower power consumption. The cache memory  40  makes a demand for higher operation speed and may comprise an SRAM with fast operation speed. 
     Currently, the data storage block  10  mainly comprises a NAND flash memory device with a large capacity and the work memory device  30  main comprises a DRAM with an excellent random access. However, if different kinds of memory devices are integrated per the block as above, problems can occur with regards to the driving circuit and fabrication aspects. Therefore, in the following example embodiment, only one device is constructed to carry out different functions. 
     That is, in this example embodiment, phase change memory devices having different phase change properties (hereinafter “phase change memory groups”) are disposed by a block such that the data processing speed and the power consumption can be compensated and the non-volatile property (That is, the data retention property) can be sustained. Also, the phase change property can be regarded as the resistance property in phase-change. The different phase change properties mean that the resistance distribution in a set state is different from the resistance distribution in a reset state. 
     For example, in this example embodiment, as shown in  FIG. 2 , a first phase change memory group  10   a  having a first phase change property as well as a flash memory device property is disposed as the data storage block  10  in the data processing system  100 . A second phase change memory group  30   a  having a second phase change property and a DRAM device property is disposed as the work memory block  30 . The first phase change property is different from the second phase change property. 
     Referring to  FIG. 3 , each of the first and second phase change memory groups  10   a  and  30   a  comprises an array of phase change memory cells  150 , each phase change memory cell comprises a variable resistor Rv and a switching device SW. The variable resistor Rv may comprise a phase change material layer (not shown) in which a resistance thereof is varied by a current and the switching device SW may be composed of a diode. All the memory cells constituting the first and second phase change memory groups  10   a  and  30   a  may be configured to have substantially the same size and substantially the same structure. 
     In the example embodiment, first and second data sensing ratios of the first and second phase change memory groups  10   a  and  30   a  are modified such that the first and second phase change memory groups  10   a  and  130   a  have different phase change properties (That is, the phase change resistance distributions) each other. 
     That is, in order for the first phase change memory group  10   a  to have a relatively higher sensing ratio, a first reset voltage V RESET1  and a first set voltage V SET1  are applied thereto such that the data of “1(RESET 1 )” and “0(SET 1 )” are written in the variable resistors Rv, respectively. A first read voltage V READ  having a lower magnitude than that of the first reset voltage V RESET1  and that of the first set voltage V SET1  is applied to the first phase change memory group  10   a  such that the data written in the variable resistors Rv are read. Herein, the first reset and set voltages (V RESET1 , V SET1 ) may be pulsed between about 10 to 500 ns so as to drive the variable resistors Rv to be sufficiently phase-changed. Preferably, the first set and reset voltages (V SET1 , V RESET1 ) may be pulsed between about 100 to 300 ns. 
     Meanwhile, in order for the second phase change memory group  30   a  to have a relatively lower sensing ratio than that of the first phase change memory group  10   a , a second reset voltage V RESET2  and the second set voltage V SET2  are applied thereto such that the data of “1(RESET 2 )” and “0(SET 2 )” are written in the variable resistors Rv. The second reset voltage V RESET2  and the second set voltage V SET2  are lower than the first reset voltage V RESET1  and the first set voltage V SET , respectively. A second read voltage V READ  has a voltage magnitude which is lower than the second reset and set voltages (V RESET2 , V SET2 ) is applied to the second phase change memory group  30   a  such that the data written in the variable resistors Rv are read. At this time, the first and second read voltages V READ  may have the values which are not affected to the phase change operation of the variable resistor RV and may be identical each other. 
     As compared with the second phase change memory group  30   a , since the first reset and set voltages (V RESET1 , V SET1 ) are set to have relatively higher voltage levels are applied to the first phase change memory group  10   a  as a result the first phase change memory group  10   a  has a high sensing ratio. That is, the phase change material corresponding to each of the variable resistors Rv in the first phase change memory group  10   a  transforms more completely between amorphous or crystalline states. Therefore, as shown in  FIG. 5 , the S/R 1  ratio, as defined by the ratio of resistance distributions corresponding to the first set SET 1  and the first reset RESET 1 , is relatively increased as compared to the S/R 2  ratio. According the first phase change memory group  10   a  exhibits a relative inherent non-volatile property as well as it ensures for sufficient capacity and is capable of random access. As a result, the program and erase procedures at a block unit level, as employed in the prior art, are unnecessary. Therefore, the data processing speeds and the life span can be improved. 
     Meanwhile, relative to the first phase change memory group  10   a , the data written in the second phase change memory group  30   a  uses lower magnitude voltages. That is, the magnitudes of second reset and set voltages (V RESET2 , V SET2 ) are lower than the first reset and set voltages (V RESET1 , V SET1 ) respectively. As a result, the phase change material layer in each of the variable resistors Rv in the second phase change memory group  30   a  only transitions partially between the amorphous and crystalline states as compared to the more complete phase transitions in the first phase change memory group  10   a . According to this, as shown in  FIG. 5 , the resistances of the second set SET 2  and the second reset RESET 2  are distributed between the first set SET 1  and the first reset and RESET 1 . As a result the second sensing ratio S/R 2 , i.e., the ratio of the resistance distributions between the second set SET 2  and the second reset RESET 2  is smaller than the first sensing ratio S/R 1 . As a result, a relative ratio of the first sensing ratio S/R 1  to the second sensing ratio S/R 2  may be about several tens through several hundreds. 
     Although the second sensing ratio S/R 2  is smaller than the first sensing ratio S/R 1 , the second phase change memory group  30   a  has a distinct resistance distribution between the second set SET 2  and the second reset RESET 2  such that it can be used to normally perform memory operations that store the data therein. 
     As compared with the first phase change memory group  10   a , the power consumption in the second phase change memory group  30   a  can be considerably reduced by applying the relatively lower second reset and set voltages V RESET2  and V SET2  and the fast operation speeds can be ensured by partially transitioning phase-change operations the second phase change memory group  30   a . Furthermore, since the second phase change memory group  30   a  also exhibits an inherent non-volatile property, in that it does not require either a refresh operation and a separate circuit which means it can ensure data integrity at the sufficiently extended retention times. 
     At this time, the first reset voltage V RESET1  can be varied depending on the size and integration degree of the phase change memory device. For example, the first reset voltage V RESET1  may be varied between about 1 to 3V. The magnitude of second reset voltage V RESET2  may be lower than the first reset voltage V RESET1  and for example, the magnitude of second reset voltage V RESET2  may be between about 0.1 to 1V. The magnitude of the first set voltage V SET1  may be slightly lower than that of the first reset voltage V RESET1 . Likewise, the magnitude of the second set voltage V SET2  may be slightly lower than that of the second reset voltage V RESET2 . Although the first set status SET 1  and the second set status SET 2  which are different are illustrated herein, it is understood that ultimately the resistance distribution of the first status SET 1  may be almost similar to that the resistance distribution of the second set status SET 2  depending on the relative differences of the respective set voltages. 
     According to this example embodiment, the sensing ratios are controlled relative to the change of the phase change resistance distributions in the phase change memory groups such that the phase change memory groups performs the flash memory and the DRAM functions respectively. Accordingly, one memory device can perform various functions. 
     If the phase change memory devices are substituted for the DRAM device and the flash memory device, the problem for the data processing speed in the flash memory device can be compensated as well as the problem for power consumption and data retention in the DRAM can be compensated, such that the function of the fusion memory device can be further improved. 
       FIG. 6  is a plan view of a fusion memory device including first and second phase change memory groups according to another example embodiment.  FIG. 7  is a stylized sectional view of the first and second phase change memory groups in  FIG. 6 . Referring to  FIGS. 6 and 7 , the fusion memory device  200  may comprise the first phase change memory group  210  and the second phase change memory group  220 . Herein, for example, the fusion memory device  200  corresponding only to the data storage block  10  and the work memory block  30  in the data processing system  100  of  FIG. 1  may be illustrated in  FIGS. 6 and 7 . The first phase change memory group  210  and the second phase change memory group  220  comprise a plurality of memory cells  215  and  225 , respectively. 
     In the example embodiment, the second memory cells  225  of the second phase change memory group  220  are shown to be smaller than the first memory cells  215  of the first phase change memory group  210 . As a result of this size difference, the first and second phase change memory groups  210  and  220  can be configured to exhibit slightly different phase change properties. Herein, the sizes of the memory cells  215  and  225  may be a factor including all dimensions of switching devices  260   a  and  260   b , dimensions of heating electrodes  275   a  and  275   b  and dimensions of phase change material layers  280   a  and  280   b . Therefore, the switching device  260   b , the heating electrode  275   b  and the phase change material layer  280   b  constituting the second memory cell  225  in the second phase change memory group  220  may be smaller than those corresponding counter parts ( 260   a ,  275   a  and  280   a ) in the first memory cells  215  in the first phase change memory group  210 . In particular, the phase change material layer  280   b  in the second phase change memory group  220  may also be sized smaller than the phase change material layer  280   a  of the first phase change memory group  210 . Herein, the reference numeral  250  designates a semiconductor substrate, the reference numeral  255  indicates a junction word line region, the reference numerals  265  and  270  indicates interlayer insulating layers, the reference numeral  285   a  indicates an upper electrode of the first memory cell  215  and the reference numeral  285   b  indicates an upper electrode of the second memory cell  225 . 
     In the embodiment where the second phase change memory group  220  having the memory cells  225  are smaller than the first memory cells  215  of the first phase change memory group  210 , then writing data in the second phase change memory group  220  can be fast while using the same voltages. 
     Herein as mentioned above, the first phase change memory group  210  exhibits an inherent non-volatile property such that it may be used as a substitute for a flash memory device. The second phase change memory group  220  has the second phase change memory cells having a smaller size than the first phase change memory cells of the first phase change memory group  210  such that the second phase change memory group  220  can be used as a substitute for the DRAM due to the improved data processing speed as compared to the slower processing speeds needed with the first phase change memory group  210 . 
     Furthermore, the phase change properties of the first and second phase change memory groups  210  and  220  can be varied by changing the structures of the phase change material layers constituting the first and second phase change memory groups  210  and  220 . 
     That is, referring to  FIG. 8 , a phase change material layer  280   c  in the first phase change memory group  210  is formed on a heating electrode  275  which has a typically planar type. The phase change material layer  280   c  has a critical dimension (CD) larger than the heating electrode  275  and is configured to be formed as a pattern having substantially the same size as that of the upper electrode  285 . 
     Meanwhile, a phase change material layer  280   d  of the second phase change material memory group  220  is configured to be formed on the heating electrode  275  as a buried type or a contact type. The phase change material layer  280   d  has a critical dimension similar to a diameter of the heating electrode  275 . The upper electrode  285  is formed to have the same pattern as the upper electrode  285  of the first phase change memory group  210 . 
     Since the second phase change memory group  220  having the buried type phase change material layer  280   d  has a narrower CD than the phase change material layer  280   c  in the first phase change memory group  210 , its volume also relatively smaller. Therefore, when the same set or reset voltage is applied to the first and second phase change memory groups  210  and  220 , the phase change in the second phase change memory group  220  is occurs more easily. 
     According to this, the second phase change memory group  220  can exhibit a faster data processing speed than that of the first phase change memory group  210 . Therefore, the second phase change memory group  220  can be used as a substitute for a DRAM. Meanwhile, since the first change memory group  210  exhibits a relatively inherent non-volatile property then it can be used as a substitute for a flash memory device. 
     Referring to  FIG. 9 , suppose that that first and second phase change memory groups  210  and  220  have the same data processing speed. If a general driving voltage having a magnitude of “a” is pulsed to the first phase change memory group  210 , and since the size of the memory cell  225  and/or the volume of the phase change material layer  280   d  in the second phase change memory group  220  are relatively smaller, the desired data processing speed can be obtained irregardless of application of the driving voltage “b” which is relatively lower than the driving voltage “a”. 
     Accordingly, an amount E 2  of energy consumption in the second phase change memory group  220  is lower than an amount E 1  of energy consumption in the first phase change memory group  210  such that the second phase change memory group  220  can be used as a substitute for a DRAM which consumes less power. 
       FIG. 10  is a result graph showing the operation speed and integration degree in the first and second phase change memory groups  210  and  220  according to the example embodiment. Referring to  FIG. 10 , the first phase change memory group  210  having a non-volatile property which is fabricated as the example embodiment that exhibits a considerably superior operation speed as compared with the flash memory device and exhibits an integration degree similar to that of the flash memory device. 
     Furthermore, the second phase change memory group  220  with compensated data processing property ensures the refresh and non-volatile property as well as it exhibits an operation speed that matches that of DRAMs and has an integration degree almost equal to that of DRAMs. As seen from the result graph, there is no problem that it substitutes the phase change memory devices for the DRAM and the flash memory device of the system in the operation speed and the integration. 
       FIG. 11  is a result graph showing the life span and the non-volatile property in the first and second phase change memory groups  210  and  220  according to the example embodiment. Referring to  FIG. 11 , the first phase change memory group  210  with non-volatile property which is fabricated as the example embodiment exhibits a considerably superior life span as compared with the flash memory device and exhibits a non-volatile property that substantially matches that of flash memory devices. 
     Since the second phase change memory group  220  with compensated data processing property exhibits a superior non-volatile property as compared with the DRAM, then it also exhibits high data retention properties. The phase change memory group  220  also has a life span that is substantially almost equal to the DRAM. According to this, it is no problem to substitute the phase change memory devices for the DRAMs and for flash memory devices in the system. 
       FIG. 12  is a diagram illustrating the first and second phase memory groups disposed on a semiconductor chip. Referring to  FIG. 12 , the fusion memory chip  300  includes a plurality of banks B 0  to B 3  and a peripheral region  310  arranged between the banks B 0  to B 3  similar to that of a conventional memory device. The peripheral region  310  includes a control circuit unit (not shown) for controlling the banks B 0  through B 3  such as a decoder and a sense amplifier and pads (not shown) for transferring external signals. It is understood herein that the banks B 0  through B 3  each represent an aggregation of a plurality of memory cells. In the example embodiment, the phase change memory devices that have different phase change properties may be disposed by the bank unit. 
     In the example embodiment, the first phase change memory groups  210  may be disposed in adjacent first and second banks B 0  and B 1  and the second phase change memory groups  220  may be disposed in adjacent memory banks B 3  and B 4 . However, it is understood herein that this dispositional configuration it is not limited thereto. The first phase change memory groups  210  may be disposed in the first and third banks B 0  and B 2  and the second phase change memory groups  220  may be disposed into the second and fourth banks B 1  and B 3 . 
     As described above, in the fusion memory device, the system units performing different functions comprises phase change memory devices which have random access property and non-volatile property and are capable of controlling the data processing speed by controlling the phase change property (resistance distribution). 
     According to this, one memory device can perform various functions such that separate driving circuits and additional fabrication processes for an integration on one semiconductor substrate are unnecessary, thereby improving the performance of the fusion memory device. 
     Furthermore, the phase change memory devices have operation speed, integration, life span and data retention time similar to that of the DRAM and flash memory devices. The phase change memory devices can solve the problem of the refresh property and long program time in the DRAM and the flash memory devices, thereby further improving the performance of the fusion memory device. 
     The inventive concept is not limited to the example embodiments. In the example embodiments, although the first and second phase change memory groups having different functions are fabricated by changing a program condition, a cell size and a structure of the phase change material layer, they may be fabricated by combining at least one or more of the change conditions. 
     While certain embodiments have been described above, it will be understood that the embodiments described are by way of example only. Accordingly, the systems and methods described herein should not be limited based on the described embodiments. Rather, the systems and methods described herein should only be limited in light of the claims that follow when taken in conjunction with the above description and accompanying drawings.