Patent Publication Number: US-8526263-B2

Title: Multi-layered memory devices

Description:
PRIORITY STATEMENT 
     This application is a divisional claiming the benefit under 35 U.S.C. §121 of U.S. application Ser. No. 12/232,146, filed on Sep. 11, 2008 now U.S. Pat. No. 7,898,893, and claims priority under 35 U.S.C. §119 to Korean Patent Application Nos. 10-2007-0092651, filed on Sep. 12, 2007, and 10-2008-0047092, filed on May 21, 2008 in the Korean Intellectual Property Office (KIPO), the entire contents of each of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     Description of the Related Art 
     In line with the developments of multimedia technologies, demand for larger-capacity information storage devices for use in computers, communication devices, or the like are increasing. In order to satisfy this increasing demand, information devices having relatively high information storage density and relatively high operating speeds have been developed. 
     Conventionally, memory devices include an active circuit unit and a memory unit. The active circuit unit includes an address decoder, a reading/recording logic controller, a sense amplifier, an output buffer, a multiplexer, and other components to read and record data. These components are generally referred to as ‘overhead’, and occupy a portion of a physical memory area. If the area occupied by the overhead is relatively small, a larger area is usable as a memory area. In order to increase density of the memory devices, a research with the aim of forming a multi-layered memory device has been conducted. 
     SUMMARY 
     Example embodiments relate to multi-layered memory devices, for example, multi-layered memory devices having a multi-layer structure including one or more memory layers arranged on at least one surface of an active circuit unit. 
     Example embodiments provide a more highly integrated multi-layered memory device, which may increase data storage density. 
     At least one example embodiment provides a multi-layered memory device. According to at least this example embodiment, the multi-layered memory device may include two or more memory units and an active circuit unit. The active circuit unit may include a decoder, and be formed between each of the two or more memory units. 
     At least one other example embodiment provides a multi-layered memory device. The multi-layered memory device may include a plurality of memory groups stacked on one another. The memory groups may include a memory unit and an active circuit configured to control the memory unit. 
     According to example embodiments, the memory unit may include one or more memory layers. The one or more memory layers may be cross-point type memory arrays. The cross-point type memory array may have a structure in which adjacent memory array layers share an electrode. A plurality of sub-arrays may be formed on the one or more memory layers. The active circuit unit may be formed on a non-silicon substrate. The non-silicon substrate may be one of a plastic substrate, a glass substrate, a ceramic substrate, an oxide substrate, and a nitride substrate. Each active circuit unit and corresponding memory unit may be grouped into a memory group. A plurality of the memory groups may be stacked on one another. Each active circuit unit may include at least one of a column decoder (CD) and a row decoder (RD). 
     According to at least some example embodiments, column address lines extending from the CD may be connected to the memory unit through vias, and row address lines extending from the RD may be connected to the one or more memory layers through vias. 
     According to at least some example embodiments, an active circuit unit may include a first active circuit and a second active circuit. The first active circuit may include a CD, whereas the second active circuit may include a RD. The memory unit may be connected to each of the first active circuit and the second active circuit. Column address lines extending from the CD of the first active circuit may be connected to the memory unit through vias, and row address lines extending from the RD of the second active circuit may be connected to the one or more memory layers through vias. 
     According to at least some example embodiments, a logic unit may be formed on a surface of one of the active circuit unit and the memory unit. The multi-layered memory device may further include a memory area formed on a substrate. The memory area may include the memory units and the active circuit unit. An input/output (I/O) chip may be connected by the memory area and a parallel bus line. A serial bus line may connect the I/O chip and a master device. 
     At least one other example embodiment provides a multi-layered memory device. The multi-layered memory device may include at least one active circuit and at least one memory unit. The at least one active circuit may include a decoder. Each of the at least one memory units may be connected to the decoder. The at least one memory unit may be separate from the at least one active circuit. The at least one active circuit may be arranged above or below the at least one memory unit. 
     According to at least some example embodiments, the at least one memory unit may include a plurality of memory layers stacked on one another. Each of the plurality of memory layers may be connected to the decoder. 
     According to at least some example embodiments, the decoder may include a column decoder and a row decoder. The column decoder may include a first column decoder circuit arranged at a first side of the at least one active circuit and a second column decoder circuit arranged at a second side of the at least one first active circuit. The row decoder may include a first row decoder circuit arranged at a third side of the at least one active circuit and a second row decoder circuit arranged at a fourth side of the at least one active circuit. The first and second sides may be opposite to each other, whereas the third and fourth sides may be opposite to each other. 
     According to at least some example embodiments, the decoder may be connected to each of the at least one memory units via address lines extending upward or downward from the at least one active circuit. The decoder may include a column decoder and a row decoder. The column decoder may be connected to each of the at least one memory unit via column address lines extending vertically upward or downward from the at least one active circuit. The column address lines may be connected to the at least one memory unit through vias arranged at least one side of the first active circuit. The vias may be offset from one another in a direction perpendicular to the direction in which the at least one side extends. 
     According to at least some example embodiments, the row decoder may be connected to each of the at least one memory unit via row address lines extending vertically upward or downward from the at least one active circuit. The row address lines may be connected to the at least one memory unit through vias arranged at least one side of the first active circuit. The vias may be offset from one another in a direction perpendicular to the direction in which the at least one side extends. 
     According to at least some example embodiments, the at least one memory unit may include at least one memory layer. The at least one memory layer may include at least one memory array. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more apparent by describing in detail example embodiments thereof with reference to the attached drawings in which: 
         FIG. 1A  is a diagram illustrating a multi-layered memory device according to an example embodiment; 
         FIGS. 1B through 1D  are diagrams illustrating memory layers according to example embodiments; 
         FIGS. 2A and 2B  are diagrams illustrating multi-layered memory devices according to example embodiments; 
         FIGS. 2C and 2D  are diagrams for describing example driving principles of multi-layered memory devices according to example embodiments; 
         FIG. 3  is a diagram illustrating a multi-layered memory device according to another example embodiment; 
         FIG. 4  is a diagram illustrating a multi-layered memory device according to another example embodiment; 
         FIG. 5  is a diagram illustrating a multi-layered memory device according to another example embodiment; 
         FIG. 6  is a diagram illustrating a multi-layered memory device according to another example embodiment; 
         FIGS. 7A and 7B  are diagrams illustrating an array structure of a decoder circuit that is a part of an active circuit unit in a structure in which a memory unit is formed on a surface of the active circuit unit of a multi-layered memory device according to example embodiments; 
         FIGS. 8A and 8B  are diagrams illustrating a structure of a multi-layered memory device in which one of a row decoder (RD) circuit and a column decoder (CD) circuit is formed below a memory unit and the other one of the RD circuit and the CD circuit is formed above the memory unit, such that information of the memory unit is recorded in and read from the multi-layered memory device according to example embodiments; 
         FIGS. 9A and 9B  are diagrams illustrating a structure of a multi-layered memory device in which vias v are formed alternately to increase density of address lines diverging from a CD and a RD in the multi-layered memory device according to example embodiments; and 
         FIG. 10  is a diagram illustrating a multi-layered memory device according to example embodiments. 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
     Various example embodiments of the present invention will now be described more fully with reference to the accompanying drawings in which some example embodiments of the invention are shown. In the drawings, the thicknesses of layers and regions are exaggerated for clarity. 
     Detailed illustrative embodiments of the present invention are disclosed herein. However, specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments of the present invention. This invention may, however, may be embodied in many alternate forms and should not be construed as limited to only the embodiments set forth herein. 
     Accordingly, while example embodiments of the invention are capable of various modifications and alternative forms, embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit example embodiments of the invention to the particular forms disclosed, but on the contrary, example embodiments of the invention are to cover all modifications, equivalents, and alternatives falling within the scope of the invention. Like numbers refer to like elements throughout the description of the figures. 
     It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of example embodiments of the present invention. As used herein, the term “and/or,” includes any and all combinations of one or more of the associated listed items. 
     Further, it will be understood that when an element is referred to as being “connected,” or “coupled,” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected,” or “directly coupled,” to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between,” versus “directly between,” “adjacent,” versus “directly adjacent,” etc.). 
     Further still, it will be understood that when an element or layer is referred to as being “formed on,” another element or layer, it can be directly or indirectly formed on the other element or layer. That is, for example, intervening elements or layers may be present. In contrast, when an element or layer is referred to as being “directly formed on,” to another element, there are no intervening elements or layers present. Other words used to describe the relationship between elements or layers should be interpreted in a like fashion (e.g., “between,” versus “directly between,” “adjacent,” versus “directly adjacent,” etc.). 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments of the invention. As used herein, the singular forms “a,” “an,” and “the,” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes,” and/or “including,” when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may in fact be executed substantially concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved. 
     A multi-layered memory device according to the present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. In the drawings, the thicknesses and widths of layers are exaggerated for clarity. 
     Multi-layered memory devices according to example embodiments may have a structure in which a plurality of memory units including one or more memory layers are formed. An active circuit unit may be included between each of the plurality of memory units. The one or more memory layers may be stacked to form each of the plurality of memory units. The active circuit unit may control each of the plurality of memory units. The active circuit unit and each of the plurality of memory units may be grouped into a memory group. The multi-layered memory device may have a structure in which a plurality of the memory groups are stacked on one another. By forming the active circuit unit on a non-silicon substrate, each of the plurality of memory units and the active circuit unit may be sequentially formed by a deposition process, not a bonding process. In a multi-layered memory device according to example embodiments, the active circuit unit may be formed in any desired position of the bottom, middle, or top of the plurality of memory units. 
       FIG. 1A  is a diagram illustrating a multi-layered memory device according to an example embodiment. Referring to  FIG. 1A , a memory unit  12  may include a plurality of memory layers a 1  through an formed on a surface of an active circuit unit  11 . The active circuit unit  11  and the memory unit  12  formed on the surface of the active circuit unit  11  may constitute an example embodiment of a multi-layered memory device. The number of memory layers a 1  through an capable of being formed on the active circuit  11  is unlimited. The active circuit unit  11  may include a decoder. The decoder may further include a row decoder (RD) and a column decoder (CD). Each of the plurality of memory layers a 1  through an may be formed to have an array structure including a plurality of memory cells. 
     Referring to  FIG. 1B , each of the plurality of memory layers a 1  through an may be a cross-point type memory array structure. In the example embodiment shown in  FIG. 1B , an information storage unit  103  and a switch structure  104  (e.g., a diode, transistor or the like) may be formed at each cross-point between a plurality of first electrode lines  101  formed in a first direction and a plurality of second electrode lines  102  formed in a second direction. The plurality of first electrode lines  101  and the plurality of second electrode lines  102  may be formed perpendicular or substantially perpendicular to one another. The information storage unit  103  may have a memory structure having various forms. For example, the information storage unit  103  may be formed of a ferroelectric capacitor, a magnetoresistive element, a phase-change element, a variable-resistance element, an antifuse, and the like, which are memory elements in a reversible structure or an irreversible structure. Also, adjacent memory layers from among the plurality of memory layers a 1  through an may be formed to share an electrode, and be stacked. 
     Each of the plurality of memory layers a 1  through an may include a memory array.  FIG. 1C  illustrates an example embodiment of a memory array  120 .  FIG. 1D  illustrates another example embodiment of a memory array including a plurality of sub-arrays  121 . Each of the plurality of memory layers a 1  through an may include a memory array such as the memory arrays shown in  FIGS. 1C and 1D . Each of the example embodiments shown in  FIGS. 1C and 1D  may be used in conjunction with one another or separate. For example, in an example embodiment, memory layer a 1  may be configured as shown in  FIG. 1C , whereas memory layer a 2  may be configured as shown in  FIG. 1D . The memory layers shown in  FIGS. 1C and 1D  may be stacked alternately to form memory devices according to example embodiments. Alternatively, each of the memory layers a 1  through an may be configured as shown in  FIG. 1C . In another example, each of the memory layers a 1  through an may be configured as shown in  FIG. 1D . 
       FIGS. 2A and 2B  are diagrams illustrating a multi-layered memory device according to another example embodiment. For example,  FIGS. 2A and 2B  illustrate a structure in which a memory group including an active circuit unit and a memory unit are stacked sequentially. 
     Referring to  FIG. 2A , the memory device may include a plurality of memory groups stacked on one another (e.g., vertically stacked). Each of the plurality of memory groups may include an active circuit and a memory unit. Each memory unit may include one or more memory layers. For example, a first memory group may include a first active circuit unit  21  and a first memory unit  22 . The first memory unit  22  may include a plurality of memory layers and may be arranged above (or on) the first active circuit  21 . The first memory group may be formed on a logic circuit or unit  20 . The logic unit  20  may also serve as an active circuit. A second memory group may include a second active circuit  23  and a memory unit  24  arranged above or on a surface of the second active circuit  23 . The second memory group may be stacked on the first memory group. A third memory group may include a third active circuit  25  and a third memory unit  26  arranged above or on a surface of the third active circuit  25 . The third memory group may be arranged on the second memory group. 
     In the structure of  FIG. 2A , each of memory units  22 ,  24 , and  26  may be formed on each of active circuit units  21 ,  23 , and  25 , respectively. The logic unit  20  may include a logic circuit, and may select one or more of the active circuit units  21 ,  23 , and  25 . Each of the active circuit units  21 ,  23 , and  25  may include a decoder, and may select one or more of the memory units  22 ,  24 , and  26 . The decoder may include a row decoder (RD) and a column decoder (CD). 
     Multi-layered memory devices according to at least this example embodiment may include a plurality of the active circuit units  21 ,  23 , and  25  capable of selecting one or more memory units  22 ,  24 ,  26  and capable of recording and reproducing information. The multi-layered memory devices may further include the logic unit  20  controlling the active circuit units  21 ,  23 , and  25 . Conventional memory devices have a structure in which an active circuit unit is formed on a silicon substrate and a plurality of memory layers are formed on the active circuit unit. However, the active circuit unit is designed to be a single unit such that many via holes are necessary and a complicated line process is required. Unlike the conventional art, the multi-layered memory device according to at least this example embodiment groups a plurality of memory layers and an active circuit unit controlling the plurality of memory layers into a memory group, and a plurality of the memory groups are stacked each other, thus, there is no limit in the number of memory units, which may be stacked. 
     Referring to  FIG. 2B , according to at least this example embodiment, the memory device may include a plurality of memory groups, each including an active circuit and a memory unit. Each memory unit may include a plurality of memory layers. The plurality of memory groups may be stacked on a logic circuit or unit. 
     In at least this example embodiment, a first memory unit  201  may be formed on a logic unit  200 . A first active circuit unit  202  may be formed on the first memory unit  201 . The first memory unit  201  and the first active circuit  202  constitute a first memory group. A second memory unit  203  and a second active circuit unit  204  may be formed on the first active circuit unit  202 . The second memory unit  203  and the second active circuit  204  constitute a second memory group. A third memory unit  205  and a second active circuit unit  206  may be formed on the second active circuit unit  204 . The third memory unit  205  and the third active circuit  206  constitute a third memory group. 
     In a structure of  FIG. 2B , active circuit units  202 ,  204 , and  206  may be formed on memory units  201 ,  203 , and  205 , respectively, and a memory group including a memory unit and an active circuit unit may be sequentially stacked on the logic unit  200 . The logic unit  200  may include a logic circuit, and may select one or more of the active circuit units  202 ,  204 , and  206 . Each of the active circuit units  202 ,  204 , and  206  may include a decoder, and may select one or more of the memory units  201 ,  203 , and  205 . The decoder may include a row decoder (RD) and a column decoder (CD). 
       FIGS. 2C and 2D  are diagrams for describing a driving principle of a multi-layered memory device according to example embodiments. 
     Referring to  FIG. 2C , the multi-layered memory device according to at least one example embodiment may have a structure in which a plurality of memory units M and a plurality of active circuit units D are formed on a logic unit  210  (e.g., as shown in  FIG. 2A  or  2 B). The logic unit  210  may be connected to the plurality of active circuit units D through decoder selection lines  221 , and may select a specific active circuit unit from among the plurality of active circuit units D. An address (a row and a column) of a desired memory cell may be input through a memory address selection line connected to the logic unit  210  and the plurality of active circuit units D. A memory address selection signal may be input through a row line  222   a  and a column line  222   b . A specific memory layer of the plurality of memory units M may be selected through a memory level decoder. This will be described in detail below with reference to  FIG. 2D . 
     Referring to  FIG. 2D , a plurality of memory units  211  and  213 , and a plurality of active circuit units  212  and  214  may be formed on the logic unit  210 . The first active circuit unit  212  may write and read data to and from the first memory unit  211 . The second active circuit unit  214  may write and read data to and from the second memory unit  213 . When an active circuit unit and a memory unit are grouped into memory groups denoted by G in  FIG. 2D , a plurality of (e.g., an unlimited number of) memory groups G may be formed on the second active circuit unit  214 . 
     The logic unit  210  may be connected to each of the active circuit units  212  and  214  through the decoder selection lines  221 . The logic unit  210  may select a specific active circuit unit from among the active circuit units  212  and  214 , through the decoder selection lines  221 . For example, in the case where the first active circuit unit  212  is selected, a selection line s 1  may be ON, whereas the rest of the decoder selection lines  221  may be OFF. Subsequently, an address (a row and a column) of a desired memory cell may be input through a memory selection line  222  connected to the logic unit  210  and the plurality of active circuit units  212  and  214 . Only the first active circuit unit  212  may be in an ON-state, and thus, only an address of specific memory cells in each of memory layers of the first memory unit  211  may be input. Afterward only a specific memory layer of the first memory unit  211  may be selected through the memory level decoder. As a result, the desired memory cell may be selected. 
       FIG. 3  is a diagram illustrating a multi-layered memory device according to another example embodiment. According to at least this example embodiment, a memory unit may be formed on each of a plurality of sides of an active circuit. 
     Referring to  FIG. 3 , memory units  32  and  33  may be formed on top and bottom (e.g., both) surfaces of an active circuit unit  31 . The first memory unit  32  may include one or more (e.g., a plurality of) memory layers b 1  through bn. The second memory unit  33  may include one or more (e.g., a plurality of) memory layers c 1  through cn. There is no limit in the number of memory layers capable of being included in the memory units  32  and  33 . The active circuit unit  31  may include a decoder capable of selecting one or more memory layers b 1  through bn of memory unit  32  and/or one or more of memory layers c 1  through cn of memory unit  33 . The active circuit  31  may include a sense amplifier, a buffer, a step-down circuit, a boosting circuit, a detecting circuit, and/or a reference voltage circuit. 
       FIG. 4  is a diagram illustrating a multi-layered memory device according to another example embodiment.  FIG. 4  illustrates a structure in which a plurality of the memory groups, each of which includes an active circuit unit and one or more memory units formed on both (e.g., opposite) surfaces of the active circuit unit, may be stacked on one another. 
     Referring to  FIG. 4 , a first memory group may be arranged on a logic circuit  40 . The first memory group may include a first active circuit unit  42  and a second memory unit  43  formed on opposite surfaces of a first memory unit  41 . A second memory group may be formed above the first memory group. The second memory group may include a third memory unit  44  and a fourth memory unit  45  formed on opposite surfaces of a second active circuit unit  45 . The logic unit  40  may include a logic circuit, and may select one or more of the active circuit units  42  and  45 . Each of the active circuit units  42  and  45  may include a decoder. The active circuit unit  42  may select one or more of the memory units  41  and  43  formed on surfaces of the active circuit unit  42 . The active circuit unit  45  may select one or more of the memory units  44  and  46  formed on surfaces of the active circuit unit  45 . 
       FIG. 5  is a diagram illustrating a multi-layered memory device according to another example embodiment. In the multi-layered memory device of  FIG. 5 , a column decoder (CD) and a row decoder (RD) may be formed on separate layers so as to select a memory unit. 
     Referring to  FIG. 5 , a first memory unit  53  may be formed on a first active circuit unit  51   a . A second active circuit unit  52   a , a second memory unit  54 , and a third active circuit unit  51   b  may be formed on the first memory unit  53 . The first active circuit unit  51   a  and the third active circuit unit  51   b  may include one of the CD and the RD. If the first active circuit unit  51   a  and the third active circuit unit  51   b  include the CD, the second active circuit unit  52   a  may include the RD. Alternatively, if the first and third active circuit units  51   a  and  51   b  include the RD, then the second active circuit  52   a  may include the CD. 
     The first memory unit  53  may include one or more memory layers d 1  through dn, and the second memory unit  54  may include one or more memory layers e 1  through en. There is no limit in the number of memory layers capable of being formed on the active circuit units. Each of the active circuit units  51   a ,  52   a , and  51   b  may be connected to one or more of the first and second memory units  53  and  54  in upper and lower directions so as to select the one or more memory layers d 1  through dn of the first memory unit  53  or the one or more memory layers e 1  through en of the second memory unit  54 . For example, if the first active circuit unit  51   a  includes the CD and the second active circuit unit  52   a  includes the RD, the first and second active circuit units  51   a  and  52   a  may be used to select the one or more memory layers d 1  through dn of the first memory unit  53 . Similarly, if the third active circuit unit  51   b  includes the CD and the second active circuit unit  52   a  includes the RD, the second and third active circuit units  52   a  and  51   b  may be used to select the one or more memory layers e 1  through en of the second memory unit  53   
       FIG. 6  is a diagram illustrating a multi-layered memory device according to another example embodiment. 
     Referring to  FIG. 6 , a first active circuit unit  61  and a first memory unit  64  may be formed on a logic unit  60 . A second active circuit unit  62  and a second memory unit  65  may be formed on the first memory unit  64 . A third active circuit unit  63  and a third memory unit  66  may be formed above the second memory unit  65 . The logic unit  60  may include a logic circuit, and may select one or more of the active circuit units  61 ,  62 , and  63 . Each of the active circuit units  61 ,  62 , and  63  may include one of a CD and a RD, and may respectively select one or more of the memory units  64 ,  65 , and  66 . According to at least this example embodiment, the first memory unit  64  may be formed on a second surface of the active circuit unit  61  and on a first surface of the second active circuit  62 . The second memory unit  65  may be formed on a second surface of the second active circuit unit  62  and a first surface of the third active circuit unit  63 . The third memory unit  66  may be formed on a second surface of the third active circuit unit  63 . By sequentially forming an active circuit unit including the CD or the RD and a memory unit on the logic unit  60 , a stacked structure may be formed. 
     Alternatively, each of the active circuit units  61 ,  62 , and  63  may include both the CD and the RD. In at least this example embodiment, the CD of the first active circuit unit  61  and the RD of the second active circuit unit  62  may be used to address the first memory unit  64 . The CD of the second active circuit unit  62  and the RD of the third active circuit unit  63  may be used to address the second memory unit  65 . 
     Alternatively, the RD of the first active circuit unit  61  and the CD of the second active circuit unit  62  may be used to address the first memory unit  64 , and the RD of the second active circuit unit  62  and the CD of the third active circuit unit  63  may be used to address the second memory unit  65 . 
     As described above, memory layers of the multi-layered memory device according to at least some example embodiments may be formed as a cross-point type memory array. For example, a plurality of lower electrode lines and a plurality of upper electrode lines crossing the plurality of lower electrode lines may be formed in each of the memory layers, and a switch structure and an electric charge storage structure may be sequentially formed in an area where the plurality of lower and upper electrode lines cross each other. The plurality of lower electrode lines and the plurality of upper electrode lines may be individually connected to the RD or the CD of the active circuit unit. 
     Each of the memory layers may include a memory array, and unlike the conventional technology, may not include a separate memory array enable circuit. In multi-layered memory devices according to at least some example embodiments, the logic unit  60  may be formed on a silicon substrate or a non-silicon substrate. For example, after the logic circuit forming the logic unit  60  is formed on one of the silicon substrate and the non-silicon substrate, an interlayer dielectrics (ILD) process may be performed. The memory unit and the active circuit unit may then be formed repeatedly on the logic unit  60 . Examples of the non-silicon substrate are a plastic substrate, a glass substrate, a ceramic substrate, an oxide substrate, or a nitride substrate. The active circuit unit may include a decoder, and optionally, a sense amplifier, a buffer, a step-down circuit, a boosting circuit, a detecting circuit, and/or a reference voltage circuit. Conventionally, the active circuit unit is formed on the silicon substrate such that an area is limited, a processable memory cell area is also limited, and the number of stackable memory layers is limited. However, according to example embodiments, the active circuit unit may be formed between each of memory units so that such limits may be overcome. 
       FIGS. 7A and 7B  are diagrams illustrating an array structure of a decoder circuit of an active circuit unit in a structure in which a memory unit is formed on one surface of the active circuit unit of a multi-layered memory device according to another example embodiment. Each decoder circuit may include a RD and a CD. 
     Referring to  FIG. 7A , a RD and a CD may be formed on an active circuit unit  71 . Row address lines r extending upward from the RD connect the active circuit unit  71  to a memory unit  72  arranged above the active circuit unit  71  through vias V. Column address lines c extending upward from the CD also connect the active circuit unit  71  to the memory unit  72  through vias V. If the memory unit  72  includes one or more memory layers, the row address lines r and the column address lines c may be connected to each of the one or more memory layers. 
     Referring to  FIG. 7B , an active circuit unit  701  may include a RD and a CD. Row address lines r extending downward from the RD connect the active circuit unit  701  to a memory unit  702  arranged below the active circuit unit  701  through vias V. Column address lines c extending downward from the CD also connect the active circuit unit  701  to the memory unit  702  through vias V. If the memory unit  702  includes one or more memory layers, the row address lines r and the column address lines c may be connected to each of the one or more memory layers. 
     In a structure in which the RD and the CD are formed on the active circuit unit  701 , and memory units (each of which includes a plurality of memory layers) are formed on both top and bottom surfaces of the active circuit unit  701 , the row address lines r and the column address lines c may be connected to each of the plurality of memory layers. 
       FIGS. 8A and 8B  are diagrams illustrating a structure of a multi-layered memory device in which one of a RD circuit and a CD circuit is formed below a memory unit, and the other one of the RD circuit and the CD circuit is formed above the memory unit, such that information is recorded in and read from multi-layered memory devices according to example embodiments. 
     Referring to  FIG. 8A , a memory unit  82  and a second active circuit unit  83  may be sequentially formed on a first active circuit unit  81 . A CD may be formed on the first active circuit unit  81 , and a RD may be formed on the second active circuit unit  83 . Column address lines c extending upward from the CD of the first active circuit unit  81  may be connected to the memory unit  82  through vias V. As shown in  FIG. 8A , the CD of the first active circuit unit  81  may be connected to memory unit  82  in an alternating manner such that adjacent columns of the memory array are connected to different sides of the CD. For example, a first of two adjacent columns may be connected to a via V at a first side of the first active circuit unit  81 , whereas a second of two adjacent columns of the memory unit  82  may be connected to a second, opposite side of the CD. Row address lines r extending downward from the RD of the second active circuit unit  83  may be connected to the memory unit  82  through vias V. As shown in  FIG. 8A , the RD of the second active circuit unit  83  may be connected to memory unit  82  in an alternating manner such that adjacent rows of the memory array are connected to different sides of the RD. For example, a first of two adjacent rows may be connected to a via V at a first side of the second active circuit unit  83 , whereas a second of two adjacent rows of the memory unit  82  may be connected to a second, opposite side of the second active circuit unit  83 . The first and second side to which the row address lines r are connected may be different from the first and second sides that the column address lines c are connected. 
     If the memory unit  82  is formed to have a plurality of memory layers, the row address lines r and the column address lines c may be connected to each of the plurality of memory layers. 
     In  FIG. 8B , column address lines c extending upward from a CD of a first active circuit unit  801  may be connected to a memory unit  802  through vias V on only one side end of the first active circuit unit  801 . Row address lines r extending from a RD of a second active circuit unit  803  may be connected to the memory unit  802  through vias V at only a front end of the second active circuit unit  803 . If the memory unit  802  includes a plurality of memory layers, the row address lines r and the column address lines c may be connected to each of the plurality of memory layers. 
       FIGS. 9A and 9B  are diagrams illustrating a structure of a multi-layered memory device in which vias V are formed alternately to increase density of address lines extending from a CD and a RD in the multi-layered memory device according to another example embodiment. 
     Referring to  FIG. 9A , a RD and a CD may be formed on ends of respective first and second sides of an active circuit unit  91 . A memory unit  92  may be formed below the active circuit unit  91 . Row address lines r and column address lines c extending from the RD and the CD, respectively, of the active circuit unit  91 , may be connected to the memory unit  92  through vias V. The vias V may be formed alternately offset from one another in a given direction. For example, the vias V connected to the row address lines r may be offset from one another in a direction that is perpendicular to a direction in which the first side of the active circuit unit  91  extends. Similarly, the vias V connected to the column address lines c may be offset from one another in a direction that is perpendicular to a direction in which the second side of the active circuit unit  91  extends. 
     Referring to  FIG. 9B , an active circuit unit  901  may include a RD and a CD. In this example embodiment, a CD may be formed on ends of first and second sides of the active circuit unit  901 , and the RD may be formed on ends of third and fourth sides of the active circuit unit  901 . The first and second sides may be opposite to one another, and the third and fourth sides may be opposite to one another. A memory unit  902  may be formed below the active circuit unit  901 . Row address lines r and column address lines c extending from the RD and the CD, respectively, of the active circuit unit  901 , may be connected to the memory unit  902  through vias V. The vias V may be formed alternately offset from one another in a given direction. For example, the vias V connected to the row address lines r may be offset from one another in a direction that is perpendicular to a direction in which the first and second sides of the active circuit unit  901  extends. Similarly, the vias V connected to the column address lines c may be offset from one another in a direction that is perpendicular to a direction in which the third and fourth sides of the active circuit unit  901  extends. 
     The position and shape of vias Via V may be selectively determined according to configuration and/or density of an array device of the memory units  92  and  902 , but example embodiments are not limited thereto. The active circuit unit and the memory unit illustrated in each of  FIGS. 7A through 9B  may be grouped into a memory group, and the memory group may be stacked repeatedly. Thus, connection lines may be simplified to reduce the number of vias as compared to a conventional memory device using only a single active circuit unit. 
       FIG. 10  is a diagram illustrating a multi-layered memory device according to another example embodiment. 
     Referring to  FIG. 10 , the multi-layered memory device  100  may include a memory area  102  formed on a substrate  101 , an input/output (I/O) chip  104 , a parallel bus line  103  connecting the memory area  102  and the I/O chip  104 , and a serial bus line  105  connecting the I/O chip  104  and a master device or module (not shown). The memory area  102  may have a multi-layered structure, for example, as discussed above. 
     According to example embodiments, various electronic elements may be manufactured given the knowledge of one of ordinary skill in the art. Multi-layered memory devices according to example embodiments may be used as, for example, media devices for various products, such as, mobile or cellular phones, smart phones, personal digital assistants (PDAs), laptop or desktop computers, digital cameras, digital camcorders, MP3 or other portable music player, etc. 
     While example embodiments have been particularly shown and described with reference to the example embodiments shown in the drawings, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.