Patent Publication Number: US-9851915-B2

Title: Two-stage read/write 3D architecture for memory devices

Description:
REFERENCE TO RELATED APPLICATION 
     This Application is a Continuation of U.S. application Ser. No. 14/259,607 filed on Apr. 23, 2014, the contents of which are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     Increasing memory capacity requirements within microelectronic devices manufactured in next-generation semiconductor technology nodes combined with lower power consumption and higher speed demands has driven an increase in the number of memory cells per bitline within memory arrays. Increasing the number of memory cells per bitline within memory arrays can be accomplished through scaling between technology nodes. However, the scaling factor for memory cells within an array can exceed that of support circuitry which surrounds the array. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates some embodiments of a memory device comprising a first memory cell array on a first tier and a second memory cell array on a second tier. 
         FIG. 2  illustrates an exemplary embodiment of a read/write timing diagram for the memory device of  FIG. 1 . 
         FIG. 3  illustrates some embodiments of a memory device comprising first and second memory cell arrays residing on first and second tiers, respectively, a control circuit configured to perform read/write operations to the first and second memory cell arrays, and a shared input/output (I/O) architecture configured to receive an input data word and further configured to output an output data word. 
         FIGS. 4A-4C  illustrate some embodiments of the shared I/O architecture of  FIG. 3 . 
         FIG. 5  illustrates some embodiments of a memory cell comprising a static random access memory (SRAM) cell. 
         FIG. 6  illustrates some embodiments of a timing diagram for a two-tier read/write operation for a memory array comprising SRAM cells. 
         FIG. 7  illustrates some embodiments of a method to read and write memory. 
         FIGS. 8A-8B  illustrate cross-sectional views of some embodiments of a memory device comprising a three-dimensional (3D) integrated chip (IC). 
     
    
    
     DETAILED DESCRIPTION 
     The description herein is made with reference to the drawings, wherein like reference numerals are generally utilized to refer to like elements throughout, and wherein the various structures are not necessarily drawn to scale. In the following description, for purposes of explanation, numerous specific details are set forth in order to facilitate understanding. It may be evident, however, to one of ordinary skill in the art, that one or more aspects described herein may be practiced with a lesser degree of these specific details. In other instances, known structures and devices are shown in block diagram form to facilitate understanding. 
     Semiconductor memory cells include volatile memory types such as static random-access memory (SRAM) or dynamic random-access memory (DRAM), or non-volatile memory types such as read-only memory (ROM), and non-volatile read-write memory (NVRWM) such as flash memory. A semiconductor memory device typically includes an array of such memory cells. Each memory cell in the array is capable of storing one or more bits of data. Therefore, an array arranged in M rows and N columns is able to store N bits of data within M words. One way to increase the capacity of the memory device (i.e., the number of bits it can store) is to shrink the memory cells making up the memory device, in accordance with Moore&#39;s Law scaling between semiconductor technology nodes, so that more memory cells can be fit into a smaller area. 
     Semiconductor scaling targets memory aggressively. As a result, the scaling factor for memory cells within the array is typically greater than the scaling factor for support circuitry which surrounds the array such as logic and analog components. Moreover, as scaling approaches the lower-bound of feature resolution achievable by optical lithography techniques, new means of scaling such as integrated chip (IC) stacking into three-dimensional (3D) chip architectures are utilized to decrease chip area. These 3D chip architectures include wafer-on-wafer, die-on-wafer, or die-on-die, which utilize bonded wafers that are electrically connected by through-silicon vias (TSVs) that are on the order of 10&#39;s of microns wide. More recently, monolithic 3D-IC integration has allowed for multiple device layers, or “tiers,” to be stacked atop one-another within thin layers of silicon (Si), and electrically connected through inter-tier vias that are typically less than about 100 nm wide. The smaller size of an inter-tier via relative to a TSV eliminates some parasitic effects associated with the comparatively large TSV. This monolithic 3D-IC integration has therefore allowed for stacking of devices within a single chip, which can be applied not only to memory cells within a memory device, but also to the support circuitry as well. 
     Accordingly, some embodiments of the present disclosure relate to a memory device wherein a single memory cell array is partitioned between two or more tiers which are vertically integrated. The memory device also includes support circuitry including a control circuit configured to read and write data to the memory cells on each tier, and a shared input/output (I/O) architecture which is connected the memory cells within each tier and configured to receive input data word prior to a write operation, and further configured to provide output data word after a read operation. Other devices and methods are also disclosed. 
       FIG. 1  illustrates some embodiments of a memory device  100  comprising a first memory cell array  102 A on a first tier  104 A and a second memory cell array  102 B on a second tier  104 B. In some embodiments, the memory device  100  comprises a two-port register file (2prf) Static Random-Access Memory (SRAM), where the first memory cell array  102 A is accessed through a first port, and the second memory cell array  102 B is accessed through a second port. The 2prf SRAM has some advantages over a one-port register file (1prf) SRAM, including the ability to perform a read and write operations simultaneously within a single clock cycle, due to the multiple ports. The 1prf SRAM, by comparison, can only be written to, or read from, within a single clock cycle. 
     For the embodiments of  FIG. 1 , the second tier  104 B is arranged over the first tier  104 A. Other embodiments comprise three or more tiers arranged over one-another in an analogous fashion, so the combined footprint of the memory device  100  is the same as that of the single memory cells array within a respective tier. The first and second memory cell arrays  102 A,  102 B each comprise an N/2×M array of memory cells  106  (e.g., SRAM, EDRAM, etc.), indicated as C ROW-COLUMN . The memory device  100  further comprises a control circuit  108  configured to perform a first read/write operation by writing a first data value (i.e., Write (1v0)) to a first group of memory cells  110  (i.e., C 0-0 , C 0-2 , . . . C 0-(n-1) ) on the first tier  104 A while concurrently reading a second data value (i.e., Read (1v1)) from a second group of memory cells  112  (i.e., C 0-1 , C 0-3 , . . . C 0-n ) on the second tier  104 B. The control circuit  108  is further configured to perform a second read/write operation by writing a third data value (i.e., Write (1v1)) to a third group of memory cells  114  (i.e., C 1-1 , C 1-3 , . . . C 1-n ) on the second tier  104 B while concurrently reading a fourth data value (i.e., Read (1v0)) from a fourth group of memory cells  116  (i.e., C 1-0 , C 1-2 , . . . C 1-(n-1) ) on the first tier  104 A. 
     By partitioning the memory cells of the memory device  100  between the first and second tiers  104 A,  104 B, a greater storage density can be realized compared to conventional memory devices. Also, splitting individual word read operations and individual word write operations across the first and second tiers further helps improve storage density relative to conventional solutions. 
       FIG. 2  illustrates an exemplary embodiment of a read/write timing diagram  200  for the memory device  100 , and is described below with reference to the features of  FIG. 1 . In some embodiments, the read/write timing diagram  200  applies to a memory device  100  comprising a 2prf SRAM. The read/write timing diagram  200  illustrates a read/write operation  202  where a first N-bit input data word is written to the memory device  100 , while a second N-bit output data word is concurrently read from the memory device  100 . 
     The write portion of this read/write operation  201  is now described. Prior to the start of the read/write operation  202 , an N-bit input data word and a write address where the N-bit input data word to be written are provided to the memory device  100 . During a first time interval  204 , a memory controller ( 108 ,  FIG. 1 ) then writes a first data value, Write (1v0)  208  (which corresponds to a first N/2 bits of the N-bit input data word) to the first memory cell array  102 A (i.e., through a first port). During a second time interval  206 , the memory controller writes a third data value, Write (1v1)  212  (which corresponds to a second N/2 bits of the N-bit input data word) to the second memory cell array  102 B (i.e., through a second port). In some embodiments, the second time interval  206  directly follows the first time interval  204 . For the embodiments of the timing diagram  200 , there is a time delta (Δt) between the first and second time intervals  204 ,  206 . Hence, at the end of the read/write operation  202 , the full N-bit input data word has been written to the memory device  100 , albeit with the N-bits of the input data word being split between the first and second tiers  104 A,  104 B. 
     Likewise, prior to the start of the read/write operation  202 , a read address is provided from which an N-bit output data word is to be read. During the first time interval  204 , a second data value, Read (1v1)  210  (which corresponds to a first N/2-bits of the N-bit output data word) is accessed from the second memory cell array  102 B (i.e., through the second port). During the second time interval  206 , a fourth data value, Read (1v0)  214  (which corresponds to the second N/2 bits of the N-bit output data word) is accessed from the first memory cell array  102 A (i.e., through the first port). At the end of the read/write operation  202 , the N-bit output data word is then provided to output pins of the memory device  100 , wherein the N-bits of the output data word have been “gathered” from over the first and second tiers  104 A,  104 B. 
       FIG. 3  illustrates some embodiments of a memory device  300  comprising first and second memory cell arrays  102 A,  102 B residing on first and second tiers  104 A,  104 B. The first and second memory cell arrays  102 A,  102 B are coupled to first and second row decoders  302 A,  302 B, respectively. The memory device  300  further comprises a control circuit  108  configured to perform read/write operations to the first and second memory cell arrays  102 A,  102 B. The control circuit  108  comprises an address decoder  304  configured to identify an odd or even address, A(m,n odd ) or A(m,n even ) within the first or second memory cell arrays  102 A,  102 B, respectively. A(m,n odd ) or A(m,n even ) correspond to a word line WL[ 0 ]-WL[m] (1v0) or WL[ 0 ]-WL[m] (1v1) within the first or second memory cell arrays  102 A,  102 B, respectively. The control circuit  108  further comprises a read/write clock (clk)  306  configured to generate a read/write clk signal (RWB), which is sent to a shared input/output (I/O) architecture  308  to control writing of input data to, and reading of output data from, the first and second memory cell arrays  102 A,  102 B. 
     The shared I/O architecture  308  is connected to the first memory cell array  102 A through first complimentary bitlines BL[ 0 ], BL[ 2 ], . . . BL[n−1], BLB[ 0 ], BLB[ 2 ], . . . BLB[n−1], and connected to the second memory cell array  102 B through second complimentary bitlines BL[ 1 ], BL[ 3 ], . . . BL[n], BLB[ 1 ], BLB[ 3 ], . . . BLB[n]. The shared I/O architecture  308  is configured to receive first and second data values, Write (1v0) and Read (1v1), as inputs and outputs, respectively, of the first read/write operation, and further configured to receive the third and fourth data values, Write (1v1) and Read (1v0), as inputs and outputs, respectively, of the second read/write operation. Details of the operation of the shared I/O architecture  308  will be demonstrated in subsequent embodiments. 
       FIG. 4A  illustrates some further embodiments of the shared I/O architecture  308 . The shared I/O architecture  308  is again connected to first and second memory sub-arrays  402 ,  404 . The first memory sub-array  402  resides on a first tier  104 A and the second memory sub-array  404  resides on a second tier  104 B. In the physical design (i.e., the manufactured circuit), the second tier  104 B is arranged in an 3D-IC package which encloses both the first and second tiers  104 A,  104 B so the second tier  104 B is arranged over the first tier  104 A, and subsequently the second memory sub-array  404  is arranged directly over the first memory sub-array  402 . For an N×M memory array, this arrangement reduces the overall footprint of the array by about 50%, as half of the cells are placed on the second tier over the first tier. 
     In some embodiments of an N×M memory array, odd columns, or first complimentary bitlines, BL[ 0 ], BL[ 2 ], . . . BL[n−1], BLB[ 0 ], BLB[ 2 ], . . . BLB[n−1], are partitioned into a first sub-array  402  residing on the first tier  104 A, and the remaining even columns, or second complimentary bitlines, BL[ 1 ], BL[ 3 ], . . . BL[n], BLB[ 1 ], BLB[ 3 ], . . . BLB[n] are partitioned into a second sub-array  404  residing on the second tier  104 B. As a result, an even column of the second sub-array  404  resides directly over an odd column of the first sub-array  402 . Within the shared I/O architecture  308  input data is written to a respective column of the first or second sub-array  402 ,  404  by a shared write element  406 . Likewise, output data is read from a respective column of the first or second sub-array  402 ,  404  by a shared read element  408 . To further reduce area in the physical design, the shared read element  408  is arranged on the second tier  104 B over the shared write element  406  on the first tier  104 A, or vice versa, to further reduce the overall footprint. 
     Collectively, the shared write elements  406  are configured to receive first and third data values, Write (1v0) and Write (1v1), and to write the first data value Write (1v0) to a first group of memory cells (i.e., row) within the first sub-array  402 , and to successively write the third data value Write (1v1) to a third group of memory cells (i.e., row) within the second sub-array  404 . Similarly, the shared read elements  408  are collectively configured to read a second data value Read (1v1) from a second group (i.e., row) of memory cells within the second sub-array  404 , and to successively read a fourth data value Read (1v0) from a fourth group (i.e., row) of memory cells within the first sub-array  404 . 
       FIG. 4B  illustrates some embodiments of a shared write element  406 . The shared write element  406  comprises first and second multiplexers (muxs)  410 A,  410 B configured to select between first or second complimentary input data signals DIN[ 0 ], DINB[ 0 ] or DIN[ 1 ], DINB[ 1 ], respectively, in response to the read/write clk signal (RWB). The shared write element  406  passes the first or second complimentary input data signals DIN[ 0 ], DINB[ 0 ] or DIN[ 1 ], DINB[ 1 ] to first or second complimentary bitlines BL[ 0 ], BLB[ 0 ] or BL[ 1 ], BLB[ 1 ], respectively, when a WPASS_LV0 signal or WPASS_LV1 signal is asserted, respectively, as will be demonstrated in  FIG. 6 . 
       FIG. 4C  illustrates some embodiments of a shared read element  408 . The shared read element  408  is configured to receive a first or second complimentary output data signal, DOUT[ 0 ], DOUTB[ 0 ] or DOUT[ 1 ], DOUTB[ 1 ], from the first or second complimentary bitlines BL[ 0 ], BLB[ 0 ] or BL[ 1 ], BLB[ 1 ], respectively, in response to a RPASS_LV0 signal or RPASS_LV1 signal, respectively, as again will be demonstrated in  FIG. 6 . The shared read element  408  comprises a differential sense amplifier (SA)  410 , comprising cross-coupled inverters, and configured to amplify the first or second complimentary output data signals, DOUT[ 0 ], DOUTB[ 0 ] or DOUT[ 1 ], DOUTB[ 1 ]. When the RPASS_LV0 signal or RPASS_LV1 signal is asserted, the first or second complimentary output data signals, DOUT[ 0 ], DOUTB[ 0 ] or DOUT[ 1 ], DOUTB[ 1 ] charge internal nodes of the differential SA  410  to slightly different potentials. The cross-coupled inverters of the differential SA  410  each comprise a pull-down element (e.g., an n-type transistor on series with a p-type transistor). When potentials discharge, the delta in voltage in conjunction with the cross-coupled configuration results in the smaller of DOUT[ 0 ], DOUTB[ 0 ] or DOUT[ 1 ], DOUTB[ 1 ] being pulled to ground (i.e., logical “0”) with the larger of DOUT[ 0 ], DOUTB[ 0 ] or DOUT[ 1 ], DOUTB[ 1 ] being pulled to its original potential (i.e., logical “1”). The shared read element  408  further comprises first and second de-multiplexers (de-muxs)  414 A,  414 B configured to select between the first or second complimentary output data signals DOUT[ 0 ], DOUTB[ 0 ] or DOUT[ 1 ], DOUTB[ 1 ], in response to the read/write clk signal (RWB). 
     In some embodiments, the memory cell  106  comprises an SRAM cell for a 2prf memory device, as is illustrated in  FIG. 5 . For the embodiments of  FIG. 5 , the memory cell  106  comprises a six-transistor (6T) SRAM, further comprising cross-coupled inverters  502  configured to store data (i.e., a single bit) on complimentary storage nodes  504 A,  504 B. The memory cell  106  is coupled to complementary bitlines (BL and BLB) through first and second pass gates  506 A,  506 B, which are controlled by a wordline (WL). In write mode, input data values DIN[ 0 ], DINB[ 0 ] or DIN[ 1 ], DINB[ 1 ] are applied to BL and BLB by the shared write element  406 . The WL is then set to high which allows the input data value and its compliment to pass to the cross-coupled inverters  502 , where it is stored as a voltage on the complimentary storage nodes  504 A,  504 B, as Q and QB, respectively 
     To read a data value from the memory cell  106 , the complimentary bitlines BL, BLB are first decoupled from the cross-coupled inverters  502  by opening the cross-coupled inverters  502  (i.e., setting the signal WL=0), thereby decoupling the complimentary bitlines BL, BLB from the complimentary storage nodes  504 A,  504 B. While decoupled, charge is leaked from a supply voltage V DD  onto the complimentary bitlines BL, BLB. This pre-charged condition often represents a condition where the complimentary bitlines BL, BLB are charged to V DD , meaning that both complimentary bitlines BL or BLB are in a logical “1” state. After pre-charging to the complimentary bitlines BL, BLB, the first and second pass gates  506 A,  506 B are again opened, causing the voltages stored on the complimentary storage nodes  504 A,  504 B, Q and QB, to transfer to the complimentary bitlines BL, BLB, respectively. The transferred voltages are then output as the complimentary output data signal, DOUT[ 0 ], DOUTB[ 0 ] or DOUT[ 1 ], DOUTB[ 1 ], and sent to the shared read element  408 . 
       FIG. 6  illustrates some embodiments of a timing diagram  600  for the two-tier read/write operation for a memory array comprising SRAM cells, and is described below with reference to the features of  FIGS. 4A-4C  and  FIG. 5 . It is appreciated that the general formulation of the timing diagram  600  and associated two-tier read/write operation for a memory array may be applied to various memory types such as SRAM, dynamic random-access memory (DRAM), or non-volatile read-write memory (NVRWM) such as flash memory, and the like. 
     At t 0  complimentary bitlines BL[ 0 ]/BLB[ 0 ] are pre-charged (or reset) to V DD  (i.e., logical “1” state). Also at t 0  read/write clk signal (RWB) is 0, corresponding to a low (i.e., “0”) read clk state, and a high (i.e., “1”) write clk state. 
     At t 1  WPASS_LV0 is asserted in the shared write element  406  so that 1v0 complimentary bitlines BL[ 0 ]/BLB[ 0 ] receive first complimentary input data signals DIN[ 0 ]/DINB[ 0 ]. Also at t 1 , WL[ 0 ] (1v0) is simultaneously asserted so that the values of DIN[ 0 ]/DINB[ 0 ] are stored as a voltage on the complimentary storage nodes  504 A,  504 B of a 1v0 memory cell  106 . 
     At t 2  WPASS_LV0 returns to 0 and a first half of a first write operation is complete. Also at t 2 , complimentary bitlines BL[ 0 ]/BLB[ 0 ] are pre-charged (or reset) to V DD . Also at t 2 , RWB is simultaneously asserted so that the first and second muxs  410 A,  410 B select the second complimentary input data signals DIN[ 1 ]/DINB[ 1 ] as inputs to the shared write element  406 . 
     At t 3  WPASS_LV1 is asserted in the shared write element  406  so that 1v1 complimentary bitlines BL[ 1 ]/BLB[ 1 ] receive the second complimentary input data signals DIN[ 1 ]/DINB[ 1 ]. Also at t 3 , WL[ 0 ] (1v2) is simultaneously asserted so that the values of DIN[ 1 ]/DINB[ 1 ] are stored as a voltage on the complimentary storage nodes  504 A,  504 B of a 1v1 memory cell  106 . 
     At t 4  WPASS_LV1 returns to 0 and a second half of the first write operation is complete. Also at t 4 , complimentary bitlines BL[ 1 ]/BLB[ 1 ] are pre-charged (or reset) to V DD . 
     At t 5  a first word cycle is complete. Note that the first (N-bit) write operation illustrated for 1v0 and 1v1 memory cells  106  above occurs within the first word cycle occurs simultaneously with a first read operation. Likewise, second write and read operations occur simultaneously within a second word cycle which immediately follows the first word cycle. 
     Simultaneously, at t 5  the second word cycle begins (i.e., Δt=0). BL[ 1 ] and BLB[ 1 ] are charged to V DD . WL[ 0 ] (1v1) is asserted, which couples BL[ 1 ], BLB[ 1 ] to the 1v1 memory cell  106 . And, RPASS_LV1 is simultaneously asserted in the shared read element  408 . 
     At t 6  SAE is asserted, and DOUT[ 1 ]/DOUTB[ 1 ] are read from BL[ 1 ]/BLB[ 1 ] through the first and second de-muxs  414 A,  414 B of the shared read element  408 . As a result, at t 6  the differential SA  410  senses the voltage difference between BL[ 1 ] and BLB[ 1 ]. 
     At t 7  RPASS_LV1 returns to zero and a first half of the second read operation is complete. Also at At t 7 , 
     At t 8  BL[ 0 ] and BLB[ 0 ] are charged to V DD . WL[ 0 ] (1v0) is asserted, which couples BL[ 0 ], BLB[ 0 ] to the 1v0 memory cell  106 . And, RPASS_LV0 is simultaneously asserted in the shared read element  408 . 
     At t 9  SAE is asserted, and DOUT[ 0 ]/DOUTB[ 0 ] are read from BL[ 0 ]/BLB[ 0 ] through the first and second de-muxs  414 A,  414 B of the shared read element  408 . As a result, at t 9  the differential SA  410  senses the voltage difference between BL[ 0 ] and BLB[ 0 ]. 
     At t 10  RPASS_LV0 returns to zero and a second half of the second read operation is complete. 
     Note that for the embodiments of a timing diagram  600  signals can be shared between the shared write element  406  and the shared read element  408 . For instance, WPASS_LV1=RPASS_LV0, and RPASS_LV1=WPASS_LV0. Moreover, as illustrated in  FIGS. 4C-4C , RWB controlling the first and second muxs  410 A,  410 B of the shared write element  406  may be inverted to generate RW to control the first and second de-muxs  414 A,  414 B of the shared read element  408   
       FIG. 7  illustrates some embodiments of a method  700  to read and write memory. While the method  700  is described below as a series of acts or events, it will be appreciated that the illustrated ordering of such acts or events are not to be interpreted in a limiting sense. For example, some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein. In addition, not all illustrated acts may be required to implement one or more aspects or embodiments of the description herein. Further, one or more of the acts depicted herein may be carried out in one or more separate acts and/or phases. 
     At  702  a memory array is partitioned into first and second tiers, wherein the second tier resides over the first tier. In some embodiments, the memory array comprises an N-bit memory array further comprising M rows and N columns. In some embodiments, partitioning the N-bit memory array into first and second tiers comprises forming a first sub-array comprising M rows and N/2 columns, where the N/2 columns of the first sub-array comprise odd numbered columns of the memory array. These embodiments further comprise forming a second sub-array comprising M rows and N/2 columns, where the N/2 columns of the second sub-array comprise even numbered columns of the N-bit memory array. 
     At  704  a first read/write operation is performed by writing a first data value to a first group of memory cells on the first tier while concurrently reading a second data value from a second group of memory cells on the second tier. 
     At  706  a second read/write operation is performed by writing a third data value to a third group of memory cells on the second tier while concurrently reading a fourth data value from a fourth group of memory cells on the first tier. 
     In some embodiments of the method  700 , the first data value is made up of N/2-bits and the third data value is made up of N/2-bits such that the first and third data values collectively correspond to an N-bit input data word provided to the memory array prior to the first read/write operation. In some embodiments of the method  700 , the second data value is made up of N/2-bits and the fourth data value is made up of N/2-bits such that the second and fourth data values collectively correspond to an N-bit output data word provided by the memory array after the first read/write operation. 
       FIG. 8A  illustrates a cross-sectional view of some embodiments of a memory device  800 A comprising a 3D-IC, further comprising a first tier  802 A vertically disposed below a second tier  804 A on a semiconductor substrate  806 A. In various embodiments, the semiconductor substrate  806 A may comprise any type of semiconductor body (e.g., silicon, silicon-germanium, silicon-on-insulator, etc.) such as a semiconductor wafer and/or one or more die on a semiconductor wafer, as well as any other type of semiconductor associated therewith. 
     The first tier  802 A comprises a first device structure (i.e., field-effect transistor)  808 A disposed over an oxide layer  810 A. In some embodiments, the first device structure  808 A is disposed over the substrate with no intervening oxide layer  810 A. A first local via  812 A connects the first device structure  808 A to a first metallization plane  814 A. Likewise, the second tier  804 A comprises a second device structure  816 A disposed over an inter-layer dielectric (ILD)  818 A. In some embodiments, the ILD  818 A comprises nearly pure Si with a thickness of less than about 1,000 nm. A second local via  812 A connects the second device structure  816 A to a second metallization plane  814 A. An inter-tier via  824 A connects the first and second device structures  808 A,  816 A through the second metallization plane  814 A. In some embodiments, the first and second device structures  808 A,  816 A reside inside 1v0 and 1v1 memory cells ( 106  of  FIG. 1 ), respectively. In some embodiments, the inter-tier via has a diameter of less than about 100 nm. In some embodiments, the first and second tiers  802 A,  804 A enclosed by a single integrated circuit package. 
       FIG. 8B  illustrates a cross-sectional view of some embodiments of a memory device  800 B comprising a 3D-IC, further comprising a first tier  802 B vertically disposed below a second tier  804 B. The first tier  802 B is disposed on a first semiconductor substrate  806 B, and the second tier  804 B is disposed on a second semiconductor substrate  808 B, which has been flipped and bonded to the first tier  802 B by an epoxy  810 B to form a face-to-face 3D-IC. 
     The first tier  802 B comprises a first device structure  812 B disposed over a first oxide layer  814 B. The second tier  804 B comprises a second device structure  816 B disposed over a second oxide layer  818 B. In some embodiments, the first or second device structure  812 B,  816 B is disposed over the first or second substrate  806 B,  808 B with no intervening first or second oxide layer  814 B,  818 B. A first local via  820 B connects the first device structure  812 B to a first metallization plane  822 B within the first tier  802 B. Second and third local vias  824 B,  828 B connect the second device structure  816 B to second and third metallization planes  826 B,  830 B, respectively. An inter-tier via  832 B connects the first and second device structures  812 B,  816 B through the third metallization plane  830 B. In some embodiments, the first and second tiers  802 B,  804 B enclosed by a single integrated circuit package. 
     It will also be appreciated that equivalent alterations and/or modifications may occur to one of ordinary skill in the art based upon a reading and/or understanding of the specification and annexed drawings. The disclosure herein includes all such modifications and alterations and is generally not intended to be limited thereby. In addition, while a particular feature or aspect may have been disclosed with respect to only one of several implementations, such feature or aspect may be combined with one or more other features and/or aspects of other implementations as may be desired. Furthermore, to the extent that the terms “includes”, “having”, “has”, “with”, and/or variants thereof are used herein; such terms are intended to be inclusive in meaning—like “comprising.” Also, “exemplary” is merely meant to mean an example, rather than the best. It is also to be appreciated that features, layers and/or elements depicted herein are illustrated with particular dimensions and/or orientations relative to one another for purposes of simplicity and ease of understanding, and that the actual dimensions and/or orientations may differ substantially from that illustrated herein. 
     Therefore, some embodiments of the present disclosure relate to a memory device wherein a single memory cell array is partitioned between two or more tiers which are vertically integrated on a single substrate. The memory device also includes support circuitry including a control circuit configured to read and write data to the memory cells on each tier, and a shared input/output (I/O) architecture which is connected the memory cells within each tier and configured to receive input data word prior to a write operation, and further configured to provide output data word after a read operation. Other devices and methods are also disclosed. 
     In some embodiments, the present disclosure relates to a memory device comprising a first memory cell array on a first tier, and a second memory cell array on a second tier, the second tier being arranged in an integrated circuit package which encloses both the first and second tiers so the second tier is arranged over the first tier, or vice versa. The memory device further comprises a control circuit configured to perform a first read/write operation by writing a first data value to a first group of memory cells on the first tier while concurrently reading a second data value from a second group of memory cells on the second tier. 
     In some embodiments, the present disclosure relates to a method to read and write memory, comprising partitioning a memory array into first and second tiers, wherein the second tier resides over the first tier, and performing a first read/write operation by writing a first data value to a first group of memory cells on the first tier while concurrently reading a second data value from a second group of memory cells on the second tier. 
     In some embodiments, the present disclosure relates to a memory device comprising first and second memory cell arrays arranged in an integrated circuit package and residing on first and second tiers, respectively, where the second tier is arranged over the first tier, or vice versa. The memory device further comprises a control circuit configured to perform a write operation by partitioning an N-bit input data word into first and third data values each comprising N/2-bits, writing the first data value to a first group of memory cells on the first tier in a first interval, and writing the third data value to a third group of memory cells on the second tier in a second interval. The control circuit is further configured to perform a read operation by reading a second data value from a second group of memory cells on the second tier in the first interval, reading a fourth data value from a fourth group of memory cells on the first tier in the second interval, wherein the second and fourth data values each comprise N/2-bits, and assembling the second and fourth data values into a N-bit output data word. The memory device further comprises a shared input/output (I/O) architecture which is connected the first and second tiers and configured to receive the N-bit input data word prior to the write operation and further configured to output the N-bit output data word after the read operation.