Abstract:
The nonvolatile ferroelectric memory device having a cell array structure including sub-bitlines and main bitlines wherein a sensing voltage of sub-bitlines is transformed into a current to induce a sensing voltage of main bitlines, comprising: a plurality of cell array blocks comprising the cell array; a cell array block driver for transmitting driving signals which drive the cell array blocks into the cell array blocks; a control circuit unit for symmetrically dividing the cell array blocks and controlling data to be written in or read from the cell array blocks; and a plurality of data buses shared in the main bitlines by using switching devices and arranged vertically in both sides of the control circuit unit, wherein a layer where the driving signals lines for transmitting the driving signals into the cell array blocks are formed is positioned above a layer where the cell arrays are formed. The multi-layer structure can reduce the layout area of chips because the repeated used driving signal lines are formed above the cell arrays.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention generally relates to nonvolatile ferroelectric memory device, and more particularly, to a nonvolatile ferroelectric memory device having a new signal line arrangement structure. The present invention effectively arranges signal lines for driving cell arrays to reduce delay of signals, and forms the signal lines of drivers above the cell array layer to decrease layout area of chip.  
           [0003]    2. Description of the Background Art  
           [0004]    Generally, a ferroelectric random access memory (hereinafter, referred to as ‘FeRAM’) has attracted considerable attention as next generation memory device because it has the same data processing speed as a DRAM and conserves data even after the power is turned off.  
           [0005]    The FeRAM includes capacitors similar to the DRAM, but the capacitors are made of a ferroelectric substance. The ferroelectric substance has the characteristic of a high residual polarization that data is not removed even after eliminating an electric field applied thereto.  
           [0006]    [0006]FIG. 1 is a characteristic curve illustrating a hysteresis loop of a general ferroelectric substance.  
           [0007]    As shown in FIG. 1, a polarization induced by an electric field remains at a certain portion (‘d’ or ‘a’ state) due to existence of the residual (or spontaneous) polarization even after the electric field is cleared.  
           [0008]    For using the ferroelectric substance, these ‘d’ and ‘a’ states may be matched to binary values of ‘1’ and ‘0’.  
           [0009]    [0009]FIG. 2 is a structural diagram illustrating a unit cell of the FRAM device.  
           [0010]    As shown in FIG. 2, the unit cell of the conventional FRAM is provided with a bitline B/L arranged in one direction and a wordline W/L arranged in another direction vertical to the bitline B/L. A plateline P/L is arranged parallel to the wordline and spaced at a predetermined interval. The unit cell is also provided with a NMOS transistor having a gate connected to an adjacent wordline W/L and a source connected to an adjacent bitline B/L, and a ferroelectric capacitor FC 1  connected between the drain terminal of the transistor T 1  and the plateline P/L.  
           [0011]    The data input/output operation of the conventional FRAM is now described as follows.  
           [0012]    [0012]FIGS. 3 a  is a timing diagram illustrating a write mode of the FRAM while FIG. 3 b  is a timing diagram illustrating a read mode of the FRAM.  
           [0013]    Referring to FIG. 3 a,  when an externally applied chip enable signal CSBPAD and a write enable signal WEBPAD transits from a high level to a low level, the array is enabled to start a write mode.  
           [0014]    Thereafter, when an address is decoded in a write mode, a corresponding wordline transits from the low level to the high level, thereby selecting the cell.  
           [0015]    During the wordline W/L maintains the high level, a ‘high’ signal of a predetermined interval and a ‘low’ signal of a predetermined interval are applied to the plateline P/L. In order to write binary logic values ‘1’ or ‘0’ in the selected cell, ‘high’ or ‘low’ signals synchronized to the write enable signal WEBPAD are applied to a corresponding bitline B/L.  
           [0016]    As shown in the following Table 1, during a ‘high’ signal is applied to the wordline W/L, if a ‘high’ signal is applied to the bitline B/L and a ‘low’ signal is applied to the plateline P/L, a logic value ‘1’ is written in the ferroelectric capacitor FC1. If the ‘low’ signal is applied to the bitline B/L and the ‘high’ signal is applied to the plateline P/L, a logic value ‘0’ is written in the ferroelectric capacitor FC1.  
                                                               TABLE 1                                       P/L                W/L: H   H   L                            B/L   H   X   1               L   0   X                      
 
           [0017]    Referring to FIG. 3B, If the externally applied chip enable signal CSBPAD is activated from the high level to the low level, all of the bitlines become equipotential to the low level by an equalizer signal before the corresponding wordline is selected.  
           [0018]    Then, each bitline becomes inactive. A corresponding wordline according to the decoded address transits from the low level to the high level to select a cell.  
           [0019]    The ‘high’ signal is applied to the plateline of the selected cell, to destroy a data Qs corresponding to a logic value ‘1’ stored in the ferroelectric memory cell. If a logic value ‘0’ is stored in the ferroelectric memory cell, its corresponding data Qns is not destroyed.  
           [0020]    The destroyed data or the non-destroyed data are outputted to bitlines according to the above-described hysteresis loop characteristics, so that a sense amplifier can sense logic values ‘1’ or ‘0’.  
           [0021]    AS shown in the hysteresis loop of FIG. 1, the state moves from ‘d’ to ‘f’ when the data is destroyed, while the state moves from ‘a’ to ‘f’ when the data is not destroyed.  
           [0022]    As a result, if the sense amplifier is enabled after a set time has elapsed, the logic value ‘1’ is output in case the data is destroyed, while the logic value ‘0’ is output in case the data is not destroyed.  
           [0023]    After the sense amplifier amplifies the data, the data should be recovered into the original data.  
           [0024]    Accordingly, the plateline P/L becomes inactive and the corresponding wordline W/L is active, to recover the data.  
           [0025]    In order to embody high integration of memory using the above-described FeRAM, it is important to effectively arrange cell arrays, peripheral controls and relevant circuits.  
           [0026]    In general, the same control blocks are repeatedly used for controlling the cell arrays. The repeated use of the control blocks causes a problem in layout of chips for high integration.  
         SUMMARY OF THE INVENTION  
         [0027]    Accordingly, it is an object of the present invention to effectively arrange cell arrays and core-related circuits of a FeRAM. The present invention has another object of reducing the area occupied by repeatedly used control blocks.  
           [0028]    A nonvolatile ferroelectric memory device of the present invention includes a plurality of cell array blocks each comprising a plurality of cell arrays for storing data; and a cell array block driver for outputting driving signals to read/write data from/to the cell array blocks; wherein driving signal line on which the driving signals are transferred is formed on a layer different from that of the plurality of the cell arrays.  
           [0029]    In order to achieve the above-described object, there is provided a nonvolatile ferroelectric memory device having a cell array structure including sub-bitlines and main bitlines wherein a sensing voltage of sub-bitlines is transformed into a current to induce a sensing voltage of main bitlines, comprising: a plurality of cell array blocks each comprising a plurality of the cell arrays for storing data; a cell array block driver for transmitting driving signals to read/write data from/to the cell array blocks wherein the cell array block driver is arranged in one side of the plurality of cell array blocks; a control circuit unit for and controlling data read/write operation of the cell array blocks wherein the control circuit unit is arranged to symmetrically divide the plurality of cell array blocks; and a plurality of data buses shared by the plurality of cell array blocks wherein the plurality of data buses arranged vertically in both sides of the control circuit unit. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0030]    [0030]FIG. 1 is a characteristic curve showing a hysteresis loop of a general ferroelectric material.  
         [0031]    [0031]FIG. 2 is a structural diagram showing a unit cell in a general nonvolatile ferroelectric memory device.  
         [0032]    [0032]FIG. 3 a  is a timing diagram showing a write mode operation of a general nonvolatile ferroelectric memory device.  
         [0033]    [0033]FIG. 3 b  is a timing diagram showing a read mode operation of a general nonvolatile ferroelectric memory device.  
         [0034]    [0034]FIG. 4 is a structural diagram showing a nonvolatile ferroelectric memory device in accordance with a first preferred embodiment of the present invention.  
         [0035]    [0035]FIG. 5 is a detail diagram showing the nonvolatile ferroelectric memory device of the present invention.  
         [0036]    [0036]FIG. 6 is a detail diagram showing a sub-cell array block of the present invention.  
         [0037]    [0037]FIG. 7 is a circuit diagram showing a main bitline pull-up controller.  
         [0038]    [0038]FIG. 8 is a circuit diagram showing a column selection unit.  
         [0039]    [0039]FIG. 9 is a circuit diagram showing a main bitline load controller and its corresponding sub-cell array.  
         [0040]    [0040]FIG. 10 is a detail diagram showing a line structure of the cell array block driver and the cell array block in accordance with the first preferred embodiment.  
         [0041]    [0041]FIG. 11 is a structural diagram showing a nonvolatile ferroelectric memory device in accordance with a second preferred embodiment of the present invention.  
         [0042]    [0042]FIG. 12 detail diagram showing the cell array block driver and a line structure of the cell array block in accordance with the second preferred embodiment.  
         [0043]    [0043]FIG. 13 is a diagram showing the nonvolatile ferroelectric memory device having a multi-layer structure in accordance with the first preferred embodiment.  
         [0044]    [0044]FIG. 14 is a diagram showing the nonvolatile ferroelectric memory device having a multi-layer structure in accordance with the second preferred embodiment.  
         [0045]    [0045]FIG. 15 is a cross-sectional diagram showing a cross-section of the chip having the multi-metal layer according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0046]    The present invention will be described in more detail referring to the accompanying drawings.  
         [0047]    [0047]FIG. 4 is a structural diagram showing a nonvolatile ferroelectric memory device in accordance with a first preferred embodiment of the present invention.  
         [0048]    Referring to FIG. 4, the nonvolatile ferroelectric memory device of the present invention comprises four cell array blocks BK 0 , BK 1 , BK 2  and BK 3 . Peripheral circuits  10  for controlling data read/write operation of the cell array blocks BK 0 -BK 3  (hereinafter, referred to as ‘control circuit unit’) such as controller, buffer, decoder, sense amplifier array and pad array are positioned in the middle of the cell array blocks BK 0 -BK 3 . As a result, the cell array blocks are symmetrically divided into two parts BK 0 , BK 1  and BK 2 , BK 3  by the control circuit unit  10 .  
         [0049]    Data buses DBL(L) and DBL(R) for connecting the cell array blocks BK 0 -BK 3  with the control circuit unit  10  are positioned between each cell array block divided by the control circuit unit  10 . The data buses DBL(L) and DBL(R) are shared in the corresponding cell array blocks BK 0 , BK 1  and BK 2 , BK 3 .  
         [0050]    In other words, the data bus DBL(L) shared in the cell array blocks BK 0  and BK 1  is positioned between the cell array blocks BK 0  and BK 1 , while the data bus DBL(R) shared in the cell array blocks BK 2  and BK 3  is positioned between the cell array blocks BK 2  and BK 3 .  
         [0051]    Cell array block drivers  20 ,  30 ,  40  and  50  for outputting driving signals driving the cell array blocks BK 0 -BK 3  are positioned in one side of the cell array blocks BK 0 -BK 3 , respectively, parallel to the data buses DBL(L) and DBL(R).  
         [0052]    [0052]FIG. 5 is a detail diagram showing the nonvolatile ferroelectric memory device of the present invention.  
         [0053]    Because each cell array blocks BK 0 -BK 3  have the same structure, one cell array block BK 0  will be described.  
         [0054]    The cell array block BK 0  comprises a plurality of sub-cell array blocks S_BK 00 -S_BK 0   n  and a plurality of sub-cell array block drivers S_BC 00 -S_BC 0   n.  The plurality of sub-cell array block drivers S_BC 00 -S_BC 0   n  transmits driving signals MBPU, MBLC, SBPD, SBPU, SBSW 1  and SBSW 2  from the cell array block driver  20  and wordline/plateline enable signals from the low address decoder (not shown) into the plurality of sub-cell array blocks S_BK 00 -S_BK 0   n.    
         [0055]    The cell array block driver  20  comprises a plurality of sub-cell array selectors  21   a  and signal drivers  21   b  corresponding to each sub-cell array block driver S_BC 00 -S_BC 0   n.  In other words, a pair of a sub-cell array selector  21   a  and a signal driver  21   b  form a sub-driver. The plurality of sub-drivers are repeatedly in the cell array block driver  20  parallel to wordlines/platelines of the cell. Signal lines where signals from the sub-cell array selector  21   a  and the signal driver  21   b  are transmitted are positioned in one side of each sub-cell array block driver S_BC 00 -S_BC 0   n  parallel to bitlines B/L of the cell.  
         [0056]    Data of the sub-cell array blocks S_BK 00 -S_BK 0   n  by driving signals from the sub-cell array block driver S_BC 00 -S_BC 0   n  are selectively transmitted into the data bus DBL(L).  
         [0057]    [0057]FIG. 6 is a detail diagram showing the sub-cell array block S_BK 00  of the present invention.  
         [0058]    The sub-cell array block S_BK 00  comprises a main bitline pull-up controller MBPUC 00 , a plurality of main bitline load controller MBLC 00 -MBLC 0   k,  a plurality of sub-cell arrays SCA 00 -SCA 0   n  (n&gt;k) corresponding to main bitline load controllers MBLC 00 -MBLC 0   k  and a column selection unit C/S 0 .  
         [0059]    In other words, one main bitline load controller MBLC 00  corresponds to the plurality of sub-cell arrays SCA 00 -SCA 0   m  (m&lt;n). A plurality of bitlines MBL 00 -MBLnn shared in the main bitline pull-up controller MBPUC 00 , the main bitline load controllers MBLC 00 -MBLC 0   k,  the sub-cell arrays SCA 00 -SCA 0   n  and the column selection unit C/S 0  are arranged in the sub-cell array block S_BK 00 . The plurality of bitlines MBL 00 -MBLnn are selectively connected to the data bus DBL(L) by the column selection unit C/S 0 .  
         [0060]    The main bitline pull-up controller MBPUC 00  pulls up voltages of the main bitlines MBL 00 -MBLnn before read/write modes. The main bitline load controllers MBLC 00 -MBLC 0   k  supply current to the main bitlines MBL 00 -MBLnn when data of the main bitlines MBL 00 -MBLnn are sensed, thereby applying load to the main bitlines MBL 00 -MBLnn.  
         [0061]    The sub-cell arrays SCA 00 -SCA 0   n  comprises sub-bitlines SBL 00 -SBLnn corresponding to the main bitlines MBL 00 -MBLnn and a plurality of sub-cell array units SCAU 000 -SCAU 0   nn  including nonvolatile ferroelectric memory cells connected to the sub-bitlines SBL 00 -SBLnn. In the sub-cell arrays SCA 00 -SCA 0   n,  wordlines WL 0 -WLn, platelines PL 0 -PLn, sub-bitline pull-down and pull-up lines SBPD and SBPU and sub-bitline switch lines SBSW 1  and SBSW 2  are arranged vertical to subbitlines SBL 00 -SBLnn shared in the sub-cell array units SCAU 00 -SCAUnn.  
         [0062]    FIGS.  7  to  9  are circuit diagrams showing the detailed structure of the cell array block BK 0 .  
         [0063]    [0063]FIG. 7 is a circuit diagram showing a main bitline pull-up controller.  
         [0064]    The main bitline pull-up controller MBPUC 00  comprises PMOS transistors P 1  connected between one of the main bitlines MBL 00 -MBLnn and a power voltage VPP(VCC). The PMOS transistors P 1  supplies the power voltage VPP(VCC) to one of the main bitlines MBL 00 -MBLnn at a precharge according to the pull-up control signal MBPUC applied to the gate of the PMOS transistor.  
         [0065]    [0065]FIG. 8 is a circuit diagram showing the column selection unit.  
         [0066]    The column selection unit C/S 0  comprises pairs of a NMOS transistor N 1  and a PMOS transistor P 2  connected in parallel between one of the bitlines MBL 00 -MBLnn and the data bus DBL(L). The pairs of the NMOS transistor N 1  and the PMOS transistor P 2  selectively connect one of the main bitlines MBL 00 -MBLnn to the data bus DBL(L) according to column selection signals CSN and CSP applied to each gate.  
         [0067]    The data transmitted into the data bus DBL(L) is transmitted into a sense amplifier of the control circuit  10 , and the data is then sensed and amplified.  
         [0068]    [0068]FIG. 9 is a circuit diagram showing the main bitline load controller MBLC 00  and its corresponding sub-cell array SCA 00  among the sub-cell arrays SCA 00 -SCA 0   m.    
         [0069]    The main bitline load controller MBLC 00  comprises a PMOS transistors P 3  connected between one of the main bitline MBL 00 -MBLnn and a power voltage VPP(VCC). The PMOS transistor P 3  loads the main bitlines MBL 00 -MBLnn by supplying the power voltage VPP(VCC) to the main bitlines MBL 00 -MBLnn according to the load control signal MBLC applied to the gate of the PMOS transistor P 3 .  
         [0070]    The sub-cell array SCA 00  comprises a plurality of sub-cell array units SCAU 000 -SCAU 00   n  having the same structure.  
         [0071]    The sub-cell array unit SCAU 00  includes NMOS transistors N 2 , N 3  and N 4 . The NMOS transistor N 2  connected between the main bitline MBL 00  and the sub-bitline SBL 00  has a gate connected to the sub-bitline selection switch line SBSW 1 . The NMOS transistor N 3  connected between the sub-bitline SBL 00  and the sub-bitline pull-up line SBPU has a gate connected to the sub-bitline selection switch line SBSW 2 . The NMOS transistor N 4  connected between the sub-bitline SBL 00  and a ground voltage has a gate connected to the sub-bitline pull-down line SBPU.  
         [0072]    The sub-cell array unit SCAU 00  also comprises a plurality of unit cells including NMOS transistors. The NMOS transistors connected between the sub-bitline SBL 00  and ferroelectric capacitors connected to the platelines PL 0 -PLn have a gate connected to the wordlines WL 0 -WLn, respectively.  
         [0073]    Additionally, the sub-cell array unit SCAU 00  comprises NMOS transistors N 5  and N 6 . The NMOS transistors N 5  and N 6  connected in series between the main bitline MBL 00  and the ground voltage have their gates connected to the sub-bitline SBL 00  and the main bitline pull-down signal MBPD, respectively.  
         [0074]    [0074]FIG. 10 is a detail diagram showing a line structure of the cell array block driver  20  and the cell array block BKO in accordance with the first preferred embodiment.  
         [0075]    In this preferred embodiment, only the line structure of the main bitline load controller MBLC and corresponding to a sub-cell array SCA 00  is illustrated.  
         [0076]    The sub-cell array selectors  21   a  and the signal drivers  21   b  are arranged in one side of the cell array block BKO parallel to wordlines/platelines WL/PL. Signal lines (hereinafter, referred to ‘first signal line’) connected to the sub-cell array selectors  21   a  and the signal drivers  21   b  and transmitting driving signals are arranged in one side of the sub-cell array block drivers S_BC 00 -S_BC 0   n  parallel to the bitlines MBL(SBL).  
         [0077]    The first signal lines corresponding to each sub-cell array block S_BK 00 -S_BK 0   n  are shared in the sub-cell array blocks S_BK 00 -S_BK 0   n,  respectively. Signal lines (hereinafter, referred to as ‘second signal line’) for transmitting the driving signals from the first signal lines into the sub-cell array block drivers S_BC 00 -S_BC 0   n  are arranged parallel to wordlines/platelines WL/PL.  
         [0078]    [0078]FIG. 11 is a structural diagram showing a nonvolatile ferroelectric memory device in accordance with a second preferred embodiment of the present invention.  
         [0079]    The nonvolatile ferroelectric memory device of the second preferred embodiment is different from that of the above-described first preferred embodiment in the position of cell array block drivers  20 ,  30 ,  40  and  50 . In this preferred embodiment, the cell array block drivers  20 ,  30 ,  40  and  50  are arranged in one side of cell array blocks BK 0 -BK 3  parallel to bitlines MBL(SBL).  
         [0080]    [0080]FIG. 12 detail diagram showing a line structure of the cell array block driver  20  and the cell array block in accordance with the second preferred embodiment.  
         [0081]    In this preferred embodiment, a plurality of pairs of sub-cell array selectors  21   a  and signal drivers  21   b  are repeatedly arranged in one sides of the cell array blocks BK 0 -BK 3  parallel to the bitlines MBL(SBL).  
         [0082]    Because the sub cell array selectors  21   a  and the signal drivers  21   b  are arranged parallel to the bitlines MBL(SBL), unlike the first preferred embodiment, first signal lines are arranged parallel to wordlines/platelines WL/PL and shared in all sub-cell array blocks S_BK 00 -S_BK 0   n  in order to apply driving signals to each sub-cell array block S_BK 00 -S_BK 0   n.  Second signal lines are arranged parallel to bitlines MBL(SBL) in order to apply driving signals from the first signal lines to sub-cell array block drivers S_BC 00 -S_BC 0   n.    
         [0083]    Here, each driver of the sub-cell array drivers S_BC 00 -S_BC 0   n  for transmitting signals from the signal drivers  21   b  into the sub-cell array block S_BK 00  comprises a transmission gate controlled by output signals of the sub-cell array selectors  21   a.    
         [0084]    However, in the cell array block driver  20  for driving the cell array blocks BK 0 -Bk 3  according to the above-described first and second preferred embodiments, a plurality of the same sub-cell array selectors  21   a  and signal drivers  21   b  are repeatedly used. The repeated use thereof increases according to high integration of chips.  
         [0085]    Due to the repeated use, the area for the first and the second signal lines occupies much space as the chips are highly integrated. As a result, the layout area of the chips are generally increased.  
         [0086]    Accordingly, in order to reduce the layout area of the chip, the multi-layer structure is used. In the multi-layer structure, the repeatedly used first and second signal lines are passed above the sub-cell array blocks S_BK 00 -S_BK 0   n  or the sub-cell array block drivers S_BC 00 -S_BC 0   n.    
         [0087]    In other words, a layer where the first and second signal lines are formed is positioned above a layer where the sub-cell array blocks S_BK 00 -S_BK 0   n  or the sub-cell array block drivers S_BC 00 -S_BC 0   n.    
         [0088]    [0088]FIG. 13 is a diagram showing the nonvolatile ferroelectric memory device having the multi-layer structure in accordance with the first preferred embodiment.  
         [0089]    As shown in FIG. 13, the multi-layer is illustrated wherein the first signal lines are passed above the cell-array block drivers S_BC 00 -S_BC 0   n.  However, the first signal lines may be passed above the sub-cell array blocks S_BK 00 -S_BK 0   n  in the multi-layer structure.  
         [0090]    In this way, the multi-layer structure does not need the conventional area wherein the first signal lines are arranged. Accordingly, although the same pair of sub-cell array selectors  21   a  and signal drivers  21   b  are repeatedly used, an additional layout area for arranging the first signal lines is not required.  
         [0091]    [0091]FIG. 14 is a diagram showing the nonvolatile ferroelectric memory device having the multi-layer structure in accordance with the second preferred embodiment.  
         [0092]    In this preferred embodiment, the first signal lines are passed above the sub-cell array block drivers S_BC 00 -S_BC 0   n  and the sub-cell array blocks S_Bk 00 -S_BK 0   n  parallel to wordlines/platelines WL/PL.  
         [0093]    For this arrangement, the first signal lines are formed on insulating layers above the layers where the sub-cell array block drivers S_BC 00 -S_BC 0   n  and the sub-cell array blocks S_BK 00 -S_Bk 0   n  are formed.  
         [0094]    The second signal lines are also formed on the same layer with the first signal lines. However, in this preferred embodiment, the multi-layer structure further comprises an intermediate layer where interconnect lines for connecting different layers electrically are formed, as shown in FIG. 15.  
         [0095]    [0095]FIG. 15 is a cross-sectional diagram showing a cross-section of the chip having the multi-metal layer structure according to the present invention.  
         [0096]    The layer L 1  is a layer where the sub-cell array blocks S_BK 00 -S_BK 0   n  or the sub-cell array block driver S_BC 00  are formed. The layer L 3  is a layer where the first and the second signal lines are formed.  
         [0097]    The layer L 2  is an intermediate layer where interconnect lines for connecting the layer L 1  to the layer L 3  are formed.  
         [0098]    It is obvious that the intermediate layer such as the layer L 2  may be plural.  
         [0099]    As discussed earlier, the nonvolatile ferroelectric memory device of the present invention can optimally regulate delay elements of signals by effectively reducing the cell array and core-related layout area. Particularly, the nonvolatile ferroelectric memory device of the present invention can reduce the size of chips by using the multi-layers a layer.