Abstract:
A controlling method of a semiconductor device provided with a memory array including a plurality of complementary cells, each cell including a first memory element and a second memory element, for holding binary data depending on a difference of threshold voltage therebetween, the controlling method comprising: performing a prewrite procedure that writes ‘0’ or ‘1’ to both of the first memory element and the second memory element.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a Continuation Application of U.S. patent application Ser. No. 15/167,596, filed on May 27, 2016, which is based on Japanese Patent Application No. 2015-158251 filed on Aug. 10, 2015 including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    This disclosure relates to a semiconductor device and more particularly, to a semiconductor device of initializing data stored in a complementary cell typed non-volatile semiconductor memory. 
         [0003]    For example, Japanese Unexamined Patent Application Publication No. 2008-117510 relates to a semiconductor memory and discloses a non-volatile semiconductor memory of a pair type of memory cells (complementary cell). A control circuit of the semiconductor memory writes the complementary data respectively in the both memory cells forming the complementary cell. A differential sense amplifier amplifies a potential difference read from the both memory cells and reads the data stored in the complementary cell. The control circuit initializes the data stored in the complementary cell. The threshold voltages of the both initialized memory cells are substantially equal. The differential sense amplifier cannot determine which threshold voltage is higher in the memory cells, due to the initialization of the data; as the result, the data of the complementary cell gets unsteady. 
       SUMMARY 
       [0004]    However, when actually performing a control for reducing the threshold voltage of the both memory cells from a state with data written in the complementary cell (where the threshold voltage of one of the memory cells is high), there is a possibility that a difference of the threshold voltage between the both memory cells before initialization remains a little. When there remains a little difference of the threshold voltage between the both memory cells, there is a problem that the data of the complementary cell before the initialization can be read out by amplifying the difference by the differential sense amplifier. 
         [0005]    This disclosure is made in order to solve the above mentioned problem and an object of the invention in some aspect is to provide a semiconductor device which performs initialization of a complementary cell completely in a simple structure. Further, another object in the other aspect is to provide a control method of a semiconductor device which performs initialization of a complementary cell completely in a simple structure. 
         [0006]    Other objects and novel characteristics will be apparent from the description of the specification and the attached drawings. 
         [0007]    A semiconductor device according to the embodiments includes a memory array having a plurality of complementary cells, each including a first memory element and a second memory element, for holding binary data depending on a difference of threshold voltage therebetween, and a control circuit for initializing the complementary cells. The control circuit performs a first initialization control of reducing the threshold voltage of both the first memory element and the second memory element of the complementary cell and changing the threshold voltage of at least one of the first memory element and the second memory element at an intermediate level that is lower than a first writing level and higher than an initialization level, a first writing control of changing the threshold voltage of one of the first memory element and the second memory element of the complementary cell at the first writing level, and a second initialization control of changing the threshold voltage of both the first memory element and the second memory element of the complementary cell at the initialization level. 
         [0008]    The semiconductor device according to one embodiment can assuredly perform the initialization of the complementary cells in a simple structure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a view showing a micro-computer  1  according to a first embodiment. 
           [0010]      FIG. 2  is a block diagram showing a sequencer according to the first embodiment. 
           [0011]      FIG. 3  is a view showing a structure of a memory module  2  according to the first embodiment. 
           [0012]      FIGS. 4A to 4D  are views each showing a structure of a memory cell and an operation voltage condition. 
           [0013]      FIG. 5  is a view showing a distribution of threshold voltage in a complementary cell. 
           [0014]      FIG. 6  is a view showing a data writing flow in the complementary cell. 
           [0015]      FIG. 7  is a view showing data writing to the complementary cell. 
           [0016]      FIG. 8  is a view showing a data initialization flow of a complementary cell in the conventional way. 
           [0017]      FIG. 9  is a view showing a transition of a threshold voltage distribution in the complementary cell (data “ 0 ”) in the conventional initialization method. 
           [0018]      FIG. 10  is a view showing a transition of the threshold voltage distribution in the complementary cell (data “ 1 ”) in the conventional initialization method. 
           [0019]      FIG. 11  is a view showing a transition of the threshold voltage distribution in the both memory cells forming the complementary cell (data “ 0 ”) in the case of initialization by an initialization method according to the first embodiment. 
           [0020]      FIG. 12  is a view showing a transition of the threshold voltage distribution in the both memory cells forming the complementary cell in the case of initialization by the initialization method according to the first embodiment. 
           [0021]      FIG. 13  is a view showing an initialization flow in the complementary cell according to the first embodiment. 
           [0022]      FIG. 14  is a view for use in describing a timing chart of a voltage to be applied to a memory gate corresponding to the initialization flow of  FIG. 13 . 
           [0023]      FIG. 15  is a view showing a transition of the threshold voltage distribution in the both memory cells forming the complementary cell (data “ 0 ”) in the case of initialization by an initialization method according to a second embodiment. 
           [0024]      FIG. 16  is a view showing a transition of the threshold voltage distribution in the both memory cells forming the complementary cell (data “ 1 ”) in the case of initialization by the initialization method according to the second embodiment. 
           [0025]      FIG. 17  is a view showing an initialization flow in the complementary cell according to the second embodiment. 
           [0026]      FIG. 18  is a view for use in describing a timing chart of a voltage to be applied to a memory gate corresponding to the initialization flow of  FIG. 17 . 
           [0027]      FIG. 19  is a view showing a transition of the threshold voltage distribution in the both memory cells forming the complementary cell (data “ 1 ”) in the case of initialization by an initialization method according to a third embodiment. 
           [0028]      FIG. 20  is a view showing an initialization flow in the complementary cell according to the third embodiment. 
           [0029]      FIG. 21  is a view for use in describing a timing chart of a voltage to be applied to a memory gate corresponding to the initialization flow of  FIG. 20 . 
           [0030]      FIG. 22  is a view showing a transition of the threshold voltage distribution in the both memory cells forming the complementary cell (data “ 1 ”) in the case of initialization by the initialization method according to the third embodiment. 
           [0031]      FIG. 23  is a block diagram showing a sequencer according to a fourth embodiment. 
           [0032]      FIG. 24  is a view showing a data initialization flow in the complementary cell according to the fourth embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0033]    Hereinafter, embodiments of the invention will be described in detail with reference to the drawings. The same codes are attached to the same or corresponding components in the drawings and their description is not repeated. 
         [0034]      FIG. 1  is a view showing a micro-computer  1  according to a first embodiment. 
         [0035]    With reference to  FIG. 1 , the micro-computer  1  includes a high speed bus HBUS and a peripheral bus PBUS. Each of the high speed bus HBUS and the peripheral bus PBUS includes a data bus, an address bus, and a control bus although it is not particularly restricted to the above. The bus is separated into two bus structure, hence to reduce a load imposed on each bus and to realize a high speed access operation. 
         [0036]    A Central Processing Unit (CPU)  5 , a bus interface  6 , and a memory module  2  are coupled to the high speed bus HBUS. The bus interface  6  performs a bus interface control or a bus bridge control on the high speed bus HBUS and the peripheral bus PBUS. The memory module  2  stores data and a program. 
         [0037]    A sequencer  3  and ports  4  and  7  for external input and output are coupled to the peripheral bus PBUS. The sequencer  3  gives an instruction to the memory module  2 . 
         [0038]    The CPU  5  gains access to the memory module  2  through the high speed bus HBUS. When instructing the memory module  2  to do writing and initialization, the CPU  5  gives an instruction to the sequencer  3  via the bus interface  6  through the peripheral bus PBUS. The sequencer  3  performs the initialization control or the writing control on the memory module  2  through the peripheral bus PBUS, based on the instruction from the CPU  5 . 
         [0039]      FIG. 2  is a block diagram showing a sequencer according to the first embodiment. 
         [0040]    With reference to  FIG. 2 , the sequencer  3  includes bus interfaces  302  and  306 , and a state machine  304 . 
         [0041]    The bus interface  302  receives the instruction from the CPU  5  through the peripheral bus PBUS. The state machine issues a control command to the memory module  2  according to the instruction input from the bus interface  302 . The bus interface  306  outputs the control command from the state machine to the memory module  2 . 
         [0042]    In another aspect, the sequencer  3  may be built in the memory module  2 . 
         [0043]      FIG. 3  is a view showing the structure of the memory module  2  according to the first embodiment. 
         [0044]    With reference to  FIG. 3 , the memory module  2  stores 1 bit of information, using two non-volatile memory cells. Specifically, the memory cell array  270  includes two respectively rewritable non-volatile memory cells MC 1  and MC 2  as a complementary cell CC for 1 bit. 
         [0045]    By way of example, the memory cells MC 1  and MC 2  are assumed to be a split-gate type flash memory cell as shown in  FIG. 4A  described later. 
         [0046]    A select line MGL of a common memory gate is coupled to the memory gates MG 1  and MG 2  of the memory cells MC 1  and MC 2 . A common word line WL is coupled to the control gates CG 1  and CG 2  of the memory cells MC 1  and MC 2 . Actually, many complementary cells CC are arranged in a matrix shape. Each of the complementary cells CC is coupled to the corresponding select line MGL and word line WL in every array unit in a row direction. The memory cells MC 1  and MC 2  are coupled to sub bit lines SBL 1  and SBL 2  respectively in every column unit. The memory cells MC 1  and MC 2  are coupled to writing main bit lines WMBL 1  and WMBL 2  respectively through the selector  272  for the sub bit lines. 
         [0047]    A plurality of sub bit lines SBL 1  and SBL 2  are respectively coupled to the main bit lines hierarchically by the selector  272 . The unit hierarchized into the sub bit line is referred to as a memory mat. The sub bit line SBL 1  of the memory cell MC 1  is coupled to one differential input terminal of the differential sense amplifier SA through a reading column selector  274  in every memory mat. On the other hand, the sub bit line SBL 2  of the memory cell MC 2  is coupled to the other differential input terminal of the differential sense amplifier SA through the reading column selector  274  in every memory mat. 
         [0048]    The word line WL is selected by a read system row selector  250 . The select line MGL and the selector  272  are selected by a rewrite system row selector  280 . The output of the differential sense amplifier SA is coupled to the reading main bit line RMBL and coupled to the high speed bus HBUS via an output buffer  260 . 
         [0049]    A write current is selectively poured in the main bit lines WMBL 1  and WMBL 2  via the clocked inverters CI 1  and CI 2  according to the latch data of the writing data latch circuits DL 1  and DL 2 . 
         [0050]    The data latch circuits DL 1  and DL 2  are selected by a rewrite system column selector  242  . The main bit lines WMBL 1  and WMBL 2  selected by the column selector  242  are respectively coupled to verify circuits VSA 1  and VSA 2  for performing verification. The verify circuits VSA 1  and VSA 2  compare the data of the memory cells MC 1  and MC 2  specified by address with the data held by the corresponding data latch circuits DL 1  and DL 2 . The verify circuits VSA 1  and VSA 2  output the comparison result to an input and output circuit  230 . The input and output circuit  230  is coupled to the peripheral bus PBUS. The comparison result of the verify circuits VSA 1  and VSA 2  is output to the sequencer  3  through the peripheral bus PBUS. 
         [0051]    The column selector  242  is selected by a column decoder  240 . A power control circuit  210  generates various types of operation powers necessary for data reading, writing, and initialization. 
         [0052]      FIGS. 4A to 4D  are views each showing a structure of a memory cell and an operation voltage condition. 
         [0053]    With reference to  FIGS. 4A to 4D , a plurality of types of memory cells are shown. 
         [0054]      FIG. 4A  shows a split-gate type flash memory cell. 
         [0055]    In the embodiment, the memory cells MC 1  and MC 2  forming the memory module  2  are described using the split-gate type flash memory cell; however, another memory cell may be used. 
         [0056]    With reference to  FIG. 4A , the memory cell includes a control gate CG and a memory gate MG arranged over the channel forming area between source and drain regions with a gate insulation film interposed therebetween. A charge trap region SiN of e.g. silicon nitride is arranged between the memory gate MG and the gate insulation film. 
         [0057]    The source or drain region at the side of the control gate CG is coupled to a bit line BL. The source or drain region at the side of the memory gate MG is coupled to a source line SL. The processing of reducing the threshold voltage Vth of the memory cell is performed under the condition of BL=Hi−Z (high impedance state), CG=1.5 V, MG=−10 V, SL=6 V, and WELL=0 V. Specifically, a high electric field between the well region WELL and the memory gate MG draws electrons from the charge trap area SiN into the well region WELL. The processing of reducing the threshold voltage Vth of the memory cell is performed by the unit of a plurality of memory cells sharing the memory gate MG. 
         [0058]    The processing of increasing the threshold voltage Vth of the memory cell is performed under the condition of BL=0 V, CG=1.5 V, MG=10 V, SL=6 V, and WELL=0 V. Specifically, a write current is made to flow from the source line SL to the bit line BL, and hot electrons generated in a portion of the boundary between the control gate and the memory gate are injected into the charge trap area SiN. Whether or not to inject the electrons into the charge trap area SiN depends on whether or not to pass an electric current to the bit line BL; therefore, the processing of increasing the threshold voltage Vth of the memory cell is performed by the unit of bit. 
         [0059]    The processing of reading data from the memory cell is performed under the condition of BL=1.5 V, CG=1.5 V, MG=0 V, SL=0 V, and WELL=0 V. When the threshold voltage Vth of the memory cell is lower, the memory cell is turned to ON state. When the threshold voltage Vth of the memory cell is higher, the memory cell is turned to OFF state. 
         [0060]    In another aspect, in  FIG. 4B , the split-gate typed memory cell is shown. A high voltage may be applied to the memory gate MG to release the electrons to the bit line BL by FN tunnel effect, hence to reduce the threshold voltage Vth. A control of increasing the threshold voltage Vth is the same as in  FIG. 4A ; therefore, its description is not repeated. 
         [0061]    In another aspect,  FIGS. 4C and 4D  show a stacked-gate flash memory cell. This memory cell is formed by stacking a floating gate FG and a control gate WL over the channel forming area between the source and drain regions with the gate insulation film interposed therebetween. As shown in  FIG. 4C , the threshold voltage Vth of the memory cell is increased by a hot carrier writing method and reduced by releasing the electrons to the well region WELL. On the other hand, as shown in  FIG. 4D , the threshold voltage of the memory cell is increased by the FN tunnel writing method and reduced by releasing the electrons to the bit line BL. 
         [0062]    Here, each voltage value shown in  FIGS. 4A to 4D  indicates only a magnitude relation relative to another voltage and it is not restricted to this. 
         [0063]      FIG. 5  is a view showing the distribution of a threshold voltage in a complementary cell. 
         [0064]    With reference to  FIG. 5 , the respective memory cells MC 1  and MC 2  can keep in a low threshold voltage state or a high threshold voltage state. Information storage by one complementary cell CC including the memory cells MC 1  and MC 2  is realized by storing complementary data in the memory cells MC 1  and MC 2 . Specifically, one memory cell MC 1  of the complementary cell CC is assumed to be a positive electrode cell and the other memory cell MC 2  is assumed to be a negative electrode cell. 
         [0065]    In the example, data “ 1 ” of the complementary cell CC means that the threshold voltage Vth of the negative electrode cell MC 2  is higher than the threshold voltage Vth of the positive electrode cell MC 1 . 
         [0066]    In the example, data “ 0 ” of the complementary cell CC means that the threshold voltage Vth of the positive electrode cell MC 1  is higher than the threshold voltage Vth of the negative electrode cell MC 2 . Here, the state of the data “ 1 ” and “ 0 ” of the complementary cell CC may be conversely correlated with a relation of the threshold voltage between the positive electrode cell MC 1  and the negative electrode cell MC 2 . 
         [0067]    In the example, the state in which both the positive electrode cell MC 1  and the negative electrode cell MC 2  of the complementary cell CC are in a low threshold voltage, is regarded as initialization state. In the initialization state, since there is little difference of the threshold voltage Vth between the both memory cells, the data of the complementary cell CC gets unsteady. 
         [0068]      FIG. 6  is a view showing a data writing flow of the complementary cell. 
         [0069]    With reference to  FIG. 6 , in reply to a writing command given from the CPU  5 , the sequencer  3  outputs the writing address information of the memory cells MC 1  and MC 2  and the voltage application condition to the memory module  2  (Step S 102 ). 
         [0070]    Next, in reply to the instruction given from the sequencer  3 , the memory module  2  changes the threshold voltage of the memory cell specified by address. Specifically, the memory module  2  changes the threshold voltage of one of the memory cells MC 1  and MC 2  in the initialization state from the low threshold voltage state to the high threshold voltage sate (Step S 104 ). In the example, the data to be held depending on the threshold voltage state of each of the memory cells MC 1  and MC 2  is also referred to as cell data. By way of example, the cell data to be held when the memory cell MC 1  or MC 2  is in the state of the low threshold voltage is defined as “ 1 ” and the cell data to be held when it is in the high threshold voltage is defined as “ 0 ”. 
         [0071]    Then, the sequencer  3  confirms whether or not the memory cells MC 1  and MC 2  specified by address arrive at a targeted threshold voltage Vth (Step S 106 ). Specifically, verify circuits VSA 1  and VSA 2  respectively compare the cell data of the memory cells MC 1  and MC 2  specified by address with the data held by the corresponding data latch circuits DL 1  and DL 2 . Based on the comparison result by the verify circuits VSA 1  and VSA 2  input through the peripheral bus PBUS, the sequencer  3  finishes a writing control when the both data (the cell data of the memory cell MC 1  and the data held by the data latch circuit DL 1 , as well as the cell data of the memory cell MC 2  and the data held by the data latch circuit DL 2 ) is in one accord. On the other hand, the sequencer  3  outputs a command for performing the writing control to the memory module  2  again when the both data is not in one accord. 
         [0072]      FIG. 7  is a view showing data writing to a complementary cell. 
         [0073]    With reference to  FIG. 7 , here, in the writing operation (Step S 104 ) of  FIG. 6 , an example of writing the data “ 1 ” in the complementary cell CC is shown. 
         [0074]    The voltage of BL=0 V, CG=1.5 V, MG=10 V, SL=6 V, and WELL=0 V is applied to the negative electrode cell MC 2 , of the memory cells MC 1  and MC 2  in the initialization state for 5 μs, hence to make the threshold voltage Vth of the negative electrode cell MC 2  from the low threshold voltage state to the high threshold voltage state. The threshold voltage Vth of the negative electrode cell MC 2  gets higher than the threshold voltage Vth of the positive electrode cell MC 1 . 
         [0075]    Accordingly, the data “ 1 ” is written in the complementary cell CC. 
         [0076]    Hereinafter, a voltage applied to the memory gate MG is also referred to as a gate voltage. 
       [Conventional Initialization Method of Complementary Cell] 
       [0077]      FIG. 8  is a view showing a data initialization flow of a complementary cell in the conventional way. 
         [0078]    With reference to  FIG. 8 , in reply to the initialization instruction given from the sequencer  3 , the memory module  2  makes the threshold voltage Vth of the memory cells MC 1  and MC 2  specified by address in the low threshold voltage state (Step S 202 ). 
         [0079]    Next, the sequencer  3  confirms whether or not the memory cells MC 1  and MC 2  specified arrive at the targeted threshold voltage Vth (Step S 204 ). 
         [0080]    Specifically, similarly to the writing verify operation, the verify circuits VSA 1  and VSA 2  respectively compare the cell data of the memory cells MC 1  and MC 2  specified by address with the data held by the corresponding data latch circuits DL 1  and DL 2 . 
         [0081]    The sequencer  3  finishes the initialization control when determining that the both data is in one accord, based on the comparison result of the verify circuits VSA 1  and VSA 2 . On the other hand, when determining that the both data is not in one accord, the sequencer  3  outputs the command for performing the initialization control to the memory module  2  again. 
         [0082]    However, in the conventional initialization method of the complementary cell as mentioned above, there is a possibility that a difference of the threshold voltage Vth between the both memory cells before the initialization control may affect the operation even after the initialization control and there is the case of not completely cancelling the difference of the threshold voltage Vth between the both memory cells. 
         [0083]      FIG. 9  is a view showing a transition of the threshold voltage distribution of the complementary cell (data “ 0 ”) according to the conventional initialization method. 
         [0084]      FIG. 9  shows the case of performing an initialization control on the state of the complementary cell data “ 0 ” when the positive electrode cell MC 1  is in the high threshold voltage state and the negative electrode cell MC 2  is in the low threshold voltage state. 
         [0085]    As the result of performing the initialization control, the both memory cells get into the low threshold voltage state. However, affected by a difference of the threshold voltage Vth between the both memory cells before the initialization control, the threshold voltage Vth of the positive electrode cell MC 1  is higher than the threshold voltage Vth of the negative electrode cell MC 2 . 
         [0086]      FIG. 10  is a view showing a transition of the threshold voltage distribution of the complementary cell (data “ 1 ”) according to the conventional initialization method. 
         [0087]      FIG. 10  shows the case of performing the initialization control on the state of the complementary cell CC data “ 1 ” when the negative electrode cell MC 2  is in the high threshold voltage state and the positive electrode cell MC 1  is in the low threshold voltage state. 
         [0088]    As the result of performing the initialization control, the both memory cells get in the low threshold voltage state. However, affected by a difference of the threshold voltage Vth between the both memory cells before the initialization control, the threshold voltage Vth of the negative electrode cell MC 2  is higher than the threshold voltage Vth of the positive electrode cell MC 1 . 
         [0089]    Accordingly, even in the initialization controlled complementary cell, by amplifying and reading a little difference of the threshold voltage Vth between the both memory cells by the differential sense amplifier SA, in the above case, it is possible to determine whether the data of the complementary cell before the initialization is “ 0 ” or “ 1 ”. In the conventional initialization method, security is low and there is a risk of data leakage. 
       First Embodiment—Initialization of Complementary Cell Using Weak Initialization 
       [0090]      FIG. 11  is a view showing a transition of a threshold voltage distribution in the both memory cells forming the complementary cell (data “ 0 ”) in the case of initialization by an initialization method according to the first embodiment. 
         [0091]    The initialization method according to the first embodiment can initialize the data completely even in the complementary cell. 
         [0092]    With reference to  FIG. 11 , the case of initializing the complementary cell CC of the data “ 0 ” will be described. 
         [0093]    The sequencer  3  performs a weak initialization control on the state of the complementary cell CC data “ 0 ” when the positive electrode cell MC 1  is in the high threshold voltage state and the negative electrode cell MC 2  is in the low threshold voltage state. The weak initialization control indicates a control of reducing the threshold voltage of the both memory cells . Specifically, it means that one threshold voltage of the both memory cells is changed to be an intermediate threshold voltage that is lower than the threshold voltage (level) of the positive electrode cell MC 1  having the data “ 0 ” written in the complementary cell CC or the threshold voltage of the negative electrode cell MC 2  having the data “ 1 ” written in the complementary cell CC and higher than the threshold voltage of the initialized controlled memory cell. As the result of performing the weak initialization control, the threshold voltage Vth of the both memory cells is reduced. 
         [0094]    Next, the sequencer  3  performs the writing control of the data “ 1 ” on the complementary cell CC. As the result of performing the writing control of the data “ 1 ”, the negative electrode cell MC 2  is turned from the low threshold voltage state to the high threshold voltage state. Further, the threshold voltage Vth of the negative electrode cell MC 2  becomes higher than the threshold voltage Vth of the positive electrode cell MC 1 . 
         [0095]    The sequencer  3  performs the initialization control. As the result of performing the initialization control, affected by a difference of the threshold voltage Vth between the both memory cells before the initialization control, the threshold voltage Vth of the negative electrode cell MC 2  is higher than the threshold voltage Vth of the positive electrode cell MC 1 . 
         [0096]    Next, the case of initializing the complementary cell CC of the data “ 1 ” will be described. 
         [0097]      FIG. 12  is a view showing a transition of a threshold voltage distribution in the both memory cells forming the complementary cell in the case of initialization by the initialization method according to the first embodiment. 
         [0098]    With reference to  FIG. 12 , the sequencer  3  performs the weak initialization control on the state of the complementary cell CC data “ 1 ” when the positive electrode cell MC 1  is in the low threshold voltage state and the negative electrode cell MC 2  is in the high threshold voltage state. As the result of performing the weak initialization control, the threshold voltage Vth of the both memory cells is reduced. 
         [0099]    Next, the sequencer  3  performs the writing control of the data “ 1 ” on the complementary cell CC. As the result of performing the writing control of the data “ 1 ”, the threshold voltage Vth of the negative electrode cell MC 2  is higher. Next, the sequencer  3  performs the initialization control. As the result of performing the initialization control, affected by a difference of the threshold voltage Vth between the both memory cells before the initialization control, the threshold voltage Vth of the negative electrode cell MC 2  is higher than the threshold voltage Vth of the positive electrode cell MC 1 . 
         [0100]    As shown in  FIGS. 11 and 12 , in the initialization method of the complementary cell according to the first embodiment, the data of the complementary cell CC becomes “ 1 ” (the threshold voltage Vth of the negative electrode cell MC 2  is higher than the threshold voltage Vth of the positive electrode cell MC 1 ) even in the case of initialization from any state of the data “ 0 ” and “ 1 ” in the complementary cell CC. 
         [0101]    Therefore, in the case of performing the initialization method based on the first embodiment, it cannot be determined whether the data of the complementary cell CC written before the initialization is “ 0 ” or “ 1 ”. According to the initialization method of the complementary cell according to the embodiment, it is possible to realize the initialization of the complementary cell with a high security. 
         [0102]    In another aspect of the first embodiment, after the sequencer  3  performs the weak initialization control, it may be considered that the sequencer  3  performs the writing control of the data “ 0 ” not the data “ 1 ” on the complementary cell CC. 
         [0103]    In  FIGS. 11 and 12 , when the sequencer  3  performs the writing control of the data “ 0 ” on the complementary cell CC after the weak initialization control, the threshold voltage Vth of the positive electrode cell MC 1  is in the high threshold voltage state. As the result of performing the writing control of the data “ 0 ”, the threshold voltage Vth of the positive electrode cell MC 1  is higher than the threshold voltage Vth of the negative electrode cell MC 2 . 
         [0104]    Next, when the sequencer  3  performs the initialization control, affected by a difference of the threshold voltage Vth between the both memory cells before the initialization, the threshold voltage Vth of the positive electrode cell MC 1  is higher than the threshold voltage Vth of the negative electrode cell MC 2 . 
         [0105]    Accordingly, when the complementary cell CC is initialized from any state of the data “ 0 ” and “ 1 ”, the data of the complementary cell CC becomes “ 0 ” (the state in which the threshold voltage Vth of the positive electrode cell MC 1  is higher than the threshold voltage Vth of the negative electrode cell MC 2 ). 
         [0106]    Accordingly, when performing the initialization method based on the first embodiment, it cannot be determined whether the data of the complementary cell CC written before the initialization is “ 0 ” or “ 1 ”. 
         [0107]      FIG. 13  is a view showing an initialization flow of the complementary cell according to the first embodiment. 
         [0108]      FIG. 14  is a view for use in describing a timing chart of a voltage to be applied to a memory gate corresponding to the initialization flow of  FIG. 13 . 
         [0109]    With reference to  FIG. 13 , the sequencer  3  performs the weak initialization control on the memory cells MC 1  and MC 2  specified by address (Step S 302 ). Specifically, at the time T 1  shown in  FIG. 14 , a power control circuit  210  applies the voltage of BL=Hi−Z (high impedance state), CG=1.5 V, MG=−5 V, SL=6 V, and WELL=0 V to the memory cells MC 1  and MC 2  specified by address for 5 μs. Actually, there is a delay to a targeted voltage (for example, MG=−5 V) being applied to the memory cells MC 1  andMC 2 ; therefore, the time of the targeted voltage being applied to the memory cells MC 1  and MC 2  is shorter than 5 μs by the time of the delay. 
         [0110]    Next, the sequencer  3  performs the writing control of the data “ 1 ” on the complementary cell CC (Step S 304 ). Specifically, at the time T 2  shown in  FIG. 14 , the power control circuit  210  applies the voltage of BL=0 V, CG=1.5 V, MG=10 V, SL=6, and WELL=0 V to the negative electrode cell MC 2  specified by address for 5 μs. As the result of applying the targeted voltage, the threshold voltage Vth of the negative electrode cell MC 2  becomes 5 V. 
         [0111]    Then, the sequencer  3  confirms whether or not the specified memory cells MC 1  and MC 2  arrive at the targeted threshold voltage Vth (Step S 306 ). Specifically, at the time T 3  shown in  FIG. 14 , the power control circuit  210  applies the voltage of BL=1.5 V, CG=1.5 V, MG=5 V, SL=0 V, and WELL=0 V to the memory cells MC 1  and MC 2  for 1 μs. 
         [0112]    The verify circuits VSA 1  and VSA 2  compare the cell data output from the memory cells MC 1  and MC 2  specified by address with the data held by the corresponding data latch circuits DL 1  and DL 2 . 
         [0113]    Based on the comparison result output from the verify circuits VSA 1  and VSA 2 , when the sequencer  3  determines that the both data is in one accord (YES in Step S 306 ), it proceeds to the next initialization step (Step S 308 ). On the other hand, when the sequencer  3  determines that the both data is not in one accord (NO in Step S 306 ), it outputs the instruction of performing the writing control of the data “ 1 ” to the memory module  2 . 
         [0114]    Next, the sequencer  3  turns the threshold voltage Vth of the memory cells MC 1  and MC 2  specified by address into the low threshold voltage (Step S 308 ). Specifically, at the time T 4  of  FIG. 14 , the power control circuit  210  applies the voltage of BL=Hi−Z (high impedance state), CG=1.5 V, MG=−10 V, SL=6 V, and WELL=0 V to the memory cells MC 1  and MC 2  for 50 μs. 
         [0115]    Next, the sequencer  3  confirms whether or not the specified memory cells MC 1  and MC 2  arrive at the targeted low threshold voltage state (Step S 310 ). Specifically, at the time T 5  shown in  FIG. 14 , the power control circuit  210  applies the voltage of BL=1.5 V, CG=1.5 V, MG=0 V, SL=0 V, and WELL=0 V to the memory cells MC 1  and MC 2  for 1 μs. The verify circuits VSA 1  and VSA 2  compare the cell data output from the specified memory cells MC 1  and MC 2  with the data held by the corresponding data latch circuits DL 1  and DL 2 . Based on the result of the comparison result output from the verify circuits VSA 1  and VSA 2 , when the sequencer  3  determines that the both data is in one accord (YES in Step S 310 ), it finishes a series of initialization control. On the other hand, when the sequencer  3  determines that the both data is not in one accord (NO in Step S 310 ), it outputs the instruction of performing the initialization control to the memory module  2  again. 
         [0116]    In  FIGS. 13 and 14 , the voltage value and the application time in each step are only one example and not restricted to these. 
         [0117]    The initialization method of a complementary cell according to the first embodiment can initialize the data stored in the complementary cell completely in the structure using the complementary cell as a storing element of a semiconductor device. 
       Second Embodiment—Initialization of Complementary Cell Using Strong Data Writing 
       [0118]      FIG. 15  is a view showing a transition of a threshold voltage distribution in the both memory cells forming the complementary cell (data  0 ) in the case of initialization by an initialization method according to a second embodiment. 
         [0119]    With reference to  FIG. 15 , the sequencer  3  performs a strong writing control of the data “ 1 ” on the complementary cell CC from the state of the complementary cell CC data “ 0 ”. The strong writing control of the data “ 1 ” means that the threshold voltage (level) of the negative electrode cell MC 2  is changed to a threshold voltage higher than the threshold voltage changed by the usual writing control of the data “ 1 ”. As the result of performing the strong writing control of the data “ 1 ”, the threshold voltage Vth of the negative electrode cell MC 2  is higher than the threshold voltage Vth of the positive electrode cell MC 1 . 
         [0120]    Next, the sequencer  3  performs the initialization control. As the result of performing the initialization control, affected by a difference of the threshold voltage Vth between the both memory cells before the initialization, the threshold voltage Vth of the negative electrode cell MC 2  is higher than the threshold voltage Vth of the positive electrode cell MC 1 . 
         [0121]    Next, the case of initializing the complementary cell CC of the data “ 1 ” will be described. 
         [0122]      FIG. 16  is a view showing a transition of a threshold voltage distribution in the both memory cells forming the complementary cell in the case of initialization by the initialization method according to the second embodiment. 
         [0123]    With reference to  FIG. 16 , the sequencer  3  performs the strong writing control of the data “ 1 ” on the complementary cell CC from the state of the complementary cell data “ 1 ”. As the result of performing the strong writing control of the data “ 1 ”, the threshold voltage Vth of the negative electrode cell MC 2  is further higher. 
         [0124]    Next, the sequencer  3  performs the initialization control. As the result of performing the initialization control, affected by a difference of the threshold voltage Vth between the both memory cells before the initialization, the threshold voltage Vth of the negative electrode cell MC 2  is higher than the threshold voltage Vth of the positive electrode cell MC 1 . 
         [0125]    As shown in  FIGS. 15 and 16 , in the initialization method of the complementary cell according to the second embodiment, the data of the complementary cell CC always becomes “ 1 ” (the threshold voltage Vth of the negative electrode cell MC 2  is higher than the threshold voltage Vth of the positive electrode cell MC 1 ) even in the case of initialization from any state of the data “ 0 ” and “ 1 ” in the complementary cell CC. Therefore, in the case of performing the initialization method according to the second embodiment, it is difficult to determine whether the data of the complementary cell CC written before the initialization is “ 0 ” or “ 1 ”. 
         [0126]    Further, compared to the initialization method of the complementary cell according to the first embodiment, the initialization method according to the second embodiment has less control steps. According to the initialization method according to the second embodiment, it is possible to realize the initialization of the complementary cell with a higher security at a higher speed. 
         [0127]    In another aspect of the second embodiment, it may be considered that the sequencer  3  performs the strong writing control of the data “ 0 ” not the strong writing control of the data “ 1 ” on the complementary cell CC before performing the initialization control. 
         [0128]    In  FIGS. 15 and 16 , the sequencer  3  performs the strong writing control of the data “ 0 ” on the complementary cell CC, instead of the strong writing control of the data “ 1 ”. As the result of performing the strong writing control of the data “ 0 ”, the threshold voltage Vth of the positive electrode cell MC 1  is higher than the threshold voltage Vth of the negative electrode cell MC 2 . Therefore, even in the case of initialization from any state of the data “ 0 ” and “ 1 ” in the complementary cell CC, affected by a difference of the threshold voltage Vth between the both memory cells before the initialization control, the threshold voltage Vth of the positive electrode cell MC 1  is higher than the threshold voltage Vth of the negative electrode cell MC 2 . In the initialization from any state of the data “ 0 ” and “ 1 ” in the complementary cell CC, the data of the complementary cell CC becomes “ 0 ” (the state in which the threshold voltage Vth of the positive electrode cell MC 1  is higher than the threshold voltage Vth of the negative electrode cell MC 2 ). As the result, the initialization method based on the second embodiment cannot determine whether the data of the complementary cell CC before the initialization is “ 0 ” or “ 1 ”. 
         [0129]      FIG. 17  is a view showing an initialization flow of the complementary cell according to the second embodiment.  FIG. 18  is a view for use in describing a timing chart of a voltage to be applied to the memory gate corresponding to the initialization flow of  FIG. 17 . With reference to  FIG. 17 , the sequencer  3  performs the strong writing control of the data “ 1 ” on the complementary cell CC (Step S 402 ). Specifically, at the time T 1  shown in  FIG. 18 , the power control circuit  210  applies the voltage of BL=0 V, CG=1.5 V, MG=15 V, SL=6 V, and WELL=0 V to the negative electrode cell MC 2  specified by address for 5 μs. As the result of the application of the targeted voltage, the threshold voltage Vth of the negative electrode cell MC 2  becomes 7 V. 
         [0130]    Then, the sequencer  3  confirms whether or not the specified memory cells 
         [0131]    MC 1  and MC 2  arrive at the targeted threshold voltage Vth or not (Step S 404 ). Specifically, at the time T 6  shown in  FIG. 18 , the power control circuit  210  applies the voltage of BL=1.5 V, CG=1.5 V, MG=7 V, SL=0 V, and WELL=0 V to the memory cells MC 1  and MC 2  for 1 μs. 
         [0132]    The verify circuits VSA 1  and VSA 2  compare the cell data output from the specified memory cells MC 1  and MC 2  with the data held by the corresponding data latch circuits DL 1  and DL 2 . Based on the comparison result output from the verify circuits VSA 1  and VSA 2 , when the sequencer  3  determines that the both data is in one accord (YES in Step S 404 ), it proceeds to the next initialization step (Step S 406 ). On the other hand, when the sequencer  3  determines that the both data is not in one accord (NO in Step S 404 ), it outputs the instruction of performing the strong writing control of the data “ 1 ” on the complementary cell CC to the memory module  2  again. 
         [0133]    The sequencer  3  turns the threshold voltage Vth of the memory cells MC 1  and MC 2  specified by address into the low threshold voltage state (Step S 406 ). Specifically, at the time T 7  shown in  FIG. 18 , the power control circuit  210  applies the voltage of BL=Hi−Z (high impedance state), CG=1.5 V, MG=−10 V, SL=6 V, and WELL=0 V to the memory cells MC 1  and MC 2  for 50 μs. 
         [0134]    The sequencer  3  confirms whether or not the memory cells MC 1  and MC 2  specified by address arrive at the targeted low threshold voltage state (Step S 408 ). Specifically, at the time T 8  shown in  FIG. 18 , the power control circuit  210  applies the voltage of BL=1.5 V, CG=1.5 V, MG=0 V, SL=0 V, and WELL=0 V to the memory cells MC 1  and MC 2  for 1 μs. 
         [0135]    The verify circuits VSA 1  and VSA 2  compare the cell data output from the specified memory cells MC 1  and MC 2  with the data held by the corresponding data latch circuits DL 1  and DL 2 . 
         [0136]    Based on the comparison result output from the verify circuits VSA 1  and VSA 2 , when the sequencer  3  determines that the both data is in one accord (YES in Step S 408 ), it finishes a series of the initialization control. On the other hand, when the sequencer  3  determines that the both data is not in one accord (NO in Step S 408 ), it returns the control to Step S 406 , where it outputs the instruction of performing the initialization control on the complementary cell CC to the memory module  2  again. 
         [0137]    In  FIGS. 17 and 18 , the voltage value and the application time in each step are only one example and not restricted to these. 
         [0138]    The initialization method of the complementary cell according to the second embodiment can initialize the data stored in the complementary cell at a higher speed and completely, in the structure using the complementary cell as a storing element of a semiconductor device. 
       Third Embodiment—Initialization of Complementary Cell with Pre-write 
       [0139]    In an initialization method of a complementary cell according to a third embodiment, the sequencer  3  performs a pre-write control, in addition to the initialization method performed in the first and second embodiments. The pre-write control indicates a control of performing the writing control of the data “ 0 ” and the writing control of the data “ 1 ” on the complementary cell CC. 
         [0140]    In the initialization method according to the first embodiment, in  FIG. 12 , after the writing control of the data “ 1 ”, the positive electrode cell MC 1  is in the low threshold voltage state. Next, when the sequencer  3  performs the initialization control, the positive electrode cell MC 1  is further reduced in the threshold voltage Vth from the low threshold voltage state. By a control of reducing the threshold voltage further from the low threshold voltage state, load is imposed on the positive electrode cell MC 1 , to shorten the lifetime of the complementary cell. 
         [0141]      FIG. 19  is a view showing a transition of the threshold voltage distribution in the both memory cells forming the complementary cell (data “ 1 ”) in the case of initialization by the initialization method according to the third embodiment. In the initialization method shown in  FIG. 19 , the sequencer  3  performs a pre-write control in addition to the control shown in  FIG. 12 . A pre-write control may be performed at any time before performing the initialization control from the writing state. In the example shown in  FIG. 19 , the sequencer  3  performs the pre-write control just before the initialization control. In  FIGS. 19 and 12 , it is the same from the writing state to the state after writing the data “ 1 ”; therefore, a description about the same portions is not repeated. 
         [0142]    With reference to  FIG. 19 , when the sequencer  3  performs the writing control of the data “ 1 ” on the complementary cell CC, the positive electrode cell MC 1  is in the low threshold voltage state and the negative electrode cell MC 2  is in the high threshold voltage state. Next, when the sequencer  3  performs the pre-write control, the threshold voltage Vth of the positive electrode cell MC 1  is in the high threshold voltage state and the threshold voltage Vth of the negative electrode cell MC 2  is higher. As the result of performing the pre-write control, affected by a difference of the threshold voltage Vth between the both memory cells before the pre-write control, the threshold voltage Vth of the negative electrode cell MC 2  is higher than the threshold voltage Vth of the positive electrode cell MC 1 . Next, the sequencer  3  performs the initialization control. As the result of performing the initialization control, affected by a difference of the threshold voltage Vth in the both memory cells before the initialization, the threshold voltage Vth of the negative electrode cell MC 2  is higher than the threshold voltage Vth of the positive electrode cell MC 1 . 
         [0143]    By the pre-write control performed by the sequencer  3 , both the memory cells MC 1  and MC 2  are in the high threshold voltage state just before the initialization control. Therefore, it is possible to reduce the load imposed on the memory cells MC 1  and MC 2  caused by the initialization control as much as possible. In the case of performing the initialization method according to the third embodiment, the load imposed on the memory cell can be reduced, hence to realize life extension of the complementary cell. 
         [0144]    In  FIG. 19 , although the initialization with the pre-write control added is performed on the complementary cell CC having the data “ 1 ” written, the similar initialization with the pre-write control added is performed also on the complementary cell CC having the data “ 0 ” written. 
         [0145]      FIG. 20  is a view showing an initialization flow of the complementary cell according to the third embodiment. 
         [0146]      FIG. 21  is a view for use in describing a timing chart of a voltage to be applied to a memory gate corresponding to the initialization flow of  FIG. 20 . In  FIGS. 20 and 13  and in  FIGS. 21 and 14 , every control other than the pre-write control is the same. Accordingly, a description about the same portions is not repeated. 
         [0147]    After determining that the specified memory cells MC 1  and MC 2  arrive at the targeted threshold voltage Vth (YES in Step S 306 ), the sequencer  3  performs the pre-write control (Step S 307 ). Specifically, at the tie T 9  shown in  FIG. 21 , the power control circuit  210  applies the voltage of BL=0 V, CG=1.5 V, MG=10 V, SL=6 V, and WELL=0 V to the memory cells MC 1  and MC 2  specified by address for 5 μs. 
         [0148]    In  FIGS. 20 and 21 , the voltage value and the application time in each step are only one example and not restricted to these. 
         [0149]    The initialization method according to the third embodiment can initialize the data stored in the complementary cell completely while suppressing the load imposed on the complementary cell, in the structure using the complementary cell as a storing element of a semiconductor device. 
         [0150]    Also the initialization method according to the second embodiment can suppress the load imposed on the complementary cell by performing the pre-write control. In the initialization method according to the second embodiment, in  FIG. 16 , the positive electrode cell MC 1  is in the low threshold voltage state just before the initialization control. Therefore, by the control of reducing the threshold voltage further from the low threshold voltage state, the positive electrode cell MC 1  has a load and the lifetime of the complementary cell is shortened. 
         [0151]      FIG. 22  is a view showing a transition of a threshold voltage distribution in the both memory cells forming the complementary cell (data “ 1 ”) in the case of initialization by the initialization method according to the third embodiment. In the initialization method shown in  FIG. 22 , the sequencer  3  performs the pre-write control, in addition to the control shown in  FIG. 16 . The pre-write control may be performed at any time before performing the initialization control from the writing state. In the example shown in  FIG. 22 , the sequencer  3  performs the pre-write control before performing the strong writing control of the data “ 1 ” on the complementary cell CC. 
         [0152]    With reference to  FIG. 22 , at first, the sequencer  3  performs the pre-write control from the state of the complementary cell CC data “ 1 ”. As the result of performing the pre-write control, the positive electrode cell MC 1  is in the high threshold voltage state and the threshold voltage Vth of the negative electrode cell MC 2  is higher. 
         [0153]    Next, the sequencer  3  performs the strong writing control of the data “ 1 ” on the complementary cell CC. As the result of performing the strong writing control of the data “ 1 ”, the threshold voltage Vth of the negative electrode cell MC 2  is further higher. Next, when the sequencer  3  performs the initialization control, affected by a difference of the threshold voltage Vth between the both memory cells before the initialization control, the threshold voltage Vth of the negative electrode cell MC 2  is higher than the threshold voltage Vth of the positive electrode cell MC 1 . 
         [0154]    Also in the initialization method according to the second embodiment, by the pre-write control performed by the sequencer  3 , the memory cells MC 1  and MC 2  are both in the high threshold voltage state just before the initialization control. Accordingly, in the case of performing the initialization method based on the third embodiment, it is possible to reduce the load imposed on the memory cell caused by the initialization control, hence to realize a life extension of the complementary cell. 
         [0155]    In  FIG. 22 , although the initialization with the pre-write control added is performed on the complementary cell CC having the data “ 1 ” written, the similar initialization with the pre-write control added is performed also on the complementary cell CC having the data “ 0 ” written. 
         [0156]    Even when the data written in the complementary cell is “ 0 ” in the first embodiment and the second embodiment, it is possible to reduce the load on the complementary cell accompanied by the initialization of the complementary cell by adding the pre-write control. 
       Fourth Embodiment—Switching between High Speed Initialization Mode and High Security Initialization Mode 
       [0157]    Compared with the conventional initialization method of the complementary cell, the initialization method according to the first to the third embodiments can perform the initialization completely but takes longer time for the initialization processing. Of the users of the complementary cell, there is someone who wants high speedy processing rather than a high security. 
         [0158]      FIG. 23  is a block diagram showing a sequencer according to a fourth embodiment. The sequencer  3 A includes a mode register  308  in addition to the bus interfaces  302  and  306  and the state machine  304 . The sequencer  3 A inputs a command from the CPU  5  to the bus interface  302  through the peripheral bus PBUS. The bus interface  302  outputs the input command to the mode register  308  and the state machine  304 . The mode register  308  determines whether the command from the CPU  5  is the high speed initialization mode of the conventional initialization method or the high security mode of the initialization method according to one of the first to the third embodiments. The mode register  308  outputs the determination result to the state machine  304 . The conventional initialization method is the initialization method shown in  FIG. 8  or the initialization method with the pre-write control added before the initialization control of the initialization method shown in  FIG. 8 . 
         [0159]    The user of the complementary cell can select the high speed initialization mode or the high security mode. The micro-computer  1  receives an input of the selection result of the user from the port  4  or the port  7 . The port  4  or the port  7  outputs the selection result of the user to the CPU  5  through the bus interface  6 . The CPU  5  outputs the selection result of the user to the sequencer  3 A through the peripheral bus PBUS. 
         [0160]    Based on the command input from the bus interface  302  and the determination result input from the mode register  308 , the state machine  304  outputs the control command corresponding to the high speed initialization mode or the high security mode to the bus interface  306 . The memory module  2  applies a predetermined voltage to the memory cells MC 1  and MC 2  according to the instruction from the sequencer  3 A. 
         [0161]    A user of the complementary cell who gives preference to the security over the processing speed can select the high security mode according to one of the first to the third embodiments. On the other hand, a user of the complementary cell who gives preference to the processing speed over the security can select the high speed initialization mode of the conventional initialization method. Accordingly, the initialization method according to the fourth embodiment can provide an initialization method of the complementary cell according to a user&#39;s need. 
         [0162]      FIG. 24  is a view showing a data initialization flow of the complementary cell according to the fourth embodiment. With reference to  FIG. 24 , the mode register  308  determines whether or not the initialization method of the complementary cell CC is a high speed initialization mode (Step S 502 ). 
         [0163]    In the mode register  308 , when the initialization method of the complementary cell CC is determined to be the high speed initialization mode (YES in Step S 502 ), the sequencer  3 A performs the pre-write control on the memory cells MC 1  and MC 2  specified by address (Step S 504 ). As the result of performing the pre-write control, the threshold voltage Vth of the both memory cells is higher. 
         [0164]    Next, the sequencer  3 A performs the initialization control on the memory cells MC 1  and MC 2  specified by address (Step S 506 ). As the result of performing the initialization control, the threshold voltage Vth of the both memory cells is in the low threshold voltage state. 
         [0165]    Then, the sequencer  3 A determines whether or not the specified memory cells MC 1  and MC 2  arrive at the targeted low threshold voltage state or not (Step S 508 ). Specifically, the verify circuits VSA 1  and VSA 2  compare the cell data of the memory cells MC 1  and MC 2  specified by address with the data held by the corresponding data latch circuits DL 1  and DL 2 . Based on the comparison result of the verify circuits VSA 1  and VSA 2 , when the sequencer  3 A determines that the both data is in one accord (YES in Step S 508 ), it finishes the writing control. On the other hand, when the sequencer  3 A determines that the both data is not in one accord (NO in Step S 508 ), it outputs the instruction of performing the initialization control to the memory module  2  again. 
         [0166]    In the mode register  308 , a control when the initialization method of the complementary cell CC is determined not to be the high speed initialization mode (NO in Step S 502 ) is the same as the initialization control flow shown in  FIG. 20 . Therefore, their detail is not repeated. In the embodiment, although the pre-write processing is performed in the high speed initialization mode (YES in Step S 502 ) and the high security mode (NO in Step S 502 ), this processing can be omitted. 
         [0167]    According to the initialization method of the complementary cell in the fourth embodiment, it is possible to provide an initialization method of the complementary cell in accordance with a user&#39;s need, even when using the complementary cell as a storing element of a semiconductor device. 
         [0168]    As set forth hereinabove, the invention made by the inventor et al. has been described specifically based on the embodiments, the invention is not restricted to the above embodiments but, needless to say, various modifications are possible in the range without departing from the spirit.