Patent Publication Number: US-2022238167-A1

Title: Semiconductor storage device

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2021-010010, filed on Jan. 26, 2021, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to a semiconductor storage device. 
     BACKGROUND 
     A NAND flash memory that executes operations such as writing, reading, and erasing of data is one example of a semiconductor storage device. The NAND flash memory includes a voltage generation circuit. The voltage generation circuit generates voltages used during operations such as writing, reading, and erasing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating an example of a configuration of a host device and a memory system including a semiconductor storage device according to an embodiment. 
         FIG. 2  is a block diagram illustrating an example of a configuration of the semiconductor storage device according to the embodiment. 
         FIG. 3  is a circuit diagram illustrating an example of a configuration of a memory cell array of the semiconductor storage device according to the embodiment. 
         FIG. 4A  is a cross-sectional view illustrating an example of a structure of the memory cell array of the semiconductor storage device according to the embodiment. 
         FIG. 4B  is a cross-sectional view illustrating another example of a structure of the memory cell array of the semiconductor storage device according to the embodiment. 
         FIG. 5  is a circuit diagram illustrating an example of a configuration of a voltage generation circuit according to the embodiment. 
         FIG. 6  is a circuit diagram illustrating an example of a configuration of a charge pump in the voltage generation circuit according to the embodiment. 
         FIG. 7  is a circuit diagram illustrating an example of a configuration of the charge pump in the voltage generation circuit according to the embodiment. 
         FIG. 8  is a timing chart illustrating an example of voltages of a bit line, a word line, a source line, and a select gate line during an erase voltage applying operation in an erase operation using the semiconductor storage device according to the embodiment. 
         FIG. 9  is a diagram illustrating a combination operation of the voltage generation circuit during the erase voltage applying operation in the erase operation using the semiconductor storage device according to the embodiment. 
         FIG. 10  is a timing chart illustrating an example of voltages of the bit line, the word line, the source line, and the select gate line during a program operation in a write operation using the semiconductor storage device according to the embodiment. 
         FIG. 11  is a diagram illustrating a combination operation of the voltage generation circuit during the program operation in the write operation using the semiconductor storage device according to the embodiment. 
         FIG. 12  is a timing chart illustrating an example of voltages of the bit line, the word line, and the select gate line during a read operation using the semiconductor storage device according to the embodiment. 
         FIG. 13  is a diagram illustrating a combination operation of the voltage generation circuit during the read operation using the semiconductor storage device according to the embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments provide a voltage generation circuit having features that prevent an increase in the area of the voltage generation circuit and an increase in the amount of current consumed by the voltage generation circuit. 
     In general, according to one embodiment, a semiconductor storage device includes a memory cell array and a voltage generation circuit configured to supply voltages of different levels to the memory cell array, the voltage generation circuit including a first charge pump having a first characteristic and a second charge pump having a second characteristic that is substantially different from the first characteristic, each charge pump having an input end and an output end. The voltage generation circuit is controlled to electrically disconnect the output end of the first charge pump and the input end of the second charge pump in a first operation during which a first voltage is supplied to the memory cell array, and to electrically connect the output end of the first charge pump and the input end of the second charge pump in a second operation during which a second voltage higher than the first voltage is supplied to the memory cell array. 
     Hereinafter, embodiments will be described with reference to the accompanying drawings. In the following description, common reference numerals are given to elements having the same function and configuration. 
     1. Embodiment 
     Hereinafter, a semiconductor storage device according to an embodiment will be described. In the following, a NAND flash memory will be described as an example of the semiconductor storage device. 
     1.1 Configuration 
     A configuration of a semiconductor storage device according to an embodiment will be described. 
     1.1.1 Memory System 
     First, a configuration example of a memory system will be described with reference to  FIG. 1 .  FIG. 1  is a block diagram illustrating an example of a configuration of a host device and a memory system including a semiconductor storage device according to an embodiment. 
     The memory system  3  communicates with, for example, an external host device  4 . The memory system  3  stores data from the host device  4 , and also reads the data requested by the host device  4 . The memory system  3  is, for example, a solid state drive (SSD) or SD™ card. 
     The memory system  3  includes a semiconductor storage device  1  and a memory controller  2 . 
     The semiconductor storage device  1  has a plurality of memory cells, and stores data in a non-volatile manner. The semiconductor storage device  1  is connected to the memory controller  2  by a NAND bus. 
     The NAND bus performs transmission and reception via a separate signal line for each of signals/CE, CLE, ALE, /WE, /RE, RE, /WP, /RB, DQ&lt;7:0&gt;, DQS, and/DQ depending on a NAND interface standard. The signal/CE is a chip enable signal and enables the semiconductor storage device  1 . The signal CLE is a command latch enable signal, and notifies the semiconductor storage device  1  that the signal DQ&lt;7:0&gt; flowing into the semiconductor storage device  1  includes a command when the signal CLE is at the “H (High)” level. The signal ALE is an address latch enable signal, and notifies the semiconductor storage device  1  that the signal DQ&lt;7:0&gt; flowing into the semiconductor storage device  1  includes an address when the signal ALE is at the “H” level. The signal/WE is a write enable signal, and instructs the semiconductor storage device  1  to receive the signal DQ&lt;7:0&gt; supplied thereto as an input. For example, the signal/WE instructs the semiconductor storage device  1  to receive the signal DQ&lt;7:0&gt; as an input signal containing a command, address, or data at the rising edge of the signal/WE at a single data rate (SDR). Alternatively, the signal/WE may instruct the semiconductor storage device  1  to receive the signal DQ&lt;7:0&gt; as an input signal containing a command or address at the rising edge of the signal/WE at a double data rate (DDR). The signal/RE is a read enable signal, and instructs the semiconductor storage device  1  to output the signal DQ&lt;7:0&gt;. For example, the signal/RE instructs the semiconductor storage device  1  to output the signal DQ&lt;7:0&gt; as data at the falling edge of the signal/RE at a single data rate. Alternatively, the signal/RE may instruct the semiconductor storage device  1  to output the signal DQ&lt;7:0&gt; as data at the falling edge and rising edge of the signal/RE at a double data rate. The signal RE is a complementary signal of the signal/RE. The signal/WP is a write protect signal, and instructs the semiconductor storage device  1  to prohibit writing and erasing of data. The signal/RB is a ready busy signal, and indicates whether the semiconductor storage device  1  is in a ready state (a state capable of accepting an external command) or in a busy state (a state not accepting an external command). The signal DQ&lt;7:0&gt; is, for example, an 8-bit signal. The signal DQS is a data strobe signal, and is used to control the operation timing of the semiconductor storage device  1  related to the signal DQ&lt;7:0&gt;. For example, the signal DQS instructs the semiconductor storage device  1  to input the signal DQ&lt;7:0&gt; as data at the falling edge and rising edge of the signal DQS at a double data rate. Further, the signal DQS is generated based on the falling edge and rising edge of the signal/RE at a double data rate, and is output, along with the signal DQ&lt;7:0&gt; as data, from the semiconductor storage device  1 . The signal/DQS is a complementary signal of the signal DQS. 
     The signal DQ&lt;7:0&gt; is transmitted and received between the semiconductor storage device  1  and the memory controller  2 , and includes a command CMD, an address ADD, and data DAT. The command CMD includes, for example, a command for causing the semiconductor storage device  1  to execute an erase operation (erase command), a command for causing the semiconductor storage device  1  to execute a write operation (write command), and a command for causing the semiconductor storage device  1  to execute a read operation (read command). The data DAT is either read data or write data. 
     The memory controller  2  receives a command from the host device  4  and controls the semiconductor storage device  1  based on the received command. Specifically, the memory controller  2  writes, in the semiconductor storage device  1 , data that is commanded to be written based on the write command received from the host device  4 . Further, the memory controller  2  reads, from the semiconductor storage device  1 , data that is commanded to be read from the host device  4  based on the read command received from the host device  4 , and transmits the data to the host device  4 . 
     Examples of the host device  4  which uses the memory system  3  described above may include a digital camera, a personal computer, and a server in a data center. 
     1.1.2 Memory Controller 
     As illustrated in  FIG. 1 , the memory controller  2  includes a central processing unit  20 , a built-in memory  21 , a buffer memory  22 , a NAND interface circuit (NAND I/F)  23 , and a host interface circuit (host I/F)  24 . The memory controller  2  is configured as, for example, a system-on-a-chip (SoC). 
     The CPU  20  controls operations of the entire memory controller  2 . The CPU  20  issues, for example, commands to instruct the semiconductor storage device  1  to execute various operations such as a write operation, a read operation, and an erase operation. 
     The built-in memory  21  is, for example, a semiconductor memory such as a dynamic random access memory (DRAM), and is used as a work area of the CPU  20 . The built-in memory  21  stores, for example, firmware for managing the semiconductor storage device  1  and various management tables. 
     The buffer memory  22  temporarily stores, for example, write data received from the host device  4 , or read data received from the semiconductor storage device  1  by the memory controller  2 . 
     The NAND interface circuit  23  is connected to the semiconductor storage device  1  via the NAND bus and takes charge of communication with the semiconductor storage device  1 . The NAND interface circuit  23  transmits the command CMD, the address ADD, and the write data to the semiconductor storage device  1  in response to an instruction of the CPU  20 . Further, the NAND interface circuit  23  receives the read data from the semiconductor storage device  1 . 
     The host interface circuit  24  is connected to the host device  4  via a host bus and takes charge of communication between the memory controller  2  and the host device  4 . The host interface circuit  24  transmits, for example, the command and data received from the host device  4  to the CPU  20  and the buffer memory  22 , respectively. 
     1.1.3 Semiconductor Storage Device 
     Next, a configuration example of the semiconductor storage device  1  according to the embodiment will be described with reference to  FIG. 2 .  FIG. 2  is a block diagram illustrating an example of a configuration of the semiconductor storage device  1  according to the embodiment. 
     The semiconductor storage device  1  includes a memory cell array  10 , an input/output circuit  11 , a logic control circuit  12 , a register  13 , a sequencer  14 , a voltage generation circuit  15 , a row decoder  16 , a sense amplifier module  17 , and a source line driver  18 . The register  13  includes an address register  13 - 1  and a command register  13 - 2 . 
     The memory cell array  10  includes a plurality of blocks BLK 0  to BLKm (m being an integer of 1 or more). Each block BLK is a set of a plurality of memory cell transistors capable of storing data in a non-volatile manner, and is used, for example, as a unit of data erase. That is, the data stored in the memory cell transistors in the same block BLK are collectively erased. A detailed configuration of the memory cell array  10  will be described later. 
     The input/output circuit  11  transmits and receives the signal DQ&lt;7:0&gt; to and from the memory controller  2 . The input/output circuit  11  transmits the address ADD and the command CMD in the signal DQ&lt;7:0&gt; to the address register  13 - 1  and the command register  13 - 2 , respectively. Further, the input/output circuit  11  transmits and receives the data DAT to and from the sense amplifier module  17 . 
     The logic control circuit  12  receives, for example, the signals/CE, CLE, ALE, /WE, /RE, RE, /WP, DQS, and/DQS from the memory controller  2 , and controls the input/output circuit  11  based on the received signals. Further, the logic control circuit  12  generates the signal/RB and transmits the signal to the memory controller  2 . 
     The register  13  stores various signals. The address register  13 - 1  stores the address ADD transmitted from the input/output circuit  11 . The address register  13 - 1  transmits the stored address ADD to the row decoder  16  and the sense amplifier module  17 . The command register  13 - 2  stores the command CMD transmitted from the input/output circuit  11 . The command register  13 - 2  transmits the stored command CMD to the sequencer  14 . 
     The sequencer  14  receives the command CMD from the command register  13 - 2 , and controls the entire semiconductor storage device  1  according to a sequence based on the received command CMD. For example, the sequencer  14  instructs the voltage generation circuit  15  to generate a voltage used in a corresponding operation when receiving the erase command, the write command, and the read command, respectively. 
     The voltage generation circuit  15  generates a voltage used for the erase operation, the write operation, and the read operation based on an instruction from the sequencer  14 , and supplies the generated voltage to the row decoder  16 , the sense amplifier module  17 , and the source line driver  18 . 
     The row decoder  16  receives a block address in the address ADD from the address register  13 - 1 , and selects any of the blocks BLK 0  to BLKm (m being an integer of 1 or more) based on the block address. The row decoder  16  applies the voltage supplied from the voltage generation circuit  15  to, for example, the selected block BLK. 
     The sense amplifier module  17  receives a column address in the address ADD from the address register  13 - 1 , and transmits the data DAT between the memory controller  2  and the memory cell array  10  based on the column address. More specifically, during the write operation, the sense amplifier module  17  receives the write data from the input/output circuit  11  and transmits the received write data to the memory cell array  10 . Further, during the read operation, the sense amplifier module  17  senses a threshold voltage of the memory cell transistor which is a target of the read operation in the memory cell array  10  to generate read data, and transmits the generated read data to the input/output circuit  11 . 
     The source line driver  18  applies the voltage supplied from the voltage generation circuit  15  to the source line of the memory cell array  10 . 
     1.1.4 Memory Cell Array 
     Next, a configuration of the memory cell array  10  of the semiconductor storage device  1  according to the embodiment will be described with reference to  FIG. 3 .  FIG. 3  is an example of a circuit diagram illustrating a configuration of the memory cell array  10  of the semiconductor storage device  1  according to the embodiment. 
     The block BLK includes, for example, four string units SU (SU 0 , SU 1 , SU 2 , and SU 3 ). Each string unit SU includes a plurality of NAND strings NS. 
     Each of the NAND strings NS has, for example, eight memory cell transistors MT (MT 0  to MT 7 ) and select transistors ST 1  and ST 2 . In addition, the number of memory cell transistors MT provided in each NAND string NS is not limited to 8, and may be 16, 32, 48, 64, 96, or 128 without being limited thereto. That is, the number of word lines WL in the block BLK is not limited to 8, and may be 16, 32, 48, 64, 96, or 128 without being limited thereto. The memory cell transistor MT has a stacked gate including a control gate and a charge storage layer. Each memory cell transistor MT is connected in series between the select transistors ST 1  and ST 2 . 
     In a block BLK, gates of the select transistors ST 1  of the string units SU 0  to SU 3  are connected to select gate lines SGD 0  to SGD 3 , respectively. Further, a gate of the select transistor ST 2  of the string unit SU in the block BLK is commonly connected to a select gate line SGS. In addition, as for the select gate line SGS, similarly to the select gate line SGD, gates of the select transistors ST 2  of the string units SU 0  to SU 3  may be connected to select gate lines SGS 0  to SGS 3  (not illustrated), respectively. The control gates of the memory cell transistors MT 0  to MT 7  in the same block BLK are connected to word lines WL 0  to WL 7 , respectively. That is, the word line WL and the select gate line SGS are commonly connected across the string units SU 0  to SU 3  in the same block BLK. Meanwhile, the select gate line SGD is connected to one string unit SU in the same block BLK. 
     Further, among the NAND strings NS arranged in a matrix in the memory cell array  10 , the other end of the select transistor ST 1  of the NAND string NS in the same row is connected to one of n bit lines BL 0  to BL(n−1) (n being an integer of 2 or more). Further, the bit line BL is commonly connected to the NAND string NS in the same row across the plurality of blocks BLK. 
     Further, the other end of the select transistor ST 2  is connected to a source line SL. The source line SL is commonly connected to the plurality of NAND strings NS across the plurality of blocks BLK. 
     As described above, the erase operation is collectively performed on, for example, the memory cell transistors MT in the same block BLK. Meanwhile, the write operation and the read operation may be collectively performed on a plurality of memory cell transistors MT commonly connected to any word line WL in any string unit SU of any block BLK. A set of memory cell transistors MT sharing the word line WL in one string unit SU is referred to as, for example, a memory cell unit MU. That is, the memory cell unit MU is a set of memory cell transistors MT on which the write operation or the read operation is collectively executed. 
     The set of 1-bit data stored in each of a plurality of memory cell transistors MT in the memory cell unit MU is defined as a “page”. One memory cell transistor MT is capable of storing, for example, 2-bit data. This 2-bit data is referred to as a lower bit and an upper bit. In this case, two pages of data are stored in the memory cell unit MU, a set of lower bits stored in the respective memory cell transistors MT in the memory cell unit MU is referred to as a lower page, and a set of upper bits is referred to as an upper page. In addition, the memory cell transistor MT is not limited to 1 or 2 bits, and may be configured to be capable of storing data of 3 bits or more. 
       FIG. 4A  is a cross-sectional view of a partial region of the block BLK. In  FIG. 4A , the X direction is a direction in which the select gate line extends, the Y direction orthogonal to the X direction in the horizontal plane is a direction in which the bit line extends, and the Z direction is the stacking direction. 
     A p-type well region (p-well)  30  is provided in a semiconductor layer. A plurality of NAND strings NS is provided on the p-type well region  30 . That is, on the p-type well region  30 , a wiring layer  31  that functions as the select gate line SGS, eight wiring layers  32  that function as the word lines WL 0  to WL 7 , and a wiring layer  33  that functions as the select gate line SGD are stacked in this order with a plurality of insulating layers interposed therebetween. In order to avoid complicating the drawings, the illustration of the plurality of insulating layers provided among a plurality of the stacked wiring layers is omitted. 
     A memory hole  34  penetrates the wiring layers  31 ,  32 , and  33  and reaches the p-type well region  30 . A pillar-shaped semiconductor layer (semiconductor pillar)  35  is provided in the memory hole  34 . Agate insulating film  36 , a charge storage layer (in one example, an insulating film)  37 , and a block insulating film  38  are sequentially provided on the side surface of the semiconductor pillar  35 . These elements constitute the memory cell transistor MT and the select transistors ST 1  and ST 2 . The semiconductor pillar  35  functions as a current path of the NAND string NS, and is a region in which a channel of each transistor is formed. The upper end of the semiconductor pillar  35  is connected to a metal wiring layer  40  that functions as the bit line BL via a contact plug  39 . 
     An n + -type diffusion region  41  into which a high-concentration n-type impurity is introduced is provided in a surface region of the p-type well region  30 . A contact plug  42  is provided on the n + -type diffusion region  41 . The contact plug  42  is connected to a metal wiring layer  43  that functions as the source line SL. Further, a p + -type diffusion region  44  into which a high-concentration p-type impurity is introduced is provided in the surface region of the p-type well region  30 . A contact plug  45  is provided on the p + -type diffusion region  44 . The contact plug  45  is connected to a metal wiring layer  46  that functions as a well wiring CPWELL. The well wiring CPWELL is wiring for applying a voltage to the semiconductor pillar  35  via the p-type well region  30 . 
     The string unit SU includes a set of a plurality of NAND strings NS arranged in the X direction in which the components described above are arranged in multiple numbers in the depth direction (X direction) of the paper surface of  FIG. 4A . 
       FIG. 4B  is a cross-sectional view of a partial region of a block BLK having another structure. In the structure of  FIG. 4B , a wiring layer  47  that functions as the source line SL is provided instead the p-type well region (p-well)  30 , and the plurality of NAND strings NS is provided on the wiring layer  47 . The wiring layer  47  and the NAND strings NS are provided over a substrate  48 . A transistor for forming a peripheral circuit such as the row decoder  16 , the sense amplifier module  17 , and the source line driver  18  are formed on the substrate  48 . In other words, the transistor for forming the peripheral circuit is formed under the memory cell transistors MT and the select transistors ST 1  and ST 2 . 
     1.1.5 Configuration of Voltage Generation Circuit 
     Next, a configuration of the voltage generation circuit  15  of the semiconductor storage device  1  according to the embodiment will be described with reference to  FIG. 5 . FIG. is a circuit diagram illustrating an example of a configuration of the voltage generation circuit  15  according to the embodiment. In  FIG. 5 , an example of a configuration of the voltage generation circuit  15  is illustrated along with the sequencer  14 . 
     The voltage generation circuit  15  is configured to output a voltage VOUTL higher than a voltage VIN from a first output end and output a voltage VOUTH higher than the voltage VOUTL from a second output end according to operations such as writing, reading, and erasing of data when the voltage VIN is input. The voltage VIN is, for example, a voltage supplied from a voltage source (not illustrated) inside the semiconductor storage device  1 . 
     The voltage VOUTL includes, for example, voltages VREAD and VPASS. The voltage VREAD is a voltage applied to the word line WL connected to the memory cell transistor MT other than a read target in the read operation. The voltage VPASS is a voltage applied to the word line WL connected to the memory cell transistor MT other than a write target in the write operation. 
     The voltage VOUTH includes, for example, voltages VPGM and VERA. The voltage VPGM is a voltage applied to the word line WL connected to the memory cell transistor MT serving as a write target in the write operation. The voltage VERA is a voltage applied to the source line SL connected to the block BLK as an erase target in the erase operation. 
     In the following description, the word line WL connected to the memory cell transistor MT other than the read target and the word line WL connected to the memory cell transistor MT other than the write target are referred to as a non-selected word line WL. Further, the word line WL connected to the memory cell transistor MT as the read target and the word line WL connected to the memory cell transistor MT as the write target are referred to as a selected word line WL. 
     The voltage generation circuit  15  includes four charge pumps CP 1  (CP 1 - 1 , CP 1 - 2 , CP 1 - 3 , and CP 1 - 4 ), four charge pumps CP 2  (CP 2 - 1 , CP 2 - 2 , CP 2 - 3 , and CP 2 - 4 ), and transistors T 1  to T 19 . The charge pump CP 1  is a charge pump having a higher current supply capacity than the charge pump CP 2 . That is, when outputting a voltage, the charge pump CP 1  is configured to be able to output a larger amount of current than the charge pump CP 2 . In other words, the maximum value of current (maximum output possible current amount) output from an output end of the charge pump CP 1  is larger than the maximum output possible current amount of the charge pump CP 2 . Therefore, when outputting the same voltage, the charge pump CP 1  may raise the voltage of a connected wiring to the voltage output from the charge pump P 1  more quickly than the charge pump CP 2 . 
     Each of the charge pump CP 1  and the charge pump CP 2  includes an input end and an output end. The charge pump CP 1  boosts a voltage input to the input end of the charge pump CP 1  and outputs the voltage from the output end of the charge pump CP 1 . The charge pump CP 2  boosts a voltage input to the input end of the charge pump CP 2  and outputs the voltage from the output end of the charge pump CP 2 . 
     Each of the transistors T 1  to T 19  is, for example, an N-type transistor. 
     The voltage VIN is input to the input end of the charge pump CP 1 - 1 . The output end of the charge pump CP 1 - 1  is connected to a node N 1 . 
     A first end of the transistor T 1  is connected to the node N 1 . A second end of the transistor T 1  is connected to a node N 2 . 
     A first end of the transistor T 2  is connected to the node N 1 . A second end of the transistor T 2  is connected to a node N 3 . 
     The voltage VIN is input to a first end of the transistor T 3 . A second end of the transistor T 3  is connected to the node N 2 . 
     The input end of the charge pump CP 1 - 2  is connected to the node N 2 . The output end of the charge pump CP 1 - 2  is connected to the node N 3 . 
     The voltage VIN is input to the input end of the charge pump CP 1 - 3 . The output end of the charge pump CP 1 - 3  is connected to a node N 4 . 
     A first end of the transistor T 4  is connected to the node N 4 . A second end of the transistor T 4  is connected to a node N 5 . 
     A first end of the transistor T 5  is connected to the node N 4 . A second end of the transistor T 5  is connected to a node N 6 . 
     The voltage VIN is input to a first end of the transistor T 6 . A second end of the transistor T 6  is connected to the node N 5 . 
     The input end of the charge pump CP 1 - 4  is connected to the node N 5 . The output end of the charge pump CP 1 - 4  is connected to the node N 6 . 
     A first end of the transistor T 7  is connected to the node N 3 . A second end of the transistor T 7  is connected to the node N 6 . 
     A first end of the transistor T 8  is connected to the node N 6 . A second end of the transistor T 8  is configured to be connectable to, for example, the row decoder  16 . The voltage VOUTL is output from the second end of the transistor T 8 . 
     The voltage VIN is input to a first end of a transistor T 9 . A second end of the transistor T 9  is connected to a node N 7 . 
     The input end of the charge pump CP 2 - 1  is connected to the node N 7 . The output end of the charge pump CP 2 - 1  is connected to a node N 8 . 
     A first end of the transistor T 10  is connected to the node N 8 . A second end of the transistor T 10  is connected to a node N 9 . 
     A first end of the transistor T 11  is connected to the node N 8 . A second end of the transistor T 11  is connected to a node N 10 . The node N 10  is configured to be connectable to, for example, the row decoder  16 , the sense amplifier module  17 , and the source line driver  18 . The voltage VOUTH is output from the node N 10 . 
     The input end of the charge pump CP 2 - 2  is connected to the node N 9 . The output end of the charge pump CP 2 - 2  is connected to a node N 11 . 
     A first end of the transistor T 12  is connected to the node N 11 . A second end of the transistor T 12  is connected to a node N 12 . 
     A first end of the transistor T 13  is connected to the node N 11 . A second end of the transistor T 13  is connected to the node N 10 . 
     The input end of the charge pump CP 2 - 3  is connected to the node N 12 . The output end of the charge pump CP 2 - 3  is connected to a node N 13 . 
     A first end of the transistor T 14  is connected to the node N 13 . A second end of the transistor T 14  is connected to a node N 14 . 
     A first end of the transistor T 15  is connected to the node N 13 . A second end of the transistor T 15  is connected to the node N 10 . 
     The input end of the charge pump CP 2 - 4  is connected to the node N 14 . The output end of the charge pump CP 2 - 4  is connected to the node N 10 . 
     A first end of the transistor T 16  is connected to the node N 3 . A second end of the transistor T 16  is connected to the node N 7 . 
     A first end of the transistor T 17  is connected to the node N 3 . A second end of the transistor T 17  is connected to the node N 9 . 
     A first end of the transistor T 18  is connected to the node N 6 . A second end of the transistor T 18  is connected to the node N 12 . 
     A first end of the transistor T 19  is connected to the node N 6 . A second end of the transistor T 19  is connected to the node N 14 . 
     The sequencer  14  is configured to be able to independently control each of the transistors T 1  to T 19  according to the erase operation, the write operation, and the read operation. 
     That is, the voltage generation circuit  15  is configured to be able to output the voltages VOUTL and VOUTH depending on the erase operation, the write operation, and the read operation by changing the electrical connections of the charge pumps CP 1 - 1  to CP 1 - 4  and the charge pumps CP 2 - 1  to CP 2 - 4  under the control of the sequencer  14 . In addition, in the following description, an operation in which the sequencer  14  controls the transistors T 1  to T 19  in order to change the electrical connections of the charge pumps CP 1 - 1  to CP 1 - 4  and the charge pumps CP 2 - 1  to CP 2 - 4  is also referred to as a combination operation. The details of the combination operation will be described later. 
     1.1.6 Configuration of Charge Pump 
     Descriptions will be made on an example of a configuration of the charge pump CP 1  and the charge pump CP 2  in the voltage generation circuit  15 . 
     (Charge Pump CP 1 ) 
     First, a configuration of the charge pump CP 1  will be described with reference to  FIG. 6 .  FIG. 6  is a circuit diagram illustrating an example of a configuration of the charge pump CP 1  according to the embodiment. 
     The charge pump CP 1  includes, for example, transistors DT (DT 1  to DT 5 ) and capacitors DC (DC 1  to DC 4 ). 
     Each of the transistors DT 1  to DT 5  is, for example, an N-type transistor. 
     A voltage VIN 1  is input to a first end and a gate of the transistor DT 1 . A second end of the transistor DT 1  is connected to a node ND 1 . 
     A first end and a gate of the transistor DT 2  are connected to the node ND 1 . A second end of the transistor DT 2  is connected to a node ND 2 . 
     A first end and a gate of the transistor DT 3  are connected to the node ND 2 . A second end of the transistor DT 3  is connected to a node ND 3 . 
     A first end and a gate of the transistor DT 4  are connected to the node ND 3 . A second end of the transistor DT 4  is connected to a node ND 4 . 
     A first end and a gate of the transistor DT 5  are connected to the node ND 4 . A voltage VOUT 1  higher than the voltage VIN 1  is output from a second end of the transistor DT 5 . 
     A first end of the capacitor DC 1  is connected to the node ND 1 . A clock signal CLKD is input to a second end of the capacitor DC 1 . 
     A first end of the capacitor DC 2  is connected to the node ND 2 . A clock signal/CLKD is input to a second end of the capacitor DC 2 . 
     A first end of the capacitor DC 3  is connected to the node ND 3 . The clock signal CLKD is input to a second end of the capacitor DC 3 . 
     A first end of the capacitor DC 4  is connected to the node ND 4 . The clock signal/CLKD is input to a second end of the capacitor DC 4 . 
     The clock signal/CLKD is, for example, an inverted signal of the clock signal CLKD. While the clock signal CLKD is at the “H” level, the nodes ND 1  and ND 3  (i.e., the first end of the capacitor DC 1  and the first end of the capacitor DC 3 ) are boosted. While the clock signal/CLKD is at the “H” level, the nodes ND 2  and ND 4  (i.e., the first end of the capacitor DC 2  and the first end of the capacitor DC 4 ) are boosted. 
     In the charge pump CP 1  described above, a configuration including one transistor DTi (i being an integer of 1 or more and 4 or less) and one capacitor DCi is referred to as a stage Stg 1  (Stg 1 - 1  to Stg 1 - 4 ). In the stage Stg 1 - i , the voltage at the second end of the transistor DTi rises by the charging of the capacitor DCi. Thus, when i is an integer of 1 or more and 3 or less, the voltage at the first end of the transistor DT(i+1) in the next stage Stg 1 -(i+1) rises. Further, when i is 4, the voltage at the first end of the transistor DT 5  rises to a voltage (VOUT 1 +Vth) obtained by adding the voltage VOUT 1  and the threshold voltage Vth of the transistor DT 5 . In this way, the stage Stg 1  functions as a structural unit that boosts the voltage input to the charge pump CP 1 . 
     The voltage VOUT 1  dropped by the influence of the threshold voltage Vth of the transistor DT 5  is output from the second end of the transistor DT 5 . 
     In addition, the charge pump CP 1  according to the embodiment includes four stages Stg 1 - 1  to Stg 1 - 4 . It is noted that the number of stages Stg 1  in the charge pump CP 1  according to the embodiment is not limited to this. The number of stages Stg 1  may be 2, 3, or 5 or more, and may be changed according to a target value of the voltage to be boosted. In this case, for example, the clock signal CLKD is input to the second end of the capacitor DCia (ia being an odd number of 1 or more). Further, for example, the clock signal/CLKD is input to the second end of the capacitor DCib (ib being an even number of 2 or more). 
     In the charge pump CP 1  having the above configuration, a boost gain VOUT 1 /VIN 1  may vary according to the height of the voltage VIN 1  input to the charge pump CP 1 . For example, the boost gain VOUT 1 /VIN 1  of the charge pump CP 1  may be lowered as the voltage VIN 1  input to the charge pump CP 1  becomes higher. 
     More specifically, in each stage Stg 1  of the charge pump CP 1 , a voltage drop occurs by the threshold voltage of the transistor DTi. Thus, when the number of stages Stg 1  of the charge pump CP 1  is increased in order to raise the voltage VOUT 1 , the influence of the voltage drop by the threshold voltage of the transistor DTi becomes larger due to an increase in the number of transistors DTi. 
     Further, for example, as the voltage at the second end of the transistor DTi of the charge pump CP 1  becomes higher, the threshold voltage of each transistor DTi becomes higher by the substrate bias effect. Thus, when the voltage VOUT 1  is set to a high voltage, the influence of the voltage drop by the threshold voltage of each transistor DTi becomes larger. 
     From the above, on the high voltage side, the influence of the voltage drop by the threshold voltage of the transistor DTi becomes larger, which makes it difficult for the charge pump CP 1  to output, for example, a voltage higher than the voltage VOUTL. That is, for example, the boost gain VOUT 1 /VIN 1  of the charge pump CP 1  may be significantly lowered when the voltage VOUT 1  becomes higher than the voltage VOUTL, so that it becomes difficult to implement an efficient voltage generation. 
     (Charge Pump CP 2 ) 
     Next, a configuration of the charge pump CP 2  will be described with reference to  FIG. 7 .  FIG. 7  is a circuit diagram illustrating an example of a configuration of the charge pump CP 2  according to the embodiment. 
     The charge pump CP 2  includes, for example, transistors VtT (i.e., VtT 1  to VtT 6  and VtTa to VtTc) and capacitors VtC (i.e., VtC 1  to VtC 4  and VtCa). 
     Each of the transistors VtT 1  to VtT 6  and VtTa to VtTc is, for example, an N-type transistor. 
     A voltage VIN 2  is input to a first end of the transistor VtT 1 . A second end of the transistor VtT 1  is connected to a node NV 1 . Agate of the transistor VtT 1  is connected to a node NV 2 . 
     The voltage VIN 2  is input to a first end of the transistor VtT 2 . A second end of the transistor VtT 2  is connected to the node NV 2 . A gate of the transistor VtT 2  is connected to the node NV 1 . 
     The voltage VIN 2  is input to a first end and a gate of the transistor VtT 3 . A second end of the transistor VtT 3  is connected to the node NV 2 . 
     A first end of the capacitor VtC 1  is connected to the node NV 1 . A clock signal CLKV 1  is input to a second end of the capacitor VtC 1 . 
     A first end of the capacitor VtC 2  is connected to the node NV 2 . A clock signal CLKV 2  is input to a second end of the capacitor VtC 2 . 
     A first end of the transistor VtT 4  is connected to the node NV 1 . A second end of the transistor VtT 4  is connected to a node NV 3 . A gate of the transistor VtT 4  is connected to a node NV 4 . 
     A first end of the transistor VtT 5  is connected to the node NV 1 . A second end of the transistor VtT 5  is connected to the node NV 4 . A gate of the transistor VtT 5  is connected to the node NV 3 . 
     A first end and a gate of the transistor VtT 6  are connected to the node NV 1 . A second end of the transistor VtT 6  is connected to the node NV 4 . 
     A first end of the capacitor VtC 3  is connected to the node NV 3 . A clock signal CLKV 3  is input to a second end of the capacitor VtC 3 . 
     A first end of the capacitor VtC 4  is connected to the node NV 4 . A clock signal CLKV 4  is input to a second end of the capacitor VtC 4 . 
     A first end of the transistor VtTa is connected to the node NV 3 . A voltage VOUT 2  higher than the voltage VIN 2  is output from a second end of the transistor VtTa. A gate of the transistor VtTa is connected to a node NVa. 
     A first end of the transistor VtTb is connected to the node NV 3 . A second end of the transistor VtTb is connected to the node NVa. A gate of the transistor VtTb is connected to the second end of the transistor VtTa. 
     A first end and a gate of the transistor VtTc are connected to the node NV 3 . A second end of the transistor VtTc is connected to the node NVa. 
     A first end of the capacitor VtCa is connected to the node NVa. A clock signal CLKV 5  is input to a second end of the capacitor VtCa. 
     The clock signal CLKV 3  is, for example, an inverted signal of the clock signal CLKV 1 . The clock signal CLKV 4  is a signal that becomes the “H” level only for a period shorter than the clock cycle of the clock signal CLKV 1  for the period during which the clock signal CLKV 1  is at the “H” level. The clock signal CLKV 5  is a signal that becomes the “H” level only for a period shorter than the clock cycle of the clock signal CLKV 3  for the period during which the clock signal CLKV 3  is at the “H” level. The clock signal CLKV 2  is the same signal as, for example, the clock signal CLKV 5 . While the clock signal CLKV 1  is at the “H” level, the first end (node NV 1 ) of the capacitor VtC 1  is boosted. While the clock signal CLKV 2  is at the “H” level, the first end (node NV 2 ) of the capacitor VtC 2  is boosted. While the clock signal CLKV 3  is at the “H” level, the first end (node NV 3 ) of the capacitor VtC 3  is boosted. While the clock signal CLKV 4  is at the “H” level, the first end (node NV 4 ) of the capacitor VtC 4  is boosted. While the clock signal CLKV 5  is at the “H” level, the first end (node NVa) of the capacitor VtCa is boosted. 
     In the charge pump CP 2  described above, a configuration including three transistors VtT (3j−2), VtT (3j−1), and VtT(3j) (j being 1 or 2) and two capacitors VtC(2j−1) and VtC(2j) is referred to as a stage Stg 2  (Stg 2 −1 and Stg 2 −2). In the stage Stg 2 - j , the charge (voltage) at the first end of the boosted capacitor VtC(2j−1) is transmitted to a node NV(2j+1) via the transistor VtT (3j+1) of the next stage Stg 2 −(j+1) as the first end of the capacitor VtC (2 (j+1)) of the next stage Stg 2 −(j+1) is boosted. Further, in the stage Stg 2 - 1 , the voltage VIN 2  input to the first end of each of the transistors VtT 1 , VtT 2 , and VtT 3  is transmitted to the node NV 1  via the transistor VtT 1  as the first end of the capacitor VtC 2  is boosted. Further, in the stage Stg 2 - 2 , the charge (voltage VOUT 2 ) at the boosted first end of the capacitor VtC 3  is output from the charge pump CP 2  via the transistor VtTa as the first end of the capacitor VtCa is boosted. Here, unlike the charge pump CP 1 , the influence of the voltage drop by the threshold voltage of each of the transistors VtT(3j+1), VtT 1 , and VtTa may be substantially ignored. In this way, the stage Stg 2  functions as the structural unit that boosts the voltage input to the charge pump CP 2 . 
     The voltage VOUT 2  at the first end of the transistor VtTa boosted as described above is output from the second end of the transistor VtTa as the first end of the capacitor VtCa is boosted. 
     In addition, the charge pump CP 2  according to the embodiment includes two stages Stg 2 . It is noted that the number of stages Stg 2  in the charge pump CP 2  according to the embodiment is not limited to this. The number of stages Stg 2  may be 3 or more, and may be changed according to, for example, a target value of the voltage to be boosted. In this case, for example, the clock signal CLKV 1  is input to the second end of the capacitor VtC(2ja−1) (ja being an odd number of 1 or more). Further, for example, the clock signal CLKV 2  is input to the second end of the capacitor VtC(2ja). Further, for example, the clock signal CLKV 3  is input to the second end of the capacitor VtC (2jb−1) (jb being an even number of 2 or more). Further, for example, the clock signal CLKV 4  is input to the second end of the capacitor VtC(2jb). 
     Unlike the charge pump CP 1 , as described above, the charge pump CP 2  having the above configuration may ignore the influence of the voltage drop by the threshold voltage of the transistor. Thus, for example, even when outputting the voltage VOUT 2  higher than the voltage VOUTL, the charge pump CP 2  may efficiently boost the voltage to output the voltage VOUT 2  higher than the voltage VOUT 1  of the charge pump CP 1 . For example, the boost gain VOUT 2 /VIN 2  of the charge pump CP 2  when the height of the voltage VOUT 2  output from the charge pump CP 2  is higher than the voltage VOUTL is larger than the boost gain VOUT 1 /VIN 1  of the charge pump CP 1  when the height of the voltage VOUT 1  output from the charge pump CP 1  is higher than the voltage VOUTL. 
     As described above, the charge pump CP 1  has a high current supply capacity at a low voltage due to a simple configuration of the charge pump CP 1 , but has a small boost gain at a high voltage due to the influence of the voltage drop by the threshold voltage of the transistor CT of each stage Stg 1 . Meanwhile, the charge pump CP 2  has a low current supply capacity by having a more complicated circuit configuration than the charge pump CP 1 , but has a large boost gain even at a high voltage since the influence of the voltage drop by the threshold voltage of the transistor may be significantly ignored. The voltage generation circuit  15  may efficiently generate voltages required for various operations by combining charge pumps of two different types and having different characteristics, namely charge pump CP 1  and charge pump CP 2 , in this way. 
     1.2 Operation 
     Next, an operation using the semiconductor storage device  1  according to the present embodiment will be described. In the following, examples of each of the erase operation, the write operation, and the read operation will be described. 
     In addition, in the following description, the word line WL and the string unit SU corresponding to the memory cell transistor MT which is a target of the write operation or the read operation are referred to as a selected word line WL and a selected string unit SU, respectively. Further, the word line WL and the string unit SU corresponding to the memory cell transistor MT which is not the target of the write operation or the read operation are referred to as a non-selected word line WL and a non-selected string unit SU, respectively. 
     Here, when the number of word lines WL in the block BLK is n (e.g., 8, 16, 32, 48, 64, 96, or 128), the number of selected word lines is 1 and the number of non-selected word lines is n−1 in the write operation or the read operation. 
     1.2.1 Erase Operation 
     First, an example of the erase operation according to the present embodiment will be described. The erase operation includes an operation of applying a voltage to the source line SL and the bit line BL (hereinafter, also referred to as an erase voltage applying operation) in order to lower the threshold voltage of the memory cell transistor MT, and an erase verification operation of determining whether the threshold voltage of the memory cell transistor MT becomes lower than a target voltage by the erase voltage applying operation. The semiconductor storage device  1  sets the threshold voltage of the memory cell transistor MT to be less than the target voltage by repeating a combination of the erase voltage applying operation and the erase verification operation. 
     Further, in the following description, the description related to the erase verification operation will be omitted, and an example of a case where the erase voltage applying operation is executed once and the voltage supplied by the voltage generation circuit  15  during the erase voltage applying operation will be mainly explained. 
     1.2.1.1 Voltage of Each Wiring During Erase Voltage Applying Operation 
     With reference to  FIG. 8 , descriptions will be made on an example of the erase voltage applying operation according to the present embodiment.  FIG. 8  is a timing chart illustrating an example of the voltage of each wiring during the erase voltage applying operation. 
     At time t 11 , the source line driver  18  applies a voltage VERA to the source line SL. 
     Further, the sense amplifier module  17  applies the voltage VERA to the bit line BL in the block BLK which is a target of the erase operation. 
     Further, the row decoder  16  applies a voltage VWLE to the word line WL in the block BLK which is the target of the erase operation. The voltage VWLE is, for example, a voltage equal to or higher than a voltage VSS and lower than the voltage VERA. However, the voltage VWLE is not limited to this, and may be a voltage lower than the voltage VSS. 
     At time t 12 , the row decoder  16  applies a voltage VSGE to the select gate lines SGS and SGD of the block BLK which is the target of the erase operation. The voltage VSGE is a voltage higher than the voltage VWLE and lower than the voltage VERA. 
     By this operation, electron-hole pairs are generated by gate-induced drain leakage (GIDL) in each of the select transistors ST 1  and ST 2  in the block BLK which is the target of the erase operation. 
     More specifically, on the select transistor ST 1  side of the NAND string NS, a GIDL current (hereinafter, also referred to as a BL side GIDL current) flows from the bit line BL toward the select transistor ST 1  by the voltage VERA applied to the bit line BL. Further, on the select transistor ST 2  side of the NAND string NS, a GIDL current (hereinafter, also referred to as an SL side GIDL current) flows from the source line SL toward the select transistor ST 2 . Due to the GIDL current, electrons of the generated electron-hole pairs move to the source line SL and the bit line BL out of a channel of the NAND string NS, and holes move into the channel of the NAND string NS. 
     The semiconductor storage device  1  raises the voltage in the channel by the holes generated in the channel of the NAND string NS as described above, and injects the holes into the charge storage layer. The semiconductor storage device  1  eliminate the electrons trapped in the charge storage layer of the memory cell transistor MT of the NAND string by combining the injected holes with any electrons previously injected into the charge storage layer of the memory cell transistor MT by the write operation. Thus, the threshold voltage of the memory cell transistor MT of the NAND string is lowered. 
     At time t 13 , the row decoder  16  applies the voltage VSS to the word line WL and the select gate lines SGS and SGD. 
     Further, the sense amplifier module  17  applies the voltage VSS to the bit line BL. 
     Further, the source line driver  18  applies the voltage VSS to the source line SL. 
     With the above, the erase voltage applying operation is terminated. 
     In addition, descriptions have been made on a case where the voltage VSGE is applied to the select gate lines SGS and SGD at time t 12 . It is noted that the present disclosure is not limited to this. The voltages applied to the respective select gate lines SGS and SGD may be voltages that allow the GIDL current to flow, and may be different voltages. 
     1.2.1.2 Combination Operation in Erase Voltage Applying Operation 
     With reference to  FIG. 9 , descriptions will be made on the generation of the voltage VERA applied to the source line SL and the bit line BL during the erase voltage applying operation.  FIG. 9  is a diagram illustrating a combination operation of the voltage generation circuit  15  during the erase voltage applying operation in the erase operation using the semiconductor storage device  1  according to the embodiment. 
     In addition, in the following description, the voltages output from the charge pumps CP 1 - 1 , CP 1 - 2 , CP 1 - 3 , and CP 1 - 4 , respectively, are referred to as voltages VOUT 1 - 1 , VOUT 1 - 2 , VOUT 1 - 3 , and VOUT 1 - 4 , respectively. Further, the voltages output from the charge pumps CP 2 - 1 , CP 2 - 2 , CP 2 - 3 , and CP 2 - 4 , respectively, are referred to as voltages VOUT 2 - 1 , VOUT 2 - 2 , VOUT 2 - 3 , and VOUT 2 - 4 , respectively. 
     In the combination operation during the erase voltage applying operation, the sequencer  14  turns on the transistors T 1 , T 4 , T 11 , T 13 , T 15 , T 16 , T 17 , T 18 , and T 19 , and turns off the transistors T 2 , T 3 , T 5 , T 6 , T 7 , T 8 , T 9 , T 10 , T 12 , and T 14 . In  FIG. 9 , the transistor that is turned on is marked with the symbol “O”, and the transistor that is turned off is marked with the symbol “X”. 
     By the above combination operation, the charge pumps CP 1 - 1  and CP 1 - 2  are connected in series in this order in the voltage generation circuit  15 . The charge pumps CP 2 - 1  and CP 2 - 2  are connected in parallel to the output end of the charge pump CP 1 - 2 . 
     Further, the charge pumps CP 1 - 3  and CP 1 - 4  are connected in series in this order. The charge pumps CP 2 - 3  and CP 2 - 4  are connected in parallel to the output end of the charge pump CP 1 - 4 . 
     The output end of each of the charge pumps CP 2 - 1 , CP 2 - 2 , CP 2 - 3 , and CP 2 - 4  is commonly connected. 
     The voltage VIN is input to the input end of the charge pump CP 1 - 1 . The charge pump CP 1 - 1  boosts the input voltage VIN to a voltage VOUT 1 - 1  and outputs the boosted input voltage to the input end of the charge pump CP 1 - 2 . The charge pump CP 1 - 2  boosts the input voltage VOUT 1 - 1  to a voltage VOUT 1 - 2  and outputs the boosted input voltage to the input end of each of the charge pumps CP 2 - 1  and CP 2 - 2 . The charge pumps CP 2 - 1  and CP 2 - 2  boost the voltage VOUT 1 - 2  input to the input end of each of the charge pumps CP 2 - 1  and CP 2 - 2  to voltages VOUT 2 - 1  and VOUT 2 - 2 , respectively, and output the boosted voltages to the node N 10 . 
     Further, the voltage VIN is input to the input end of the charge pump CP 1 - 3 . The charge pump CP 1 - 3  boosts the input voltage VIN to a voltage VOUT 1 - 3  and outputs the boosted input voltage to the input end of the charge pump CP 1 - 4 . The charge pump CP 1 - 4  boosts the input voltage VOUT 1 - 3  to a voltage VOUT 1 - 4  and outputs the boosted input voltage to the input end of each of the charge pumps CP 2 - 3  and CP 2 - 4 . The charge pumps CP 2 - 3  and CP 2 - 4  boost the voltage VOUT 1 - 4  input to the input end of each of the charge pumps CP 2 - 3  and CP 2 - 4  to voltages VOUT 2 - 3  and VOUT 2 - 4 , respectively, and output the boosted voltage to the node N 10 . The voltage VERA (VOUTH) is output from the node N 10  to the sense amplifier module  17  and the source line driver  18  based on the voltages VOUT 2 - 1 , VOUT 2 - 2 , VOUT 2 - 3 , and VOUT 2 - 4 . 
     With the above, the voltage VERA is supplied to the source line SL and the bit line BL in the block BLK which is the target of the erase operation under the control of the sequencer  14 . 
     1.2.2 Write Operation 
     Next, brief descriptions will be made on an example of the write operation according to the present embodiment. 
     The write operation includes a program operation and a write verification operation. The program operation is an operation of raising the threshold voltage by injecting electrons into the charge storage layer (or maintaining the threshold voltage by prohibiting the injection). The write verification operation is an operation of reading data after the program operation and determining whether the threshold voltage of the memory cell transistor MT has reached a target voltage. The semiconductor storage device  1  raises the threshold voltage of the memory cell transistor MT to the target voltage by repeating a combination of the program operation and the write verification operation. 
     In the following description, the description related to the write verification operation will be omitted, and an example of a case where the program operation is executed once and the voltage supplied by the voltage generation circuit  15  during the program operation will be mainly explained. 
     1.2.2.1 Program Operation 
     The program operation of the present embodiment will be described with reference to  FIG. 10 .  FIG. 10  is a timing chart illustrating an example of the voltage of each wiring during the program operation using the semiconductor storage device according to the embodiment. 
     Hereinafter, an operation of raising the threshold voltage of the memory cell transistor MT is referred to as “0” program operation, and an operation of maintaining the threshold voltage of the memory cell transistor MT is referred to as “1” program operation. 
     As to the voltage of the bit line BL illustrated in the upper part of  FIG. 10 , the bit line BL (“1”) corresponding to the memory cell transistor MT which is a target of the “1” program operation. On the other hand, the bit line BL (“0”) corresponding to the memory cell transistor MT which is a target of the “0” program operation. 
     At time t 21 , the sense amplifier module  17  applies a voltage VBL to the bit line BL (“1”) to perform a BL precharge. Meanwhile, the voltage VSS is applied to the bit line BL (“0”). 
     Further, the row decoder  16  selects any one block BLK from a plurality of blocks BLK, and also selects anyone string unit SU from a plurality of string units SU. Then, the row decoder  16  applies a voltage VSD 1  to the select gate line SGD (i.e., the selected SGD in  FIG. 10 ) in the selected string unit SU. Assuming that the threshold voltage of the select transistor ST 1  is Vtsg, the voltage VSD 1  is a voltage that is equal to or higher than “VBL+Vtsg” and that turns on the select transistor ST 1 . Meanwhile, the row decoder  16  applies the voltage VSS to the select gate line SGD (non-selected SGD in  FIG. 10 ) of the non-selected string unit SU and turns off the corresponding select transistor ST 1 . Further, the row decoder  16  applies the voltage VSS to the select gate line SGS and turns off the select transistor ST 2 . 
     Further, the source line driver  18  applies a voltage VSL (&gt;VSS) to the source line SL. 
     At time t 22 , the row decoder  16  lowers the voltage applied to the select gate line SGD of the selected string unit SU from the voltage VSD 1  to a voltage VSD 2 . For example, the voltage VSD 2  is a voltage that is lower than the voltage VSD 1 , and is equal to or lower than the voltage VBL and turns on the select transistor ST 1  in which the voltage VSS is applied to the bit line BL, but turns off the select transistor ST 1  in which the voltage VBL is applied to the bit line BL. Thus, the channel of the NAND string NS corresponding to the bit line BL (“1”) is in the floating state electrically isolated from the bit line BL and the source line SL. 
     By changing the voltage of the bit line BL as described above, the “0” program operation and the “1” program operation may be set for each bit line BL in the same program operation. 
     At time t 23 , the row decoder  16  selects any one word line WL in the selected block BLK, applies a voltage VPGM to the selected word line WL (selected WL in  FIG. 10 ) while also applying a voltage VPASS to the non-selected word line WL (non-selected WL in  FIG. 10 ). 
     In the NAND string NS corresponding to the bit line BL (“0”), the select transistor ST 1  is turned on. Then, the channel voltage of the memory cell transistor MT connected to the selected word line WL becomes VSS. Accordingly, the voltage difference (VPGM-VSS) between the control gate and the channel becomes larger, and as a result, electrons are injected into the charge storage layer, so that the threshold voltage of the memory cell transistor MT is raised. 
     In the NAND string NS corresponding to the bit line BL (“1”), the select transistor ST 1  is in the cutoff state. Therefore, the channel of the memory cell transistor MT connected to the selected word line WL is in the floating state. Thus, the channel voltage rises by the capacitive coupling of the channel and the word line WL. Accordingly, the voltage difference between the control gate and the channel becomes smaller, and as a result, electrons are hardly injected into the charge storage layer, so that the threshold voltage of the memory cell transistor MT is maintained. 
     At time t 24 , the row decoder  16  applies the voltage VSS to the selected word line WL and the non-selected word line WL. Thus, the injection of charges into the charge storage layer is terminated. 
     At time t 25 , the row decoder  16  applies the voltage VSS to the select gate line SGD. 
     Further, the sense amplifier module  17  applies the voltage VSS to the bit line BL. 
     Further, the source line driver  18  applies the voltage VSS to the source line SL. 
     With the above, the program operation is terminated. 
     In addition,  FIG. 10  is merely an example of the timing chart of the program operation according to the present embodiment, and a magnitude relationship of the voltages applied to each of the bit line BL, the word line WL, the source line SL, and the select gate lines SGS and SGD does not necessarily correspond to a magnitude relationship of the voltages illustrated in  FIG. 10 . For example, in  FIG. 10 , the voltages VBL and VSD 2  are illustrated as equivalent voltages, but the voltages VBL and VSD 2  may be different from each other. 
     1.2.2.2 Combinant Operation in Program Operation 
     The generation of the voltages VPASS and VPGM applied to the word line WL during the program operation will be described with reference to  FIG. 11 .  FIG. 11  is a diagram illustrating a combination operation of the voltage generation circuit  15  during the program operation in the write operation using the semiconductor storage device  1  according to the embodiment. 
     In the combination operation during the program operation, the sequencer  14  turns on the transistors T 2 , T 3 , T 5 , T 6 , T 7 , T 8 , T 9 , T 10 , T 12 , and T 14 , and turns off the transistors T 1 , T 4 , T 11 , T 13 , T 15 , T 16 , T 17 , T 18 , and T 19 . In  FIG. 11 , the transistor that is turned on is marked with the symbol “O”, and the transistor that is turned off is marked with the symbol “X”. 
     By the above combination operation, the charge pumps CP 1 - 1 , CP 1 - 2 , CP 1 - 3 , and CP 1 - 4  are connected in parallel in the voltage generation circuit  15 . The output end of each of the charge pumps CP 1 - 1 , CP 1 - 2 , CP 1 - 3 , and CP 1 - 4  is commonly connected. 
     Further, in the voltage generation circuit  15 , the charge pumps CP 2 - 1 , CP 2 - 2 , CP 2 - 3 , and CP 2 - 4  are connected in series in this order. 
     The voltage VIN is input to the input end of each of the charge pumps CP 1 - 1  to CP 1 - 4 . The charge pumps CP 1 - 1  to CP 1 - 4  boost the input voltage VIN to voltages VOUT 1 - 1  to VOUT 1 - 4 , respectively, and output the boosted input voltage to the first end of the transistor T 8 . The voltage VPASS (VOUTL) is supplied from the second end of the transistor T 8  to the row decoder  16  based on the voltages VOUT 1 - 1  to VOUT 1 - 4 . 
     Further, the voltage VIN is input to the input end of the charge pump CP 2 - 1  via the transistor T 9 . The charge pump CP 2 - 1  boosts the input voltage VIN to a voltage VOUT 2 - 1  and outputs the boosted input voltage to the input end of the charge pump CP 2 - 2 . The charge pump CP 2 - 2  boosts the input voltage VOUT 2 - 1  to a voltage VOUT 2 - 2  and outputs the boosted input voltage to the input end of the charge pump CP 2 - 3 . The charge pump CP 2 - 3  boosts the input voltage VOUT 2 - 2  to a voltage VOUT 2 - 3  and outputs the boosted input voltage to the input end of the charge pump CP 2 - 4 . The charge pump CP 2 - 4  boosts the input voltage VOUT 2 - 3  to a voltage VPGM(VOUTH) and outputs the boosted input voltage to the row decoder  16 . 
     With the above, under the control of the sequencer  14 , the voltage VPGM is supplied to the selected word line WL, and the voltage VPASS is supplied to the non-selected word line WL. 
     1.2.3 Read Operation 
     First, an example of the read operation according to the present embodiment will be described. In addition, in the following description, in order to simplify the description, a case where 1-bit data is read in one read operation will be described. 
     1.2.3.1 Voltage of Each Wiring during Read Operation 
     The voltage of each wiring during the read operation will be described with reference to  FIG. 12 .  FIG. 12  is a timing chart illustrating an example of the voltage of each wiring during the read operation. 
     At time t 31 , the row decoder  16  applies a voltage VSGD to the select gate line SGD (i.e., the selected SGD in  FIG. 12 ) corresponding to the selected string unit SU. Further, the row decoder  16  applies the voltage VSS to the select gate line SGD (i.e., the non-selected SGD in  FIG. 12 ) corresponding to the non-selected string unit SU. Further, the row decoder  16  applies, for example, a voltage equivalent to the voltage VSGD to the select gate line SGS. The voltage VSGD is a voltage that is applied to the select gate lines SGD and SGS during the read operation and turns on the corresponding select transistors ST 1  and ST 2 . Thus, the select transistor ST 1  and the select transistor ST 2  of the selected string unit SU are turned on, and the select transistor ST 1  of the non-selected string unit SU is turned off. 
     Further, the row decoder  16  applies the voltage VREAD to the non-selected word line WL (i.e., the non-selected WL in  FIG. 12 ) and applies a voltage VCGRV to the selected word line WL (i.e., the selected WL in  FIG. 12 ). The voltage VREAD is a voltage higher than the voltage VCGRV (VREAD&gt;VCGRV). The voltage VREAD is a voltage that is applied to the non-selected word line WL during the read operation and turns on the corresponding memory cell transistor MT. The voltage VCGRV is a voltage depending on the threshold voltage of the memory cell transistor MT which is a target of the read operation. More specifically, for example, when the threshold voltage of the memory cell transistor MT which is the target of the read operation is higher than the voltage VCGRV, the memory cell transistor MT is turned off, and when the threshold voltage is equal to or less than the voltage VCGRV, the memory cell transistor MT is turned on. 
     At time t 32 , the sense amplifier module  17  sets the voltage of the bit line BL to the voltage VBL. The voltage VBL is, for example, a voltage lower than the voltage VCGRV (VCGRV&gt;VBL). 
     At time t 33 , the row decoder  16  applies the voltage VSS to the selected word line WL and the non-selected word line WL, and the select gate line SGD and the select gate line SGS corresponding to the selected string unit SU and the non-selected string unit SU. 
     Further, the sense amplifier module  17  applies the voltage VSS to the bit line BL. 
     With the above operation, data is read from the memory cell transistor MT corresponding to the selected word line WL of the selected string unit SU. 
     In addition,  FIG. 12  is merely an example of the timing chart of the read operation according to the present embodiment, and a magnitude relationship of the voltages applied to each of the bit line BL, the word line WL, the source line SL, and the select gate line SGD does not necessarily correspond to a magnitude relationship of the voltages illustrated in  FIG. 12 . For example, in  FIG. 12 , the voltages VREAD and VSGD are illustrated as equivalent voltages. Alternatively, the voltages VREAD and VSGD may be different from each other. 
     1.2.3.2 Generation of Voltage Applied to Word Line During Read Operation 
     The generation of the voltage VREAD applied to the word line WL during the read operation will be described with reference to  FIG. 13 .  FIG. 13  is a diagram illustrating the generation of the voltage VREAD by the voltage generation circuit  15  during the read operation using the semiconductor storage device  1  according to the embodiment. 
     In the combination operation during the read operation, the sequencer  14  turns on the transistors T 2 , T 3 , T 5 , T 6 , T 7 , and T 8 , and turns off the transistors T 1 , T 4 , and T 9  to T 19 . In  FIG. 13 , the transistor that is turned on is marked with the symbol “O”, and the transistor that is turned off is marked with the symbol “X”. 
     By the above combination operation, the charge pumps CP 1 - 1 , CP 1 - 2 , CP 1 - 3 , and CP 1 - 4  are connected in parallel in the voltage generation circuit  15 . The output end of each of the charge pumps CP 1 - 1 , CP 1 - 2 , CP 1 - 3 , and CP 1 - 4  is commonly connected. 
     Further, the charge pumps CP 2 - 1  to CP 2 - 4  are electrically isolated from the charge pump CP 1  and a voltage source that supplies the voltage VIN. 
     The voltage VIN is input to the input end of each of the charge pumps CP 1 - 1  to CP 1 - 4 . Each of the charge pumps CP 1 - 1  to CP 1 - 4  boosts the input voltage VIN to voltages VOUT 1 - 1  to VOUT 1 - 4 , respectively, and output the boosted input voltage to the first end of the transistor T 8 . The voltage VREAD (VOUTL) is output from the second end of the transistor T 8  to the row decoder  16  based on the voltages VOUT 1 - 1  to VOUT 1 - 4 . 
     In addition, the voltage VOUTH is not output from the node N 10  during the read operation. 
     As described above, the voltage VREAD is supplied to the non-selected word line WL under the control of the sequencer  14 . 
     1.3 Effects 
     According to the present embodiment, it is possible to prevent an increase in the area of the voltage generation circuit  15  and an increase in the amount of current consumed by the voltage generation circuit  15 . The effects of the embodiment will be described below. 
     The voltage generation circuit  15  is configured to electrically disconnect between the charge pump CP 1  and the charge pump CP 2  during the read operation and the write operation. Specifically, the charge pump CP 1  is mainly used to generate the voltages VREAD and VPASS supplied to n−1 non-selected word lines WL among n (e.g., 8, 16, 32, 48, 64, 96, or 128) word lines in the block BLK. Further, the charge pump CP 2  is mainly used to generate the voltage VPGM supplied to one selected word line WL. This enables efficient voltage generation. 
     In addition, the charge pump CP 1  has a lower boost gain in a high voltage region than the charge pump CP 2  by the voltage drop due to the threshold voltage of each transistor CT, but has a high current supply capacity in a low voltage region. Therefore, it is advantageous to generate a voltage that is a relatively low voltage but has a large capacitive load of a charge target, such as the voltages VREAD and VPASS. Meanwhile, since the charge pump CP 2  has a more complicated configuration than the charge pump CP 1  and thus, has a lower current supply capacity than the charge pump CP 1 . However, the influence of the voltage drop due to the threshold voltage of each transistor VtT may be substantially ignored, the charge pump CP 2  has a higher boost gain than the charge pump CP 1  in a high voltage region. Therefore, it is advantageous to generate a voltage that is a relatively high voltage but has a small capacitive load of a charge target, such as the voltage VPGM. 
     According to the present embodiment, the voltage generation circuit  15  uses the charge pump CP 1  and the charge pump CP 2  properly in the read operation and the write operation in order to generate a voltage suitable for each characteristic. Thus, it is possible to prevent an increase in the amount of current consumed by the voltage generation circuit  15  and the circuit area. 
     Further, the voltage generation circuit  15  is configured to electrically connect between the output end of the charge pump CP 1  and the input end of the charge pump CP 2  during the erase operation. Specifically, the voltage generation circuit  15  generates the voltage VERA by using the charge pump CP 1  for boosting in a low voltage region and the charge pump CP 2  for boosting in a high voltage region during the erase operation while also combining the charge pumps. Thus, by connecting the charge pump CP 1  and the charge pump CP 2  in series, it is possible to obtain a high current supply capacity of the charge pump CP 1  in a high voltage region (when generating the voltage VERA). Therefore, it is possible to supply the voltage VERA which is a high voltage and has a large capacitive load of a charge target. Further, the charge pump CP 1  and the charge pump CP 2  used for the write operation and the read operation may be diverted. Therefore, it is possible to avoid a decrease in boost gain that may occur when the charge pump CP 1  is used for boosting in a high voltage region. Accordingly, it is possible to prevent an increase in the amount of current consumed by the voltage generation circuit  15  and the circuit area. 
     Further, the voltage generation circuit  15  commonly connects the input end of each of the charge pumps CP 2 - 1  and CP 2 - 2  to the output end of the charge pump CP 1 - 2  during the erase operation. Further, the voltage generation circuit  15  commonly connects the input end of each of the charge pumps CP 2 - 3  and CP 2 - 4  to the output end of the charge pump CP 1 - 4  during the erase operation. In this way, by connecting the input ends of the two charge pumps CP 2  in parallel to the output end of one charge pump CP 1 , it is possible to obtain a current supply capacity higher than that when one charge pump CP 2  is connected to the output end of the charge pump CP 1  (it is possible to supplement the low current supply capacity of the charge pump CP 2 ). 
     2. Others 
     In addition, the configurations of the charge pump CP 1  and the charge pump CP 2  are not limited to the example described in the embodiment. For example, for the charge pump CP 1 , a charge pump having a higher current supply capacity than that of the charge pump CP 2  may be used. Further, for the charge pump CP 2 , for example, a charge pump having a boost gain that does not change significantly when outputting a voltage equal to or lower than the voltage VERA may be used. 
     More specifically, the charge pump CP 1  may include a transistor having a three-layered structure including, for example, a P-type substrate, an N-type layer embedded in the substrate, and a P-type well formed in the embedded layer. 
     When the transistor having a three-layered structure is used for boosting in a high voltage region, the thickness of the substrate may be increased, for example, in order to prevent the generation of leakage current flowing from the N-type embedded layer to the outside of the substrate. However, an increase in the thickness of the substrate is not desirable because of a limitation by the semiconductor storage device  1  accompanied by an improvement in storage capacity. 
     According to the present embodiment, the charge pump CP 1  may be used for boosting in a low voltage region in the erase operation. Therefore, the generation of leakage current may be substantially ignored, and an increase in the thickness of the substrate may be prevented. Further, since the transistor having the three-layered structure reduces the influence of the voltage of the substrate on the voltage drop due to the threshold voltage of the transistor, a decrease in the boost gain of the charge pump CP 1  is prevented. 
     Further, the charge pump CP 1  and the charge pump CP 2  in the embodiment may be provided respectively in physically different regions within the voltage generation circuit  15 . 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the disclosure. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the disclosure. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the disclosure.