JP5092006B2 - Nonvolatile semiconductor memory device and control method thereof - Google Patents

Description

  The present invention relates to a nonvolatile semiconductor memory device and a control method thereof.

  Non-volatile semiconductor memory devices (non-volatile memories) are used in a wide range of fields such as computers, communications, measuring devices, automatic control devices, and daily equipment used in the vicinity of individuals as large-capacity and small-sized information recording media. Note that the application software used in the above-described computer or the like is preferably capable of bug correction and upgrade, and therefore a non-volatile memory capable of rewriting data is used. Non-volatile memory includes, for example, flash memory and RRAM (Resistive Random Access Memory).

The configuration and operation of each of the flash memory and RRAM will be described.
First, the flash memory will be described. As the flash memory, for example, there is an ETOX (registered trademark of Intel Corporation) type flash memory.

Here, FIG. 8 shows a schematic configuration example of a memory cell array A _T of ETOX-type flash memory, memory cell array A _T is configured to include a plurality of memory cells (ETOX cells). Memory cell array _{A T} shown in FIG. 8, m × n pieces of ETOX cell _{M T} are arranged in a matrix, the gate terminal of the memory cell _{M T} in the same row is the same word line WLi (i = 1 to m, e.g. , m = 2048 in), the same column of the memory cell drain terminal of _{M T} are same bit line BLj (j = 1 to n, for example, n = 512 in), the source terminals of all the memory cells _{M T} of the common Each is connected to a source line SL. The ETOX type flash memory further includes a row decoder that applies a voltage to the word line WLi (i = 1 to m) based on a row address signal as a peripheral circuit of the memory cell array _AT , and a bit line based on a column address signal. A column decoder for applying a voltage to BLj (j = 1 to n) and an erasing circuit for applying a high voltage Vpp (for example, 12 V) to the source line SL based on an erasing signal are provided.

  FIG. 9 shows a configuration of an ETOX cell that is a memory cell constituting the ETOX type flash memory. As shown in FIG. 9, the ETOX cell includes a source 103 and a drain 102 having a polarity different from that of the semiconductor substrate 101 formed in the semiconductor substrate 101, a gate insulating film 104 formed on the semiconductor substrate 101, and a gate insulating film 104. The floating gate 105, the interlayer insulating film 106, and the control gate 107 are formed in a region corresponding to the source / drain region.

  Hereinafter, each of the write operation, read operation, and erase operation of the ETOX cell will be briefly described. In the flash memory, a state in which the threshold voltage of the memory cell is high is referred to as a write state “0”, and a state in which the threshold voltage of the memory cell is low is referred to as an erase state “1”.

First, writing operation will be described ETOX cell _{M T.} Write operation of the ETOX cells _{M T,} compared programming target cell _{M T} is a memory cell _{M T} to be written, a source voltage Vs of a low voltage to the source 103 (e.g. 0V), high drain than the source voltage Vs to the drain 102 A voltage Vd (for example, 6 V) is applied by applying a high gate voltage Vg (for example, 12 V) to the control gate 107. At this time, hot electrons are generated in the source-drain region of the semiconductor substrate 101 and injected into the floating gate, and the threshold voltage of the ETOX cell rises.

Incidentally, the memory cell such as ETOX cells, from variations in the manufacturing process, since the variation in writing characteristics occurs after the write operation, the threshold voltage Vthp (e.g. 5.3V write judgment threshold voltage is a predetermined write target cell M _T ) A write verify operation is performed to determine whether or not the above is satisfied. In the write verify operation, the reference cell write target cell M _T and the threshold voltage is the threshold voltage for determining a write, a voltage is applied at a predetermined write verify voltage condition, the threshold of the threshold voltage is the reference cell write target cell M _T When it is determined that the voltage is equal to or higher than the voltage, it is determined that the write operation is normally completed. If it is not determined that the write operation has been completed normally, a write verify operation is performed after the rewrite operation and the rewrite operation. Note that the determination has been write target cell M _T and the write operation after rewriting has been completed successfully, by comparing the threshold voltage with the over-write determination threshold voltage, verify whether or not a write-over state To do.

Next, read operation will be described in ETOX cell _{M T.} The read operation of the ETOX cells _{M T,} compared reading target cell _{M T} is a read target memory cell _{M T,} the source voltage Vs of a low voltage to the source 103 (e.g. 0V), slightly higher than the source voltage Vs to the drain 102 the drain voltage Vd (e.g. 1V), the drain voltage Vd higher than the gate voltage Vg (e.g. 5V) respectively applied to the control gate 107, the read target cells by excessive current flowing between the source and drain of the read target cell M _T M It is determined whether the state of _T is a writing state or an erasing state. Specifically, the current value of the current flowing between the source and drain of the read target cell M _T is smaller than a predetermined determination current value is determined to be written state "0", it is larger than the determination current value It is determined that the erase state is “1”.

Subsequently, the erase operation will be described of ETOX cell _{M T.} Erase operation of ETOX cell _{M T,} compared erasing target cell _{M T} is a memory cell _{M T} to be erased, the source voltage Vs of the high voltage to the source 103 (for example, 12V), and the gate voltage of the low voltage to the control gate 107 Vg (for example, 0 V) is applied, and the drain 102 is set in a floating state. At this time, a Fowler-Nordheim current flows between the floating gate and the source via the tunnel oxide film 104 of the erasing target cell M _T, electrons are extracted from the floating gate 105 the threshold voltage of the erased cell M _T may lower.

After the erase operation, performing the erase verify operation determines whether the threshold voltage of the erased cell M _T is less than or equal to a predetermined erasure determination threshold voltage Vthe (e.g. 3.1 V). In the erase verify operation, the reference cell erased cell M _T and the threshold voltage is the threshold voltage for determining the erase, the voltage is applied with a predetermined erase verify voltage condition, the threshold of the threshold voltage is the reference cell to be erased cell M _T When it is determined that the voltage is equal to or lower than the voltage, it is determined that the erasing operation is normally completed. If it is not determined that the erase operation has been normally completed, the erase verify operation is performed after the re-erase operation and the re-erase operation.

  By the way, the erase speed of the erase operation is generally 0.6 to 1 second, which is slower than the write speed of the write operation. For this reason, in an actual device, the process is performed in units of blocks including a plurality of, for example, 64 kbyte memory cells.

  Next, the RRAM will be described. The RRAM is a resistive nonvolatile memory using a variable resistance element whose electric resistance reversibly changes when a voltage pulse is applied.

Here, FIG. 10 shows a schematic configuration example of a memory cell array A _R of RRAM, the memory cell array A _R is constituted by a plurality of memory cells M _R. Memory cells M _R is configured with one transistor T and one variable resistive element R, one end of the variable resistor element R is connected to the drain terminal of the transistor T. Memory cell array A _R shown in FIG. 10, m × n number of memory cells M _R are arranged in a matrix, the gate terminal of the transistor T in the same row is the same word line WLi (i = 1~m), the same the other end of the variable resistive element R column the same bit line BLj (j = 1~n), the source terminals of all the memory cells M _R to a common source line SL, and are respectively connected. RRAM further as a peripheral circuit of the memory cell array _{A R,} a row decoder for applying a voltage to the word line WLi (i = 1~m) based on the row address signal, the bit line BLj based on the column address signal (j = 1 to n) includes a column decoder for applying a voltage, and an erasing circuit for applying a voltage to the source line SL based on an erasing signal.

  FIG. 11 shows a schematic configuration example of the variable resistance element R. As shown in FIG. 11, the variable resistance element R has a very simple structure in which a lower electrode 211, a variable resistor 212, and an upper electrode 213 are stacked in this order. The variable resistance element R can reversibly change the resistance value by applying a voltage pulse between the upper electrode 213 and the lower electrode 211. Data can be stored by changing the resistance state by this reversible resistance changing operation (hereinafter referred to as “switching operation” as appropriate). Here, the case where the variable resistance element R is in the low resistance state will be described as the write state, and the case where the variable resistance element R is in the high resistance state will be described as the erase state.

Figure 12 is a schematic cross sectional view of a memory cell M _R constituting the memory cell array A _R in FIG. Memory cells M _R, as described above, to form a single memory cell in the transistor T and the variable resistance element R.

  The transistor T includes a gate insulating film 203 and a gate electrode 204 stacked on the semiconductor substrate 201, and a drain diffusion region 205 and a source diffusion region 206 formed in the semiconductor substrate 201. An element isolation region 202 for electrically isolating each transistor T is formed. In FIG. 12, a first interlayer insulating film 207 made of BPSG (Boron Phosphorous Silicate Glass) is formed on the semiconductor substrate 101 and the transistor T.

  In FIG. 12, the variable resistance element R is formed on the first interlayer insulating film 207. Similar to FIG. 11, the variable resistance element R is a lower electrode composed of a TiN film 211b having a thickness of 100 nm and a Ti film 211a having a thickness of 50 nm. 211, a variable resistor 212 made of cobalt oxide having a thickness of 5 to 50 nm, and an upper electrode 213 made of a Ta film having a thickness of 100 nm are stacked in this order. The lower electrode 211 is electrically connected to the drain diffusion region 205 of the transistor T through a contact electrode 208 made of a conductive metal. The variable resistor 212 may be composed of nickel oxide or tantalum oxide instead of cobalt oxide, or may be composed of an oxide of a fiber metal element such as zinc oxide or niobium oxide. Further, the lower electrode 211 and the upper electrode 213 may be made of a material such as titanium nitride, Pt, Ir, Os, Ru, Rh, Pd, Al, or W. In FIG. 12, a second interlayer insulating film 209 having a thickness of 50 to 60 nm is formed on the first interlayer insulating film 207 and the variable resistance element R.

  Further, in FIG. 12, the gate electrode 204 of the transistor T forms a word line WLi. Further, the source line wiring 215 constituting the source line SL is formed on the second interlayer insulating film 209 using TiN / Al—Si / TiN / Ti, and the source diffusion region 206 of the transistor T via the contact electrode 214. And is electrically connected. A bit line wiring 217 constituting the bit line BLi is formed on the second interlayer insulating film 209 and is electrically connected to the upper electrode 213 of the variable resistance element R through the contact electrode 216. Further, a third interlayer insulating film 218 is formed on the source wiring 215, the bit line wiring 217 and the second interlayer insulating film 209, a fourth interlayer insulating film 219 is formed on the third interlayer insulating film 218, and a fourth interlayer insulating film 219 is formed on the fourth interlayer insulating film 219. A surface protective film 220 made of a SiN film is formed.

As shown in FIG. 12, the configuration in which the transistor T and the variable resistance element R is placed in series, the transistor T of the memory cell M _R selected by the voltage change of the word line WLi is turned on, further, the bit line only the variable resistor element R of the memory cell M _R selected by a voltage change in BLi selectively write to, or has a configuration that can be erased.

  Hereinafter, each of the write operation, the read operation, and the erase operation of the variable resistance element will be described. Here, a case will be described in which the structure and material of the variable resistance element R are configured so that the characteristics are asymmetric, and voltage pulses having different polarities are applied in the write operation and the erase operation.

First, an explanation will be made of the write operation of the variable resistive element R constituting the memory cell M _R. Variable in the write operation of the resistance element R, the word line WLi (i = 1~m) to a predetermined write row voltage is connected to the write target cell M _R is a memory cell M _R to be written, for example, a 2V, write target the 0V respectively applied to the word line WLi other word lines WLi to connect to cell _{M R.} Also, 0V predetermined write column voltage to the bit line BLj (j = 1 to n) to be connected to the write target cell _{M R,} e.g., a 2V, to the write target cell _M bit line BLj other bit line BLj is connected to _R Are applied respectively. Further, 0 V is applied to the source line SL. The write row voltage applied to the word line WLi is connected to the write target cell M _R, as the variable resistive element R is low-resistance state, the variable resistor R across voltage difference between the resistance of the variable resistor element R of The value is set to be larger than the value for changing the value (threshold voltage value of the switching operation).

Thus, the voltage of positive polarity is applied to the variable resistor element R of the write target cell M _R, a low resistance state resistance is reduced. Note that the non-programming target cell M _R, which is a memory cell M _R other than the write target cell M _R, no voltage is applied, the write is not performed.

Incidentally, the memory cell M _R of the RRAM, similarly to the ETOX cells, since the variation from the variation in the manufacturing process to the write characteristics occurs after the write operation, performs a write verify operation.

Next, an explanation will be made of the read operation of the variable resistive element R constituting the memory cell M _R. Variable in the read operation of the resistance element R, the word line WLi (i = 1~m) to a predetermined read row voltage is connected to the reading target cell M _R is a memory cell M _R being read, for example, a 2V, read target the 0V respectively applied to the word line WLi other word lines WLi to connect to cell _{M R.} The predetermined read column voltage to the bit line BLj is connected to the reading target cell _{M R} (j = _1~n), for example, 0.7 V, and the reading target cell _M bit lines other than the bit line BLj is connected to the _R BLj 0V is applied to each. Further, 0 V is applied to the source line SL. The read column voltage applied to the word line WLi is connected to the reading target cell M _R, as the resistance value of the variable resistor element R is not changed, the variable resistive element the voltage across differential threshold voltage value of the switching operation of the R Set to be smaller.

If the variable resistor element R of the read target cell M _R is in the low resistance state, the current value of the current flowing through the memory cell M _R is increased, if the variable resistor element R has a high resistance, flows through the memory cell M _R since the current value of the current decreases, by detecting the current value of the current flowing through the memory cell M _R, it is possible to detect the state of the memory cell.

Subsequently, the erase operation will be described of the memory cell M _R. In the erase operation of the variable resistor element R, for example, the word line WLi (i = 1~m) to a predetermined erase row voltage to be connected to the erasing target cell _{M R} is a memory cell _{M R} to be erased, for example, a 2V, the 0V respectively applied to the word line WLi other than the word line WLi is connected to the erasing target cell _{M R.} Also, 0V to the bit line BLj is connected to the erasing target cell _{M R (j = 1~n),} 2V is respectively applied to the bit line BLj other than the bit line BLj is connected to the erasing target cell _{M R.} Further, a predetermined source voltage, for example, 2V is applied to the source line SL.

Thus, a negative voltage is applied to the variable resistor element R of the erasing target cell M _R, the resistance value is high resistance state increases. Note that the non-erased cell M _R, which is a memory cell M _R other than the erasing target cell M _R, no voltage is applied to the variable resistor element R, the erase is not performed. Incidentally, the erase line voltage applied to the word line WLi is connected to the erasing target cell M _R is the voltage at which the transistor T is turned ON constituting the erasing target cell M _R, the source voltage applied to the source line SL is deleted as the voltage across differential of the variable resistive element R constituting the target cell M _R is greater than the threshold voltage value of the switching operation, respectively set.

Incidentally, the writing operation and the erasing operation of the RRAM, the description has been given of the case of applying a voltage pulse having different polarities, as another method of changing the resistance value of the variable resistor element R constituting the memory cell M _R of the RRAM, e.g. There is a method of applying voltage pulses having different pulse widths in the write operation and the erase operation.

Further, as another method of changing the resistance value of the variable resistor element R constituting the memory cell M _R of the RRAM, row decoder, column decoder, the load resistance characteristic variable circuit, and a signal line for connecting these circuits of the load resistance characteristics of the load circuit defined by the synthesis circuit of the parasitic resistance and the like, by switching in the erase operation and the write operation, the nonvolatile semiconductor changing the value of the variable resistive element R constituting the memory cell M _R There is a storage device (see, for example, Patent Document 2).

  In the nonvolatile semiconductor memory device described in Patent Document 2, a load resistance characteristic variable circuit is provided between the voltage generation circuit and the row decoder, and the load resistance characteristic of the load circuit electrically connected in series to the selected memory cell is written. Switching between time and erase operation. Detailed principles and operations are described in Patent Document 2.

  Incidentally, the writing speed and erasing speed of the RRAM are several tens of nanoseconds when a voltage of 1.5 V to 3 V is applied to the variable resistance element R, which is faster than the flash memory. For this reason, unlike the flash memory, the erase operation of the RRAM does not need to be performed in units of blocks but can be performed in units of bits. Thus, for example, in an RRAM that can simultaneously perform a write operation and an erase operation, such as the RRAM described in Patent Document 2, the write operation, the read operation, and the erase operation can be performed in the same cycle.

JP 2002-537627 A JP 2007-188603 A H. Pagnia et al., “Bistable Switching in Electroformed Metal-Insulator-Metal Devices”, Phys. Stat. Sol. (A), vol. 108, pp. 11-65, 1988. JP-A-9-97218 JP 2001-67258 A

  In recent years, since the capacity of application software and data tends to increase, it has become a problem to speed up the data rewriting operation in the above-described nonvolatile memory such as flash memory and RRAM.

  Some flash memories have a burst function that continuously performs a write operation using a plurality of write commands. However, in a flash memory having a burst function, the entire write operation is proportional to the number of write commands handled by the burst function. This will increase the time it takes. Then, as described above, since the application software and data capacity has been increasing in recent years, the number of write commands handled by the burst function tends to increase. It will be more prominent. For this reason, particularly in a flash memory having a burst function, it is desired to shorten the time required for the rewrite operation.

  On the other hand, in the RRAM, the time required for the rewrite operation is shorter than that in the flash memory. However, as in the case of a flash memory, especially in the case of a configuration having a burst function, the capacity of application software and data tends to increase. is expected. For this reason, also in the RRAM having the burst function, it is desired to shorten the time required for the rewrite operation, as in the case of the flash memory.

  The present invention has been made in view of the above problems, and an object thereof is to provide a nonvolatile semiconductor memory device capable of performing a rewrite operation of a memory cell at high speed.

  In order to achieve the above object, a non-volatile semiconductor memory device according to the present invention includes a variable resistance element and a transistor whose electrical resistance reversibly changes when a voltage pulse is applied, and information is obtained depending on the resistance state of the variable resistance element. A plurality of non-volatile memory cells that store the memory cells, the plurality of memory cells are arranged in a matrix, the first terminals of the memory cells in the same row are connected to a common word line, and the memory cells in the same column Common to both the first subbank and the second subbank, a memory cell array comprising a first subbank having a second terminal connected to a common bit line, and a second subbank having the same configuration as the first subbank. A row decoder configured to apply a voltage simultaneously to the corresponding word lines of each of the first subbank and the second subbank; and A first column decoder for applying a voltage to the bit line of the sub-bank; a second column decoder for applying a voltage to the bit line of the second sub-bank; and a write operation, a write verify operation, and the write verify operation for the memory cell array The erase operation is normally performed in the rewrite operation with respect to the memory cell determined to have not been normally performed in the above, the write verify operation with respect to the rewrite operation, the erase operation, the erase verify operation, and the erase verify operation. A re-erase operation for the memory cell determined not to be performed, and a control circuit for controlling the erase verify operation for the re-erase operation, the control circuit including the write operation or the first sub-bank The erasing operation, and A first operation cycle for performing a read operation for the write verify operation or a read operation for the erase verify operation on the second subbank, and the read operation for the write verify operation on the first subbank or the A read operation for an erase verify operation and a second operation cycle for performing the write operation or the erase operation on the second sub-bank are alternately executed, and the first operation cycle and the second operation cycle include: The first feature is that the length is the same regardless of the type of the target motion.

  In the nonvolatile semiconductor memory device according to the present invention having the above characteristics, in the first operation cycle, the control circuit causes the rewrite operation or the reerase operation to the first subbank and the rewrite to the second subbank. A read operation for the write verify operation for the write operation or a read operation for the erase verify operation for the re-erase operation is performed, and the write verify for the re-write operation for the first subbank is performed in the second operation cycle. The second feature is that the read operation for the erase verify operation for the read operation or the re-erasure operation for the operation, and the rewrite operation or the re-erasure operation for the second sub-bank are performed.

  In the nonvolatile semiconductor memory device according to the present invention having any one of the above characteristics, the control circuit performs the write operation on any single bit or any single byte in the first subbank and the second subbank. The write verify operation, the rewrite operation, the write verify operation for the rewrite operation, the erase operation, the erase verify operation, the reerase operation, and the erase verify operation for the reerase operation can be controlled. This is the third feature.

  In the nonvolatile semiconductor memory device according to the present invention having any one of the above characteristics, the memory cell array is configured to be capable of simultaneously executing the write operation and the erase operation in the first subbank, and the memory cell array in the second subbank. A fourth feature is that the write operation and the erase operation can be executed simultaneously.

  In the nonvolatile semiconductor memory device according to the present invention having any one of the above characteristics, the control circuit performs the write operation and the write verify operation on a unit memory cell group including a predetermined number of memory cells by one write command. A burst function that performs several consecutive times according to a burst length, and in the write operation by the burst function, a subsequent address from the start address of the unit memory cell group specified by the write command is sent to the first sub-bank A fifth feature is that the write operation and the write verify operation by the burst function are completed in the first operation cycle or the second operation cycle. .

  In the nonvolatile semiconductor memory device according to the present invention having any one of the above characteristics, the control circuit performs the erase operation and the erase verify operation on a unit memory cell group composed of a predetermined number of memory cells by one erase command. A burst function that is continuously performed in accordance with a burst length, and in the erase operation by the burst function, a subsequent address from the start address of the unit memory cell group specified by the erase command is sent to the first sub-bank. A sixth feature is that the write operation and the write verify operation by the burst function are completed in the first operation cycle or the second operation cycle. .

  In the nonvolatile semiconductor memory device according to the present invention having the above characteristics, the control circuit configures another subbank pair in an intermediate cycle between the first operation cycle and the second operation cycle of the predetermined subbank pair. Executing at least one of the first operation cycle for one of the subbanks and the second operation cycle for the other subbank, and concurrently configuring the predetermined subbank pair in the intermediate cycle A seventh feature is that at least one of the read operation for the erase verify operation for the re-erase operation for the sub-bank and the re-erase operation for the other sub-bank is executed. To do.

  In order to achieve the above object, a method for controlling a nonvolatile semiconductor memory device according to the present invention includes a variable resistance element and a transistor whose electrical resistance reversibly changes when a voltage pulse is applied, and the resistance of the variable resistance element A plurality of non-volatile memory cells for storing information according to a state; a plurality of the memory cells are arranged in a matrix; the first terminals of the memory cells in the same row are connected to a common word line; A memory cell array comprising: a first subbank having a second terminal of a memory cell connected to a common bit line; a second subbank having the same configuration as the first subbank; the first subbank and the second subbank; A row decoder for applying a voltage simultaneously to the corresponding word lines in the first subbank and the second subbank, A first column decoder for applying a voltage to the bit line of the first subbank; a second column decoder for applying a voltage to the bit line of the second subbank; a write operation to the memory cell array; a write verify operation; It is determined that the write operation is not normally performed in the write verify operation, the rewrite operation for the memory cell, the write verify operation for the rewrite operation, the erase operation, the erase verify operation, and the erase operation in the erase verify operation. A control method for a nonvolatile semiconductor memory device, comprising: a re-erase operation for the memory cell that is determined not to be normally performed; and a control circuit that controls the erase verify operation for the re-erase operation. Before the first sub-bank A first operation step of performing a write operation or an erase operation, a read operation for the write verify operation for the second subbank or a read operation for the erase verify operation, and the write verify operation for the first subbank. The first operation step is performed alternately with the read operation for the read operation or the erase verify operation for the second sub-bank and the second operation step for performing the write operation or the erase operation with respect to the second sub-bank. The first feature is that the second operation step has the same length regardless of the type of the target operation.

  In the control method of the nonvolatile semiconductor memory device according to the present invention having the above characteristics, the control circuit may perform the write operation on any single bit or any single byte in the first subbank and the second subbank, The write verify operation, the rewrite operation, the write verify operation for the rewrite operation, the erase operation, the erase verify operation, the reerase operation, and the erase verify operation for the reerase operation can be controlled. This is the second feature.

  The method of controlling a nonvolatile semiconductor memory device according to the present invention having any one of the above features is characterized in that the memory cell array is configured to be able to simultaneously execute the write operation and the erase operation in the first subbank. The third feature is that the write operation and the erase operation can be executed simultaneously.

  According to the nonvolatile semiconductor memory device having the above characteristics, the row decoder is provided in common in the first subbank and the second subbank, and for the write operation for one subbank and the write verify operation for the other subbank in the same cycle. By configuring so as to execute the read operation, the write time can be shortened in the entire write operation and write verify operation for the memory cell array.

  According to the nonvolatile semiconductor memory device having the above characteristics, since the row decoder is configured in common in the first subbank and the second subbank, the sense amplifier for the read operation can be shared, and the memory cell array can be configured with a simple device configuration. It is possible to shorten the write time in the entire write operation and write verify operation.

  Furthermore, according to the nonvolatile semiconductor memory device having the above characteristics, since the read operation for the write operation and the write verify operation is executed during the same cycle, the power consumption is leveled.

  According to the nonvolatile semiconductor memory device having the above characteristics, the row decoder is provided in common for the first subbank and the second subbank, and during the same cycle, the erase operation for one subbank and the erase verify operation for the other subbank are performed. Therefore, it is possible to shorten the erase time in the entire erase operation and erase verify operation for the memory cell array. In addition, when a cell to be written and a cell to be erased are mixed in one subbank, in particular, a nonvolatile semiconductor memory device capable of performing a write operation and an erase operation simultaneously in bit units, for example, a write operation and an erase operation. In the RRAM that changes the load resistance characteristic of the load circuit, the operation time can be shortened in the entire write operation and erase operation.

  Embodiments of a nonvolatile semiconductor memory device according to the present invention (hereinafter simply referred to as “device of the present invention” as appropriate) will be described below with reference to the drawings.

<First Embodiment>
1st Embodiment of this invention apparatus is described based on FIGS. Here, FIG. 1 shows a schematic configuration example of the device 1 of the present invention, and FIG. 2 shows a configuration of a memory cell array of the device 1 of the present invention. In the present embodiment, the case where the device 1 of the present invention is an RRAM will be described.

  As shown in FIG. 1, the device 1 of the present invention includes a memory cell array including two subbanks, a first subbank SB1 and a second subbank SB2, and a first subbank SB1 based on an instruction from a control circuit 10 to be described later. And a row decoder DR for applying a voltage to the word lines WL1 to WLm of the second subbank SB2, and a first column decoder for applying a voltage to the bit lines BL11 to BL1n of the first subbank SB1 based on an instruction from the control circuit 10 to be described later. DC1, a second column decoder DC2 for applying a voltage to the bit lines BL21 to BL2n of the second subbank SB2 and an operation including a write operation and a write verify operation based on an instruction from the control circuit 10 described later. A control circuit 10 is provided. In the present embodiment, the inventive device 1 has a burst function for continuously executing a plurality of write commands.

As shown in FIG. 2, the first subbank SB1 of the memory cell array includes one transistor T and one variable resistance element R, and a memory cell M in which one end of the variable resistance element R is connected to the drain terminal of the transistor T. _A plurality of _Rs are provided. The first sub-bank SB1 is, m × n number of memory cells M _R are arranged in a matrix, (corresponding to the first terminal) the gate terminal of the transistor T in the memory cell M _R of the same row the same word line WLi in (i = 1 to m), the one end of the variable resistive element R constituting the memory cell _{M R} of the same column (corresponding to the second terminal) is the same bit line BL1j (j = 1~n), first sub-bank the source terminal of the transistor T constituting the all the memory cells M _R of SB1 is a common source line SL1, are respectively connected. First sub-bank SB1 of the present embodiment, the voltage application state to the gate terminal of the transistor T (first terminal), switches the selection and non-selection of the memory cell M _R, one end of the variable resistive element R (second terminal) operation of the memory cell M _R by the voltage application state to (a write operation, read operation, erase operation) is configured to switch. The switching between the write operation and the erase operation includes a method of applying voltage pulses having different polarities, a method of applying voltage pulses having different pulse widths, and a method of switching the load resistance characteristics of the load circuit. Use is optional. The switching between the writing operation and the erasing operation is not the gist of the present invention, but the details are described in Patent Document 2.

The second sub-bank SB2 of the memory cell array, as shown in FIG. 2, similarly to the first sub-bank SB1, is constituted by a plurality of memory cells M _R, m × n number of memory cells M _R is the matrix are arranged, the gate terminal of the transistor T in the memory cell M _R of the same row (corresponding to the first terminal) the same word line WLi (i = 1 to m), constituting the memory cell M _R on the same column to one end of the variable resistive element R (corresponding to the second terminal) is the same bit line BL2j (j = 1~n), the source terminal of the transistor T constituting the all the memory cells _{M R} of the second sub-bank SB2 is common Each is connected to the source line SL2. Similar to the first sub-bank SB1, second sub-bank SB2 is the voltage application state to the gate terminal of the transistor T (first terminal), it switches the selection and non-selection of the memory cell M _R, of the variable resistor element R one end (second terminal) operation of the memory cell M _R by the voltage application state to (a write operation, read operation, erase operation) is configured to switch.

In the present embodiment, even-numbered addresses (A _C1 , A _{C1 + 2} , A _C2 , A _{C2 + 2} ) are allocated to the first subbank SB ₁ , and odd-numbered addresses (A _{C1 + 1} , A _{C1 + 3} , A _{C2 + 1} , A _{C2 + 3} ) are allocated to the second subbank SB 2. ing. The address assignment is not limited to this. For example, addresses are assigned alternately every two addresses (A _C1 and A _{C1 + 1} are assigned to the first subbank SB1, and A _{C1 + 2} and A _{C1 + 3} are assigned to the second subbank SB2. For example, the address may be alternately assigned every predetermined number.

  The control circuit 10 receives an externally input command and controls each circuit unit, an instruction control unit 11 for storing each externally input address signal, an output output from the first subbank SB1 or the second subbank SB2. An output control unit 13 that performs data output control, a buffer 14 that stores output data and externally input externally input data, a row address buffer 15 that stores a row address of address signals stored in the buffer 12, and a read operation A read unit 16 that controls the output data, a comparison unit 17 that compares output data and write data (expected value of external input data), a buffer 18 that stores an address signal AddCr from the read unit 16, a write operation, a write verify operation, and an erase Write / erase unit 1 for controlling operation and erase verify operation , The operation switch control unit 20 and, is configured to include a sub-bank control unit 21.

The write / erase unit 19, the signal Comp outputted from the comparing unit 17, to indicate that a write operation is not normally finished, the address of the write target cell M _R the write operation has not ended normally and accumulating write data by sub-bank output signal indicating that the write operation is not performed normally WE, signal indicating the address of a write target cell M _R AddOW, and a signal DAtOw indicating the write data to the sub-bank control unit 21 To do.

  The subbank control unit 21 performs a signal RWA indicating whether an operation to be performed on the first column decoder DC1 of the first subbank SB1 is a write operation, an erase operation, or a read operation, and the signal RWA is a write operation or an erase operation. When the signal indicates that the number of bits of data is a bit to be written or erased, a signal WEA indicating a column address, a signal ADA indicating a column address, and a signal DWA indicating write data are output. A signal DRA indicating read data is received from the column decoder DC1.

In the present embodiment, for explanation, a first sub-bank SB1 and all the memory cells M _R are erased state "1" of the second sub-bank SB2, described case of writing in the writing state "0". When the value of the expected value and the memory cell M _R of the external input data is different, it is determined that there is write data, and performs a write or erase operation, in the present embodiment, all the memory cells M _R because There is assumed a case where the erase state "1", the expected value of the external input data as a target cell write the memory cell M _R in the written state "0", it executes the write operation. Specifically, for example, in the present embodiment, when the external input data D0~D7 is "00000001", the memory cell _{M R} of the address _{A C2 + 3} of the second sub-bank SB2 is assigned is a write target cell, When the signal ADA is the column address _{AC2 + 3} , the signal DWA is in the write state “0”.

  Similarly, the sub-bank control unit 21 uses the signal RWB and the signal RWA indicating whether the operation to be performed is the write operation, the erase operation, or the read operation for the second column decoder DC2 of the second sub-bank SB2. When indicating an erasing operation, a signal WEB indicating which bit of data is a bit to be written or erased, a signal ADB indicating a column address, and a signal DWB indicating write data are output, A signal DRB indicating read data is received from the first column decoder DC1.

  Hereinafter, the processing operation of the device 1 of the present invention will be described with reference to FIGS. Here, FIG. 3 shows an operation procedure of a write operation and a write verify operation for the first subbank SB1 of the device 1 of the present invention, and FIG. 4 shows a timing chart of the write operation and the write verify operation of the device 1 of the present invention. ing.

  In the present embodiment, the device 1 of the present invention has a first operation cycle in which a write operation for the first subbank SB1 and a read operation in the write verify operation for the second subbank SB2 are performed, and a read operation in the write verify operation for the first subbank SB1. And a second operation cycle for performing a write operation on the second subbank SB2 are alternately executed. FIG. 3 shows the operation procedure of the first subbank SB1, but the operation procedure of the second subbank SB2 is such that the correspondence between each cycle and each operation in the operation procedure of the first subbank SB1 It is the composition which changed the cycle.

FIG. 4 shows a case where a write command _WB4 for sequentially writing four write data (with a burst length of 4) is input by the burst function. In the present embodiment, a case where the write data has a 1-bit configuration will be described for the sake of explanation. More specifically, in FIG. 4, the burst function, a row address _{A R1,} the write address (column _address) write instruction to the memory cell _{M R} of the first sub-bank SB1 represented by _{A C1} writes write data D0 to D3 _{W B4} when shows the case where row addresses _{a R1,} write command _{W B4} for writing write data D4~D7 the memory cell _{M R} of the second sub-bank SB2 indicated by the write address _{a C2} is input continuously. The column addresses of the write data D1 to D3 are automatically set to A _{C1 + 1} , A _{C1 + 2} and A _{C1 + 3} by the burst function, and the column addresses of the write data D5 to D7 are automatically set by the burst function. A _{C2 + 1} , A _{C2 + 2} and A _{C2 + 3} are set. In FIG. 4, the write data D0 to D7 are sequentially input to the buffer 14 so as not to change at the rising timing of each clock signal in synchronization with the clock signal.

In FIG. 4, “W” of the signal RWA and the signal RWB is a write operation, “V” is a read operation for the write verify operation, and “W _R ” is a rewrite operation when the write verify result is “Fail”. “V _R ” indicates a read operation for a write verify operation relative to a rewrite operation.

The device 1 of the present embodiment of the present embodiment starts the write operation when the write command A by the burst function is input and the address _AR1 indicating the row address is input to the buffer 12 (time t2, step # 101). The row address buffer 15 outputs the address _AR1 input to the buffer 12 to the row decoder DR. Subsequently, the first write command W is input to the instruction control unit 11, the write address (column address) is stored in the buffer 12, and the external input data is stored in the buffer 14. Specifically, in FIG. 4, at the falling edge of the clock time t3~ time t4, the write command W is the instruction control unit 11, the write address _{A C1} buffer 12, the write data D0 is in the buffer 14, respectively input Is done.

In the initial cycle (time t7 to time t8 in FIG. 4), the subbank control unit 21 of the inventive device 1 performs a write operation on the first subbank SB1 (step # 102). Specifically, at time t7 in FIG. 4, the transistor T of the write target cell M _R of the first sub-bank SB1 indicated by the write address A _C1 to the ON state, the resistance value of the variable resistor element R according to the write data D0 A write voltage is applied to change the to a write state.

Sub-bank control unit 21 of the device 1 of the present invention (corresponding to the second operation cycle, the time t8~ time t9 in Fig. 4) initial second cycle in respect programming target cell _{M R} of the first sub-bank SB1, write verify A read operation for the operation is performed (step # 103). Specifically, it reads the write target cell _{M R} of the first sub-bank SB1 indicated by the write address _{A C1,} and outputs the read data Q0 as data DatC.

At this time, further, in parallel, the sub-bank control unit 21 of the device 1 of the present invention performs a write operation to the write target cell _{M R} of the second sub-bank SB2 (Step # 102). Specifically, with respect to the write target cell M _R of the second sub-bank SB2 indicated by the write address A _{C1 + 1,} applying a write voltage corresponding to the write data D1.

In the next first cycle (corresponding to the first operation cycle, time t9 to time t10 in FIG. 4), the subbank control unit 21 of the inventive device 1 performs the first operation on the write address A _{C1 + 2} as the operation on the first subbank SB1. since a write operation, to write the target cell _{M R} indicated by the write address _{a C1 + 2,} by applying a voltage corresponding to the write data D2, it performs a write operation (YES branched at step # 112). The comparison unit 17 of the device 1 of the present invention compares the value of the data DatC read in the immediately preceding second cycle with the value of the signal DatO, and the values of the data Q0 and the data D0 from time t9 to time t10 in FIG. The result is output to the write / erase unit 19 as a result signal Comp (step # 111). From time t9 to time t10 in FIG. 4, “Err0” indicating that the values of the data Q0 and the data D0 do not match is output as the result signal Comp.

In parallel, the sub-bank control unit 21 of the device 1 of the present invention, as the operation for the second sub-bank SB2, to programming target cell M _R indicated by the write address A _{C1 + 1,} performs the read operation for the write verify operation, read Data Q1 is output as data DatC (step # 103).

The subbank control unit 21 of the device 1 of the present invention is indicated by the write address AC1 _{+ 2} as the operation for the first subbank SB1 in the next second cycle (corresponding to the second operation cycle, time t10 to time t11 in FIG. 4). to programming target cell _{M R,} it performs the read operation for the write verify operation, and outputs the read data Q2 as the data DatC (step # 122). The write / erase portion 19 of the device 1 of the present invention, based on the result signal Comp outputted from the comparing unit 17 in the first cycle immediately before, whether the writing operation to write the target cell M _R was successful determines (step # 121), if it is determined that not successful, to the sub-bank control unit 21, a signal indicating that the write operation is not completed normally WE, the address of the write target cell M _R A signal AddOw indicating a write data and a signal DatOw indicating write data are output. Specifically, at time t10 to time t11 in FIG. 4, the write / erase unit 19 writes the write verify because the result signal Comp output from the comparison unit 17 in the immediately preceding first cycle is “Err0”. results determined to be Fail, to sub-bank control unit 21, signals WE, signal indicating the address _{a C1} AddOw, and outputs a signal DatOw indicating the data D0.

In parallel, the sub-bank control unit 21 of the device 1 of the present invention, as the operation for the second sub-bank SB2, since the first write operation to the write address _{A C1 + 3,} with respect to programming target cell _{M R} indicated by the write address _{A C1 + 3} Then, a write voltage corresponding to the write data D3 is applied to perform a write operation (YES branch at step # 112). The comparison unit 17 of the device 1 of the present invention compares the value of the data DatC (data Q1) read in the immediately preceding first cycle with the value of the signal DatO (data D1), and writes the result as a result signal Comp. / Output to erasure unit 19 (step # 111). From time t10 to time t11 in FIG. 4, “Err1” indicating that the values of the data Q1 and the data D1 do not match is output as the result signal Comp.

The subbank control unit 21 of the device 1 of the present invention is a target of a rewrite operation as an operation on the first subbank SB1 in the next first cycle (corresponding to the first operation cycle, time t11 to time t12 in FIG. 4). If there is a rewrite target cell M _R, the rewriting operation for rewriting target cell M _R, when rewriting target cell M _R is not, if there is write data for other programming target cell M _R is , writing operation to the write target cell _{M R} (YES branched at step # 112). Specifically, at time t11~ time t12 in FIG. 4, in a second cycle immediately preceding, from the write / erase unit 19, signals WE, signal indicating the address _{A C1} AddOw, signal indicating the data D0 DatOw is output because there, it determines that there is a rewrite target cell M _R, to rewrite target cell M _R of the first sub-bank SB1 indicated by the write address a _C1, in accordance with the write data D0, writing for a rewrite operation A voltage is applied (step # 113). The comparison unit 17 of the device 1 of the present invention compares the value of the data DatC (data Q2) read in the immediately preceding second cycle with the value of the signal DatO (data D2), and writes the result as a result signal Comp. / Output to erasure unit 19 (step # 111). At time t11 to time t12 in FIG. 4, “Pass2” indicating that the values of the data Q2 and the data D2 match is output as the result signal Comp.

In parallel, the sub-bank control unit 21 of the device 1 of the present invention, as the operation for the second sub-bank SB2, to programming target cell M _R indicated by the write address A _{C1 + 3,} performs the read operation for the write verify operation, read Data Q3 is output as data DatC (step # 122). Further, since the write / erase unit 19 of the device 1 of the present invention has a result signal Comp output from the comparison unit 17 in the immediately preceding first cycle at time t11 to time t12 in FIG. It is determined that the result of the write verification is Fail, and the signal WE, the signal AddOw indicating the address AC1 _{+ 1,} and the signal DatOw indicating the data D1 are output to the sub bank control unit 21.

The sub-bank control unit 21 of the inventive device 1 is indicated by the write address A _C1 as the operation for the first sub-bank SB1 in the next second cycle (corresponding to the second operation cycle, time t12 to time t13 in FIG. 4). to rewrite target cell M _R, performs the read operation for the write verify operation for rewriting operation, and outputs the read data Q0 as data DatC (step # 122). Further, since the write / erase unit 19 of the device 1 of the present invention has a result signal Comp output from the comparison unit 17 in the immediately preceding first cycle from time t12 to time t13 in FIG. determines that the write operation to the write target cell M _R indicated by the write address a _{C1 + 2} is successful, the output of such signals WE for sub-bank control unit 21 is not performed.

In parallel, the sub-bank control unit 21 of the device 1 of the present invention operates as the operation for the second sub-bank SB2, from the write / erase unit 19 in the immediately preceding first cycle, from the signal WE, the signal AddOw indicating the address AC1 _{+ 1} , and the data D1. since the signal DatOw is output indicating, determines that there is a rewrite target cell _{M R} (YES branched at step # 112), the rewrite target cell _{M R} of the second sub-bank SB2 indicated by the write address _{a C1 + 1} On the other hand, a write voltage for a rewrite operation is applied according to the write data D1 (step # 113). The comparison unit 17 of the device 1 of the present invention compares the value of the data DatC (data Q3) read in the immediately preceding first cycle with the value of the signal DatO (data D3), and writes the result as a result signal Comp. / Output to erasure unit 19 (step # 111). From time t12 to time t13 in FIG. 4, “Err3” indicating that the values of the data Q3 and the data D3 do not match is output as the result signal Comp.

The subbank control unit 21 of the device 1 of the present invention operates as the operation for the first subbank SB1 in the immediately preceding second cycle in the next first cycle (corresponding to the first operation cycle, time t13 to time t14 in FIG. 4). since the signal WE is not outputted from the write / erase unit 19, a rewrite target cell M _R is determined that there is no. Further, the sub-bank control unit 21, since the write command _{W B4} data D4~D7 to the address _{A C2} continuously by the burst function is entered, it is determined that there is a write target cell _{M R} (step # 112 YES branch), with respect to programming target cell _{M R} of the first sub-bank SB1 represented by address _{a C2,} in accordance with the write data D4, applying a write voltage for writing operation (step # 113). The comparison unit 17 of the device 1 of the present invention compares the value of the data DatC (data Q0) read in the immediately preceding second cycle with the value of the signal DatO (data D0), and writes the result as a result signal Comp. / Output to erasure unit 19 (step # 111). From time t13 to time t14 in FIG. 4, “Pass0” indicating that the values of the data Q0 and the data D0 match is output as the result signal Comp.

In parallel, the sub-bank control unit 21 of the device 1 of the present invention, as the operation for the second sub-bank SB2, to rewrite target cell M _R indicated by the write address A _{C1 + 1,} performs the read operation for the write verify operation, Read data Q1 is output as data DatC (step # 122). Further, since the write / erase unit 19 of the device 1 of the present invention has a result signal Comp output from the comparison unit 17 in the immediately preceding second cycle from time t13 to time t14 in FIG. It is determined that the result of the write verification is Fail, and the signal WE, the signal AddOw indicating the address AC1 _{+ 3,} and the signal DatOw indicating the data D3 are output to the sub bank control unit 21.

Sub-bank control unit 21 of the device 1 of the present invention, the following second cycle (corresponding to the second operation cycle, the time t14~ time t15 in FIG. 4), examples of the operation for the first sub-bank SB1, indicated by the write address _{A C2} to programming target cell _{M R,} it performs the read operation for the write verify operation, and outputs the read data Q4 as data DatC (step # 122). Further, since the write / erase unit 19 of the device 1 of the present invention has a result signal Comp output from the comparison unit 17 in the immediately preceding first cycle from time t14 to time t15 in FIG. the write operation to rewrite target cell M _R is determined to have completed successfully as indicated by the write address a _C1, the output of such signals WE for sub-bank control unit 21 is not performed.

In parallel, the sub-bank control unit 21 of the device 1 of the present invention operates as the operation for the second sub-bank SB2, from the write / erase unit 19 in the immediately preceding first cycle, from the signal WE, the signal AddOw indicating the address AC1 _{+ 3} , and the data D3. since the signal DatOw is output indicating, determines that there is a rewrite target cell _{M R} (YES branched at step # 112), the rewrite target cell _{M R} of the second sub-bank SB2 indicated by the write address _{a C1 + 3} On the other hand, a write voltage for a rewrite operation is applied according to the write data D3 (step # 113). The comparison unit 17 of the device 1 of the present invention compares the value of the data DatC (data Q1) read in the immediately preceding first cycle with the value of the signal DatO (data D1), and writes the result as a result signal Comp. / Output to erasure unit 19 (step # 111). From time t14 to time t15 in FIG. 4, “Pass1” indicating that the values of the data Q1 and the data D1 match is output as the result signal Comp.

The subbank control unit 21 of the device 1 of the present invention operates as the operation for the first subbank SB1 in the immediately preceding second cycle in the next first cycle (corresponding to the first operation cycle, time t15 to time t16 in FIG. 4). since the signal WE is not outputted from the write / erase unit 19, a rewrite target cell M _R is determined that there is no. Further, the sub-bank control unit 21, the write address _{A C2 + 2} in the buffer 12, since the data D6 in the buffer 14 is stored, determines that there is a write target cell _{M R} (YES branched at step # 112), writing to programming target cell _{M R} of the first sub-bank SB1 represented by address _{a C2 + 2,} in accordance with the write data D6, applying a write voltage for writing operation (step # 113). The comparison unit 17 of the device 1 of the present invention compares the value of the data DatC (data Q4) read in the immediately preceding second cycle with the value of the signal DatO (data D4), and writes the result as a result signal Comp. / Output to erasure unit 19 (step # 111). From time t15 to time t16 in FIG. 4, “Pass4” indicating that the values of the data Q4 and the data D4 match is output as the result signal Comp.

In parallel, the sub-bank control unit 21 of the device 1 of the present invention, as the operation for the second sub-bank SB2, to rewrite target cell M _R of the second sub-bank SB2 indicated by the write address A _{C1 + 3,} write verification for rewrite operation A read operation for the operation is performed, and read data Q3 is output as data DatC (step # 122). Further, since the write / erase unit 19 of the device 1 of the present invention has a result signal Comp output from the comparison unit 17 in the immediately preceding second cycle from time t15 to time t16 in FIG. determines that the write operation to the write target cell M _R indicated by the write address a _C2 is successful, the output of such signals WE for sub-bank control unit 21 is not performed.

The sub-bank control unit 21 of the device 1 of the present invention is indicated by the write address AC2 _{+ 2} as the operation for the first sub-bank SB1 in the next second cycle (corresponding to the second operation cycle, time t16 to time t17 in FIG. 4). to programming target cell _{M R} of the first sub-bank SB1, it performs the read operation for the write verify operation, and outputs the read data Q6 as the data DatC (step # 122). Further, since the write / erase unit 19 of the device 1 of the present invention has a result signal Comp output from the comparison unit 17 in the immediately preceding first cycle from time t16 to time t17 in FIG. determines that the write operation to the write target cell M _R indicated by the write address a _C2 is successful, the output of such signals WE for sub-bank control unit 21 is not performed.

In parallel, since the signal WE is not output from the write / erase unit 19 in the immediately preceding first cycle as the operation for the second subbank SB2, the subbank control unit 21 of the device 1 of the present invention does not output the second subbank SB2. to determine not rewrite target cell M _R. Further, the sub-bank control unit 21, the address _{A C2 + 1} in the buffer 12, since the data D5 in the buffer 14 is stored, determines that there is a write target cell _{M R} (YES branched at step # 112), the write address to programming target cell _{M R} of the second sub-bank SB2 indicated by a _{C2 + 1,} in accordance with the write data D5, applying a write voltage for writing operation (step # 113). The comparison unit 17 of the device 1 of the present invention compares the value of the data DatC (data Q3) read in the immediately preceding first cycle with the value of the signal DatO (data D3), and writes the result as a result signal Comp. / Output to erasure unit 19 (step # 111). From time t16 to time t17 in FIG. 4, “Pass3” indicating that the values of the data Q3 and the data D3 match is output as the result signal Comp.

In the next first cycle (time t17 to time t18 in FIG. 4), the subbank control unit 21 of the device 1 of the present invention operates as a signal for the first subbank SB1 from the write / erase unit 19 in the immediately preceding second cycle. since the WE is not outputted, it is determined that there is no re-programming target cell M _R in the first sub-bank SB1. Further, the sub-bank control unit 21, since the address assigned to the buffer 12 to the sub-bank SB1 is not stored, the first sub-bank SB1 determines that there is no write target cell M _R (step # 112 is NO branch ). The comparison unit 17 of the device 1 of the present invention compares the value of the data DatC (data Q6) read in the immediately preceding second cycle with the value of the signal DatO (data D6), and writes the result as a result signal Comp. / Output to erasure unit 19 (step # 111). From time t17 to time t18 in FIG. 4, “Err6” indicating that the values of the data Q6 and the data D6 do not match is output as the result signal Comp.

In parallel, the sub-bank control unit 21 of the device 1 of the present invention, as the operation for the second sub-bank SB2, to programming target cell M _R indicated by the write address A _{C2 + 1,} performs the read operation for the write verify operation, read Data Q5 is output as data DatC (step # 122). Further, since the write / erase unit 19 of the device 1 of the present invention has a result signal Comp output from the comparison unit 17 in the immediately preceding second cycle from time t17 to time t18 in FIG. the write operation to rewrite target cell M _R is determined to have completed successfully as indicated by the write address a _{C1 + 3,} the output of such signals WE for sub-bank control unit 21 is not performed.

In the next second cycle (time t18 to time t19 in FIG. 4), the write / erase unit 19 of the device 1 of the present invention outputs the operation for the first subbank SB1 from the comparison unit 17 in the immediately preceding first cycle. Since the result signal Comp is “Err6”, it is determined that the result of the write verification is Fail, and the signal WE, the signal AddOw indicating the address AC2 _{+ 2,} and the signal DatOw indicating the data D6 are sent to the subbank control unit 21. Output. Further, the subbank control unit 21 determines whether or not the write operation for the first subbank SB1 is completed. As of time t18~ time t19 in FIG. 4, the write operation to the write target cell M _R represented by address A _{C2 + 2} has not been completed, the write operation for the first sub-bank SB1 is determined to not completed (step (No branch at # 123).

In parallel, the sub-bank control unit 21 of the device 1 of the present invention, as the operation for the second sub-bank SB2, to programming target cell M _R indicated by the write address A _{C2 + 3,} by applying a write voltage corresponding to the write data D7 The write operation is performed (YES branch at step # 112). The comparison unit 17 of the device 1 of the present invention compares the value of the data DatC (data Q5) read out in the previous first cycle with the value of the signal DatO (data D5), and writes the result as a result signal Comp. / Output to erasure unit 19 (step # 111). From time t18 to time t19 in FIG. 4, “Pass5” indicating that the values of the data Q5 and the data D5 match is output as the result signal Comp.

In the next first cycle (corresponding to the first operation cycle, time t19 to time t20 in FIG. 4), the subbank control unit 21 of the device 1 of the present invention writes data in the immediately preceding second cycle as an operation on the first subbank SB1. / since the signal WE is output from the erase unit 19 judges that there is a rewrite target cell _{M R} (YES branched at step # 112), with respect to rewriting target cell _{M R} indicated by the write address _{a C2 + 2} Then, a write voltage for the rewrite operation is applied according to the write data D6 (step # 113).

In parallel, the sub-bank control unit 21 of the device 1 of the present invention, as the operation for the second sub-bank SB2, to programming target cell M _R indicated by the write address A _{C2 + 3,} performs the read operation for the write verify operation, read Data Q7 is output as data DatC (step # 122). Further, since the write / erase unit 19 of the device 1 of the present invention has a result signal Comp output from the comparison unit 17 in the immediately preceding first cycle from time t19 to time t20 in FIG. write operation of the write target cell M _R indicated by the write address a _{C2 + 3} is determined to have ended normally, the output of such signals WE for sub-bank control unit 21 is not performed.

Sub-bank control unit 21 of the device 1 of the present invention, in the subsequent second cycle (time t20~ time t21 in FIG. 4), as the operation for the first sub-bank SB1, the rewrite target cell _{M R} indicated by the write address _{A C2 + 2} On the other hand, a read operation for a write verify operation with respect to the rewrite operation is performed, and read data Q6 is output as data DatC (step # 122). Further, since the result signal Comp is not output from the comparison unit 17 in the immediately preceding first cycle from the time t20 to the time t21 in FIG. Output of WE etc. is not performed.

In parallel, since the signal WE is not output from the write / erase unit 19 in the immediately preceding first cycle as the operation for the second subbank SB2, the subbank control unit 21 of the device 1 of the present invention does not output the second subbank SB2. to determine not rewrite target cell M _R. Further, the sub-bank control unit 21, since the write address is not stored in the buffer 12, the second sub-bank SB2 determined that there is no write target cell _{M R} (step # 112 in the NO branch). The comparison unit 17 of the device 1 of the present invention compares the value of the data DatC (data Q7) read in the immediately preceding first cycle with the value of the signal DatO (data D7), and writes the result as a result signal Comp. / Output to erasure unit 19 (step # 111). From time t20 to time t21 in FIG. 4, “Pass7” indicating that the values of the data Q7 and the data D7 match is output as the result signal Comp.

  In the next cycle (time t21 to time t22 in FIG. 4), the comparison unit 17 of the device 1 of the present invention operates as the operation for the first subbank SB1, and the value of the data DatC (data Q6) read in the immediately preceding second cycle. The value of the signal DatO (data D6) is compared, and the result is output to the write / erase unit 19 as a result signal Comp (step # 111). From time t21 to time t22 in FIG. 4, "Pass6" indicating that the values of the data Q6 and the data D6 match is output as the result signal Comp.

In parallel, the sub-bank control unit 21 of the device 1 of the present invention, as the operation for the second sub-bank SB2, the second cycle immediately before, no rewriting target cell M _R and the write target cell M _R is the second sub-bank B2 Therefore, it is determined whether or not the write operation for the second subbank SB2 is completed. At time t20~ time t21 in FIG. 4, since the result signal Comp outputted from the comparing unit 17 in the second cycle of the immediately preceding is a "PASS 7", for re-programming target cell _{M R} indicated by the write address _{A C2 + 3} determines that the writing operation has been normally completed, it is determined that the write operation to all of the write target cell M _R of the second sub-bank SB2 is complete (YES branch at step # 123), the write operation to the second sub-bank SB2 Exit.

Subsequently, the write / erase unit 19 of the device 1 of the present invention operates as the first subbank SB1, and the result signal Comp output from the comparison unit 17 at time t21 to time t22 is “Pass6”. determines that the write operation to the write target cell M _R indicated by a _{C2 + 2} is successful, the output of such signals WE for sub-bank control unit 21 is not performed. Subsequently, sub-bank control unit 21 of the present invention device 1 determines that there is no re-programming target cell M _R in the first sub-bank SB1 since the signal WE is not output, further, the write address is stored in the buffer 12 since not, determines that the first sub-bank SB1 no programming target cell _{M R} (nO branched at step # 112). Further, the sub-bank control unit 21 determines that the time t22~ time t21 in FIG. 4, the write operation for all the write target cell _{M R} of the first sub-bank SB1 is completed (YES branched at step # 123), The write operation for the first subbank SB1 is terminated. Thereby, the write operation to the first subbank SB1 and the second subbank SB2 of the memory cell array is completed.

  As can be seen from FIG. 4, in the present embodiment, the write operation and the write verify operation for the second subbank SB2 are completed within the period of the write operation and the write verify operation for the first subbank SB1, and the first subbank SB1 and Compared with the case where the write operation and the write verify operation are sequentially performed on the second subbank SB2, the time required for the write operation and the write verify operation is reduced by the time of the write operation and the write verify operation on the second subbank SB2 in the entire memory cell array. ing.

Second Embodiment
A second embodiment of the device 1 of the present invention will be described with reference to FIGS. In the present embodiment, a case will be described in which the configuration of the subbanks of the memory cell array is different from that of the first embodiment.

  Here, FIG. 5 shows a schematic configuration example of the inventive device 1 of the present embodiment. As shown in FIG. 5, the inventive device 1 of the present embodiment includes a memory cell array including four subbanks, a first subbank SB1 to a fourth subbank SB4, and words of the first subbank SB1 and the third subbank SB3. A first row decoder DR1 that applies a voltage to the line, a second row decoder DR2 that applies a voltage to the word lines of the second subbank SB2 and the fourth subbank SB4, and a first subbank SB1 based on an instruction from the control circuit 10 described later. From the first column decoder DC1 for applying a voltage to the bit line of the second sub-bank SB2, and a second column decoder DC2 for applying a voltage to the bit line of the second subbank SB2 based on an instruction from the control circuit 10 to be described later. A third column decoder DC3 for applying a voltage to the bit line of the third sub-bank SB3 based on the instruction, a control circuit to be described later A fourth column decoder DC4 that applies a voltage to the bit line of the fourth subbank SB4 based on an instruction from 0, and a control circuit 10 that controls each operation including a write operation and a write verify operation are configured. Yes. Also, the inventive device 1 of the present embodiment has a burst function for continuously executing a plurality of write commands, as in the first embodiment.

  The configurations of the first subbank SB1, the second subbank SB2, the first column decoder DC1, and the second column decoder DC2 are the same as those in the first embodiment. The configurations of the third subbank SB3 and the fourth subbank SB4 are the same as the configurations of the first subbank SB1 and the second subbank SB2 of the first embodiment. In the present embodiment, the first subbank SB1 and the third subbank SB3 constitute one subbank pair, and a common first row decoder DR1 is provided. In addition, the second subbank SB2 and the fourth subbank SB4 constitute one subbank pair, and a common second row decoder DR2 is provided.

In the present embodiment, as shown in FIG. 5, addresses of multiples of 4 (A _C1 , A _C2 ,...) Are assigned to the first subbank SB1 and addresses of multiples of 4 _{+ 1} (A _{C1 + 1} ,. A _{C2 + 1} ,... Is a multiple of 4 _{+ 2} address (A _{C1 + 2} , A _{C2 + 2} ,...) In the third subbank SB3, and a multiple of 4 _{+ 3} address (A _{C1 + 3} , A _{C2 + 3} ) is in the fourth subbank SB4. ,...) Are assigned respectively.

  Although not shown, the control circuit 10 receives an externally input command and controls an instruction control unit 11 for controlling each circuit unit, a buffer 12 for storing an externally input address signal, the first subbank SB1 or the second subbank SB2. An output control unit 13 that performs output control of the output data that has been output, a buffer 14 that stores output data and externally input externally input data, and a row address that stores a row address of address signals stored in the buffer 12 The buffer 15, the read unit 16 for controlling the read operation, the comparison unit 17 for comparing the output data and the write data, the buffer 18 for storing the address signal AddCr from the read unit 16, the control of the write operation, the write verify operation and the erase operation Write / erase unit 19 for performing the operation, operation switching control unit 20, and It is configured to include a sub-bank control unit 21.

  Hereinafter, the processing operation of the inventive device 1 of the present embodiment will be described with reference to FIG. Here, FIG. 6 shows a timing chart of the write operation and the write verify operation in the present embodiment.

  In the present embodiment, as shown in FIG. 6, four cycles are sequentially repeated. In the first cycle, a write operation for the first subbank SB1 and a read operation for the write verify operation for the third subbank SB3 are performed. Do. In the second cycle, a write operation for the second subbank SB2 and a read operation for the write verify operation for the fourth subbank SB4 are performed. In the third cycle, a read operation for a write verify operation for the first subbank SB1 and a write operation for the third subbank SB3 are performed. In the fourth cycle, a read operation for a write verify operation for the second subbank SB2 and a write operation for the fourth subbank SB4 are performed.

  Then, the rewrite operation for the first subbank SB1 is performed in the second cycle, and the read operation for the write verify operation for the rewrite operation is performed in the fourth cycle. Similarly, the rewrite operation for the third subbank SB3 is performed in the fourth cycle, and the read operation for the write verify operation for the rewrite operation is performed in the second cycle. The rewrite operation for the second subbank SB2 is performed in the third cycle, and the read operation for the write verify operation for the rewrite operation is performed in the first cycle. The rewrite operation for the fourth subbank SB4 is performed in the first cycle, and the read operation for the write verify operation for the rewrite operation is performed in the third cycle.

  As described above, in FIG. 6, the rewrite process and the read operation for the write verify operation for the rewrite process are performed in an intermediate cycle between the cycles for performing the write process and the read operation for the write verify operation. Therefore, it is possible to reduce the time required for the write operation and the write verify operation in the entire memory cell array.

<Another embodiment>
<1> In the first embodiment, the case where the memory cell array includes two subbanks has been described. In the second embodiment, the case where the memory cell array includes four subbanks has been described. However, the present invention is not limited to this. The memory cell array may include more subbanks as long as the number of subbanks is an even number. In this case, a common row decoder is configured for each subbank pair, and a column decoder is configured for each subbank.

<2> In the above first and second embodiments, for purposes of explanation, all the memory cells M _R of the first sub-bank SB1 and the second sub-bank SB2 is erased state, has been described a case where writing to the write state However, it is not limited to this.

For example, in an RRAM that can simultaneously perform a write operation and an erase operation, such as an RRAM that switches load resistance characteristics of a load circuit described in Patent Document 2 between a write operation and an erase operation, in the first operation cycle, On the other hand, at least one of the erase operation for erasing target cell M _R and the write operation to the write target cell M _R, and, for the read operation and the erasing target cell M _R for write verify operation for the write target cell M _R of the second sub-bank configured to perform at least one read operation for the erase verify operation, in the second operation cycle, the read operation erased cell for write verify operation for the write target cell M _R of the first sub-bank M for the erase verify operation with respect to _R On the other hand, at least one of viewing out operation, and, at least one of a read operation for the erase verify operation for the read operation and the erasing target cell M _R for write verify operation for the write target cell M _R of the second sub-bank It may be configured to execute.

<3> In the first and second embodiments, the write time required for the write operation and the read time required for the read operation are substantially the same, and other write verify operations after the read operation are performed in the next cycle of the read operation. Although the case where it performs is demonstrated, it is not restricted to this. When the read time is considerably shorter than the write time, the operation after the read operation of the write verify operation for the other subbank may be advanced in the same cycle as the write operation for one subbank.

<4> In the first and second embodiments described above, the case where one write data has a 1-bit configuration has been described for the sake of explanation. However, the present invention is not limited to this. In the case of a multi-bit configuration, for example, as shown in FIG. 13, a subbank pair may be provided for each corresponding bit, that is, a subbank pair having the same number as the data length of write data may be provided. In FIG. 13, j is the data length-1 of the write data.

  In addition, for example, an address corresponding to each bit of the write data may be configured to correspond to the write data having a multi-bit configuration by adding (bit ordinal −1) to the head address. . In this case, when the burst function is provided, the start address of the column address of each write data to be automatically generated is set to the column address specified by the write command (data length of write data × (ordinal number of write data− 1)) is added and set.

Schematic partial block diagram showing a schematic configuration example of a nonvolatile semiconductor memory device according to the present invention 1 is a schematic partial block diagram showing a schematic configuration example of a memory cell array constituting a nonvolatile semiconductor memory device according to the present invention. 7 is a flowchart showing an operation procedure of a write operation and a write verify operation of the nonvolatile semiconductor memory device according to the present invention. Timing chart showing the operation of the write operation and the write verify operation of the nonvolatile semiconductor memory device according to the present invention Schematic partial block diagram showing a schematic configuration example in the second embodiment of the nonvolatile semiconductor memory device according to the present invention. Timing chart showing the operation of the write operation and the write verify operation in the second embodiment of the nonvolatile semiconductor memory device according to the present invention. Schematic partial block diagram showing a schematic configuration example of a memory cell array configured in another embodiment of a nonvolatile semiconductor memory device according to the present invention. Schematic partial circuit diagram showing a schematic configuration example of a memory cell array of an ETOX type flash memory Schematic partial block diagram showing a schematic configuration example of an ETOX cell constituting an ETOX type flash memory Schematic partial circuit diagram showing a schematic configuration example of a memory cell array of RRAM Schematic partial block diagram showing a schematic configuration example of a variable resistance element constituting an RRAM memory cell Schematic partial sectional view showing a schematic configuration example of a memory cell of RRAM Schematic partial block diagram showing a schematic configuration example in another embodiment of a nonvolatile semiconductor memory device according to the present invention.

DESCRIPTION OF SYMBOLS 1 Nonvolatile semiconductor memory device 10 concerning this invention Control circuit 11 Instruction control part 12 Buffer 13 Output control part 14 Buffer 15 Row address buffer 16 Reading part 17 Comparison part 18 Buffer 19 Writing / erasing part 20 Operation switching control part 21 Subbank control Part 101 Semiconductor substrate 102 Drain 103 Source 104 Gate insulating film 105 Floating gate 106 Interlayer insulating film 107 Control gate 201 Semiconductor substrate 202 Element isolation region 203 Gate insulating film 204 Gate electrode 205 Drain diffusion region 206 Source diffusion region 207 First interlayer insulating film 208 Contact electrode 209 Second interlayer insulating film 211 Lower electrode 211a Ti film 211b TiN film 212 Variable resistor 213 Upper electrode 214 Contact electrode 215 Source line wiring 216 Contact Electrode 217 bit line wiring 218 third interlayer insulating film 219 fourth interlayer insulating film 220 surface protective film DC1 first column decoder DC2 second column decoder DC3 third column decoder DC4 fourth column decoder DR row decoder DR1 first row decoder DR2 Second row decoder SB1 First subbank SB2 Second subbank SB3 Third subbank SB4 Fourth subbank BL Bit line SL Source line WL Word line A Memory cell array T Transistor R Variable resistance element

Claims (9)

A variable resistance element and a transistor whose electric resistance reversibly changes by applying a voltage pulse, a plurality of nonvolatile memory cells that store information according to a resistance state of the variable resistance element, and a plurality of the memory cells A first sub-bank arranged in a matrix, wherein the first terminals of the memory cells in the same row are connected to a common word line, and the second terminals of the memory cells in the same column are connected to a common bit line; A memory cell array comprising a second subbank having the same configuration as the first subbank;
A row decoder that is provided in common to the first subbank and the second subbank and applies a voltage simultaneously to the corresponding word lines of the first subbank and the second subbank;
A first column decoder for applying a voltage to the bit lines of the first subbank;
A second column decoder for applying a voltage to the bit lines of the second sub-bank;
A write operation on the memory cell array, a write verify operation, a rewrite operation on the memory cell determined to have not been performed normally in the write verify operation, a write verify operation on the rewrite operation, an erase operation, An erase verify operation, a re-erase operation for the memory cell that is determined to have not been normally performed in the erase verify operation, and a control circuit that controls the erase verify operation for the re-erase operation. ,
A first operation cycle in which the control circuit performs the write operation or the erase operation for the first subbank and the read operation for the write verify operation or the read operation for the erase verify operation for the second subbank. When,
The read operation for the write verify operation for the first subbank or the read operation for the erase verify operation and the second operation cycle for performing the write operation or the erase operation for the second subbank are alternately performed. Run to
The non-volatile semiconductor memory device, wherein the first operation cycle and the second operation cycle have the same length regardless of the type of target operation. In the first operation cycle, the control circuit performs a read operation for the write verify operation for the rewrite operation or the reerase operation for the first subbank and the rewrite operation for the second subbank, or A read operation for the erase verify operation with respect to the re-erase operation is performed,
In the second operation cycle, the read operation for the write verify operation for the rewrite operation for the first subbank or the read operation for the erase verify operation for the reerase operation, and for the second subbank The nonvolatile semiconductor memory device according to claim 1, wherein the rewriting operation or the reerasing operation is performed.   The control circuit is configured to perform the write verify on the write operation, the write verify operation, the rewrite operation, and the rewrite operation on any single bit or any single byte in the first subbank and the second subbank. 3. The nonvolatile memory according to claim 1, wherein the erase verify operation for the operation, the erase operation, the erase verify operation, the re-erase operation, and the re-erase operation is controllable. Semiconductor memory device.   The memory cell array is configured such that the write operation and the erase operation can be performed simultaneously in the first subbank, and the write operation and the erase operation can be performed simultaneously in the second subbank. The nonvolatile semiconductor memory device according to claim 1, wherein the nonvolatile semiconductor memory device is a memory device. The control circuit includes a burst function that performs the write operation and the write verify operation on a unit memory cell group including a predetermined number of memory cells in succession according to a burst length by one write command. In the write operation by function, from the head address of the unit memory cell group specified by the write command, the subsequent address is automatically distributed and set to the first subbank and the second subbank,
5. The nonvolatile semiconductor memory according to claim 1, wherein the write operation and the write verify operation by the burst function are completed in the first operation cycle or the second operation cycle. 6. apparatus. The control circuit has a burst function that performs the erase operation and the erase verify operation on a unit memory cell group composed of a predetermined number of memory cells in succession according to a burst length by one erase command, In the erasing operation by function, from the head address of the unit memory cell group specified by the erasing command, the subsequent address is automatically assigned to the first subbank and the second subbank, and set.
6. The nonvolatile semiconductor memory according to claim 1, wherein the write operation and the write verify operation by the burst function are completed in the first operation cycle or the second operation cycle. 7. apparatus. A variable resistance element and a transistor whose electric resistance reversibly changes by applying a voltage pulse, a plurality of nonvolatile memory cells that store information according to a resistance state of the variable resistance element, and a plurality of the memory cells A first sub-bank arranged in a matrix, wherein the first terminals of the memory cells in the same row are connected to a common word line, and the second terminals of the memory cells in the same column are connected to a common bit line; A memory cell array comprising a second subbank having the same configuration as the first subbank;
A row decoder that is provided in common to the first subbank and the second subbank and applies a voltage simultaneously to the corresponding word lines of the first subbank and the second subbank;
A first column decoder for applying a voltage to the bit lines of the first subbank;
A second column decoder for applying a voltage to the bit lines of the second sub-bank;
A write operation on the memory cell array, a write verify operation, a rewrite operation on the memory cell determined to have not been performed normally in the write verify operation, a write verify operation on the rewrite operation, an erase operation, An erase verify operation, a re-erase operation for the memory cell that is determined to have not been normally performed in the erase verify operation, and a control circuit that controls the erase verify operation for the re-erase operation. A method for controlling a non-volatile semiconductor memory device,
A first operation step of performing the write operation or the erase operation on the first subbank and the read operation for the write verify operation or the read operation for the erase verify operation on the second subbank;
The read operation for the write verify operation for the first subbank or the read operation for the erase verify operation and the second operation step for performing the write operation or the erase operation for the second subbank are alternately performed. Run to
The method for controlling a nonvolatile semiconductor memory device, wherein the first operation step and the second operation step have the same length regardless of the type of target operation.   The control circuit is configured to perform the write verify on the write operation, the write verify operation, the rewrite operation, and the rewrite operation on any single bit or any single byte in the first subbank and the second subbank. The nonvolatile semiconductor memory according to claim 7, wherein the erase verify operation for the operation, the erase operation, the erase verify operation, the re-erase operation, and the re-erase operation is controllable. Control method of the device. The memory cell array is configured such that the write operation and the erase operation can be performed simultaneously in the first subbank, and the write operation and the erase operation can be performed simultaneously in the second subbank. 9. The method for controlling a nonvolatile semiconductor memory device according to claim 7, wherein:

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