JP5039099B2 - Nonvolatile semiconductor memory device - Google Patents

Description

  The present invention relates to a data writing technique for a nonvolatile memory, and more particularly to a technique that is effective when applied to a reduction in variation in writing characteristics in a MONOS (Metal Oxide Nitride Semiconductor) type memory cell.

  As an electrically rewritable nonvolatile memory, for example, a flash memory using a floating gate type memory cell is widely known. However, various MONOS memory cells have been proposed due to market demands such as low power consumption and high-speed data writing.

  For example, in a MONOS type memory cell, a voltage (for example, about 0.77 V) slightly higher than the threshold value of the word gate (control gate) is applied to the word line in order to limit the data write current to about 10 μA. (See Patent Document 1). That is, the data write current is controlled by the word gate voltage. Note that the bit line voltage at the time of data writing is fixed to about 0V.

  Moreover, although it is a floating gate type memory cell, there is one in which variation in write characteristics is suppressed (see Patent Document 2).

  In this case, local bit lines are connected to two diffusion layers of an AG-AND (Assist Gate AND) type memory cell, and a switch is connected to each local bit line, global bit line, and common source line. Through.

  In the data write, the parasitic capacity of the local bit line on the memory gate side from the global bit line is charged with about 4V, and the global bit line and the local bit line on the memory gate side are separated by a switch.

  Thereafter, the local bit line on the assist gate side is connected to the common source line, and the charge accumulated in the local bit line on the memory gate side is caused to flow to the memory cell, thereby generating SSI (Source Side channel hot injection). Write to a 1-bit memory cell.

  As a result, even if the threshold voltage of the assist gate MOS transistor varies, the charge used for data writing is constant, so that variation in data writing characteristics is suppressed.

JP 2001-148434 A JP 2002-197876 A

  However, the present inventors have found that the additional information writing technique in the semiconductor integrated circuit device as described above has the following problems.

  When controlling the voltage value of a word gate (hereinafter referred to as a select gate) in order to control the data write current of a MONOS type memory cell, the voltage value becomes a voltage value close to the threshold voltage of the select gate MOS transistor. .

  Therefore, the write current depends on the threshold voltage of the select gate MOS transistor. Since the select gate MOS transistor is a part of the memory cell, the gate length Lg is almost the minimum dimension, and the variation of the threshold voltage with respect to the manufacturing variation is large. For this reason, there is a problem that the variation in the write current of each memory cell in the memory mat becomes large, and the variation in the threshold value of the memory gate at the time of writing varies.

  Further, when suppressing variation in write characteristics in the floating gate type memory cell, the local bit line can be separated from the global bit line by a switch, and the local source line can be separated from the common source line by the switch.

  Further, since the number of memory cells connected to the local bit line and the local source line is relatively large, the wiring capacity of the local bit line and the local source line is also relatively large. A relatively large amount of charge stored can be used. Further, since the amount of charge is substantially constant, variation in write characteristics can be suppressed.

  However, in the case of a small-capacity memory, providing a switch on the local source line connected to the diffusion layer region (source terminal) on the memory gate side of each memory cell increases the layout area due to an increase in overhead. The local source line is directly connected to the common source line without providing a switch.

  Therefore, since the parasitic capacitance of the common source line is connected to a large number of memory cells, the charge accumulated in the parasitic capacitance of the wiring due to the write data is not necessarily evenly distributed to the memory cells, and variation in write characteristics can be suppressed. It will not be possible.

  An object of the present invention is to provide a nonvolatile memory capable of realizing high-speed data writing and low power consumption by greatly reducing variations in threshold voltage fluctuation amount of nonvolatile memory cells during data writing. A semiconductor memory device and a semiconductor integrated circuit device are provided.

  The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

Of the inventions disclosed in the present application, the outline of typical ones will be briefly described as follows.
(1) The nonvolatile semiconductor memory device of the present invention is a current supply control transistor connected in series between the voltage source and the nonvolatile memory cell, or connected in series between the nonvolatile memory cell and the reference potential. Any one of the current absorption control transistors is provided, and the current supply control transistor or the current absorption control transistor flows in the nonvolatile memory cell during data writing by operating in the current saturation region in the current-voltage characteristic. The current is controlled.
(2) Further, the nonvolatile semiconductor memory device of the present invention includes a current supply control transistor connected in series between the voltage source and the nonvolatile memory cell, and a series connection between the nonvolatile memory cell and the reference potential. The current supply control transistor and the current absorption control transistor are operated in a current saturation region in the current-voltage characteristics, thereby allowing a current flowing in the nonvolatile memory cell during data writing. Is to control.

Moreover, the outline | summary of the other invention of this application is shown briefly.
(3) Furthermore, the present invention has a nonvolatile storage unit and a central processing unit, and the central processing unit can execute a predetermined process and give an operation instruction to the nonvolatile storage unit. The nonvolatile memory unit is a semiconductor integrated circuit device having a plurality of nonvolatile memory cells for storing information, and the nonvolatile memory unit is a current supply connected in series between a voltage source and the nonvolatile memory cells. Either a control transistor or a current absorption control transistor connected in series between a nonvolatile memory cell and a reference potential is provided. The current supply control transistor or the current absorption control transistor has a current-voltage characteristic. By operating in the current saturation region, the current flowing through the nonvolatile memory cell during data writing is controlled.
(4) Moreover, this invention has a non-volatile memory | storage part and a central processing unit, This central processing unit can perform a predetermined | prescribed process, and can perform an operation instruction to a non-volatile memory | storage part, The nonvolatile memory unit is a semiconductor integrated circuit device having a plurality of nonvolatile memory cells for storing information, and the nonvolatile memory unit is a current connected in series between a voltage source and a nonvolatile memory cell. A supply control transistor, and a current absorption control transistor connected in series between the nonvolatile memory cell and the reference potential, and the current supply control transistor and the current absorption control transistor include a current in a current-voltage characteristic. By operating in the saturation region, the current flowing in the nonvolatile memory cell is controlled at the time of data writing.

  Among the inventions disclosed in the present application, effects obtained by typical ones will be briefly described as follows.

  (1) By controlling the value of the current flowing through the nonvolatile memory cell at the time of data writing, variation in the threshold fluctuation amount of the nonvolatile memory cell can be greatly reduced.

  (2) Further, according to the above (1), current consumption at the time of writing can be reduced, so that the power circuit and the like can be miniaturized and the speed of the writing operation can be realized.

  (3) Further, according to the above (1) and (2), it is possible to realize a reduction in size and performance of a nonvolatile semiconductor memory device and a semiconductor integrated circuit device using the same.

1 is a block diagram of a flash memory according to an embodiment of the present invention. FIG. 2 is a configuration diagram of a write circuit, a current trimming circuit, and a flash memory array provided in the flash memory of FIG. 1. FIG. 3 is an explanatory diagram of electrical characteristics of a constant current source transistor provided in the write circuit of FIG. 2. FIG. 2 is an explanatory diagram of write / erase / read operations in a memory cell provided in the flash memory of FIG. 1. 2 is a timing chart of a write operation in the flash memory of FIG. 1. FIG. 2 is an explanatory diagram showing a configuration example in which a flash memory array provided in the flash memory of FIG. 1 has a hierarchical structure. FIG. 6 is an explanatory diagram showing another configuration example in which the flash memory array provided in the flash memory of FIG. 1 has a hierarchical structure. FIG. 8 is a timing chart when data is written to a memory cell provided in the flash memory array of FIG. 7. FIG. 1 is a block diagram of a single-chip microcomputer with built-in flash memory according to an embodiment of the present invention. FIG. FIG. 7 is a configuration diagram of another embodiment of a write circuit, a current trimming circuit, and a flash memory array provided in the flash memory of FIG. 1. 11 is a timing chart of a write operation in the flash memory of FIG. 10. FIG. 11 is a configuration diagram of a CG driver in the flash memory array of FIG. 10.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiment, and the repetitive description thereof will be omitted.

  1 is a block diagram of a flash memory according to an embodiment of the present invention, FIG. 2 is a configuration diagram of a write circuit, a current trimming circuit, and a flash memory array provided in the flash memory of FIG. 1, and FIG. FIG. 4 is an explanatory diagram of electrical characteristics of a constant current source transistor provided in the write circuit of FIG. 2, and FIG. 4 is an explanatory diagram of write / erase / read operations in a memory cell provided in the flash memory of FIG. FIG. 5 is a timing chart of the write operation in the flash memory of FIG. 1, FIG. 6 is an explanatory diagram showing a configuration example in which the flash memory array provided in the flash memory of FIG. 1 has a hierarchical structure, and FIG. FIG. 8 is an explanatory diagram showing another configuration example in which the flash memory array provided in the flash memory of FIG. 1 has a hierarchical structure, and FIG. A timing chart for writing data into a memory cell provided in Yumemoriarei, FIG. 9 is a block diagram of a microcomputer built-in flash memory single chip according to an embodiment of the present invention.

  In the present embodiment, a flash memory (nonvolatile semiconductor memory device) 1 includes a control circuit 2, an input / output circuit 3, an address buffer 4, a row decoder 5, a column decoder 6, and a verify sense amplifier circuit, as shown in FIG. 7, a high-speed read sense amplifier circuit 8, a write circuit 9, a flash memory array 10, a power supply circuit 11, and the like.

  The control circuit 2 temporarily stores a control signal input from a host such as a connected microcomputer, and controls the operation logic. Various data such as data read from or written to the flash memory array 10 and program data are input to and output from the input / output circuit 3. The address buffer 4 temporarily stores an address input from the outside.

  A row decoder 5 and a column decoder 6 are connected to the address buffer 4. The row decoder 5 performs decoding based on the column (row) address output from the address buffer 4, and the column decoder 6 performs decoding based on the row (column) address output from the address buffer 4.

  The verify sense amplifier circuit 7 is a sense amplifier for erase / write verify, and the high-speed read sense amplifier circuit 8 is a read sense amplifier used at the time of data reading. The write circuit 9 latches write data input via the input / output circuit 3 and controls data writing.

  In the flash memory array 10, memory cells, which are the smallest storage unit, are regularly arranged in an array. The memory cells provided in the flash memory array 10 can electrically erase or write data, and do not require a power source for storing data.

  The power supply circuit 11 includes a voltage generation circuit that generates various voltages used at the time of data writing, erasing, and verification, and a current trimming circuit (trimming unit) 11a that generates an arbitrary voltage value and supplies the voltage to the writing circuit 9. Consists of

  The configuration of the write circuit 9 and the current trimming circuit 11a will be described with reference to FIG. The write circuit 9 is connected to each of the bit lines BL0 to BLn. Here, the configuration of the write circuit 9 connected to the bit line BL0 will be described, but the write circuit 9 connected to the other bit lines BL1 to BLn also has the same configuration.

  The write circuit 9 includes a constant current source transistor (current absorption control transistor) 12, a latch switch 13, a negative AND circuit 14, and a write latch 15. The constant current source transistor 12 and the latch switch 13 are made of, for example, an N-channel MOS (Metal Oxide Semiconductor).

  A bit line BL0 is connected to one of connection portions of the constant current source transistor 12 and the latch switch 13. Memory cells (nonvolatile memory cells) MM00 to MMn0 are connected to the bit line BL0.

  The selection gate 102 (FIG. 4) and the memory gate 100 (FIG. 4) of the memory cells MM00 to MMn0 are commonly connected by the selection gate line CG0 and the memory gate line MG0, respectively, and the source 103 (FIG. 4) is Commonly connected by the source line SL0.

  A current trimming circuit 11 a is connected to the gate of the constant current source transistor 12, and an output portion of the NAND circuit 14 is connected to the other connection portion of the constant current source transistor 12. The constant current source transistor 12 is a constant current source that makes the write current constant.

  A latch switch signal is connected to the gate of the latch switch 13 so that the latch switch signal is input. The other connection portion of the latch switch 13 is connected to the input portion of the write latch 15.

  The latch switch 13 is turned on only when write data is input, and is turned off otherwise to protect the write data. The write latch 15 is a circuit that accumulates write data.

  The other input section of the NAND circuit 14 is connected to the output section of the write latch 15, and the other input section of the NAND circuit 14 is connected so that a write pulse is input. .

  Here, the constant current source transistor 12 will be described.

  FIG. 3A is a diagram showing the channel length dependence of the threshold voltage of the constant current source transistor 12. In this figure, the vertical axis represents the threshold voltage of the constant current source transistor 12, and the horizontal axis represents the channel length.

  The channel length of the constant current source transistor 12 is, for example, twice or more longer than the channel length of the selection gate of the memory cell, and the variation amount of the threshold voltage is smaller than the variation amount of the channel length. .

  FIG. 3B shows the channel width dependence of the threshold voltage in the constant current source transistor 12. In this figure, the vertical axis represents the threshold voltage of the constant current source transistor 12, and the horizontal axis represents the channel width.

  The channel width of the constant current source transistor 12 is, for example, twice or more longer than the channel width of the selection gate of the memory cell, and the variation amount of the threshold voltage is smaller than the variation amount of the channel width.

  Further, FIG. 3C is a diagram showing the drain-source voltage dependence of the drain-source current. In this figure, the vertical axis represents the drain-source current, and the horizontal axis represents the drain-source voltage.

  As shown in the figure, the operation region of the constant current source transistor 12 is a region where the fluctuation amount of the drain-source current is smaller than the fluctuation amount of the drain-source voltage.

  In addition, the current trimming circuit 11 a includes a trimming register (trimming information storage unit) 16 and a decoder circuit 17. The current trimming information stored in the trimming register 16 is converted into a predetermined voltage value by the decoder circuit 17 and applied to the gate of the constant current source transistor 12. The trimming register 16 stores not only current trimming information but also other trimming information.

  Further, the configuration of the memory cell MM and data writing / erasing / reading will be described with reference to FIG.

  As shown in FIG. 4, the memory cell MM is composed of two transistors, a selection MOS transistor and a charge storage MOS transistor. In the memory cell MM, a diffusion layer including a source 103 and a drain 104 is formed.

  A charge storage layer 101 and a memory gate 100 are formed in a stacked structure on a semiconductor substrate 105 between the source 103 and the drain 104 via a gate oxide film, and a selection gate 102 is formed on the adjacent side. It has a configuration. The charge storage layer 101 includes a nitride film, a floating gate, and the like.

  When data is written in the memory cell MM, as shown in FIG. 4A, for example, about 8 V is applied to the memory gate 100, about 5 V is applied to the source 103, about 0 V is applied to the semiconductor substrate 105, the selection gate 102, A voltage is applied to the drain 104 so that a current of, for example, about 1 μA flows between the drain 104 and the source 103. At this time, source side injection occurs, and electrons are stored in the charge storage layer 101. Therefore, the memory cell current at the time of reading is reduced.

  When erasing data in the memory cell MM, as shown in FIG. 4B, for example, the memory gate 100 has a voltage of about 10V, the selection gate 102 has a voltage of about 1.5V, the source 103, the drain 104, and the semiconductor substrate 105. When about 0 V is applied to each, the electrons stored in the charge storage layer 101 are emitted to the memory gate 100, and the current of the memory cell MM during reading increases.

  In FIG. 4B, a voltage of about 8 V is applied to the memory gate 100, but the voltage applied to the memory gate 100 is not limited to this.

  When reading data from the memory cell MM, as shown in FIG. 4C, for example, the select gate 102 has a voltage of about 1.5 V, the drain 104 has a voltage of about 1.0 V, the memory gate 100, the source 103 and the semiconductor substrate 105 have About 0 V is applied, and the magnitude of the memory cell current is determined by a sense amplifier.

  In FIG. 4C, a voltage of about 0 V is applied to the memory gate 100, but the voltage applied to the memory gate 100 is not limited to this.

  Next, the operation of the flash memory 1 in the present embodiment will be described.

  First, the operation of the write circuit 9 when writing data to the memory cell MM00 will be described.

  First, for example, about 8 V is applied to the memory gate line MG0, about 5 V is applied to the source line SL0, and about 1.5 V is applied to the selection gate line CG0.

  At this time, in the write circuit 9, the write pulse 0 and the output of the write latch 15 are Hi signals, and the output of the NAND circuit 14 is Lo signal. At this time, a constant current of about 1 μA, for example, flows through the constant current source transistor 12, and the bit line BL0 is pulled out with a constant current of about 1 μA, and a current flows through the memory cell MM00.

  In the non-written memory cell MM01, about 8V is applied to the memory gate, about 5V is applied to the source, and about 1.5V is applied to the selection gate. In the write circuit 9 connected to the memory cell MM01, the write pulse 1 or the output of the write latch 15 is a Lo signal, and the output of the NAND circuit 14 is a Hi signal.

  If the voltage of the Hi signal is about 1.5V, for example, the write circuit 9 supplies about 1.5V to the bit line BL1, the selection MOS transistor of the memory cell MM01 is not turned on, and writing does not occur.

  In the non-written memory cells MMn0 and MMn1, no voltage is applied to the memory gate 100, the source 103, and the selection gate 102, so that no writing occurs.

  In the present invention, the write current is not controlled by the selection gate voltage of the memory cell, but the write current is controlled by connecting the constant current source of the constant current source transistor 12 to the bit line. Further, the memory cell applicable to the present invention is not limited to the memory cell shown in FIG. 4, and any memory cell may be used as long as it is a memory cell connected in parallel to the bit line.

  Further, the write operation in the flash memory 1 will be described with reference to the timing chart of FIG.

  Here, FIG. 5 shows signal timings in the selection gate line CG0, the memory gate line MG0, the source line SL0, and the bit lines BL0 and BL1, respectively, from the top to the bottom.

  For example, when data is written to the memory cell MM00, first, about 1.5 V is applied to the selection gate line CG0. Then, about 5 V is applied to the source line SL0 and about 1.5 V is applied to the bit lines BL0 and BL1, and then about 8 V is applied to the memory gate line MG0.

  The reason why the bit lines BL0 and BL1 are applied to 1.5 V before 8 V is applied to the memory gate line MG0 is to prevent write disturb that occurs before the write conditions are satisfied.

  When the voltage values of the selection gate line CG0, the source line SL0, and the memory gate line MG0 satisfy the write condition, the write circuit 9 is connected to a constant current source for an optimum write time, and the bit line BL0 is pulled out with a constant current. A current is passed through the cell MM00.

  In FIG. 2, data is not written to the memory cell MM01. However, when data is written to the memory cell MM01, as shown in FIG. 5, after writing the memory cell MM00, the optimum write time in the write circuit 9 Only the constant current source is connected, the bit line BL1 is pulled out with a constant current, and a current flows through the memory cell MM01. That is, the write pulse is applied for an optimum time in the order of the bit lines BL.

  Further, the selection gate line CGn, the source line SLn, and the memory gate line MGn connected to the non-written memory cells MMn0 and MMn1 are 0 V during this period.

  The operation timing of the write circuit 9 is not limited to that shown in FIG. 5. For example, the write circuit 9 of the memory cell MM00 and the write circuit 9 of the memory cell MM01 are simultaneously operated to set the bit lines BL0 and BL1 to a constant current. You may make it pull out with.

  FIG. 6 is a diagram illustrating a configuration example in which the flash memory array 10 provided in the flash memory 1 has a hierarchical structure. Here, the circuit configurations of the write circuit 9 and the current trimming circuit 11a are the same as those in FIG.

  The memory cells MM (FIG. 4) are regularly arranged in an array. The selection gate 102, the memory gate 100, and the source 103 of the memory cell MM are the selection gate lines CG0 to CGn, the memory gate lines MG0 to MGn, and the source line. Each of them is commonly connected by SL0 to SLn.

  The drains 104 of the memory cells MM are commonly connected by the sub bit line LBL, and are connected to the main bit line MBL via the hierarchical MOS transistor ZM.

  A write circuit 9 is connected to each main bit line MBL, and a hierarchical gate line Z0 is connected to the gate of the hierarchical MOS transistor ZM.

  When data is written to the memory cell MM00, for example, about 8V is applied to the memory gate line MG0, for example, about 5V is applied to the source line SL0, for example, about 1.5V is applied to the selection gate line CG0, and to 1.5V to the hierarchical gate line Z0. Apply degree. In the write circuit 9, the write pulse 0 and the output of the write latch 15 are Hi signals, and the output of the NAND circuit 14 is a Lo signal.

  At this time, a constant current of, for example, about 1 μA flows through the constant current source transistor 12, the main bit line MBL0 is pulled out with a constant current of, for example, about 1 μA, and a current flows through the memory cell MM00.

  A voltage of about 8V is applied to the memory gate 100, a voltage of about 5V to the source 103, and a voltage of about 1.5V to the selection gate 102 are applied to the non-written memory cell MM01. The output of the pulse 1 or the write latch 15 is a Lo signal, and the output of the NAND circuit 14 is a Hi signal.

  If the voltage of the Hi signal is about 1.5V, for example, the write circuit 9 supplies about 1.5V to the main bit line MBL1, the selection MOS transistor of the memory cell MM01 is not turned on, and writing does not occur.

  Further, no voltage is applied to the memory gate 100, the source 103, and the selection gate 102 of the non-written memory cells MMn0 and MMn1, so that writing does not occur.

  Further, the timing chart of data writing in the case of the configuration shown in FIG. 6 is almost the same as the timing chart described in FIG. 5, but regarding the timing of applying 1.5 V to the hierarchical gate line Z, the sub-bit line In order to charge 1.5 V to LBL, the timing is the same as when 5 V is applied to the source line SL0 and 1.5 V is applied to the bit lines BL0 and BL1.

  Next, FIG. 7 is a diagram showing another example of a configuration in which the flash memory array 10 in the flash memory 1 has a hierarchical structure.

  The memory cells MM (FIG. 4) are regularly arranged in an array, and the selection gate 102, the memory gate 100, and the source 103 of the memory cell MM include selection gate lines CG0 to CGn, memory gate lines MG0 to MGn, The source lines SL0 to SLn are commonly connected.

  Further, the drain 104 of the memory cell MM is commonly connected by the sub bit line LBL, and is connected to the main bit line MBL via the hierarchical MOS transistors ZM0 and ZM1.

  The sub bit line LBL is connected to a voltage source via a charging transistor (current supply control transistor) CM, and a current mirror circuit 18 is connected to the gate of the charging transistor CM. The current mirror circuit 18 generates a certain current based on the trimming information of the decoder circuit 17 and uses the charging transistor CM as a constant current source.

  The current mirror circuit 18 has a configuration in which two transistors 18a and 18b are connected in series between a voltage source and a reference potential. Transistor 18a is a P-channel MOS, and transistor 18b is an N-channel MOS.

  Here, since the constant current source transistor 12 is an N-channel MOS transistor, the current trimming information is for an NMOS transistor. However, since the charging transistor CM is a P-channel MOS transistor, the current trimming information is converted into a PMOS transistor by the current mirror circuit 18.

  The gate of the transistor for charging CM is connected to the gate of the transistor 18a and the connecting portion of the transistors 18a and 18b. A decoder circuit 17 provided in the current trimming circuit 11a is connected to the gate of the transistor 18b.

  Two sub bit lines LBL are connected in parallel to the main bit line MBL via hierarchical MOS transistors ZM0 and ZM1. A write circuit 9 is connected to the main bit line MBL. Although the case where two sub bit lines LBL are connected in parallel to the main bit line MBL has been described here, a plurality of sub bit lines LBL may be connected in parallel.

  The gates of these hierarchical MOS transistors ZM0 and ZM1 are connected to receive gate signals Z0 and Z1.

  Further, the write circuit 9 has a configuration in which transistors 19 and 20 are newly provided in the constant current source transistor 12, the latch switch 13, and the write latch 15, which have the same configuration as the write circuit shown in FIG. The circuit configuration of the current trimming circuit 11a is the same as that in FIG.

  Transistors 19 and 20 are formed of an N-channel MOS. One connection portion of the transistor 19 is connected to the other connection portion of the constant current source transistor 12.

  One connection portion of the transistor 20 is connected to the other connection portion of the transistor 19, and a reference potential (VSS) is connected to the other connection portion of the transistor 20.

  The output of the write latch 15 is connected to the gate of the transistor 19, and an ON / OFF operation is performed based on the data stored in the write latch 15. The gate of the transistor 20 is connected to receive a write pulse, and an ON / OFF operation is performed based on the write pulse.

  When writing data into the memory cell MM00, for example, about 8V is applied to the memory gate line MG0, about 5V is applied to the source line SL0, about 1.5V is applied to the selection gate line CG0, and about 1.5V is applied to the hierarchical MOS gate line Z0. To do.

  In the write circuit 9, the write pulse 0 and the output of the write latch 15 are Hi signals, the transistors 19 and 20 are turned on, and the wiring nl becomes a Lo signal.

  At this time, a constant current of, for example, about 1 μA flows through the constant current source transistor 12, the main bit line MBL0 is pulled out with a constant current of, for example, about 1 μA, and a current flows through the memory cell MM00.

  In addition, a voltage of about 8 V is applied to the memory gate 100, a voltage of about 5 V is applied to the source 103, and a voltage of about 1.5 V is applied to the selection gate 102 in the non-written memory cell MM01.

  Since the constant current source is connected to the main bit line MBL0, the hierarchical MOS transistor ZM1 must be turned off. At this time, since the sub bit line LBL1 is open, a write disturb occurs in the memory cell MM01.

  In order to prevent this, the sub-bit line LBL1, for example, a charging transistor CM1 for charging to 1.5 V is connected to the sub-bit line LBL1. Similarly, the charging transistor CM is connected to the other subbit line LBL. Charging transistor CM is formed of, for example, a P-channel MOS.

  The charging transistor CM only needs to be able to charge the sub-bit line LBL. For example, the charging transistor CM may have a current capability of about 0.5 μA, and is preferably a constant current source in consideration of manufacturing variations and temperature characteristics.

  In FIG. 2, about 1.5 V is applied from the write circuit 9 to the bit line BL in order to realize non-write. In the configuration of FIG. Since it is charged to about 5 V, it is not necessary to have a function of outputting about 1.5 V in the writing circuit 9.

  Therefore, in the write circuit 9, when the write pulse 1 or the output of the write latch 15 is a Lo signal, the transistor 19 or the transistor 20 is turned off and the wiring nl is opened. Therefore, the write circuit 9 opens the main bit line MBL1.

  However, there is no problem even if the writing circuit 9 has a function of outputting about 1.5V. Further, no voltage is applied to the memory gate 100, the source 103, and the selection gate 102 in the non-written memory cells MMn0, MMn1, MMn2, and MMn3. Therefore, writing does not occur.

  In the configuration of FIG. 7, the gates of the charging transistors CM are connected in common. Therefore, a charging current of about 0.5 μA always flows during writing. Therefore, in order to reduce the write current to about 1 μA, the drawing current of the constant current source (constant current source transistor 12) connected in the write circuit 9 is set to about 1.5 μA, which is the sum of the write current and the charging transistor current. It is necessary to.

  Further, although the gates of the charging transistors CM are commonly connected, the gates of the charging transistors CM may be selected for each address without being commonly connected.

  Further, in FIG. 7, the constant current source transistor 12 is an N-channel MOS transistor and the charging transistor CM is a P-channel MOS transistor. However, the present invention is not limited thereto.

  Further, although the charging transistor CM is made a constant current source using the current trimming circuit 11a, it may be made a constant current source by another method. Further, a NAND circuit may be provided in place of the transistors 19 and 20.

  Here, an operation when data is written in the memory cell MM00 in FIG. 7 will be described with reference to a timing chart of FIG.

  In FIG. 8, from the top to the bottom, the selection gate line CG0, the memory gate line MG0, the source line SL0, the hierarchical MOS gate line Z0, the sub bit lines LBL0, LBL1, LBL2, LBL3, and the main bit line MBL0, Signal timings in MBL1 are shown respectively.

  First, about 1.5 V is applied to the selection gate line CG0. Then, about 5V is applied to the source line SL0 and about 1.5V to the hierarchical MOS gate line Z0, the charging transistor CM is turned on, and about 1.5V is applied to the sub bit lines LBL0, LBL1, LBL2, and LBL3, respectively. Thereafter, about 8 V is applied to the memory gate line MG0.

  The reason why the sub-bit lines LBL0, LBL1, LBL2, and LBL3 are applied to about 1.5 V before applying about 8 V to the memory gate line MG0 is to prevent write disturb that occurs before the write conditions are satisfied.

  When the voltage values of the selection gate line CG0, the source line SL0, and the memory gate line MG0 satisfy the write condition, the write circuit 9 is connected to a constant current source for an optimum write time, and the main bit line MBL0 is pulled out with a constant current. A current is passed through the memory cell MM00.

  In FIG. 7, data is not written to the memory cell MM02. However, if data is written to the memory cell MM02, the memory circuit MM00 is written as shown in FIG. Connected to a current source, the main bit line MBL1 is pulled out with a constant current, and a current flows through the memory cell MM02. That is, the write pulse is applied for an optimal time in the order of the main bit line MBL.

  In addition, the selection gate line CGn, the source line SLn, and the memory gate line MGn connected to the non-write memory cells MMn0, MMn1, MMn2, and MMn3 are 0 V in this period.

  The operation timing of the write circuit 9 is not limited to that shown in FIG. 8. For example, the write circuit 9 of the memory cell MM00 and the write circuit 9 of the memory cell MM02 are simultaneously operated to set the main bit lines MBL0 and MBL1. You may make it pull out with an electric current.

  FIG. 9 is a block diagram of a single-chip microcomputer (semiconductor integrated circuit device) MC with a built-in flash memory, which is an example of a semiconductor integrated circuit device according to the present invention.

  The microcomputer MC is a system LSI having an on-chip flash memory (nonvolatile storage unit) 1a having the same configuration as the flash memory 1 (FIG. 1). In addition, a CPU (central information processing device) 21 is provided. , CPG 22, DMAC 23, timer 24, SCI 25, ROM 26, BSC 27, RAM 28, input / output ports IOP1 to IOP9, and the like.

  A CPU (Central Processing Unit) 21 controls all of the microcomputer MC based on a program stored in the ROM 26.

  A ROM (Read Only Memory) 26 stores programs to be executed by the CPU 21 and fixed data. A RAM (Random Access Memory) 28 stores a calculation result by the CPU 21 and provides a work area for the CPU 21.

  A DMAC (Direct Memory Access Controller) 23 controls the transfer of data between the ROM 26 and the RAM 28 and an externally connected main memory in predetermined block units.

  An SCI (Serial Communication Interface) 25 performs serial communication with an external device. The timer 24 counts the set time, and when the set time is reached, sets a flag or generates an interrupt request.

  A CPG (Clock Pulse Generator) 22 generates a clock signal having a certain frequency and supplies a system clock as an operation clock. The input / output ports IOP1 to IOP9 are input / output terminals for externally connecting the microcomputer.

  In the microcomputer MC, the CPU 21, the flash memory 1a, the ROM 26, the RAM 28, the DMAC 23, and some input / output ports IOP1 to IOP5 are connected to each other by a main address bus IAB and a main data bus IDB.

  Further, peripheral circuits such as the timer 24 and the SCI 25 and the input / output ports IOP1 to IOP9 are mutually connected by a peripheral address bus PAB and a peripheral data bus PDB.

  The BSC 27 controls transfer of signals between the main address bus IAB and the main data bus IDB, the peripheral address bus PAB, and the peripheral data bus PDB, and controls the state of each bus.

  Thereby, according to the present embodiment, the constant current source transistor 12 performs data writing with a constant current, so that variation in the threshold fluctuation amount of the memory cell MM can be greatly reduced, and writing is performed. Current consumption can be reduced.

  Further, by reducing the current consumption, the number of simultaneous writings to the memory cell MM can be increased, and the writing operation of the flash memories 1 and 1a can be speeded up.

  Furthermore, in the embodiment of the present invention, the flash memory array 10 of the flash memory 1 has the configuration shown in FIGS. 2, 6, and 7, respectively, but the configuration of the flash memory array 10 is not limited to this. Is not to be done.

  10 and 11 show different configurations of the flash memory array shown in FIG. 2 and its operation timing chart. In FIG. 10, a voltage of 1.2 V is applied to the selection gate line CG0 connected to the selection gate 102 of the memory cells MM00 to MMn0, and the voltage between the selection gate 102 and the memory gate 100 is larger than that in the configuration of FIG. It is configured to cause high electric field concentration.

  By applying a voltage of 1.5 V to the selection gate line CG, the saturation voltage level becomes relatively lower in the change of the threshold voltage of the memory gate 100 than when 1.2 V is applied. Alternatively, the stress applied to the insulating film of the memory gate 100 during the write operation can be relatively reduced, and the number of rewrites can be relatively improved.

  On the other hand, by applying a voltage of 1.2 V to the selection gate line CG, the saturation voltage level becomes higher with the change in the threshold voltage of the memory gate 100, so that the data retention characteristic can be improved. Become.

  In the CG driver shown in FIG. 12, the voltage applied to the selection gate line CG is configured to be selectable between 1.5V and 1.2V, and the voltage applied to the selection gate line CG is configured to be selectable. Is done.

  In normal use, 1.5 V is applied to the selection gate line CG, and 1.2 V is selected to further improve the data retention characteristic. For example, 1.2 V is selected. Select from the relationship.

  A method for selecting which of 1.5V and 1.2V is applied to the selection gate line is not particularly limited, and it may be a command from the outside, setting a selection value in a predetermined register, or the like.

  As mentioned above, the invention made by the present inventor has been specifically described based on the embodiments of the invention. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention. Needless to say.

  For example, in the above embodiment, the voltage to be supplied to the constant current source transistor is generated by the current trimming circuit, but another circuit configuration may be used as long as the circuit generates the constant current source.

  The present invention is suitable for high-speed data writing and low power consumption technology in a nonvolatile semiconductor memory device.

1 Flash memory (nonvolatile semiconductor memory device)
1a Flash memory (nonvolatile storage unit)
2 control circuit 3 input / output circuit 4 address buffer 5 row decoder 6 column decoder 7 verify sense amplifier circuit 8 high-speed read sense amplifier circuit 9 write circuit 10 flash memory array 11 power supply circuit 11a current trimming circuit (trimming section)
12. Transistor for constant current source (current absorption control transistor)
13 Latch switch 14 NAND circuit 15 Write latch 16 Trimming register (trimming information storage)
17 Decoder circuit 18 Current mirror circuit 18a, 18b Transistor 19, 20 Transistor 21 CPU (central information processing device)
22 CPG
23 DMAC
24 Timer 25 SCI
26 ROM
27 BSC
28 RAM
100 Memory Gate 101 Charge Storage Layer 102 Select Gate 103 Source 104 Drain 105 Semiconductor Substrate MM Memory Cell (Nonvolatile Memory Cell)
ZM Hierarchical MOS transistor CM Charging transistor (current supply control transistor)
MC microcomputer (semiconductor integrated circuit device)
IOP1 to IOP9 I / O port BL Bit line CG Select gate line MG Memory gate line SL Source line LBL Sub-bit line MBL Main bit line

Claims (4)

A plurality of nonvolatile memories connected to the bit line, the source line, the first control line, and the second control line;
Each of the nonvolatile memories has a drain terminal formed on the bit line, a source terminal formed on the source line, a first control terminal formed on the channel formed on the first control line, and a first formed on the channel formed on the channel. 2 control terminals are connected to the second control line,
Having a charge storage layer between the first control terminal and the channel, the storage state of the nonvolatile memory is determined by the amount of electrons trapped in the charge storage layer;
In the write operation of the nonvolatile memory, a voltage for performing a write operation is applied to each of the bit line, the source line, and the first control line, and the number of rewrites and data Depending on which of the retention characteristics is prioritized, one of the first write voltage and the second write voltage is selectively applied to the second control line,
The first write voltage applied to the second control line when priority is given to the number of times of rewriting is compared with the second write voltage applied to the second control line when priority is given to the data retention characteristic. High voltage,
Electrons generated by the current flowing through the channel between the drain terminal and the source terminal of the nonvolatile memory and the first write voltage or the second write voltage applied to the second control terminal are the first A nonvolatile semiconductor memory device, wherein control is performed so that the charge storage layer is injected by a voltage applied to a control terminal. In the nonvolatile semiconductor memory device according to claim 1 Symbol placement,
A non-volatile semiconductor memory device comprising a register for storing information as to which of the first write voltage and the second write voltage is applied. In the nonvolatile semiconductor memory device according to claim 1 or 2, wherein,
Before SL nonvolatile semiconductor memory device first pin is characterized and in that it has a charge storage region. In the nonvolatile semiconductor memory device according to any one of claims 1 to 3
In the write operation to the non-volatile memory, after applying the write voltage to the second control line and applying the voltage for performing the write operation to the source line and the bit line, the first control line A non-volatile semiconductor memory device, wherein a control for applying a voltage for performing the write operation is performed on the non-volatile semiconductor memory device.

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