WO2015022743A1 - 半導体装置 - Google Patents
半導体装置 Download PDFInfo
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- WO2015022743A1 WO2015022743A1 PCT/JP2013/071956 JP2013071956W WO2015022743A1 WO 2015022743 A1 WO2015022743 A1 WO 2015022743A1 JP 2013071956 W JP2013071956 W JP 2013071956W WO 2015022743 A1 WO2015022743 A1 WO 2015022743A1
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C16/00—Erasable programmable read-only memories
- G11C16/02—Erasable programmable read-only memories electrically programmable
- G11C16/06—Auxiliary circuits, e.g. for writing into memory
- G11C16/34—Determination of programming status, e.g. threshold voltage, overprogramming or underprogramming, retention
- G11C16/3436—Arrangements for verifying correct programming or erasure
- G11C16/3454—Arrangements for verifying correct programming or for detecting overprogrammed cells
- G11C16/3459—Circuits or methods to verify correct programming of nonvolatile memory cells
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C16/00—Erasable programmable read-only memories
- G11C16/02—Erasable programmable read-only memories electrically programmable
- G11C16/06—Auxiliary circuits, e.g. for writing into memory
- G11C16/10—Programming or data input circuits
- G11C16/14—Circuits for erasing electrically, e.g. erase voltage switching circuits
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C16/00—Erasable programmable read-only memories
- G11C16/02—Erasable programmable read-only memories electrically programmable
- G11C16/04—Erasable programmable read-only memories electrically programmable using variable threshold transistors, e.g. FAMOS
- G11C16/0408—Erasable programmable read-only memories electrically programmable using variable threshold transistors, e.g. FAMOS comprising cells containing floating gate transistors
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C16/00—Erasable programmable read-only memories
- G11C16/02—Erasable programmable read-only memories electrically programmable
- G11C16/04—Erasable programmable read-only memories electrically programmable using variable threshold transistors, e.g. FAMOS
- G11C16/0408—Erasable programmable read-only memories electrically programmable using variable threshold transistors, e.g. FAMOS comprising cells containing floating gate transistors
- G11C16/0425—Erasable programmable read-only memories electrically programmable using variable threshold transistors, e.g. FAMOS comprising cells containing floating gate transistors comprising cells containing a merged floating gate and select transistor
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C16/00—Erasable programmable read-only memories
- G11C16/02—Erasable programmable read-only memories electrically programmable
- G11C16/04—Erasable programmable read-only memories electrically programmable using variable threshold transistors, e.g. FAMOS
- G11C16/0408—Erasable programmable read-only memories electrically programmable using variable threshold transistors, e.g. FAMOS comprising cells containing floating gate transistors
- G11C16/0441—Erasable programmable read-only memories electrically programmable using variable threshold transistors, e.g. FAMOS comprising cells containing floating gate transistors comprising cells containing multiple floating gate devices, e.g. separate read-and-write FAMOS transistors with connected floating gates
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C16/00—Erasable programmable read-only memories
- G11C16/02—Erasable programmable read-only memories electrically programmable
- G11C16/06—Auxiliary circuits, e.g. for writing into memory
- G11C16/26—Sensing or reading circuits; Data output circuits
- G11C16/28—Sensing or reading circuits; Data output circuits using differential sensing or reference cells, e.g. dummy cells
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C16/00—Erasable programmable read-only memories
- G11C16/02—Erasable programmable read-only memories electrically programmable
- G11C16/06—Auxiliary circuits, e.g. for writing into memory
- G11C16/34—Determination of programming status, e.g. threshold voltage, overprogramming or underprogramming, retention
- G11C16/3436—Arrangements for verifying correct programming or erasure
- G11C16/344—Arrangements for verifying correct erasure or for detecting overerased cells
- G11C16/3445—Circuits or methods to verify correct erasure of nonvolatile memory cells
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C16/00—Erasable programmable read-only memories
- G11C16/02—Erasable programmable read-only memories electrically programmable
- G11C16/06—Auxiliary circuits, e.g. for writing into memory
- G11C16/26—Sensing or reading circuits; Data output circuits
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C16/00—Erasable programmable read-only memories
- G11C16/02—Erasable programmable read-only memories electrically programmable
- G11C16/06—Auxiliary circuits, e.g. for writing into memory
- G11C16/34—Determination of programming status, e.g. threshold voltage, overprogramming or underprogramming, retention
- G11C16/3436—Arrangements for verifying correct programming or erasure
- G11C16/3454—Arrangements for verifying correct programming or for detecting overprogrammed cells
Definitions
- the present invention relates to a semiconductor device, for example, a semiconductor device including two nonvolatile memory cells that hold complementary data.
- the address of the memory cell array (1) is set while the first erasing write end signal (FWE) is inactive. Sequential update and write before erase. Then, when this memory becomes an active level, it performs verification for each address, and controls to perform pre-erase writing (pre-write) and verification again only on the address for which the verification result is defective.
- FWE first erasing write end signal
- Patent Document 2 in the erase operation mode, at least a plurality of memory cells in the erase unit in the memory array are read and charges are accumulated in the floating gate.
- a prewrite operation for setting a predetermined amount of write states by repeating the unit write operation and the write determination operation is performed on the memory cells that have not been performed.
- the memory performs an erasing operation for setting a predetermined amount of erasing states by repeating the erasing operation and the erasing determination operation for the plurality of memory cells in the erasing unit at a time under the erasing reference voltage.
- this memory performs a write operation for setting a predetermined amount of write state by repeating a unit write operation and a write determination operation for a selected memory cell.
- the threshold voltages of the two cells are both reduced by erasing the twin cell data.
- the difference between the threshold voltages of the two cells in the write state before erasing the twin cell data may remain after erasing the twin cell data. Therefore, although the twin cell data is erased, the write state before erasing the twin cell data is read, which may cause a security problem.
- Patent Document 1 speeds up the prewrite sequence, and cannot solve the security problem that the write data before erasing the twin cell data is read in the twin cell.
- the control circuit receives the twin cell data erase request until the threshold voltage of the first storage element and the threshold voltage of the second storage element reach a predetermined write verify level.
- the first stage process for increasing the threshold voltage of one or both of the first memory element and the second memory element is controlled.
- the control circuit after executing the first stage process, until the threshold voltage of the first storage element and the threshold voltage of the second storage element reach a predetermined erase verify level, the threshold voltage of the first storage element and the second storage element Controls the execution of the second stage process that decreases both threshold voltages.
- FIG. 3 is a flowchart showing a procedure for erasing twin cell data from a memory array in the semiconductor device of the first embodiment. It is a figure showing the structure of the microcomputer of 3rd Embodiment. It is a figure showing the structure of a flash memory module.
- A) is a figure showing the example of the bias voltage given to a split gate type flash memory element.
- B) is a figure showing the example of the bias voltage given to the stacked gate type flash memory element using a hot carrier write system.
- (C) is a figure showing the example of the bias voltage given to the stacked gate type
- FIG. 6 is a diagram illustrating a configuration of an erase verify circuit. It is a figure showing the structure of the write latch circuit of the positive side of 2nd Embodiment.
- FIG. 6 is a diagram illustrating a configuration of an erase verify circuit. It is a figure showing the structure of the write latch circuit of the positive side of 2nd Embodiment.
- FIG. 6 is a diagram illustrating a configuration of a negative-side write latch circuit according to a second embodiment. It is a flowchart showing the procedure of the erasure
- FIG. 1 is a diagram illustrating the configuration of the semiconductor device according to the first embodiment.
- the semiconductor device 100 includes a memory array 101 and a control circuit 105.
- Memory array 101 includes a plurality of twin cells 104.
- the twin cell 104 holds binary data (twin cell data) according to a difference in threshold voltage Vth, and includes a first memory element 102 and a second memory element 103 that can be electrically rewritten.
- control circuit 105 When the control circuit 105 receives the request for erasing the twin cell data, the control circuit 105 and the second storage element 102 and the second storage element 102 until the threshold voltage Vth of the first storage element 102 and the second storage element 103 reaches a predetermined write verify level. The execution of the first stage process for increasing the threshold voltage Vth of both or one of the memory elements 103 is controlled.
- the control circuit 105 executes the first storage element 102 and the second storage element 103 until the threshold voltage Vth of the first storage element 102 and the second storage element 103 reaches a predetermined erase verify level after the execution of the first stage process.
- the execution of the second-stage process for decreasing both the threshold voltages Vth is controlled.
- FIG. 2 is a flowchart showing a procedure for erasing twin cell data from the memory array 101 in the semiconductor device of the first embodiment.
- control circuit 105 receives the erase request signal ERQ (step S101). Next, the control circuit 105 determines the threshold value of both or one of the first memory element 102 and the second memory element 103 until the threshold voltage Vth of the first memory element 102 and the second memory element 103 reaches a predetermined write verify level. The execution of the first stage process for increasing the voltage is controlled (step S102).
- control circuit 105 performs the first memory element 102 and the second memory until the threshold voltage Vth of the first memory element 102 and the second memory element 103 reaches a predetermined erase verify level after the execution of the first stage process.
- the execution of the second stage process for decreasing both the threshold voltages Vth of the elements 103 is controlled (step S103).
- the difference between the threshold voltages Vth of the first memory element 102 and the second memory element 103 is reduced by the first stage process, so that the first memory element after the second stage process is used.
- the threshold voltage Vth of the second memory element 103 and the threshold voltage Vth of the second memory element 103 are not related to the magnitude of the threshold voltage Vth of the first memory element 102 and the threshold voltage Vth of the second memory element 103 before erasing the twin cell data. Can be. As a result, it is possible to solve the security problem that the write state before erasing the twin cell data is read out.
- FIG. 3 is a diagram illustrating the configuration of the microcomputer 1 according to the second embodiment.
- the microcomputer (MCU) 1 shown in FIG. 3 is formed on a single semiconductor chip such as single crystal silicon by, for example, complementary MOS integrated circuit manufacturing technology.
- the microcomputer 1 has a high-speed bus HBUS and a peripheral bus PBUS, although not particularly limited.
- the high-speed bus HBUS and the peripheral bus PBUS are not particularly limited, but each have a data bus, an address bus, and a control bus. By providing two buses, it is possible to reduce the load on the bus and to guarantee a high-speed access operation compared to the case where all circuits are commonly connected to the common bus.
- the high-speed bus HBUS includes a central processing unit (CPU) 2, a direct memory access controller (DMAC) 3, a bus interface control between the high-speed bus HBUS and the peripheral bus PBUS, or a bus that includes an instruction control unit and an execution unit to execute instructions.
- a bus interface circuit (BIF) 4 that performs bridge control is connected.
- RAM random access memory
- FMDL flash memory module
- the peripheral bus PBUS controls a flash sequencer (FSQC) 7 that performs command access control to the flash memory module (FMDL) 6, external input / output ports (PRT) 8 and 9, timer (TMR) 10, and microcomputer 1.
- FSQC flash sequencer
- FMDL flash memory module
- PRT external input / output ports
- TMR timer
- microcomputer 1 microcomputer 1.
- a clock pulse generator (CPG) 11 for generating an internal clock CLK is connected.
- the microcomputer 1 includes a clock terminal to which an oscillator is connected to XTAL / EXTAL or an external clock is supplied, an external hardware standby terminal STB for instructing a standby state, an external reset terminal RES for instructing a reset, an external power supply A terminal Vcc and an external ground terminal Vss are provided.
- the flash sequencer 7 as a logic circuit and the flash memory module 6 having an array configuration are designed using different CAD tools, and are therefore shown as separate circuit blocks for convenience.
- Configure flash memory The flash memory module 6 is connected to the high-speed bus HBUS via a read-only high-speed access port (HACSP).
- the CPU 2 or the DMAC 3 can read-access the flash memory module 6 from the high-speed bus HBUS via the high-speed access port.
- the CPU 2 or the DMAC 3 issues a command to the flash sequencer 7 via the peripheral bus PBUS via the bus interface 4 when performing write and initialization access to the flash memory module 6.
- the flash sequencer 7 initializes the flash memory module and controls the write operation from the peripheral bus PBUS through the low-speed access port (LACSP).
- LACSP low-speed access port
- FIG. 4 is a diagram showing the configuration of the flash memory module 6.
- the flash memory module 6 stores 1-bit information using two nonvolatile memory cells. That is, the memory array (MARY) 19 includes a plurality of two rewritable nonvolatile memory cells MC1 and MC2 as 1-bit twin cells. FIG. 4 representatively shows only one pair. In this specification, the memory cell MC1 is called a positive cell, and the memory cell MC2 is called a negative cell.
- the flash memory module 6 may include a plurality of memory cells that store 1-bit information using a single nonvolatile memory cell. In such a case, it is often arranged separately in the flash memory module 6 in units of memory blocks divided in units smaller than the memory array or the memory array.
- the volatile memory cells MC1 and MC2 are, for example, split gate type flash memory elements exemplified in FIG.
- This memory element has a control gate CG and a memory gate MG disposed on a channel formation region between the source / drain regions via a gate insulating film.
- a charge trap region (SiN) such as silicon nitride is disposed between the memory gate MG and the gate insulating film.
- the source or drain region on the selection gate side is connected to the bit line BL, and the source or drain region on the memory gate side is connected to the source line SL.
- BL Hi ⁇ Z (high impedance state)
- CG 1.5V
- MG ⁇ 10V
- SL 6
- WELL 0V
- This processing unit is a plurality of memory cells sharing the memory gate MG.
- BL 0V
- CG 1.5V
- MG 10V
- SL 6
- WELL 0V
- a write current is supplied from the source line SL to the bit line, thereby controlling the control gate CG.
- Hot electrons generated at the boundary between the memory gate MG and the memory gate MG are injected into the charge trap region (SiN). Since the electron injection is determined by whether or not a bit line current is passed, this process is controlled in units of bits.
- the memory element is not limited to the split gate type flash memory element, and may be a stacked gate type flash memory element exemplified in FIGS. 5B and 5C.
- This memory element is configured by stacking a floating gate FG and a control gate WL via a gate insulating film on a channel formation region between a source / drain region.
- the threshold voltage Vth is increased by the hot carrier writing method, and the threshold voltage Vth is decreased by the emission of electrons to the well region WELL.
- the threshold voltage Vth is increased by the FN tunnel writing method, and the threshold voltage Vth is decreased by the emission of electrons to the bit line BL.
- the voltage applied to the memory gate MG, control gate CG, source line SL, WELL, and bit line BL described above is generated and supplied by the power supply circuit (VPG) 31 under the control of the flash sequencer 7.
- the memory element is a split gate flash memory element.
- Information storage by one twin cell composed of the nonvolatile memory cells MC1 and MC2 is performed by storing complementary data in the nonvolatile memory cells MC1 and MC2.
- each of the memory cells MC1 and MC2 has cell data “1” (low threshold voltage state; state in which the threshold voltage is smaller than the erase verify level) or cell data “0” (high threshold voltage state; the threshold voltage is in the erase verify state). State above the level).
- the twin cell data “0” is a state in which the positive cell MC1 holds the cell data “0” and the negative cell MC2 holds the cell data “1”.
- the twin cell data “1” is a state in which the positive cell MC1 holds the cell data “1” and the negative cell MC2 holds the cell data “0”.
- the state in which the positive cell MC1 and the negative cell MC2 of the twin cell both hold the cell data “1” is an initialized state, and the twin cell data becomes indefinite.
- the initialized state is also called a blank erase state.
- twin cell data erasure Further, changing from the initialized state to the twin cell data “1” holding state or the twin cell data “0” holding state is called normal writing.
- pre-write When erasing twin cell data, once the cell data of both the positive cell MC1 and the negative cell MC2 is set to “0” (referred to as pre-write), an erase pulse is applied to store both cell data. Processing to set “1” is performed.
- the voltage applied to both the positive cell MC1 and the negative cell MC2 is made smaller than that in the normal writing, or the writing pulse is weaker than in the normal writing by shortening the period for giving the writing pulse. To do.
- the increase amount of the threshold voltage of the memory cell having the smaller threshold voltage is smaller than the increase amount of the threshold voltage Vth during normal writing.
- the purpose of performing the pre-write is to reduce variations in erasing stress between the positive cell MC1 and the negative cell MC2 and suppress deterioration of retention characteristics.
- a voltage smaller than the voltage during general normal write (increase Vth) shown in FIG. 5 is applied during prewrite.
- FIG. 7A shows a sequence for erasing twin cell data “0”.
- the erase of the twin cell data “0” when executed, both cells are initialized by the prewrite, but before the erase, Since the threshold voltage Vth of the positive cell MC1 is larger than the threshold voltage Vth of the negative cell MC2, it is assumed that this relationship may be maintained even after erasing.
- the threshold voltage Vth between the positive cell MC1 and the negative cell MC2 is different regardless of the initialized state. Data “0” equal to “0” may be read out.
- FIG. 7B shows a sequence for erasing twin cell data “1”.
- the threshold voltage Vth of the negative cell MC2 is larger than the threshold voltage Vth of the positive cell MC1, it is assumed that this relationship may be maintained even after erasing.
- the threshold voltage Vth of the positive cell MC1 and the negative cell MC2 is different regardless of the initialized state. There is a possibility of reading data “1” equal to “1”.
- the embodiment of the present invention aims to solve such a possible problem.
- twin-cell memory cells MC1 and MC2 typically shown in FIG. 4, the memory gate MG is connected to the common memory gate selection line MGL, and the control gate CG is connected to the common word line WL.
- twin cells are arranged in a matrix and connected to the corresponding memory gate selection line MGL and word line WL in an array unit in the row direction.
- the memory cells MC1 and MC2 are connected to the sub bit line SBL on a column basis, and are connected to the write main bit line WMBL via the sub bit line selector 20.
- a plurality of sub bit lines SBL are hierarchized by the sub bit line selector 20 and connected to the write main bit line WMBL.
- a unit hierarchized in the sub-bit line SBL is referred to as a memory mat.
- Source line SL is connected to ground voltage Vss.
- the sub bit line SBL of the memory cell MC1 is connected to one input terminal of the hierarchical sense amplifier SA via the read column selector 22 for each memory mat.
- the sub bit line SBL of the memory cell MC2 is connected to the other input terminal of the hierarchical sense amplifier SA via the read column selector 22 for each memory mat.
- the word line WL is selected by the first row decoder (RDEC1) 24.
- the memory gate selection line MGL and the sub bit line selector 20 are selected by the second row decoder (RDEC2) 25.
- the selection operation by the first row decoder 24 and the second row decoder 25 follows the address information supplied to the HACSP in the read access, and follows the address information supplied to the LACSP in the data write operation and the initialization operation.
- the output of the hierarchical sense amplifier SA is connected to the data bus HBUS_D of the high-speed bus HBUS via the output buffer (OBUF) 26.
- the write main bit line WMBL is set so that a write current selectively flows according to the latch data of the write latch circuit 54.
- the write latch circuit 54 is selected by the rewrite column selector 28.
- the rewrite main bit line WMBL selected by the rewrite column selector 28 is connected to the verify sense amplifier VSA.
- the output of the verify sense amplifier VSA and the write latch circuit 54 are connected to an input / output circuit (IOBUF) 29 interfaced with the data bus (PBUS_D) of the peripheral bus PBUS.
- IBUF input / output circuit
- the rewrite column selector 28 is selected by a column decoder (CDEC) 30.
- CDEC column decoder
- the power supply circuit (VPG) 31 generates various operating voltages necessary for reading, writing, and initialization.
- the timing generator (TMG) 32 generates an internal control signal that defines internal operation timing in accordance with an access strobe signal supplied from the CPU 2 or the like to the HACSP, an access command supplied from the FSQC 7 to the LACSP, or the like.
- the control unit of the flash memory is composed of the FSQC 7 and the timing generator 32.
- FIG. 8 is a diagram showing a detailed circuit configuration of the twin cell data read system, write system, and erase system of the second embodiment.
- Eight examples of WMBL_0P to WMBL_3P and WMBL_0N to WMBL_3N are illustrated as write main bit lines, and one memory mat is illustrated as a memory mat connected thereto.
- SBL_0P to SBL_7P and SBL_0N to SBL_7N are arranged as sub bit lines, and two sub bit lines SBL are assigned to one write system main bit line WMBL.
- the numerical suffixes in the reference numerals attached to the sub-bit lines SBL not shown in the figure mean the column numbers of the twin cells.
- the suffix P of the alphabet means that it is a subbit line connected to one memory cell MC1 (positive cell) of the twin cell, and the suffix N is a subbit line connected to the other memory cell MC2 (negative cell) of the twin cell. It means that there is.
- the suffix P of the alphabet in the reference numerals attached to the write main bit line WMBL means that the write main bit line is connected to the positive cell MC1 of the twin cell, and the suffix N is the write main bit connected to the negative cell MC2 of the twin cell. It means a line, and the numerical suffix means the lower column number of the corresponding twin cell column numbers.
- Selection signals YR0N to YR7N that switch-control the read column selector 22 select a pair of sub bit lines SBL having the same column number of the twin cells, and select the sub bit line SBL_iP on the positive cell side and the sub bit line SBL_iN on the negative cell side.
- the hierarchical sense amplifier SA has a current source transistor (not shown) at each differential input terminal, and the current source transistor is activated in the read operation.
- the twin cell is selected by the word line in the read operation, the positive cell MC1 and the negative cell MC2 of the selected twin cell are complementarily switched in accordance with the stored twin cell data, thereby the difference between the hierarchical sense amplifiers SA.
- a potential difference is formed at the dynamic input terminal.
- the twin cell data is output to the read main bit line RMBL.
- Another sub bit line which is not selected at that time is arranged between the pair of sub bit lines selected by the read column selector 22 according to the column number arrangement of the twin cells and the selection form of the sub bit lines by the read column selector 22. It has come to be.
- the read discharge circuit 40 is a circuit that selectively connects the sub bit line SBL to the ground voltage Vss by the discharge signals DCR0 and DCR1, and connects the sub bit line SBL that is not selected by the sub bit line selector 20 to the ground voltage Vss. Connect to.
- the inverted write data supplied from the data bus PBUS_D to the inverted signal line NSL is selected by the rewrite column selector 28. Supplied. ENDT is an input gate signal for write data to the signal lines PSL and NSL.
- write data input from the data bus PBUS_D is input to the signal lines PSL and NSL as complementary data and is latched by the pair of write latch circuits 54Pj and 54Nj selected by the rewrite column selector 28.
- One of the write latch circuits 54Pj and 54Nj latches data “1” and the other latches data “0”.
- the write current from the source line SL does not flow through the main bit line WMBL corresponding to the latch data “1”, and the main bit line WMBL corresponding to the latch data “0” corresponds to the pulse width of the write pulse WPLS.
- a write current flows from the source line SL.
- cell data “0” is written into one memory cell of the selected twin cell (that is, the threshold voltage Vth is increased), and cell data “1” is written into the other memory cell (that is, The threshold voltage Vth does not change).
- the verify sense amplifiers VSA_P and VSA_N To the verify sense amplifiers VSA_P and VSA_N.
- the verify sense amplifier VSA_P checks whether the threshold voltage Vth of the positive cell MC1 is higher than the write verify level WREV by comparing the magnitude relationship between the current output from the positive cell MC1 and the reference current.
- the verify sense amplifier VSA_P outputs “L” level when the threshold voltage Vth of the positive cell MC1 is higher than the write verify level WREV.
- the verify sense amplifier VSA_P outputs “H” level when the threshold voltage Vth of the positive cell MC1 is equal to or lower than the write verify level WREV.
- the verify sense amplifier VSA_N checks whether the threshold voltage Vth of the negative cell MC2 is higher than the write verify level WREV by comparing the magnitude relationship between the current output from the negative cell MC2 and the reference current.
- the verify sense amplifier VSA_N outputs “L” level when the threshold voltage Vth of the negative cell MC2 is higher than the write verify level WREV.
- the verify sense amplifier VSA_N outputs an “H” level when the threshold voltage Vth of the negative cell MC2 is equal to or lower than the write verify level WREV.
- the data held in the write latch circuits 54Pj and 54Nj in which the write data is stored in the write operation are transmitted to the signal lines PSDL and NSL by the rewrite column selector 28.
- the data write state of the positive cell MC1 is verified by checking the coincidence between the output of the verify sense amplifier VSA_P and the non-inverted write data of the signal line PSL with the exclusive OR gate EXOR_P.
- the data write state of the negative cell MC2 is verified by checking the coincidence of the output of the verify sense amplifier VSA_N and the inverted write data of the inverted signal line NSL with the exclusive OR gate EXOR_N.
- a logical product is obtained by AND gate AND with respect to the output OUT1 of the exclusive OR gate EXOR_P and the output OUT2 of the exclusive OR gate EXOR_N, and the result of the logical product is a write verify result OUT3 for 1-bit write data. Output from AND gate AND.
- a logical product is obtained for all the outputs of the exclusive OR gates for a plurality of bits to obtain a verification result.
- the verification result OUT3 is supplied to the flash sequencer 7 through the peripheral data bus PBUS_D.
- the output OUT1 of the exclusive OR gate EXOR_P and the output OUT2 of the exclusive OR gate EXOR_N are selectively supplied to the flash sequencer 7 through the peripheral data bus PBUS_D via the data selector SEL.
- the write system discharge circuit 41 is a circuit that selectively connects the main bit line WMBL to the ground voltage Vss by the discharge signals DCW0 and DCW1, and sets the main bit line WBML that is not selected by the rewrite column selector 28 to the ground voltage Vss. Connecting.
- the erase verify circuit 90 is provided for each erase unit and executes erase verify.
- the storage information of each twin cell in the erase target region is output to the sub bit lines SBL_iP and SBL_iN and sent to the verify sense amplifiers ESA_Pi and ESA_Ni.
- FIG. 9 is a diagram showing the configuration of the erase verify circuit 90.
- the erase unit is a twin cell of (M + 1) columns. That is, 2 ⁇ (M + 1) columns of memory cells are erase units.
- the erase verify circuit 90 includes verify sense amplifiers ESA_P0 to ESA_PM, verify sense amplifiers ESA_NO to ESA_NM, AND gates LG0 to LGM, and an AND gate LGA.
- the verify sense amplifier ESA_Pi outputs an “H” level when the threshold voltage Vth of the positive cell MC1 is smaller than the erase verify level EREV.
- the verify sense amplifier ESA_Pi outputs “L” level when the threshold voltage Vth of the positive cell MC1 is equal to or higher than the erase verify level EREV.
- the verify sense amplifier ESA_Ni checks whether the threshold voltage Vth of the negative cell MC2 is lower than the erase verify level EREV by comparing the magnitude relationship between the current output from the negative cell MC2 and the reference current.
- the verify sense amplifier ESA_Ni outputs “H” level when the threshold voltage Vth of the negative cell MC2 is smaller than the erase verify level EREV.
- the verify sense amplifier ESA_Ni outputs “L” level when the threshold voltage Vth of the negative cell MC2 is equal to or higher than the erase verify level EREV.
- the AND gate LGi outputs a logical product of the verify sense amplifier ESA_Pi and the verify sense amplifier ESA_Ni.
- the AND gate LGA outputs the logical product OUT4 of the outputs of the AND gates LG0 to LGM to the flash sequencer 7 through the peripheral data bus PBUS_D.
- the write latch circuit 54Pi includes a set unit 281, a data input unit 82, a data holding unit 83, a setting unit 84, and an inverter IV4.
- the set unit 281 includes a P-channel MOS transistor P1 and an N-channel MOS transistor N21.
- P-channel MOS transistor P1 is provided between a line of power supply voltage VDD and node NDP1.
- the gate of P channel MOS transistor P1 receives inverted latch set high signal / LSH.
- N-channel MOS transistor N21 is provided between node NDP1 and the ground voltage Vss line.
- N channel MOS transistor N21 has its gate receiving latch set row signal LSL.
- the data input unit 82 includes an inverter IV1 and a switch SW1.
- Inverter IV1 receives latch switch signal LSW.
- the switch SW1 receives non-inverted data transmitted through the non-inverted signal line PSL, and is controlled by the latch switch signal LSW and the output of the inverter IV1 (that is, the inverted signal of the latch switch signal LSW).
- the switch SW1 transmits non-inverted data transmitted through the non-inverted signal line PSL to the node NDP1 when the latch switch signal LSW is at “H” level.
- Data holding unit 83 includes inverters IV2 and IV3 that are alternately connected.
- the input of inverter IV2 and the output of inverter IV3 are connected to node NDP1, and the output of inverter IV2 and the input of inverter IV3 are connected to node NDP2.
- Setting portion 84 includes P-channel MOS transistors P2, P3, N-channel MOS transistors N2, N3, N4 and an inverter IV5 provided between the power supply voltage VDD line and the ground voltage Vss line.
- Inverter IV5 receives program pulse valid signal PPE.
- the gate of P channel MOS transistor P2 is connected to the output of inverter IV5.
- the gate of P channel MOS transistor P3 and the gate of N channel MOS transistor N2 are connected to node NDP2.
- N channel MOS transistor N3 has its gate receiving program pulse valid signal PPE.
- N channel MOS transistor N4 has its gate receiving write pulse WPLS.
- Node NDP3 between P channel MOS transistor P3 and N channel MOS transistor N2 is connected to main bit line WMBL_iP.
- the twin cell data “1” When the twin cell data “1” is written, the “H” level is sent through the non-inverted signal line PSL, the data of the node NDP1, that is, the write latch data becomes the “H” level, and the voltage of the main bit line WMBL_iP becomes VDD It becomes.
- the main bit line WMBL_iP is connected to the ground voltage Vss, and a write current flows through the main bit line WMBL_iP.
- the latch set low signal LSL is set to the “H” level and the inverted latch set high signal / LSH is set to the “H” level, so that the data of the node NDP1, that is, the write latch data becomes the “L” level.
- the main bit line WMBL_iP is connected to the ground voltage Vss, and a write current flows through the main bit line WMBL_iP.
- the write latch circuit 54Ni includes a set unit 291, a data input unit 92, a data holding unit 93, a setting unit 94, and an inverter IV9.
- the set unit 291 includes a P-channel MOS transistor P4 and an N-channel MOS transistor N25.
- P-channel MOS transistor P4 is provided between a line of power supply voltage VDD and node NDN1.
- the gate of P channel MOS transistor P4 receives inverted latch set high signal / LSH.
- N-channel MOS transistor N25 is provided between node NDN1 and the ground voltage Vss line.
- N channel MOS transistor N25 has its gate receiving latch set row signal LSL.
- the data input unit 92 includes an inverter IV6 and a switch SW2.
- Inverter IV6 receives latch switch signal LSW.
- the switch SW2 receives the inverted data transmitted through the inverted signal line NSL, and is controlled by the latch switch signal LSW and the output of the inverter IV6 (that is, the inverted signal of the latch switch signal LSW).
- the switch SW2 transmits the inverted data transmitted through the inverted signal line NSL to the node NDN1 when the latch switch signal LSW is at “H” level.
- the data holding unit 93 includes inverters IV7 and IV8 that are alternately connected.
- the input of inverter IV7 and the output of inverter IV8 are connected to node NDN1, and the output of inverter IV7 and the input of inverter IV8 are connected to node NDN2.
- Setting unit 94 includes P channel MOS transistors P5, P6, N channel MOS transistors N6, N7, N8 provided between the line of power supply voltage VDD and the line of ground voltage Vss, and inverter IV10.
- Inverter IV10 receives program pulse valid signal PPE.
- P channel MOS transistor P5 has its gate connected to the output of inverter IV10.
- the gate of P channel MOS transistor P6 and the gate of N channel MOS transistor N6 are connected to node NDN2.
- N channel MOS transistor N7 has its gate receiving program pulse valid signal PPE.
- N channel MOS transistor N8 has its gate receiving write pulse WPLS.
- Node NDN3 between P channel MOS transistor P6 and N channel MOS transistor N6 is connected to main bit line WMBL_iN.
- the “L” level is sent through the inverted signal line NSL, the data of the node NDN1, that is, the write latch data becomes the “L” level, and the write pulse WPLS is activated
- the main bit line WMBL_iN is connected to the ground voltage Vss, and a write current flows through the main bit line WMBL_iN.
- the twin cell data “0” when the twin cell data “0” is written, the “H” level is transmitted through the inverted signal line NSL, the data of the node NDN1, that is, the write latch data becomes the “H” level, and the voltage of the main bit line WMBL_iN is VDD.
- the latch set low signal LSL is set to the “H” level and the inverted latch set high signal / LSH is set to the “H” level, so that the data of the node NDN1, that is, the write latch data becomes the “L” level.
- the main bit line WMBL_iN is connected to the ground voltage Vss, and a write current flows through the main bit line WMBL_iN.
- FIG. 12 is a flowchart showing the procedure of the twin cell data erasing process of the second embodiment.
- the flash sequencer 7 sets an erase target area (step S101).
- the flash sequencer 7 controls writing in both cells (positive cell MC1 and negative cell MC2) with verification in steps S102 to S106.
- the flash sequencer 7 sets the write latch data to all the cells (positive cell MC1 and negative cell MC2) included in the erase target area to “0”. Specifically, the flash sequencer 7 sets the latch set high signal to “L” level and the latch set low signal to “H” level in the write latch circuit 54Pi of FIG. As a result, the data of the node NDP1, that is, the write latch data becomes the “L” level. Further, the flash sequencer 7 sets the latch set high signal to “L” level and the latch set low signal to “H” level in the write latch circuit 54Ni of FIG. As a result, the data of the node NDN1, that is, the write latch data becomes “L” level (step S102).
- the flash sequencer 7 sets the write mode (step S103).
- the flash sequencer 7 applies a write voltage to all the cells in the erase target area. That is, the flash sequencer 7 sets the voltage of the memory gate MG to 10V, the voltage of the source line SL to 6V, and the voltage of the control gate CG to 1.5V.
- the main bit line WMBL_iP is connected to the ground voltage Vss, and a write current flows through the main bit line WMBL_iP.
- a write current flows through the sub bit lines SBL_iP and SBL_i + 4P connected to the main bit line WMBL_iP.
- the main bit line WMBL_iN is connected to the ground voltage Vss, and a write current flows through the main bit line WMBL_iN.
- a write current flows through the sub bit lines SBL_iN and SBL_i + 4N connected to the main bit line WMBL_iN.
- the threshold voltages Vth of all the cells included in the erasure target area increase (step S104).
- verify sense amplifier VSA_P outputs an “L” level signal when threshold voltage Vth of positive cell MC1 is higher than write verify level WREV.
- the verify sense amplifier VSA_N outputs an “L” level signal when the threshold voltage Vth of the negative cell MC2 is higher than the write verify level WREV.
- the exclusive OR gate EXOR_P outputs an exclusive OR of the output of the verify sense amplifier VSA_P and the write latch data “0” output from the write latch circuit 54Pi to the signal line PSL.
- the output OUT1 of the exclusive OR gate EXOR_P is sent to the flash sequencer 7 through the peripheral data bus PBUS_D.
- the output OUT1 becomes “H” level when the threshold voltage Vth of the positive cell MC1 is larger than the write verify level WREV.
- the exclusive OR gate EXOR_N outputs an exclusive OR of the output of the verify sense amplifier VSA_N and the write latch data “0” output from the write latch circuit 54Ni to the inverted signal line NSL.
- the output OUT2 of the exclusive OR gate EXOR_N is sent to the flash sequencer 7 through the peripheral data bus PBUS_D.
- the output OUT2 becomes “H” level when the threshold voltage Vth of the negative cell MC2 is higher than the write verify level WREV (step S105).
- step S106 If the threshold voltage Vth of all the cells included in the erase target area is not greater than the write verify level WREV (NO in step S106), the flash sequencer 7 maintains the write mode. That is, the processes of steps S104 and S105 are repeated.
- step S106 If the threshold voltage Vth of all the cells included in the erase target area is greater than the write verify level WREV (YES in step S106), the flash sequencer 7 controls the next erase process (step S107).
- FIG. 13 is a flowchart showing the procedure for erasing the twin cell data.
- the flash sequencer 7 sets the erase mode (step S801).
- the flash sequencer 7 applies an erasing voltage to all the cells included in the erasure target area. That is, the flash sequencer 7 sets the voltage of the memory gate MG to 10V, the voltage of the source line SL to 6V, and the voltage of the control gate CG to 1.5V (step S802).
- verify sense amplifier ESA_Pi outputs an “H” level signal when threshold voltage Vth of positive cell MC1 is smaller than erase verify level EREV.
- the verify sense amplifier ESA_Ni outputs an “H” level signal when the threshold voltage Vth of the negative cell MC2 is lower than the erase verify level EREV.
- the AND gate LGi outputs a logical product of the output of the verify sense amplifier ESA_Pi and the output of the verify sense amplifier ESA_Ni.
- the AND gate LGA outputs a logical product of the outputs of the AND gates LG0 to LGM.
- the output OUT4 of the AND gate LGA is sent to the flash sequencer 7 through the peripheral data bus PBUS_D.
- the output OUT4 has threshold voltages Vth of all positive cells MC1 included in the erase target region lower than the erase verify level EREV, and threshold voltages Vth of all negative cells MC2 included in the erase target region are lower than the erase verify level EREV. If it is also smaller, it becomes “H” level (step S803).
- the flash sequencer 7 maintains the erase mode. That is, the processes in steps S802 and S803 are repeated.
- the flash sequencer 7 ends the erase process.
- FIG. 14 is a diagram illustrating an example of a change in the threshold voltage Vth of the positive cell MC1 and the negative cell MC2 due to the erasure of the twin cell data in the second embodiment.
- FIG. 14A shows an example in which the twin cell data is “1”.
- the threshold voltage Vth of the positive cell MC1 and the negative cell MC2 is increased by writing to both cells with verify in the first stage. Since the threshold voltage Vth of the negative cell MC2 reaches the saturation level, the increase amount is small.
- the threshold voltage Vth of the positive cell MC1 becomes larger than the write verify level WREV, and the difference from the threshold voltage Vth of the negative cell MC2 becomes small. Therefore, in the blank erase state after the second-stage erase process, the difference between the threshold voltages Vth of the positive cell MC1 and the negative cell MC2 is very small. As a result, it is possible to prevent data “1” held in the twin cell from being read before the twin cell data is erased.
- FIG. 14B shows an example in which the twin cell data is “0”.
- the threshold voltage Vth of the positive cell MC1 and the negative cell MC2 is increased by writing to both cells with verify in the first stage. Since the threshold voltage Vth of the positive cell MC1 reaches the saturation level, the increase amount is small.
- the threshold voltage Vth of the negative cell MC2 becomes larger than the write verify level WREV, and the difference from the threshold voltage Vth of the positive cell MC1 becomes small. Therefore, in the blank erase state after the second-stage erase process, the difference between the threshold voltages Vth of the positive cell MC1 and the negative cell MC2 is very small. As a result, it is possible to prevent data “0” held in the twin cell from being read before erasing the twin cell data.
- the threshold voltage of both cells when a request for erasing twin cell data is received, the threshold voltage of both cells is increased to exceed the write verify level before the threshold voltage of both cells is decreased. Like that. As a result, the threshold voltage of both cells after decreasing the threshold voltage of both cells can be made independent of the write state before erasing the twin cell data, and the write state before erasing the twin cell data can be read. Can solve the problem.
- FIG. 15 is a flowchart showing the procedure of the erasing process of twin cell data according to the third embodiment.
- the flash sequencer 7 sets an erase target area (step S201).
- the flash sequencer 7 controls both cell writing without verification in steps S202 to S205.
- the flash sequencer 7 sets the write latch data to all the cells (positive cell MC1 and negative cell MC2) included in the erase target area to “0”. Specifically, the flash sequencer 7 sets the latch set high signal to “L” level and the latch set low signal to “H” level in the write latch circuit 54Pi of FIG. As a result, the data of the node NDP1, that is, the write latch data becomes the “L” level. Further, in the write latch circuit 54Ni of FIG. 10, the latch set high signal is set to the “L” level, and the latch set low signal is set to the “H” level. As a result, the data of the node NDN1, that is, the write latch data becomes “L” level (step S202).
- the flash sequencer 7 sets the writing mode (step S203).
- the flash sequencer 7 applies a write voltage to all the cells in the erase target area. That is, the flash sequencer 7 sets the voltage of the memory gate MG to 10V, the voltage of the source line SL to 6V, and the voltage of the control gate CG to 1.5V.
- the voltage to be applied is made smaller than the voltage for normal writing, or the period during which the write pulse WPLS is applied is shortened to perform weaker writing than in normal writing. It may be a thing.
- the increase amount of the threshold voltage of the memory cell having the smaller threshold voltage is smaller than the increase amount of the threshold voltage Vth during normal writing.
- the main bit line WMBL_iP is connected to the ground voltage Vss, and a write current flows through the main bit line WMBL_iP.
- a write current flows through the sub bit lines SBL_iP and SBL_i + 4P connected to the main bit line WMBL_iP.
- the main bit line WMBL_iN is connected to the ground voltage Vss, and a write current flows through the main bit line WMBL_iN.
- a write current flows through the sub bit lines SBL_iN and SBL_i + 4N connected to the main bit line WMBL_iN.
- the threshold voltages Vth of all the cells included in the erase target area increase (step S204).
- step S204 controls negative cell writing without verification in the next steps S206 to S209.
- the flash sequencer 7 sets the write latch data to the negative cell MC2 included in the erase target area to “0”, and sets the write latch data to the positive cell MC1 to “1”. Specifically, the flash sequencer 7 sets the latch set high signal to “H” level and the latch set low signal to “L” level in the write latch circuit 54Pi of FIG. As a result, the data of the node NDP1, that is, the write latch data becomes “H” level. Further, the flash sequencer 7 sets the latch set high signal to “L” level and the latch set low signal to “H” level in the write latch circuit 54Ni of FIG. As a result, the data of the node NDN1, that is, the write latch data becomes “L” level (step S206).
- the flash sequencer 7 sets the write mode (step S207).
- the flash sequencer 7 applies a write voltage to all the cells in the erase target area. That is, the flash sequencer 7 sets the voltage of the memory gate MG to 10V, the voltage of the source line SL to 6V, and the voltage of the control gate CG to 1.5V.
- the voltage to be applied is made smaller than the voltage for normal writing, or the period during which the write pulse WPLS is applied is shortened to perform weaker writing than in normal writing. It may be a thing.
- the main bit line WMBL_iP is connected to the power supply voltage VDD, and no write current flows through the main bit line WMBL_iP.
- no write current flows through the sub bit lines SBL_iP and SBL_i + 4P connected to the main bit line WMBL_iP.
- the main bit line WMBL_iN is connected to the ground voltage Vss, and a write current flows through the main bit line WMBL_iN.
- a write current flows through the sub bit lines SBL_iN and SBL_i + 4N connected to the main bit line WMBL_iN.
- the threshold voltage Vth of all the negative cells MC2 included in the erase target area is increased (step S208).
- step S208 controls the next erase process (step S107).
- FIG. 16 is a diagram illustrating an example of a change in the threshold voltage Vth of the positive cell MC1 and the negative cell MC2 due to the erasure of the twin cell data in the third embodiment.
- FIG. 16A shows an example in which the twin cell data is “1”.
- the threshold voltage Vth of the positive cell MC1 and the negative cell MC2 increases by writing to both cells without verification in the first half of the first stage. Further, the threshold voltage Vth of the negative cell MC2 is further increased by the writing to the negative cell MC2 without verification in the latter half of the first stage, and as a result, the threshold voltage Vth of the positive cell MC1 and the threshold voltage Vth of the negative cell MC2 are increased.
- the difference widens. Therefore, in the blank erase state after the erase process, the difference in threshold voltage Vth between the positive cell MC1 and the negative cell MC2 can be detected. As a result, the data “1” held in the twin cell may be read before the twin cell data is erased. However, this is not a problem as will be described later.
- FIG. 16B shows an example in which the twin cell data is “0”.
- the threshold voltage Vth of the positive cell MC1 and the negative cell MC2 increases by writing to both cells without verification in the first half of the first stage. Furthermore, the threshold voltage Vth of the negative cell MC2 is further increased by writing to the negative cell MC2 without verification in the latter half of the first stage. As a result, the threshold voltage Vth of the positive cell MC1 and the threshold voltage Vth of the negative cell MC2 are increased. The difference is reduced. Therefore, in the blank erase state after the erase process, the difference between the threshold voltages Vth of the positive cell MC1 and the negative cell MC2 becomes very small, and the read data has a value in which “0” or “1” varies randomly. As a result, it is possible to prevent data “0” held in the twin cell from being read before the twin cell data is erased.
- twin cell data “1” is accurately read out as “1”, but the twin cell data “0” is read out as “0” or surely read out as “1”. Not. As a result, it becomes difficult to specify the value of the twin cell data according to the read value, and it is possible to solve the security problem that the write state before erasing the twin cell data is read.
- FIG. 17 is a flowchart showing the procedure of the twin cell data erasing process according to the modification of the third embodiment.
- the flash sequencer 7 sets the write latch data to the negative cell MC2 included in the erase target area to “0”, and sets the write latch data to the positive cell MC1 to “1”. Specifically, the flash sequencer 7 sets the latch set high signal to “H” level and the latch set low signal to “L” level in the write latch circuit 54Pi of FIG. As a result, the data of the node NDP1, that is, the write latch data becomes “H” level. Further, the flash sequencer 7 sets the latch set high signal to “L” level and the latch set low signal to “H” level in the write latch circuit 54Ni of FIG. As a result, the data of the node NDN1, that is, the write latch data becomes “L” level (step S906).
- the flash sequencer 7 sets the write mode (step S907).
- the flash sequencer 7 applies a write voltage to all the cells in the erase target area. That is, the flash sequencer 7 sets the voltage of the memory gate MG to 10V, the voltage of the source line SL to 6V, and the voltage of the control gate CG to 1.5V.
- the voltage to be applied is not made smaller than the normal write voltage, and the period for applying the write pulse WPLS is not shortened.
- the main bit line WMBL_iP is connected to the power supply voltage VDD, and no write current flows through the main bit line WMBL_iP.
- no write current flows through the sub bit lines SBL_iP and SBL_i + 4P connected to the main bit line WMBL_iP.
- the main bit line WMBL_iN is connected to the ground voltage Vss, and a write current flows through the main bit line WMBL_iN.
- a write current flows through the sub bit lines SBL_iN and SBL_i + 4N connected to the main bit line WMBL_iN.
- the threshold voltage Vth of all the negative cells MC2 included in the erase target area is increased (step S908).
- a write verify check is performed. That is, the verify sense amplifier VSA_N outputs an “L” level signal when the threshold voltage Vth of the negative cell MC2 is higher than the write verify level WREV.
- the exclusive OR gate EXOR_N outputs an exclusive OR of the output of the verify sense amplifier VSA_N and the write latch data “0” output from the write latch circuit 54Ni to the inverted signal line NSL.
- the output OUT2 of the exclusive OR gate EXOR_N is sent to the flash sequencer 7 through the peripheral data bus PBUS_D.
- the output OUT2 becomes “H” level when the threshold voltage Vth of the negative cell MC2 is higher than the write verify level WREV (step S909).
- the flash sequencer 7 maintains the write mode. That is, the processes in steps S908 and S909 are repeated.
- the flash sequencer 7 controls the next erase process (step S107). .
- the threshold voltage Vth of the negative cell MC2 is surely made larger than the erase verify level, so that security can be more reliably ensured.
- FIG. 18 is a flowchart showing the procedure of the twin cell data erasing process of the fourth embodiment.
- the flash sequencer 7 sets an erase target area (step S301).
- the flash sequencer 7 controls the reading of the twin cell data in the erase target area.
- the flash sequencer 7 applies a read voltage to all the cells (positive cell MC1 and negative cell MC2) in the erase target area. That is, the flash sequencer 7 sets the voltage of the memory gate MG to 0V, the voltage of the source line SL to 0V, and the voltage of the control gate CG to 1.5V.
- the twin cell data is “0”
- the data sent from the hierarchical sense amplifier SA to the flash sequencer 7 is “0”
- the twin cell data is “1”
- the data is sent from the hierarchical sense amplifier SA to the flash sequencer 7.
- the obtained data is “1” (step 302).
- the flash sequencer 7 controls writing of the selected cell with verify in steps S303 to S307.
- the flash sequencer 7 sets the write latch data to the negative cell MC2 to “0” and sets the write latch data to the positive cell MC1 to “1”.
- the flash sequencer 7 sets the write latch data to the negative cell MC2 to “1” and sets the write latch data to the positive cell MC1 to “0”.
- the flash sequencer 7 sets the latch set high signal to “L” level and sets the latch set low signal to “H” in the write latch circuit 54Pi of FIG. Set to level.
- the data of the node NDP1, that is, the write latch data becomes the “L” level.
- the flash sequencer 7 sets the latch set high signal to “H” level and the latch set low signal to “L” level in the write latch circuit 54Pi of FIG. .
- the data of the node NDP1, that is, the write latch data becomes “H” level.
- the flash sequencer 7 sets the latch set high signal to “L” level and the latch set low signal to “H” level in the write latch circuit 54Ni of FIG. Set. As a result, the data of the node NDN1, that is, the write latch data becomes “L” level.
- the flash sequencer 7 sets the latch set high signal to “H” level and the latch set low signal to “L” level in the write latch circuit 54Ni of FIG. . As a result, the data of the node NDN1, that is, the write latch data becomes “H” level (step S303).
- the flash sequencer 7 sets the write mode (step S304).
- the flash sequencer 7 applies a write voltage to all the cells in the erase target area. That is, the flash sequencer 7 sets the voltage of the memory gate MG to 10V, the voltage of the source line SL to 6V, and the voltage of the control gate CG to 1.5V.
- the main bit line WMBL_iP is connected to the ground voltage Vss, and the write current is applied to the main bit line WMBL_iP. Flowing. As a result, a write current flows through the sub bit lines SBL_iP and SBL_i + 4P connected to the main bit line WMBL_iP.
- the main bit line WMBL_iP is connected to the power supply voltage VDD, and the write current is applied to the main bit line WMBL_iP. Not flowing. As a result, no write current flows through the sub bit lines SBL_iP and SBL_i + 4P connected to the main bit line WMBL_iP.
- the main bit line WMBL_iN is connected to the ground voltage Vss, and the write to the main bit line WMBL_iN is performed. Current flows. As a result, a write current flows through the sub bit lines SBL_iN and SBL_i + 4N connected to the main bit line WMBL_iN.
- the main bit line WMBL_iN is connected to the power supply voltage VDD, and the write current is applied to the main bit line WMBL_iN. Not flowing. As a result, no write current flows through the sub bit lines SBL_iN and SBL_i + 4N connected to the main bit line WMBL_iN.
- the threshold voltage Vth of the positive cell MC1 or the negative cell MC2 having the smaller threshold voltage Vth among both cells included in the erasure target region increases (step S305).
- a write verify check is performed. That is, when the read data is “1”, the verify sense amplifier VSA_P outputs an “L” level signal when the threshold voltage Vth of the positive cell MC1 is higher than the write verify level WREV.
- the exclusive OR gate EXOR_P outputs an exclusive OR of the output of the verify sense amplifier VSA_P and the write latch data “0” output from the write latch circuit 54Pi to the signal line PSL.
- the output OUT1 of the exclusive OR gate EXOR_P is sent to the flash sequencer 7 through the peripheral data bus PBUS_D.
- the output OUT1 becomes “H” level when the threshold voltage Vth of the positive cell MC1 is larger than the write verify level WREV.
- the verify sense amplifier VSA_N when the read data is “0”, the verify sense amplifier VSA_N outputs an “L” level signal when the threshold voltage Vth of the negative cell MC2 is higher than the write verify level WREV.
- the exclusive OR gate EXOR_N outputs an exclusive OR of the output of the verify sense amplifier VSA_N and the write latch data “0” output from the write latch circuit 54Ni to the inverted signal line NSL.
- the output OUT2 of the exclusive OR gate EXOR_N is sent to the flash sequencer 7 through the peripheral data bus PBUS_D.
- the output OUT2 becomes “H” level when the threshold voltage Vth of the negative cell MC2 is higher than the write verify level WREV (step S306).
- the flash sequencer 7 Maintains the write mode. That is, the processes of steps S305 and S306 are repeated.
- step S107 If the threshold voltage Vth of the memory cell in which the threshold voltage Vth of all the cells included in the erase target area is increased is higher than the write verify level WREV (YES in step 307), the flash sequencer 7 Controls the next erasure process (step S107).
- FIG. 19 is a diagram illustrating an example of a change in the threshold voltage Vth of the positive cell MC1 and the negative cell MC2 due to the erasure of the twin cell data in the fourth embodiment.
- FIG. 19A shows an example in which the twin cell data is “1”.
- the twin cell data is “1”
- the negative cell MC2 has a lower threshold voltage Vth than the positive cell MC1.
- the threshold voltage Vth of the negative cell MC2 increases by writing to the selected cell with verification in the latter half of the first stage. As a result, the difference between the threshold voltage Vth of the positive cell MC1 and the threshold voltage Vth of the negative cell MC2 is reduced.
- the difference between the threshold voltages Vth of the positive cell MC1 and the negative cell MC2 becomes very small, and the read data has a value in which “0” or “1” varies randomly.
- the threshold voltage Vth of the positive cell MC1 is not increased in the first stage, stress applied to increase the threshold voltage can be reduced.
- FIG. 19B shows an example in which the twin cell data is “0”.
- the twin cell data is “0”
- the threshold voltage Vth of the positive cell MC1 is smaller than that of the negative cell MC2.
- the threshold voltage Vth of the positive cell MC1 increases by writing to the selected cell with verification in the latter half of the first stage. As a result, the difference between the threshold voltage Vth of the positive cell MC1 and the threshold voltage Vth of the negative cell MC2 is reduced.
- the difference between the threshold voltages Vth of the positive cell MC1 and the negative cell MC2 becomes very small, and the read data has a value in which “0” or “1” varies randomly. As a result, it is possible to prevent data “0” held in the twin cell from being read before the twin cell data is erased. Further, since the threshold voltage Vth of the negative cell MC2 is not increased in the first stage, the stress applied to increase the threshold voltage can be reduced.
- FIG. 20 is a flowchart showing the procedure of the twin cell data erasing process of the fifth embodiment.
- the flash sequencer 7 sets an erase target area (step S401).
- the flash sequencer 7 controls both cell writing without verification in steps S402 to S405. Since the processing in steps S402 to S405 is the same as the processing in steps S202 to S205 in FIG. 15, the description will not be repeated.
- step 406 the flash sequencer 7 reads the twin cell data in the area to be erased. Since the process of step S406 is the same as the process of step S302 of FIG. 18, the description will not be repeated.
- the flash sequencer 7 controls writing of the selected cell with verification in steps S407 to S411.
- the processing in steps S407 to S411 is the same as the processing in steps S303 to S307 in FIG. 18, and therefore description thereof will not be repeated.
- FIG. 21 is a diagram illustrating an example of changes in the threshold voltage Vth of the positive cell MC1 and the negative cell MC2 due to the erasing of the twin cell data in the fifth embodiment.
- FIG. 21A shows an example in which the twin cell data is “1”.
- the threshold voltage Vth of the positive cell MC1 and the negative cell MC2 increases by writing to both cells without verification in the first step of the first stage.
- the twin cell data is “1”
- the negative cell MC2 has a lower threshold voltage Vth than the positive cell MC1.
- the threshold voltage Vth of the negative cell MC2 further increases by writing to the selected cell with verification in the third step of the first stage. As a result, the difference between the threshold voltage Vth of the positive cell MC1 and the threshold voltage Vth of the negative cell MC2 is reduced.
- the difference between the threshold voltages Vth of the positive cell MC1 and the negative cell MC2 becomes very small, and the read data has a value in which “0” or “1” varies randomly.
- the threshold voltage Vth of the positive cell MC1 is not increased in the first stage, stress applied to increase the threshold voltage can be reduced.
- FIG. 21B shows an example in which the twin cell data is “0”.
- the threshold voltage Vth of the positive cell MC1 and the negative cell MC2 increases by writing to both cells without verification in the first step of the first stage.
- the twin cell data By reading the twin cell data in the second step of the first stage, it is found that the twin cell data is “0”, and the positive cell MC1 has a lower threshold voltage Vth than the negative cell MC2.
- the threshold voltage Vth of the positive cell MC1 further increases by writing to the selected cell with verification in the third step of the first stage. As a result, the difference between the threshold voltage Vth of the positive cell MC1 and the threshold voltage Vth of the negative cell MC2 is reduced.
- the difference between the threshold voltages Vth of the positive cell MC1 and the negative cell MC2 becomes very small, and the read data has a value in which “0” or “1” varies randomly. As a result, it is possible to prevent data “0” held in the twin cell from being read before the twin cell data is erased. Further, since the threshold voltage Vth of the negative cell MC2 is not increased in the first stage, the stress applied to increase the threshold voltage can be reduced.
- the present invention is not limited to the above embodiment, and includes, for example, the following modifications.
- the semiconductor device has both the above-described first-stage function and the pre-write (non-verify both-cell weak write) function as described in FIG. It is good also as what can be switched.
- MCU 1 microcomputer
- CPU central processing unit
- DMAC direct memory access controller
- BIF bus interface circuit
- RAM random access memory
- FMDL 6 flash memory module
- FSQC flash Sequencer
- PRT External I / O port
- TMR 10 Timer
- CPG 11 Clock pulse generator
- MAY 19,100 Memory array
- 20 Sub-bit line selector 22 Read column selector, 24 first row decoder (RDEC1), 25 second row decoder (RDEC2), 28 rewrite column selector, 29 input / output circuit (IOBUF), 30 column decoder (CDEC), 31 power supply circuit (VPG), 32, timing Generator (TMG), 40 read system discharge circuit, 41 write system discharge circuit, 281, 291 set unit, 82, 92 data input unit, 83, 93 data holding unit, 84, 94 setting unit, 90 erase verify circuit, 100 semiconductor Device, 101 memory array, 102 first storage element, 103 second storage element, 104 twin cell, 105 control circuit, 54Pi
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- Engineering & Computer Science (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Read Only Memory (AREA)
Abstract
Description
[第1の実施形態]
図1は、第1の実施形態の半導体装置の構成を表わす図である。
メモリアレイ101は、複数個のツインセル104を含む。ツインセル104は、閾値電圧Vthの相違によって2値データ(ツインセルデータ)を保持し、それぞれが電気的に書換え可能な第1記憶素子102と第2記憶素子103とからなる。
次に、制御回路105は、第1記憶素子102と第2記憶素子103の閾値電圧Vthが所定の書込みベリファイレベルとなるまで、第1記憶素子102と第2記憶素子103の両方または一方の閾値電圧を増加させる第1段階処理の実行を制御する(ステップS102)。
本実施の形態の半導体装置は、マイクロコンピュータである。
(マイクロコンピュータ)
図3は、第2の実施形態のマイクロコンピュータ1の構成を表わす図である。
図4は、フラッシュメモリモジュール6の構成を表わす図である。
図7(a)に示すように、ツインセルデータ“0”の消去を実行する場合に、プレライトによって、両方のセルが共にセルデータ“1”を保持するイニシャライズ状態となるが、消去前はポジティブセルMC1の閾値電圧Vthの方がネガティブセルMC2の閾値電圧Vthよりも大きいため、消去後でもこの関係が維持される可能性が想定される。この関係が維持された状態で読み出しを実施すると、イニシャライズ状態にも関わらずポジティブセルMC1とネガティブセルMC2の閾値電圧Vthに差があるために、不定値ではなく実質的に直前のツインセルデータ“0”と等しいデータ“0”を読み出してしまう可能性がある。
図7(b)に示すように、ツインセルデータ“1”の消去を実行する場合に、プレライトによって、両方のセルが共にセルデータ“1”を保持するイニシャライズ状態となるが、消去前はネガティブセルMC2の閾値電圧Vthの方がポジティブセルMC1の閾値電圧Vthよりも大きいため、消去後でもこの関係が維持される可能性が想定される。この直前のツインセルデータ状態で読み出しを実施すると、イニシャライズ状態にも関わらず、ポジティブセルMC1とネガティブセルMC2の閾値電圧Vthに差があるために、不定値ではなく実施的に直前のツインセルデータ“1”と等しいデータ“1”を読み出してしまう可能性がある。
図8は、第2の実施形態のツインセルデータの読出し系、書込み系、消去系の詳細な回路構成を表わす図である。書込み系の主ビット線としてWMBL_0P~WMBL_3P、WMBL_0N~WMBL_3Nの8本が例示され、そこに接続するメモリマットとして1個のメモリマットが例示される。特に制限されないが、副ビット線としてSBL_0P~SBL_7P、SBL_0N~SBL_7Nが配置され、1本の書込み系主ビット線WMBLに対して2本の副ビット線SBLが割り当てられる。
ポジティブセルMC1に割り当てられる主ビット線WMBL_iP(i=0~3)に対応する書込みラッチ回路54Piには、データバスPBUS_Dから非反転信号線PSLに供給された書込みデータが書換え列セレクタ28で選択されて供給される。
図10は、第2の実施形態の書込みラッチ回路54Pi(i=0~3)の構成を表わす図である。図10に示すように、書込みラッチ回路54Piは、セット部281と、データ入力部82と、データ保持部83と、設定部84と、インバータIV4とを備える。
インバータIV2の入力およびインバータIV3の出力がノードNDP1に接続され、インバータIV2の出力およびインバータIV3の入力がノードNDP2に接続される。
設定部84は、電源電圧VDDのラインと接地電圧Vssのラインとの間に設けられたPチャネルMOSトランジスタP2,P3と、NチャネルMOSトランジスタN2,N3,N4と、インバータIV5とを含む。インバータIV5は、プログラムパルス有効信号PPEを受ける。PチャネルMOSトランジスタP2のゲートは、インバータIV5の出力と接続される。PチャネルMOSトランジスタP3のゲートおよびNチャネルMOSトランジスタN2のゲートは、ノードNDP2に接続される。NチャネルMOSトランジスタN3のゲートは、プログラムパルス有効信号PPEを受ける。NチャネルMOSトランジスタN4のゲートは、書込みパルスWPLSを受ける。PチャネルMOSトランジスタP3とNチャネルMOSトランジスタN2との間のノードNDP3が主ビット線WMBL_iPに接続される。
設定部94は、電源電圧VDDのラインと接地電圧Vssのラインとの間に設けられたPチャネルMOSトランジスタP5,P6と、NチャネルMOSトランジスタN6,N7,N8と、インバータIV10を含む。インバータIV10は、プログラムパルス有効信号PPEを受ける。PチャネルMOSトランジスタP5のゲートは、インバータIV10の出力と接続される。PチャネルMOSトランジスタP6のゲートおよびNチャネルMOSトランジスタN6のゲートは、ノードNDN2に接続される。NチャネルMOSトランジスタN7のゲートは、プログラムパルス有効信号PPEを受ける。NチャネルMOSトランジスタN8のゲートは、書込みパルスWPLSを受ける。PチャネルMOSトランジスタP6とNチャネルMOSトランジスタN6との間のノードNDN3が主ビット線WMBL_iNに接続される。
図12は、第2の実施形態のツインセルデータの消去処理の手順を表わすフローチャートである。
次に、フラッシュシーケンサ7が、ステップS102~S106のベリファイあり両セル(ポジティブセルMC1とネガティブセルMC2)の書込みを制御する。
次に、フラッシュシーケンサ7が、消去対象領域のすべての両セルに書込み用の電圧を印加する。すなわち、フラッシュシーケンサ7は、メモリゲートMGの電圧を10V、ソース線SLの電圧を6V、コントロールゲートCGの電圧を1.5Vに設定する。
フラッシュシーケンサ7が、消去モードに設定する(ステップS801)。
第1段階のベリファイあり両セルへの書込みによって、ポジティブセルMC1およびネガティブセルMC2の閾値電圧Vthが増加する。ネガティブセルMC2の閾値電圧Vthは、飽和レベルに達するため増加量は、少量である。
第1段階のベリファイあり両セルへの書込みによって、ポジティブセルMC1およびネガティブセルMC2の閾値電圧Vthが増加する。ポジティブセルMC1の閾値電圧Vthは、飽和レベルに達するため増加量は、少量である。ここで、書込みベリファイが行なわれるため、ネガティブセルMC2の閾値電圧Vthが書込みベリファイレベルWREVよりも大きくなり、ポジティブセルMC1の閾値電圧Vthとの差が微小となる。そのため、第2段階の消去処理後のブランク消去状態では、ポジティブセルMC1とネガティブセルMC2の閾値電圧Vthに差が微小となる。その結果、ツインセルデータ消去前に、ツインセルが保持しているデータ“0”が読み出されるのを防止することができる。
図15は、第3の実施形態のツインセルデータの消去処理の手順を表わすフローチャートである。
次に、フラッシュシーケンサ7は、ステップS202~S205のベリファイなし両セル書込みを制御する。
次に、フラッシュシーケンサ7が、消去対象領域のすべての両セルに書込み用の電圧を印加する。すなわち、フラッシュシーケンサ7は、メモリゲートMGの電圧を10V、ソース線SLの電圧を6V、コントロールゲートCGの電圧を1.5Vに設定する。ここで、上記説明したプレライトと同様に、印加する電圧を通常の書込み用の電圧よりも小さくしたり、書込みパルスWPLSを与える期間を短くすることによって、通常の書込み時よりも弱い書込みを行なうものとしてもよい。プレライトでは、閾値電圧が小さい方のメモリセルの閾値電圧の増加量が、通常の書込み時の閾値電圧Vthの増加量よりも小さくなる。
次に、フラッシュシーケンサ7が、消去対象領域のすべての両セルに書込み用の電圧を印加する。すなわち、フラッシュシーケンサ7は、メモリゲートMGの電圧を10V、ソース線SLの電圧を6V、コントロールゲートCGの電圧を1.5Vに設定する。ここで、上記説明したプレライトと同様に、印加する電圧を通常の書込み用の電圧よりも小さくしたり、書込みパルスWPLSを与える期間を短くすることによって、通常の書込み時よりも弱い書込みを行なうものとしてもよい。
第1段階の前半のベリファイなし両セルへの書込みによって、ポジティブセルMC1およびネガティブセルMC2の閾値電圧Vthが増加する。さらに、第1段階の後半のベリファイなしネガティブセルMC2への書込みによって、ネガティブセルMC2の閾値電圧Vthがさらに増加するが、これによってポジティブセルMC1の閾値電圧VthとネガティブセルMC2の閾値電圧Vthとの差が広がる。そのため、消去処理後のブランク消去状態では、ポジティブセルMC1とネガティブセルMC2の閾値電圧Vthの差が検出可能となる。その結果、ツインセルデータ消去前に、ツインセルが保持しているデータ“1”が読み出される可能性がある。しかし、これは後述するように問題とならない。
第1段階の前半のベリファイなし両セルへの書込みによって、ポジティブセルMC1およびネガティブセルMC2の閾値電圧Vthが増加する。さらに、第1段階の後半のベリファイなしネガティブセルMC2への書込みによって、ネガティブセルMC2の閾値電圧Vthがさらに増加し、その結果、ポジティブセルMC1の閾値電圧VthとネガティブセルMC2の閾値電圧Vthとの差が縮小する。そのため、消去処理後のブランク消去状態では、ポジティブセルMC1とネガティブセルMC2の閾値電圧Vthの差が微小となり、読み出されるデータは“0”または“1”がランダムに変動する値となる。その結果、ツインセルデータ消去前に、ツインセルが保持しているデータ“0”が読み出されるのを防止できる。
[第3の実施形態の変形例]
図17は、第3の実施形態の変形例のツインセルデータの消去処理の手順を表わすフローチャートである。
次に、フラッシュシーケンサ7が、消去対象領域のすべての両セルに書込み用の電圧を印加する。すなわち、フラッシュシーケンサ7は、メモリゲートMGの電圧を10V、ソース線SLの電圧を6V、コントロールゲートCGの電圧を1.5Vに設定する。ここでは、プレライトのように、印加する電圧を通常の書込み用の電圧よりも小さくしたり、書込みパルスWPLSを与える期間を短くすることは行なわれない。
図18は、第4の実施形態のツインセルデータの消去処理の手順を表わすフローチャートである。
次に、フラッシュシーケンサ7が、消去対象領域のツインセルデータの読み出しを制御する。フラッシュシーケンサ7が、消去対象領域のすべての両セル(ポジティブセルMC1とネガティブセルMC2)に読出し用の電圧を印加する。すなわち、フラッシュシーケンサ7は、メモリゲートMGの電圧を0V、ソース線SLの電圧を0V、コントロールゲートCGの電圧を1.5Vに設定する。ツインセルデータが“0”の場合に、階層センスアンプSAからフラッシュシーケンサ7へ送られるデータは“0”となり、ツインセルデータが“1”の場合に、階層センスアンプSAからフラッシュシーケンサ7へ送られるデータは“1”となる(ステップ302)。
次に、フラッシュシーケンサ7が、ステップS303~S307のベリファイあり選択セルの書込みを制御する。
次に、フラッシュシーケンサ7が、消去対象領域のすべての両セルに書込み用の電圧を印加する。すなわち、フラッシュシーケンサ7は、メモリゲートMGの電圧を10V、ソース線SLの電圧を6V、コントロールゲートCGの電圧を1.5Vに設定する。
第1段階の前半のツインセルデータの読出しによって、ツインセルデータが“1”であり、ネガティブセルMC2の方がポジティブセルMC1よりも閾値電圧Vthが小さいことがわかる。第1段階の後半のベリファイあり選択セルへの書込みによって、ネガティブセルMC2の閾値電圧Vthが増加する。その結果、ポジティブセルMC1の閾値電圧VthとネガティブセルMC2の閾値電圧Vthとの差が縮小する。そのため、消去処理後のブランク消去状態では、ポジティブセルMC1とネガティブセルMC2の閾値電圧Vthの差が微小となり、読み出されるデータは“0”または“1”がランダムに変動する値となる。その結果、ツインセルデータ消去前に、ツインセルが保持しているデータ“1”が読み出されるのを防止できる。また、第1段階において、ポジティブセルMC1の閾値電圧Vthを増加させないので、閾値電圧を増加させるためにかかるストレスが低減できる。
第1段階の前半のツインセルデータの読出しによって、ツインセルデータが“0”であり、ポジティブセルMC1の方がネガティブセルMC2よりも閾値電圧Vthが小さいことがわかる。第1段階の後半のベリファイあり選択セルへの書込みによって、ポジティブセルMC1の閾値電圧Vthが増加する。その結果、ポジティブセルMC1の閾値電圧VthとネガティブセルMC2の閾値電圧Vthとの差が縮小する。そのため、消去処理後のブランク消去状態では、ポジティブセルMC1とネガティブセルMC2の閾値電圧Vthの差が微小となり、読み出されるデータは“0”または“1”がランダムに変動する値となる。その結果、ツインセルデータ消去前に、ツインセルが保持しているデータ“0”が読み出されるのを防止できる。また、第1段階において、ネガティブセルMC2の閾値電圧Vthを増加させないので、閾値電圧を増加させるためにかかるストレスが低減できる。
図20は、第5の実施形態のツインセルデータの消去処理の手順を表わすフローチャートである。
次に、フラッシュシーケンサ7は、ステップS402~S405のベリファイなし両セル書込みを制御する。ステップS402~S405の処理は、図15のステップS202~S205の処理と同様なので、説明を繰り返さない。
図21は、第5の実施形態における、ツインセルデータの消去によるポジティブセルMC1とネガティブセルMC2の閾値電圧Vthの変化の例を表わす図である。
第1段階の1番目のステップのベリファイなし両セルへの書込みによって、ポジティブセルMC1およびネガティブセルMC2の閾値電圧Vthが増加する。第1段階の2番目のステップのツインセルデータの読出しによって、ツインセルデータが“1”であり、ネガティブセルMC2の方がポジティブセルMC1よりも閾値電圧Vthが小さいことがわかる。第1段階の3番目のステップのベリファイあり選択セルへの書込みによって、ネガティブセルMC2の閾値電圧Vthがさらに増加する。その結果、ポジティブセルMC1の閾値電圧VthとネガティブセルMC2の閾値電圧Vthとの差が縮小する。そのため、消去処理後のブランク消去状態では、ポジティブセルMC1とネガティブセルMC2の閾値電圧Vthの差が微小となり、読み出されるデータは“0”または“1”がランダムに変動する値となる。その結果、ツインセルデータ消去前に、ツインセルが保持しているデータ“1”が読み出されるのを防止できる。また、第1段階において、ポジティブセルMC1の閾値電圧Vthを増加させないので、閾値電圧を増加させるためにかかるストレスが低減できる。
第1段階の1番目のステップのベリファイなし両セルへの書込みによって、ポジティブセルMC1およびネガティブセルMC2の閾値電圧Vthが増加する。第1段階の2番目のステップのツインセルデータの読出しによって、ツインセルデータが“0”であり、ポジティブセルMC1の方がネガティブセルMC2よりも閾値電圧Vthが小さいことがわかる。第1段階の3番目のステップのベリファイあり選択セルへの書込みによって、ポジティブセルMC1の閾値電圧Vthがさらに増加する。その結果、ポジティブセルMC1の閾値電圧VthとネガティブセルMC2の閾値電圧Vthとの差が縮小する。そのため、消去処理後のブランク消去状態では、ポジティブセルMC1とネガティブセルMC2の閾値電圧Vthの差が微小となり、読み出されるデータは“0”または“1”がランダムに変動する値となる。その結果、ツインセルデータ消去前に、ツインセルが保持しているデータ“0”が読み出されるのを防止できる。また、第1段階において、ネガティブセルMC2の閾値電圧Vthを増加させないので、閾値電圧を増加させるためにかかるストレスが低減できる。
本発明の実施の形態では、ツインセルデータの消去要求を受けたときに、第1記憶素子102と第2記憶素子103の閾値電圧が所定の書込みベリファイレベルとなるまで、第1記憶素子102と第2記憶素子103の両方または一方の閾値電圧を増加させる第1段階処理の実行を制御するものとしたが、本発明は、上記第1段階の処理に限定されるものではない。
Claims (7)
- 閾値電圧の相違によって2値データを保持し、それぞれが電気的に書換え可能な第1記憶素子と第2記憶素子とからなるツインセルを複数個含むメモリアレイと、
前記ツインセルデータの消去要求を受けたときに、前記第1記憶素子の閾値電圧と前記第2記憶素子の閾値電圧が所定の書込みベリファイレベルとなるまで、前記第1記憶素子と前記第2記憶素子の両方または一方の閾値電圧を増加させる第1段階処理の実行を制御し、
前記第1段階処理の実行後に、前記第1記憶素子の閾値電圧と前記第2記憶素子の閾値電圧が所定の消去ベリファイレベルとなるまで、前記第1記憶素子の閾値電圧と前記第2記憶素子の閾値電圧をともに減少させる第2段階処理の実行を制御する制御部とを備えた、半導体装置。 - 前記半導体装置は、ベリファイ用センスアンプを備え、
前記制御部は、前記第1段階処理において、前記第1記憶素子の閾値電圧と前記第2記憶素子の閾値電圧をともに増加させるとともに、前記ベリファイ用センスアンプに前記第1記憶素子の閾値電圧と前記書込みベリファイレベルとを比較させ、かつ前記第2記憶素子の閾値電圧と前記書込みベリファイレベルとを比較させる、請求項1記載の半導体装置。 - 前記半導体装置は、ベリファイ用センスアンプを備え、
前記制御部は、前記第1段階処理において、前記第1記憶素子の閾値電圧と前記第2記憶素子の閾値電圧をともに増加させる処理が所定回数実行されるように制御し、その後、前記第1記憶素子と前記第2記憶素子のうちの予め定められた一方の記憶素子の閾値電圧を増加させるとともに、前記ベリファイ用センスアンプに前記一方の記憶素子の閾値電圧と前記書込みベリファイレベルとを比較させる、請求項1記載の半導体装置。 - 前記半導体装置は、ベリファイ用センスアンプを備え、
前記制御部は、前記第1段階処理において、前記ツインセルデータを読み出す処理が実行されるように制御し、その後、前記第1記憶素子および前記第2記憶素子のうち前記読み出されたツインセルデータに応じて選択された記憶素子の閾値電圧を増加させるとともに、前記ベリファイ用センスアンプに前記選択された記憶素子の閾値電圧と前記書込みベリファイレベルとを比較させる、請求項1記載の半導体装置。 - 前記半導体装置は、ベリファイ用センスアンプを備え、
前記制御部は、前記第1段階処理において、前記第1記憶素子の閾値電圧と前記第2記憶素子の閾値電圧をともに増加させる処理が所定回数実行されるように制御し、その後、前記ツインセルデータを読み出す処理が実行されるように制御し、その後、前記第1記憶素子および前記第2記憶素子のうち前記読み出されたツインセルデータに応じて選択された記憶素子の閾値電圧を増加させるとともに、前記ベリファイ用センスアンプに前記選択された記憶素子の閾値電圧と前記書込みベリファイレベルとを比較させる、請求項1記載の半導体装置。 - 前記制御部は、前記所定回数実行される前記第1記憶素子の閾値電圧と前記第2記憶素子の閾値電圧をともに増加させる処理において、閾値電圧が小さい方の記憶素子の閾値電圧の増加量が通常の書き込み時よりも小さくなるように前記第1記憶素子と前記第2記憶素子に与える電圧を制御する、請求項3または5記載の半導体装置。
- 閾値電圧の相違によって2値データを保持し、それぞれが電気的に書換え可能な第1記憶素子と第2記憶素子とからなるツインセルを複数個含むメモリアレイと、
前記ツインセルデータの消去要求を受けたときに、第1段階処理と、その後の第2段階処理の実行を制御する制御部とを備え、
前記制御部は、前記第1段階処理において、前記第1記憶素子の閾値電圧と前記第2記憶素子の閾値電圧をともに増加させる処理が所定回数実行されるように制御し、その後、前記第1記憶素子と前記第2記憶素子のうちの予め定められた一方の記憶素子の閾値電圧を増加させる処理が所定回数実行されるように制御し、
前記第2段階処理において、前記第1記憶素子の閾値電圧と前記第2記憶素子の閾値電圧が所定の消去ベリファイレベルとなるまで、前記第1記憶素子の閾値電圧と前記第2記憶素子の閾値電圧をともに減少させる第2段階処理の実行を制御する、半導体装置。
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