JP2008041157A - Memory cell, and nonvolatile storage device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To keep an operation speed equivalent to that of a DRAM device and to store data when power is turned off. <P>SOLUTION: This memory cell has a first field effect transistor (FET) whose first control terminal is connected to a first control signal line and whose first terminal is connected to a bit line; a capacitor whose one end is connected to the second terminal of the first FET and the other end of which is connected to a first reference potential; a second FET whose third terminal is connected to a storage node connected with the second terminal of the first FET and the one end of the capacitor and whose second control terminal is connected to a second control signal line; and a nonvolatile storage element whose one end is connected to the fourth terminal of the second FET and the other end of which is connected to a second reference potential, substitutes for a part of refresh operation and stores information when power is turned off. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a memory cell in which a nonvolatile function is added to a volatile memory device and a nonvolatile memory device, and more particularly, to a memory cell in which a nonvolatile memory cell having a nonvolatile memory element is added to a DRAM (Dynamic Random Access Memory) cell. It is to provide a non-volatile storage device.

FIG. 11 shows an entire block configuration of a conventional DRAM device 300 and a circuit configuration of a memory cell. The DRAM device 300 includes a word line driver / nonvolatile memory element driving circuit 310, a memory cell array 320, a decoder / control circuit 340, a cell plate potential (Vcp) generation circuit 350, a write buffer / sense amplifier 360, and the like.
In this memory cell array 320, memory cells C0,0 to Cn-1, m-1 are arranged in a matrix of n rows and m columns, and each memory cell C0,0 to Cn-1, m-1 is composed of a select transistor and a capacitor. It is configured.
The DRAM device 300 shown in FIG. 11 in which the memory cells C0,0 to Cn−1, m−1 are composed of 1T (transistor) -1C (capacitor) is widely used as a most general memory in semiconductors for all purposes. Used, it is very good in terms of high-speed performance and stable operation.
However, since the stored information is lost when the power is turned off, it cannot be used as it is for a nonvolatile memory. In addition, a memory holding operation called refresh is required at regular intervals even during the power-on period.
On the other hand, flash memory is generally used as a non-volatile memory, but the NOR / NAND type has a slow write / erase speed of 10 microseconds to 10 milliseconds, and the number of rewrites is about 100,000 times. Therefore, even if it is suitable for data storage use and file storage use, it is difficult to say that it is a general-purpose nonvolatile memory.
Patent Document 3 discloses another nonvolatile memory device in which a memory cell includes only a nonvolatile memory element and an access transistor.
JP-A-5-226667 JP 2005-25914 A JP 2005-216387 A JP 2005-268591 A

As described above, a method using an external NOR type or NAND type flash memory is used as a method of saving the memory information of the DRAM device when the power is turned off. However, a large bus wiring capacity or external connection terminal capacity is charged. Because of the discharge, the power consumption for data transfer increases, and there are problems that the data transfer time becomes longer due to the slow write / erase speed to the flash memory. Inappropriate.
Furthermore, since power is consumed in a refresh operation involving charging / discharging of the bit line capacity, there is a problem that standby power consumption of the DRAM device increases with increasing integration.
In addition, as an example of a nonvolatile memory device, Patent Document 3 discloses a nonvolatile memory device in which a memory cell is configured only by a nonvolatile memory element and an access transistor. In this case, during normal operation, it takes time to write data to the nonvolatile memory element from the outside. Therefore, the operation speed is slower than the DRAM device, and the number of rewrites is limited. There is a problem in that it is difficult to use for applications.
The present invention has been made in view of the above problems, and an object thereof is to provide a storage device in which a nonvolatile function is added to a DRAM device. Here, the addition of a nonvolatile function to the DRAM device means (1) saving information when power is turned off (hereinafter referred to as “save operation”) and re-reading operation of saved information when power is turned on (hereinafter referred to as “restore operation”). ), And (2) an operation of omitting (partly replacing) the refresh operation.

  The memory cell of the present invention includes a first field effect transistor in which a first control terminal is connected to a first control signal line, a first terminal is connected to a bit line, and one end of the first field effect transistor. A capacitor connected to the second terminal of the transistor and having the other end connected to the first reference potential, and a storage node connected to the second terminal of the first field effect transistor and one end of the capacitor 3 is connected, the second control terminal is connected to the second control signal line, the second field effect transistor, one end is connected to the fourth terminal of the second field effect transistor, A nonvolatile memory element having the other end connected to the second reference potential.

  A nonvolatile memory device according to the present invention includes a memory cell having nonvolatile memory elements arranged in a matrix and a word line that commonly connects the gate terminals of the first field effect transistors for accessing the memory cell in the row direction. A bit line that commonly connects the drain ends of the first field effect transistors in the column direction, a second reference potential supply line that commonly connects one end of the nonvolatile memory elements in the row direction, and the nonvolatile memory A second signal line commonly connecting the gate terminals of the control field effect transistors in the row direction in the row direction. The memory cell has a gate connected to the word line and a drain connected to the bit line. A first field effect transistor connected; a capacitor having one end connected to the source of the first field effect transistor and the other end connected to a reference potential; A second field effect transistor for control having a drain connected to a storage node to which a source of the first field effect transistor and one end of the capacitor are connected, and a gate connected to the second signal line; Is connected to the source of the second field effect transistor, and the other end of the nonvolatile memory element is connected to the second reference potential supply line.

The nonvolatile memory device of the present invention includes a decoder / control circuit to which address data, a clock, a control signal, etc. are supplied, which decodes the address data and generates a first control signal, that is, a word line selection signal at a predetermined timing. A word line driver / driving circuit which is supplied with the word line selection signal and outputs a word line drive signal for driving a word line of an arbitrary memory cell; and the word line drive signal and bit for selecting the memory cell A volatile first memory cell selected by a line control signal, connected to a storage node of the volatile first memory cell, controlled by second and third control signals, and The memory cells having one memory cell and a non-volatile second memory cell for exchanging, storing, and erasing data are arranged in a matrix Has a Moriseruarei, via the bit line connected to the select transistor of the first memory cell of the volatile, the write buffer / sense amplifier for writing read data.
By providing a non-volatile memory cell in the first volatile memory cell, the data in the non-volatile memory cell is transferred to the volatile memory cell in the same cell during a period in which no data is written to the volatile memory cell from the outside. The operation equivalent to the refresh operation is performed.
When the power is turned off, the data in the volatile memory cell is transferred to the nonvolatile memory cell and stored therein, thereby storing the data during the power-off period.

  The memory cell and the nonvolatile memory device of the present invention save the stored information when the power is turned off (save operation) and reread the saved information when the power is turned on while maintaining the operation speed and ease of use of the DRAM device. Operation) and a non-volatile function of omission of refresh operation (partial replacement) can be realized.

FIG. 1 shows the configuration of the memory cell 100 according to the first embodiment of the present invention. FIG. 2 shows the electrical characteristics of the nonvolatile memory (nonvolatile variable resistance) element 7 constituting the memory cell 100, I (current) −V. (Voltage) characteristics and R (resistance) -V (voltage) characteristics are shown.
The operation mechanism of the non-volatile memory (ARAM) element 7 is described in detail in the above-mentioned reference 3.
In order to clarify the terms hereinafter, a cell corresponding to a DRAM cell is referred to as a volatile memory cell (or simply a DRAM cell), a cell having a nonvolatile function is referred to as a nonvolatile memory cell, and these are collectively referred to as one cell unit. A circuit is defined as a memory cell.

First, FIG. 1 shows a circuit configuration of a memory cell 100 according to the first embodiment of the present invention.
The memory cell 100 includes a volatile DRAM cell (volatile memory cell) and a nonvolatile memory cell. The DRAM cell is composed of an NMOS transistor 1 and a capacitor 2, and the nonvolatile memory cell is composed of an NMOS transistor 6 and a nonvolatile memory element 7.
Next, the connection configuration of these elements will be described. The drain of the select transistor NMOS transistor 1 is connected to the bit line 3, the gate is connected to the word line 4, and the source is connected to one terminal of the capacitor 2 and the drain of the charge transfer NMOS transistor 6. The other terminal of the capacitor 2 is connected to the terminal of the cell plate electrode (VCP).
The gate of the NMOS transistor 6 is connected to the nonvolatile memory element control signal line (NV _- EN line) 8, and the source is connected to one terminal of the nonvolatile memory element 7. The other terminal of the nonvolatile memory element 7 is connected to a nonvolatile memory element power source (PWR line) 9.
The control signals supplied to the nonvolatile memory element control signal line (NV _- EN line) 8 and the nonvolatile memory element power supply (PWR line) 9 will be described in detail later with reference to timing charts.

2A and 2B show electrical characteristics when a nonvolatile variable resistance element is used as the nonvolatile memory element 7. FIG. The nonvolatile memory element 7 is not limited to a nonvolatile variable resistance element, and corresponds to a predetermined electrical characteristic, for example, “1” or “0” by voltage, current, or other electrical action. Any data can be used as long as the data is retained after the power is turned off.
FIG. 2A shows current-voltage (IV) characteristics of the nonvolatile memory element 7. In the initial state where the applied voltage is near 0 [V], the resistance value is large and the current hardly flows. However, when the write threshold voltage Vw is 0.5 to 1 [V] or more, the resistance value rapidly decreases, As a result, current flows. At this time, the resistance value of the nonvolatile memory element 7 changes from a high resistance value to a low resistance value, and the resistance value is maintained. When the applied voltage is further increased, the nonvolatile memory element 7 exhibits ohmic characteristics, and current flows in proportion to the voltage. Thereafter, even if the applied voltage is decreased to 0 V, the nonvolatile memory element 7 continues to maintain the low resistance value.

  Next, when a negative voltage is applied to the nonvolatile memory element 7 and the applied voltage is further increased toward the negative voltage side, the current increases accordingly, but when the erase threshold voltage −Ve is reached, the current rapidly decreases. To do. At that time, the resistance value of the nonvolatile memory element 7 changes to the same high resistance as in the initial state, and the resistance value is maintained. Thereafter, even if the applied voltage is returned to 0 V, the nonvolatile memory element 7 continues to hold the high resistance value.

FIG. 2B shows the voltage and resistance characteristics of the nonvolatile memory element 7. When the voltage range applied to the nonvolatile memory element 7 is -Ve to Vw, the resistance value changes greatly, the resistance value at the time of writing is small, and the resistance value at the time of erasing is large. The change ratio of this resistance is about 10 ¹ to 10 ⁵ .
Even when the applied voltage is set to Vw or more or −Ve or less, the nonvolatile memory element 7 maintains the resistance value at the time of writing or erasing.
Thus, since the nonvolatile memory element 7 has the above-described voltage-current (or voltage-resistance) characteristics, it has a memory function. Therefore, the nonvolatile memory element 7 is combined with a DRAM cell to form a nonvolatile memory. A cell and a nonvolatile memory device using the cell can be realized.
Further, although the example of the variable resistance element is shown as the nonvolatile memory element (ARAM) 7, the ON / OFF change ratio of this resistance is required to be about 100 times. As another variable resistance element, for example, there is a chalcogenite phase change memory.
The nonvolatile memory element 7 is not limited to a variable resistance element. As another example of a memory operation type, a nonvolatile FeRAM capable of writing / erasing data by changing a voltage applied to the nonvolatile memory element 7 (Ferroelectric capacitor).

Next, the operation of the memory cell 100 shown in FIG. 1 will be described with reference to timing charts of the respective operation modes shown in FIGS.
FIG. 3 and FIG. 4 are timing charts for explaining operations around the memory cell during a read operation and a write operation of a general DRAM cell, respectively. Recently, a synchronous DRAM device is common, but in order to simplify the description, an EDO (Extended Data Out) DRAM device will be described as an operation example of the DRAM portion.

First, an operation of reading data from a volatile memory cell composed of an access transistor (NMOS transistor (N-channel Metal Oxide Semiconductor)) 1 and a capacitor 2 to the outside will be described using the timing chart of FIG.
For example, during a read operation of a volatile memory cell composed of the capacitor 2 and the NMOS transistor 1, the row address X is determined at the falling edge of the / RAS (Row Address Strobe) input (RAS inversion) signal (FIG. 3 (c)). A certain word line 4 is selected and has a high potential (FIG. 3 (h)). Then, the bit line 3 changes slightly higher or lower than the reference potential according to the potential state of the cell internal storage node 10 (of the volatile memory cell) (FIG. 3 (g)). In this state, the sense amplifier connected to the bit line 3 is activated to drive the potential of the bit line 3 and the cell internal storage node 10 to VDD (power supply voltage) or 0 (ground potential) (FIG. 3 (i )).
After that, a bit line having a column address Y determined at the falling edge of the input of the / CAS (Column Address Strobe) signal (CAS inversion) is selected (FIGS. 3B and 3C). Data of “1” or “0” is output to the output terminal according to the potential state. Thereafter, the word line 4 returns to a low potential at the rising edge of the input of the / RAS signal (FIGS. 3A and 3H), the cell internal storage node 10 is electrically disconnected from the bit line 3, and the memory cell is disconnected. The data holding state is entered and a series of read operations are completed.

Next, an operation of writing data to the volatile memory cell from the outside will be described using the timing chart of FIG.
In the write operation, as in the read operation, the address X is determined at the falling edge of the input of the / RAS signal, the word line 4 is selected (FIGS. 4A, 4C, and 4H), and the bit line 3 Then, VDD (power supply voltage) or 0 potential is sensed and output (FIG. 4 (g)). In this state, the column address Y is determined at the falling edge of the / CAS signal (FIG. 4C), and the input of the / WE (WE (write enable) inverted) signal is set to a low potential (FIG. d)), the bit line 3 is driven by the write buffer up to VDD or 0 [V] in accordance with “1” or “0” data of the input terminal (FIG. 4G). At the same time, the potential of the storage node 10 in the cell is also driven to the same potential as that of the bit line 3, and the write operation is executed (FIG. 4 (i)). Thereafter, at the rising edge of the input of the / RAS signal, the word line 4 returns to the low potential (FIGS. 4A and 4H), the cell internal storage node 10 is electrically disconnected from the bit line 3, and the memory cell is disconnected. A data holding state is entered, and a series of writing operations is completed (FIG. 4 (i)).
During the write operation, the flag (FLAG) corresponding to the selected word line 4 is set to “1” for the purpose of controlling the refresh operation described later.

Next, the operation around the memory cell (100) during the refresh operation will be described with reference to the timing chart of FIG.
FIG. 5 shows a timing chart when an external write operation is performed (FLAG = 1) from the previous refresh to the current refresh period. When no data is written to the volatile memory cell from the outside, no flag (FLAG = 0) is set.
First, the word line 4 for which the address X is determined at the falling edge of the input of the / RAS signal is selected (FIGS. 5A, 5C, and 5H). As in the read operation, the VDD or 0 potential is sensed and driven on the bit line 3 in accordance with the potential state of the cell internal storage node 10 (FIG. 5G), and the potential remains as it is. (A refresh operation of a general DRAM device is performed) (FIG. 5 (i)).
At this time, the nonvolatile memory element control signal line (NV_EN line) 8 is set to a high potential while the word line 4 remains at a high potential (FIG. 5 (j)), and the cell internal storage node 10 and the nonvolatile memory (variable resistance) ) The element 7 is brought into conduction (FIG. 5 (i)). The nonvolatile memory element power supply line (PWR line) 9 is kept at a high potential during the period 101 shown in FIG. 5J (FIGS. 5J and 5K). In this state, the nonvolatile memory element 7 is erased and becomes high resistance.
Next, the PWR line 9 is changed to a low potential in the form of a pulse for a period of 102 (FIGS. 5 (j) and (k)), so that data is stored in the nonvolatile storage element 7 in accordance with the potential state of the cell internal storage node 10. The operation of whether recording is performed or whether the data erase state is maintained is executed. That is, when the potential of the cell internal storage node 10 is VDD, a recording operation is performed on the nonvolatile storage element 7 and the resistance becomes low (FIGS. 5K and 5I).
When the potential of the cell internal storage node 10 is 0 [V], the nonvolatile storage element 7 remains in the erased state (high resistance) and nothing happens (FIG. 5 (i)).

In this manner, information in the cell internal storage node 10 can be transferred (saved) to the nonvolatile storage element (nonvolatile variable resistance element) 7.
Note that the flag corresponding to the word line 4 selected during the refresh operation is cleared to “0” (FLAG = 0).

Next, a refresh operation when no external write operation is performed (FLAG = 0) from the previous refresh to the current refresh period will be described using the timing chart of FIG.
In this case, the word line 4 of the selected row address remains at a low potential (FIG. 6 (h)), and the NV_EN line 8 inside the memory cell has a high potential in the form of a pulse for the period 103 shown in FIG. 6 (j). By doing so (FIG. 6J), the cell internal storage node 10 and the nonvolatile storage element 7 are made conductive. Then, when the nonvolatile memory element 7 is in a recording state (low resistance), charge is replenished from the PWR line 9 to the cell internal storage node 10 and an operation similar to the refresh operation is performed (FIG. 6 (i), ( j), (k)).
In this series of operations, there is neither charge / discharge of the bit line 3 nor sense amplifier operation, so the power consumption is almost zero.

Next, operations immediately after power-on and immediately before power-off will be described.
FIG. 7 shows a timing chart immediately after power-on. The operation of the memory cell immediately after power-on will be described using this timing chart. The word line 4 for which the address X is determined at the falling edge of the / RAS signal input is selected (FIGS. 7A, 7C, 7H), and “0” is written in the memory cell (FIG. 7 ( i)). Thereafter, the access transistor 1 is closed, and the MOS transistor 6 for controlling the non-volatile memory element (for charge transfer) is made conductive only for the period 104 (FIG. 7 (j)), and non-volatile by the charge injection operation similar to the case of FIG. The storage information of the storage element 7 is restored to the cell internal storage node 10 (FIGS. 7 (i) and (j)).
During the operation period immediately after the power is turned on, the flag corresponding to the selected word line 4 is cleared to “0” (FLAG = 0) for the purpose of performing the refresh operation control as described above.

Next, the operation of the memory cell immediately before power off will be described.
If the flag (FLAG) = 1 immediately before power off, the information in the cell internal storage node 10 is saved in the nonvolatile storage element 7 by performing the same operation as the refresh operation shown in FIG.
On the other hand, if the flag (FLAG) = 0 immediately before the power is turned off, no special operation for restoration is performed.

As described above, by adding a nonvolatile function to the DRAM memory cell, stored information can be saved in the nonvolatile memory element 7 when the power is turned off (hereinafter referred to as “save operation”). Information saved in the volatile memory element 7 can be read back into the volatile memory cell (also referred to as “restore operation”).
In addition, data can be stored in the nonvolatile memory element 7 after the power is turned off, and a flag is set and reset according to a write state to the volatile memory cell from the outside, and data is transmitted between the nonvolatile memory cell and the volatile memory cell. Thus, the refresh operation of the so-called DRAM device can be replaced by performing the data refresh operation.

Next, FIG. 8 shows a resistance value setting method when a nonvolatile variable resistance element is used for the nonvolatile memory element 7.
In a DRAM device, in general, in a data holding state (access transistor; in a state in which the NMOS transistor 1 is closed), the potential of the cell internal storage node 10 is the junction leakage current between the N-type diffusion layer and the P well or the gate oxide film of the access transistor. Because of this leakage current, it has a property of gradually approaching a low potential (ground) from a high potential (VDD).

  Although the operation of the memory cell 100 has been described so far, the adaptive condition is based on the assumption that the stable potential of the storage node (10) described above is set to a low (LOW) potential. The operation of the memory cell in this case corresponds to Case 1 shown in FIG. 8, the resistance of the nonvolatile memory element 7 is set to “low” resistance value for the data of DRAM “1”, and the data value of DRAM “0” is set to “high”. Set to resistance value. The PWR line potential is normally high (VDD; power supply voltage), and a negative pulse is applied to the PWR line during the SAVE operation.

  However, depending on the device structure, there is a case where the potential of the storage node 10 has a property of gradually approaching the high potential (power supply voltage VDD) from the low potential (ground) in the data holding state. In that case, if each condition setting is changed to “Case-II” shown in FIG. 8, the nonvolatile DRAM device described in the present invention can be realized. Detailed setting conditions of the nonvolatile memory element 7 are shown in FIG.

  The operation of the memory cell in which the stable potential of the storage node potential is set to a high (High) potential corresponds to Case II shown in FIG. 8, and the resistance of the nonvolatile storage element 7 is set to the “high” resistance value in the data of DRAM “1”. The “low” resistance value is set in the data of the DRAM “0”. The PWR line potential is normally low (0 [V]; ground potential), and a positive pulse is applied to the PWR line during the SAVE operation.

  As described above, the nonvolatile memory cell of the present invention can be operated stably by changing the set potential supplied to the nonvolatile memory element 7 even if the stability condition of the storage node potential changes. This is particularly useful when leakage current becomes a problem.

FIG. 9 shows the overall configuration and memory cells of a nonvolatile memory device 200 according to the second embodiment of the present invention.
The nonvolatile memory device 200 includes a word line driver / nonvolatile memory element driving circuit 210, a memory cell array 220, a decoder / control circuit 240, a cell plate potential (Vcp) generation circuit 250, a write buffer / sense amplifier 260, and the like. Yes.

The word line driver / nonvolatile memory element driving circuit 210 includes, for example, a NAND circuit 211 and a buffer circuit of an inverter 212 for the word lines WL0 to WLn-1, and the word line supplied from the decoder / control circuit 240. The word lines WL0 to WLn-1 are selected by the selection signal.
Further, a control voltage for controlling on / off of the charge transfer transistor is supplied to the nonvolatile memory element control signal lines NV-EN0 to NV-ENn-1 other than the word line selection signal, and the volatile memory cell and the nonvolatile memory cell Transfer data between them.
Further, the voltage for writing / erasing the nonvolatile memory element 7 is supplied to the nonvolatile memory element power supply lines PWR0 to PWRn-1, and the data at the time of refresh or power-off is held.

In the memory cell array 220, the memory cells 100 shown in FIG. 1 are arranged in a matrix of n rows and m columns, and a word line driver / nonvolatile memory element driving circuit is connected to the memory cells MC0,0 to MCn-1, m-1. The control signal output from 210 is supplied.
As shown in FIG. 1, the memory cells MC0,0 to MCn-1, m-1 are composed of volatile memory cells and nonvolatile memory cells, and the volatile memory cells are connected to word lines WL0 to WLn-1. Data writing and reading are controlled by the bit lines BL0 to BLn-1. A predetermined voltage is supplied from the cell plate potential (Vcp) generation circuit 250 to the cell plate electrode VCP of each capacitor.
In the nonvolatile memory cell, the charge transfer transistor is controlled to be turned on / off by a nonvolatile memory element control signal (NV-EN0 to NV-ENn-1), and data is transferred. Data is written and erased by applying a voltage for (PWR0 to PWRn-1) to the nonvolatile memory element.

The decoder / control circuit 240 is supplied with address data, a clock, a control signal, etc., decodes the address data, and synchronizes with the clock signal to generate a row address selection signal, a column address selection signal, and a nonvolatile memory element control signal (NV). -EN0 to NV-ENn-1) control signal, word line (WL0 to WLn-1) control signal, non-volatile memory element power supply (PWR0 to PWRn-1) voltage are generated, and other WE (write enable) , RE (read enable) and the like are generated.
In addition to generating these control signals, the flag is set to “0” immediately after power-on, and when an operation for writing data to the volatile memory cell from the outside occurs, the flag is set to “1” and refreshed. When the operation ends, a flag control signal for setting the flag to “0” again is generated.

  Cell plate potential (Vcp) generation circuit 250 is constituted by a voltage generation circuit, a timing generation circuit, and the like, and in response to a control signal from decoder / control circuit 240, the capacitor of memory cells MC0, 0 to MCn−1, m−1. A voltage is supplied to the cell plate electrode (VCP) at a predetermined timing.

The write buffer / sense amplifier (circuit) 260 includes a buffer circuit and a sense amplifier circuit connected to the bit lines BL0 to BLm-1, and inputs data IN to the memory cells MC0,0 to MCn-1, m-1. When writing, data is output to the bit lines BL0 to BLm-1 through the buffer circuit at a predetermined timing.
At the time of data reading, data (voltage) having a small amplitude read from the memory cells MC0,0 to MCn-1, m-1 is supplied to the sense amplifier through the bit line, and the data is amplified to a predetermined voltage. And then output (OUT).

Next, the operation of the nonvolatile memory (nonvolatile DRAM) device 200 will be described with reference to FIGS. FIG. 10 shows a list of functional operations of the nonvolatile memory device 200.
The column column of this list shows the operation mode, and the row column shows the operation items of the memory cells MC0,0 to MCn-1, m-1. As operation modes, there are an operation immediately after power-on, a read from a volatile cell to the outside, a write to the volatile cell from the outside, a refresh operation when the flags are “1” and “0”, and an operation before power-off. is there.
The operation items of the memory cells (MC0,0 to MCn-1, m-1) are read (Read), write (Write), save (Save), restore (Restore), and flag (FLAG) setting operations. is there.
Here, terms are defined. Save refers to an operation of transferring data stored in a volatile memory cell (access transistor (NMOS transistor) 1, capacitor 2) to the nonvolatile memory element 7 of the nonvolatile memory cell in the same memory cell. Shows an operation of transferring data stored in the nonvolatile memory element 7 to a volatile memory cell in the same cell.

  The operation after power-on is the same as that described with reference to FIG. First, the volatile memory cells of the data of all the memory cells MC0,0 to MCn−1, m−1 are first cleared (“0” or “1”), and then stored in the nonvolatile memory element 7. The restore operation is performed by transferring the stored data to the volatile memory cell, and the initial setting is completed. At this time, the flag is cleared.

When the initial setting operation of the volatile memory cell after the power is turned on, a normal operation as a DRAM device is started, and the nonvolatile function is not involved at all for external writing and external reading operations.
The flag is set (FLAG = 1) when there is a write to the volatile cell from the outside. Except for setting the flag, the operation is completely the same as a general DRAM operation, and is the same as the description of FIGS. Therefore, detailed description is omitted here.

  As for the refresh operation, as shown in FIG. 6, the memory cells MC0, 0 to MCn−1, m−1 connected to the corresponding word lines WL0 to WLn−1 are externally connected during the period from the previous refresh to the current refresh. In the case where the write operation is not performed (FLAG = 0), the NMOS transistor 6 for controlling the nonvolatile memory (variable resistance) element is made conductive while the access transistor (memory cell 100 in FIG. 1) is closed and restored. By performing the operation, a refresh operation is performed, which is an alternative to the refresh of the DRAM device.

  On the other hand, as shown in FIG. 5, when an external write operation is performed during the period from the previous refresh to the current refresh (FLAG = 1), the bit lines BL0 to BLm performed in a normal DRAM device. A refresh operation with charge / discharge of −1 is performed, and a save operation for transferring cell information to the nonvolatile memory element 7 is performed.

  Next, immediately before the power is turned off, if a write operation is performed from the outside during the period from the previous refresh to the current refresh, the data in the volatile memory cell is stored in the same cell as shown in FIG. A save operation for transferring to the nonvolatile memory element is performed. On the other hand, when no external write operation is performed during the period from the previous refresh to the current refresh (FLAG = 0), the cell information is already stored in the nonvolatile memory element of the nonvolatile memory cell as shown in FIG. Has been saved, and no special action for refresh is performed.

  By these operations, the above-described nonvolatile DRAM function can be realized. In order to perform the above operation, the nonvolatile DRAM device needs to have a flag of 1 bit or more for each word line. These flag setting conditions are shown in FIG.

FIG. 10 shows a list regarding the flag setting conditions and the operation modes of the nonvolatile memory device 200 described above.
This list is associated with the timing charts of FIG. 3 to FIG. 7, and shows an explanation regarding the operation of the nonvolatile memory device 200.
There are two operation modes: the operation immediately after turning on the power, the reading from the volatile cell to the outside (operation), the writing from the outside to the volatile cell (operation), the refresh operation and the operation before turning off the power. There is an operation when an external write operation is performed (FLAG = 1) and when a write operation is not performed (FLAG = 0) during the refresh period from this refresh.
In each operation mode, the numbers shown in the row column indicate the memory cell operation order. Since these operations have already been performed in the description of the operation related to the memory cell 100, they are omitted here.

Therefore, the memory cell and the nonvolatile memory device of the present invention operate at the same operation speed as the DRAM device, and can store stored information even when the power is turned off.
Also, it is not always necessary to perform refresh operation at regular intervals even during the power-on period, and during the period when there is no operation to write data to the volatile memory cell from the outside, the data of the nonvolatile memory cell is transferred to the volatile memory cell in the same cell. Therefore, the operation equivalent to the refresh operation can be performed and the power consumption can be reduced.

  As described above, according to the present invention, while maintaining the operation speed and ease of use of the DRAM device, (1) saving information when the power is turned off (save operation) and re-reading the restoration information when the power is turned on Operation and (2) Omission of refresh operation (substitution for one minute) and a memory cell and a nonvolatile memory device to which a nonvolatile function is added can be realized.

FIG. 3 is a diagram illustrating a circuit configuration of a memory cell according to the first embodiment. It is a figure which shows the electrical property of the non-volatile memory element which comprises the memory cell of FIG. 2 is a timing chart for explaining the operation of the memory cell of FIG. 1. 2 is a timing chart for explaining the operation of the memory cell of FIG. 1. 2 is a timing chart for explaining the operation of the memory cell of FIG. 1. 2 is a timing chart for explaining the operation of the memory cell of FIG. 1. 2 is a timing chart for explaining the operation of the memory cell of FIG. 1. 2 is a timing chart for explaining the operation of the memory cell of FIG. 1. The circuit structure of the non-volatile memory | storage device of 2nd Embodiment is shown. 10 is an operation list for explaining the operation of the nonvolatile memory device shown in FIG. 9. The circuit structure of the volatile memory | storage device of a prior art example is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,6 ... NMOS transistor, 2 ... Capacitor, 3, BL0-BLm-1 ... Bit line, 4, WL0-WLn-1 ... Word line, 5 ... Cell plate electrode (VCP), 7 ... Nonvolatile memory element, 8 _{, NV - EN0~NV - ENn-1} ... nonvolatile memory device control signal line _(NV - EN lines), 9, PWR0~PWRn-1 ... nonvolatile memory element power supply line (PWR line), 100, MC0,0~ MCn-1, m-1, C0,0 to Cn-1, m-1 ... memory cell, 200 ... nonvolatile memory device, 210,310 ... word line driver / nonvolatile memory element drive circuit, 220,320 ... memory Cell array, 240, 340 ... Decoder / control circuit, 250, 350 ... Cell plate potential (Vcp) generation circuit, 260, 360 ... Write buffer / sense amplifier, 300 ... RAM devices.

Claims (13)

A first field effect transistor having a first control terminal connected to the first control signal line and a first terminal connected to the bit line;
A capacitor having one end connected to the second terminal of the first field effect transistor and the other end connected to a first reference potential;
A third terminal is connected to the storage node to which the second terminal of the first field effect transistor and one end of the capacitor are connected, and a second control terminal is connected to the second control signal line. Two field effect transistors;
A non-volatile memory element having one end connected to a fourth terminal of the second field effect transistor and the other end connected to a second reference potential. The memory cell according to claim 1, wherein the nonvolatile memory element records and erases information by changing the second reference potential and applying a voltage having a different polarity to both ends of the nonvolatile memory element. Memory cells having nonvolatile memory elements arranged in a matrix;
A word line of a first control signal line for commonly connecting the gate terminals of the first field effect transistors for accessing the memory cells in the row direction;
A bit line commonly connecting the drain ends of the first field effect transistors in a column direction;
A second reference potential supply line for commonly connecting one end of the nonvolatile memory element in the row direction;
A second signal line for commonly connecting the gate terminals of the control field effect transistors of the nonvolatile memory element in the row direction;
The memory cell is
The first field effect transistor having a gate connected to the word line and a drain connected to the bit line;
A capacitor having one end connected to the source of the first field effect transistor and the other end connected to a first reference potential;
A second field effect transistor for control having a drain connected to a storage node to which a source of the first field effect transistor and one end of the capacitor are connected, and a gate connected to the second signal line;
A non-volatile memory device comprising: a non-volatile memory element having one end connected to the source of the second field effect transistor and the other end connected to the second reference potential supply line. The second reference potential supply line applies a pulsed first voltage only when an information recording / erasing operation is performed on the nonvolatile memory element, and the supply of the first voltage is stopped. The second voltage is set to a second voltage, and the second signal line applies a pulsed high voltage only when the stored data is transferred between the memory cell storage node and the nonvolatile storage element, The non-volatile memory device according to claim 3, wherein when the data is not transferred, the low voltage is set. When recording and erasing information in the nonvolatile memory element in the memory cell, the word line is set to a high potential to make the first field effect transistor conductive, and the second signal line is set to a high potential. The second field effect transistor is turned on, the second reference potential supply line is set to the second potential, and the erasing operation of the nonvolatile memory element information is performed. The non-volatile memory element performs a recording operation by setting the second reference potential supply line to a first voltage in a pulsed form while the second field effect transistor is conductive, and from the non-volatile memory element to the memory cell storage node When transferring data, the word line is set to a low potential to close the first field effect transistor, and the second signal line is set to a high potential in the form of a pulse so that the second field effect transistor is turned on. Through so, non-volatile memory device according to claim 4, wherein transferring information to the memory cell storage node from the non-volatile memory element. With respect to the refresh operation periodically having a flag of 1 bit or more for each word line and holding the storage node information of the memory cell, the memory cell connected to the word line is externally connected in one refresh operation period. The nonvolatile operation according to claim 3, wherein when the write operation is executed, the flag is set to the first state, and when the write operation is not executed, the refresh operation is controlled by setting the flag to the second state. Storage device. When a memory cell connected to the word line is not externally written during one refresh operation period, the memory cell is closed to the first field effect transistor by lowering the word line in the next refresh operation, The second signal line is set to a high potential in the form of a pulse to turn on the second field effect transistor, and the information is transferred from the nonvolatile memory element to the memory cell storage node, thereby performing an alternative function of the refresh operation. The nonvolatile memory device according to claim 6. A decoder / control circuit that is supplied with address data and a first control signal, decodes the address data, and generates a word line selection signal at a predetermined timing;
A word line driver / drive circuit that is supplied with the word line selection signal and outputs a word line drive signal for driving a word line of an arbitrary memory cell;
A volatile first memory cell selected by the word line driver signal and a bit line control signal for selecting the memory cell, and a storage node of the volatile first memory cell; The memory cells controlled by the third control signal and having the non-volatile second memory cells for exchanging data, storing and erasing data with the volatile first memory cells are arranged in a matrix A cell array;
A non-volatile memory device comprising: a write buffer / sense amplifier for writing / reading data via the bit line connected to the first field effect transistor for selection of the volatile first memory cell. The nonvolatile memory device according to claim 8, wherein the volatile first memory cell includes a capacitor connected to the storage node and the first field effect transistor for access. The nonvolatile second memory cell is controlled by the second control signal in the memory cell, controlled by the second field effect transistor for transferring data, and the third control signal, and the data The nonvolatile memory device according to claim 8, further comprising: a nonvolatile memory element that stores and erases data. When data is written to the volatile first memory cell via the bit line, the data stored in the storage node is stored in the memory cell in the same memory cell by the second control signal. The second field effect transistor is controlled and transferred to the non-volatile memory element, and the non-volatile element is controlled by the third control signal to store the data, and is stored in the volatile first memory cell. When data writing is stopped via the bit line, the data stored in the storage node is controlled by the second control signal to control the second field effect transistor in the same memory cell. The non-volatile storage device according to claim 10, wherein the data is transferred to a storage element and stored. In the memory cell, immediately after the power is turned on, after the data of the volatile first memory cell is reset, the second field effect transistor is controlled by the second control signal, and the nonvolatile second The nonvolatile memory device according to claim 10, wherein data stored in the memory cell is transferred to the volatile first memory cell, and the data is stored. When the write operation of the volatile first memory cell is performed from the previous refresh period to the current refresh period before the power is turned off, the memory cell receives the second control signal according to the second control signal. The field effect transistor is controlled, the data of the volatile first memory cell is transferred to the nonvolatile second memory cell, and the nonvolatile element is controlled by the third control signal, so that the data The non-volatile storage device according to claim 10.

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