JP2006032526A - Ferroelectric memory device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ferroelectric memory which has a long service life and can be used for a wide range of application by a technique with actual results in production without spending a long development period of a newly unique material, by using a ferroelectric capacitor for non-destructive reading out and a present method to utilize a ferroelectric thin film material, in view of the drawbacks with the conventional main ferroelectric memory that it has a limited service life because of destructive reading out of data, a ferroelectric memory for nondestructive reading out has the complicated composition of ferroelectric film, development requires much time, and there are difficulties in ensuring reliability or manufacturing. <P>SOLUTION: Materials with different work functions are used as two electrode materials of a ferroelectric capacitor 2, and a polarization potential-applied voltage characteristic is moved in parallel in the direction of a voltage axis, resulting in making a hysteresis characteristic to be asymmetric. A micro-voltage of anti-voltage or less is applied to the ferroelectric capacitor so as to read out in a non-destructive manner a memory data of one or zero from the asymmetry of the polarization potential-applied voltage characteristic, in a state where two different residual potentials are kept. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a ferroelectric memory device in which data is read nondestructively in a ferroelectric memory, which is a non-volatile memory, in order to extend the life depending on the number of times a memory element is read.

In recent years, the importance of electrically writable and erasable nonvolatile memories in the memory field has increased. There are various types of nonvolatile memories, but ferroelectric memories are attracting attention from the viewpoints of high speed, low voltage characteristics, low power consumption, and the like. The specific configuration of the ferroelectric memory is various as shown in the following examples.
As an example of a ferroelectric memory, a charge exceeding a coercive voltage is applied to a ferroelectric capacitor that defines two states depending on the remanent polarization state inside the ferroelectric film, and the internal memory of 1 or 0 is taken out. There is a way to detect the condition. FIG. 9 shows this method in a simplified manner.

In FIG. 9, curves passing through four characteristic points 1001, 1002, 1003, and 1004 indicate the characteristics of the applied voltage V and the internal polarization charge Q applied between the first terminal and the second terminal of the ferroelectric capacitor. Represents.
A characteristic point 1001 indicates a state in which a positive voltage V higher than that of the first terminal is applied to the second terminal of the ferroelectric capacitor, and a characteristic point 1002 indicates a state in which a positive voltage V higher than that of the second terminal is applied to the first terminal. Is shown. At the characteristic point 1001 and the characteristic point 1002, the polarization inside the ferroelectric capacitor is positive or negative, that is, reverse polarization.

  If the potential difference between the first terminal and the second terminal of the ferroelectric capacitor that was in the state of the characteristic point 1001 is now zero, the internal polarization is stored as remanent polarization, and the state shown in the characteristic point 1004 is obtained. If the potential difference between the first terminal and the second terminal of the ferroelectric capacitor that was in the state of the characteristic point 1002 is set to 0, the internal polarization is stored as remanent polarization, and the state shown in the characteristic point 1003 is obtained.

Therefore, the internal polarization charge of the ferroelectric capacitor and the applied voltage have hysteresis characteristics, and at the same time, even if the terminals at both ends of the ferroelectric capacitor are opened and the voltage is zero, the residual polarization varies depending on the previous state. have. These two states correspond to the characteristic point 1003 and the characteristic point 1004, respectively.
Now, when the voltage V (ΔVB) is applied to the second terminal with the first terminal as a reference from the state where the terminals at both ends of the ferroelectric capacitor are opened, the characteristic point 1001 is moved. At this time, if the previous state is the characteristic point 1003, the charge of ΔQHB shown in FIG. 9 is taken out, and if it is the state of the characteristic point 1004, the charge of ΔQLB is taken out. As apparent from FIG. 9, ΔQLB << ΔQHB, the previous state stored as the remanent polarization can be determined as 1 or 0.

Since such a method takes out electric charges, that is, destroys data, it is a method generally called destructive reading. An example of this method is disclosed in Patent Document 1.
On the other hand, as a non-destructive readout method, a ferroelectric thin film is provided above the gate electrode of an insulated gate field effect transistor (hereinafter abbreviated as MOSFET), and the threshold voltage of the MOSFET depends on the polarization state of the ferroelectric thin film. Therefore, there is a method of detecting the difference between written polarization directions, that is, 1 or 0. As an example of this, the one shown in Patent Document 2 is known.

Further, by devising the material of the ferroelectric thin film, as shown in FIG. 10, the polarization-electric field hysteresis characteristic is made asymmetric, and the difference in the slope of the characteristic corresponding to the characteristic point 1103 and the characteristic point 1104 shown in FIG. Therefore, there is a method in which a weak voltage is applied to a ferroelectric capacitor and the state is detected without data destruction. As this example, what is shown to patent document 3 and patent document 4 is known.
JP-A-11-39882 JP 2002-543627 A Japanese Patent Laid-Open No. 2-198094 JP-A-5-82800

However, the conventional ferroelectric memory as described above has the following problems.
That is, in the method described with reference to FIG. 9 or disclosed in Patent Document 1 for destructive reading, it is necessary to rewrite the lost data after reading the data. For this reason, data writing and data erasure are repeated, and at present, the number of data rewrites is limited to 10 ¹⁰ to 10 ¹² times, and if this limit is reached, the life as a ferroelectric material is given. There is a bug. For this reason, a static random access memory (hereinafter abbreviated as SRAM) in which data is frequently read and written cannot be used in terms of quality and reliability, and there is a problem that its application is limited.

Further, in the method of disposing the ferroelectric thin film on the gate electrode of the MOSFET disclosed in Patent Document 2, due to the difficulty in formation with the ferroelectric material placed on the gate, at present one day There is a problem that the data of the ferroelectric thin film formed on the gate disappears in about one week.
Further, there is a method of making the ferroelectric thin film asymmetric with the hysteresis characteristic of the polarization charge-applied voltage shown in Patent Documents 3 and 4 and using the asymmetry to read data nondestructively. In addition, it is not easy in practice to obtain a material material having complicated nonlinear hysteresis characteristics as shown in the representative diagram of Japanese Patent Application Laid-Open No. H11-133, and Patent Document 4. However, there is a problem that development delays and manufacturing problems are likely to occur.

  Therefore, an object of the present invention is to solve such a problem, and the object is to use a ferroelectric thin film material that uses a ferroelectric capacitor, performs nondestructive readout, and has a proven track record. By using a method that can be used as it is, a ferroelectric memory that can be used for a wide range of applications including SRAMs with a long service life, no new special material development period, and a method that has been proven in production. It is to provide.

In order to solve the above-described problems and achieve the object of the present invention, each invention is configured as follows.
That is, in the first invention, the ferroelectric film is sandwiched between the first electrode made of the first conductive material and the second electrode made of the second conductive material having a work function different from that of the first conductive material. A plurality of memory cells having a ferroelectric capacitor having a structure, an address selection circuit for selecting one of the plurality of memory cells, and a ferroelectric capacitor of the memory cell selected by the address selection circuit. A write circuit for applying a voltage larger than the coercive electric field of the dielectric film, and a read for applying a voltage smaller than the coercive electric field of the ferroelectric film to the ferroelectric capacitor of the memory cell selected by the address selection circuit And at least a circuit.

  A second invention is a structure in which a ferroelectric film is sandwiched between a first electrode made of a first conductive material and a second electrode made of a second conductive material having a work function different from that of the first conductive material. When writing data to the ferroelectric capacitor, a voltage larger than the coercive electric field of the ferroelectric film is applied to the ferroelectric capacitor. When reading data from the ferroelectric capacitor, a voltage smaller than the coercive electric field of the ferroelectric film is applied to the ferroelectric capacitor.

According to a third invention, in the first or second invention, the first conductive material is an oxide conductive film, and the second conductive material is a metal film.
According to a fourth invention, in the first or second invention, the first conductive material is a conductive film made conductive by doping a semiconductor film with impurity atoms, and the second conductive material is a metal It consists of a membrane.

According to a fifth invention, in the first or second invention, the first conductive material is made of a metal film, and the second conductive material is a metal having a work function different from that of the metal of the first conductive material. It consists of a membrane.
According to a sixth invention, in the first or second invention, the first conductive material is a conductive film made conductive by doping impurity atoms into a semiconductor film, and the second conductive material is the above-mentioned The conductive film is made conductive by doping impurity atoms into a semiconductor film having a different valence from the impurity atoms contained in the first conductive material.

According to a seventh invention, in the fourth or sixth invention, the conductive film made conductive by doping impurity atoms into the semiconductor film is polysilicon, and the impurity atoms are trivalent or pentavalent atoms. It consists of a price.
According to an eighth aspect of the present invention, there is provided a strong structure in which a ferroelectric film is sandwiched between a first electrode made of a metal film in close contact with a first conductive material and a second electrode made of a metal film in close contact with a second conductive material. A plurality of memory cells having a dielectric capacitor, an address selection circuit for selecting one of the plurality of memory cells, and a ferroelectric capacitor of the memory cell selected by the address selection circuit A write circuit for applying a voltage larger than the coercive electric field, and a read circuit for applying a voltage smaller than the coercive electric field of the ferroelectric film to the ferroelectric capacitor of the memory cell selected by the address selection circuit, At least.

  According to a ninth aspect of the present invention, there is provided a strong structure in which a ferroelectric film is sandwiched between a first electrode made of a metal film in close contact with a first conductive material and a second electrode made of a metal film in close contact with a second conductive material. A memory cell having a dielectric capacitor is provided, and when writing data to the ferroelectric capacitor, a voltage larger than the coercive electric field of the ferroelectric film is applied to the ferroelectric capacitor, When data is read from the ferroelectric capacitor, a voltage smaller than the coercive electric field of the ferroelectric film is applied to the ferroelectric capacitor.

According to a tenth aspect, in the eighth or ninth aspect, the first conductive material or the second conductive material is a conductive film made conductive by doping impurity atoms into a semiconductor film.
According to an eleventh aspect, in the tenth aspect, the conductive film made conductive by doping impurity atoms into the semiconductor film is polysilicon, and the impurity atoms have a trivalent or pentavalent valence. .

In a twelfth aspect based on the eighth or ninth aspect, the first conductive material or the second conductive material is made of an oxide conductive film.
A thirteenth invention is a plurality of memories having a ferroelectric capacitor having a structure in which a ferroelectric film is sandwiched between a first electrode made of a metal film in close contact with a first conductive material and a second electrode made of a metal film. A voltage larger than the coercive electric field of the ferroelectric film is applied to a cell, an address selection circuit for selecting one of the plurality of memory cells, and a ferroelectric capacitor of the memory cell selected by the address selection circuit And a read circuit for applying a voltage smaller than the coercive electric field of the ferroelectric film to the ferroelectric capacitor of the memory cell selected by the address selection circuit.

  According to a fourteenth aspect of the invention, there is provided a memory cell having a ferroelectric capacitor having a structure in which a ferroelectric film is sandwiched between a first electrode made of a metal film in close contact with a first conductive material and a second electrode made of a metal film. When writing data to the ferroelectric capacitor, a voltage larger than the coercive electric field of the ferroelectric film is applied to the ferroelectric capacitor, and data is written from the ferroelectric capacitor. When reading, a voltage smaller than the coercive electric field of the ferroelectric film is applied to the ferroelectric capacitor.

According to a fifteenth aspect, in the thirteenth or fourteenth aspect, the first conductive material is a conductive film made conductive by doping a semiconductor film with impurity atoms.
According to a sixteenth aspect, in the fifteenth aspect, the conductive film made conductive by doping impurity atoms into the semiconductor film is polysilicon as a semiconductor film, and the impurity atoms are trivalent or pentavalent atoms. It consists of a price.

In a seventeenth aspect based on the thirteenth or fourteenth aspect, the first conductive material is an oxide conductive film.
In an eighteenth aspect based on any one of the first to seventeenth aspects, the ferroelectric capacitor constitutes a one-transistor / one-capacitor type memory cell.
In a nineteenth aspect based on any one of the first to seventeenth aspects, the ferroelectric capacitor constitutes a one-capacitor type memory cell.

In a twentieth aspect based on any one of the first to seventeenth aspects, the ferroelectric thin film of the ferroelectric capacitor is made of PZT, PZTN, or SBT.
As described above, the ferroelectric memory device of the present invention has a structure in which a ferroelectric film is sandwiched between the conductive materials having different work functions as the first electrode and the second electrode, or a work function difference between the electrodes. A ferroelectric capacitor having an equivalent structure is used as a component of the memory cell, and when reading data, a voltage lower than the coercive voltage of the ferroelectric film is applied to read the memory information.

  Therefore, according to the above configuration, the first electrode and the second electrode sandwiching the ferroelectric thin film move in parallel with respect to the voltage direction applied by the polarization-electric field hysteresis characteristic of the ferroelectric thin film, and are strongly When the voltage applied to the dielectric capacitor is zero, there is an asymmetry in the applied voltage-current characteristics due to the difference in the internal polarization state, so the residual charge due to the difference in current that occurs when a voltage less than the coercive voltage is applied. It is possible to detect whether the internal state is 1 or 0. Therefore, since data information can be read without data destruction, there is an effect that the lifetime becomes very long.

Further, since non-destructive reading is performed, there is an effect that rewriting of data is unnecessary and cycle time in the reading operation can be shortened.
As described above, since a non-volatile memory that can be read quickly and has a long life is realized, there is an effect that it is possible to configure a ferroelectric memory for a wide range of applications that replaces the SRAM.
Furthermore, in the above configuration, since only materials having different work functions are used for the electrodes, it is not necessary to develop a special new ferroelectric thin film having asymmetric hysteresis characteristics. Since the material may be used as it is, there is an effect that it is realized at an early stage and is easy to manufacture.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Operational principle of the present invention)
Prior to describing the embodiment of the ferroelectric memory device of the present invention, the operating principle of the present invention will be described with reference to FIG.
Here, FIG. 1 is a diagram showing the polarization charge and applied voltage characteristics (hysteresis characteristics) of a ferroelectric capacitor used as a memory cell (memory element) of the ferroelectric memory device of the present invention. The characteristic of FIG. 1 is a characteristic obtained by translating the polarization charge-applied voltage characteristic of FIG. 8 showing the characteristic of a conventional general ferroelectric capacitor in the voltage axis direction. The specific configuration of the ferroelectric capacitor having the characteristics shown in FIG. 1 will be described later, and the operation principle of the present invention will be described below assuming that the ferroelectric capacitor having the characteristics shown in FIG. 1 is obtained. .

A ferroelectric capacitor having the characteristics shown in FIG. 1 includes two first terminals and a second terminal, as will be described later. The positive potential applied to the second terminal with respect to the first terminal is represented by the horizontal axis in FIG. A positive direction of a certain applied voltage.
In the ferroelectric capacitor, when a voltage sufficiently higher than that of the first terminal is applied to the second terminal, the ferroelectric capacitor is polarized to the characteristic point 101 in FIG. In this state, if the voltage between the first terminal and the second terminal is 0 [V], the internal polarization is stored as remanent polarization, and the polarization charge shown on the vertical axis of the characteristic point 104 is stored inside.

On the other hand, in the ferroelectric capacitor, when a voltage sufficiently higher than that of the second terminal is applied to the first terminal, the ferroelectric capacitor is polarized to 102 characteristic point. When the ferroelectric capacitor in the state of the characteristic point 102 is opened and the potential difference between the first terminal and the second terminal is zero, the internal polarization is stored as remanent polarization, and the vertical axis of the characteristic point 103 is It will be in the state with the remanent polarization shown.
At the characteristic point 103 and the characteristic point 104, the potential difference between the first terminal and the second terminal is zero. Nevertheless, the characteristic point 103 has the negative remanent polarization shown in FIG. 1, and the characteristic point 104 has the positive remanent polarization shown in FIG. In other words, the remanent polarization memorizes two states when left as a ferroelectric capacitor.

  Next, a positive weak voltage ΔVN, that is, a voltage equal to or lower than the coercive voltage is applied to the second terminal with the first terminal as a reference in the positive direction. At this time, if the previous state is at the characteristic point 103, the charge ΔQHN of the difference between the characteristic point 103 and the characteristic point 105 is output. On the other hand, if the previous state is the characteristic point 104, it is expected that a charge ΔQLN corresponding to the difference between the characteristic point 104 and the characteristic point 106 is output. However, in the case of the characteristic point 104, actually, even if the voltage ΔVN is applied, it does not return to the characteristic point 106 but has a hysteresis characteristic and is polarized more than the characteristic point 106 as indicated by the characteristic point 107 in FIG. The effect of remains.

Therefore, the difference charge amount ΔQ′LN between the characteristic point 104 and the characteristic point 107 is smaller than the difference charge amount ΔQLN between the characteristic point 104 and the characteristic point 106. That is, when the same slight positive voltage is applied to a ferroelectric capacitor whose internal state is unknown, an electric charge of ΔQHN or ΔQ′LN appears.
ΔQHN and ΔQ′LN are charge amounts clearly different from those in FIG. This is because in FIG. 1, the slope of the characteristic curve is greatly different in the vicinity of the characteristic point 103 and the characteristic point 104. For this reason, the internal state can be known by detecting the difference.

Here, only a slight voltage ΔVN equal to or lower than the coercive voltage is applied, and when data is read, it does not move to the characteristic point 101 or the characteristic point 102, and therefore the data is not destroyed. That is, data can be read nondestructively.
In the case of the characteristic point 106 in FIG. 1, if the applied voltage ΔVN is set to zero and released, the characteristic point 104 is restored. Further, in the case of the characteristic point 107 and the characteristic point 105, when the applied voltage ΔVN is canceled by canceling the applied voltage ΔVN, the characteristic point 104 and the characteristic point 103 are not necessarily completely restored. As you can see, it is insignificant. Since the displacement is very small as compared with the destructive readout that reads at least the characteristic point 101, the life of the ferroelectric capacitor is greatly extended.
(Configuration and operation of memory cell)
Next, a configuration example of a memory cell using the ferroelectric capacitor having hysteresis characteristics shown in FIG. 1 will be described with reference to FIG.

As shown in FIG. 2, this memory cell is of a so-called 1-transistor 1-capacitor (1T1C) type composed of one ferroelectric capacitor 211 and one transistor 212, and has a word line (WL) 213. , Bit line (BL) 214, and plate line (PL) 215.
More specifically, the transistor 212 is an N-type insulated gate field effect transistor (hereinafter abbreviated as MOSFET). The word line 213 is connected to the gate electrode of the MOSFET 212, and the bit line 214 is connected to a first terminal serving as a source electrode or a drain electrode of the MOSFET 212. The plate line 215 is connected to the first electrode of the ferroelectric capacitor 211, and the second electrode of the ferroelectric capacitor 211 is connected to the second terminal serving as the drain electrode or the source electrode of the MOSFET 212.

In practice, a plurality of memory cells shown in FIG. 2 are arranged in a matrix (array), and a plurality of word lines, bit lines, and plate lines exist and are shared at the same time.
Next, a method of writing data in the memory cell having the above configuration shown in FIG. 2 will be described.

  First, when data is written in the ferroelectric capacitor 211, the MOSFET 212 is turned on by setting the word line 213 to a positive potential for the target memory cell. When a negative potential or a zero potential is applied to the bit line 214 and a sufficient positive potential V is applied to the plate line 215, the polarization state of the characteristic point 101 in FIG. At this time, even if the applied voltage is released, the positive internal polarization at the point indicated by the characteristic point 104 is stored in the ferroelectric capacitor 211 as remanent polarization.

On the other hand, if a positive potential V having a sufficient value is applied to the bit line 214 and a negative potential or a zero potential is applied to the plate line 215, the polarization state of the characteristic point 102 in FIG. At this time, the positive internal polarization indicated by the characteristic point 103 is stored in the ferroelectric capacitor 211 even when the applied voltage is released.
With the above operation, even if the applied voltage is released, two different states as remanent polarization can be written as data.

Next, a method for reading the data written as described above will be described with reference to FIG.
First, the bit line (BL) 214 is precharged to zero potential as shown in FIG. Then, the word line (WL) 213 is set to a positive potential as shown in FIG. 3B, and the MOSFET 212 is turned on. Next, the bit line 214 is disconnected to enter a zero potential floating state. Further, as shown in FIG. 3C, a slight voltage ΔVN equal to or lower than the coercive voltage is applied to the plate line (PL) 215. Then, the voltage ΔVN is applied to the ferroelectric capacitor 211, and the charge of ΔQHN or ΔQ′LN as shown in FIG. 1 is output to the bit line (BL) 214. As a result, the bit line (BL) 214 appears as a potential change of the voltage ΔVHN or the potential ΔVLN reflecting the parasitic capacitance of the bit line 214 as shown in FIG.

As described above, the potential ΔVHN or the potential ΔVLN output to the bit line 214 is detected by the sense amplifier circuit shown in FIG.
The sense amplifier circuit includes a comparator circuit 420 as shown in FIG. As shown, the comparator circuit 420 includes an input signal terminal 421, a reference voltage terminal 422, and an output terminal 423.

A signal Vref that is an intermediate potential of ΔVHN or ΔVLN is applied to the reference voltage terminal 422. There are various methods for generating the intermediate potential. For example, ΔVHN or ΔVLN generated in two dummy cells are combined to generate an intermediate potential, and this generated potential is applied to the reference voltage terminal 422.
As a result, the comparator circuit 420 compares the potential ΔVHN or potential ΔVLN generated on the bit line 214 with the intermediate potential to determine whether the read data is “1” or “0”, and the determination result is output to the output terminal. From 423, a digital signal “1” or “0” is output.

In the above operation, the data in the memory cell is not destroyed. Therefore, the memory cell shown in FIG. 2 does not require a data rewrite cycle.
(Configuration of ferroelectric memory device)
Next, an outline of the overall configuration of an embodiment of the ferroelectric memory device of the present invention using the memory cell shown in FIG. 2 will be described with reference to FIG.

As shown in FIG. 5, the ferroelectric memory device includes a memory cell group 531, a word line selection circuit 532, a bit line selection circuit 533, a sense circuit 534, a write circuit 535, and an input / output circuit 536. And an overall control circuit 537.
In the memory cell group 531, the memory cells shown in FIG. 2 are arranged in an array. The word line selection circuit 532 and the bit line selection circuit 533 select a word line and a bit line connected to a plurality of memory cells arranged in the memory cell group 531, respectively. One desired memory cell in 531 can be selected.

  The write circuit 535 writes data that has passed through the input / output circuit 536 to the memory cell selected by the word line selection circuit 532 and the bit line selection circuit 533 in accordance with a command from the overall control circuit 537. The sense circuit 534 reads data stored in the memory cells selected by the word line selection circuit 532 and the bit line selection circuit 533 in accordance with a command from the overall control circuit 537, and outputs the read data to the input / output circuit 536. To do.

  In the ferroelectric memory device shown in FIG. 5, the word line selection circuit 532, the bit line selection circuit 533, and the overall control circuit 537 function as an address selection circuit that selects memory cells. The write circuit 535, the input / output circuit 536, and the overall control circuit 537 function as a write circuit. Further, the sense circuit 534, the input / output circuit 536, and the overall control circuit 537 function as a reading circuit.

In FIG. 2, the plate line 215 is shown. However, the reason why the plate line is not described in FIG. 5 is that there is a plate line that does not exist depending on the memory cell. In FIG. Not.
(Modification of memory cell)
Next, a second configuration example of the memory cell used in the ferroelectric memory device of the present invention will be described with reference to FIG.

  In FIG. 6, 311A and 311B are ferroelectric capacitors having the hysteresis characteristics shown in FIG. 1, 316 is a word line, and 317A and 317B are bit lines. As shown in FIG. 3, there are a plurality of word lines and bit lines, and a ferroelectric capacitor is formed at the intersection. The configuration of the memory cell in FIG. 6 is a so-called one-capacitor (1C) type in which one memory is constituted by one ferroelectric capacitor.

Even in a memory cell having such a configuration, data can be read nondestructively as in the memory cell shown in FIG. In the configuration of the memory cell of FIG. 6, the plate line shown in FIG. 2 does not exist.
(Other characteristics of ferroelectric capacitors)
Next, the second characteristic of the polarization charge-applied voltage characteristic of the ferroelectric capacitor used in the ferroelectric memory device of the present invention will be described with reference to FIG.

In FIG. 1, as the characteristics of the ferroelectric capacitor according to the present invention, the characteristics of the conventional general ferroelectric capacitor are shifted in the voltage axis direction and in the right direction as a whole. The characteristics are shifted in the left direction as a whole with the voltage as the horizontal axis.
Next, data writing and reading operations in the ferroelectric capacitor having hysteresis characteristics shown in FIG. 7 will be described.

A ferroelectric capacitor having the characteristics shown in FIG. 7 includes a first terminal and a second terminal. A positive potential applied to the second terminal with respect to the first terminal is defined as a positive voltage applied to the applied voltage on the horizontal axis in FIG. The direction.
In the ferroelectric capacitor, when a voltage sufficiently higher than that of the first terminal is applied to the second terminal, the ferroelectric capacitor is polarized to the characteristic point 701 in FIG. In this state, if the voltage between the first terminal and the second terminal is zero, the internal polarization is stored as remanent polarization, and the polarization charge shown on the vertical axis of the characteristic point 704 is stored inside.

On the other hand, in the ferroelectric capacitor, when a voltage sufficiently higher than the second terminal is applied to the first terminal, the ferroelectric capacitor is polarized to the characteristic point 702. Then, when the ferroelectric capacitor that was in the state of the characteristic point 702 is opened and the potential difference between the first terminal and the second terminal is zero, the internal polarization is stored as remanent polarization, and the vertical axis of the characteristic point of 703 is It will be in the state with the remanent polarization shown.
Next, a positive weak voltage ΔVN, that is, a voltage equal to or lower than the coercive voltage is applied to the second terminal with respect to the first terminal in the negative direction. At this time, if the previous state is at the characteristic point 703, the charge ΔQHN of the difference between the characteristic point 703 and the characteristic point 705 is output. On the other hand, if the previous state is the characteristic point 704, the charge ΔQLN that is the difference between the characteristic point 704 and the characteristic point 706 is output.

As can be seen from the above description, in the case of FIG. 7, the data is obtained at the characteristic point 703 having negative remanent polarization and the characteristic point 704 having positive remanent polarization when released at the applied voltage of 0 [V]. Although stored, the characteristic point 703 and the characteristic point 704 have different polarization charge-applied voltage characteristics. Even in this case, data can be read nondestructively using a slight voltage ΔVN that is equal to or lower than the coercive voltage. .
(Structural example of ferroelectric capacitor)
Next, a specific structural example of the ferroelectric capacitor according to the present invention having the characteristics shown in FIGS. 1 and 7 will be described in consideration of the conventional example.

FIG. 11 shows a cross-sectional view of the structure of a conventional ferroelectric capacitor, for comparison with the structure of the ferroelectric capacitor according to the present invention.
As shown in FIG. 11, a conventional ferroelectric capacitor is formed on an insulating substrate 1240 and sandwiches both sides of a ferroelectric film 1241 between metal electrodes 1242 and 1243 made of a metal film. An electric signal is supplied to the metal electrode 1242 and the metal electrode 1243.

The insulating substrate 1240 is a substrate mainly composed of silicon dioxide (SiO ₂ ), and is configured to mount a ferroelectric capacitor. For the ferroelectric film 1241, PZT, PZTN, SBT or the like is generally used. The above-mentioned PZT is a generic name for Pb (Zr, Ti) O ₃ , PZTN is a generic name for a part of Ti of PZT replaced with Nb, and SBT is SrBi ₂ Ta ₂ O _9. Or it is a general term for the composition close | similar to it. The metal electrode 1242 and the metal electrode 1243 are generally made of platinum (Pt).

The hysteresis characteristic of the polarization charge-applied voltage characteristic of the conventional ferroelectric capacitor having the structure shown in FIG. 11 is as shown in FIG. The characteristics shown in FIG. 8 are symmetrical with respect to the applied voltage on the horizontal axis.
FIG. 12 is a cross-sectional view showing a first example of the structure of a ferroelectric capacitor used in the ferroelectric memory device of the present invention.

  As shown in FIG. 12, this ferroelectric capacitor is formed on an insulating substrate 1340 mainly composed of silicon dioxide, and includes a metal electrode 1342 made of a metal film and an oxide conductive film 1344 that functions as an electrode. The both sides of the ferroelectric film 1341 are sandwiched. Electric signals are supplied to the metal electrode 1342 and the oxide conductive film 1344 as an electrode.

As the material of the ferroelectric film 1341, PZT, PZTN, SBT, or the like is used similarly to the ferroelectric film 1241 shown in FIG. Further, RuO ₂ , IrO _2, or the like is used as the material of the oxide conductive film 1344 that is the first electrode, and platinum (Pt) is used as the material of the metal electrode 1342 that is the second electrode.
Here, the first electrode and the second electrode may be formed from metal films made of materials having different work functions.

  In the ferroelectric capacitor having such a configuration, the constituent material is different between the oxide conductive film 1344 as the first electrode and the metal electrode 1342 as the second electrode. For this reason, there is a work function difference between the two electrodes, and the polarization charge-applied voltage characteristic deviates on the voltage axis and translates by that work function difference (see, for example, FIG. 1). Further, the work function difference also changes depending on what is selected as the material of the first electrode and the second electrode, and the degree and direction of movement of the characteristics can also be changed.

FIG. 13 is a sectional view showing a second example of the structure of a ferroelectric capacitor used in the ferroelectric memory device of the present invention.
As shown in FIG. 13, this ferroelectric capacitor is formed on an insulating substrate 1440 mainly composed of silicon dioxide, and includes an oxide conductive film 1445 functioning as an electrode and a metal electrode 1443 made of a metal film. The both sides of the ferroelectric film 1441 are sandwiched. Electrical signals are supplied to the oxide conductive film 1445 and the metal electrode 1443 as electrodes, respectively.

Here, the structural difference between FIG. 13 and FIG. 12 is the difference in whether the metal electrode is used for the upper electrode or the lower electrode, and the direction of movement of the polarization charge-applied voltage characteristics is different. Both can be selected depending on the difficulty in manufacturing.
FIG. 14 is a cross-sectional view showing a third example of the structure of the ferroelectric capacitor used in the ferroelectric memory device of the present invention.

  As shown in FIG. 14, this ferroelectric capacitor is formed on an insulating substrate 1540 mainly composed of silicon dioxide, and two sides of the ferroelectric film 1541 are formed by two metal electrodes 1542 and 1543 made of a metal film. In addition, the conductive film 1553 is brought into close contact with the surface side of the metal electrode 1542. An electric signal is directly supplied to the metal electrode 1542, and an electric signal is supplied to the metal electrode 1543 through the conductor film 1553.

  The conductor film 1553 is made of polysilicon containing impurity atoms. Polysilicon is a semiconductor, but can be treated as a conductor because it has conductivity by doping impurity atoms. Therefore, although the conductor film 1553 is made of silicon, since silicon is a tetravalent atom, trivalent atomic boron (boron B), pentavalent atomic phosphorus (phosphorus P), or the like is used as an impurity atom. The

  In the ferroelectric capacitor having such a structure, since the conductor film 1553 containing impurities is added to the surface of the metal electrode 1543, the polarization charge-applied voltage characteristic is the work function of the conductor film 1553 and the metal electrode 1543. Translate by the difference. At this time, depending on whether a trivalent atom or a pentavalent atom is selected as the impurity atom added to silicon forming the conductor film 1553, the direction of movement of the characteristic curve can be selected, and the ion of the impurity atom Since the work function changes depending on the amount of doping, the amount of parallel movement can be changed.

In the ferroelectric capacitor shown in FIG. 14, the conductor film 1553 is brought into close contact with the surface of the metal electrode 1543. However, the metal electrode 1543 may be formed only of the conductor film 1553 made of polysilicon.
FIG. 15 is a sectional view showing a fourth example of the structure of the ferroelectric capacitor used in the ferroelectric memory device of the present invention.

  As shown in FIG. 15, this ferroelectric capacitor is formed on an insulating substrate 1640 mainly composed of silicon dioxide, and two sides of the ferroelectric film 1641 are formed by two metal electrodes 1642 and 1643 made of a metal film. In addition, the conductor film 1652 is closely attached to the surface side of the metal electrode 1642. The conductor film 1652 is made of polysilicon similar to the conductor film 1543 shown in FIG. An electric signal is directly supplied to the metal electrode 1643, and an electric signal is supplied to the metal electrode 1642 through the conductor film 1652.

In the ferroelectric capacitor having such a structure, since the conductor film 1652 containing impurities is adhered (added) to the surface side of the metal electrode 1642, the polarization charge-applied voltage characteristics thereof are the conductor film 1652 and the metal electrode. Translate by 1642 work function difference.
Here, the structural difference between FIG. 15 and FIG. 14 is the difference in whether a conductor film made of polysilicon is used for the upper electrode or the lower electrode, and the direction of movement of the polarization charge-applied voltage characteristics is different.

FIG. 16 is a sectional view showing a fifth example of the structure of the ferroelectric capacitor used in the ferroelectric memory device of the present invention.
As shown in FIG. 16, this ferroelectric capacitor is formed on an insulating substrate 1740 mainly composed of silicon dioxide, and two sides of the ferroelectric film 1741 are formed by two metal electrodes 1742 and 1743 made of a metal film. In addition, the conductive films 1752 and 1753 made of polysilicon containing different impurity atoms are brought into close contact with the surface sides of the metal electrodes 1742 and 1743, respectively. An electric signal is supplied to the metal electrode 1742 via the conductor film 1752, and an electric signal is supplied to the metal electrode 1743 via the conductor film 1753.

  In the ferroelectric capacitor having such a structure, the metal electrode 1742 has a conductive film 1752 containing a first impurity atom in close contact with the surface side, and the metal electrode 1743 has a first impurity atom on the surface side. A conductor film 1753 containing different second impurity atoms is in close contact. For this reason, the polarization charge-applied voltage characteristics of the ferroelectric capacitor move in parallel by the sum of the work function difference between the conductor film 1752 and the metal electrode 1742 and the work function difference between the conductor film 1753 and the metal electrode 1743. Therefore, the amount of parallel movement of the polarization charge-applied voltage characteristic can be set large and freely.

In the ferroelectric capacitor of FIG. 16, the conductor films 1752 and 1753 are in close contact with the surfaces of the metal electrodes 1742 and 1743, respectively, but the metal electrodes 1742 and 1743 are only the conductor films 1752 and 1753 made of polysilicon. It may be formed by.
FIG. 17 is a sectional view showing a sixth example of the structure of the ferroelectric capacitor used in the ferroelectric memory device of the present invention.

  As shown in FIG. 17, this ferroelectric capacitor is formed on an insulating substrate 1840 mainly composed of silicon dioxide, and two sides of the ferroelectric film 1841 are formed by two metal electrodes 1842 and 1843 made of a metal film. At the same time, the metal electrode 1843 has a conductor film 1853 in close contact with the back side thereof. The conductor film 1853 is made of polysilicon similar to the conductor film 1553 shown in FIG. The metal electrodes 1842 and 1843 are supplied with electrical signals.

Comparing the ferroelectric capacitor having such a structure with that shown in FIG. 14, the upper conductor film 1553 and the metal electrode 1543 shown in FIG. 14 are arranged above and below the metal electrode 1843 and the conductor film 1853 in FIG. The point that is replaced is different.
Therefore, in the ferroelectric capacitor shown in FIG. 17, the polarization charge-applied voltage characteristic is translated in the same manner as the characteristic of the ferroelectric capacitor shown in FIG. The choice of the structure shown in FIG. 14 or the structure shown in FIG. 17 mainly depends on ease of manufacturing and reliability.

FIG. 18 is a sectional view showing a seventh example of the structure of the ferroelectric capacitor used in the ferroelectric memory device of the present invention.
As shown in FIG. 18, this ferroelectric capacitor is formed on an insulating substrate 1940 mainly composed of silicon dioxide, and the two sides of the ferroelectric film 1941 are formed by two metal electrodes 1942 and 1943 made of a metal film. In addition, the metal electrode 1942 has a conductive film 1952 in close contact with the back surface thereof. The conductor film 1952 is made of polysilicon similar to the conductor film 1652 shown in FIG. An electric signal is supplied to each of the metal electrodes 1942 and 1943.

Comparing the ferroelectric capacitor having such a structure with that shown in FIG. 15, the lower conductor film 1652 and the metal electrode 1642 shown in FIG. 15 are arranged above and below the metal electrode 1942 and the conductor film 1952 in FIG. The point that is replaced is different.
Therefore, in the ferroelectric capacitor shown in FIG. 18, the polarization charge-applied voltage characteristic moves in the same manner as the characteristic of the ferroelectric capacitor shown in FIG. The choice of the structure of FIG. 15 or the structure of FIG. 18 mainly depends on ease of manufacture and reliability.

FIG. 19 is a cross-sectional view showing an eighth example of the structure of the ferroelectric capacitor used in the ferroelectric memory device of the present invention.
As shown in FIG. 19, this ferroelectric capacitor is formed on an insulating substrate 2040 mainly composed of silicon dioxide, and two sides of the ferroelectric film 2041 are formed by two metal electrodes 2042 and 2043 made of a metal film. In addition, the metal electrode 2042 has a conductor film 2052 in close contact with the back surface thereof, and the metal electrode 2043 has a conductor film 2053 in close contact with the back surface thereof.

The conductor films 2052 and 2053 are made of polysilicon containing different impurity atoms in the semiconductor film, similarly to the conductor films 1752 and 1753 shown in FIG. In addition, electrical signals are supplied to the metal electrodes 2042 and 2043, respectively.
Comparing the ferroelectric capacitor having such a structure with that shown in FIG. 16, the lower metal electrode 1742 and the conductor film 1752 and the upper metal electrode 1743 and the conductor film 1753 shown in FIG. The difference is that the metal electrode 2042 and the conductor film 2052 and the metal electrode 2043 and the conductor film 2053 are interchanged.

Therefore, in the ferroelectric capacitor shown in FIG. 19, the polarization charge-applied voltage characteristic moves in the same manner as the characteristic of the ferroelectric capacitor shown in FIG. The choice of the structure of FIG. 16 or the structure of FIG. 19 mainly depends on ease of manufacture and reliability. Further, in the structure of FIG. 19, the amount of parallel movement of the polarization charge-applied voltage characteristics can be set freely and freely like the structure of FIG.
(Other)
The present invention is not limited to the above embodiment. The essence of the present invention is that the polarization charge-applied voltage characteristic as a ferroelectric capacitor is translated in the voltage axis direction by utilizing the difference in work function of the electrode material of the two terminals sandwiching the ferroelectric film. The hysteresis characteristic when the dielectric capacitor is viewed from the outside is made asymmetric, and the internal state is detected by utilizing the difference in output charge due to the minute voltage resulting from the asymmetry. Therefore, other methods may be used as long as the above conditions are satisfied.

For example, the method using the electrode materials having different work functions used in FIGS. 12 and 13 may be combined with the method using the conductor film used in FIGS.
As for the memory cell structure, 1T1C and 1C have been described with reference to FIGS. 2 and 6. However, the nondestructive reading method of the present invention can be applied to destructive reading of a 2T2C memory cell structure that has been conventionally used. Life can be extended. In addition, the present invention can be similarly applied to other memory cell structures if the peripheral circuit control method is changed.

In addition, the circuit of FIG. 4 is shown as the sense amplifier circuit, but this is an example of the simplest circuit for explaining the circuit operation principle, and there are actually various circuits that are used. Can do.
Further, the configuration example of the entire memory device is shown in the circuit block diagram of FIG. 5, but this is an example of the simplest general circuit block of the memory device, and the circuit block may be divided or integrated. However, other functional circuits may be added.

Further, as the material of the ferroelectric film, materials other than the above-described PZT, PZTN, and SBT may be used. For example, there are (Ba, Sr) TiO ₃ , Bi ₄ Ti ₃ O ₁₂ , BaBiNb ₂ O ₉ and the like. Moreover, it is innumerable if the composition ratio changes.
In addition to RuO ₂ and IrO ₂ described above, SrRuO ₃ , RhO _2, etc. may be used as the material for the oxide conductive film.

The material for the electrode of the metal film may be other than the above-described platinum (Pt), and Ta or Ti may be used, or a Pt / Ti alloy may be used.
Further, the material of the conductor film containing impurity atoms in the semiconductor film may be other than polysilicon, and other atoms are also effective if the impurity atoms are trivalent or pentavalent atoms.
Furthermore, if the doping amount of impurity atoms is changed, the work function is changed, and the amount of movement for translating the polarization charge-applied voltage characteristic as a ferroelectric capacitor in the voltage axis direction can be changed and adjusted to an appropriate value. As described above, the material and the structure may be selected depending on the optimum characteristics and manufacturing problems that match the characteristics of the ferroelectric film.

It is a characteristic view which shows the 1st example of the characteristic of the polarization charge and applied voltage of the ferroelectric capacitor used for the ferroelectric memory device of this invention. 1 is a circuit diagram showing a first configuration example of a memory cell used in a ferroelectric memory device of the present invention. FIG. FIG. 3 is a timing chart showing a signal or displacement of each part when data is read from the memory cell shown in FIG. 2. FIG. 3 is a circuit diagram of a sense amplifier used in the ferroelectric memory device of the present invention. 1 is a block diagram showing an overall configuration outline of a ferroelectric memory device of the present invention. It is a circuit diagram which shows the 2nd structural example of the memory cell used for the ferroelectric memory device of this invention. It is a characteristic view which shows the 2nd example of the characteristic of the polarization charge and applied voltage of the ferroelectric capacitor used for the ferroelectric memory device of this invention. It is a characteristic view which shows an example of the polarization charge-applied voltage characteristic of the conventional ferroelectric capacitor. It is a characteristic view which shows an example of the characteristic of the polarization charge and applied voltage of the ferroelectric capacitor used for the conventional destructive read ferroelectric memory device. It is a characteristic view which shows the other example of the characteristic of the polarization charge and applied voltage of the ferroelectric capacitor used for the conventional nondestructive readout ferroelectric memory device. It is sectional drawing which shows the structure of the ferroelectric capacitor used for the conventional ferroelectric memory device. It is sectional drawing which shows the 1st example of the structure of the ferroelectric capacitor used for the ferroelectric memory device of this invention. It is sectional drawing which shows the 2nd example of the structure of the ferroelectric capacitor used for the ferroelectric memory device of this invention. It is sectional drawing which shows the 3rd example of the structure of the ferroelectric capacitor used for the ferroelectric memory device of this invention. It is sectional drawing which shows the 4th example of the structure of the ferroelectric capacitor used for the ferroelectric memory device of this invention. It is sectional drawing which shows the 5th example of the structure of the ferroelectric capacitor used for the ferroelectric memory device of this invention. It is sectional drawing which shows the 6th example of the structure of the ferroelectric capacitor used for the ferroelectric memory device of this invention. It is sectional drawing which shows the 7th example of the structure of the ferroelectric capacitor used for the ferroelectric memory device of this invention. It is sectional drawing which shows the 8th example of the structure of the ferroelectric capacitor used for the ferroelectric memory device of this invention.

Explanation of symbols

211, 311A, 311B ... Ferroelectric capacitor, 212 ... MOSFET, 213, 316 ... Word line, 214, 317A, 317B ... Bit line, 215 ... Plate line, 420 ... Comparator circuit, 421 ... input signal terminal, 422 ... reference voltage terminal, 423 ... output terminal, 531 ... memory cell group, 532 ... word line selection circuit, 533 ... bit line selection Circuit 534... Sense circuit 535... Write circuit 536 .. input / output circuit 537... Overall control circuit 1240, 1340, 1440, 1540, 1640, 1740, 1840, 1940, 2040 ..Substrate, 1241, 1341, 1441, 1541, 1641, 1741, 1841, 1941 ... ferroelectric film, 242, 1243, 1342, 1443, 1542, 1543, 1642, 1643, 1742, 1743, 1842, 1843, 1942, 1943, 2042, 2043 ... Metal electrode, 1344, 1445 ... Oxide conductive film, 1553 , 1652, 1752, 1753, 1853, 1952, 2052, 2053 ... conductor films

Claims (20)

A ferroelectric capacitor having a structure in which a ferroelectric film is sandwiched between a first electrode made of a first conductive material and a second electrode made of a second conductive material having a work function different from that of the first conductive material. A plurality of memory cells having;
An address selection circuit for selecting one of the plurality of memory cells;
A write circuit for applying a voltage larger than the coercive electric field of the ferroelectric film to the ferroelectric capacitor of the memory cell selected by the address selection circuit;
A readout circuit for applying a voltage smaller than the coercive electric field of the ferroelectric film to the ferroelectric capacitor of the memory cell selected by the address selection circuit;
A ferroelectric memory device characterized by comprising: A ferroelectric capacitor having a structure in which a ferroelectric film is sandwiched between a first electrode made of a first conductive material and a second electrode made of a second conductive material having a work function different from that of the first conductive material. A memory cell having
When writing data to the ferroelectric capacitor, a voltage larger than the coercive electric field of the ferroelectric film is applied to the ferroelectric capacitor,
When reading data from the ferroelectric capacitor, a voltage smaller than the coercive electric field of the ferroelectric film is applied to the ferroelectric capacitor. In claim 1 or claim 2,
The ferroelectric memory device, wherein the first conductive material is made of an oxide conductive film, and the second conductive material is made of a metal film. In claim 1 or claim 2,
The ferroelectric memory device, wherein the first conductive material is a conductive film made conductive by doping impurity atoms into a semiconductor film, and the second conductive material is a metal film. In claim 1 or claim 2,
The ferroelectric memory device, wherein the first conductive material is made of a metal film, and the second conductive material is made of a metal film having a work function different from that of the metal of the first conductive material. In claim 1 or claim 2,
The first conductive material is a conductive film made conductive by doping impurity atoms into a semiconductor film, and the second conductive material is a semiconductor having a valence different from the impurity atoms contained in the first conductive material A ferroelectric memory device comprising a conductive film doped with impurity atoms to be conductive. In claim 4 or claim 6,
2. A ferroelectric memory device according to claim 1, wherein the conductive film made conductive by doping impurity atoms into the semiconductor film is polysilicon, and the impurity atoms have a trivalent or pentavalent valence. A plurality of ferroelectric capacitors having a structure in which a ferroelectric film is sandwiched between a first electrode made of a metal film in close contact with a first conductive material and a second electrode made of a metal film in close contact with a second conductive material Memory cells,
An address selection circuit for selecting one of the plurality of memory cells;
A write circuit for applying a voltage larger than the coercive electric field of the ferroelectric film to the ferroelectric capacitor of the memory cell selected by the address selection circuit;
A readout circuit for applying a voltage smaller than the coercive electric field of the ferroelectric film to the ferroelectric capacitor of the memory cell selected by the address selection circuit;
A ferroelectric memory device characterized by comprising: A memory having a ferroelectric capacitor having a structure in which a ferroelectric film is sandwiched between a first electrode made of a metal film in close contact with a first conductive material and a second electrode made of a metal film in close contact with a second conductive material With cells,
When writing data to the ferroelectric capacitor, a voltage larger than the coercive electric field of the ferroelectric film is applied to the ferroelectric capacitor,
When reading data from the ferroelectric capacitor, a voltage smaller than the coercive electric field of the ferroelectric film is applied to the ferroelectric capacitor. In claim 8 or claim 9,
The ferroelectric memory device, wherein the first conductive material or the second conductive material is a conductive film made conductive by doping impurity atoms into a semiconductor film. In claim 10,
2. A ferroelectric memory device according to claim 1, wherein the conductive film made conductive by doping impurity atoms into the semiconductor film is polysilicon, and the impurity atoms have a trivalent or pentavalent valence. In claim 8 or claim 9,
The ferroelectric memory device, wherein the first conductive material or the second conductive material is made of an oxide conductive film. A plurality of memory cells having a ferroelectric capacitor having a structure in which a ferroelectric film is sandwiched between a first electrode made of a metal film in close contact with a first conductive material and a second electrode made of a metal film;
An address selection circuit for selecting one of the plurality of memory cells;
A write circuit for applying a voltage larger than the coercive electric field of the ferroelectric film to the ferroelectric capacitor of the memory cell selected by the address selection circuit;
A readout circuit for applying a voltage smaller than the coercive electric field of the ferroelectric film to the ferroelectric capacitor of the memory cell selected by the address selection circuit;
A ferroelectric memory device characterized by comprising: A memory cell having a ferroelectric capacitor having a structure in which a ferroelectric film is sandwiched between a first electrode made of a metal film in close contact with a first conductive material and a second electrode made of a metal film;
When writing data to the ferroelectric capacitor, a voltage larger than the coercive electric field of the ferroelectric film is applied to the ferroelectric capacitor,
When reading data from the ferroelectric capacitor, a voltage smaller than the coercive electric field of the ferroelectric film is applied to the ferroelectric capacitor. In claim 13 or claim 14,
The ferroelectric memory device according to claim 1, wherein the first conductive material is a conductive film made conductive by doping impurity atoms into a semiconductor film. In claim 15,
A conductor film made conductive by doping impurity atoms into the semiconductor film is polysilicon as a semiconductor film, and the impurity atoms are composed of trivalent or pentavalent valences. apparatus.   15. The ferroelectric memory device according to claim 13, wherein the first conductive material is an oxide conductive film. In any one of Claims 1-17,
2. The ferroelectric memory device according to claim 1, wherein the ferroelectric capacitor constitutes a one-transistor / one-capacitor type memory cell. In any one of Claims 1-17,
The ferroelectric memory device comprises a one-capacitor type memory cell. In any one of Claims 1-17,
A ferroelectric memory device, wherein the ferroelectric thin film of the ferroelectric capacitor is made of PZT, PZTN, or SBT.

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