JP2010027698A - Storage element and storage device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a storage element and a storage device that store applied pressure without using a piezoelectric element. <P>SOLUTION: A plurality of storage elements are arranged longitudinally and laterally. Each storage element is provided with a resistance varying part 1 having a resistance varying element and a current varying part 2 whose flowing current varies in accordance with applied pressure. A constant voltage is applied to the current varying part 2. A bit line BL is connected between the resistance varying part 1 and current varying part 2, and one of the source and drain of a transistor 3 is connected to the other end of the resistance varying part 1. The other of the source and drain of the transistor 3 is connected to a signal line SL, and the gate of the transistor 3 is connected to a word line WL. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a storage element and a storage device that store an applied pressure.

  In recent years, information terminal devices having a function called a pen tablet have been used. In a pen tablet, when pressure is applied to the surface of the panel with a pen, the locus is displayed. Therefore, it is possible to draw characters and pictures. There are pen tablets that identify the intensity of pressure and express shades. As such a pen tablet, there are one in which a pressure gauge is built in the pen and another in which a pressure gauge is built in a panel such as a touch panel.

  However, if the pen has a built-in pressure gauge, no drawing can be performed without the pen, and precise drawing is possible unless the user performs delicate pressure control. The target is limited. For example, when drawing the surface of an object with irregularities, if the panel has a built-in pressure gauge, precise drawing is performed simply by pressing the object against the panel. With the built-in one, drawing cannot be performed in such a simple way.

  On the other hand, in the case where a pressure gauge is built in the panel, it is necessary to lay a piezoelectric element having a complicated structure such as a semiconductor strain gauge on the panel in the manufacturing process. For this reason, formation of the piezoelectric element itself and subsequent film formation are difficult. Further, when the piezoelectric element is miniaturized, the obtained detection signal becomes weak. As a result, an amplifier circuit that amplifies the output voltage is indispensable for detecting the pressure level.

  Furthermore, a memory element such as a memory is indispensable for later use of the detection result regardless of whether the position of the pressure gauge is a pen or a panel.

JP 58-086630 A JP 2004-139411 A JP 07-319603 A JP-A-61-107419 JP 2002-149346 A

  The objective of this invention is providing the memory | storage element and memory | storage device which can memorize | store the applied pressure without using a piezoelectric element.

  As a result of intensive studies to solve the above-mentioned problems, the present inventor has come up with the following aspects of the invention.

  The memory element is provided with a resistance change element, and a current change means that is connected to the resistance change element and changes a limit value of a current flowing through the resistance change element in accordance with an external pressure. Yes. In the storage device, a plurality of the storage elements are arranged side by side.

  According to the storage element or the like, since the resistance value of the resistance change element is set according to the limit value of the current changed by the current change means, the pressure can be stored without using the piezoelectric element. .

  Hereinafter, embodiments will be described in detail with reference to the accompanying drawings.

(First embodiment)
First, the first embodiment will be described. FIG. 1 is a circuit diagram showing the structure of the memory device according to the first embodiment.

  As shown in FIG. 1, the storage device is provided with a plurality of storage elements arranged side by side in the vertical and horizontal directions. Each memory element is provided with a resistance change unit 1 including a resistance change element, and a current change unit 2 in which a flowing current changes in accordance with an applied pressure. A constant voltage is supplied to the current changing unit 2 from a voltage applying unit (not shown).

  A bit line BL is connected between the resistance change unit 1 and the current change unit 2, and one of the source and drain of the transistor 3 is connected to the other end of the resistance change unit 1. The other source / drain of the transistor 3 is connected to the signal line SL, and the gate of the transistor 3 is connected to the word line WL. For example, the signal line SL and the bit line BL are shared between a plurality of storage elements arranged in the vertical direction, and the word line WL is shared between the plurality of storage elements arranged in the horizontal direction.

  Here, the structure of the memory element will be described. 2A and 2B are diagrams illustrating a configuration of the memory element, in which FIG. 2A is a layout diagram, and FIG. 2B is a cross-sectional view taken along line II in FIG. In the layout diagram (a), some components are omitted.

  As shown in FIG. 2, a thin film transistor is provided on the glass substrate 11. That is, the gate electrode 12, the gate insulating film 13, and the channel 14 are formed on the glass substrate 11, and the source / drain electrodes 15a and 15b are formed with the channel 14 interposed therebetween. This thin film transistor corresponds to the transistor 3 in FIG.

A resistance change element 16 is formed on the source / drain electrode 15b. The resistance change element 16 is composed of a film having a single transition metal oxide (TMO) such as NiO _x and TiO _x , for example. This variable resistance element 16 corresponds to the variable resistance portion 1 in FIG.

  An interlayer insulating film 17 is formed to cover the thin film transistor and the resistance change element 16. A plug 20 connected to the source / drain electrode 15 a is formed in the interlayer insulating film 17, and the plug 20 is formed on the interlayer insulating film 17. A signal line SL connected to is formed. An interlayer insulating film 18 that covers the signal line SL is formed on the interlayer insulating film 17, and a plug 21 connected to the resistance change element is formed in the interlayer insulating films 18 and 17. A pad may be formed on the interlayer insulating film 17, and the plug 21 may be divided between the interlayer insulating films 18 and 17 through the pad. A bit line BL connected to the plug 21 is formed on the interlayer insulating film 18. An interlayer insulating film 19 that covers the bit line BL is formed on the interlayer insulating film 18. The interlayer insulating films 17 to 19 are, for example, silicon oxide films.

  A transparent electrode 23 (lower electrode film) made of indium tin oxide (ITO) or the like is selectively formed on the interlayer insulating film 19. One transparent electrode 23 is provided for each memory element.

  Further, a flexible transparent substrate 31 having a plurality of spacers 41 formed on the interlayer insulating film 19 and the transparent electrode 23 and having a flexible transparent electrode 32 (upper electrode film) formed on one side thereof. Are arranged while the transparent electrode 32 is in contact with the spacer 41. For example, the transparent substrate 31 is made of polyethylene terephthalate (PET), and the spacer 41 is made of an insulator such as silicone rubber or EPD (ethylene / propylene / diene terpolymer) rubber. The transparent electrode 32 is supplied with a constant voltage V. The combination of the transparent electrodes 23 and 32 corresponds to the current changing portion 2 in FIG. The spacer 41 is preferably provided in the vicinity of the thin film transistor and the bit line BL for protection. Further, the outer peripheral portion of the transparent electrode 32 is fixed to the outer peripheral portion of the interlayer insulating film 19 via a seal member or the like (not shown). The spacer 41 can be formed, for example, by performing patterning using a photolithography technique after applying a raw material.

  Here, the property of the substance constituting the variable resistance element 16 will be described. The resistance change element 16 is made of a material whose resistance value changes in response to an external electrical stimulus. Such substances can be roughly classified into two types according to their electrical characteristics. One is sometimes called a bipolar material and the other is called a unipolar material.

Examples of the bipolar material include SrTiO ₃ and SrZrO ₃ doped with a small amount of impurities such as Cr. Pr _(1-x) Ca _x MnO _3, La _(1-x) Ca _x MnO _{3, and the} like that exhibit supergiant magnetoresistance (CMR) are also bipolar materials. When a voltage exceeding a certain threshold is applied to a thin film or bulk material made of a bipolar material, a change in resistance occurs. However, the resistance remains stable before and after the change. After a change in resistance occurs, applying a voltage of another threshold or higher than the reverse polarity will return the resistance of the bipolar material to the same level as the original resistance. As described above, in the bipolar material, it is necessary to apply voltages having different polarities to change the resistance.

For example, SrZrO ₃ doped with 0.2% Cr is known as a bipolar material. When a negative voltage is applied, the absolute value of the current increases rapidly in the vicinity of -0.5V. That is, the resistance of SrZrO ₃ changes abruptly from high resistance to low resistance. Such a phenomenon of switching from high resistance to low resistance and the process thereof may be referred to as a set. Next, when the voltage is swept in the positive direction, the value of the current rapidly decreases in the vicinity of + 0.5V. That is, the resistance of SrZrO ₃ rapidly returns from a low resistance to a high resistance. Such a phenomenon of switching from low resistance to high resistance and the process thereof may be referred to as reset. Each resistance is stable within a range of ± 0.5 V, and is maintained even when no voltage is applied. Therefore, by making the high resistance state and the low resistance state correspond to “0” and “1”, respectively, the bipolar material can be used for the memory. Note that the threshold voltage at which the resistance changes depends on the material, crystallinity, and the like. Further, it is possible to change the resistance by applying not only a direct current voltage but also a pulse voltage.

Monopolar materials include single transition metal oxides (TMO) such as NiO _x and TiO _x . In a unipolar material, the change in resistance occurs regardless of the polarity of the applied voltage, and the absolute value of the voltage that causes a change from low resistance to high resistance (reset) is changed from high resistance to low resistance (s set). ) Is smaller than the absolute value of the voltage. Also, like the bipolar material, the resistance remains stable before and after the change. Also, the change in resistance is reversible. Therefore, the magnitude of the resistance can be switched without changing the polarity of the voltage. Thus, in a unipolar material, it is necessary to apply a voltage having a single polarity to each other in order to change the resistance. When a pulse voltage is applied, the above behavior is confirmed when the pulse width is fixed.

FIG. 3 is a graph showing current-voltage characteristics of a thin film of TiO _x that is a unipolar material. When a voltage is applied to a thin film having a high resistance (1), the resistance rapidly decreases at a certain voltage (about 1.5 V), and the current rapidly increases (2). Thereafter, when the voltage is lowered while applying a current limit (limit value: 20 mA) (3), the current returns to zero with the resistance kept low (4). By such treatment, the resistance of the thin film changes from high resistance to low resistance. That is, the set process is manifested. This low resistance state is maintained even when no voltage is applied. The reason why the current is limited is that if the current limit cannot be applied, a large current flows through the thin film and is destroyed.

  On the other hand, when a voltage is applied to a thin film having a low resistance (5), the resistance rapidly increases at a certain voltage (about 1.2 V), and the current rapidly decreases (6). Thereafter, when the voltage is lowered (7), the current returns to 0 while the resistance is high. By such treatment, the resistance of the thin film changes from low resistance to high resistance. In other words, a reset process appears. This high resistance state is maintained even when no voltage is applied.

  Therefore, by making the high resistance state and the low resistance state correspond to “0” and “1”, respectively, it is possible to use a unipolar material for the memory. That is, in the example shown in FIG. 3, the resistance of the unipolar material can be identified from the current value when a voltage of about 0.2 V is applied, and either “0” or “1” is stored from this resistance. Can identify.

Furthermore, such a material also has a property that the resistance value in the low resistance state differs depending on the magnitude of the current limit. That is, there is a property that the resistance value in the low resistance state decreases as a larger current flows during setting. FIG. 4 is a graph showing the current limit dependence of the current-voltage characteristics of the TiO _x thin film. The solid line in FIG. 4 indicates the characteristics when the limit value is 20 mA, the two-dot chain line indicates the characteristics when the limit value is 15 mA, and the broken line indicates the characteristics when the limit value is 10 mA. As shown in FIG. 4, the resistance value in the low resistance state decreases as the limit value increases, that is, as the current flowing during setting increases.

  Accordingly, if the limit value of the current limit at the time of setting is made variable, the resistance value in the low resistance state can be made variable. When the pressure applied to the storage device is associated with the limit value, it is possible to recognize the applied pressure by detecting the resistance value in the low resistance state.

  Next, the operation of the storage device configured as described above will be described.

  First, the operation during storage will be described. At the time of storage, the resistance change element 16 of the resistance change unit 1 of each storage element is reset to be in a high resistance state. Next, the signal line SL is grounded, and a constant voltage V is applied to the transparent electrode 32. Further, a voltage for turning on the thin film transistor is applied to the word line WL, and the bit line BL is opened.

  In this state, if no pressure is applied to the storage element, the transparent electrode 32 and the transparent electrode 23 are not conductive as shown in FIG. No voltage is applied. For this reason, the resistance value of the resistance change unit 1 does not change and remains in a high resistance state.

  Thereafter, when a pressure is applied to the memory element with the pen 51 or the like, the transparent electrode 32 and the transparent electrode 23 are electrically connected as shown in FIGS. Begins to flow. The magnitude of this current reflects the magnitude of the applied pressure. That is, as shown in FIG. 5B, when a weak pressure is applied, the contact area between the transparent electrode 32 and the transparent electrode 23 is small, so the resistance of the current changing portion 2 is high and the current value is small. It will be a thing. On the other hand, as shown in FIG. 5C, when a strong pressure is applied, the contact area between the transparent electrode 32 and the transparent electrode 23 is large, so that the resistance of the current changing portion 2 is low and the current value is large. It will be a thing. In addition, since the current changing unit 2 is connected in series to the resistance changing unit 1, the magnitude of the current flowing through the current changing unit 2 is the current limit current value of the resistance changing unit 1. Therefore, the resistance change unit 1 is set with a current limit according to the magnitude of the applied pressure, and the state of the resistance change unit 1 transitions to a low resistance state with a resistance value according to the current limit. . This transition occurs in all the memory elements to which a pressure equal to or higher than a predetermined value is applied.

  In this way, a resistance value corresponding to the applied pressure is set in the resistance change unit 1. This resistance value is maintained unless a reset voltage is applied later. That is, the resistance change unit 1 functions as a nonvolatile memory cell.

  Next, the operation at the time of reading will be described. At the time of reading, the application of the constant voltage V to the transparent electrode 32 is stopped, and a predetermined voltage is applied to the bit line BL. Then, the word lines WL are sequentially scanned. That is, a voltage for turning on the transistor 3 is sequentially applied to the word line WL. As a result, in the memory element in which the transistor 3 is turned on, a current corresponding to the resistance value flows through the resistance change unit 1, and the magnitude of this current via the bit line BL by a current detection circuit (not shown) or the like. Is detected. Since the current value and the resistance value have a one-to-one correspondence, and the resistance value and the applied pressure have a one-to-one correspondence, the applied pressure can be read from the current value. it can.

  According to such a storage device, it is possible to accurately detect and store the pressure applied from the outside with a simple configuration without using a piezoelectric element. Therefore, it is possible to accurately detect and memorize the writing pressure from the pen 51 and the surface of an object with unevenness. In addition, since the storage device itself can store the pressure, it is not necessary to provide a memory or the like outside. Further, since the difference between the upper limit and the lower limit of the resistance value in the low resistance state in the resistance change element 16 is extremely large, it is possible to accurately memorize the strength of the pressure without using an amplifier circuit at the time of reading. Easy to recognize pressure. In addition, the formation of the resistance change element 16 is easy to incorporate into a normal semiconductor device manufacturing process. Furthermore, there is no reduction in resistance margin due to miniaturization. For this reason, it is preferable compared with a piezoelectric element. Moreover, it can be overwritten by re-applying the pen 51 to the place where the pressure is once applied.

(Second Embodiment)
Next, a second embodiment will be described. Although the first embodiment can accurately store the pressure, the stored pressure cannot be read in real time and used for display. The second embodiment enables real-time display. FIG. 6 is a circuit diagram showing a configuration of the memory element in the second embodiment.

  In the second embodiment, in each storage element, one of the source and drain of the read transistor 4 is connected to the bit line BL. The other source / drain of the read transistor 4 is connected to the bit line BL2, and the gate of the read transistor 4 is connected to the word line WL2. Other configurations are the same as those of the first embodiment.

  In such a second embodiment, during storage, the same control as in the first embodiment is performed, and a voltage for sequentially turning on the read transistor 4 is applied to the word line WL2. Then, the potential of the bit line BL, that is, the potential between the resistance change unit 1 and the current change unit 2 is read through the bit line BL2. This potential reflects the magnitude of the applied pressure. Accordingly, a resistance value corresponding to the applied pressure is set in the resistance changing unit 1, and the magnitude of the applied pressure can be read and displayed according to this. That is, real-time display is possible.

  In any of the embodiments, the magnitude of the constant voltage V is not particularly limited. However, for example, it is preferable that the resistance change element 16 is set to a magnitude that can be set even when the lowest pressure to be detected is applied.

The material of the resistance change element 16 is not particularly limited, and may be either a unipolar material or a bipolar material. Monopolar materials include titanium oxide (TiO _x ), nickel oxide (NiO _x ), yttrium oxide (YO _x ), cerium oxide (CeO _x ), magnesium oxide (MgO _x ), zinc oxide ( ZnO _x ), tungsten oxide (WO _x ), niobium oxide (NbO _x ), aluminum oxide (AlO _x ), and silicon oxide (SiO _x ). In addition, these oxides doped with a different kind of element (for example, titanium, nickel, yttrium, cerium, magnesium, zinc, tungsten, niobium, aluminum, silicon) from the elements constituting the oxide It may be used. In particular, nickel oxide doped with titanium is preferable. On the other hand, examples of the bipolar material include oxides of plural kinds of metals or semiconductors such as Pr _(1-x) Ca _x MnO ₃ , La _(1-x) Ca _x MnO ₃ , SrTiO _3, and SrZrO _3. It is done. Furthermore, the resistance change element 16 does not need to be composed of only one layer made of the oxide as described above, and may include two or more of these oxide layers.

  Further, an electrode made of Pt, Ir, W, TiN, Ru, ITO, or the like may be provided between the resistance change element 16 and the source / drain electrode 15b and the plug 21. When these electrodes are provided, the property of the resistance change element 16 is easily stabilized.

  Hereinafter, various aspects of the present invention will be collectively described as supplementary notes.

(Appendix 1)
A resistance change element;
Current changing means connected to the variable resistance element and changing a limit value of a current flowing through the variable resistance element according to the magnitude of pressure from the outside;
A memory element comprising:

(Appendix 2)
The storage element according to appendix 1, wherein the current changing unit changes a limit value of a current when the variable resistance element transitions from a high resistance state to a low resistance state.

(Appendix 3)
The memory element according to appendix 1 or 2, further comprising voltage application means for applying a voltage to a series body of the resistance change element and the current change means.

(Appendix 4)
The current changing means is
A first electrode connected to the variable resistance element;
A flexible second electrode facing the first electrode;
4. The memory element according to any one of appendices 1 to 3, wherein:

(Appendix 5)
The variable resistance element includes an oxide layer composed of an oxide of one element selected from the group consisting of titanium, nickel, yttrium, cerium, magnesium, zinc, tungsten, niobium, aluminum, and silicon. The memory element according to any one of appendices 1 to 4, characterized by:

(Appendix 6)
The memory element according to appendix 5, wherein the oxide layer is configured by doping the oxide with an element different from an element constituting the oxide.

(Appendix 7)
The memory element according to any one of appendices 1 to 4, wherein the variable resistance element includes an oxide layer composed of oxides of a plurality of types of elements of metal or semiconductor.

(Appendix 8)
The oxide layer includes _one selected from the group consisting of Pr _(1-x) Ca _x MnO ₃ , La _(1-x) Ca _x MnO ₃ , SrTiO _3, and SrZrO _3. 8. The memory element according to 7.

(Appendix 9)
The memory element according to any one of appendices 1 to 4, wherein the variable resistance element includes a nickel oxide layer doped with titanium.

(Appendix 10)
10. The memory element according to any one of appendices 5 to 9, wherein the resistance change element includes two or more oxide layers.

(Appendix 11)
A memory device comprising a plurality of memory elements according to any one of appendices 1 to 10 arranged side by side in the vertical and horizontal directions.

1 is a circuit diagram showing a structure of a storage device according to a first embodiment. It is a figure which shows the structure of a memory element. Current of a thin film of TiO _x - is a graph showing the voltage characteristic. Current of a thin film of TiO _x - a graph showing the current limit dependency of voltage characteristics. It is a figure which shows operation | movement of a memory element. It is a circuit diagram which shows the structure of the memory element in 2nd Embodiment.

Explanation of symbols

1: Resistance changing portion 2: Current changing portion 3: Transistor 4: Reading transistor BL, BL2: Bit line SL: Signal line WL, WL2: Word line

Claims (5)

A resistance change element;
Current changing means connected to the variable resistance element and changing a limit value of a current flowing through the variable resistance element according to the magnitude of pressure from the outside;
A memory element comprising:   The memory element according to claim 1, wherein the current changing unit changes a limit value of a current when the variable resistance element transitions from a high resistance state to a low resistance state.   The memory element according to claim 1, further comprising a voltage applying unit that applies a voltage to a series body of the variable resistance element and the current changing unit. The current changing means is
A first electrode connected to the variable resistance element;
A flexible second electrode facing the first electrode;
4. The memory element according to claim 1, comprising:   5. A storage device comprising a plurality of storage elements according to claim 1, which are arranged side by side in the vertical and horizontal directions.

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