Magnetoresistive storage device and ferroelectric storage device

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention enables a fine-shaped magnetoresistive storage element and a ferroelectric resistance change type that operate at a low voltage, and a high-density magnetoresistive effect type storage device with a large operating margin and a high-density ferroelectric resistance change type. It realizes a storage device.

【0002】

[Conventional technology]

A solid-state storage device (MRAM) using a magnetoresistive effect (MR) film was proposed by Schwee (Reference 1), and is a ward wire that is a current line for generating a recording magnetic field and a sense for reading using an MR film. Various types of MRAM consisting of lines have been studied (Reference 2). For these storage devices, NiFe films or the like showing an anisotropic MR effect (AMR) with an MR change rate of about 2% were used, and improvement of output was an issue.

【0003】

It was discovered that an artificial lattice film composed of magnetic films exchanged and bonded via a non-magnetic film exhibits a giant magnetoresistive effect (GMR), and (Reference 3) MRAM using a GMR film was proposed (Reference). Reference 4). However, although the GMR film composed of this antiferromagnetic exchange-coupled magnetic film shows a large MR change rate, it requires a larger applied magnetic field than the AMR film, and has a problem that a large information recording and reading current are required. is there.

【0004】

In contrast to the above exchange-bonded GMR film, there is a spin valve film as a non-bonded GMR film, which uses an antiferromagnetic film (Reference 5) and a (semi) hard magnetic film (Semi). References 6) are available, which have the same low magnetic field as the AMR film and show a larger MR change rate than the AMR film. The present invention is an MRAM using a spin valve type using an antiferromagnetic film or a hard magnetic film, and shows that this storage element has non-destructive readout characteristics (NDRO) (Reference 7). ..

【0005】

The non-magnetic layer of the above GMR film is a conductor film such as Cu, but the non-magnetic layer is Al.₂O₃Research on tunnel-type GMR films (TMRs) using oxide insulating films such as MgO and MgO has also become active, and MRAM using these TMR films has also been proposed. It is known that the MR effect (CPPMR) when a current is passed through the film surface of the GMR film is greater than the MR effect (CIPMR) when a current is passed through the film surface. Higher output is expected due to higher impedance.

【0006】

The TMR element is an Al between the two magnetic layers.₂O₃It is an element with a simple structure in which an ultra-thin insulating film made of oxides such as MgO and MgO is inserted, and is expected because it reduces costs from the manufacturing aspect. However, even a TMR element using a tunnel type GMR film (TMR) has an MR change rate of about 25%, and the output voltage of the element can only change by about 25%. The power supply voltage of ordinary silicon MOS semiconductor devices is becoming lower year by year due to miniaturization, and it is predicted that the power supply voltage will be 0.5V or less after 2010. At this time, if only 25% of the output voltage changes, only an amplitude of about 0.13V can be obtained, and the circuit operation margin becomes very small. In order to improve this point, it is considered to form a memory cell by combining these TMR elements and MOS elements. For example, there is a method in which a TMR element is connected in series with the source electrode of the MOS element, and a change in the source resistance due to the TMR element is converted into a change in the drain current of the MOS element and read out. In this case, an Nch MOS element is usually used as the selection transistor. The gate electrode of the MOS element corresponds to the word line of a memory such as DRAM. When the memory cell is not selected, the gate electrode is 0V, and when the memory cell is selected, the power supply voltage is set. An appropriate bias voltage is applied to the drain electrode. When a memory cell is selected, a current flows between the source and drain, but the substrate is biased according to the magnitude of the source resistance by the TMR element, and the current between the source and drain changes depending on the resistance of the TMR element. To do. This difference in current is amplified by a sense amplifier or the like, and the magnitude of the resistance of the TMR element is finally converted into 0 and 1 of the voltage to read the memory contents.

【0007】

[Problems to be Solved by the Invention]

However, even when the above method is used, a step of once converting the difference in the current flowing through the memory cell into a voltage is required, which is disadvantageous in terms of power consumption and operating speed. Further, as the power supply voltage becomes lower due to miniaturization in the future, the amount of current flowing through the transistor decreases, the voltage applied to the resistor of the TMR element installed on the source side decreases, and as a result, the substrate bias effect decreases. When the substrate bias effect is reduced, the difference in the reading current becomes small, the operating margin is lowered, and reading becomes difficult, and in the worst case, a malfunction is caused.

【0008】

[Means for solving problems]

When the storage element according to the first invention of the present invention is used, the potential of the gate electrode of the field effect transistor can be changed by increasing the ratio of the resistance between the first resistance element and the second resistance element. It is possible to make two states, one is a state above the threshold value and the other is a state below the threshold value. This makes it possible to directly convert the difference in the current flowing through the memory cell into a voltage, and it is possible to realize a high-performance storage element in terms of power consumption and operating speed. In particular, if the storage element according to the third invention of the present invention is used, even if a magnetoresistive element having a resistance change of several tens of percent is used, the potential of the gate electrode of the field effect transistor can be combined with an element having a negative resistance. Can be set to two states, one is above the threshold of the field effect transistor and the other is below the threshold. Further, if the storage element according to the sixth aspect of the present invention is used, the memory element can be formed by using a ferroelectric effect type element instead of the magnetoresistive effect element. Since all of these can take a large signal amplitude, the operation margin is large, the stored contents can be easily read out, and there is no concern of causing a malfunction.

【0009】

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment) In the conventional method, a step of once converting the difference in the current flowing through the memory cell into a voltage is required. In order to eliminate this, it is necessary to output the memory contents directly as a voltage. Figure 1 shows a circuit diagram showing the concept. The TMR element 101 and the load element 102 are connected in series, and the storage node 106, which is the connection portion thereof, is connected to the gate electrode of the field effect transistor 103. The other terminal of the load element 102 is connected to the ground wire 108, and the other terminal of the TMR element 101 is connected to the word wire 107. When the word line 107 is 0V, the potential of the storage node 106 is also 0V. When a voltage is applied to the word line, the potential internally divided by the ratio of the resistance values of the TMR element 101 and the load element 102 becomesOccurs on storage node 106. When the resistance value of the TMR element 101 changes due to the current flowing through the TMR control line (not shown), the potential of the storage node 106 also changes accordingly, and the value of the current flowing between the source 104 and the drain 105 of the field effect transistor 103. Also changes. If the potential of the storage node 106 is larger than the threshold Vt of the field effect transistor 103, a current flows between the source 104 and the drain 105, and if the potential of the storage node 106 is smaller than the threshold Vt of the field effect transistor 103, a current flows between the source 104 and the drain 105. No current flows. Therefore, if the potential of the storage node 106 can be created in two states, one is larger than the threshold value Vt of the transistor 103 and the other is smaller than the threshold value Vt of the transistor 103, the ON / OFF of the field effect transistor 103 can be directly controlled by the difference in the state of the TMR element. it can. However, the resistance change of the TMR element is about 25%, and it is not possible to create two states when the potential of the storage node 106 as described above is larger than or smaller than the threshold value Vt of the transistor 103. This will be described with reference to the figures. FIG. 2 shows the relationship between the characteristics of the TMR element 101 and the load element 102 and the potential of the storage node 106 when a fixed resistor is used as the load element 102. For simplicity, the characteristics of each element are linearly approximated. Here, the TMR element characteristic 111 is defined as ON when the resistance is low and OFF when the resistance is high, and is shown by a solid line and a broken line, respectively. When the TMR element is ON, the potential of the storage node 106 is the potential V at the intersection of the load element characteristic 112 and the TMR element characteristic 111 shown by the solid line._HWill be. Similarly, when the TMR element is OFF, the potential of the storage node 106 is the potential V at the intersection of the load element characteristic 112 and the TMR element characteristic 111 shown by the broken line._LWill be. V as shown in Figure 2_HAnd V_LThe difference between the two states is very small, and it is not possible to create two states, one is larger than the threshold value Vt of the transistor 103 and the other is smaller than the threshold value Vt of the transistor 103. Cannot be controlled directly.

【0010】

In order to increase the potential difference of the storage node 106, it can be realized by optimizing the characteristics of the load element in addition to increasing the resistance change of the TMR element. This will be described with reference to the figures. FIG. 3 shows the relationship between the characteristics of the TMR element and the load element and the potential of the storage node when the improved load element having the improved characteristics is used. The improved load element characteristics are represented by 122a in the low voltage part and 122b in the high voltage part. Similar to FIG. 2, the TMR element characteristic 111 is defined as ON when the resistance is low and OFF when the resistance is high, and is shown by a solid line and a broken line, respectively. When the TMR element is OFF, the potential of the storage node 106 is the potential V at the intersection of the improved load element characteristic 122a and the TMR element characteristic 111 shown by the broken line._LWill be. Similarly, when the TMR element is ON, the potential of the storage node 106 is the potential V at the intersection of the improved load element characteristic 122b and the TMR element characteristic 111 shown by the solid line._HWill be. In this way, when the improved load element is used, V is much larger than when the conventional fixed resistor is used._HAnd V_LThe difference can be obtained. Using such a load element, it is possible to create two states in which the potential of the storage node 106 is larger than or smaller than the threshold value Vt of the transistor 103 shown in FIG. 1, and as a result, the field effect transistor shown in FIG. 1 can be created. It is possible to directly control the ON / OFF of 103.

【0011】

The necessary requirement for the improved load element is that the low voltage portion is represented by 122a and the high voltage portion is represented by 122b, and any device can be used as long as this characteristic is satisfied. Figure 4 shows an example. FIG. 4 shows a case where an NDR element having a negative resistance is used as the load element. The NDR element can be formed by using silicon, a compound semiconductor, or the like. As an element for developing negative resistance, an element using an interband tunnel phenomenon such as an Esaki diode (tunnel diode) or an element using a subband resonance tunnel phenomenon such as a resonance tunnel diode (RTD) is used. It is possible. Needless to say, any other element that can express negative resistance as a result by using a surface level or the like can be used.

【0012】

In the case of the example shown in FIG. 4, the characteristics of the NDR element are expressed as 132, and the voltage applied to both ends of the element is V._PIn the following regions, the larger the applied voltage, the larger the current will flow. However, the voltage applied to both ends of the element is V._PWith the above V_VIn the following regions, the larger the applied voltage, the smaller the current that flows. Furthermore, the voltage applied to both ends of the element is increased to V._VIn the above region, the larger the applied voltage, the larger the current will flow. Here, the TMR element characteristic 111 is defined as ON when the resistance is low and OFF when the resistance is high, and is shown by a solid line and a broken line, respectively. When the TMR element is OFF, the potential of the storage node 106 is the potential V at the intersection of the NDR element characteristic 132 and the TMR element characteristic 111 shown by the broken line._LWill be. Similarly, when the TMR element is ON, the potential of the storage node 106 is the potential V at the intersection of the NDR element characteristic 132 and the TMR element characteristic 111 shown by the solid line._HWill be. When an NDR element is used in this way, V is much larger than when a conventional fixed resistor is used._HAnd V_LThe difference can be obtained. Therefore, when the NDR element is used, the potential of the storage node 106 can be created in two states, one is larger than the threshold value Vt of the transistor 103 shown in FIG. 1 and the other is smaller than the threshold value Vt of the transistor 103 shown in FIG. It is possible to directly control ON / OFF.

【0013】

The results when an interband tunnel diode (IBTD element) using silicon is used as the NDR element will be described with reference to FIGS. 5 and 6. FIG. 5 shows a circuit diagram of a memory element when an IBTD element is used as a load. Further, FIG. 6 shows the relationship between the characteristics of the TMR element and the IBTD element constituting the circuit and the potential of the storage node. In FIG. 5, the TMR element 201 and the IBTD element 202 are connected in series, and the storage node 206, which is the connection portion thereof, is connected to the gate electrode of the field effect transistor 203. The other terminal of the load element 202 is connected to the ground wire 208, and the other terminal of the TMR element 201 is connected to the word wire 207. When the word line 207 is 0V, the potential of the storage node 206 is also 0V. When a voltage of 0.6V is applied to the word line 207, when the resistance of the TMR element 201 is high and it is in the OFF state, the characteristics of the TMR element are shown by a broken line, and the storage node 206 becomes about 0.03V. On the other hand, when the resistance of the TMR element 201 is low and is in the ON state, the characteristics of the TMR element are shown by a solid line, and the storage node 206 is about 0.42 V. Therefore, the potential difference of the storage node 206 when the resistance of the TMR element 201 is low and high is 0.39 V. The threshold value Vt of the field effect transistor 203 is set to 0. If it is designed to be about 2V, when the resistance of the TMR element 201 is high and it is in the OFF state, the potential of the storage node 206 becomes smaller than the threshold value Vt of the field effect transistor 203, and no current flows between the source 204 and the drain 205. .. On the other hand, when the resistance of the TMR element 201 is low and is in the ON state, the potential of the storage node 206 becomes larger than the threshold value Vt of the field effect transistor 203, and a current flows between the source 204 and the drain 205. Therefore, depending on the state of the TMR element, it is possible to create two states, one in which the potential of the storage node 206 is larger than the threshold value Vt of the transistor 203 and the other in which it is smaller, and the ON / OFF of the field effect transistor 203 is directly controlled. be able to. When a fixed resistor is used as the load element, from FIG. 6, the storage node 206 when the TMR element 201 is OFF is about 0.25V, and the storage node 206 when the TMR element 201 is ON is about 0.33V. The potential difference of the storage node 206 when the TMR element 201 is ON / OFF is only 0.08V. Therefore, by using the IBTD element as the load element, the potential difference can be expanded nearly 5 times, resulting in high performance. A memory element can be realized.

【0014】

On the other hand, in order to form the storage element, it is possible to use another element instead of the TMR element shown in FIG. For example, the same function can be realized by an element that causes a resistance change by using a ferroelectric film. FIG. 7 shows a structural diagram of an element that causes a resistance change using a ferroelectric film. An insulating film 302 is provided on the semiconductor resistance layer 301a, and a ferroelectric film 303 is provided on the insulating film 302. Further, a metal electrode 304 is provided above the metal electrode 304. Metal electrodes 305a and 305b are provided at both ends of the semiconductor resistance layer 301a. When a voltage is applied between one of the metal electrode 305a or the metal electrode 305b and the metal electrode 304, polarization occurs in the dielectric film 303, and this polarization is not eliminated even after the applied voltage is removed. At this time, a semiconductor depletion layer 301b is formed between the semiconductor resistance layer 301a and the insulating film 302 according to the polarization in the ferroelectric film 303. This semiconductor depletion layer 301b exhibits a very high resistance to the majority carriers in the semiconductor resistance layer 301a. Therefore, when a voltage is applied between the metal electrode 305a and the metal electrode 305b, the current hardly flows in the semiconductor depletion layer 301b, but flows only in the semiconductor resistance layer 301a. Therefore, the thicker the semiconductor depletion layer 301b, the greater the resistance between the metal electrode 305a and the metal electrode 305b. Conversely, when a reverse voltage is applied between one of the metal electrodes 305a or 305b and the metal electrode 304, reverse polarization occurs in the ferroelectric film 303, and in this case also after the applied voltage is removed. But this polarization is not eliminated. In this case, polarization occurs in the ferroelectric film 303, but the semiconductor depletion layer 301b does not occur between the semiconductor resistance layer 301a and the insulating film 302. Therefore, when a voltage is applied between the metal electrode 305a and the metal electrode 305b, a large current flows through the semiconductor resistance layer 301a, and the resistance becomes small. In this way, the resistance between the metal electrode 305a and the metal electrode 305b can be changed depending on the polarization direction of the ferroelectric film 303. The resistance between the metal electrode 305a and the metal electrode 305b is approximately the width of the semiconductor resistance layer 301a. Is inversely proportional to. Therefore, when comparing the case where there is no depletion layer and the case where the semiconductor depletion layer 301b occupies half the width of the semiconductor resistance layer 301a, the resistance has a ratio of 1: 2. Therefore, the same function can be realized by using this element in place of the TMR element 201 of FIG. An example of the memory element thus formed is shown in FIG. Since the function is the same as that of the storage element shown in FIG. 5, a detailed description is omitted, but the ferroelectric resistance element 510, which is a variable resistance element by the ferroelectric polarization described above, is used, and the metal electrode of FIG. 7 is used. The 305a and the metal electrode 305b are connected to the word line 507 and the storage node 506, respectively. The metal electrode 304 in FIG. 7 is connected to the rewriting electrode 511. As described above, when reading the stored contents, a voltage is applied to the word line 507, and when updating the stored contents, the polarization direction of the ferroelectric substance is changed by using the rewriting electrode 511, and the resistance value of the ferroelectric resistance element is changed. change. In this way, the storage element can be realized.

【0015】

[Effect of the invention]

As described above, according to the present invention, by skillfully combining a variable resistance element and a negative resistance element, it is possible to directly convert the difference in the current flowing through the memory cell into a voltage, and power consumption and operation. A high-performance storage element can be realized in terms of speed. In particular, even if a magnetic resistance effect element or a strong dielectric effect type element with a resistance change of several tens of percent is used as a variable resistance element, the potential of the gate electrode of the field effect transistor can be changed to the electric potential by combining it with an element having negative resistance. Effect It is possible to set two states, one is above the threshold of the transistor and the other is below the threshold. Since each of these storage elements can take a large signal amplitude, the operation margin is large, the stored contents can be easily read out, and there is no concern of causing a malfunction.

[Simple explanation of drawings]

[Figure 1]

Configuration diagram of the storage element of the present invention [Figure 2]

Characteristic diagram of element elements and memory elements constituting the conventional memory element [Fig. 3]

Necessary requirements for element element characteristics constituting the storage element of the present invention and characteristic diagram of the storage element [Fig. 4]

Characteristic diagram of element elements and memory elements constituting the memory element of the present invention [Fig. 5]

Configuration diagram of the storage element of the present invention [Fig. 6]

Characteristic diagram of element elements and memory elements constituting the memory element of the present invention [Fig. 7]

Configuration diagram of element elements constituting the storage element of the present invention [Fig. 8]

Configuration diagram of the storage element of the present invention [Explanation of symbols]

101 TMR element 102 Load element 103 field effect transistor 104 Source 105 drain 106 Storage node 107 word line 108 Ground wire