JP6598166B2 - Phase change material and phase change type memory device - Google Patents

Description

  The present invention generally relates to a phase change material suitable for a memory element material and a phase change memory element using the material, and more particularly to a phase change material capable of reducing drive energy required for a phase change, and the material. The present invention relates to a phase change type memory device using the above.

In recent years, with the rapid market expansion of electronic devices, there is a demand for improving the performance of existing nonvolatile flash memories, and the development of next-generation nonvolatile memories that greatly exceed the performance of flash memories has been actively conducted. As a next-generation nonvolatile memory, magnetoresistive memory (MRAM: M agnetoresistive R andom A ccess M emory), ferroelectric memory (FeRAM: Fe rroelectric R andom A ccess M emory), phase-change memory (PCRAM: P hase C hange R andom a ccess M emory) , resistance-change memory (ReRAM: Re sistive R andom a ccess M emory) and the like have been researched and developed actively. In particular, since PCRAM has a simple memory cell structure, it is superior to other memories in terms of integration as well as manufacturing cost.

  A phase change material is used for the information recording layer of the PCRAM, and information is recorded by utilizing a change in electrical resistance accompanying a phase change between the amorphous phase and the crystal phase of the phase change material.

  The phase change material in the amorphous phase state is changed to the crystal phase state by heating to a temperature higher than the crystallization temperature Tc, and the phase change material in the crystal phase state is heated to the melting point Tm higher than the crystallization temperature Tc. Then, it changes to an amorphous phase state by rapid cooling.

  For the phase change between the amorphous phase and the crystalline phase of the phase change material, Joule heat by an electric pulse is used, for example, Joule heating to a melting point Tm or higher, followed by rapid cooling to an amorphous phase to obtain a reset state [0], Information is recorded as a set state [1] by heating to a crystal phase by Joule heating above the crystallization temperature Tc and below the melting point Tm.

Currently, Ge ₂ Sb ₂ Te ₅ (GST) used for DVD-RAM is widely studied as a phase change material for PCRAM (see, for example, Non-Patent Documents 1 and 2).

  On the other hand, along with further increase in capacity due to further miniaturization of PCRAM, there is a demand for improvement of operation guarantee temperature (improvement of high temperature data retention) and reduction of power consumption accompanying data rewriting.

  Patent Document 1 discloses a nonvolatile memory using a GeSbTe compound as a phase change material. However, as shown in Non-Patent Document 1, the crystallization temperature Tc of the amorphous phase of the GeSbTe compound is as low as about 150 ° C. Therefore, since the thermal stability of the amorphous phase is low and the high temperature data retention property may be fragile, the operation guarantee temperature is not sufficient.

As a phase change material having a high crystallization temperature, Patent Document 2 discloses a phase change material in which Sb and Te are main components and at least one kind of element is added as an additional element. C, N, Ag, In, P and Ge are described. That is, Patent Document 2 discloses that a crystallization temperature of 160 ° C. or higher and a crystallization activation energy of 2.5 eV or higher in a phase change material containing Sb and Te as main components and at least one additional element as an additional element. Is disclosed. The example of Patent Document 2 describes a phase change material containing N, Ge, B, P, and Ag as additional elements in an Sb ₇₅ Te ₂₅ alloy. However, the phase change material described in Patent Document 2 has been developed as a phase change recording material for optical recording media, and there is no description regarding the electrical resistance between the amorphous phase and the crystalline phase.

In addition, existing phase change materials such as the GeSbTe compound described above have a lower electrical resistance in the crystalline phase than in the amorphous phase (usually, in the phase change material, the crystalline phase is more than three orders of magnitude more electrically than the amorphous phase. Low resistance). As is generally known, the Joule heating value Q is represented by Q = I ² Rt. Here, I is current, R is electrical resistance, and t is time. Therefore, when considering the PCRAM memory element, since the amorphous phase has a high electric resistance, the drive current when the phase is changed to the crystalline phase by heating to the crystallization temperature Tc or higher by Joule heating can be small. Therefore, the power consumption for rewriting from the amorphous phase state to the crystalline phase state is small. On the other hand, in order to change the crystalline phase to the amorphous phase, it must be heated to a melting point Tm or higher, which is a temperature higher than the crystallization temperature Tc, and since the crystalline phase has a low electrical resistance, the melting point Tm There is a drawback that a large drive current is required for heating as described above, resulting in high power consumption.

In Patent Document 3, as the phase change material to reduce the high-temperature data retention and data rewriting _{power, Ge x M y Te 100-} x-y ( wherein in the formula, M, Al, Si, Cu, an In and Sn 1 represents an element selected from the group consisting of: x is in the range of 5.0-50.0 (at.%), Y is in the range of 4.0-45.0 (at.%), And 40 (at ..)), and phase change memory elements using the same are disclosed. The phase change material is selected to satisfy:.%) ≦ x + y ≦ 60 (at.%). _{Ge x M y Te 100-x} -y phase change material is excellent in high-temperature data retention because of its high crystallization temperature than conventional materials (Tc ≧ 190 ℃). In addition, since it has a low melting point Tm of about 510 ° C. depending on the composition, excessive heating is not necessary to make the phase change material amorphous, compared with a conventional phase change material such as a GeSbTe compound (Tm≈620 ° C.). Data rewriting power consumption can be reduced. However, like the GeSbTe compound, the electrical resistance of the crystalline phase is three orders of magnitude lower than that of the amorphous phase, and a large drive current is still required to change the phase from the crystalline phase to the amorphous state. This is not sufficient.

  As described above, the phase change material that has already been proposed is required as a material for the PCRAM memory element. 1) High-temperature data retention capability, and 2) Low power consumption during data rewriting, There is no material that satisfies the requirements and can be sufficiently put into practical use.

Japanese Patent No. 3896576 JP 2000-343830 A Japanese Patent No. 5403565

N. Yamada et al. J. et al. “Rapid-phase transitions of GeTe-Sb2Te3 pseudo-amorphous thin films for an optical disk memory” Appl. Phys. 69 (5) (1991) p2849 Motoyasu Terao, “Phase Change Memory (PRAM)” Applied Physics Vol. 75, No. 9 (2006), p1098

  The present invention was made for the purpose of improving the above-described problems of the conventional phase change material, and has a novel composition suitable for obtaining a phase change memory element excellent in practicality, It is another object of the present invention to provide a phase change memory device using the same.

From the viewpoint of the high-temperature data retention performance of PCRAM, the crystallization temperature Tc of the amorphous phase of the phase change material needs to be sufficiently high. In addition, from the viewpoint of data rewriting power consumption of PCRAM, it is particularly important to reduce the driving energy (driving current) required for “phase change from crystalline phase to amorphous phase”, which requires heating to the melting point Tm or higher. It is. From the relationship of Q = I ² Rt described above, when trying to obtain the same Joule heat generation amount Q, a smaller electric current I is required when the electric resistance R is higher. That is, in the phase change memory element, the electric resistance of the crystal phase of the phase change material needs to be sufficiently high in order to reduce the driving energy required for the phase change from the crystal phase to the amorphous phase.

However, as described above, in the general phase change material currently developed, the resistance value of the amorphous phase is larger than the resistance value of the crystal phase, and in order to increase the data reading accuracy, It is also said that an electric resistance ratio between crystal phases of 10 ² or more is necessary. As a result, in the current phase change material, the resistance value of the crystal phase is generally small, and this is a big bottleneck for the demand for reducing the data rewriting power consumption of PCRAM.

However, as a result of studies by the present inventors, it has been found that there are phase change materials in which the resistance value of the crystal phase is larger than the resistance value of the amorphous phase. By using a material in which the magnitude relation of the resistance value between phases is reversed from that of a general phase change material, it is possible to significantly reduce the data rewriting power consumption of the PCRAM. Furthermore, the present inventors have found that even when the electrical resistance ratio between the amorphous phase and the crystalline phase measured by the phase change material itself is not so large, when the phase change type memory element is formed using the material, the amorphous phase and the crystalline phase are formed. found that electrical resistance ratio of the interphase is obtained as two digits, i.e. 10 ^more. This indicates that the phase change memory element can have sufficient reliability for data reading.

  As a result of diligent research based on the above findings, the present inventors have obtained an amorphous phase in a material mainly composed of Cr, Ge and Te, have a high crystallization temperature, and the crystalline phase is more amorphous. It was found to have a higher electrical resistance.

  Therefore, the first aspect of the present invention provides a phase change material having Cr, Ge, and Te as main components and having a resistance value in a crystalline phase larger than a resistance value in an amorphous phase.

  In the first aspect, 15% (at.%) Or more of Cr may be included. The phase change material according to the first aspect may have a crystallization temperature at which transition from the amorphous phase to the crystalline phase is 270 ° C. or higher. Further, at least one element selected from the group consisting of N, O, Al, Si, Cu, and Sb may be included as an additional element M in an amount of 0.01 to 5.0 (at.%) As a whole.

The phase change material according to the first aspect has a general chemical formula between the Cr, Ge, and Te.
Cr _x Ge _y Te _100-xy
In the range of 15.0-25.0 (at.%), Y is in the range of 15.0-25.0 (at.%), And 34.0 (at.%). ≦ x + y ≦ 48.0 (at.%) May be selected. In addition, the additional element M is
M _z (Cr _x Ge _y Te _100-xy ) _100-z
Where z may be selected to be 0.01-5.0 (at.%).

  In a second aspect of the present invention, a substrate, a memory layer formed of the phase change material according to the first aspect on the substrate, and first and second electrode layers for energizing the memory layer are provided. A phase change memory device is provided.

  In the phase change material according to the present invention, the crystallization temperature is as high as 270 ° C. or higher. Therefore, the thermal stability of the amorphous phase of this material is very high. In these materials, the electrical resistance of the crystal phase is higher than the electrical resistance of the amorphous phase. Therefore, the power consumption when changing the phase from the crystalline phase to the amorphous phase by Joule heat is small. As a result, it is possible to configure a highly practical phase change type memory element using this material.

FIG. 4 is a table showing the composition and physical characteristics of phase change materials according to various embodiments of the present invention, where Tc is the crystallization temperature, Ramo is the electrical resistance of the amorphous phase, Rcry is the electrical resistance of the crystal phase, and ΔR. Indicates a value obtained by dividing the electrical resistance of the crystal phase by the electrical resistance of the amorphous phase. 6 is a graph showing temperature dependence of electrical resistance of phase change material thin films according to various embodiments of the present invention. It is a graph which shows the Kissinger plot obtained in Example 10 shown in FIG. Is a graph showing the relationship between the time to failure t _F and temperature obtained from the graph of FIG. It is a figure which shows the crystallization temperature when an additional element is added to the material which has a composition of Example 10 as a table | surface. It is a graph which shows the influence of the heat processing temperature which it obtained about Example 10 shown in FIG. 1 and has on the contact specific resistance between W electrode / phase change material. 1 is a schematic cross-sectional view of a phase change memory device according to an embodiment of the present invention. 10 is a graph showing a memory operation of the memory element shown in FIG. 7 manufactured using Example 10. The TEM photograph in the temperature of 260 degreeC and 290 degreeC of the sample of Example 10 is shown. The TEM photograph in the temperature of 350 degreeC and 380 degreeC of the sample of Example 10 is shown.

  As a result of various experiments conducted by the inventors in pursuit of a material having a high crystallization temperature and a crystal phase having a high electric resistance, the object of the present invention is achieved in a material having the following characteristics. I found that I can achieve it. A part of the result of the experiment conducted by the present inventors is shown in FIG. 1 described later. In the embodiment described below, the phase change material having a crystallization temperature Tc of 270 ° C. or higher and an electric resistance of the crystal phase higher than that of the amorphous phase is a phase change material that achieves the object of the present invention. did.

As shown in FIG. 1, this phase change material is composed mainly of Cr, Ge, and Te, the resistance value of the crystal phase is higher than the resistance value of the amorphous phase, and / or the crystallization temperature Tc is higher than 270 ° C. It is. In addition, the general chemical formula,
Cr _x Ge _y Te _100-xy
And x is in the range of 15.0-25.0 (at.%), Y is in the range of 15.0-25.0 (at.%), And 34.0 (at.%). ≦ x + y ≦ 48.0 (at.%) May be selected.

  The reason why Cr is 15.0 (at.%) To 25.0 (at.%) Is that if it is less than 15.0 (at.%), The electric resistance of the crystal phase is low, and a sufficient power consumption reduction effect is obtained. This is because if it is not obtained and exceeds 25.0 (at.%), The crystallization temperature becomes low and the thermal stability of the amorphous phase cannot be obtained. The reason why Ge is 15.0 (at.%) To 25.0 (at.%) Is that the amorphous phase has a higher electric resistance ratio than the crystalline phase if it is less than 15.0 (at.%). If it exceeds 25.0 (at.%), The crystallization temperature becomes low, and the electrical resistance of the amorphous phase becomes very large compared to the crystalline phase. Also, the reason why the total of Cr and Ge is 34.0 (at.%)-48.0 (at.%) Is that the electrical resistance of the crystal phase is sufficiently low if it is less than 34.0 (at.%). This is because the effect of reducing power consumption cannot be obtained, and if it exceeds 48.0 (at.%), The crystallization temperature is lowered, and the electrical resistance of the crystal phase is smaller than that of the amorphous phase. .

Further, as an additional element, at least one element M selected from the group consisting of N, O, Al, Si, Cu, and Sb,
M _z (Cr _x Ge _y Te _100-xy ) _100-z
Where z may be selected to be 0.01-5.0 (at.%).

  By adding 0.01-5.0 (at.%) Of N, O, Al, Si, Cu and Sb, the crystallization temperature can be increased. 0.01 at. If it is less than%, the effect of increasing the crystallization temperature is not sufficiently exhibited, and 5.0 at. If it exceeds 50%, in the case of N and O, a nitride or oxide containing Cr as a main component is formed and no phase change occurs, and in the case of Al, Si, Cu and Sb, it does not contribute to the phase change. This is because a compound phase is generated and adversely affects the repetitive characteristics of the phase change between amorphous and crystal.

  By forming the phase change material of the present invention on a substrate, a nonvolatile phase change memory element can be obtained. In particular, the nonvolatile memory element includes an insulating layer and a phase change material layer formed on the insulating layer, and includes an electrode layer sandwiched between or at both ends of the phase change material layer, Desirably, the exposed portion of the phase change material layer is covered with an insulating layer. Examples of the electrode layer include W, TiN, TiW, Al, and Cu.

The production method of the present invention _{materials, Cr x Ge y Te 100-} x-y (x:. 15.0-25.0 (at%), y:. 15.0-25.0 (at%), 34.0 (at.%) ≦ x + y ≦ 48.0 (at.%)), A film is formed on various substrates by physical vapor deposition (sputtering or the like) using various targets. The target is formed by changing the film formation output and adjusting the concentration by multi-source sputtering using pure Cr, pure Ge, pure Te or each binary alloy (Cr—Ge, Cr—Te, Ge—Te alloy). Alternatively, a film is formed using a ternary alloy target (Cr—Ge—Te alloy) whose components are adjusted in advance. Also, if necessary, the film deposition output is adjusted as appropriate using multi-source sputtering using one or more pure targets selected from Al, Si, Cu and Sb, or an alloy target whose components have been adjusted in advance. Thus, the components are adjusted to form a film. As for the addition of N and O, the film can be formed by reactive physical vapor deposition while adjusting the flow rate of N ₂ gas, O ₂ gas or N ₂ / O ₂ mixed gas. Here, the substrate temperature during film formation can be changed from room temperature to 500 ° C. as required. When the substrate temperature is lower than the crystallization temperature of the material to be manufactured, the material exhibits an amorphous phase, and when the substrate temperature is higher than the crystallization temperature, the material exhibits a crystalline phase.

FIG. 1 is a table showing measured values of physical properties of phase change materials according to various embodiments of the present invention. Hereinafter, the present invention will be described in more detail with reference to FIG. In addition, in FIG. 1, in order to make an understanding of this invention easy, the comparative example 1-11 which has a composition different from the range of this invention is shown. The material shown in Example 1-12 in the figure basically has a composition of Cr _x Ge _y Te _100-xy . Here, 34.0 (at.%) ≦ x + y ≦ 48.0 (at.%). In the table of FIG. 1, atomic concentrations (at.%) Of Cr, Ge, and Te are shown, but this includes impurities inevitably contained in the film forming raw material. Usually, such inevitable impurities are on the order of several ppm to several tens of ppm, and therefore do not have a great influence on the physical properties of the phase change material after film formation.

  As a sample for measuring physical properties, a thin film having the composition of Example 1-12 and Comparative Example 1-11 was formed to a thickness of 200 nm on a substrate using an RF sputtering apparatus. Pure elements Cr, Ge, and Te were used as targets, and the film formation output of each target was changed to prepare amorphous phase thin films having various compositions.

  FIG. 1 shows the crystallization temperature Tc (° C.), the amorphous phase electrical resistance Ramo (Ω), the crystalline phase electrical resistance Rcry (Ω), and the electrical resistance ratio ΔR between the crystalline phase and the amorphous phase of the material having each composition. It was. Here, Ramo was the electrical resistance value of the amorphous phase when heated to 60 ° C. in the two-terminal method. Further, the sample after the temperature was raised and crystallized was cooled, and the electric resistance value of the crystal phase when the temperature reached 60 ° C. was defined as Rcry. The electric resistance ratio ΔR was a ratio of “the electric resistance value of the amorphous phase at 60 ° C.” and “the electric resistance value of the crystal phase at 60 ° C.”.

  FIG. 2 shows an example of an electrical resistance-temperature curve obtained in electrical resistance measurement (temperature increase rate: 9.2 ° C./min) during the temperature increase process using the two-terminal method. Curves A and B in FIG. 2 show changes in electrical resistance at the time of temperature increase obtained for the samples of Example 2 and Example 10 and curves C and D for the samples of Comparative Example 1 and Comparative Example 6. The behavior of the sample of Example 10 will be described. The amorphous phase exhibits a low electric resistance, and the electric resistance gradually decreases as the temperature rises, and the electric resistance greatly decreases between 250 ° C. and 290 ° C. At this time, the temperature at which the electrical resistance change with respect to the temperature is the largest can be defined as the crystallization temperature Tc. Thereafter, the electrical resistance rises, and the electrical resistance rises while showing the temperature dependence of the semiconductor electrical resistance in the temperature lowering process. Example 2 shows a similar behavior.

  As shown in FIG. 1, it is understood that all of the phase change materials of Examples 1-12 have a crystallization temperature of 270 ° C. or higher, and the thermal stability of the amorphous phase is high.

  Further, as shown by ΔR in FIG. 1, all of the samples of Example 1-12 have ΔR> 1, and it can be seen that the crystal phase has higher electrical resistance than the amorphous phase. Here, the reason why ΔR is larger than 1, that is, the electrical resistance of the crystalline phase is higher is that the crystalline phase of the material of the present invention has semiconducting properties. This can be understood from the fact that the electrical resistance increases when the material is cooled after crystallization, as shown in Examples 2 and 10 of FIG. That is, the crystal phase of the material of the present invention is crystallized into a semiconductor having a higher electric resistance than the amorphous phase (semiconductor property), so that ΔR is considered to be larger than 1.

  On the other hand, in Comparative Example 1-11, although the crystallization temperature is relatively high, it can be seen that the electrical resistance sharply decreases with crystallization (FIG. 2: curves C and D). Further, from FIG. 1, ΔR <1, and in any of the comparative examples, the amorphous phase has higher electrical resistance than the crystalline phase. As shown in Comparative Example 1 of FIG. 1, it can be seen that the crystal phase of a conventional phase change material such as Ge-Te tends to decrease in electrical resistance with cooling and behaves like a metal. That is, in the conventional phase change material, the electrical resistance is drastically lowered by transition from an amorphous phase exhibiting semiconducting properties to a crystalline phase exhibiting metallic properties. In addition, the material made of Cr—Ge—Te shown in Comparative Examples 2 to 11 also has the effect of reducing power consumption during data rewriting because the electrical resistance of the crystal phase is low as in the case of the conventional phase change material. poor.

Next, the Kissinger plot shown below from the crystallization temperature obtained by measuring the activation energy for crystallization of Example 10 while changing the heating rate (9 ° C./min−50° C./min). Obtained by law.
ln (α / (Tc) ² ) = − Ea / kTp + Const.
Here, α: temperature rising rate, Tp: heat flow peak temperature, Ea: activation energy, k: Boltzmann constant.

  FIG. 3 shows the result of Kissinger plot for Example 10. From this result, the activation energy for crystallization shows a large value of 3.8 eV, and from the viewpoint of activation energy, excellent amorphous It is confirmed that the phase has thermal stability.

Usually, the amorphous phase is crystallized by holding it for a long time even at a temperature below the crystallization temperature Tc. Crystallization of the amorphous phase below the crystallization temperature Tc in the phase change material means failure of the PCRAM device. In the future, it is intended to be used in a high temperature environment such as the automobile field, and the guaranteed operation temperature of the PCRAM device is 125 ° C. and more than 10 years. Therefore, the working temperature when the failure time is 10 years (in other words, the maximum guaranteed operating temperature in 10 years) from the activation energy and crystallization temperature of Example 10 according to the Ozawa method shown in the following formula. ) Here, in this experiment, the time during which the amorphous phase was crystallized at a certain temperature by 10% was defined as the failure time.
t _F = θnexp (Ea / RTi)
θn = (Ea / αR) p (Ea / RT ^10% )
Where t _F : failure time, Ea: activation energy, Ti: temperature at failure time, α: heating rate, R: gas constant, T ^10% : temperature at which 10% crystallization occurs at a certain heating rate is there. The p (Ea / RT ^10% ) function is represented by the following equation.
logp (Ea / RT ^10% ) = -2.315-0.4567 (Ea / RT ^10% )

  FIG. 4 shows the result of using the Ozawa method for Example 10, where the vertical axis indicates the failure time and the horizontal axis indicates 1 / kT. Here, k is Boltzmann's constant and T is temperature. From this figure, the guaranteed operating temperature can be evaluated by extrapolating the data points at each crystallization temperature up to 10 years and estimating the temperature at that time. From this result, it can be seen that the sample of Example 10 has an operation guarantee temperature of about 190 ° C. This temperature exceeds the value of 10 years at 125 ° C., which is the required value of the operation guarantee temperature after 2011, and it can be seen that this sample is also excellent in thermal stability.

FIG. 5 shows the crystallization temperature when an additional element was added to the sample of Example 10 (crystallization temperature: 270 ° C.). In this case, the additional element M is
M _z (Cr _x Ge _y Te _100-xy ) _100-z
And z is selected to be 0.01-5.0 (at.%). For example, Example 13 shows a material obtained by adding N to the material of Example 10 shown in FIG. 1 so that z becomes 2.0 (at.%). Similarly, Example 14 to Example 20 show a material obtained by adding the illustrated additional element M to the material of Example 10 in the concentration shown in the drawing. As is clear from FIG. 5, it can be seen that the crystallization temperature is increased by adding one or more elements of N, O, Al, Si, Cu and Sb to the material of Example 10. In addition, although it did not experiment about the other Example materials 1-9, 11, and 12, it is possible to estimate that there is a tendency similar to the case of Example 10. Therefore, it is possible to increase the thermal stability of the amorphous phase by adding additional elements to the material of the present invention as necessary.

  Subsequently, examples of the memory characteristics using the phase change material of the present invention will be described. In general, a phase change memory applies an electric pulse through an electrode and joule heats the phase change material to change the phase. In addition, the larger the electrical resistance ratio obtained by the phase change, the higher the data reading accuracy. In recent years, miniaturization of memory cell structures has become important with the high integration of memories, but with miniaturization, the total electrical resistance of memory devices is not the electrical resistance value of the phase change material itself, but the electrode / Dominated by contact resistance between phase change materials. Therefore, for Example 10, W was used as an electrode using the CTLM method, and the contact specific resistance of the W / phase change material was measured. (For the CTLM method, see, for example, EK Chua et al. Appl. Phys. Lett. 101 (2012) 012107.)

  FIG. 6 is a diagram showing the results of measuring the contact specific resistance of Example 10 by the CTLM method. The vertical axis represents the contact specific resistance, and the horizontal axis represents the heating temperature of the sample. As shown in the figure, five types of temperatures of 150 ° C., 270 ° C., 290 ° C., 350 ° C., and 380 ° C. were selected, and after heating the sample to each temperature, the contact specific resistance was measured at room temperature. From this result, it can be seen that as the crystallization progresses, the contact specific resistance value increases, and in the sample heated to 380 ° C., a resistance ratio of two digits or more is obtained compared to the sample heated to 150 ° C. This indicates that sufficient data reading reliability can be obtained as a practical phase change memory.

Subsequently, the memory cell shown in FIG. 7 was manufactured using the sample shown in Example 10, and the memory switching operation by applying the pulse voltage was investigated. Here, FIG. 7 shows a cross-sectional view of the phase change nonvolatile memory cell structure used in this experiment. In the figure, 1 is a SiO ₂ / Si substrate, 2 is a lower electrode layer formed on the substrate 1, 3 is a phase change material layer formed of the material of Example 10 shown in FIG. 1, and 4 is a phase change material layer 3. SiO ₂ layer 5 covering a part of the surface of the upper electrode layer 5 is an upper electrode layer formed on the SiO ₂ layer 4 in contact with the phase change material layer 3. Note that the upper and lower electrode layers 2 and 5 were made of W in this experiment.

FIG. 8 shows changes in electrical resistance when a pulse voltage is applied to the manufactured memory device. The initial state was an amorphous state showing a low electric resistance, and the resistance value was 2.1 × 10 ⁵ Ω. When a voltage of 0.4 V was applied thereto with a pulse width of 20 ns, crystallization occurred, and the electrical resistance increased to 1.4 × 10 ⁸ Ω. Even if a voltage of 0.4 V or more is applied, the high electric resistance state is maintained, but when a voltage of 1.5 V is applied with a pulse width of 20 ns, amorphization occurs and the electric resistance is reduced to 5.5 × 10 ⁵ Ω. It turned out to decrease. This value is almost the same value as in the initial state. From this, it was confirmed that the material of the present invention can write and erase information by Joule heating using electric pulses.

  FIGS. 9 and 10 (a) to (d ′) show TEM (transmission electron microscope) photographs taken by heating the sample of Example 10 to a plurality of temperatures. These TEM photographs show that the sample of Example 10 changes from an amorphous phase to a crystalline phase with temperature. FIG. 9A is a TEM photograph taken at 260 ° C. just before the crystallization temperature Tc (270 ° C.), and it can be seen that the sample shows an amorphous phase. (B) is a TEM photograph taken at 290 ° C. immediately after the crystallization temperature Tc, and as is clear from the enlarged view (b ′) of (b), at this temperature, the sample of Example 10 is It turns out that it has changed from the amorphous phase to the crystalline phase. (C) of FIG. 10 is a TEM photograph in which the sample of Example 10 is heated to a higher temperature of 350 ° C., and (c ′) is an enlarged view thereof. (D) is a TEM photograph of the sample of Example 10 heated to a temperature of 380 ° C., and (d ′) is an enlarged view thereof. As is clear from FIGS. (B ′), (c ′) and (d ′), when the sample 10 is further heated beyond the crystallization temperature Tc, the crystal grains become coarser as the temperature rises. I understand. The material of Example 10 shows a rare behavior in which the electrical resistance increases in the crystal phase. However, even in the temperature range where the unique behavior is observed, normal grain coarsening occurs structurally. I understand.

  The phase change material of the present invention has an effect that a crystal phase having a high crystallization temperature and an electric resistance higher than that of an amorphous phase can be obtained. Therefore, by using the phase change material, it can be used for a nonvolatile semiconductor memory having high temperature data retention and low power consumption. Further, it can be used not only for a semiconductor memory but also for an optical recording medium such as a DVD-RAM using the reflectance of laser light in a crystalline phase and an amorphous phase as in GST. The present invention is not limited to the above-described embodiments. That is, other examples, aspects, and the like within the scope of the technical idea of the present invention are naturally included.

1 SiO ₂ / Si substrate 2 W lower electrode layer 3 Phase change material layer 4 SiO ₂ dielectric layer 5 W upper electrode layer

Claims (4)

The main component is Cr, Ge, and Te, and the resistance value in the crystal phase is larger than the resistance value in the amorphous phase .
CrxGeyTe100-xy
In the range of 15.0-25.0 (at.%), Y is in the range of 15.0-25.0 (at.%), And 34.0 (at.%). Phase change material selected to satisfy ≦ x + y ≦ 48.0 (at.%) . The phase change material according to claim 1 , wherein the crystallization temperature at which the amorphous phase transitions to the crystalline phase is 270 ° C. or higher. 3. The phase change material according to claim 1, wherein at least one element selected from the group consisting of N, O, Al, Si, Cu, and Sb is added as an additional element M for a total 0.01-5. Phase change material containing 0 (at.%). A substrate, a memory layer formed of the phase change material according to any one of claims 1 to 3 on the substrate, and first and second electrode layers for energizing the memory layer. A phase change memory element.