JP2016015464A - Write-once-read-many solid-state memory - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a write-once-read-many solid-state memory which allows for long term storage of recorded data with high reliability.SOLUTION: In a write-once-read-many solid-state memory 1 sandwiching a recording layer 13 between a first electrode 11 and a second electrode 12, the recording layer 13 changes irreversibly from noncrystalline state to crystalline state, when a predetermined voltage is applied between the first electrode 11 and second electrode 12. The recording layer 13 contains, at least, a metallic element of low electrical resistivity, a metallic element for promoting crystallization by heat, and a predetermined metallic compound.

Description

  The present invention relates to a write-once solid-state memory that holds recorded information.

As a semiconductor nonvolatile memory for data storage, a NAND type or NOR type flash memory is generally used.
A flash memory has a thin floating gate layer in the vicinity of a gate electrode in a field effect transistor (FET) structure, and traps electrons in the floating gate layer by applying a predetermined high voltage to the gate electrode during recording. . In addition, the flash memory reproduces a signal of “0” or “1” by flowing a predetermined current between the source and the drain and determining whether electrons are trapped in the floating gate layer during reproduction. .

  The NAND type flash memory is currently mass-produced with a cell constituting a unit (rule) of 19 nm in accordance with the miniaturization of the recording cell size. By the way, it is known that in the NAND flash memory, electrons trapped in the floating gate layer leak out over time.

  Here, since the number of electrons that can be trapped is smaller in the cell configured with the narrow rule than in the cell configured with the wide rule, the time that can hold the electrons stored in the floating gate layer, That is, there is a problem that the data holding time is short.

  Actually, the data endurance of SSD (Solid State Memory) equipped with a rule 28 nm generation NAND flash chip is about 5 years, but the SSD endurance equipped with a 25 nm or 19 nm generation NAND flash chip is 3 years. It is about a year.

  On the other hand, as a next-generation new memory, a high-speed nonvolatile resistance change memory (ReRAM) using a metal compound in which an electric field-induced giant resistance change phenomenon occurs as a resistance change recording material has been developed. ReRAM has a simple structure, is small, has a large capacity, and is expected to record data with high speed and low power consumption.

  A phase change memory (Phase Change RAM, PCRAM) using a phase change recording material such as GeSbTe has also been developed. GeSbTe is generally used as a recording material for rewritable optical disks. The PCRAM is a memory that utilizes a phenomenon in which a phase transition is made into an amorphous state by applying a constant pulse voltage to a crystallized low-resistance phase-change recording material, resulting in a high resistance.

  As a write-once memory, there is a write-once optical disk. A write-once optical disc melts a recording material by the thermal energy of the condensed laser beam, and reproduces a signal of “0” or “1” by reading a difference in reflectance of the melted recording mark.

  In Non-Patent Document 1, a metal crystal in a metal compound grows by thermal energy, and a crystal part and an oxide part exist separately in a recording mark at the same time, but the reflectivity is different. Is described.

  Non-Patent Document 1 shows a conceptual diagram of a recording mechanism in FIG. 1 shows. Non-Patent Document 1 has the following description. The unrecorded state is a state where the metal oxide is in an amorphous (non-crystalline) state and fine particles of Te or Pd—Te are scattered. In this state, when the condensed laser light is irradiated, the Te crystal and the Pd-Te crystal grow and enlarge due to thermal energy, and the recording mark exists in two states.

  Non-Patent Document 2 shows a micrograph of a recording mark after recording in FIG. 4 (a). Non-Patent Document 2 describes that, in an unrecorded metal oxide, the recorded mark after recording is divided into a white part of the oxygen part and a black part of the grown crystal part. ing.

  According to Non-Patent Document 1, when stored at a temperature of 30 ° C. and a humidity of 50%, which corresponds to an environment such as an office, the recorded state is maintained for about 1000 years, and the temperature is 25 ° C. and the humidity is 50%. It is described that the state after recording is maintained for about 2000 years.

Japanese Patent No. 4968547 Japanese Patent No. 4854729

Proceedings SPIE Vol. 6282 62822F-1, 2006 Proceedings SPIE Vol. 695, p2-p. 9, 1986

By the way, flash memory, ReRAM, and PCRAM have a feature that the resistance value can be reversibly changed by applying a predetermined voltage.
For this reason, when a voltage is applied for some reason from the outside, the recording state changes, and there is a possibility that the data is changed, altered, or erased. In addition, when a NAND flash memory is configured with a rule of a unit of 20 nm or less, a small amount of electrons trapped in the floating gate layer leaks, so that the data guarantee lifetime in the product is shortened and data cannot be stored for a long time. .

  An object of the present invention is to provide a write-once solid-state memory capable of storing recorded data with high reliability for a long period of time.

  The write once solid memory according to the present invention is a write once solid memory in which a recording layer is sandwiched between a first electrode and a second electrode, and the recording layer is located between the first electrode and the second electrode. When a predetermined voltage is applied to, the structure changes irreversibly from an amorphous state to a crystalline state.

  According to this configuration, the write-once solid-state memory has a predetermined voltage applied between the first electrode and the second electrode, and the recording layer changes irreversibly from the amorphous state to the crystalline state. By recording data depending on whether the is in an amorphous state or a crystalline state, the recorded data can be stored with high reliability for a long period of time.

  In the write-once solid-state memory, a heater layer made of a predetermined material is formed between the first electrode and the recording layer, and the heater layer is formed between the first electrode and the second electrode. Heat may be stored when a voltage is applied, and the recording layer may be irreversibly changed from an amorphous state to a crystalline state by heat released from the heater layer.

  According to such a configuration, the write-once solid-state memory uses a Joule heat emitted from a heater layer that supports the generation of heat, so that minute metal crystal grains in the compound grow and are sandwiched between electrodes. Since the resistance of the material changes from a high resistance state to a low resistance state in an irreversible state, recorded data can be stored with high reliability for a long period of time.

  In the write-once solid-state memory, the recording layer is composed of at least a metal element that has a low electrical resistivity and promotes crystallization by heating and a metal compound that includes the metal element and has a high electrical resistivity. Has been.

  According to such a configuration, the write-once solid-state memory is irreversibly changed from a non-crystalline state to a crystalline state because the recording layer is heated, thereby helping the existence of itself that promotes crystallization. Since it changes, the recorded data can be stored for a long time with high reliability.

  In the write-once type solid-state memory, the recording layer is heated with at least a first metal element having a low electrical resistivity, and promotes crystallization of itself by being heated, and promotes crystallization of the first metal element. 2 metal elements and a metal compound having a high electrical resistivity containing the second metal element.

  According to such a configuration, the write-once solid-state memory has an amorphous state in which the first metal element having a low electrical resistivity is also helped by the presence of the second metal element that promotes crystallization when the recording layer is heated. Therefore, the recorded data can be stored for a long time with high reliability.

  In the write-once memory, the recording layer exhibits a memory function depending on the presence or absence of heating, and is composed of a thin film of 1 to 50 nm.

  According to this configuration, the write-once solid-state memory exhibits a memory function by recording data with the non-crystalline state (high resistance state) set to “0” and the crystalline state (low resistance state) set to “1”, for example. can do.

  In the write-once solid-state memory, the metal element and metal compound constituting the recording layer have a low melting point property with a melting point of 1000 ° C. or lower.

  With such a configuration, the write-once solid-state memory can change the structure of the material of the recording layer at a low temperature, and can efficiently form a current path in the recording layer.

  In the write-once solid-state memory, the recording layer is composed of a metal element and a metal compound whose electric resistance value is reduced to 1/10 or less when the amorphous state is changed to the crystalline state.

  In such a configuration, the write-once solid-state memory can accurately identify “0” or “1” as a recorded value based on a large difference in electrical resistance value.

In the write-once solid-state memory, the metal element is Te and the metal compound is TeO ₂ .

  According to such a configuration, the write-once solid-state memory is irreversibly changed from a non-crystalline state to a crystalline state due to the presence of Te that promotes crystallization when the recording layer is heated. Therefore, the recorded data can be stored for a long time with high reliability.

In the write-once solid-state memory, the metal element is Bi and the metal compound is Bi ₂ O ₃ .

  According to such a configuration, the write-once solid-state memory is irreversibly changed from a non-crystalline state to a crystalline state due to the presence of Bi that promotes crystallization by heating the recording layer. Therefore, the recorded data can be stored for a long time with high reliability.

In the write once solid memory, the first metal element is Pd, the second metal element is Te, and the metal compound is TeO ₂ .

  According to such a configuration, similarly, the write-once solid-state memory has a structure in which the recording layer is heated to help the presence of Te that promotes crystallization, so that Pd having a low electrical resistivity is changed from an amorphous state to a crystalline state. Since it changes reversibly, the recorded data can be stored for a long time with high reliability.

  According to the present invention, recorded data can be stored for a long time with high reliability.

It is sectional drawing which shows the 1st structure of a write-once type solid memory. It is sectional drawing which shows the 2nd structure of a write-once type solid memory. It is a figure where it uses for description about the state change before and after applying a predetermined voltage to the write-once type solid memory concerning the 1st composition. It is a figure where it uses for description about the state change before and after applying a predetermined voltage to the write-once type solid state memory concerning the 2nd composition. It is a figure where it uses for description about the state change of a recording layer. It is sectional drawing which shows the structure of a memory element. It is a figure which shows the 1st result which experimented. It is a figure which shows the 2nd result of experiment.

As shown in FIG. 1, the write-once solid-state memory 1 according to this embodiment includes a recording layer 13 sandwiched between a first electrode 11 and a second electrode 12.
The recording layer 13 is irreversibly changed from an amorphous state to a crystalline state when a predetermined voltage is applied between the first electrode 11 and the second electrode 12.

  Specifically, the write-once solid-state memory 1 is configured such that the recording layer 13 is not changed from an amorphous state to a crystalline state by heat generated when a predetermined voltage is applied between the first electrode 11 and the second electrode 12. It changes reversibly.

  According to such a configuration, the write-once solid-state memory 1 uses the recorded data for recording data depending on whether the recording layer 13 is in an amorphous state or a crystalline state. Can be saved.

  As shown in FIG. 2, the write-once solid-state memory 1 has a recording layer 13 sandwiched between a first electrode 11 and a second electrode 12, and a predetermined layer between the first electrode 11 and the recording layer 13. A heater layer 14 made of a material is formed.

The heater layer 14 stores heat when a predetermined voltage is applied between the first electrode 11 and the second electrode 12.
The recording layer 13 is irreversibly changed from an amorphous state to a crystalline state by heat released from the heater layer 14.

  According to such a configuration, the write-once solid-state memory 1 uses the Joule heat emitted from the heater layer 14 that supports the generation of heat, so that minute metal crystal grains in the compound grow, and the interelectrode Since the resistance of the recording material sandwiched between the layers changes from a high resistance state to a low resistance state in an irreversible state, the recording material 13 is used for data recording depending on whether the recording layer 13 is in an amorphous state or a crystalline state. Thus, the recorded data can be stored for a long time with high reliability.

  The recording layer 13 may be composed of at least a metal element that has a low electrical resistivity and promotes crystallization by heating and a metal compound that includes the metal element and has a high electrical resistivity. In the present embodiment, heating means heating caused by application of electricity or / and heat energy, but is not particularly limited thereto.

  According to such a configuration, the write-once solid-state memory 1 helps the existence of the recording layer 13 to promote crystallization by heating the recording layer 13 so that the metal element having a low electrical resistivity is changed from the amorphous state to the crystalline state. Since it changes reversibly, the recorded data can be stored for a long time with high reliability.

  The recording layer 13 may be composed of at least a metal element having a low electrical resistivity, a metal element that promotes crystallization of the metal element by heating, and a predetermined metal compound.

  According to such a configuration, the write-once solid-state memory 1 helps the presence of the metal element that promotes crystallization when the recording layer 13 is heated, so that the metal element having a low electrical resistivity is crystallized from an amorphous state. Since the state is irreversibly changed, the recorded data can be stored for a long time with high reliability by using the recording layer 13 for recording data depending on whether the recording layer 13 is in an amorphous state or a crystalline state.

  The recording layer 13 exhibits a memory function depending on the presence or absence of heating, and is composed of a 1 to 50 nm thin film.

  According to such a configuration, the write-once solid-state memory 1 has a memory function by, for example, recording data with an amorphous state (high resistance state) set to “0” and a crystalline state (low resistance state) set to “1”. It can be demonstrated.

The metal element and metal compound constituting the recording layer 13 have a low melting point property with a melting point of 1000 ° C. or less.
With such a configuration, the write-once solid-state memory 1 can change the material structure of the recording layer at a low temperature, and can efficiently form a current path in the recording layer.

The metal element may be Te.
Metal compound may be a TeO _2.
According to such a configuration, the write-once solid-state memory 1 is irreversible from the amorphous state to the crystalline state due to the presence of Te that promotes crystallization when the recording layer 13 is heated. Therefore, the recorded data can be stored for a long time with high reliability.

The metal element having a low electrical resistivity may be Pd.
Te may be the metal element that promotes crystallization of the metal element by being heated.
Predetermined metal compound may be a TeO _2.

According to such a configuration, the write-once solid-state memory 1 has the recording layer 13 heated to help the presence of Te that promotes crystallization, so that Pd having a low electrical resistivity changes from an amorphous state to a crystalline state. Since it changes irreversibly, the recorded data can be stored for a long time with high reliability by using it for data recording depending on whether the recording layer 13 is in an amorphous state or a crystalline state.
Note that the metal element having a low electrical resistivity may be any element other than Pd that is of the same family as Pd and whose resistivity changes when heated. Further, the recording layer 13 should have a higher ratio of the metal element having a low electrical resistivity.

<Example 1>
Here, Example 1 will be described.
The basic structure of the write once solid memory 1 is shown in FIG.
The recording layer 13 is composed of Pd—Te metal fine particles (13a in FIG. 3), Te metal fine particles (13b in FIG. 3), and amorphous TeO ₂ metal oxide (13c in FIG. 3) having a low electrical resistivity. It consists of A voltage is applied from above and below the recording layer 13 by the first electrode 11 and the second electrode 12.
By applying a voltage between the electrodes, the Pd—Te crystal or the Te crystal is enlarged, that is, crystallized in TeO ₂ .
By the way, Pd has an electrical resistivity of 10.8 × 10 ⁻⁶ Ωcm and behaves almost as a conductor.

The recording layer 13 grows Pd—Te metal fine particles by applying a predetermined voltage to the amorphous state (amorphous state) of the metal oxide of TeO ₂ that has been in a high resistance state with a metal oxide until then. Then, it becomes enlarged (13d in FIG. 3), and Te metal fine particles grow and enlarge (13e in FIG. 3). Then, a current path (P in FIG. 3) due to the Pd—Te crystal is generated in TeO ₂ and the recording layer 13 is in a low resistance state.

Since this structural change is physically an irreversible change, the amorphous state and the crystalline state are maintained for a long time.
For example, the write-once solid-state memory 1 can be used as a memory that is not tampered by recording data with the amorphous state (high resistance state) set to “0” and the crystalline state (low resistance state) set to “1”. it can.
The recording layer 13 is a thin film having a thickness of about 1 to 5 nm, for example.

<Example 2>
Next, Example 2 will be described.
The basic structure of the write once solid memory 1 is shown in FIG. The write once solid memory 1 according to the second embodiment is the same as the write once solid memory 1 according to the first embodiment, except that a heater layer 14 is formed between the first electrode 11 and the recording layer 13. In addition, although the heater layer 14 is demonstrated as what is comprised with tungsten (W), it is not restricted to this. Tungsten (W) is a conductor having an electrical resistivity of 5.65 × 10 ⁻⁶ Ωcm.

By applying a voltage between the electrodes, heat is stored in the heater layer 14 and Joule heat is generated. Joule heat promotes melting of TeO _{2 in} the recording layer 13 and enlarges the Pd—Te or Te metal crystal.
By the way, Pd has an electrical resistivity of 10.8 × 10 ⁻⁶ Ωcm and behaves almost as a conductor.
The recording layer 13 is an amorphous TeO ₂ metal oxide (13c in FIG. 4), which has been in a high resistance state with a metal oxide, and Pd—Te metal fine particles (13a in FIG. 4) having a low electrical resistivity. On the other hand, by applying a predetermined voltage, the Pd—Te metal fine particles grow and enlarge (13d in FIG. 4), and the Te metal fine particles grow and enlarge (13e in FIG. 4). Then, a current path (P in FIG. 4) due to the Pd—Te crystal is generated in TeO ₂ and the recording layer 13 is in a low resistance state.

Since this structural change is physically an irreversible change, the amorphous state and the crystalline state are maintained for a long time.
For example, the write-once solid-state memory 1 can be used as a memory that is not tampered by recording data with the amorphous state (high resistance state) set to “0” and the crystalline state (low resistance state) set to “1”. it can.
The recording layer 13 is a thin film having a thickness of about 1 to 5 nm, for example. The heater layer 14 is a thin film having a thickness of about 10 to 50 nm, for example.

<Example 3>
Next, an embodiment in which the recording layer 13 is composed of Te metal fine particles and amorphous TeO ₂ metal oxide will be described with reference to FIG. In the following embodiments, the write-once solid-state memory 1 (see FIG. 1) having a configuration in which the recording layer 13 is sandwiched between the first electrode 11 and the second electrode 12 will be described. However, the present invention is not limited to this. Alternatively, the write-once solid-state memory 1 (see FIG. 2) having a configuration in which a heater layer 14 made of a predetermined material is formed between the first electrode 11 and the recording layer 13 may be used.

In the write-once solid-state memory 1, Te is a typical element that has a low electrical resistivity and promotes crystallization of itself by heating. Further, representative of a given metal compound, a TeO _2.

In the recording layer 13, the metal elements constituting the metal compound are scattered in the metal compound.
Moreover, the metal-metal compound laminated | stacked between electrodes is comprised by the very thin film | membrane about 1-50 nm. When the film thickness is about 1 to 10 nm, it becomes easier to cause structural changes and resistance changes.

According to such a configuration, the write-once solid-state memory 1 has a low electrical resistivity and the presence of Te (13a in FIG. 5) that promotes crystallization when the recording layer 13 is heated. The filled TeO ₂ melts. Next, Te separated from molten TeO ₂ is adsorbed to Te scattered and present in the metal compound, and Te is enlarged and grows.

Then, in the recording layer 13 thinly laminated between the electrodes, before heating, the high-resistance metal compound TeO ₂ (13b in FIG. 5) was almost an insulator, but by heating, A large number of conductive Tes are enlarged, and the enlarged Tes (13e in FIG. 5) come close to each other to generate a current path (P in FIG. 5).

Therefore, the write-once solid-state memory 1 generates a current path in the recording layer 13 due to heating, and enters a low resistance state. Therefore, the ease of flow of the current applied between the electrodes changes before and after heating.
In this way, the resistance between the electrodes changes from a high state to a low state before and after heating. This structural change is an irreversible change that does not return to the original metal-metal compound state.

  For example, the write-once solid-state memory 1 can be used as a memory that is not tampered by recording data with the amorphous state (high resistance state) set to “0” and the crystalline state (low resistance state) set to “1”. The recorded data can be stored for a long time with high reliability.

Similarly, the state of the metal-metal compound is not limited to the structure of Te—TeO ₂ , and further includes a combination of Pd, Te, Pd—Te, and TeO ₂ containing a metal element Pd having a lower electrical resistance value. But you can. In the case of such a configuration, in the write-once solid memory 1, the metal element having a low electrical resistivity is Pd, the metal element that promotes crystallization of the metal element by heat is Te, and a predetermined metal compound Is TeO ₂ .

<Example 4>
Next, an example in which the recording layer 13 is composed of Bi metal fine particles and amorphous Bi ₂ O ₃ metal oxide will be described with reference to FIG. In this configuration, Te (13a in FIG. 5) of Example ₃ is replaced with Bi, and TeO ₂ (13b in FIG. 5) is replaced with Bi ₂ O ₃ . In the following embodiments, the write-once solid-state memory 1 (see FIG. 1) having a configuration in which the recording layer 13 is sandwiched between the first electrode 11 and the second electrode 12 will be described. However, the present invention is not limited to this. Alternatively, the write-once solid-state memory 1 (see FIG. 2) having a configuration in which a heater layer 14 made of a predetermined material is formed between the first electrode 11 and the recording layer 13 may be used.

In the write-once solid-state memory 1, Bi is used as a metal element that has a low electrical resistivity and promotes crystallization of itself by heating. Bi ₂ O ₃ is used as the predetermined metal compound.

In the recording layer 13, the metal elements constituting the metal compound are scattered in the metal compound.
Moreover, the metal-metal compound laminated | stacked between electrodes is comprised by the very thin film | membrane about 1-50 nm. When the film thickness is about 1 to 10 nm, it becomes easier to cause structural changes and resistance changes.

According to such a configuration, the write-once solid-state memory 1 has a low electrical resistivity and the presence of Bi (13a in FIG. 5) that promotes crystallization when the recording layer 13 is heated. The filled Bi ₂ O ₃ (13b in FIG. 5) melts. Next, Bi separated from the melted Bi ₂ O ₃ is adsorbed to Bi scattered and present in the metal compound, and Bi is enlarged and grows.

In the recording layer 13 that is thinly laminated between the electrodes, before heating, the high-resistance metal compound Bi ₂ O _{3 is} almost an insulator, but by heating, a large amount of conductivity is obtained. The Bi that has enlarged and the enlarged Bi (13e in FIG. 5) come close to each other to generate a current path (P in FIG. 5).

Therefore, the write-once solid-state memory 1 generates a current path in the recording layer 13 due to heating, and enters a low resistance state. Therefore, the ease of flow of the current applied between the electrodes changes before and after heating.
In this way, the resistance between the electrodes changes from a high state to a low state before and after heating. This structural change is an irreversible change that does not return to the original metal-metal compound state.

  For example, the write-once solid-state memory 1 can be used as a memory that is not tampered by recording data with the amorphous state (high resistance state) set to “0” and the crystalline state (low resistance state) set to “1”. The recorded data can be stored for a long time with high reliability.

<Example 5>
Next, a memory element (cell) 100 using the write-once solid-state memory 1 described above will be described. The configuration of the memory element 100 is shown in FIG. The memory element 100 uses the write-once solid-state memory 1 according to the second embodiment, but is not limited thereto, and the write-once solid-state memory 1 according to the first embodiment may be used. The memory element 100 is a MOS transistor type memory element, but is not limited thereto.

  In the memory element 100, an N-type source electrode 102, a drain electrode 103, and a gate electrode 104 are formed on a P-type substrate 101. The write once solid memory 1 is formed on the drain electrode 103.

  A source line 105 (SL) is connected to the source electrode 102. A bit line 106 (BL) is connected to the write-once solid-state memory 1. A word line 107 (WL) is connected to the gate electrode 104.

  The memory element 100 reads a current I output from the bit line 106 via the write-once solid-state memory 1 by applying a read voltage V to the word line 107 to cause a current to flow between the source and drain. Thus, the information recorded in the recording layer 13 is read out.

Specifically, the memory element 100 calculates the resistance value R from Ohm's law based on the voltage V applied to the word line 107 and the current I read from the bit line 106, and according to the calculated resistance value R. To determine “1” or “0”.
When the resistance value R is large, the recording layer 13 is in an amorphous state, and when the resistance value R is small, the recording layer 13 is in a crystalline state.

When the recording layer 13 is in an amorphous state, even if a read voltage is applied to the word line 107, no current flows through the recording layer 13, or a small amount of current flows. No detection or only a small amount of current can be detected.
On the other hand, when the recording layer 13 is in a crystalline state, by applying a read voltage to the word line 107, a current flows through the recording layer 13, and a constant current can be detected at the bit line 106.

  Further, when a recording high voltage is applied to the recording layer 13 via the word line 107, Joule heat is generated with the assistance of the heater layer 14, and the memory material is melted. As a result, the recording layer 13 is separated from the amorphous (amorphous) state of the metal compound into an oxide and a metal crystal having a low electrical resistivity, and the recording layer 13 grows and grows irreversibly. Wake up.

As shown in FIG. 4, the recording layer 13 is formed with a current path P and is in a low resistance state. In such a state, the memory element 100 can detect a current passing through the current path P by applying a read voltage to the word line 107.
In this way, the memory element 100 detects a discrete value of “1” or “0” based on the state of irreversible change in the recording layer 13.

  In addition, a plurality of the memory elements 100 described above are formed in a matrix, and writing and reading on the bit lines and the word lines are performed by arbitrary memory elements, whereby a large-capacity memory device can be configured. it can.

In addition, in the metal oxide of TeO ₂ , the written information can be maintained for 1000 years or more in a normal environment (for example, temperature 30 ° C., humidity 50%), so that it is configured as a memory device for long-term storage. be able to.

In addition, in recent years, with the aim of realizing a society that can recycle resources that are friendly to the earth and human environment, there are cases in which electronic devices must use highly toxic metals (such as arsenic). When recycling, there is a problem that they are difficult to reuse.
However, Bi-based compound materials have low toxicity. In particular, Bi ₂ O ₃ has extremely low toxicity as it is used for drugs. If a solid-state memory containing Bi-based compound material is produced or discarded, there is little damage caused by dust in the production process or destruction / disassembly process, including a series of material use cycles of production and disposal. Solid-state memory devices can be constructed with materials that are friendly to the environment.

<Experimental example 1>
A sample was actually made and measured for resistance. FIG. 7 shows the measurement results. FIG. 7 (a) shows the measurement results of resistance change by the metal element and metal compound corresponding to Example 3, and FIG. 7 (b) shows the measurement result of resistance change by the metal element and metal compound corresponding to Example 1. )Pointing out toungue.

The sample whose resistance value was measured was formed on a substrate using an RF magnetron sputtering apparatus. The metal target used was metal target Te is mixed interspersed TeO _2, and, using a metal target Te and Pd were mixed interspersed TeO _2.

FIG. 7 (a) shows the result of measuring the resistance value of a sample formed using a metal target in which Te is dispersed in TeO ₂ by resistance measurement by the four-terminal method, and the resistance of Te. The result of measuring the value is shown.
Although it is desirable that there is a difference of 10 times or more between these resistance values in terms of discrimination accuracy between “0” and “1” as a memory, as can be seen from FIG. By forming a current path of Te crystal, the resistance value decreased by two digits or more, and a large change in resistance was confirmed before and after the change.

  Further, FIG. 7A shows a value (733 ° C.) that is a basis for the occurrence of a structural change in the material of the recording layer 13 at a low melting point. Due to the heat energy applied from the outside, the melting point is reached at a temperature of 1000 ° C. or lower, although it is higher than normal temperature, a current path is generated in a local portion, causing a resistance change (lower resistance).

FIG. 7B shows the result of measuring the resistance value by measuring the resistance by the four-terminal method for a sample formed using a metal target in which Te and Pd are mixed in TeO ₂ , and Te. The result of having measured the resistance value of the sample which mixed Pd and Pd is shown.
Although it is desirable that there is a difference of 10 times or more between these resistance values in terms of discrimination accuracy between “0” and “1” as a memory, as can be seen from FIG. 7B, the Pd-Te crystal In addition, by forming a current path of Te crystal, the resistance value decreased by about three orders of magnitude, and a large change in resistance was confirmed before and after the change compared to Example 3.

<Experimental example 2>
FIG. 8 shows the measurement results of the resistance change by the metal element and metal compound corresponding to Example 4.

The sample whose resistance value was measured was formed on a substrate using an RF magnetron sputtering apparatus. Moreover, the metal target used was a metal target in which Bi was scattered and mixed in Bi ₂ O ₃ .

FIG. 8 shows the result of actually measuring the resistance value of the sample formed using the metal target mixed with Bi ₂ O _{3 in} which Bi is dispersed by the resistance measurement by the four-terminal method, and the resistance value of Bi. The result of having measured is shown.
Although it is desirable that there is a difference of 10 times or more between these resistance values in terms of discrimination accuracy between “0” and “1” as a memory, as can be seen from FIG. By forming a current path, the resistance value decreased by 4 digits or more, and a large resistance change was confirmed before and after the change.

  Further, FIG. 8 shows a value (820 ° C.) that is the basis for the occurrence of a structural change in the material of the recording layer 13 at a low melting point. Due to the heat energy applied from the outside, the melting point is reached at a temperature of 1000 ° C. or lower, although it is higher than normal temperature, a current path is generated in a local portion, causing a resistance change (lower resistance).

DESCRIPTION OF SYMBOLS 1 Write-once solid memory 11 1st electrode 12 2nd electrode 13 Recording layer 14 Heater layer

Claims (10)

In a write once solid memory in which a recording layer is sandwiched between a first electrode and a second electrode,
The write-once solid-state memory, wherein the recording layer changes irreversibly from an amorphous state to a crystalline state when a predetermined voltage is applied between the first electrode and the second electrode. A heater layer made of a predetermined material is formed between the first electrode and the recording layer,
The heater layer stores heat when a predetermined voltage is applied between the first electrode and the second electrode,
The write-once solid-state memory according to claim 1, wherein the recording layer is irreversibly changed from an amorphous state to a crystalline state by heat released from the heater layer.   2. The recording layer is composed of at least a metal element that has a low electrical resistivity and promotes crystallization of itself when heated, and a metal compound that includes the metal element and has a high electrical resistivity. Or a write-once solid-state memory according to 2.   The recording layer includes at least a first metal element having a low electrical resistivity, a second metal element that promotes crystallization of the first metal element when heated, and promotes crystallization of the first metal element; 3. The write-once solid-state memory according to claim 1, wherein the write-once solid-state memory is composed of a metal compound containing the second metal element and having a high electrical resistivity.   The write-once solid-state memory according to claim 3 or 4, wherein the recording layer exhibits a memory function depending on the presence or absence of heating and is composed of a thin film of 1 to 50 nm.   The write-once solid-state memory according to claim 3 or 4, wherein the metal element and the metal compound constituting the recording layer have a low melting point property of a melting point of 1000 ° C or lower.   5. The recording layer according to claim 3, wherein the recording layer is composed of a metal element and a metal compound whose electrical resistance value is reduced to 1/10 or less when the amorphous state is changed to the crystalline state. Write-once solid-state memory. The metal element is Te;
The write-once solid-state memory according to claim 3, wherein the metal compound is TeO ₂ . The metal element is Bi;
The write-once solid-state memory according to claim ₃ , wherein the metal compound is Bi ₂ O ₃ . The first metal element is Pd;
The second metal element is Te;
The write-once solid-state memory according to claim 4, wherein the metal compound is TeO ₂ .

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