Negative differential resistance element

Abstract

To provide a negative differential resistance element in which the width of a voltage section in a region showing negative differential resistance (NDR) is wide and the ratio of current values at the start and end is large.SOLUTION: A negative differential resistance element 1 includes a pair of electrodes 20 and 40, and a semiconductor layer 30 positioned between the pair of electrodes 20 and 40, and the semiconductor layer 30 includes a polyoxometalate containing tungsten, and a smoothing agent, and the semiconductor layer 30 has a thickness of 200 nm or more.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a negative differential resistance element.

Background Art

[0002] A general resistance element has the property that the current value increases when the voltage is increased, like Ohm's law. On the other hand, the existence of a negative differential resistance (NDR) element having a voltage range in which the current value decreases when the voltage is increased is known. FIG. 1 shows a general current-voltage curve of a negative differential resistance element. In FIG. 1, in the voltage range 0 to V1, the current value increases with an increase in voltage, but in the voltage range V1 to V2, the current value decreases with an increase in voltage. And when the voltage range is V2 or more, the current value increases again when the voltage is increased. Here, assuming that the current value when the voltage is V1 is I1 and the current value when the voltage is V2 is I2, in the voltage range V1 to V2, the current value decreases from I1 to I2, that is, the differential of the voltage with respect to the current is negative, so it can be said that it shows negative differential resistance (NDR).

[0003] Examples of elements showing NDR include tunnel diodes, Gunn diodes, lambda diodes, dynatron oscillators, gas discharge tubes such as neon tubes, and fluorescent lamps. When a DC voltage is applied to a negative differential resistance element, the resulting current value is positive, so the power generated there is positive and heat is generated. On the other hand, since the current obtained with respect to an AC voltage has a phase difference of 180 degrees, the generated power is negative and power can be generated. In reality, power cannot be generated without a power source, so it is necessary to superimpose a DC voltage on the AC voltage. By superimposing a DC voltage on an AC voltage in the NDR region, the AC power can be amplified using the power generated using the DC voltage component as a power source. Also, depending on the conditions of the circuit to be incorporated, oscillation is also possible, and NDR oscillators can mainly be used at high frequencies of microwave or higher where feedback oscillators do not function sufficiently. As a microwave energy source, it is virtually the only solid-state energy source in the millimeter-wave and terahertz-wave regions. Thus, negative differential resistance elements are very useful, but the materials showing NDR are limited, and the search for more high-performance materials is actively underway. The performance of a negative differential resistance element is better when the width of the voltage region showing NDR (V2 - V1) and the ratio of the current value at the start of the region to the current value at the end of the region (I1 / I2) are large, and its improvement is desired.

[0004] Well-known materials having NDR for a long time include, for example, GaAs and InP (Non-Patent Document 1). Also, recently, decamolybdodicosammonium, which is a polyoxometalate, has been reported as a material showing NDR (Non-Patent Document 2). Furthermore, tungsten oxide is also known as a material showing NDR (Non-Patent Document 3).

Prior Art Documents

Non-Patent Documents

[0005]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, for the materials disclosed in Non-Patent Document 1 above, generally, the width of the voltage range showing NDR characteristics is about 1V, and further improvement is required. Also, for the materials disclosed in Non-Patent Document 2 above, it is a confirmation by tunneling spectroscopy, and there are problems in actually using them as thin films. Further, in Non-Patent Document 3 above, although the NDR characteristics of tungsten oxide thin films fabricated by a coating method are disclosed, currently, the width of the voltage range showing NDR is about 1V, and also, the ratio of the current values at the start and end of the region is not large. Therefore, the development of a negative differential resistance element with a wide voltage range showing NDR characteristics and a large ratio of the current values at its start and end has become an issue.

[0007] Therefore, an object of the present invention is to solve the problems of the above prior art and provide a negative differential resistance element having a wide voltage range showing negative differential resistance (NDR) and a large ratio of the current values at its start and end.

Means for Solving the Problems

[0008] The gist configuration of the present invention for solving the above problems is as follows.

[0009] The negative differential resistance element of the present invention includes a pair of electrodes and a semiconductor layer positioned between the pair of electrodes. The semiconductor layer includes a polyoxometalate containing tungsten and a smoothing agent. The thickness of the semiconductor layer is characterized by being 200 nm or more. The negative differential resistance element of the present invention has a wide voltage range in the region showing NDR, and a large ratio of the current values at its start and end points.

[0010] In a preferred example of the negative differential resistance element of the present invention, the thickness of the semiconductor layer is 400 nm or more. In this case, the NDR characteristics become larger.

[0011] In another preferred example of the negative differential resistance element of the present invention, the polyoxometalate is phosphotungstic acid represented by the formula: H3PW 12 O 40 This phosphotungstic acid has particularly high solubility in a solvent and is more likely to form a thick-film semiconductor layer.

[0012] In another preferred example of the negative differential resistance element of the present invention, the smoothing agent is dipyrazino[2,3-f:2’,3’-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile (HAT-CN). This HAT-CN can suppress the generation of coarse particles due to the crystallization of the polyoxometalate containing tungsten during the formation of the coating film, and can further improve the smoothness of the surface of the formed film (semiconductor layer).

[0013] The negative differential resistance element according to a preferred embodiment of the present invention has a plurality of regions showing negative differential resistance characteristics. Such a negative differential resistance element can be applied to various uses by using its characteristics.

Advantages of the Invention

[0014] According to the present invention, it is possible to provide a negative differential resistance element having a wide voltage range in the region showing NDR and a large ratio of the current values at its start and end points.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Mode for Carrying Out the Invention

[0016] Hereinafter, the negative differential resistance element of the present invention will be illustrated and described in detail based on its embodiments.

[0017] The negative differential resistance element of the present invention includes a pair of electrodes (anode and cathode) and a semiconductor layer located between the pair of electrodes. Here, in the negative differential resistance element of the present invention, the semiconductor layer contains a polyoxometalate containing tungsten and a smoothing agent, and the thickness of the semiconductor layer is 200 nm or more.

[0018] As described above, conventionally, tungsten oxide has been known to exhibit NDR characteristics, but the voltage interval width showing NDR is narrow, and the ratio of the current values at the start and end is small. In contrast, in the present invention, a polyoxometalate containing tungsten and a smoothing agent are used, and the film surface is smoothed so that coarse crystal grains are not formed during coating and film formation, thereby forming a smooth film with a thickness of 200 nm or more, and applying the film to the semiconductor layer of the negative differential resistance element to realize a negative differential resistance element having a large voltage width in the region showing NDR characteristics and a large ratio of the current values at the start and end.

[0019] The polyoxometalate containing tungsten is a cluster molecule composed of an anion formed by condensation of an oxo acid of a metal containing tungsten and a cation such as a proton. Different from general metal oxides, the polyoxometalate containing tungsten has the characteristic of high solubility in polar solvents. Also, usually, in the sol-gel process used for forming a metal oxide film, it is necessary to perform firing at a high temperature of several hundred degrees Celsius for oxidation after coating and film formation. However, the polyoxometalate containing tungsten is originally oxidized and does not require high-temperature firing. Therefore, in the case of the polyoxometalate containing tungsten, it is only necessary to remove the solvent in the film, and the heating and drying temperature may be about the boiling point of the solvent. In addition, as another commonly used method, coating of nanoparticles can be mentioned, but there is a problem that it is difficult to produce nanoparticles with a particle size on the order of nanometers. On the other hand, since commercially available products of polyoxometalates containing tungsten are sold at low cost, they can be easily obtained and used.

[0020] In the negative differential resistance element of the present invention, a semiconductor layer having a thickness of 200 nm or more and containing a polyoxometalate containing tungsten is used. As described above, the polyoxometalate containing tungsten has very high solubility in a polar solvent, and a semiconductor layer having a thickness of 200 nm or more can be easily formed. However, when the thickness increases, there is a problem that the smoothness of the surface of the semiconductor layer formed by coating deteriorates. This is presumably because when a thin film (semiconductor layer) is formed from a solution, the polyoxometalate containing tungsten crystallizes, and large crystal grains are formed, resulting in the loss of smoothness. On the other hand, in the present invention, a smoothing agent is included in the semiconductor layer together with the polyoxometalate containing tungsten to improve the smoothness of the surface of the semiconductor layer. This is presumably because the addition of the smoothing agent controls the crystallization behavior of the polyoxometalate containing tungsten and suppresses the generation of coarse particles, resulting in a smooth film. Thereby, even a semiconductor layer having a thickness of 200 nm or more can have a smooth surface, and the negative differential resistance element of the present invention having such a semiconductor layer between a pair of electrodes (anode and cathode) has a large voltage interval width and a ratio of the current values at the start and end. Therefore, the negative differential resistance element of the present invention has a wide voltage interval in the region showing NDR, and a large ratio of the current values at the start and end.

[0021] The negative differential resistance element according to a preferred embodiment of the present invention has a plurality of regions showing negative differential resistance characteristics. Such a negative differential resistance element can be applied to various uses by using its characteristics.

[0022] Next, an embodiment of the negative differential resistance element of the present invention will be described in detail with reference to the drawings. FIG. 2 is a cross-sectional schematic view for explaining an example of the negative differential resistance element of the present embodiment.

[0023] The negative differential resistance element 1 of the present embodiment shown in FIG. 2 includes a pair of electrodes 20 and 40, and a semiconductor layer 30 positioned between the pair of electrodes 20 and 40. In FIG. 2, the electrode 20 is provided on the substrate 10, the semiconductor layer 30 is provided on the electrode 20, and the electrode 40 is further provided on the semiconductor layer 30. The electrode 20 formed on the substrate 10 may be an anode or a cathode. Here, when the electrode 20 is an anode, the electrode 40 becomes a cathode, while when the electrode 20 is a cathode, the electrode 40 becomes an anode. Also, in FIG. 2, the electrode 20, the semiconductor layer 30, and the electrode 40 are encapsulated by a sealing structure 50. Between the pair of electrodes 20 and 40, in addition to the semiconductor layer 30, another functional layer may be included. For example, a diode element, an organic EL element, a quantum dot EL element, or a solar cell element may be included. The negative differential resistance element 1 can generate optical pulses by being used as an oscillator in combination with an EL element.

[0024] (Substrate 10) The substrate 10 is made of materials such as glass, quartz, and plastic, and can be used as appropriate. Examples of the plastic material used for the substrate 10 include polyethylene terephthalate, polyethylene naphthalate, cycloolefin polymer, polyamide, polyethersulfone, polymethyl methacrylate, polycarbonate, and polyarylate. The material of the substrate 10 may use only one type or a combination of two or more types.

[0025] (Electrode 20) The electrode 20 is not particularly limited, and any of the electrode materials generally used in organic electronic elements can be suitably used. Examples of the material of the electrode 20 include ITO (indium tin oxide), IZO (indium zinc oxide), FTO (fluorine tin oxide), InSnZnO (indium zinc tin oxide, ITZO), In3O3, SnO2, Sb-containing SnO2, Al-containing ZnO, aluminum, silver, and the like. ITO (indium tin oxide) is preferably used for the electrode 20 of the negative differential resistance element 1 of the present embodiment.

[0026] (Semiconductor layer 30) The semiconductor layer 30 contains a polyoxometalate containing tungsten and a planarizing agent. The thickness of the semiconductor layer 30 is 200 nm or more. The semiconductor layer 30 may be composed only of a polyoxometalate containing tungsten and a planarizing agent, or may further contain additives other than the planarizing agent.

[0027] --Polyoxometalate-- As shown in Japanese Patent Application No. 2021-22105 filed by the inventor, the polyoxometalate containing tungsten has the property that its electrical resistance changes once an electric current flows through it. The NDR characteristics in the present invention are obtained from the second and subsequent measurements. For the NDR characteristics to appear, it is preferable that the thickness of the semiconductor layer 30 is larger. In the present invention, the thickness of the semiconductor layer 30 is 200 nm or more. Note that if the thickness of the semiconductor layer 30 is less than 200 nm, it does not exhibit NDR characteristics.

[0028] The polyoxometalate containing tungsten is preferably a heteropolyoxometalate containing tungsten. A heteropolyoxometalate containing tungsten is a compound having a structure in which heteroatoms (P 5+ , Si 4+ , Ge 4+ , Bi 3+ , etc.) are at the center and polyatoms (W 6+ ) are coordinated to the heteroatoms via oxygen, and structures such as the Keggin type and the Dawson type are known.

[0029] Examples of the polyoxometalate containing tungsten include phosphotungstic acid (PWA) and silicotungstic acid (SWA). Here, as phosphotungstic acid (PWA), phosphotungstic acid represented by the formula: H3PW 12 O 40 and phosphotungstic acid hydrate represented by the formula: H3PW 12 O 40 ·nH2O (n in the formula is an arbitrary number) can also be used.

[0030] The polyoxometalate has the formula: H3PW12 O 40 Particularly preferably, it is phosphotungstic acid represented by. This phosphotungstic acid has particularly high solubility in a solvent and is more likely to form a semiconductor layer of a thick film.

[0031] The polyoxometalate containing tungsten is not particularly limited, and a commercially available product may be used, or it may be synthesized and used. Examples of commercially available products include phosphotungstic acid (PWA) manufactured by MP Bio. Phosphotungstic acid (PWA) can be purchased at a price of 100 yen or less per gram and is a low-cost material. Phosphotungstic acid (PWA) is a cluster molecule composed of four tungsten trioxides and phosphoric acid, and structures such as the Keggin type are known. Phosphotungstic acid (PWA) has high solubility in polar solvents. For example, in acetonitrile, 1 g / mL or more can be dissolved, so it is easy to form a thick film of several hundred nm or more.

[0032] The content of the polyoxometalate containing tungsten in the semiconductor layer 30 is preferably 90% by mass or more, more preferably 95% by mass or more, and preferably 99.5% by mass or less, more preferably 99% by mass or less.

[0033] --Smoothing agent-- The smoothing agent is an additive that has the effect of suppressing the crystallization of the polyoxometalate containing tungsten during the formation of the coating film and smoothing the semiconductor layer 30. As the smoothing agent, any compound that has the effect of suppressing the deterioration of the smoothness of the film surface by preventing the generation of coarse particles due to the crystallization of the polyoxometalate containing tungsten can be used. Among the smoothing agents having such an effect, the following structural formula:

Chemical formula

[0034] The surface average roughness Ra of the surface of the semiconductor layer 30 is preferably 1 nm or less. When the surface average roughness Ra is 1 nm or less, short circuits are less likely to occur, and stable NDR characteristics can be obtained. In the present invention, the surface average roughness Ra of the semiconductor layer 30 is measured by an atomic force microscope (AFM).

[0035] The content of the smoothing agent in the semiconductor layer 30 is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and preferably 10 parts by mass or less, more preferably 3 parts by mass or less, based on 100 parts by mass of the polyoxometalate. When the content of the smoothing agent is 0.5 parts by mass or more based on 100 parts by mass of the polyoxometalate, the smoothness of the surface of the semiconductor layer 30 is further improved. Also, when the content of the smoothing agent is 10 parts by mass or less based on 100 parts by mass of the polyoxometalate, the NDR characteristics are enhanced.

[0036] --Thickness of the semiconductor layer-- The thickness of the semiconductor layer 30 is 200 nm or more, preferably 300 nm or more, more preferably 400 nm or more, and preferably 1200 nm or less, more preferably 1000 nm or less. When the thickness of the semiconductor layer 30 is 400 nm or more, the NDR characteristics become larger. Also, when the thickness of the semiconductor layer 30 is 1000 nm or less, it becomes difficult for cracks to occur in the semiconductor layer 30. In the present invention, the thickness of the semiconductor layer 30 is measured by spectroscopic ellipsometry.

[0037] (Electrode 40) The electrode 40 is not particularly limited, and any electrode used in a negative differential resistance element can be used. Examples of the material of the electrode 40 include aluminum, silver, ITO (indium tin oxide), IZO (indium zinc oxide), FTO (fluorine tin oxide), InSnZnO (indium zinc tin oxide, ITZO), In3O3, SnO2, Sb-containing SnO2, Al-containing ZnO, and the like. Aluminum is preferably used for the electrode 40 of the negative differential resistance element 1 of the present embodiment.

[0038] (Sealing structure 50) For the sealing structure 50, a hollow sealing structure using a glass cap often used in the production of organic EL elements, a solid sealing structure in which a gas barrier substrate with an adhesive is attached to the element, a film sealing structure using a highly transparent material, or the like can be used.

[0039] (Forming method) In the negative differential resistance element 1 shown in FIG. 2, the method of forming the electrode 20, the semiconductor layer 30, and the electrode 40 is not particularly limited, and chemical vapor deposition (CVD) methods such as plasma CVD, thermal CVD, and laser CVD, which are vapor deposition methods, dry plating methods such as vacuum evaporation, sputtering, and ion plating, spraying methods, and wet plating methods such as electrolytic plating, immersion plating, and electroless plating, which are liquid phase deposition methods, sol-gel methods, MOD methods, spray pyrolysis methods, printing techniques such as doctor blade methods using fine particle dispersions, spin coating methods, inkjet methods, and screen printing methods can be used, and an appropriate method can be selected and used according to the material. These methods are preferably selected according to the characteristics of the materials of each layer, and the manufacturing methods may be different for each layer.

Example

[0040] The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the following examples at all.

[0041] <Formation of semiconductor layer> The glass substrate was washed, followed by UV ozone treatment, and then transferred into a glove box filled with nitrogen. An acetonitrile solution of phosphotungstic acid (PWA) prepared at a concentration of 790 mg / mL and a solution in which 1 part by mass of HAT-CN was added to 100 parts by mass of phosphotungstic acid (PWA) were prepared. Each solution was dropped onto the glass substrate fixed on the spin table of a spin coater and spin-coated at 5000 rpm for 180 seconds. Next, heat treatment was performed at 150 °C for 10 minutes under nitrogen to remove the solvent.

[0042] The appearance of the PWA film without the addition of HAT-CN was cloudy. This is because the film surface was not smooth and light was diffusely reflected. It is considered that a smooth film surface was not formed because PWA crystallized. On the other hand, the film with the addition of HAT-CN was colorless and transparent, and no cloudiness was observed. This indicates that the PWA film was smoothed by the addition of HAT-CN. It is considered that HAT-CN prevented the crystallization of PWA. The film thickness measured by spectroscopic ellipsometry was 1 μm.

[0043] Next, an acetonitrile solution of phosphotungstic acid (PWA) at a concentration of 1000 mg / mL and a solution in which 1 part by mass of HAT-CN was added to 100 parts by mass of phosphotungstic acid (PWA) were prepared, and using these solutions, film formation was performed in the same manner as above. The appearance of the film was colorless and transparent, and the film thickness was 1.5 μm, but it was confirmed that cracks of a visible size were present in the film.

[0044] <Examination of Smoothing Agent> An acetonitrile solution of phosphotungstic acid (PWA) adjusted to a predetermined concentration so as to obtain film thicknesses of 173 nm, 600 nm, and 1000 nm, and a solution in which 0.5 parts by mass, 1 part by mass, or 3 parts by mass of HAT-CN, phosphomolybdic acid (PMA), or CuI was added to 100 parts by mass of phosphotungstic acid (PWA) was prepared. Each solution was dropped onto a glass substrate fixed on the spin table of a spin coater and spin-coated at 5000 rpm for 180 seconds. Next, heat treatment was performed at 150 °C for 10 minutes under nitrogen to remove the solvent. For the formed film, the surface average roughness Ra was measured with an atomic force microscope (AFM). For AFM analysis, Bruker Dimension icon was used, and the analysis was performed under the conditions of a field of view: 500 nm × 500 nm and 0.5 Hz. The results are shown in Table 1. In Table 1, "unmeasurable" indicates that the surface roughness was large and AFM analysis could not be performed.

[0045]

Table 1

[0046] From Table 1, it can be seen that when the film thickness is 200 nm or more, although the surface average roughness Ra of the film increases, HAT-CN acts as a smoothing agent. Also, when the film thickness is 200 nm or more, it can be seen that as the addition amount of HAT-CN increases, the surface average roughness Ra of the film decreases and the smoothness improves.

[0047] <Fabrication of Negative Differential Resistance Element> A glass substrate with an ITO film having a width of 3 mm and a thickness of 150 nm was cleaned, subsequently treated with UV ozone, and transferred into a glove box filled with nitrogen. An acetonitrile solution of phosphotungstic acid (PWA) adjusted to a predetermined concentration and a solution prepared by adding 1 part by mass of HAT-CN to 100 parts by mass of phosphotungstic acid (PWA) were prepared so as to obtain a desired film thickness. Each solution was dropped onto the glass substrate with ITO fixed on the spin table of a spin coater and spin-rotated at 5000 rpm for 180 seconds to form a coated film. The prepared film (semiconductor layer) was · A PWA film with a thickness of 424 nm (Comparative Example 1), · A film of 100 parts by mass of PWA and 1 part by mass of HAT-CN with a thickness of 173 nm (Comparative Example 2), · A film of 100 parts by mass of PWA and 1 part by mass of HAT-CN with a thickness of 424 nm (Example 1), · A film of 100 parts by mass of PWA and 1 part by mass of HAT-CN with a thickness of 1 μm (Example 2), as follows. Next, a heat treatment was performed at 150 °C for 10 minutes under nitrogen to remove the solvent.

[0048] Next, the substrate was transferred into a vacuum chamber, and an anode of 100 nm was vapor-deposited with Al at a film formation rate of 1 - 10 Å / sec. Subsequently, the substrate was taken out from the vacuum chamber into a glove box filled with nitrogen, and the element part was covered with a UV-curable adhesive in a glass tube with a desiccant and sealed hollow by UV irradiation. The area of the fabricated element is 9 mm 2 as follows. Each of those fabricated in the comparative examples and examples contains 10 equivalent elements.

[0049] <Measurement results for verification> The voltage was gradually increased from 0 V, and the upper limit voltages of 7 V for the 173-nm element, 17 V for the 424-nm element, and 40 V for the 1-μm element were applied. As described above, PWA has the characteristic that its resistance changes greatly once current flows. In this test, the results measured at the fifth time are described.

[0050] --Verification 1-- First, measurements were made with ITO as the cathode and Al as the anode. Among them, for the device (Comparative Example 1-1) having a PWA film with a thickness of 424 nm, a large short circuit was obtained and stable results could not be obtained. The measurement results for the device containing 100 parts by mass of PWA and 1 part by mass of HAT-CN are shown in Fig. 3 (thickness 173 nm, Comparative Example 2-1), Fig. 4 (thickness 424 nm, Example 1-1), and Fig. 5 (thickness 1 μm, Example 2-1), respectively.

[0051] Different from Comparative Example 1-1, in Example 1-1 and Example 2-1, due to the effect of adding HAT-CN, crystallization was suppressed, so a uniform film was formed and characteristics could be measured stably. In Comparative Example 2-1, the current value increased monotonically with the increase in voltage and did not show NDR characteristics. Table 2 summarizes the respective voltages V1, V2 and their width (V2 - V1), I1, I2, and I1 / I2.

[0052]

Table 2

[0053] For the device of Example 1-1 with a semiconductor layer thickness of 424 nm, V2 - V1 was 8.4 V, showing a large voltage width. Also, for the device of Example 1-1, I1 / I2 was 1.2, and the ratio of current values was also sufficiently large. Also, for the device of Example 2-1 with a semiconductor layer thickness of 1 μm, V2 - V1 was 6 V, the voltage width was large, I1 / I2 was 7.2, and the current value ratio was very large. Also, in Example 2-1, two regions showing NDR characteristics appeared, and Table 2 shows the characteristics of the first NDR region.

[0054] --Verification 2-- Next, measurements were made with ITO as the anode and Al as the cathode. A device different from the device measured above was measured. Among these, for the device having a PWA film with a thickness of 424 nm (Comparative Example 1-2), large short circuits were obtained and stable results could not be obtained. The measurement results for the device containing 100 parts by mass of PWA and 1 part by mass of HAT-CN are shown in Fig. 6 (173 nm, Comparative Example 2-2), Fig. 7 (424 nm, Example 1-2), and Fig. 8 (1 μm, Example 2-2), respectively.

[0055] Unlike Comparative Example 1-2, in Example 1-2 and Example 2-2, due to the effect of adding HAT-CN, crystallization was suppressed, so a uniform film was formed and characteristics could be measured stably. In Comparative Example 2-2, the current value increased monotonically with the increase in voltage and did not show NDR characteristics. Table 3 summarizes the respective voltages V1, V2 and their width (V2 - V1), I1, I2, and I1 / I2.

[0056]

Table 3

[0057] For the device of Example 1-2 with a semiconductor layer film thickness of 424 nm, V2 - V1 showed a large voltage width of 8.2 V. Also, for the device of Example 1-2, I1 / I2 was 1.4, and the ratio of the current values was also sufficiently large. Also, for the device of Example 2-2 with a semiconductor layer film thickness of 1 μm, V2 - V1 was 4 V, the voltage width was large, I1 / I2 was 11, and the current value ratio was very large. Also, in Example 2-2, when the region showing NDR characteristics was roughly divided, two regions appeared, and Table 3 shows the characteristics of the first NDR region. For the characteristics of the region showing the second NDR characteristics in the devices of Example 2-1 and Example 2-2, they are shown in Table 4.

[0058]

Table 4

[0059] The addition of a smoothing agent such as HAT-CN is necessary to improve the quality of the film (semiconductor layer) and prevent the short circuit of the negative differential resistance element. The reason why a larger thickness of the semiconductor layer results in a larger current value ratio is considered to be that the NDR characteristics are an effect derived from the bulk characteristics of the polyoxometalate film, and it is easier to obtain the bulk effect with a thicker film. The reason why the polyoxometalate containing tungsten exhibits NDR characteristics is not necessarily clear. However, like a Gunn diode, electrons were originally conducting in a conduction band with high mobility, but as the voltage increased, the potential rose, and electrons transitioned to another conduction band with low mobility, resulting in an increase in resistance.

Industrial Applicability

[0060] The negative differential resistance element of the present invention can be used in a tunnel diode, a Gunn diode, a lambda diode, a dynatron oscillator, or an amplifier for alternating current power to contribute to performance improvement.

Explanation of Reference Numerals

[0061] 1: Negative differential resistance element 10: Substrate 20: Electrode 30: Semiconductor layer 40: Electrode 50: Sealing structure

Claims

1. A negative differential resistance element comprising a pair of electrodes and a semiconductor layer positioned between the pair of electrodes, wherein the semiconductor layer contains a polyoxometalate containing tungsten and a smoothing agent, wherein the thickness of the semiconductor layer is 200 nm or more, and wherein the smoothing agent is dipyrazino[2,3-f:2',3'-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile (HAT-CN), characterized by a negative differential resistance element.

2. The negative differential resistance element according to claim 1, wherein the thickness of the semiconductor layer is 400 nm or more.

3. The polyoxometalate is phosphotungstic acid represented by the formula: H ３ PW １２ O ４０ The negative differential resistance element according to claim 1 or 2, which is.

4. The negative differential resistance element according to any one of claims 1 to 3, having a plurality of regions exhibiting negative differential resistance characteristics.

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