JPH01243594A - Negative low resistance element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a negative resistance element (semiconductor device) having an insulator or semiconductor layer made of an organic film.

[Prior Art] Semiconductor elements that exhibit N-type negative resistance in DC voltage-current characteristics (voltage-controlled negative resistance) include tunnel diodes (Esaki diodes) having PM junctions and metal/oxide film/ Tunnel diodes, which have long been known to have a metal junction structure and are being applied to oscillation, switching, memory, etc., have improved their characteristics (expanded negative resistance range, increased speed). ), a steeper change in impurity concentration at the junction surface is required.

The P
By separating the layer and the N layer, the above object can be achieved. However, it is difficult to form an extremely thin insulating or semiconducting medium without defects or holes between such junctions, and this has not been achieved to date.

On the other hand, HIM type elements have a simple structure and do not require expensive semiconductor materials or manufacturing equipment, and therefore have extremely high industrial value.

[Problems to be solved by the invention] However, conventionally known MIM devices using an oxide film in one layer have device characteristics inferior to tunnel diodes, and also have poor reproducibility of characteristics, making it difficult to create devices with uniform characteristics. Furthermore, it is difficult to obtain a high-quality oxide film, and it is difficult to produce it only on a limited number of metals (for example, aluminum), and the degree of freedom in selecting the material used for the underlying metal is low.

In view of the above points, the present invention uses a thin, uniform, defect-free organic film in the insulating or semiconducting region constituting the negative resistance element, The purpose of this is to significantly improve the performance (reproducibility and reproducibility).

[Means for Solving the Problem] In order to solve the above-mentioned problems and achieve the object of the present invention, the present inventors have conducted extensive research on a negative resistance element having a metal/organic film/metal junction structure. As a result, it was discovered that such an element exhibits extremely good negative resistance characteristics, and that an organic film is suitable as a tunnel region, leading to the present invention.

That is, the present invention relates to a metal/organic film/metal structure.

Alternatively, using an organic film in the tunnel region due to the development of negative resistance characteristics, such as a P layer/organic film/N layer structure,
This realizes an element with improved characteristics.

Recent advances in organic film formation technology, as typified by the Langmuir-Prodgett method (LB method), have enabled film thickness control of a wide variety of organic molecules to the single-molecule level.
Moreover, it has become possible to form it on any substrate in a uniform and defect-free state. An ultra-thin organic film that is formed by a simple manufacturing process and is as dense or defect-free as, or even more dense than, an inorganic insulating film is suitable for forming the tunnel region.

In addition to film thickness, the main parameter that determines the magnitude of tunnel current is the height of the barrier in electrical potential. Since most of the currently known organic molecules exhibit insulating or semi-insulating (semi-conducting) properties, they satisfy the requirements for materials that form potential barriers to metals or semiconductors. Furthermore, the types of organic molecules are extremely diverse, and the barrier height of organic molecules can be freely controlled through molecular design and chemical synthesis. This feature, which has a huge variety and allows the electrical properties to be controlled, is unique to organic materials and is not found in inorganic materials conventionally used for tunnel regions.

The present invention provides a negative resistance element that uses an organic film having the above characteristics as a tunnel region and has significantly improved device characteristics (expansion of negative resistance region, increased speed, and reproducibility). Its typical basic configuration is shown in FIGS. 1 and 2.

Figure 1 shows metal 1. Organic film 2. The materials constituting the 0M layer, which is a schematic diagram of the configuration of a MID type negative resistance element formed of metal 3, are Au, Ag, and AI.

Conventionally known metals and alloys such as Pt and Pt can be used. As a method for forming such a material on a supporting substrate or an organic film, the objects of the present invention can be sufficiently achieved by conventionally known thin film manufacturing techniques. In particular, when forming on an organic film, it is desirable to adopt a method that can form the film under conditions of 300°C or less from the viewpoint of the heat resistance of the organic film.For example, as a suitable method for forming a metal layer that can be used in the present invention, Examples include a vacuum evaporation method and a sputtering method. still,
In addition to the exemplified metals, the M layer can also be made of materials that, in principle, have a sufficiently high density of freely movable carriers (electrons or holes) in the medium, and whose work function is greater than the electron affinity of the organic film. If so, it can be applied. This includes various semiconductors such as graphite and Si. Regarding semiconductors, degenerate semiconductors are particularly preferred from the viewpoint of carrier density at room temperature. In addition to inorganic materials, we also use tetracyanoki dimethane (TCNO) and tetrathiafulvalene (TT).
It is also possible to apply organic conductors such as charge transfer complexes represented by F). The materials used and the manufacturing method do not limit the invention in any way.

On the other hand, the form of the organic film constituting one layer only needs to be sufficiently thin and uniform to allow tunneling current to flow. Specifically, it is desirable that the film thickness be at least 100 nm or less. More preferably, if the film thickness is 30 ns or less and 0.3 ns or more, a sufficient tunnel current can flow without shorting between the electrodes. Note that the material and the method for forming the same are not limited in any way; however, in a preferred embodiment of the present invention, the organic film is a monomolecular film or a monomolecular cumulative film made of organic molecules having both hydrophilic sites and hydrophobic sites. Consisted of. Typical examples of components of the hydrophobic portion of such molecules include various hydrophobic groups such as generally widely known saturated and unsaturated hydrocarbon groups, fused polycyclic aromatic groups, and chain polycyclic phenyl groups. Examples include groups. Each of these groups may be used singly or in combination to form a hydrophobic site.On the other hand, typical constituent elements of a hydrophilic site include, for example, a carboxyl group, a sulfonic acid group, or a quaternary amino group. Examples include various wood-loving groups. These monomolecular films or monomolecular "cumulative films" of molecules having both hydrophilic and hydrophobic parts have a high degree of order, and are extremely advantageous in that they can be easily formed into uniform, defect-free ultra-thin films. It is. More specifically, squarylium bis-6-octyl azulene, araxic acid, polyamic acid, copper phthalocyanine, etc. are particularly preferred.

A suitable method for forming an organic film layer on the surface of an arbitrary substrate is the LB method. In order to increase the yield of tunnel current, it is sometimes required that the film thickness be several layers or less and be uniform, but such a configuration can be easily realized using the LB method.

In addition, in the present invention, the substrate for supporting the above-mentioned M layer and one layer laminate structure may be made of any material such as metal, glass, ceramics, or plastic material, and may also be made of biomaterials with extremely low heat resistance. Can be used. Such a substrate may have any shape, preferably a flat plate, but
This is because the LB method is not limited to a flat plate, that is, the LB method has the advantage that a film can be formed in accordance with any shape of the surface of the substrate.

FIG. 2 is a schematic diagram of the structure of a PIN junction type negative resistance element consisting of a laminated structure of a P-type semiconductor layer 4, an organic film layer 2, and an N-type semiconductor layer 5. The P layer and the N layer are made of a semiconductor such as Si or Ge that has a very high impurity concentration, for example, 2 x 1019c+w-3 or more. Regarding the type of impurity, it must be present in a high concentration without segregation in the semiconductor, and must be able to generate acceptors or donors with good efficiency (activation rate).

For example, for Si, boron (B), phosphorus (P), arsenic (As), antimony (sb), etc. are preferable.For semiconductor formation methods and impurity implantation methods, conventionally known thin film The growth method is sufficient to achieve the purpose of the present invention.

Further, the amorphous film, supporting substrate, etc. can be considered in exactly the same way as in the case of the MIX type element. In fact, good device characteristics have been obtained with monomolecular or monomolecular cumulative films formed by the LB method.

The characteristics exhibited by the negative resistance element according to the present invention and the effects of the present invention will be described in detail below along with Examples.

[Example] Example 1 A glass substrate 6 (manufactured by Corning, Inc. @7059) that had been hydrophobically treated by being left in saturated vapor of hexamethyldisilane (HMDS) overnight was used as a support, and a metal (base electrode) 7 was placed on the substrate. An element having a structure of 8 layers of monomolecular cumulative film/9 metals (upper electrode) was formed. FIG. 3 shows an outline of the element shape.

The upper and lower electrodes, which are perpendicular to each other, are both in the form of a stripe with a width of 1+sm, and vacuum evaporation using a conventionally known resistance heating method was used for fabrication. The base electrode 7 was made by depositing 5 layers of Cr as an undercoat layer and then depositing 30 nm of Au on top.

The monomolecular cumulative film 8 was formed by laminating squarylium bis-6-octyl azulene (SOAZ) on the above electrode by the LH method. Details of the formation method are described below.

A chloroform solution in which 5OAZ was dissolved at a concentration of 0.2 mg/sl was spread on an aqueous phase at a water temperature of 20°C to form a monomolecular film on the water surface. After the solvent has been removed by evaporation, the surface pressure of the monomolecular film is increased to 20 mN/lII, and while this is kept constant, the substrate on which the base electrode has been deposited is gently moved at a speed of 10 mm/min across the water surface. followed by 5
Two layers of Y-type monomolecular film were accumulated on the substrate by gently pulling up the Y-type monomolecular film in 1 minute. Furthermore, the above operation was repeated five times to form a cumulative film of 10 layers (M thickness: 15 nm).

Upper electrode materials include Ai', Ag, Au, and Pt.
Experiments were conducted on each. That is, using one of the metals mentioned above as the upper electrode 9, the characteristics and stability of the fabricated device were investigated. The results are described below.

Figure 4 shows the current-voltage characteristics when the upper electrode is made of AI.As the applied voltage increases, the current clearly decreases from about 2.5 layers onwards, indicating voltage-controlled negative resistance characteristics. There is. Although there are some variations depending on the prepared sample,
The current starts to increase again from about the 6th layer. The ratio (PV ratio) between the maximum current value (peak value, P value) shown before and after the second layer and the minimum value (valley value, V value) shown at the point where the current starts to increase again is a significantly large value of about 2000. Ta.

On the other hand, similar negative resistance characteristics were obtained for the material in which ag was used as the upper electrode. However, the variation between samples was larger than in the case of Ai), and the peak value varied by nearly one order of magnitude around 1 mA. Also, the one with the highest PV ratio was 500. Furthermore, while the electrical properties of the AR main electrode sample do not change much even if left for several weeks, in the case of the Ag electrode, the flowing current value varies from ]/2 to 17
It has decreased to about 5. In addition, many of the samples using Au or Pt as the upper electrode had a short circuit (resistance value of 10Ω or less) between the upper and lower electrodes, but negative resistance characteristics were observed in those with insulation. Ta. In addition, at this time, the current value is generally higher than that of the Ai) electrode, and the PV
The ratio was also around 100. In the case of Au and Pt, the organic film may be damaged during vapor deposition.

However, in all of the above elements, negative resistance characteristics with a PV ratio of two to three digits were obtained, indicating that such elements are extremely promising.

Example 2 The upper electrode material was AR, and NIN was prepared in the same manner as in Example 1.
A type negative resistance element was fabricated. However, by repeating the accumulation operation an appropriate number of times, the film thickness (number of layers) of 5OAZ can be reduced to 2,
Six types of samples with 4, 6, 10, 20, and 30 layers (1,5 layers m/1 layer) were investigated.

As a result, for the 2-layer and 4-layer samples, there was a short circuit between the upper and lower electrodes. On the other hand, in the sample with 30 layers, almost no current flowed (less than IILA) and no negative resistance could be observed.

A clear negative resistance was observed for the 6, 10, and 20-layer sample (PV ratio of 2 to 3 digits), and the peak current was approximately 10 mA.

A correlation between 2 mA, 0.1 mA and film thickness was also observed. To increase the amount of current, it is necessary to reduce the film thickness. Furthermore, when increasing the speed of the device, it is necessary to minimize the distance traveled by the carriers, and from this point of view as well, it is desirable to make one layer as thin as possible. Although insulating properties were not obtained for the two-layer and four-layer samples here, we believe that if film formability improves in the future, good negative resistance characteristics can be obtained even under such conditions.

Example 3 The upper electrode material was Ag, and HIM was performed in the same manner as in Example 1.
A type negative resistance element was fabricated. However, the experiment was conducted using a stack of monomolecular stacked films made of different materials in one layer.

Specifically, 5OAZ (abbreviated as S) and araxic acid (A
5(8)/A(2),
5(4)/A(2)/5t(4), A(2)/5(
We investigated three types of samples laminated with the configuration shown in 8) ((
) indicates the number of layers).

Regarding S/A/S and A/S configuration elements,
Compared to the element shown in Example 1, the current value flowing through the element is 2.
．． Although it is 3 times larger, the PV ratio is similar (100 to 1000
) values are shown. On the other hand, regarding the sample with S/A configuration,
Although the current value is slightly small (peak value 0.1mA order)
An extremely large value of approximately 3000 was obtained for the Pv ratio.

The current valley value is considered to be caused by the flow of carriers over the potential barrier created by the organic film layer. It is considered that the existence of a potential barrier due to alaxic acid higher than that of 5OAZ causes a large decrease in the Bevarray value compared to the peak value, resulting in an improvement in the Pv ratio. Regarding devices with A/S and S/A/S configurations, it is believed that there are problems with the film formability and film quality of araxic acid or 5OAZ formed on araxic acid. This is because when a MIX type element was fabricated in which one layer was formed of alaxic acid alone, a short circuit occurred between the upper and lower electrodes even though the thickness was 40 layers in terms of 5 OAZ film thickness. At least under such circumstances, it can be said that araxic acid has lower film-forming properties than 5OAZ.

Example 4 An old X-type negative resistance element having the same structure as in Example 1 was fabricated using AP as the upper electrode material and using a polycarbonate substrate as the support. Note that the hydrophobic treatment step shown in Example 1 was omitted. In addition, copper phthalocyanine formed by vacuum evaporation (resistance heating) method was used for the first layer, the evaporation port temperature was kept constant at 500°C, the substrate temperature was kept at room temperature, and the gas pressure was 3X.
1O-5torr, deposition rate 0. Vapor deposition was performed under the condition of O8 nm/sec. At this time, four types of samples were prepared with film thicknesses of 5°10 and 20.40 m by changing the deposition time, and their current-voltage characteristics were measured.

Negative resistance was observed only for the sample with 40 layer m;
In all samples below layer m, there was a short circuit between the upper and lower electrodes.

Also, for the sample with 40 layers m, the peak current was 0.5 m
Although the flow rate was about A, the pv ratio was less than lθ.

These problems are considered to be due to a decrease in film density and uniformity when fabricated by vapor deposition compared to the LB method. Therefore, the effective film thickness that contributes to electrical characteristics is 4
It should be thinner than the 0 layer meal. Conversely, it can be said that the optimal film thickness for developing negative resistance is influenced by parameters such as film quality.

Example 5 P type crystalline silicon wafer (B doped, resistivity 0.
1G, 20.4G, 60.100 in the same manner as in Example 1, directly onto the polyamic acid single molecule
Heat treatment (30
0° C. for 10 minutes) to imidize the polyamino acid. Cumulative single molecule H(0,
Further, N゛-type amorphous silicon is formed on the 4 layers m / 1 layer by glow discharge decomposition method (GD method), and a PIN is formed.
The conditions for producing amorphous Si, which produced a negative resistance element having a junction, were as follows: introduced gas 5iHn+PH3C flow rate ratio 20:
1), gas pressure 0.5 torr, substrate temperature 220°C,
The high frequency power was 10 layers W/c 2, the deposition rate was 4 nm/min, and the film thickness was 200 nm.

For the device fabricated by the above process, a dot-shaped Aβ electrode with a diameter of 2 mm was formed on the amorphous Si, and metal probes were placed at two locations on the electrode and the exposed portion of the substrate Si, and both ends were The electrical characteristics between the two were measured.

As a result, when the cumulative number of layers was 20 or less, there was a short circuit between the upper and lower electrodes, but negative resistance was observed for elements with 40, 80, and 100 layers. In particular, the highest Pv ratio was obtained in the 80th layer, which was about 50 times.

However, despite the fact that the device has not been optimally designed and despite the use of an amorphous semiconductor, it is possible to obtain a relatively large negative resistance with a relatively large Pv ratio even in a PIN junction type device. It became clear.

[Effect of the Invention 1] Compared to conventionally known negative resistance elements, the device characteristics can be greatly improved. In particular, it was possible to easily realize a device that has a significantly high peak valley ratio, which indicates the magnitude of negative resistance, and that operates stably even at room temperature.

On the other hand, since it uses inexpensive organic materials and the manufacturing process is simple, it has a significant economic effect. Furthermore, since the characteristics of the organic film are relatively unaffected by the material of the underlying layer, there is a large degree of freedom in the device form.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of the configuration of a MIX type negative resistance element, Fig. 2 is a schematic diagram of the configuration of a PIN junction type negative resistance element, Fig. 3 is a schematic diagram of the element shape according to the embodiment, and Fig. 4 is the upper electrode A
I! A graph showing the current-voltage characteristics when .

Claims (5)

[Claims] (1) A negative resistance element in a semiconductor device exhibiting negative resistance characteristics consisting of an insulator or semiconductor layer and a pair of electrode portions sandwiching the medium layer, wherein the medium layer is made of an organic film. (2) The negative resistance element according to claim 1, wherein the organic film has a thickness of 100 nm or less. (3) The negative resistance element according to claim 1, wherein the organic film has a thickness of 30 nm or less and 0.3 nm or more. (4) The negative property according to claim 1, wherein the organic film is constituted by a monomolecular film or a monomolecular cumulative film of an organic compound having at least a hydrophilic site and a hydrophobic site. Resistance element. (5) In a semiconductor device exhibiting negative resistance characteristics consisting of an insulator or semiconductor layer and a pair of electrodes sandwiching the medium layer, the medium layer may be an organic film and an inorganic film, or a combination of organic films made of different materials. A negative resistance element comprising a laminated structure.