JPH02215173A - Switching element and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve a switching element in repetition stability and to micronize an electrode by a method wherein an organic insulating thin film is provided between a pair of electrodes, a second organic insulating layer is provided between, the electrodes and the thin film to limit a conductive area between the electrodes, and a memorizing property is given to the switching characteristic of an switching element. CONSTITUTION:After the surface of a glass board 1 is cleaned enough, a lower electrode 2 of Au is provided to the center of the surface providing Cr as an undercoat layer, a monomolecular accumulated layer is deposited on the surface of the board 1 including the lower electrode 2. Then, an electrode step protective layer 4 is formed thereon and the part of it corresponding to the electrode 2 is removed, and an upper electrode 5 is made to coat the whole face as being in contact with the monomolecular accumulated layer 3. In a switching element structured as above, when a voltage is applied between a lower and an upper electrode, a memorizing property is given to a current-voltage characteristic, whereby not only the switching element can be made stable in switching characteristic but also the electrodes can be made micronized and high in density.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an MIN device having an organic insulating layer. The present invention also relates to a MIN structure switching element having memory properties, in which the upper and lower electrodes are formed using ring graphie technology.

[Prior art] Recently, interest in molecular electronics, which seeks to apply the functionality of organic molecules to electronic devices, has been increasing. Research is becoming more active.

LB films are made by stacking organic molecules one molecular layer at a time, and the film thickness can be controlled in units of molecular length.
- Many attempts have been made to use this as an insulating film because it can form homogeneous ultra-thin films.
, L. Larkins et al↑bin 5o
lid films 99.1983) Metals/Insulators/
Tunnel junction device with metal (1M) structure [G, L, L
"Electronics Letters" by Arkingetal
Thin Solid Films” (↑hiXISolid
Films) Volume 88 (1983)] and metal-insulator-semiconductor (NIS) structure light emitting devices [G, G, R
Elsctronjcs Letts J by Oberts et al.
ers) Vol. 20, p. 489 (1984)] or switching elements [N, J, ↑Homas et a
``Electronics Letters J'' by Electr.
onics Letters) Volume 20.

83B (1984)].

[Problem to be solved by the invention] Although device characteristics have been investigated through the series of studies mentioned above, variations in characteristics between devices and lack of reproducibility and stability, such as changes over time, remain unresolved problems. .

Furthermore, conventionally, the electrodes used in the above studies have been formed by mask vapor deposition. If the electrode is formed using the mask evaporation method, the electrode area.

The shape cannot be arbitrarily selected and is limited, which poses a problem in the production of integrated circuits. On the other hand, if the electrode area shape can be arbitrarily selected, it is expected that the device characteristics or the driving method of the device will be improved.

[Means and effects for solving the problems] In order to solve the above problems, the present inventors completed the present invention as a result of intensive research. That is, the present invention has an organic insulating thin film between a pair of electrodes, and a second organic insulating thin film is provided between the stepped portion of the electrode and the organic insulating thin film, and the current-carrying area between the electrodes is The present invention provides a switching element and a method for manufacturing such an element, which are characterized in that the switching characteristics are limited and the switching characteristics have a memory property.

The present invention will be explained in detail below.

Regarding the formation of the first organic insulating layer of the present invention, specifically, it is possible to apply a vapor deposition method, a cluster ion beam method, etc.; The LB method is highly preferred.

Generally, most organic materials exhibit insulating or semi-insulating properties, but organic materials with excellent heat resistance and solvent resistance suitable for the present invention are the following polymer compounds.

For example, polyimides obtained by cyclizing polyamic acids, polyamic acid salts, and polyamic acid esters, which have a repeating unit represented by the general formula (1) and have a weight average molecular weight of 20,000 to 3 million, are cyclized and imidized. It is something.

General formula (1) In the formula, R1 is a tetravalent group containing at least 6 carbon atoms, and specific examples include the following.

Further, R2 is a divalent group containing at least two carbon atoms, and specific examples include the following.

Further, R3 is a monovalent group having at least 6 carbon atoms, or a quaternary ammonium salt having at least 6 carbon atoms, and has the structure shown in general formula (2).

General formula (2) % formula %) Further, the substrate may be any metal, glass, ceramic material, etc. as long as it has excellent heat resistance and solvent resistance.

Next, in the switching element of the present invention, in order to stabilize the characteristics of the element, a second insulating layer is formed on the electrode step portion to maintain organic insulation wII! Provide l. Regarding the formation of the second organic insulating protective film, it is possible to use a negative organic resist material, but it is also possible to use a negative-type organic resist material, but it is also possible to use a molecule that has a polymerization part in the molecule and also has a hydrophobic part and a lignophilic part. is formed into a monomolecular film or a monomolecular cumulative film, and subsequently a dye material is formed into a monomolecular film or a monomolecular cumulative film on the monomolecular cumulative film, using a conventional latent image forming method (for example, Japanese Patent Publication No. 1
As amphiphilic molecules having a polymerization moiety in the molecule, it is possible to obtain a desired organic insulating protective film using the following general formulas (1), (2), and (3).
) are listed.

R+-(-CH2←X-R2(1) However, X = COO, C0NH, 000°R1coCH
3-, CH2-CH-.

R2xH, -CH-CH2, -CCCHs)mCH2-
-CH2Cl-CH2゜10≦n≦25 )1+CHz)-Qa+ C-Cs -(-CH2)-
X-R2 (2) However, x = coo, coxu,
oco.

R2=H, -CH閤CH2, -C(CH3)-(Ib
.

-GHz CH-CHt * 0≦m, n, 10≦m+n≦25 p However, R+xH, CH3゜-5i (C1h) q (CiHs) r mxo ~3 nxO~10 q+r The thickness of the organic insulating film is between 500A and 100A, preferably between 100A and 3000A.

On the other hand, in the switching element of the present invention, the electrodes are formed using lithography technology. The lithography technique involved is a lift-off process.

Conventionally known techniques such as photoetching processes are sufficient. The electrode material may be any material that has high conductivity5, such as Au, Pt, and Ag.

Pd, Aj? , I! Numerous materials such as metals such as I, Sn, and Pb, and alloys thereof can be considered. Further, the width of the electrode can be formed in the range of 10 μm to Is2. In the present invention, since the fine electrode is formed by phosphorography technology, the switching speed can be increased.

Furthermore, such lithography technique can also be applied to the formation of the second organic insulating layer.

[Example] A detailed explanation will be given below using examples.

Example 1 A device having the structure shown in FIG. 1 was produced by the following procedure. The cleaned glass substrate is subjected to ultrasonic treatment and baking using butyl acetate as a pretreatment. Hexamethyldisilazane (HMDS) is applied to the substrate using a spinner, and after baking, a negative resist material (trade name RD) is applied. -2000%-10) was applied with a spinner and prebaked.

At this time, the film thickness was set to 0.7 gm. continue,
Exposure, development, and post-baking were performed to create a desired resist pattern.

On such a substrate, Cr was deposited as an undercoat layer to a thickness of 100 A using a vacuum evaporation method, and Au was further deposited using the same method (thickness: 1100 A).The substrate was subjected to a seven-ton ultrasonic treatment and dimethylformamide (DNF). ) Ultrasonic treatment, pure water cleaning, baking, and lift-off to create 10 width pots 1
A base electrode was formed.

The substrate was left in saturated HMDS vapor for a day and night to perform hydrophobic treatment. A 20-layer cumulative film (thickness: 80A) of a polyimide monolayer was formed on the substrate using the LB method to make it insulating.

The details of the method for producing the polyimide monomolecular cumulative film are described below.

The polyamic acid shown in formula (4) was dissolved in N,N-dimethylacetamide solvent (monomer equivalent concentration I
10-3M), then mixed with a separately prepared IX 10-3M solution of M,N-dimethyloctadecylamine in a surrounding solvent at a ratio of 1:2 (V/V) to obtain octadecylamine polyamic acid represented by formula (5). A salt solution was prepared.

(CH2) 17 CH3 The solution was developed on an aqueous phase consisting of pure water at a water temperature of 20°C,
A monomolecular film was formed on the water surface. After removing the solvent, reduce the surface pressure to 2
While keeping the zero surface pressure raised to 5 mN/m constant, the substrate with the base electrode was moved at a speed of 55 ash in the direction across the water surface.
After gently dipping in /sin, it was then gently pulled up in 5 layers/sin to create a Y-shaped monomolecular cumulative film of 2 layers.

Such operations were repeated to form a 20-layer monomolecular cumulative film of polyamic acid octadecylamine salt.

Next, heat treatment is performed on the substrate at 300°C for 10 minutes,
By imidizing polyamic acid octadecylamine salt, a monomolecular imide cumulative film was obtained.

On such a substrate, a diacetylene compound represented by formula (7) H23-CII C-Car C-(CH2)8-
COOH (7) was accumulated by the LH method.

The method for producing a monomolecular cumulative film of a diacetylene compound will be described in detail below.

The diacetylene compound was dissolved in chloroform at 1×10−3
A solution containing M at a concentration of 4 x 10-4 at a water temperature of 20°C
It was developed on an aqueous phase (pH 8,8) containing M MnC1'z to form a monomolecular film on the water surface. After the solvent was evaporated and removed, the substrate with the lower electrode was moved at a speed of 1 in the direction across the water surface while keeping the surface pressure constant and the surface pressure increased to 20 mN/m.
Gently immerse at 0 mm/sin, then at the same speed of 10
-m/win to create a two-layer Y-type monomolecular cumulative film. This operation was repeated to form a monomolecular cumulative film of 50 layers of a diacetylene compound.

Next, squarylumbisu〇-octyl azulene (
A monomolecular cumulative film of SOAZ) is formed on the substrate. The method for producing the 5OAZ monomolecular cumulative film will be described in detail below.

A chloroform solution in which 5OAZ was dissolved at a concentration of 1.times.10 to 3 M was spread on an aqueous phase consisting of pure water at a water temperature of 20.degree. C. to form a monomolecular film on the water surface. After removing the solvent, reduce the surface pressure to 20m
N/layer, and while keeping this constant, move the substrate across the water surface at a speed of 5 layers m/wi! After being gently immersed in I and then gently pulled up in 5 layers m/sin, a Y-type monomolecular cumulative film of 2 layers was created.

This operation was repeated to form a 6-layer 5OAZ monomolecular cumulative film.

A latent image was formed on the substrate by irradiating a semiconductor laser with a wavelength of 830 nm (laser beam diameter 1 μ layer, irradiation time 200 ns/1 dot, output 3 layers V) through a desired mask pattern.

Next, the substrate is uniformly and sufficiently irradiated with ultraviolet rays having a wavelength of 254 nm to polymerize the desired pattern of the diacetylene compound. Immersing such a substrate in an ethanol solution,
The opening irradiated with the semiconductor laser and the 5OAZ monomolecular cumulative film are peeled off.

Ai) was deposited on the substrate with a thickness of 10GO by vacuum evaporation method.
0-order positive resist material (trade name: OMR) to be deposited
-83) with a spinner to a film thickness of 1.2 layers, perform exposure, latent image, and post bake, then H3
PO4:HNO3:C1hCOOH:1hO=18
: Etch Ai) into the desired pattern with a 1:2:l solution. Such a substrate was subjected to acetone ultrasonic treatment, DMF
The resist was removed by ultrasonication and washing with pure water, and baking was performed to create an upper electrode. The width of such an electrode was lOO12.

When we measured the current-voltage characteristics (1-V characteristics) when voltage was applied between the upper and lower electrodes of the sample prepared as described above, we observed memory switching characteristics that were previously unknown in other samples. did.

(Fig. 2) Furthermore, the stable ON state as shown in Fig. 3!
S (resistance value of several tens of Ω) and OFF state S (resistance value of MΩ or more) can be created, and switching from ON to OFF shows a constant threshold voltage (about 1 to 2 V/20 layers), and O
Switching from FF to ON occurs at about -2 to 5V, and the switching speed is 0N10 in psec order.
The FF ratio (ratio of resistance values in ON state and OFF state) was 5 digits or more. The switching threshold voltage showed a tendency to increase as the number of insulating layers increased. As a result, the switching characteristics were unstable for the 4-layer and 6-layer samples, and
Switching no longer occurs in the layer sample. Here, the film thickness per layer of the polyimide monomolecular cumulative film measured by the erisinmetry method was several amps. In addition, when a triangular wave with a peak value of ±8 V and an alternating electric field frequency of 2 Hz is continuously applied, 1
The repetition stability was evaluated based on the number of repetitions until the electrode broke due to heat generation, and the number of repetitions was 5
It was 100 times.

Example 2 In the same manner as in Example 1, a lower electrode was formed by a lift-off process, and a 20-layer monomolecular polyimide cumulative film was further formed by the LB method.

A desired upper electrode was formed on the substrate by the same photoetching process as in Example 1. Furthermore, the width of the electrode was 20 μm.

Polyisobutyl methacrylate (PIBM) represented by the formula (8) was accumulated on the substrate by the CH3 2 CH2 CH3-CI-C)13 LB method.

Hereinafter, a method for producing a monomolecular cumulative film of PIBN will be described in detail.

Using a mixed solvent of benzene: n-hexane = 10:1,
A PIBM(7) IX 10-3M (7) solution was prepared. This was developed on a water phase with a water temperature of 20°C, the surface pressure was increased to 12 N/layer, and a monomolecular film was formed on the water surface.While maintaining a constant zero surface pressure, the substrate with the lower electrode was placed on the water surface. The membrane was gently immersed in one layer at a speed of 10 mm in the transverse direction, and then gently pulled up at the same speed of 10 layers intestine/intestine to form a two-layer Y-shaped monomolecular cumulative film. This operation was repeated to form a 50-layer PIBM monomolecular cumulative film. Subsequently, a six-layer 5OAZ monomolecular cumulative film is formed on the substrate in the same manner as in Example 1, and a desired pattern is further formed in the same manner as in Example 1 to serve as a protective film for the electrode step portion.

On this substrate, AR is deposited to a thickness of 3000 Å by vacuum evaporation, and as in Example 1, the Al is patterned using lithography technology to form a desired lead-out electrode of the upper electrode.

When the IV characteristics of the sample prepared as described above were measured in the same manner as in Example 1, the same memory switching characteristics as in Example 1 were observed. Switching speed is p8ec
It was an order. Furthermore, the 0NlOFF ratio was more than 5 digits, and the number of repetitions was 4 x 107 times.

Example 3 Similar to Example 1, using a lift-off process,
After forming a lower electrode layer with an electrode width of 20 μm.

A 20-layer polyimide monomolecular cumulative film is created by the LB method.

A negative resist material (trade name 0DOR-1) is applied on such a substrate.
20) Film thickness: 100A, 20OA, 500A
A, 100OA.

Coating is performed using a spinner to obtain 3000A, 5000A, 1S, and 2ILm, respectively, and the desired pattern is obtained by performing exposure, development, and post-baking.

In the same manner as in Example 1, a film of Al was deposited on the substrate to a thickness of 100 mm.
0-order positive resist material deposited at 0A (trade name ^Z
1370) with a spinner to a film thickness of 1.2 #Lm.
shall be. This is subjected to fog light, development, and post-bake.

Then H3P0*:HNO3:CH3GOOH:HzO
Etch the AR with a solution of = 18:1:2:1 to obtain the desired pattern. The substrate was subjected to A7T ultrasonic treatment, DNF ultrasonic treatment, and purified water cleaning.
(A2137G) was peeled off to create a desired upper electrode. The width of the electrode was 20 layers.

When the IV characteristics of the sample prepared as described above were measured in the same manner as in Example 1, the same memory switching characteristics as in Example 1 were observed. The switching speed is p! et
It was C order. Further, the 0N10FF ratio was over 5 digits, and the number of repetitions was 4 x 107 times.

If the thickness of the insulating film at the electrode step part is thinner than 50OA,
The insulating properties of the insulating film could not be sufficiently ensured, and the upper electrode was likely to break off at the end of 2.

Comparative Example 1 A base electrode is formed in the same manner as in Example 1, and a 20-layer polyimide monomolecular cumulative film is formed.

5i02 was deposited on the substrate to a thickness of 300 mm using a vacuum evaporation method.
0A deposited zero-order positive resist material (trade name ^Z
1370) using a spinner to a film thickness of 1.2 μl. After pre-baking this, it was exposed and developed.

Post-bake, then HF: NH4F = l
: Perform etching with the solution No. 7 to pattern 5i02 and protect the electrode step portion. The resist is removed from the substrate by acetone ultrasonic cleaning, DNF ultrasonic cleaning, and pure water cleaning, and then baking is performed.

An upper electrode is formed on the substrate in the same manner as in Example 1. The size of the electrode was 20 mm.

When the IV characteristics of such a sample were measured in the same manner as in Example 1, memory switching characteristics similar to those in Example 1 were observed. However, the repetition stability was lower than in the above example, being 2×10 7 times.

Comparative Example 2 A device was produced in the same manner as in Example 1. At this time, the electrode widths were set to 150 pm and 11 pm. Such an electrode width is the size that is formed by conventional mask deposition.

When the current-voltage characteristics of such an element were measured, switching characteristics with memory properties similar to those of Example 1 were obtained, but the switching speeds were 30 nsec and 70 nsec, respectively.
It was 0 nsec.

[Effect of the invention] The present invention has the effects described below.

(2) After the LB film was accumulated, the step portion of the lower electrode was protected with an organic insulating film that was not damaged by vapor deposition, thereby improving the repeat stability of the switching characteristics of the MIII device.

■ By using lithography technology to form the electrodes of MIN devices, which are made by accumulating polymer compounds with excellent heat resistance and solvent resistance using the LB method and using them as insulating layers, it is possible to miniaturize and increase the density of the electrodes. Ta.

■ The switching speed has been increased by making the electrodes finer using lithography technology in the electrode formation method for MIN devices, which is an insulating layer made by accumulating polymeric compounds with excellent heat resistance and solvent resistance using the LB method. became possible.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the configuration of a specific example of the MIM element of the present invention. In addition, Figs. 2 and 3 are characteristic diagrams showing the electrical characteristics (1-V characteristics) obtained in such an element, and Fig. 3 is an electrical characteristic diagram of ON state and OFF state confirmed in such an element. This shows that. 1: Substrate 2: Lower electrode 3: Monomolecular cumulative film (LB film)

Claims (8)

[Claims] (1) An organic insulating thin film is provided between a pair of electrodes, and a second insulating layer made of an organic insulating protective film is provided between the electrodes and the organic insulating thin film, and a current-carrying area between the electrodes is provided. limit,
A switching element characterized by having memory properties in its switching characteristics. (2) The switching element according to claim 1, wherein the thickness of the organic insulating thin film sandwiched between the pair of electrodes is 20 Å or more and 1000 Å or less. (3) The switching element according to claim 1, wherein the organic insulating thin film sandwiched between the pair of electrodes is made of polyimide. (4) A method for manufacturing a switching element according to claim 1, characterized in that the electrodes are miniaturized using lithography technology. (5) The second organic insulating protective film formed on the organic insulating thin film is etched by a lithography method to form the current-carrying region and further to create an upper electrode. 4. The device manufacturing method described in 4. (6) After forming the upper electrode on the organic insulating thin film, etching the upper electrode using a lithography method to make it finer and covering the entire surface with an insulating layer, forming a layer for contacting the upper electrode. 5. The device manufacturing method according to claim 4, wherein the opening is etched to form the extraction electrode. (7) A process in which the organic insulating protective film forms a latent image by irradiating infrared rays on a monomolecular cumulative film in which a polymerizable amphiphilic compound and a dye material are laminated; 5. The method for producing an element according to claim 4, wherein the latent image is formed by irradiating the latent image with a visible light. (8) The device manufacturing method according to claim 4, wherein the organic insulating protective film is formed of a negative type organic resist material.