JPH02237070A - Formation of charge transfer complex layer - Google Patents

Abstract

PURPOSE:To form a uniform, dense charge transfer complex layer so as to obtain a memory element provided with the charge transfer complex layer, which is excellent in a voltage- current (VI) characteristic and reproducibility and able to keep a voltage to the layer constant and to prevent the conduction between an upper electrode and a substrate by a method wherein a charge transfer complex compound crystal layer is formed on the primary face of a base, and then the crystal layer is brought into contact with solvent to be treated. CONSTITUTION:For instance, when a substrate 1 formed of Cu is dipped into a TCNQ/ acetonitrile solution, a charge transfer complex layer 13 composed of acicular crystals 11 and prismatic crystals 12 is formed on the surface of the substrate 1. When the substrate is dipped into acetonitrile as it stands still, the prismatic crystals 12 higher than the acicular crystals 11 in solubility are eluted and removed. The prismatic crystals 12 are dissolved into acetonitrile in a process in which the prismatic crystals 12 are eluted and removed, which is grow in other acicular crystals among the existent acicular crystals 11. By this setup, a uniform and dense charge transfer complex layer 13 can be obtained. Even if an upper electrode is formed on the charge transfer complex layer 13 obtained as above for the manufacture of a memory element, a direct conduction between the upper electrode and a substrate 1 is prevented and an excellent V-I characteristic can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement in a method for forming a charge transfer complex layer. [Prior art] As is well known? , 7.8.8-tetracyanoquinodimethane (TCNQ). Complex salts consisting of inorganic or organic cations are known as electrically conductive compounds. These materials have recently attracted great interest as materials for memory or capacitors. U.S.P. No. 4507672 (190) is C
A method for producing a memory element using a complex salt of u and TCNQ and its characteristics are disclosed. That is, in this publication, a copper substrate is brought into contact with a TCNQ solution, which is a neutral acetate, and a metal salt Ill! is deposited on a steel substrate. After forming, applying an electrical potential to this thin film changes it from the first resistance state to the second resistance state.
Switching to the resistive state is self-contained. FIG. 2 shows a cross-sectional view of the memory element. 1 in the figure is a metal substrate made of copper, for example, which functions as a lower electrode. On this metal substrate 1, a polycrystalline charge transfer complex layer (hereinafter referred to as a complex layer) 2 and an upper electrode 3 are formed. Note that 4.5 indicates a conductive paste. In a memory element having such a configuration, when a voltage is applied to the complex layer 2 through a series resistor (not shown) between the metal five plate 1 and the upper electrode 3, the voltage and current (Vl
) characteristics are obtained. In other words, the Vl characteristic of the complex layer 2 changes discontinuously at the threshold voltage ±V+ (V), and for example, when the voltage applied to the complex layer 2 in a high resistance state exceeds the threshold voltage +Vs (V), , changes along the load line from a high resistance state to a low resistance state. The above memory device is manufactured as follows. ■First, the oxide layer on the substrate. Remove organic matter. ■Next, the Jingki substrate is converted into a neutral acceptor molecule (TCNQ).
The product is saturated with acetonitrile, or a solvent in which methanol or TCNQ is soluble. As a result, oxidation-reduction occurs immediately and a polycrystalline film grows on the substrate. The reaction is terminated by removing the plate consisting of the substrate and the thin film from the a7tonitrile solution. (2) Next, the substrate is cleaned using acetonitrile for cleaning. The purpose of this cleaning is to remove neutral acceptor molecules (TCNQ) in the thin film made of Cu and TCNQ. (2) Next, the substrate is vacuum dried to remove the cleaning acetonitrile. (2) An upper electrode is formed on the complex layer by a pressure bonding method or a sputtering method to manufacture a memory element. The material of the upper electrode is aluminum. Gold, indium, etc. are used. The memory element thus obtained has the advantage that it can be manufactured relatively easily compared to IC memory. [Problems to be Solved by the Invention] However, the prior art has the following problems. (2) Since there are many gaps in the complex layer 2 itself, there was a problem that even when a voltage was applied, the complex layer 2 did not exhibit good Vl characteristics or that reproducibility between devices was not observed. (2) The spacing between the upper electrode 3 on the complex layer 2 and the substrate 1 was not constant, and the voltage applied to the complex layer 2 was not constant. (2) There was a problem that there was a portion where the upper electrode 3 and the substrate 1 were directly electrically connected. The present invention was made in view of the above circumstances, and exhibits uniform and dense properties, good (1) characteristics, and reproducibility between elements, and furthermore, the voltage applied to the complex layer is constant, and conduction between the upper electrode and the substrate is avoided. An object of the present invention is to provide a method for forming a charge transfer complex layer that can be used as a charge transfer complex layer. [al! Means for Solving Xi] The present inventors observed the surface of a charge transfer complex layer formed on a substrate by a conventional method using an electron microscope, and found that FIG.
Photographs of the particle structure as shown in Figure 6 (1(it)Ox) were obtained. From this photograph, it was confirmed that the complex layer was not uniform and was composed of needle-like crystals and prismatic crystals (however, depending on the processing conditions of the U-plate, it was not necessarily made up of only these crystals). Further, when the above complex layer was observed in more detail, it was found that the needle-like crystals were almost aligned in the growth direction, but lacked compactness. In addition, it was confirmed that the prismatic crystals were not uniform in size and orientation direction, had many gaps, and lacked compactness. For this reason, the present inventors noticed that there is a difference in the solubility of needle-like crystals and prismatic crystals in organic solvents (e.g., acetonitrile), and found that the Remove the columnar crystals and leave only the needle-like crystals, making them uniform. It is possible to form a dense charge transfer complex layer. That is, in the present invention, a solution of a composition that is an electron acceptor dissolved in a solvent is brought into contact with a base material of a composition that is an electron donor, and crystals of a T-transfer complex compound are formed on the main surface of the base material. A method for forming a charge transfer complex layer, comprising a first step of forming a layer, and a second step of treating the crystal layer by bringing a solvent into contact with the crystal layer. [Function] In the present invention, for example, the solubility of prismatic crystals in acetonitrile is greater than that of needle-like crystals. Therefore, by immersing a complex layer consisting of prismatic crystals and needle-like crystals in static acetonitrile for a long time, only the prismatic crystals in the upper layer can be eluted (dissolved) and removed. In addition, in the process of removing (dissolving) the prismatic crystals, new acicular crystals grow on the exposed surface of the substrate in the gaps between the acicular crystals using the prismatic crystals dissolved in acetonitrile as a raw material, resulting in uniform and dense charge. A mobile complex layer is obtained. Examples of the present invention will be described below. [Example 1] This will be explained with reference to FIGS. 1(A) to 1(C). However, the same members as those of the conventional device (FIG. 2) will be described with the same reference numerals. (2) First, a substrate 1 made of, for example, Cu was ultrasonically cleaned in acetone to remove oil and fat. Next, the oxide layer on the surface was removed using hydrofluoric acid. Subsequently, the substrate 1 was treated with 50mj of acetonitrile! for T C N Q 10
It was immersed in a TCNQ/acetonitrile solution in which Qmg was dissolved. Furthermore, after immersion, at a reaction temperature of 20°C, 30 to 40
After seconds (reaction time) had elapsed, the substrate 1 was taken out from the solution (as shown in FIG. 1(A)). As a result, a needle crystal 11 and a prismatic crystal l2 are formed on the surface of the Go board 1.
It was confirmed that an electron 6i7 transfer complex layer 13 was formed (as shown in FIG. 1(A)). Here, the acicular crystals 11 were mainly formed in an orderly manner on the substrate 1, but the prismatic crystals 12 were mainly formed on the acicular crystals 11, and their arrangement. The slope etc. were random. Note that the acetonitrile used was purified and subjected to N2 bulb ringing. ■Next, this substrate 1 was left standing in 40 ml of acetonitrile at a cleaning temperature of 20"C for 1 hour (cleaning time).
Soaked. As a result, first, the prismatic crystals 12 were removed, resulting in a state as shown in FIG.
Figure (C) (Illustrated). Here, in the process of (dissolving) and removing the prismatic crystals 12, new acicular crystals grow on the exposed surface of the substrate in the gaps between the acicular crystals 11 using the prismatic crystals 12 dissolved in acetonitrile as a raw material. A uniform and dense charge transfer complex layer l3 was obtained. In addition, it was confirmed by infrared spectroscopy that the charge transfer complex layer 13 was C u-T CN Q. Thereafter, acetonitrile is removed by vacuum drying, and then aluminum is deposited on the complex layer to form an upper electrode, thereby obtaining a memory element. According to the first embodiment, the substrate 1 made of copper is
After being immersed in the NQ/acetonitrile solution, the prismatic crystals 12, which have a higher solubility than the needle crystals 11, are eluted and removed because they are immersed in acetonitrile under predetermined conditions. In addition, prismatic crystals l2 were eluted. During the removal process, the prismatic crystals 12 are dissolved in the acetonitrile, which enters the gaps between the existing needle crystals 11 and another needle crystal grows. This ensures uniformity. A dense charge transfer complex layer l3 can be obtained. Moreover, the charge transfer complex layer 13 obtained in this way
Even if a memory element is manufactured by forming the upper electrode 3 thereon, the upper electrode 3 and the substrate 1 will not be directly electrically connected, and a good V
l characteristics were obtained. FIG. 7 shows a photograph (1000 times magnification) taken by a scanning electron microscope (SEM) showing the particle structure of the charge transfer complex layer formed in Example 1. Figure 5 mentioned above! From FIG. 6 (conventional) and FIG. 7, it was confirmed that the surface of the complex layer thin film according to the present invention was much more uniform and dense than the conventional one. Furthermore, FIG. 4 shows the V! of the above memory element. Show characteristics. [Example 2] First, a substrate was treated in the same manner as in Example 1, and then the substrate was immersed in a TCNQ/acetanilyl solution for about 30 to 40 seconds. Subsequently, the substrate was immersed in 40 ml of acetonitrile at 70'C for several minutes in a stationary state to remove the prismatic crystals and form a charge transfer complex layer. Thereafter, vacuum drying, formation of an upper electrode, etc. were performed in the same manner as in Example 1, to manufacture a memory element. According to Example 2, a more uniform and dense thin film was obtained compared to Example 1. FIG. 8 shows a scanning electron microscope [1'! (SEM) photograph (1000x) is shown. Example 3 First, a plurality of striped lower n-electrodes made of copper were formed on one surface of a substrate made of glass. Next, a cell transfer complex layer was formed on this lower electrode by the method described in the above example. Next, a plurality of upper electrodes made of aluminum were formed to intersect with the lower electrode, thereby manufacturing a plurality of memory elements. According to Example 3, a uniform and dense charge transfer complex layer was obtained as in Example 1, and exhibited good VI characteristics. In addition to Examples 1 to 3 above, experiments were also conducted for Examples 4 to 9 under the conditions shown in Table 1 below in the same manner as Example 1, and all results were reproducible and stable. Sample obtained. Table 1 [Effects of the Invention] As detailed above, according to the present invention, uniform, dense, and good IV characteristics can be obtained. It is possible to provide a method for forming a charge transfer complex layer that exhibits device-to-device reproducibility, maintains a constant voltage across the complex layer, and avoids conduction between the upper electrode and the substrate.

[Brief explanation of drawings]

Figures 1 (A) to (C) are explanatory diagrams showing the method of forming a charge transfer complex layer of the present invention in the order of steps, Figure 2 is a sectional view of a conventional memory element, and Figure 3 is a VIR characteristic of this memory element. Figure, 4th
The figure shows the VIQ characteristic diagram of the memory element according to the present invention, and FIGS. 5 and 6 show the particle structure of the conventional charge transfer complex layer, respectively.
7 and 8 are SEM photographs of the particle structure of the charge transfer complex layer according to the present invention, respectively. DESCRIPTION OF SYMBOLS 1... Substrate, 3... Upper electrode, 1l... Needle crystal, l2... Prismatic crystal, l3... Charge transfer complex layer. Figure 1 Applicant's agent Patent attorney Takehiko Suzue Figure 2 '\h4 Figure 5 Figure 6

Claims (2)

[Claims] (1) A solution of the electron acceptor composition dissolved in a solvent is brought into contact with the base material of the electron donor composition to form a crystalline layer of the charge transfer complex compound on the main surface of the base material. 1st
A method for forming a charge transfer complex layer, comprising the steps of: and a second step of treating the crystal layer by bringing a solvent into contact with the crystal layer. (2) The first step of forming a charge transfer complex compound in the first step
A composite crystal layer of the crystal and the second crystal is formed on the base material surface, and the second crystal is dissolved in the solvent in the second step to form a charge transfer complex crystal consisting only of the first crystal. The method for forming a charge transfer complex layer according to claim 1, wherein the layer is formed on the surface of the substrate.