JP4796741B2 - Method for forming a layer containing metal, silicon, germanium and oxygen on a surface - Google Patents

Description

The present invention relates to a method of forming a layer containing metal or silicon or germanium and oxygen on a surface.

Optical devices such as displays and backlights for liquid crystal displays with organic electroluminescent diodes (OLEDs) have been greatly developed. An important advantage of OLEDs is the luminous efficiency, which is often measured as the external quantum efficiency , expressed in candelas per amp, and / or the luminous efficiency, expressed in lumens per watt. Is done. The luminous efficiency of the OLED is particularly important because it determines the power consumption by the OLED during light emission and thereby determines the battery life of the portable device.

The general structure of OLED (shown in Figure 1) is a transparent conductor, such as inner surfaces of indium tin oxide glass substrate (1) (2) is covered by the charge injected onto the coating (3) an organic and / or organometallic chemical layer that performs charge transport and / or light emission (4), and then one or more layers (typically an aluminum layer ( made of metal is a very positive capped (5)) in 6).

A very thin dielectric layer, such as silicon dioxide , adjacent to the indium tin oxide layer (eg, less than 1 nm thick ) accelerates charge injection from the indium tin oxide and increases the luminous efficiency of the device. However, in particular, a glass substrate used in manufacturing the OLED, for example, it is very difficult to uniformly sedimentary thin dielectric layer over a large area, such as 400 × 400 mm ^2. Any attempt such deposited by conventional methods such as sputtering or electron beam evaporation, while some areas that will be covered by a thick dielectric layer than 1nm, the other areas of less than 1nm thick dielectric layer I know I will have it . This change in the thickness of the dielectric layer causes a change in voltage required for light emission, and the voltage increases as the thickness of the dielectric layer increases. As the voltage increases, the luminous efficiency decreases, thus reducing the battery life of portable devices using OLEDs. Since the thickness of the dielectric layer is small, a slight change such as 0.2 nm greatly changes the performance of the OLED.

According to a first aspect of the present invention there is provided a method of forming a layer comprising silicon (or germanium) and oxygen on a surface as defined in claims 1-7. According to a second aspect of the present invention there is provided an electroluminescent device incorporating a layer as claimed in claims 8 and 9.
Embodiments of the present invention will be described below with reference to the accompanying schematic drawings.

The present invention can provide a very thin uniform dielectric material layer on the surface of a transparent conductive metal oxide such as indium tin oxide. The thickness of the dielectric material layer is less than 3 nm, preferably less than 2 nm, very preferably less than 1 nm. With the present invention, the luminous efficiency was able to demonstrate that increased from 1.5 to 2.3lm / W.

This new technology involves the use of organic materials containing silicon or germanium , such as organosilane materials that are readily available for general use as adhesion promoters. Typical organosilane adhesion promoter, 3-aminopropyl - a triethoxysilane, is supplied from the de Yupon Corporation under the tradename V M 651. Other materials such as hexamethyldisiloxane can be used as an alternative.

The surface of indium tin oxide is first exposed to a liquid or gaseous organosilane adhesion promoter, which is a traditional use as an adhesion promoter. This results in a very thin and uniform layer of organosilane that bonds to the ITO and glass surfaces via silicon-oxygen bonds . The organosilane layer also contains organic groups. In the case of VM651, this group is a 3-aminopropyl group. A surface having such a layer is often referred to as a “priming”.

"Subbing" substrate is subsequently processed, i.e. treated with an oxidizing medium such as a glow discharge comprising oxygen plasma or oxygen radicals in the absence of an organic silane. The oxidation medium adds oxygen to this part of the adsorbed layer to be oxidized and oxidizes, so in this example, the organic part is oxidized to water and volatile species such as carbon dioxide, and the surface of ITO is coated with silicon dioxide . It would be to leave a thin layer. This technique therefore provides an easy means of producing a thin uniform layer of dielectric material. This layer, because it is possible to contain other components such as hydrogen and carbon, silicon oxide layer is not necessarily stoichiometric.

Because of its chemical structure, organosilane adhesion promoters are often described as producing a single layer on a suitable substrate. The present inventors have, it was confirmed that this is not the case necessarily.

An example of a process that describes in more detail is given below, and an example of a cross-sectional view of an apparatus made according to the present invention is shown in FIG. A glass substrate (1) coated with a layer of indium tin oxide (2), which can be purchased from several suppliers such as, for example, US Applied Film or Taiwan Merck Display Technology, It is cleaned and patterned using standard detergents and photolithography processes .

After the final stage of the photolithographic process, i.e., after stripping the photoresist, the substrate is washed in detergent, thoroughly washed with deionized water, dried and calcined at 105 ° C. 30 min. After cooling, the substrate is selected from the group consisting of methanol (95 ml), water (5ml) and 3-aminopropyl - primed by (2000 rpm in 30 seconds) by spin coating at solvent solution consisting of triethoxysilane (3 drops), then with 105 ° C. Store in dry nitrogen atmosphere until needed .

Just before the formation of OLED devices, primed substrate is exposed to an oxygen plasma to form consisting of silicon and oxygen, or a thin electroformed layer (10). As an example, an Emitech K1050X plasma etcher was run at 100 watts for 2 minutes, resulting in acceptable processing. The substrate is then immediately transferred to a vacuum deposition system where, for example, the next layer is continuously deposited. That is, 4,4-bis [N-(1-naphthyl) -N- phenyl - amino] diphenyl (NPD) (3) and tri scan (8-hydroxy - quinolato) aluminum (AlQ) (4), lithium fluoride (5) and aluminum (6) with thicknesses of 50, 50, 1.5 and 150 nm, respectively. For comparison, a similar OLED device was produced that did not have an organic layer and that had an organic silane layer but no organosilane oxidation treatment. External quantum efficiency ( cd / A ) and luminous efficiency (lm / W) were measured . It is shown in Table 1 below.

酸化有機シラン層の利点は、より低い電圧で同じ電荷量を注入でき、よってＯＬＥＤディスプレイ又はバックライトを有するポータブル製品の電池の長寿命化をもたらすより高い発光効率を提供することができることである。

The advantage of oxidized organosilane layer is that it can provide a high luminous efficiency than can inject the same amount of charge at a lower voltage, thus resulting in long battery life of portable products having an OLED display or backlight .

The advantage of other oxidized organic silane layers is that the reproducibility of the OLED device characteristics of a device having this is better than a device having no oxidized organic silane layer. As an example, the current-voltage curves of three devices made without an oxidized organosilane layer are shown in FIG. The curves for three devices with an oxidized organosilane layer are shown in FIG. In both, the structure of the device used to impart this characteristic ITO / NPD / ALQ / LiF / Al were Tsu der.

Despite the device manufactured in exactly the same way in all other respects, the current-voltage curve of the device made with the oxidized organosilane layer shows very little broadening.

The influence of the thickness of the NPD layer (in the range of 50 nm to 250 nm) of the organosilane treated and standard plasma treated ITO / NPD / AlQ / LiF / Al equipment is shown in FIGS.

FIG. 5 shows the relationship between the current density and the voltage accompanying the change in the NPD thickness of the organosilane treatment or standard plasma treatment apparatus. The current decreases as the NPD thickness increases, but the decrease is more pronounced for plasma-only devices. The reduced sensitivity to the NPD thickness shown in the organosilane processing apparatus of FIG. 5 is also reflected in FIG. 6, where the NPD thickness is increased in the standard plasma processing apparatus compared to the organosilane processing apparatus. Accordingly, it is shown that the voltage required for 30 cd / m ² increases more remarkably. This indicates that the organosilane layer improves the efficiency of hole injection. Compared to organosilane processing equipment , the high voltage requirement at large NPD thickness in the case of standard plasma processing equipment is also shown in lower light emission results.

A further comparative example of the organic silane process is provided using the OLED having a host or Ranaru emitting layer doped with iridium dendrimer material. In particular, the light emitting layer, 4,4'-N, N'-dicarbazole - biphenyl (CBP) 20 wt% first generation iridium dendrimer in the host (G1IrDen), or 4,4 ', 4''- tri ( consists N- carbazolyl) either a mixture of 13 wt% G1IrDen in triphenylamine (TCTA) host. The solution of such mixtures are made using chloroform and toluene, respectively, then, the organic silane treatment, or is spun on ITO substrate of a standard plasma treatment. Then, an electron transport layer (2, 2 ', 2''- (1,3,5-phenylene) tris [1-phenyl--1H- Ben's Imida zone Lil] (TPBI) 50 nm and a cathode layer (LiF / Al) is Ru are deposited by thermal evaporation. Figure 7 shows an improvement in lifetime of the organic silane treatment apparatus as compared to standard plasma processing apparatus both CBP and TCTA host material.

In addition to the organic part used in the light-emitting layer of the above-described embodiment, an organosilane layer provided by the method of the invention it is believed to be usable in the polymer light-emitting layer. Such preferred electroluminescent device containing polymer, be ITO / TOS / PFO / Ca / Al ( blue emitter) and ITO / TOS / (PFO + 5 % BT) / Ca / Al ( yellow emitter) , wherein, TOS is processed organosilane layer, PFO is poly [9,9-di - (2-ethylhexyl) fluorenyl-2,7 '] - a di-yl]), BT is poly [(9 , 9-di-n-octylfluorenyl-2,7′-diyl) -co- (1,4-benzo {2,1 ′, 3-thiadazole})].

Suitable organosilanes are carbon-containing compounds having the formula (X) ₃ SiR. Here, X is a hydrolyzable group such as OEt, OMe or Cl, and R is an organic moiety such as an alkyl chain that selectively contains a functional group such as NH ₂ . R must oxidize to a volatile species , so R can include the following elements: C, H, N, O, and S. As is known, organosilanes having this formula can be chemically adsorbed on ITO to form a monolayer bonded by O-Si bonds .

ここで、ｎ＝０、１、２、３であり、Ｒは、アルキル基である。特別な例は、ヘキサメチルジシロキサンを含む。 Depending on the conditions used, but a plurality of layers that could be formed on the surface of the first layer, this is not necessarily a drawback. However, this layer is preferably thinner than 12 monolayers.
Siloxane can also be used. These have the following formula.

Here, n = 0, 1, 2, and 3, and R is an alkyl group. A particular example includes hexamethyldisiloxane.

Is a good dielectric volatile oxides _{(e.g., GeO x, AlO x, TiO} x , etc.) viewed including the element Z to form a remainder of the molecule is oxidized, so long as to form a volatile compound, an organic silane Other compounds are also suitable. The preferred compound will also preferably be chemically or physically adsorbed to the anode surface to form a uniform thin film. As organosilane, organotitanate, known as adhesion promoters capable of forming a thin film on ITO. The nature of the dielectric film produced is clearly one criterion for selecting the desired compound.

Formation of monomolecular layers of an organic silane on ITO are well known, self-assembled coupling techniques generally are well known. There is an example use of organic silane in the manufacture of electroluminescent devices, for example, in U.S. Patent 5677545, in order to form an alignment layer, a polymer having a fixed group is deposited on the ITO. In Japanese Patent 06325345, an organosilane compound is chemically absorbed on the cathode layer, and then a luminescent material is deposited thereon . However, in all these cases, the organosilane compound remains in the device and is therefore a composition different from that of the present invention and has a different purpose.

In the above embodiment, the surface of the dielectric material is formed is substantially transparent conductive anode made of ITO, if desired, tin oxide, indium oxide, zinc oxide or zinc-doped indium oxide other such Materials can be used as an alternative.

In the above embodiment , the glow discharge gas was oxygen . For example, other oxidizing media, such as nitrous oxide supply of oxygen radicals in the plasma may be used as an alternative.

A sectional view of a conventional organic light emitting device is shown. 1 shows a cross-sectional view of an organic light emitting device of the present invention. 3 shows current-voltage characteristics of three conventional organic light emitting devices. 3 shows current-voltage characteristics of three organic light-emitting devices of the present invention. Having different NPD thicknesses, three organic silane treated, and three plasma treated device current - voltage characteristics thereof are shown. Figure 2 shows the voltage, yield and luminous efficiency of organosilane and plasma treated devices with increasing NPD layer thickness. Figure 2 shows the lifetime characteristics of two organosilane treated and two plasma treated devices.

1 glass substrate 2 of indium tin oxide (ITO) layer 3 4, 4-bis [N-(1-naphthyl) -N- phenyl - amino] diphenyl (NPD) layer 4 tri scan (8-hydroxy - quinolato) aluminum ( AlQ) layer 5 lithium fluoride layer 6 aluminum layer thin electroformed layer comprising 10 silicon and oxygen

Claims (4)

A layer containing an oxidized organic silane is formed on the surface of the transparent conductive anode formed on the substrate, and a dielectric layer that promotes injection of holes from the anode to the light emitting layer is formed between the anode and the light emitting layer. A method of manufacturing an electroluminescent device comprising forming between,
a. By exposing the surface of the transparent conductive anode formed on the substrate to a liquid or gas containing organosilane, a monomolecular layer adsorption layer of 11 layers or less is formed on the surface,
b. Separating the surface on which the adsorption layer is formed from the liquid or gas;
c. Converting the adsorption layer to a layer comprising oxidized organosilane by exposing the adsorption layer to an oxidizing medium to form the dielectric layer having a thickness of less than 2 nm;
Here, the organic silane satisfies the general formula (X) ₃ SiR, in which X is a hydrolyzable group, and R is an organic part. The method of claim 1, wherein X comprises OEt, OMe, or Cl. The method according to claim 1 or 2, wherein R is an alkyl group. The method according to claim 1, wherein the oxidation medium comprises a gas containing oxygen radicals generated by glow discharge .

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