EP0044326A1 - Conductane transparent laminate, method for the preparation thereof and utilisation thereof - Google Patents

Abstract

This proposed conductance laminate contains a "rare earth" (it is an oxide of a rare earth metal). In order to ensure that this laminate has sufficient free electron conductance, this "rare earth" is usually combined with the oxide of another element such as tin, germanium or cadmium. In which case which of the two combined elements provides the host network and which other element constitutes the auxiliary does not matter. In order to prepare this conductive laminate, it is recommended to use dissolved organometallic compounds at the start and, in this case, the rare earth metal will be inserted in a compound of general formula CpmLnR3-m or LnR3.Lm ( Cp = cyclopentadiene; Ln = ele from the third secondary group; R = alkyl, aryl, allyl, amine, alkoxide, carboxylate, cyano, Cl, Br, I, organosilyl, organogermyle, organostannyl; L = ether, tetrahydrofuran, diglyme, amine , organophosphine; 1 (Alpha) m (Alpha) 3). Such a conductance laminate is particularly used as an electrode (9, 11) in passive electro-optical displays, such as for example liquid crystal indicators.

Description

Transparent conductive layer, process for its production and its use

The invention relates to a conductive layer according to the preamble of claim 1 and also relates to manufacturing techniques and uses for this conductor. Such an In ₂ O ₃ : Sn electrode, produced from volatile organometallic compounds in a CVD process, is described in "Thin Solid Films" 29 (1975) 155.

Transparent electrode coatings usually consist of a doped indium or tin oxide. These materials enable layers with a thickness in the range of a few 10 ² nm transmittances> 80% and

Surface resistance values <50 Ω / ♢ and thus generally meet the requirements placed on them. In some cases, however, the electrode is required to have properties which - within the framework of the previously known preparation techniques - cannot be achieved with materials based on indium oxide or tin oxide. For example, the heating layer on the windshield of a vehicle should have a sheet resistance <10 Ω / ♢, and in the case of highly multiplexable liquid crystal displays, thin-film electrodes are required which have a sheet resistance value of around 50 Ω / ♢ even with thicknesses of a few 10 nm. In addition, the previously developed manufacturing processes for indium oxide or tin oxide coatings - chemical vapor deposition or sputtering with subsequent etching out of the electrode structure - are quite complex are and also require such high process temperatures that one is often dependent on expensive substrates. This disadvantage is particularly important when it comes to coating inexpensive mass-produced items such as window panes or electro-optical displays in a manner suitable for series production. In addition, it is already foreseeable today that indium and tin will become considerably more expensive in the coming years, as their consumption is constantly increasing and supplies are limited.

Based on this situation, the object of the invention is to provide a guiding layer that absorbs little visible light, still conducts well even if its thickness is small compared to the wavelengths of the light, and also enables an electrode to be produced without an etching step gets along and the substrate is not thermally stressed too much. This object is achieved by a conductive layer with the features of claim 1. The soils contained in a conductive layer according to the invention are, by definition, oxides of the elements of the third subgroup, i.e. scandium, yttrium, as well as lanthanum and the elements of the lanthanide series (cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thullium , Ytterbium, lutetium).

The invention is based on the observation that the transition elements proposed here also have semiconductor properties in their oxides and can thereby achieve considerable conductivity values. The conduction mechanism of such semiconductors is probably the same as that of an indium oxide based semiconductor: An electronic third-party line arises from defects in the lattice, i.e. essentially from missing oxygen atoms or from introduced foreign atoms in which the higher-value ones act as donors and the atoms with less value act as acceptors. In their pure state, rare earth metals and their oxides are very expensive substances, mainly because they are always present as mixtures in nature and are very difficult to separate. Fortunately, such a separation is not necessary for the proposed control layer, since, as has been found, the individual rare earths practically do not differ with regard to the criteria relevant here. It has also been shown that the rare earth metals or their mixtures can easily be converted into organometallic compounds which - depending on the vapor pressure and solubility - allow various application techniques: in addition to the CVD process, also immersion, spraying and centrifugal techniques and the so-called "Roller coating", with which thin electrodes can be printed in their final contours. Depending on the type of mixture used, the thermal oxidation of the organometallic compounds can be carried out at temperatures between 50 ° C. and 500 ° C. and in periods between 10 minutes and 5 hours. The result is an attractive price alternative to the previously used transparent electrode materials, the cost advantage of which will have an even greater impact in the future, as the rare earth metals, contrary to their name, are not uncommon (the content of Sc, Y, La , Ce, Nd, Yb in the solid earth crust is 10 ^-2 to 10 ^-3 %; Pr, Sm, Eu, Gd, Tb, Dy, Ho, Er, Lu occur about as frequently as Sn, namely 10 ^-3 to 10%; the proportion of Tm is 10 -4 to 10 ^-5 %; In has a frequency between

10 ^-5 and 10 ^-6 %).

In the case of the proposed conductive layer, the conduction is normally brought about by doping with an element of a different value. It is basically irrelevant whether the rare earth metals are part of the regular host lattice or act as an impurity. The conditions are most favorable when the rare earths are combined with tin oxide. Good results can also be obtained if an oxide of germanium or cadmium is used instead of tin oxide. It may even be sufficient to assemble the conductive layer exclusively from rare earths; because individual rare earth metals (cerium, europium and ytterbium) can have different values. For this reason, it should in principle also be possible to form the conductive layer from the oxide of a single rare earth metal present in different valence states.

Further advantageous refinements and developments of the invention, in particular convenient manufacturing processes and applications in which the advantages of the proposed conductive layer are particularly effective, are the subject of additional claims.

The proposed solution will now be explained in more detail using several examples with reference to the attached figure. The figure shows a schematically held side section of a reflective liquid crystal display with a seven-segment number display. The display contains in detail a front linear polarizer 1, a front carrier plate 2, a rear carrier plate 3, a rear linear polarizer 4 crossed to the front and a reflector 6. The two plates are tightly connected to one another by a frame 7. The chamber bounded by the frame and the two plates is filled with a liquid crystal layer 8. The plates 2, 3 each have on their mutually facing surfaces conductive coatings (front electrode from separately controllable segment electrodes 9, continuous rear electrode 11) and orientation layers 12, 13. The liquid crystal cell works on the principle of the so-called "rotary cell", which is described in detail in the DE-AS 21 58 563 is described.

The electrodes are designed according to the requirements of the individual case. A large number of material combinations and process variants are available within the scope of the invention. This diversity will be illustrated below with the help of a few examples.

Usable guiding layers result if one proceeds as follows in each of these examples:

The two compounds are dissolved in 50 ml solvent under an inert gas atmosphere (argon). 2 g of the dominant constituent are dissolved, the correspondingly smaller amount of the doping constituent. Then glass plates are immersed in the solution under argon. The plates are then dried in air at 130 ° C. and then heated to 400 ° C. with the simultaneous action of water vapor and oxygen.

The invention is not limited to the exemplary embodiments described. So it is not always necessary to start from substances in the form of dissolved organometallic compounds; CVD processes are also conceivable, for example, in which the material to be evaporated is in a solid or gaseous state. In addition, the proposed conductive layers are not only used as thin-film electrodes of liquid crystal displays, but are also suitable wherever an economically producible transparent electrode is required.

Claims

Claims 1. Transparent conductive layer, containing an oxide of an element from the third group of the periodic table, so that the oxide is a rare earth. 2. The conductive layer according to claim 1, which contains various rare earths. 3. guiding layer according to claim 1 or 2, so that it also contains an oxide of a metal from the second or fourth group of the periodic table. 4. conductive layer according to claim 3, that the metal is cadmium, tin or germanium. 5. conductive layer according to claim 1 or 2, d a d u r c h g ek e nn z e i c hn e t that they also Contains aluminum oxide, gallium oxide or indium oxide. 6. A process for producing a conductive layer according to one of claims 1 to 5, since you draw rchgeke nn that first of all at least of the rare earth metal and preferably of all metals which are present in the finished conductive layer as oxides, an organometallic compound, the Compound of rare earth the general formula Cp ₃ Ln, Cp ₂ LnR ¹ , CpLnR ¹ R ² , LnR ¹ R ² R ³ or LnR ¹ R ² R ^3. L _m has (1 ≤ m ≤ 3; Cp = C ₅ H ₅ ; Ln = Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu; R ¹ , R ² , R ³ = alkyl, Aryl, allyl, amine, alkoxide, carboxylate, cyano, Cl, Br, J, organosilyl, organogermyl, organostannyl, where the radicals R ¹ , R ² , R ^{3 can be the} same or different; L = tetrahydrofuran, ether, diglyme, amine, organophosphine), that one then dissolves the organometallic compound (s) in an organic solvent and finally applies the solution thus obtained to a substrate and by heating the expels organic components of the solution and converts the metal (s) into its oxide (s). 7. The method according to claim 6, dadurchgeke nn zeic hn et that when an oxide of aluminum, gallium, germanium, indium or cadmium is also present in the finished conductive layer and this oxide is formed from another compound, this compound has the general formula A1R ¹ R ² R ³ , GaR ¹ R ² R ³ , GeR ¹ R ² R ³ R ⁴ , InR ¹ R ² R ³ or CdR ¹ R ² , with R ¹ , R ² , R ³ , R ⁴ = Alkyl, aryl, alkoxide, allyl, amine, carboxylate, CN, where the radicals R ¹ , R ² , R ³ , R ^{4 can be the} same or different. 8. Use of a conductive layer according to one of claims 1 to 5 as an electrode of a passive electro-optical display, in particular a liquid crystal display.