WO2011061111A2

WO2011061111A2 - Method for producing silver-containing structures, products comprising silver-containing structures and use of the same

Info

Publication number: WO2011061111A2
Application number: PCT/EP2010/067272
Authority: WO
Inventors: Volker Arning; Jürgen STEIGER
Original assignee: Evonik Degussa Gmbh
Priority date: 2009-11-19
Filing date: 2010-11-11
Publication date: 2011-05-26
Also published as: DE102009053943A1; TW201132794A; WO2011061111A3

Abstract

The present invention relates to a method for producing a silver-containing structure of at least one chemical silver compound, comprising the steps: a) providing a substrate, b) applying a composition containing the chemical silver compound on the substrate, c) optionally drying the substrate coated with the composition, and d) converting at least a part of the composition containing the chemical silver compound on the substrate into a silver-containing structure, wherein the chemical silver compound is silver lactate and the conversion is carried out by i) exposing the part of the silver lactate-containing composition, which is to be converted, on the substrate to a radiation selected from an electromagnetic radiation and an electron radiation and ii) supplying thermal energy to the entire coated substrate. The invention further relates to electric and electronic products comprising said silver-containing structures and to the use of said silver-containing structures.

Description

Process for the production of silver-containing structures, the silver-containing structures and their use

The present invention relates to processes for producing silver-containing structures, electrical and electronic products comprising at least one producible silver-containing structure according to the method and the use of the

according to the invention can be generated silver-containing structures.

Printing technology is an interesting and efficient way to fabricate electronic structures, particularly circuits, by enabling easy and efficient production of a wide variety of structures. In this respect, there is a great interest in printing processes for the production of electronic structures. For the

Production of the respective structures, in particular of the switching elements, and to achieve the respective desired properties, electrically functional printing inks are required for the production of printed electronics.

In addition to the insulators and the active semiconducting material systems, an essential class of electronic structures is the conductor. Although the function of the conductivity can be realized in principle by carbon black or graphite systems or electrically conductive polymers (for example PEDOTPSS or polyaniline), the

However, the conductivity of these structures is far from sufficient for many applications.

Therefore, metallic structures are preferably used in applications in which a low electrical resistance is achieved or structures with a high level are achieved

Conductivity should be achieved. Particularly preferably, the metallic structures are made of copper or silver.

Since the surface of printed systems is very large due to the thin layers, surface reactions (such as oxidation) play an important role. Silver oxide is very conductive compared to other oxides such as CuO or Al2O3 and affects the conductivity of a silver layer correspondingly less. For this Reason silver systems are particularly well suited for printed circuit traces, as they maintain the high conductivity even in the case of a surface oxidation of the silver structure.

In many applications, e.g. In the case of RFID antennas or solar cell electrodes, silver pastes containing silver particles are used to produce silver-containing structures. However, these systems are not as conductive due to the particle-particle resistors (only about 1/10 of the volume conductivity of elemental silver), on the other hand, the systems are too thick and too rough for use in many due to the micrometer-sized particles electrical elements, in particular

Transistors, diodes and memories.

In principle, nanoparticular systems can be used instead to produce thin conductive layers. However, the problem of particle-particle resistances persists. The preparation of the silver-containing nanoparticles and in particular their stabilization in solution continue to be extremely complicated.

An alternative should therefore be chemical silver compounds (compounds of covalent nature and salts), since the layers produced from them should show at least similar, if not better, properties than nanoparticle systems, and the preparation of the corresponding printing inks is much simpler and easier to stabilize.

However, not all silver salts or silver compounds are equally suitable for the production of electronic structures, as for example the

Film forming properties play an important role in the expression of a closed layer.

For example, K.F. Teng and R.W. Vest in IEEE Transactions on Components, Hybrids, and Manufacturing Technology, Vol. 1 1, no. 3, 1988, the generation

metallic structures by the printing of silver neodecanoate solutions, the thermally converted to silver. The effect of temperature in this thermal conversion is further studied by AL Dearden et al., Macromol. Rapid Commun. 2005, 26, 315-318. Although conductive layers are produced for the

However, conversion times required are too long (50 or at least 5

Minutes) in order to be able to be realized in conventional printing systems without delaying the overall process. Furthermore, the achievable conductivities are in many cases not sufficient.

Describe a silver-trifluoroacetate-based organometallic ink

Kaydanova et al. in Conference Paper NREL / CP-520-33594. Curtis et al.

in NREL / CP-520-31020 describe inks containing i.a. Silver hexafluoroacetylacetonate-1, 5-cyclooctadiene. However, these inks do not lead to

satisfactory results.

The Materials Science and Engineering B 1 17 (2005), 1 1 -16 describes a process using silver salts in combination with amines. For the structured production of silver tracks

On surfaces, an amine-containing silver complex is first brought to the surface and then irradiated with UV light. Subsequently, however, the layer must be used to produce elemental silver with reducing agents such as hydrazine or

Sodium borohydride are reacted. The disadvantage here is that thus very reactive and dangerous substances are used. Furthermore, the resulting layers are not yet of sufficient conductivity.

Another way to synthesize silver-containing layers is taught by Bidoki et al., J. Mikromech. Microeng. 17 (2007), 967-974, describe the use of silver salt solutions based on silver acetate, lactate, nitrate, carbonate, - chloride or salicylate, which after being applied to a surface with a

Allow reducing agent to convert. As already mentioned above, however, the use of reducing agents is disadvantageous. JP 10-312715 A finally teaches the preparation of silver structures from organic or inorganic silver compounds via irradiation, preferably UV radiation. As usable organic silver compounds, silver acetate, silver lactate, silver oxalate, silver citrate, silver acrylate, silver tartrate, silver glutamate, silver alginate and silver gluconate are mentioned. As the inorganic silver compound, silver nitrate is mentioned. However, the resulting structures are crater-shaped and can not be used for purposes requiring fine structures. Furthermore, the resulting conductivity of the structures described herein is unsatisfactory.

It is thus the object of the present invention to provide a process based on chemical silver compounds, which reproducibly produces even very fine silver structures with particularly high conductivity via a process which can be integrated in conventional printing plants (in particular with short conversion times for the conversion of the soluble silver compounds into silver) can.

This object is achieved by the method mentioned in the main claim for producing a silver-containing structure of at least one

chemical silver compound comprising the steps of a) providing a substrate, b) applying a composition containing the chemical silver compound to the substrate, c) optionally drying the composition coated substrate, and d) converting at least a portion of the composition containing the chemical silver compound the substrate into a silver-containing structure characterized in that the chemical silver compound is silver lactate and the conversion by i) irradiating the portion of the silver lactate-containing composition to be converted on the substrate by irradiation with radiation

selected from electromagnetic radiation and electron radiation and ii)

Applying thermal energy to the entire coated substrate takes place.

In the context of the present invention, a silver-containing "structure" is any two-dimensional one that can be produced on the substrate by a coating process, ie essentially (ie neglecting the thickness of the coating produced) silver-containing design (in particular planar partial coatings of the substrate and / or substantially of several linear partial structures

composite interconnects) to understand. A "silver-containing" structure is to be understood as a structure that comprises elementary silver after conversion.

The silver-containing structure is preferably a pure silver structure. These structures have the advantage that they can be used to achieve particularly good conductivities. Pure silver structures can be achieved by containing the composition containing the chemical silver compound as the only precursor compound of a conductor silver lactate.

The substrate used in the method according to the invention is preferably a substrate consisting of glass, silicon, silicon dioxide, a metal or transition metal oxide, a metal or a polymeric material, in particular PI or PET. In this case, the silver-containing structure can be applied both directly to the surface of the substrate and also be applied to the substrate itself at least partially coated conductor, semiconductor and / or insulator layers.

The substrate may or may not be pretreated. However, to ensure optimal wetting of the substrate, the substrate should be left in front of the substrate

Application of the composition by, for example, a corona process or a chemical process (in particular by applying a suitably suitable primer) are pretreated.

Very good conductivities can be achieved when the

Composition comprising the chemical silver compound from 10 to 30 wt .-% silver lactate, 70 - 90 wt .-% solvent and 0 - 1 wt .-% of a surfactant.

Surprisingly, it was also found that layers of heated solutions of silver lactate showed particularly good conductivities. One or more solvents may be used in the composition, ie the composition may contain both a solvent or a mixture of different solvents. Aprotic and weakly protic solvents, ie those selected from the group of aprotic nonpolar solvents, ie alkanes, substituted alkanes, alkenes, alkynes, aromatics with or without aliphatic or aromatic substituents, halogenated hydrocarbons, are preferably usable for the process according to the invention in the formulation. Tetramethylsilane, the group of aprotic polar solvents, ie the ethers, aromatic ethers, substituted ethers, esters or acid anhydrides, ketones, tertiary amines, nitromethane, DMF (dimethylformamide), DMSO (dimethylsulfoxide) or propylene carbonate and the weak protic solvents, ie the alcohols , the primary and secondary amines and formamide, as well as water. Particularly preferably usable solvents are water, alcohols and toluene, xylene, anisole, mesitylene, n-hexane, n-heptane, tris (3,6-dioxaheptyl) -amine (TDA), 2-aminomethyltetrahydrofuran, phenetole, 4-methylanisole, 3-Methylanisole, methyl benzoate, N-methyl-2-pyrrolidone (NMP), tetralin, ethyl benzoate and diethyl ether. Very particularly preferred solvents are water, methanol, ethanol, isopropanol, tetrahydrofurfuryl alcohol, tert-butanol and toluene, and mixtures thereof.

Preferred surfactants which can be used to achieve improved wetting of the surface are, for example, under the trade names ^Tego® Wet 250, ^Tego® Wet 270, ^Tego® Wet 505, ^Tego® Wet 260, ^Tego® Wet 280, ^Tego® Wet 510, ^Tego® Wet 265, ^Tego® Wet 500, ^Tego® Wet KL 245 (all from Evonik Goldschmidt GmbH) and BYK 340, BYK 345, BYK 347 or BYK 348 (all cited from Byk Additives, Wesel, Germany). A product available under the trade Tego ^® WET 505 alcohol alkoxylate of Evonik Goldschmidt GmbH, Essen, Germany is very particularly preferably used.

The application of the composition is particularly advantageous with a

Coating process selected from printing processes (in particular flexographic / gravure printing, inkjet printing, offset printing, digital offset printing and screen printing),

Spray method, spin-coating method, dipping method ("Dip-coating") and methods selected from meniscus coating, slit coating, slot die coating, and curtain coating.

After application and before conversion, the coated substrate may continue to be dried. Essentially, the solvent is removed without the silver lactate already being converted to elemental silver. Corresponding measures and conditions for this are known to the person skilled in the art. Typically, the drying temperatures do not exceed 100 ° C.

The conversion of the silver lactate is carried out in the present case by i) irradiating the part of the silver lactate-containing composition to be converted on the substrate by irradiation with radiation selected from electromagnetic radiation and electron radiation and ii) supplying thermal energy.

In principle, the supply of thermal energy can take place before, during or after the irradiation. However, particularly good results are achieved when the thermal energy is applied after the irradiation of the part of the silver lactate-containing composition which is to be converted.

The irradiation of the part of the silver lactate-containing to be converted

Composition is made with radiation selected from electromagnetic

Radiation, preferably UV radiation, X-ray or gamma radiation, and

Electron beams. Very particular preference is UV radiation. This can preferably be irradiated by using a mercury vapor lamp.

The irradiation dose should be at least 3 J / cm ² to achieve very good results. This can be achieved, for example, when using a commercial 133W / cm lamp in 20 seconds. Very particularly fine and thus preferred structures, which have the advantage of being particularly well suited for fine printed conductors, can be produced by irradiating the at least one part of the composition comprising the chemical silver compound by a mask which predetermines a corresponding structure. For structures with thicknesses of at least one micrometer, this is preferably done in a direct exposure process in which the mask itself

located directly in the beam path between the radiation source and the coated substrate. To produce finer structures, preference can be given to using reduction optics, in particular lens systems or mirror optics, with which a reduced image of the mask can be produced on the coated surface. Corresponding devices and methods for this are known in the art and are often called photolithography.

The supply of thermal energy may be carried out by the methods known to those skilled in the art, e.g. using hot air, a hot plate, IR radiation or a

Microwave treatment, done. In this case, the finally achievable after a previous irradiation conductivity is not dependent on the temperature that is used for the conversion. However, the higher the temperature used, the faster the achievement of the finally achievable conductivity. In order to reach the final achievable conductivity within a short time (maximum 10 minutes supply of thermal energy), the coated substrate should be heated to at least 160 ° C.

In addition to the above-mentioned overcome disadvantages, the method according to the invention has the further advantage that in the event that only a part of the composition containing the chemical silver compound on the substrate to be converted into a silver-containing structure and therefore only this part was irradiated, the unirradiated part can be easily removed by washing with suitable solvents. In principle, this is not necessary, since the non-converted silver lactate having partial layer on the surface does not conduct sufficiently to act in electronic applications very disturbing. However, to achieve particularly good tracks for electronic applications may be preferred unconverted silver lactate on the surface of the substrate with suitable solvents such as water or the aforementioned organic solvents

be washed off. Particular preference is given to using water as the solvent.

The present invention furthermore relates to the electrical or electronic products obtainable by the process according to the invention which have a substrate and at least one silver structure applied by the process according to the invention. As already stated above, such a substrate is preferably a substrate consisting of glass, silicon, silicon dioxide, a metal or transition metal oxide, a metal or a polymeric material, in particular PI or PET. In this case, the silver-containing structure can be applied both directly to the surface of the substrate and also be applied to the substrate itself at least partially coated conductor, semiconductor and / or insulator layers. Of course, the electrical or electronic product does not have to have the silver-containing structure as the last-applied topmost coating, but after the application of the silver-containing structure it may also be at least partially coated with at least one conductor, semiconductor and / or insulator layer.

The present invention furthermore relates to the use of silver-containing structures produced by the process according to the invention for producing electronic components, in particular RFID tags, transistors, diodes, memories, displays and sensors.

The following examples illustrate the subject matter of the present invention in more detail without being self-limiting. Examples

example 1

Consistently concentrated 15% silver salt solutions (silver decanoate in xylene, silver lactate in water) are spin-coated onto a glass substrate and converted to the conditions given in the table below to give the indicated conductivities.

In contrast to corresponding silver nucleodecanoate solutions, silver lactate solutions can thus be converted by a combination of UV radiation and subsequent thermal energy into conductive structures with particularly high conductivities. It is also interesting for the application that the silver lactate is not or only slightly conductive after thermal treatment without prior UV treatment.

Example 2

Silver lactate was synthesized by the addition of silver oxide (Riedl de Häen, Seelze, Germany) to dissolved lactic acid (Sigma Aldrich, Seelze, Germany) in water. Unreacted silver oxide was removed by filtering. The water was evaporated and the silver lactate dried at 35 ° C under reduced pressure.

A 17% strength by weight aqueous silver lactate solution at 35 ° C. was prepared from the substance obtained. The surface energy of the solution was determined by adding 1 part per thousand of a surfactant (Tego Wet 505, Evonik Goldschmidt GmbH, Essen, Germany).

Germany) in order to achieve a better wetting of the substrates.

Before spin coating, the solution was filtered through a 0.45 μm hydrophilic PVDF filter (Millipore Millex HV PVDF, Schwalbach, Germany).

Spin coating was performed with the following parameters: 1) acceleration to 750 rpm within 2 s; 2) spinning at 750 rpm for 20 s; 3) decelerate to 0 rpm within 5 s. The layer thickness was carried out after thermal annealing with a surface profilometer (KLA Tencor, San Jose / CA, USA, P15). Layer thicknesses of 100-120 nm are achieved.

Irradiation with UV light was carried out with a commercial mercury-vapor lamp (133 W / cm) in a UV band system (UV-Tech Silberberger + Co, Stuttgart, Model 6019). Cans between 0 and 15 J / cm ^{2 were} used.

The UV dose was with a UV puck from EIT, Pfungstadt, under

Consideration of UVA, UVB and UVC light (230-390nm wavelength) determined. Subsequently, the films were baked on a precision hot plate (Präzitherm PZ28-2, Harry Gestigkeit, Dusseldorf) at various set temperatures between 120 and 220 ° C, in particular 140, 160 and 180 ° C.

The real-time conductivity measurements were taken with a four-point measuring head

(Model SP4-62-085-TBY, Sel-Tek, Motherwell, UK)

Hot plate was installed and connected to a SourceMeter (Model 2400, Keithley Instruments, Cleveland, Ohio, USA).

Results:

The conductivity of the resulting silver lactate films at a constant temperature for the supply of thermal energy is dependent on the UV dose and the irradiation time. Optimum results, that is, sufficient conductivities within a short time, can be achieved at 160 ° C at radiation doses of at least 3 J / cm ² . See Figure 1.

At constant UV dose (15 J / cm ² ) optimal conductivities can be achieved within a short enough time by temperatures of at least 160 ° C. See Figure 2.

With appropriate choice of temperature and UV strength, the process can thus be integrated into conventional printing processes.

Example 3

Organic field-effect transistors were constructed by coating silver lactate on N-doped silicon wafers, exposing the required structures through a UV belt system using a mask, and washing the undeveloped areas with water. The conductivity of the structures was according to the

thermal conversion at about 2 ohms / square and the two finger structures

(Source and drain) were electrically isolated.

Poly-3-hexylthiophene (sepiolide P100, BASF, Ludwigshafen) was from 5%

Formed chloroform solution and measured in yellow space. The channel length of the Transitors was 170 μηη. The width-to-length ratio was 150 μηη. See Figure 3.

By selective exposure through a photomask source-drain structures were generated from which thin-film transistors could be constructed.

Claims

claims:

1 . A method of producing a silver-containing structure from at least one chemical silver compound, comprising the steps

a) providing a substrate,

b) applying a composition containing the chemical

Silver compound on the substrate,

c) optionally drying the substrate coated with the composition; and d) converting at least a portion of the composition containing the chemical silver compound on the substrate into a silver-containing structure characterized in that

the chemical silver compound is silver lactate and

i) irradiating the part of the silver lactate-containing composition to be converted on the substrate by irradiation with radiation selected from electromagnetic radiation and electron radiation and ii) supplying thermal energy to the entire coated substrate.

2. The method according to claim 1,

characterized in that

the composition containing the chemical silver compound as the only precursor compound of a conductor silver lactate.

3. The method according to claim 2,

characterized in that

the composition comprising the chemical silver compound consists of 10 to 30% by weight of silver lactate, 70 to 90% by weight of solvent and 0 to 1% by weight of a surfactant.

4. The method according to any one of the preceding claims,

characterized in that the application of the composition containing the chemical

Silver compound selected by a coating method

Printing process, spraying method, spin coating method, dipping method and method selected from Meniscus Coating, Slit Coating, Slot Die Coating and Curtain Coating takes place.

5. Method according to one of the preceding claims,

characterized in that

the feeding of thermal energy takes place after the irradiation of the part of the silver lactate-containing composition which is to be converted.

6. The method according to any one of the preceding claims,

characterized in that

irradiation with radiation selected from UV radiation, X-ray or gamma radiation takes place.

7. The method according to any one of the preceding claims,

characterized in that

the irradiation of the at least one part of the composition containing the chemical silver compound is effected by a mask which predetermines a corresponding structure.

8. The method according to any one of the preceding claims,

characterized in that

unconverted silver lactate on the surface of the substrate is washed off with a solvent selected from the group of aprotic and weak protic solvents, the group of aprotic polar solvents, the group of weak protic solvents and water.

9. An electrical or electronic product comprising a substrate and at least one silver-containing structure applied by a method according to the preceding claims.

10. Use of at least one producible by a process according to claims 1 to 8 silver-containing structure for the production of electronic components.