WO2006133820A1

WO2006133820A1 - Method for producing anisotropic waveguide structures for transmitting lightwaves

Info

Publication number: WO2006133820A1
Application number: PCT/EP2006/005284
Authority: WO
Inventors: Max Hunziker; Matthias Weber
Original assignee: Atotech Deutschland Gmbh
Priority date: 2005-06-15
Filing date: 2006-06-02
Publication date: 2006-12-21
Also published as: DE102005027676A1

Abstract

A description is given of a method for producing anisotropic waveguides 5 the method comprises the following stages: (i) application of a photo-orientable polymer layer (2) to a substrate (1), (ii) exposure of the coated substrate through a patterned photomask (3) and a linearly polarizing polarizer (4) for orienting and crosslinking the exposed part of the coated substrate, a photo-oriented polymer network being obtained, (iii) removal of the photomask (3), (iv) rotation of the polarizer (4) through l°-180° and whole-area exposure of the coated substrate, (v) application of liquid-crystalline monomers (6) to the exposed layer and heating of the monomers to a temperature above their clearing point, slow cooling of the monomer layer to a temperature below its clearing point for its orientation according to that of the photo-oriented polymer network, and (vi) photo-induced crosslinking of the oriented liquid-crystalline monomer layer (6).

Description

METHOD FOR PRODUCING ANISOTROPIC WAVELINE STRUCTURES FOR TRANSMITTING LIGHT WAVES

The invention relates to a method for the production of anisotropic waveguides for the transmission of light waves.

The direction of light is based on total reflection at the transition between two different optically dense media, which does not absorb the wavelengths of the light to be transported in order to minimize the optical loss. The conductive medium (core) has a higher refractive index than the surrounding medium (cladding). The differences in refractive index between core and cladding define (typically between 0.01-0.1) the appropriate angles of incidence for the fiber optic cable.

The transmission of data by means of fiber-optic cable is mainly used in telecommunications by means of fiber-optic cable (point-to-point connections in various areas such as Submarine, Long Haul, Metro Backbone, Metro Access (BPA Report 762, "OPTICAL BACKPLANES, A Global Market and Technology Review 2000 - 2005 "), where bridges of up to several thousand kilometers are bridged) and optical elements (multiplexers, demultiplexers, etc.) The technologically and physically caused bottleneck in conventional electrical connection technology and the sharp increase in the necessary data transfer rate have resulted Increasing research and development activities in the integration of optical signal network structures on printed circuit boards in combination with electrical connections (hybrid technology) .The successful integration requires the ability to build more complex optical interconnect structures.

Current printed circuit board (PCB) optical waveguides are based on isotropic materials (ie, the refractive index is macroscopic in all) Directions are the same size). In order to generate planar structures, essentially two fundamentally different methods are used:

1. Indirect Processes: Here is used medium hot stamp (Lehmacher, Neyer, Electronic Letters Vol 36, No. 12, 2000, pp. 1052-1053, E. Griese, D. Krabe, E. Strake in "Interconnects in VLSI Design" , Ed H. Grabinski, Kluwer Academics

Publishers, Boston (MA), 2000), Laser Ablation (M. Kowatsch in Optical Assembly and Connection Technology in Electronic Assembly Production ", Ed. W. Scheel, Verlag Dr. Markus A. Detert, Templin / Uckermark, 2002, R. Osella - me, S. Taccheo, G. Cerullo, M. Marangoni, G. Sorbello, D. PoIIi, S. De Sisvestri, P. Laporta, and R. Ramponi, SPIE Photonics Fabrication Europe, Oct. 28-Nov 1, 2002, Bruges (Belgium)), Photolithographic (DeForest, "Photoresist", 1975, p.2,3, US 4,609,252) or Etching Structures (K. Schmieder "Simple Integration Techniques for Printed Circuit Board Optical Waveguides", Photonic 2001, May 17-18, 2001, Electronic Forum), either first the waveguide core and then the cladding is produced or a depression is produced in the cladding, which is then filled with the core material. Disadvantages of these methods are that they require very many process steps, produce rough surfaces, e.g. can not be applied over a large area (heating stamping process), require expensive tools or generate dust (ablation).

2. Direct Methods: The waveguide structures are written directly in a suitable substrate by means of a light, laser or ion beam or generated by irradiation with light through a photomask. These methods are based on the local refractive index change in the treatment area. Known processes are photolocking (US Pat. No. 3,809,732), photo-bleaching (Electronics Lett., 26, 1990, p. 379), photocrosslinking (US Pat. No. 3,809,686), diffusion process (US Pat. No. 5,402,514), laser ablation or ion bombardment (Peter Sträub "The Optoboard Technology ", MQS Nordic Days, August 30-31, 2001. Disadvantages of these methods are the high process time in the "Writing" methods (especially for more complex structures) and the aging of unexposed areas.

Isotropic waveguides have the major disadvantage that the optical loss in curved structures can be very large and thus waveguides with radii of less than a few centimeters no longer effectively direct the light.

Very few materials are symmetrical and spherical and therefore have anisotropy at the microscopic level. On the macroscopic level, this anisotropy is averaged out by a statistical distribution of all orientations in all three spatial directions for gaseous, liquid, and disordered solid materials, and the material exhibits no or only weak anisotropy, while matter with far-reaching order like crystals or Liquid crystals may also be anisotropic in the macroscopic range.

Anisotropic waveguides (US Pat. No. 5,949,943) can be produced from anisotropic materials, two types in principle being distinguished:

1. Waveguide core is made of anisotropic and mantle of isotropic materials (or vice versa core isotropic and mantle of anisotropic materials), the anistropic molecules and thus the refractive index are aligned so that the conditions for wave conduction in the conductor (high refractive index in the Core, lower in the coat) is met.

2. Waveguide core and cladding are made of anisotropic materials, with the anistropic molecules, and thus the refractive index, aligned to meet the conditions for waveguiding in the conductor (high refractive index in the core, lower in the cladding).

To produce anisotropic waveguides, it is necessary to control the orientation of the molecules and thus the anisotropy. Typical methods for controlling the orientation are the stretching of polymers in the heat, the photopolymerization of suitable monomers in an electrical or magnetic Field or brushing a suitable support material onto which liquid crystals (or liquid crystal polymers) are subsequently applied, which then orient themselves to the fine scratches (J. Cognard "Alignment of Nematic Liquid Crystals & Their Mixtures", Mol. Crysta. Liq. Cryst. Supplement Ser. (Gordon & Breach, New York, 1982).) They are frequently used in LCD production Disadvantages of these methods is the low spatial resolution, different orientations on a surface can not be produced or only over many process steps. a continuous spatial change of orientation is not possible.

A high spatial resolution technique is provided by the LPP / LCP technology (US 5,389,698, US 5,602,661). Irradiation of a linearly photopolymerizable polymer (LPP) with linearly polarized light results in a photoreaction between two polymers only between molecules that are parallel to the polarization direction of the incident light. Thereby, the optical anisotropy is transferred into a steric anisotropy of the polymer layer, thus being excellent as an orientation layer for optically anisotropic material (such as liquid crystals). After application of the liquid-crystal monomers, these align according to the orientation layer and can be crosslinked by photolysis. In the resulting, crosslinked liquid crystal layer (LCP), the orientations of the liquid crystals are frozen and thermally stable.

The invention has for its object to provide a method for producing anisotropic waveguide structures and in particular curved anisotropic waveguide structures, preferably with tight curve radii, which has or requires few process steps. Preferably, the method should have the potential for the full-surface generation of the waveguide structures in a Photoly- seschritt.

Furthermore, the method should be able to use materials which have high thermal stability. Moreover, single-mode waveguides with widths of only 10 μm should preferably be realized in a simple manner using the method. be lisiert. The method should continue to be free of dust, which is disadvantageous in the known Abtragungsverfahren. Finally, the process should lead to waveguides with smooth surfaces and also be applicable to non-planar surfaces.

The invention relates to a process for the production of anisotropic waveguides for the transmission of light waves, which comprises the following steps (see FIG.

(i) applying a photo-orientable polymer layer (2) to a substrate (1),

(ii) exposing the coated substrate through a patterned photomask (3) and a linear polarizing polarizer (4) to orient and crosslink the exposed portion of the coated substrate to yield a photopatterned polymer network,

(iii) removing the photomask (3),

(iv) rotating the polarizer (4) by 1 ° -180 ° and exposing the coated substrate over the whole area,

(v) applying liquid crystalline monomers (6) to the exposed layer and heating the monomers to a temperature above their clearing point, slowly cooling the monomer layer to a temperature below its clearing point to its orientation corresponding to that of the photo-oriented polymer network and

(vi) Photo-induced crosslinking of the oriented liquid-crystalline monomer layer (6).

The invention further relates to a process which comprises the following steps (see Figure 2):

(i) applying a photo-orientable polymer layer (2) to a substrate (1), (ii) exposing the coated substrate through a patterned polarizing mask (7) having differently oriented polarizers, the orientation corresponding to the structure to be imaged, for orientation and crosslinking of the photo-orientable polymer layer to yield a photo-oriented polymer network,

(iii) applying liquid crystalline monomers (6) to the exposed layer and heating the monomers to a temperature above their clearing point, slowly cooling the monomer layer to a temperature below its clearing point to its orientation corresponding to that of the photo-oriented polymer network and

(iv) photo-induced crosslinking of the oriented liquid-crystalline monomer layer.

In the method of the invention, a photo-orientable polymer layer is first applied to a substrate such as e.g. FR-4 laminates, epoxy and polyimide films, copper, glass, etc. applied. Corresponding polymers are known, for example, from US Pat. No. 5,389,698 and European Patent Application EP 0 753 785 A1. These are in particular cinnamic acid derivatives of the formula

where n is an integer of 400-600. Preferably, these photo-orientable polymers have a high glass transition temperature (about 130 ⁰ C). They can be dissolved and processed in known solvents, for example methyl cellosolve acetate or cyclopentanone. Usually, the concentration of the photo-orientable polymer is in the range of 0.2-20%, preferably 0.5-10%, and more preferably 1-3%. The solution of the photo-orientable polymer can be prepared by any coating method for liquids, such as bar coating, roller coating, curtain coating, spray coating, miniscus coating, etc, preferably by spin-coating at turns in the range of 200 U / min to 3000 U / min applied.

After application, the layer is dried at a temperature of 160 ⁰ C over a period of 10 min. Typically, layer thicknesses in the range of 10-1000 nm, preferably 50-100 nm, are achieved.

Thereafter, the photo-orientable polymer layer is passed through a patterned photomask, e.g. a photomask with linear structures, and a linearly polarizing filter (the polarization direction is, for example, perpendicular to the propagation direction of the linear structures) irradiated. According to a first embodiment of the method according to the invention, the photomask is removed after the irradiation and the polarizer is rotated through an angle in the range of 1 ° - 180 ° and preferably 45 ° - 85 ° or 95 ° - 135 °, followed by a full-surface exposure of the coated substrate.

According to a second embodiment of the method according to the invention, a structured polarization mask is used instead of the photomask with linear structures and the linearly polarizing filter, which contains the structures to be imaged in the form of differently oriented polarizers (see FIG. This makes it possible to realize a multiplicity of different orientations in one exposure step, whereas according to the first embodiment of the method according to the invention one mask and one exposure step are necessary for each orientation. The preparation of such masks is described in European patent application EP 0 753 785 A1. Two types are displayed:

1. The principle of the mask is based on the ability of liquid crystals to turn the electric field of light. Such a photomask has two photo-orientated polymers are located between the liquid crystalline polymers. (Seele, H., Benecke, C. and Bacheis, T. SID DIGEST 03, 1162 (2003)). In the upper part of the mask, the preferred direction of the liquid-crystalline units all point in the same direction, while in the lower part they have locally different directions. The orientations of linearly polarized light which transilluminates this mask are thereby rotated locally differently.

2. Another variant is the coating of a differently oriented photo-oriented polymer with a mixture of liquid-crystalline polymers and a dichroic substance (such as cyanoterphenyl). These

Substances have the properties of absorbing different wavelengths differently depending on the orientation and therefore serve as molecular polarizers. The dichroic molecules orient themselves the same way as the liquid crystalline monomers according to the given orientation of the photo-oriented polymers. By crosslinking the liquid-crystalline

Monomers, the molecules are frozen in position. Isotropic light, which passes through such masks, then has locally different polarization directions. In addition to the use of isotropic light, the masks have the further advantage that they have direct contact with the photo-orientable polymer to be patterned and thus have less aberrations due to non-collimated light. However, the lifetime of these masks is limited by the photolytic destruction of the dichroic molecules.

The irradiation of the photo-orientable polymer layer with linearly polarized light is generally carried out at room temperature with a radiation energy in the range of about 10 - 400 mJ / cm ² and preferably 150 mJ / cm ² and leads to a photoreaction between two polymer molecules in parallel lie to the polarization direction of the incident light. This results in the orientation and cross-linking of the exposed portion of the coated substrate using a photo-oriented Polymer network is obtained. As a result, the optical anisotropy is transferred into a steric anisotropy of the polymer layer, which is outstandingly suitable as an orientation layer for optically anisotropic material such as liquid crystals. After the application of the liquid crystal monomers, these align according to the orientation layer and can be crosslinked by photolysis. In the crosslinked liquid crystal layer, the orientations of the liquid crystals are frozen and thermally stable.

Such liquid-crystalline monomers are described, for example, in European Patent Application EP 1 094 103 A1. These are in particular the following monomers:

Other liquid crystalline monomers which can be used in the process of the present invention are disclosed in U.S. Patent No. 5,602,661. There, as well as in the aforementioned European patent application, it is also described how the crosslinkable liquid crystalline monomers can be mixed, dissolved and applied to the photo-oriented polymer network.

Thus, for example, the monomers are dissolved in N-methylpyrrolidone or cyclopentanone, so that solutions typically containing 10 - 50% (w / w) can be obtained. This solution is in turn applied by any coating method for liquids preferably by spin-coating. Subsequently, the monomers are heated to a temperature above their clearing point and then cooled slowly (ie over a period of about 15 minutes or at a cooling rate of 1 K / min) so that they can align according to the already existing orientation layer.

For photo-induced crosslinking, the liquid-crystalline layer is preferably irradiated in a nitrogen atmosphere. The irradiation can be carried out at ambient temperature with a radiation energy in the range of 1-10 J / cm ^2, preferably about 2 J / cm ² . The invention is explained in more detail by the attached figures:

Figure 1 and Figure 2 show schematically the steps of the inventive method for producing linear anisotropic waveguides.

FIG. 3 schematically shows a structured polarization mask which has differently oriented polarizers (the direction of the double arrows corresponds to the respective polarization direction), the orientation corresponding to the curved structure to be imaged.

Figure 4 shows linear anisotropic waveguide structures (made by the method shown in Example 1) viewed through crossed polarizers. The different brightnesses correspond to different orientations of the liquid crystals.

Figure 5 shows linear anisotropic waveguide structures (made with the method shown in Example 2) viewed through crossed polarizers. The different brightnesses correspond to different orientations of the liquid crystals.

FIG. 6 shows the scattered light image of the waveguide obtained with the structured polarization mask shown in FIG. 3 with a radius of curvature of 2 mm and a width of 10 microns. From the left, the light is coupled in by means of a GRIN fiber (GRadient Index, describe in F. Pedrotti, L: Pedrotti, W. Bausch, H. Schmidt "Optics for Engineers", Springer Verlag, Berlin, 1996).

FIG. 7 shows schematically exemplary dimensions of the structured polarization mask used in the method according to the invention.

The anisotropic waveguides produced by the method according to the invention can be used for transmitting light waves in corresponding components, in particular in printed circuit boards and chip carriers (chip-to-chip).

The waveguides produced by the method according to the invention surprisingly show an effective waveguide up to radii of curvature of only 2 mm without coupling out light in contrast to isotropic waveguides of a few cm.

In general, with the method according to the invention anisotropic waveguides with radii of curvature of up to a few 100 .mu.m can be produced and preferably up to 1 mm can be obtained.

Surprisingly, it has also been found that there is a region between the core and the surrounding medium in which the orientations of the liquid crystals are slippery and not volatile. Furthermore, it was surprisingly found that there were left and right rotating changes in the orientations when the liquid crystals are oriented in the core at 90 ° to the shell and that even at angles below 80 ° or above 100 ° a uniform rotation is found.

The inventive method is characterized by a few process steps. Furthermore, by using a polarization mask shown schematically in FIG. 3, it is possible to produce waveguide structures in a photolysis step. The inventive method leads in particular with curved structures to an improved transmission of light waves. Single-mode waveguides with widths of only 10 μm can be made easier by the procedure Be realized manner. Compared to known methods such as removal method, it also has the advantage that there is no dust. The surfaces of the obtained waveguides are smooth and the method can also be applied to non-completely planar surfaces.

The invention is explained in more detail by the following examples:

Example 1 (see Figure 1): Preparation of linear anisotropic waveguides, wherein the liquid crystals have an angle of 90 ° between the core and cladding

A glass plate (1) with a low surface roughness (Schott D263T) of R _A <5 nm (report by U. Memmert, Atotech Deutschland GmbH, SXM, 02.24.2004) was in an ultrasonic bath (filled with a 2% Stammopur solution ) cleaned. After drying, the photo-orientable polymer layer 2 (Staralign 2100, commercial product from Vantico, Switzerland, 2% dissolved in cyclopentanone) was applied to the glass plate by spin-coating at 3000 rpm. The layer was then at 150 ⁰ C for 10 minutes on a heated bench dried and had a thickness of about 50 nm. Subsequently, the film was exposed for 60 seconds through a photomask (3) with linear structures and a linear polarizing filter (4) (P-UV2 , Schneider Optische Werke GmbH; polarization direction perpendicular to the propagation direction of the linear structures) with a 1 kW Hg high pressure lamp (Thermo Oriel, model 92542) at room temperature with UV light (5) exposed (about 35 mW / cm ² ). The mask was removed, the polarizer was rotated by 90 ^° C. and the entire surface of the layer was exposed for 30 s with the same lamp.

Subsequently, a solution of liquid-crystalline monomers (6) (Opalval 2130, commercial product from Vantico, Switzerland, 30% in cyclopentanone) was spin-coated onto the photo-oriented polymer layer at 1000 rpm The layer was heated to 55 ° C. by means of a heat bench and cooled slowly (ie over a period of about 15 minutes or at a cooling rate of 1 K / min), so that the monomers could align in accordance with the orientation layer. reduced crosslinking, the monomer layer was irradiated in a nitrogen atmosphere at room temperature for 6 minutes with a 150 W UV lamp (7) (Walter Lemmen, Aktina S, main emission around 360 nm, 8 mW / cm ² ). The crosslinked liquid crystal layer was stable against mechanical and thermal stress. Looking at the cross-linked layer under crossed polarizers, it was recognized that it was birefringent (see Figure 4). The transitions between the cladding and the core of the waveguides were clearly visible. In the transition region between the cladding and the core, the orientation of the liquid crystals changes continuously from 90 ° (core) to 0 ° (cladding), the change taking place both clockwise and anticlockwise. From the frontal coupling of light by means of GRIN fibers and simultaneous measurement of the scattering losses over the length of a 100 μm wide waveguide, the attenuation to 7.7 dB / cm at 780 nm could be determined.

Example 2: Preparation of linear anisotropic waveguides, wherein the liquid crystals have an angle of 80 ° between the core and the cladding

A photo-orientable monomer layer was prepared as in Example 1 with the polarizer rotated only 80 ° between the first and second exposures. Subsequently, as in Example 1, the liquid-crystalline layer was produced and crosslinked. If the crosslinked layer was observed under crossed polarizers, the transitions between the cladding and the core of the waveguides were once again recognized; however, a direction of rotation of the liquid crystals in the same direction appeared in this region (see FIG. 5). From the frontal coupling of light by means of GRIN fibers and simultaneous measurement of the scattering losses over the length of a 100 μm wide waveguide, it was possible to determine the attenuation to be 5.8 dB / cm at 780 nm. Example 3: Production of curved anisotropic waveguides by means of a structured polarization mask

A structured polarization mask (see FIG. 3) contains the structures to be imaged as locally differently oriented polarizers. In this way, curved structures can be produced with the polarization direction in the core perpendicular to the direction of the waveguide and the liquid crystals in the cladding at an angle of 85 ° to those in the core. A photo-oriented polymer layer was prepared as in Example 1 using the patterned polarizing mask instead of the polarizing film. Subsequently, as in Example 1, the liquid-crystalline polymer layer was produced and crosslinked. Looking at the cross-linked layer under crossed polarizers, the transitions between the cladding and the core of the curved waveguides were visible. FIG. 6 shows the end-side coupling of light by means of a GRIN fibers into a waveguide with a width of 10 μm and a radius of 2 mm. Clearly the very good guidance of the light is to be seen.

LIST OF REFERENCE NUMBERS

(1) Substrate

(2) photo-orientable polymer layer

(3) patterned photomask

(4) linearly polarizing polarizer

(5) UV light

(6) liquid crystalline monomer

(7) structured polarization mask with differently oriented polarizers

Claims

PATENTA NSPRÜ CHE

1. A method of making anisotropic waveguides for transmitting light waves, comprising the steps of:

(i) applying a photo-orientable polymer layer (2) to a substrate

(1).

(ii) exposing the coated substrate through a patterned photomask (3) and a linear polarizing polarizer (4) to orient and crosslink the exposed portion of the coated substrate, thereby obtaining a photo-oriented polymer network,

(iii) removing the photomask (3),

(vi) photo-induced cross-linking of the oriented liquid crystalline monomer (6).

2. Method of Making Anisotropic Waveguides for Transmission of Light Waves, By the Following Steps:

3. The method according to claim 2, characterized in that the structure to be imaged is curved.

4. The method according to claim 3, characterized in that the curvature has a radius of less than 10 mm, preferably less than 5 mm and more preferably less than 1 mm.

5. The method according to claim 1 or 2, characterized in that applying the photo-orientable polymer layer in a thickness of 30 - 100 nm on the substrate.

6. The method according to claim 1 or 2, characterized in that the photocurable polymer layer with UV light (5) cures.

7. The method according to claim 1 or 2, characterized in that one uses as a photo-orientable polymer layer, a layer containing cinnamic acid derivatives.

8. The method according to claim 7, characterized Porsche Style nzeich net that as cinnamic acid derivative

where n is an integer of 400-600.

9. The method according to claim 1 or 2, characterized g eken nzeich net that is used as liquid-crystalline monomers (6) photocrosslinkable liquid-crystalline diacrylate monomers.

10. The method according to claim 9, characterized Porsche Style nzeich net that one Diacrylatmonomere from the group consisting of

selects.

11. Anisotropic waveguide, obtainable by the method according to claims 1 to 10.

12. Use of the waveguide according to claim 11 in the manufacture of printed circuit boards.

13. Printed circuit board, containing the waveguide according to claim 11.

14. Use of the waveguide according to claim 11 in the production of chip carriers.

15. Chip carrier, containing the waveguide according to claim 11.

16. Use of the waveguide according to claim 11 in the production of silicon chips.

17. Silicon chips, containing the waveguide according to claim 11.