ITCS20120003A1 - MACHINE FOR DEPOSITION CONTROLLED ON FIBER OPTICS OF MATERIALS IN LIQUID PHASE, POLYMERIC, NON-POLYMERIC, PHOTOSENSITIVE AND NOT, ALSO IN SOLUTION. - Google Patents

Description

DESCRIPTION

Machine for the controlled deposition on optical fibers of materials in liquid phase, polymeric, non-polymeric, photosensitive and not, even in solution.

Summary

The present invention relates to the realization of a device and a process suitable for the deposition of materials in the liquid phase, polymeric and non, in solution, by means of rotation on the termination of optical fibers.

The technique is borrowed from the process called â € œSpin Coatingâ €, used for the production of similar films on large substrates, typically in the order of cm <2>. The spin coating of polymeric and non-polymeric solutions is a deposition technique on a substrate blocked on a rotating disk. This technique is widely used for the production of organic films on planar substrates and exploits the centrifugal force, the surface tension and the uniform evaporation of any solvent contained in the polymer solution to be deposited. In the spin coating process the substrate is first covered by the polymeric solution, then it is accelerated to a suitable rotation speed, remaining there for a predetermined time. During the rotation, in particular in the acceleration phase, the excess part of the solution is expelled from the substrate by the rotational movement (centrifugal force). The final thickness of the film can be determined on the basis of the properties of the polymer and the solvent, the speed and duration of the rotation [1,2], being, however, independent of the size of the substrate and the quantity of the solution initially deposited [3] . During rotation, the film continues to thin slowly until it reaches an equilibrium thickness, making the final thickness essentially due to the evaporation of the solvent, according to the law [2]:

1

à © 3 æ <Ï…> 0 ù 3

<h f = c 0ê ç à ·> ö

ç (1)

<ê> à «<2> à ̈ (1 −cà · <eú>

0) Ï ‰ 2

à ̧ <ú> à "

Where: hfà ̈ the final thickness of the film, c0à ̈ the initial concentration of the solution, Î1⁄20 = Î · / Ï Ã ̈ the initial kinematic viscosity of the solution, Ï and Î · are the density and viscosity of the solution, Ï ‰ It is the speed of rotation, and represents the speed of evaporation of the solvent.

The technique described above is used to deposit polymeric and non-polymeric materials on extended planar substrates, typically in the order of cm <2>. The object of the patent is instead the deposition of the same type of materials on the termination of the optical fiber, which has a typical size in the order of 100 µm <2>, which requires the adoption of particular measures to minimize the effects on board and for the fixing system of the sample (optical fiber) to the plate. To obtain the desired deposition it was necessary to conceive a rotating plate with particular characteristics: three through holes with diameters of 150 microns, 260 microns and 300 microns respectively were made, so as to be able to house both the standard single-mode optical fibers ( with a total diameter of 125 microns) with and without protective coating (Cladding, which involves a total diameter of 250 microns) and some types of multimode fibers (with a diameter of 300 microns). The three holes made are equally spaced both from each other and from the center of the turntable, made of plastic (eg nylon, PTFE) or metal (eg aluminum, copper, steel). The distance of the holes from the center of the aluminum plate is chosen appropriately to ensure at the same time that they are sufficiently distant from the edge of the plate itself and from its center where the rotation speed is zero. It was therefore decided to make the three holes equally spaced by at least 2 cm arranged on the circumference with a radius of 3 cm, concentric with the turntable. These data are to be considered indicative and not binding.

The optical fiber to be â € œcoatedâ € is inserted and blocked in the hole of the appropriate diameter, making its termination emerge from the surface of the plate. The height of the fiber that emerges from the plate must be chosen in such a way as to avoid both stagnation of the material and that the emerging part of the fiber, exposed to the air, does not break or vibrate excessively during rotation.

Subsequently, the polymeric solution is introduced onto the rotating disk making sure to completely cover the tip of the fiber to be coated. The choice of the material to be deposited fell on a positive tone electro-resist (ZEP 520A, ZEON Chemicals) since this material, normally deposited by spin coating on planar substrates, is widely used in nanoelectronics processes to create appropriate coatings .

*; Context of the invention; At this point, it is appropriate to make some distinctions between the present invention and some similar inventions. ; According to our best knowledge, among the procedures reported in the patents for the deposition of thin nanometric layers on optical fiber, there are the Langmuir-Blodgett (LB) [4] and Ionic Self Assembly Monolayer (ISAM) [5] techniques (also called Electrostatic Self Assembly Monolayer (ESAM) or Layerby-Layer (LbL)). However, no invention is reported in which a device is presented that allows to deposit nanometric thickness films on the termination of an optical fiber, by means of the spin coating technique. ; The spin coating technique is very simple and fast compared to the LB or ISAM technique. In fact, these two techniques involve the deposition of one molecular layer at a time. Each molecular layer is a few nanometers thick. Although this provides an extremely precise control of the thickness of the deposited layer, however, to reach film thicknesses of the order of hundreds of nanometers, used for example in classical or electron beam lithography, it is necessary to deposit dozens of monomolecular layers with a consequent expenditure. of time and resources. The LB technique requires sophisticated equipment that is not immediate and simple to use. The ISAM technique, on the other hand, while not requiring complex equipment, is nevertheless slow and requires a more complicated preparation of the solutions, as well as a greater control of the conditions of these solutions, since a small variation of the pH can considerably influence the characteristics. of the deposited layers with consequent reproducibility problems. ;; *

Detailed description of the invention Object of the invention is the realization of a machine dedicated to the deposition on optical fiber of polymeric and non-polymeric materials, in solution, which overcomes the drawbacks and solves the problems inherent to the techniques described above. With this invention it is possible to integrate polymeric and non-polymeric materials with single-mode and multimode optical fibers in order to be able to realize new devices entirely in optical fiber.

Therefore, the object of the present invention is a machine dedicated to optical fiber deposition, which is equipped with a rotating plate suitable for the deposition of thin and uniform films, of polymeric and non-polymeric material, in solution, on the termination of a properly housed optical fiber. in the dish itself.

Preferably according to the invention, the rotating support of the machine in which the optical fiber is housed has a circular section with a diameter chosen appropriately to make holes on the plate itself equally spaced from each other, adequately distant from the center and from the edge of the plate. rotating. Preferably according to the invention, said support has a circular section and is perforated, in equidistant points, at a distance from the center of rotation such as to eliminate the effects of the presence of the edge of the plate on the shape of the free surface of the film.

Preferably according to the invention, said holes have a circular section and diameters suitable for housing optical fibers of different thickness. Preferably according to the invention, the coatings which can be made according to this invention are of polymeric and non-polymeric material, with a thickness ranging from a few to hundreds of nanometers.

The invention will now be described, for illustrative but not limitative purposes, for the deposition on the termination of a standard singlemode optical fiber, with particular reference to the attached figures, in which:

Figure 1 shows the schematic of the positioning of the optical fiber inside the spin coater plate. This figure also shows the realization, in the lower part of the plate, of a chamber suitable to contain the part of optical fiber protruding from the bottom of the plate itself.

Figure 2, by way of example, shows an optical microscope image of the tip of a standard singlemode optical fiber covered with a layer of electro-sensitive material, obtained by rotating the spin coater plate (in which the optical fiber) at a speed of 2000 rpm for 30 seconds.

Figure 3 shows, by way of example, the thickness measurement, by means of an optical profilometer, of a thin film made by rotating the spin coater plate (in which the optical fiber is inserted) at a speed equal to 6000 rpm. min for 30 seconds.

Figure 4 shows, by way of example, the thickness measurement, by means of an optical profilometer, of a thin film made by rotating the spin coater plate (in which the optical fiber is inserted) at a speed equal to 2000 rpm. min for 30 seconds.

Figure 5 shows, by way of example, the thickness measurement, by means of an optical profilometer, of a double coating made by applying the procedure described in the following patent report twice.

Figure 6 shows, by way of example, the thickness measurement performed for two films obtained on two different standard singlemode optical fibers, using the same rotation speed of 2000 rpm for a time equal to 30 seconds.

The particular case of the optical fiber deposition process applied to standard singlemode optical fibers is reported below. The diameter of the fiber core (Corning SMF-28) is equal to 9 microns, the diameter including the mantle is 125 microns. The external protective acrylate coating leads to an overall diameter of about 250 microns.

The deposition procedure consists of five steps: 1) the optical fiber, deprived of the protective coating, is cut by means of a precision cutter, in order to obtain a flat termination, on which to deposit the desired material;

2) the optical fiber is subsequently housed and blocked in the hole present in the plate with the flat termination, protruding from the plate as shown in figure 1;

3) the optical fiber is immersed in the polymeric solution to be deposited;

4) the plate, with the optical fiber inserted inside it, is brought to the desired rotation speed for a certain time;

5) the thin film, obtained on the flat termination of the optical fiber, is thermally cured through the use of a hot plate to avoid that part of the solvent is still present in the coating.

Therefore, the optical fiber is cut at one termination (after removing the protective coating for a length of about 2 cm, using a special stripper) with a precision cutter for optical fibers, to obtain a flat surface, taking care to leave a line uncoated approximately 5-7 mm from the flat termination.

The rotating plate of the machine (10 cm in diameter and 1 cm in thickness) has been drilled about 3 cm from the center to house the optical fiber. The hole made has a diameter of 0.260 mm, so as to be able to house the optical fiber, fixing it on its plastic coating to the underside of the spin coater plate, using a special locking system. The fiber is inserted vertically inside the hole, as shown in figure 1, keeping, outside the plate, the flat end to be covered for a length of approximately 0.500-0.750 mm.

The tip of the fiber has been covered with a layer of electro-resist (ZEP 520A, ZEON Chemicals) by rotating the plate at a constant speed between 2000 rpm and 6000 rpm, depending on the desired thickness for a duration about 30 seconds; subsequently, the coating deposited on the tip of the fiber was thermally cured at 180 ° C for 2 minutes, using a hot plate.

An example of deposition on the termination of the optical fiber is shown in figure 2 (rotation speed equal to 2000 rpm, rotation time equal to 30 sec.). In order to validate the process, the film was perforated using an excimer laser (with an operating wavelength equal to 248 nm), in order to estimate its thickness with an optical profilometer (Veeco, Wyko 9.100 NT); depending on the speed used, thicknesses ranging from 100 nm (as shown in figure 3) to 200 nm (as shown in figure 4) were obtained; moreover, the diameter of the zone of uniform thickness, around the center of the optical fiber, is about 45 microns (as shown in figures 3,4,5,6); applying the same procedure twice, it was possible to obtain double thicknesses as shown in figure 5 (rotation speed, in both cases, equal to 2000 rpm).

Furthermore, in order to test the reproducibility of the process, the thickness measurement was also performed for two films obtained on two different standard single-mode optical fibers, using the rotation speed of 2000 rpm for a time equal to 30 seconds. As can be seen from figures 6a and 6b, the two films have almost the same thickness.

Therefore, with this invention it is possible to obtain uniform and repeatable polymeric coatings on the termination of optical fibers and it is also possible to significantly vary the thicknesses obtainable by varying the rotation speed alone, the rotation time, or both, or by applying the procedure several times. described above.

REFERENCES

[1] Emslie A., Bonner F., and Peck L., "Flow of a Viscous Liquid on a Rotating Disk," Journal of Applied Physics, Vol. 29, p. 858, (1958).

[2] Meyerhofer D., "Characteristics of Resist Films Produced by Spinning," Journal of Applied Physics, Vol. 49, p. 3993, (1978).

[3] Lai J.H., â € œAn investigation of spin coating of electron resistâ € Polim. Eng. Sci. 19, 1117-1121, (1979).

[4] James et al. U.S. Pat. No. 0002606 A1 filed on 1/2005.

[5] Wang et al. U.S. Pat. 7,336,861 B2 filed on 02/26/2008.

Claims (4)

CLAIMS Although the invention has been described in terms of preferred exemplifications, those skilled in the art will recognize that the invention can be put into practice with appropriate modifications in the spirit and within the scope of the following claims. Having described our invention, what we claim as new and want to be assured with this patent relationship is as follows: 1. Machine for the controlled deposition of materials in liquid phase, polymeric, non-polymeric, photosensitive and not, also in solution on the termination of optical fibers in general. 2. Machine according to claim 1, which comprises a rotating plate provided with through holes, of suitable diameter, suitable for housing the optical fibers. 3. Machine, according to claims 1 and 2, which comprises a rotating plate equipped with through holes, with diameters suitable for housing optical fibers of different thicknesses, spaced from the center of the plate and from the edge thereof in order to avoid center of rotation where the centrifugal force is zero, and the edge of the rotating plate where a deformation of the film surface can occur. 4. Machine dedicated to the deposition of thin films on the termination of the optical fiber, whose rotating plate integrates in the lower part a chamber which acts as a container for the section of optical fiber in excess and protruding from the bottom of the plate itself.