RU2548945C2 - Microstructural elements selecting electromagnetic emission and method of their manufacturing - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention is used for selection of electromagnetic emission. Essence of the invention lies in manufacturing of a microstructural element as a perforated mesh structure, which volume is made mainly of polymer film and its all surface, including inner cavities, is metalised.

EFFECT: potential forming of perforated films within range of thickness from several micrometres up to several millimetres.

5 cl, 3 dwg

Description

The present invention relates to a design and a method of manufacturing microstructural elements for the selection of electromagnetic radiation, made in the form of a grid (both regular and irregular) structures (including spatially profiled surface), such as, for example, resonant-band filters, converters phases and polarizations, diffraction focusers of radiation, etc., designed for spatial, frequency, phase and polarization selection of electromagnetic radiation, top The biology of which is selected in such a way as to ensure the given electrodynamic characteristics of the structure.

The design and method [described by Reinhard Ulrich - Interference Filters for the Far Infrared // Applied Optics, October 1968, Vol.7, No. 10, pp.1987-1996], where the design of the metal mesh structure (MCC), were selected as an analogue represents a thin-film copper structure with a thickness of ~ 1 μm, formed using photolithography on the surface of a supporting polyethylene-terephthalate film with a thickness of ~ 2.5 μm (see Figure 1).

The device selected as an analogue has the following main drawback, due to the "presence" of the supporting polymer film in the holes formed in the metal layer, which is expressed both in spurious dissipative energy losses of the selectable electromagnetic radiation in the polymer film material and, in general, in distortion selective properties of the grid structure.

As a prototype, the design (see Fig. 2a) and the method [described in the work by Kuznetsov S.A., Goldenberg B.G., Kalinin P.V. et al. Development of copper grid structures for frequency and spatial selection of THz radiation from a Novosibirsk free electron laser // Surface. X-ray, synchrotron, and neutron studies, 2009, No. 9, pp. 38-49], where the MCC structure is a free-hanging copper film structure ~ 80 μm thick (formed using deep X-ray lithography on the surface of a conductive glassy carbon substrate using a rhenium separation layer thick ~ 1 μm, see Fig.2b).

A method of manufacturing an MCC prototype comprises the following steps:

• prepare the surface of the initial electrically conductive substrate - glassy carbon plate (planarization and reduction of the roughness of its working surface);

• form a resistive mask on its working surface (using synchrotron X-ray lithography);

• conduct electrochemical deposition on the working surface of the substrate through a resistive mask of a metal separation (rhenium) layer with a thickness of ~ 1 μm;

• conduct electrochemical deposition on the working surface of the substrate through a resistive mask of a metal (copper) film ~ 10 ÷ 400 microns thick;

• remove the resistive mask (removal of resist residues from the working surface, control of the geometric dimensions and quality of the deposited mesh);

• peel the metal mesh structure from the original substrate;

• fix the metal mesh structure on the supporting frame.

The disadvantage of the prototype is the complex technology of its manufacture and the difficulties caused by the technology that arise in the manufacture of thin (thickness ≤ 10 μm) metal mesh structures, in particular, during the peeling operation of the film mesh structure from the initial substrate, which is fraught with damage, especially in the case of thin (thickness ≤ 10 μm) of metal films. There are also a number of problems in the fabrication by the prototype method of very thick (≤ 400 μm thick) mesh structures, since the typical rate of galvanic growth of metal films is ~ 10 μm / hour, their growth will last about a week (and, in general, requires organization continuous process with automatic tracking and maintenance of the required electrolyte parameters, such as temperature, concentration, acidity, etc.). Since the physical parameters of the microstructural elements under consideration depend not only on the topology of the metal mesh structure in its working plane, but also on the thickness of this structure, there is a need to manufacture film structures whose thicknesses are outside the previously specified range, which will expand the range of such devices with new features.

The proposed design of a perforated metallized mesh structure (hereinafter referred to as pseudo-metal mesh structure (PMSS)), which is a perforated polymer metallized chemically film, and the method of its manufacture are free from the disadvantages inherent in the prototype.

In order to reduce the cost of microstructural elements for the selection of electromagnetic radiation, made in the form of grid structures and expand their product range, which is achieved by switching to a simpler technology for their manufacture, which allows to form perforated (with through holes) metallized films (see Figure 3) in the thickness range from a few micrometers to several millimeters (including with a spatially profiled surface), it is proposed to use a method containing a trace The most advanced technological operations:

1. prepare (clean) the surface of the x-ray sensitive polymer film and give it a certain predetermined shape;

2. create a hidden image in the film using X-ray lithography (carry out a single (or multiple) exposure of the film by X-ray radiation through the X-ray template);

3. exhibit the exposed film (as a result, a surface profile and through holes are formed);

4. carry out the deposition of metal on a perforated polymer film (metallize its surface, for example, by chemical means);

5. fix the obtained metallized film on a supporting frame (ring).

In some cases, fixing the film to the support frame can be carried out at the very beginning and combined with operation 1, this does not matter.

Figure 1 schematically shows the design of a microstructural element selected as an analogue for the selection of electromagnetic radiation, where a perforated thin layer of metal 2 is formed on the surface of the polymer film 1, and the film itself is fixed on the supporting frame 3.

Figure 2a schematically depicts one of the final stages of manufacturing a microstructural element selected as a prototype made in the form of a grid structure, where a resistive mask 5 is formed on the surface of the glassy carbon substrate 4, through which layers are sequentially galvanically deposited: a thin separation rhenium layer 6 and a copper film 2.

On figb schematically shows the design of the selected as a prototype microstructural element, where the "peeled" perforated copper film 2 is fixed on the supporting frame 3.

Figure 3 schematically shows the proposed design of the microstructural element in the form of a pseudo-metal mesh irregular structure (PMSS), where the perforated polymer film 1, coated with a thin layer of metal 2, is attached to the supporting frame 3.

An example of a specific implementation. For the implementation of the proposed design of the microstructural element in the form of PMSS, a dacron film 10 μm and 100 μm thick was taken. Circles with a diameter of ~ 60 mm were cut from it, which were exposed at the LIGA station [described in the work by Gancelev A.N., Goldenberg B.G., Kondratiev V.I. et al. LIGA-station on the VEPP-3 drive // Surface. X-ray, synchrotron and neutron studies, 2002, No. 9. S.30-35] through the X-ray template. Typical exposure doses in this case were ~ 200–400 kJ / cm ³ , then the films appeared in a 9% aqueous NaOH solution (at T≈45 ° C) ~ 1 hour. At the next stage, chemical silvering of their surface was performed (the thickness of the silver deposit was ~ 1 μm). After that, the films were fixed on the support frame (support ring) and a thin (~ 0.1 μm thick) layer of aluminum was sprayed (to prevent silver corrosion) on both surfaces of the films. In addition, filters for terahertz radiation from sheet organic glass with a thickness of 1 mm were also made using this technology.

An important point is the fact that the chemical method of metal deposition provides metallization of the internal cavities of the holes, as a result of which the entire surface of the polymer substrate is coated with a continuous (electrically inextricable) metal film acting as a skin layer in interaction with radiation.

The amplitude-frequency characteristics of terahertz filters implemented in the form of PMSS correspond to the calculations and are approximately the same as for metal mesh structures with a similar hole configuration (since the surface skin layer is “responsible” for the interaction with electromagnetic radiation), while the manufacturing technology PMSS is much simpler than the previously described technology for producing MSS.

In addition, as a rule, the metallized surface of PMSS is characterized by a lower roughness (which in some cases affects the selective properties of the microstructural element), compared with electroforming thick samples of MCC (since galvanic growing of thick metal films with a smooth surface is a separate technical problem).

The manufacture of microstructural elements in the form of grid (both regular and irregular) structures with a spatially profiled surface (in general, giving the elements new functional properties) involves the creation of a smooth or stepwise distribution of the exposure dose over the surface of the irradiated polymer film (or sheet), which then translates into a difference in the etching rates of different surface areas in the developer. There are several ways to achieve this:

• conducting dynamic X-ray lithography (in which during the exposure, according to a certain law, the relative relative motion of the processed film (or sheet) and the X-ray pattern is carried out),

• using an X-ray template with a different thickness masking layer (ie, its thickness is a function of location (from coordinate) on the working surface of the template),

• conducting multiple exposure of the film (or sheet) using a set of several X-ray templates and the procedure for linking (combining) their topology with a latent image formed in the polymer;

• combining the above methods.

Claims (5)

1. A microstructural element for the selection of electromagnetic radiation, made in the form of a perforated mesh structure with a highly conductive external surface, characterized in that the bulk of the structure is made of a polymer film (or polymer sheet) and its entire surface, including internal cavities, is metallized (made of metal with high electrical conductivity). 2. The microstructural element for the selection of electromagnetic radiation according to claim 1, characterized in that its working surface is spatially profiled. 3. A method of manufacturing a microstructural element for the selection of electromagnetic radiation, made in the form of a perforated mesh structure, which includes the processes of x-ray exposure of hydrocarbon polymers through an x-ray template and the formation of highly conductive layers, characterized in that the mesh structure is made of a film (or sheet) of an x-ray hydrocarbon polymer by manifestations of the latent image formed in it using x-ray lithography, and then the whole overhnost resulting metallised structure. 4. The method according to claim 3, characterized in that the surface of the perforated mesh structure is chemically metallized. 5. The method according to PP.3 and 4, characterized in that the metal surface of the perforated mesh structure, if necessary, to protect it from corrosion, is coated by spraying with a thin film of a more corrosion-resistant material (preferably metal or an alloy with high electrical conductivity).

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