FR2670201A1 - PROCESS FOR MICROSTRUCTURING SUPERCONDUCTING OXIDE CERAMICS. - Google Patents

Abstract

The invention relates to a method for microstructuring oxidized superconducting ceramics (1). - A closed metal layer (3) is placed on the oxidized ceramic (1), - A photosensitive varnish mask (4) is placed on the metal layer (3), - Areas of the non-metallic layer (3) are removed. covered by the photosensitive varnish mask (4), - the photosensitive varnish mask (4) is removed, - said radiation is applied to the masked oxide ceramic (1), through the areas of the metal layer (3) initially covered by the photosensitive varnish mask, - areas of the metal layer (3) initially covered by the photosensitive varnish mask (4) are eliminated.

Description

Process for microstructuring oxidized ceramics above

  conductive. The present invention relates to a method of

  microstructuring of oxide superconducting ceramics.

  Microstructuring means that by creating layers of different electrical conductivity usually microscopically small electronic components

  are made (microchips) The superconducting ceramics

  these are oxides which contain rare earth elements or lead, barium, calcium, strontium, bismuth, thallium, copper or mixtures thereof or a material containing a chalcogenide such as sulfur, In particular, they include so-called high temperature superconductors, for example substances which exhibit the superconducting effect also at temperatures of about 30 K. In the German Angewandte Chemie 99 (1987) N 011, 1201-1203, describes a method for controlling the superconducting properties of oxide ceramics by reduction and oxidation. Oxidized ceramics are

  in this case subjected to heat treatment under

oxygen sphere.

  In US Applied Physics Letters 55 (19), November 6, 1989, pages 2032-2034, describes a method of manufacturing a Josephson junction between oxide ceramics superconducting On an oxidized ceramic is deposited a layer of metal closed By contribution

  of a layer of photoresist on the metal layer

  that and then ionic radiation, ohmic contacts

  are isolated from the metal layer.

  DE 38 14 277 A1 discloses a method of microstructuring high temperature superconductors, wherein the properties of the material are modified by oxidation or reduction induced by

  The structuring takes place while the

  The disadvantage of this method is that the resolving power is limited, according to the desired microstructure on the surface of the material.

  by the diameter of the laser beam A control of the properties

  electrical structures of structures made during the

  In addition, the point-in-time exploration of the material to be structured using the laser beam requires

an important time.

  The object of the present invention is to provide a process for the microstructuring of superconducting oxide ceramics, which has, with respect to the processes

  known, increased resolution power.

  According to the invention, on the layer of

  oxidized ramique is deposited a mask and then this layer of masked oxidized ceramic is irradiated The various steps of the method consist in arranging a closed metal layer on the oxidized ceramic having a photoresist mask on the metal layer

  eliminate areas of the undecovered metallic layer

  green photosensitive varnish mask eliminate photosensitive varnish mask apply said radiation on the oxide ceramic

  masked, through the areas of the metal layer

  originally covered with the photoresist mask remove areas of the coated metal layer

  initially by the photoresist mask.

  The wavelengths of the radiation used are less than 1000 nm, and particularly in the range of visible, ultraviolet or X radiation or mixtures

  of them One can thus use not only a ray-

  monochromatic material (eg from an excimer laser of 308 nm wavelength) but also

  continuous wavelength spectrum radiation.

  radiation is preferably carried out at room temperature

  or below the transition temperature in the su-

  praconducteur. Thanks to the irradiation, a chemical transformation is triggered (photochemically induced reaction), in

  which oxygen is extracted from the oxidized ceramic.

  Through oxidation, this reaction can be further reversed. During the reduction, the hydrogen contained in the oxidized ceramic or a suitable atmosphere containing hydrogen can serve as a reducing partner. The chemical reaction for the oxidized ceramic Y Ba 2 Cu 307 (Y Ba Cu O is also cited ) is described by the following reaction equation Y Ba 2 37-x + YH 2> Y Ba 2 Cu 307 (x) + YH O

  The symbol "O" indicates the difference most of the time

  7 -xq is stoichiometric oxygen content in the case of layers made from these compounds Depending on the duration of the irradiation and the radiated power,

  for example, specific electrical resistance, temperature,

  In addition, the resulting oxygen vacancies in the oxide layer act as centers of fixation for the magnetic flux in the superconductor ( fixation centers influence the field dependence of the electrical properties of a superconductor in an external magnetic field). It is particularly advantageous that with the aid of deposited contacts, preferably in gold, for example, according to the method of the four points, the modification of the electrical properties can be obtained during the irradiation Are carried out in others the measurement of the dependence vis-a-vis

  the temperature of the electrical resistance and the den-

  critical current with and without external magnetic field

laughing.

  After obtaining the desired parameters, irrational

  diation is interrupted The photochemically induced reaction

  is thus interrupted and another reaction suppressed.

  The parameters obtained are no longer modified.

  The chemical reaction induced by the irradiation takes place only at the irradiated points of the oxidized ceramic. For this reason, the process can be carried out

  independently of morphology, amorphous, polycrystalline

  tallin, epitaxial, monocrystalline, of the above material

  driver. The process according to the invention will be described in detail with reference to the accompanying drawing, in which: FIGS. 1 to 9 show the various process steps with a view to microstructuring an oxide ceramic layer, FIG. of a ceramic oxide layer Y Ba Cu O at room temperature depending on the duration of irradiation by a

electromagnetic radiation.

  Figures 1 to 9 show the different stages of pro-

  yielded by microstructuring an oxidized ceramic layer

  1 is the superconducting layer of ceramics

  The oxidized ceramic layer 1 is coated on the entire surface of a metal layer 3, for example made of Niobium (FIG. 2). On the metal layer 3, the oxide layer 1 is deposited on a layer 2 support (FIG. help

  lithographic means, a layer of

  sible structure 4 is deposited (Figure 3).

  of the photosensitive varnish, the metal layer 3 deposited on the entire surface protects the underlying layer

  of oxidized ceramic 1 of the aqueous developer.

  Areas not covered by the layer of photo-lacquer

  4 of the metal layer 3 are removed by a reactive plasma etching process, for example, by the RIE (reactive ion etching) method using argon ions and tetrafluormethane, wherein the underlying layer of oxidized ceramic 1 is not attacked (Figure 4) Next, the layer of photoresist 4

  is removed by an appropriate solvent (removal process

  (Figure 5) The irradiation of the oxidized ceramic layer 1 masked in this way is then carried out

(Figure 6).

  Thus, the electrical conductivity of the exposed zones 6 of the oxidized ceramic layer 1 is determined in a desired manner, for example in a semiconducting manner, of

  strongly ohmic, or insulating way (Figure 7).

  The increase of the resistance as a function of the irradiation time is for example represented in FIG. 10. After the irradiation, the remains of the metal layer 3 are eliminated by the plasma etching process.

  reagent already mentioned in the description of the Figure

  4 (FIG. 8) and thus the non-irradiated zone 7 of the oxide ceramic layer 1, which is also superconducting,

is exposed (Figure 9).

  FIG. 10 represents, for example, the shape of the electrical resistance of an oxide layer of Y 2 Ba 2 Cu 307 (in logarithmic scale) at ambient temperature as a function of the irradiation time by a

  electromagnetic radiation (in addition to the duration of irrational

  diation, the pace of resistance also depends on

  the intensity of the radiated power).

  During the first hour of radiation, the value of the resistance grows approximately logarithmically, then transforms into a saturation phase, in which growth always becomes lower As the irradiation proceeds at room temperature, the value of the resistance the non-irradiated layer is not zero,

  because the oxide ceramics do not go into the superconducting

  than far below the ambient temperature.

  Unlike structuring processes con-

  naked, for example wet chemical etching, ion etching or laser ablation, the structuring takes place

  here without removal of material A thermal after-treatment

  Moreover, the advantage of the microstructured oxide ceramic layer, which is necessary in the case of ionic etching and laser ablation, is superfluous. Another advantage lies in the fact that the oxidized ceramic layer is modified only locally. edge engraving or along grain boundaries, as well as

  observed in known methods, does not occur.

  Thanks to the contribution of the invention to the

  metal layer, the oxidized ceramic layer does not come into

  contact with aqueous fluids, for example during the development of

  photosensitive varnish in any step of the process, so that the often observed degradation of the

does not happen.

Claims (5)

R E V E N D I C A T I ON   1 Microstructuring process by creating zones and tracks of different electrical conductivity of oxide ceramics (1) superconducting, in particular for the manufacture of electronic components, the electrical properties of the oxide ceramics (1) being adjusted by means of electromagnetic irradiation of the range of wavelengths less than 1000 nm, this irradiation triggering   a chemical transformation of the oxidized ceramics (1),   characterized in that it comprises the steps of:   have a closed metal layer (3) on the ceramics   that oxidized (1) have a photoresist mask (4) on the metal layer (3) remove areas of the metal layer (3) uncovered from the photoresist mask (4) remove the photoresist mask (4) applying said radiation to the masked oxidized ceramic (1) through the areas of the metal layer (3) initially covered by the photoresist   to eliminate areas of the metallic layer (3)   tialement covered with the photoresist mask (4). Process according to Claim 1, characterized   in that it is used as above-oxidized ceramics conductive Y Ba 2 Cu 307.   Process according to any one of the claims   previous ones, characterized in that the modification of   Electrical properties are monitored during said irradiation.   Process according to any one of the claims   preceding, characterized in that a reversible reduction or oxidation of the oxidized ceramic is triggered by the irradiation. Process according to Claim 4, characterized in that the radiation-induced reduction of the oxidised ceramic is obtained with hydrogen or   compounds thereof as a reducing partner.   Process according to claim 5, characterized in that the radiation-induced reduction is   triggered by the hydrogen itself contained in the ceramics   oxidized compound or compounds thereof.   Process according to claim 5, characterized in that a suitable atmosphere in which the oxidized ceramic is located is used for the radiation-induced reduction, which contains hydrogen or compounds   of it serving as a discount partner.