Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Distributive type parameters
Reexamination Certificate
2001-01-05
2003-08-12
Oda, Christine K. (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Distributive type parameters
C324S633000, C324S071600, C324S719000
Reexamination Certificate
active
06605949
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention resides in a quasi-hemispherical Fabry-Perot resonator for determining the surface resistance of a thin-film material in the mm wave range.
For the manufacture of information processing components (for example, filters, oscillators) thin-film materials with good conductivity, which may also consist of a high temperature superconductive material (for example, YBCO), are structured in a particular way. The thin material films are formed on large surface area substrates (wafers) by sputter- and vapor deposition processes. For the certification of a suitable film manufacturing process, certain material parameters (among others the transition temperature T
e
, the critical current density j
c
) are determined in a non-destructive manner, wherein the surface current resistance R
s
is the most important. With localized scanning, which determines this parameter over the wafer surface area of interest in a quantitative manner, the reproductivity and the homogeneity of the superconductive film properties are determined.
Regarding the use of Fabry-Perot resonators for the temperature dependent determination of R
s
at low temperatures using superconductive mirror materials (niobium) reports are available by Komiyama et al. (in Appl. Phys. LeH. 64(4), Jan. 22, 1996, p. 562-563 under the title Penetration depth measurements . . . ”) and in the WUB-DIS 94-9 by S. Orbach-Werbig under the title “Oberflächenimpedanz epitaktisch autgewachsener Yba
2
Cu
3
O
7-8
films at 87 GHz”. Whereas the first publication reports of no provisions for localized measurements, in accordance with the second publication a displacement was provided for by a hand-operated drive for rotating the probe. Localized R
s
determinations at a given temperature (77° K.) are performed using normally conductive mirror materials (aluminum): Martens et al. (U.S. Pat. No. 5,239,269).
The convention documents of the MIOP 97 by R. Heidinger and R. Schwab disclose a quasi-hemispherical Fabry-Perot resonator for determining the surface resistance in the millimeter wave range. Changes of the DC conductivity in the mirror materials and changes of R
s
resulting therefrom were found over a wide temperature range of 20-340° K. They were recorded for various material configurations (Cu, Ag, brass) by way of grade measurements over the whole test specimen, that is, not in a localized manner. In a second resonator with an especially focused mirror configuration, which resonator can be operated only at room temperature, the registration of local R
s
—inhomogeneities is demonstrated by way of demonstration mirrors with an abrupt resistance change. The experiment is made in the open, that is, not in a closed environment.
The solution formulas known so far do not provide for any, or at least not for any satisfying, combined localized and temperature dependent quantitative determination of the R
s
—values. In the described systems, which are based on superconductive niobium, it is not possible to arrange the coupling geometry in such a way that stray losses at the coupling openings are small. The reason herefor is that, in comparison with the copper used in connection with the invention, niobium is difficult to machine. Another reason is the necessary high-frequency examination of the geometry below the shift temperature of niobium (9.4° K.), which does not permit any direct corrective measures. With these experiments, so far, no absolute values for the localized surface resistance R
s
have been determined.
Solution formulas of the localized measurements are failing because there is no reliable systematic definition, since the manual object guidance is sluggish and not sufficiently accurate (Orbach (1994)). The localized measurements with (quasi) co-focal Fabry-Perot resonators do not have the necessary stability of the temperature environment because they are not equipped with a kryo-system appropriate for performing T-variable measurements.
It is the object of the present invention to delimit unsuitable film areas by identifying areas with increased surface resistance values, which are the result of outside influences. Predetermined comparison measurements of the temperature depending on R
s
over the surface area will provide for a suitable data base for quantifying the amount of the outside influence on the material quality and the local temperature gradient for a systematic correlation with the sputtering or vapor deposition parameters.
SUMMARY OF THE INVENTION
In a quasi-hemispherical Fabry-Perot resonator for the non-destructive determination of the surface resistance R
s
of electrically conductive thin material films, spherical and planar mirrors are disposed opposite each other in a double shielded cooled resonator space structure supported on individual base plates and the planar mirror, on which a wafer with the thin material film is supported, is mounted on a support arm which extends through the double shield structure. Shield sections through which the support arm extends are supported on pivot arms which are pivotally mounted in the center of the base plates and the shield sections are engaged by the support arm so that they move along with the support arm when the support arm is moved sidewardly for a positioning change of the planar mirror thereby preventing radiation leakage from the resonator space.
The invention resides in the combination of a highly developed invention measuring technique for a high resolution quantitative determination of R
s
by means of a (quasi) hemispherical resonator arrangement with copper mirrors and a suitable evaporation kryostatic system which, using two radiation shields and a suitable placement of computer-controlled adjustment elements, provide for a reproducible position and temperature variation of the superconductive thin film sample in the millimeter wave beam.
The inner radiation shield is completely surrounded by an outer shield. Both consist of a base plate through which a coolant flows and on which the mirror cover is disposed. The two base plates are, with respect to the coolant flow, arranged in series wherein the coolant flows first through the inner radiation shield, which is supported on the outer radiation shield in a mechanically stable manner by legs which have a low heat conductivity.
The quasi-hemispherical resonator is supported on the base plate of the inner radiation shield in good heat transfer contact therewith. The spherical mirror is firmly mounted on the base plate in good heat transfer relationship therewith. Symmetrically to the projected resonator axis, the base plate carries at least two heating elements, whose heat input to the spherical mirror is monitored and is controlled by temperature sensors arranged in the heat transfer path to the spherical mirror. The plane mirror is disposed on the movable extension arm, which has a low heat conductivity and therefore is connected to the base plate by way of a flexible (metal) band having a good heat conductivity for maintaining the defined kryosystem temperature. It provides for a certain displacement freedom, particularly a rotation of the mirror up to 360° about the resonator axis. Furthermore, the plane mirror can be separately heated by means of a heating element mounted thereon. The temperature of the mirror is monitored and controlled by an associated temperature sensor. The heating element provides for well-defined heat input for obtaining a thermal equilibrium between the mirrors also during warm-up.
The second radiation shield is also supported on the mounting plate in heat transfer uncoupled relationship therefrom. The resonator is mounted on the mounting plate indirectly and the extension arm is mounted with its base directly on the mounting plate.
To accommodate the low-conductivity extension arm, each of the radiation shields includes a window through which the extension arm extends so that they can be removed during necessary manipulations (for example, a change of the sample) within the resonator space. In order to keep the radiation shields always closed su
Burbach Jakob
Halbritter Jürgen
Heidinger Roland
Schwab Reiner
Bach Klaus J.
Forschungszentrum Karlsruhe GmbH
Oda Christine K.
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