Open resonator and electrical conductivity measurement method using same

Abstract

Provided is an open resonator that makes it possible to measure the electrical conductivity of a sample more accurately and efficiently. An open resonator according to the present disclosure is used for measuring the electrical conductivity of a sample, said open resonator comprising: a first concave reflecting mirror that has a concave first reflection surface which comprises a metal; a first sample-holding housing that has a first through hole through which the central axis of the first reflection surface passes, a first surface, and a second surface which is opposite from the first surface; a second sample-holding housing that has a third surface which is opposite from the second surface and a fourth surface which is opposite from the third surface, and that sandwiches the sample with the first sample-holding housing by movement of the position of the third surface with respect to the second surface of the first sample-holding housing; and a holding member that is for keeping constant a first distance between the first reflection surface and a surface of the sample which is opposite from the second surface of the first sample-holding housing when the sample is sandwiched between the first sample-holding housing and the second sample-holding housing.

Description

Open resonator and method for measuring conductivity using the same

[0001] The present invention relates to an open resonator suitable for measuring the conductivity of a sample.

[0002] Millimeter-wave frequencies are used in applications such as automotive radar, wireless communications, and high-speed digital devices. Improved position resolution in radar, increased communication speeds in wireless communications, and faster processing speeds in digital devices are essential challenges, and millimeter-wave frequencies are expected to continue to increase. Currently, the 75-80 GHz, 40 GHz, and 28 GHz bands are used in cutting-edge devices, respectively. Future frequencies are expected to exceed 100 GHz. Furthermore, discussions are underway regarding the use of frequencies up to 330 GHz for the sixth-generation (6G) communications network, which will replace the fifth-generation (5G) communications network. Accordingly, measurements of the properties of materials used in these devices using higher frequencies are becoming increasingly necessary. Among these material properties, energy loss due to the skin effect of millimeter waves at higher frequencies becomes a major issue, making measurement of material conductivity an essential task.

[0003] Patent Document 1 discloses a Fabry-Perot resonator for measuring the surface resistance in the millimeter wave band of a thin film material formed on a wafer by a sputtering process or a vapor deposition process.

[0004] Also, Non-Patent Document 1 discloses a Fabry-Perot resonator for measuring bulk conductivity.

[0005] In a Fabry-Perot resonator, an input signal with a frequency of, for example, about 100 GHz is input between a concave reflecting mirror and a planar metal sample, which are arranged opposite each other, to perform resonance measurement and obtain a resonance waveform. A network analyzer is often used for resonance measurement. The network analyzer is connected to the Fabry-Perot resonator to obtain a graph (resonance waveform) with frequency on the horizontal axis and transmitted signal strength (transmission coefficient) on the vertical axis, and the resonance characteristics are measured. Here, "resonance characteristics" refers to the center frequency of resonance (resonance frequency) and the Q value (in this specification, the ratio (f / BW) of the center frequency (f) and the 3 dB bandwidth (BW) is used). The conductivity of a metal sample to be measured is generally calculated or simulated from the resonance characteristics of a metal (e.g., copper or silver) with a known conductivity and the resonance characteristics of the metal sample. For example, the conductivity of copper is 5.8 × 10 ７ In the high frequency range, even if the conductivity is the same, the resistance value increases due to the skin effect. When measuring conductivity using a Fabry-Perot resonator, a metal with a known conductivity is used as a reference and the conductivity is measured. In this case, the conductivity is 5.8 x 10 ７ The value obtained by normalizing S / m to 1 is expressed as the specific conductivity (hereinafter, sometimes simply referred to as "conductivity").

[0006] To achieve stable conductivity measurements using a Fabry-Perot resonator, the distance between the metal sample and the reflective surface of the concave reflector must be maintained with nanometer-order precision (less than 10 nm). The sample serves as the resonant reflector, and conductivity is calculated from changes in the Q value of its resonant characteristics. However, if the resonant frequency changes, the Q value cannot be accurately measured. The resonant frequency is determined by the distance between the concave reflector and the sample. Therefore, to measure the resonant characteristics near the desired frequency, the reflective surface of the sample must be precisely positioned. Because the measurement sample always has a certain thickness, fixing the surface opposite the reflective surface of the sample will shift the resonant frequency depending on the thickness of the sample. Since there are no standards for conductivity measurements using a Fabry-Perot resonator, achieving stable measurements has been difficult. To automatically filter out unwanted resonances from among the numerous resonances and find the desired resonance using software, the distance between the reflective surface of the concave reflector and the reflective surface of the measurement sample must be precisely aligned.

[0007] Conventional Fabry-Perot resonators for measuring conductivity are vertical and use gravity for positioning. Figure 12 is a cross-sectional schematic diagram showing the configuration of a conventional Fabry-Perot resonator 150. In the conventional Fabry-Perot resonator 150, when a sample 55 is placed on the sample stage 50 at the bottom of the resonator while the distance L between the reflective surface of the concave reflecting mirror 51 and the sample mounting surface of the sample stage 50 is fixed, the distance D between the concave reflecting mirror 51 and the reflective surface of the sample 55 changes depending on the thickness t of the sample 55, and the measured resonant frequency changes accordingly. If the resonant frequency varies depending on the thickness t of the sample 55, it becomes impossible to obtain a correlation with a reference (standard metal sample). If the distance D between the concave reflecting mirror 51 and the reflective surface of the sample 55 changes depending on the thickness of the sample 55, causing the resonant frequency to shift, it becomes difficult to find the resonant waveform of the sample 55 that corresponds to the resonant waveform of the reference. Furthermore, it is difficult to determine whether to move the sample 55 closer to or farther from the concave reflecting mirror 51 in order to match the distance D when measuring the resonance characteristics of the reference.

[0008] WO 00 / 08477

[0009] J. Cuper, B. Salski, T. Karpisz, A. Pacewicz, P. Kopyt, Conductivity measurement in mm-wave band with a Fabry-Perot open resonator, IEEE / MTT-S International Microwave Symposium, 996-998, 2020

[0010] The object of the present disclosure is to provide an open-type resonator that makes it easy to adjust the distance between a concave reflecting mirror and the reflecting surface of a sample, and that can measure the conductivity of a sample more accurately and efficiently, and a method for measuring conductivity using the same.

[0011] The open-type resonator of the present disclosure is an open-type resonator used to measure the conductivity of a sample, and comprises: a first concave reflecting mirror having a concave first reflecting surface made of metal; a first through hole through which the central axis of the first reflecting surface passes, a first surface and a second surface facing the first surface; a second sample holding housing having a third surface facing the second surface and a fourth surface facing the third surface, the second sample holding housing sandwiching the sample between itself and the first sample holding housing by moving the position of the third surface relative to the second surface of the first sample holding housing; and a holding member for maintaining a constant first distance between the surface of the sample sandwiched between the first sample holding housing and the second sample holding housing that faces the second surface of the first sample holding housing and the first reflecting surface.

[0012] The method for measuring conductivity disclosed herein is a method for measuring conductivity using the above-mentioned open-type resonator, and includes the steps of: placing a reference metal having a known conductivity between the first sample holding housing and the second sample holding housing, and measuring a first resonance characteristic; placing the sample between the first sample holding housing and the second sample holding housing, and measuring a second resonance characteristic; and calculating the conductivity of the sample using the known conductivity, a Q value obtained from the measured first resonance characteristic, and a Q value obtained from the measured second resonance characteristic.

[0013] According to the open-type resonator and the method for measuring conductivity using the same disclosed herein, when measuring conductivity using a Fabry-Perot resonator, it is possible to accurately and easily adjust the position of the sample to be measured, and the conductivity of the sample can be measured accurately and efficiently.

[0014] Schematic cross-sectional view showing the configuration of a Fabry-Perot resonator according to embodiment 1. Block diagram of a resonance characteristic measurement system using a Fabry-Perot resonator. Plan view showing the configuration of a sample holder of the Fabry-Perot resonator according to embodiment 1. Diagram showing attachment of a sample to the sample holding plate of the Fabry-Perot resonator according to embodiment 1. Explanatory diagram showing the movement of the resonance waveform when the distance between the concave reflecting mirror and the sample changes due to differences in the film thickness of the sample ((a) reference position, (b) position 200 μm closer). Schematic cross-sectional view showing the configuration of a Fabry-Perot resonator according to embodiment 2. Diagram showing the change in calculated specific conductivity when the distance between the concave reflecting mirror and the sample changes. Configuration of a Fabry-Perot resonator according to embodiment 3. 9B is a schematic cross-sectional view showing a method for measuring conductivity using a Fabry-Perot resonator according to a third embodiment (measurement of resonance characteristics of a reference); FIG. 9C is a flowchart showing a method for measuring conductivity using a Fabry-Perot resonator according to a third embodiment (measurement of resonance characteristics of a sample); FIG. 9D is a flowchart following the flowchart of FIG. 9A (measurement of resonance characteristics of a sample); FIG. 9E is a schematic cross-sectional view showing the configuration of a Fabry-Perot resonator according to a conventional example;

[0015] (Embodiment 1) Fig. 1 is a schematic diagram showing a cross section of a Fabry-Perot resonator 110 according to embodiment 1. As shown in Fig. 1, the Fabry-Perot resonator 110 according to embodiment 1 has a fixing base 10, a concave reflecting mirror 11, a sample holder 20, and a sample holding plate 31. The Fabry-Perot resonator 110 is an example of an open-type resonator. In the following explanation, an XYZ orthogonal coordinate system shown in Fig. 1 will be used, in which the X direction corresponds to the up-down direction, the Y direction corresponds to the front-back direction, and the Z direction corresponds to the left-right direction.

[0016] As shown in FIG. 1 , a concave reflecting mirror 11 having a concave reflecting surface 12 and a sample holder 20 are fixed to the fixing stage 10. The concave reflecting mirror 11 is positioned so that the central axis C of the reflecting surface 12 is parallel to the Z axis and the reflecting surface 12 faces the sample holder 20 and the sample holding plate 31. As will be described in detail later, the sample holding plate 31 holds a sample 35, the conductivity of which is to be measured. The sample holder 20 holds the sample holding plate 31, which holds the sample 35 between it. In this case, the sample 35 is positioned substantially perpendicular to the central axis C and facing the reflecting surface 12, with a predetermined distance D (corresponding to the first distance) between the center of the reflecting surface 12 and the surface (reflecting surface) of the sample 35 facing it. The fixing stage 10 is a holding member that maintains the distance D between the concave reflecting mirror 11 and the sample holder 20 at a constant value. In the Fabry-Perot resonator 110, the distance D is set to 60 mm.

[0017] The reflecting surface 12 is a sphere with a radius R of 96 mm and a concave depth of 23 mm. The reflecting surface 12 is made of metal. In the Fabry-Perot resonator 110, the entire concave reflecting mirror 11 is made of copper, but the reflecting surface 12 may also be made of copper. Alternatively, it may be made of silver instead of copper. Furthermore, these metals may be plated or coated with resin.

[0018] 1, an input waveguide 41 and an output waveguide 42 are arranged in the concave reflecting mirror 11 near the central axis C. An input excitation hole 15 and an output excitation hole 16 having minute diameters for forming a coupling state that obtains desired resonance characteristics are formed at the tip openings of the input waveguide 41 and the output waveguide 42 on the reflecting surface 12 side. The input waveguide 41 is a signal input section to which an input signal for measuring the resonance characteristics of a sample is input, and the output waveguide 42 is a signal output section from which a detection signal is output.

[0019] 2 is a block diagram of a resonance characteristic measuring system 100 using a Fabry-Perot resonator 110. As shown in FIG. 2, the resonance characteristic measuring system 100 includes the Fabry-Perot resonator 110, a network analyzer 200, and a controller 300.

[0020] The network analyzer 200 outputs a millimeter-wave signal and inputs it to an input waveguide 41, which is a signal injection portion of the Fabry-Perot resonator 110. The network analyzer 200 also detects the millimeter-wave signal, which is input from the input waveguide 41 and transmitted through the Fabry-Perot resonator 110, from an output waveguide 42, which is a signal detection portion of the Fabry-Perot resonator 110. The network analyzer 200 then displays on a display portion a waveform (resonance waveform) with the horizontal axis representing frequency and the vertical axis representing transmission attenuation (transmission coefficient), based on the output millimeter-wave signal and the millimeter-wave signal detected after transmitting through the Fabry-Perot resonator 110.

[0021] FIG. 3 is a plan view schematically illustrating the configuration of the sample holder 20 of the Fabry-Perot resonator 110 according to the first embodiment. The sample holder 20 includes a first sample holder 21A (an example of a first sample holder) and a second sample holder 21B (an example of a second sample holder), which are arranged opposite each other, and four springs 25. The first sample holder 21A is fixed to the support base 10. The first sample holder 21A and the second sample holder 21B are substantially rectangular. The first sample holder 21A has a first surface facing the concave reflecting mirror 11 and a second surface facing the first surface. The second sample holder 21B has a third surface facing the second surface of the first sample holder 21A and a fourth surface facing the third surface. The four springs 25 are arranged near the four corners between the second surface of the first sample holder 21A and the third surface of the second sample holder 21B. The first holding housing 21A is provided with a through hole 24 (an example of a first through hole). The through hole 24 is a circular hole that penetrates the first holding housing 21A in the Z direction.

[0022] The second holding housing 21B is attracted to the first holding housing 21A by the attractive force generated by the spring 25, and the sample holding plate 31 holding the sample 35 therebetween is sandwiched between the second surface of the first holding housing 21A and the third surface of the second holding housing 21B. When sandwiching the sample holding plate 31 holding the sample 35 between the first holding housing 21A and the second holding housing 21B, a magnet and a magnetic body may be disposed in the first holding housing 21A and the second holding housing 21B, respectively, so that the second holding housing 21B is attracted to the first holding housing 21A by the magnetic force generated between the magnet and the magnetic body.

[0023] 4 is a diagram showing the attachment of a sample 35 to the sample holding plate 31 of the Fabry-Perot resonator 110. The first sample holding plate 31A has an outer surface (first surface), an inner surface (second surface) that are parallel to each other, and a circular through-hole 32 (an example of a second through-hole) that penetrates the outer and inner surfaces. The second sample holding plate 31B has an inner surface (third surface) and an outer surface (fourth surface) that are parallel to each other. The sample 35 is attached to the sample holding plate 31, positioned between the inner surfaces of the first sample holding plate 31A and the second sample holding plate 31B. 1 , the sample holding plate 31 holding the sample 35 is inserted into the sample holder 20 with the outer surface of the first sample holding plate 31A abutting against the second surface of the first holding housing 21A, the outer surface of the second sample holding plate 31B abutting against the third surface of the second holding housing 21B, and the sample 35 exposed from the through-holes 24 and 32 and facing the concave reflecting mirror 11. In the first embodiment, the sample holding plate 31 is an aluminum plate (aluminum plate) having a uniform thickness. Plates made of other non-magnetic metals or resins may also be used as the sample holding plate 31.

[0024] (Measurement of Conductivity) The process (steps) for measuring conductivity using the Fabry-Perot resonator 110 are as follows: 1) Connect the Fabry-Perot resonator 110, network analyzer 200, and controller 300 with cables. 2) Measure the resonance characteristics (first resonance characteristics) with the sample holding plate 31 sandwiching a reference metal (reference) with known conductivity inserted into the sample holder 20, and determine the Q value Q0 from the bandwidth of the resonance waveform and the resonance frequency f0. 3) Sandwich the sample 35 between the sample holding plates 31. 4) Insert the sample holding plate 31 sandwiching the sample 35 into the sample holder 20. 5) Measure the resonance characteristics (second resonance characteristics) of the sample 35, and determine the Q value Qs from the bandwidth of the resonance waveform and the resonance frequency fs. 6) Calculate the conductivity of the sample 35 from the conductivity σ0, Q value Q0, resonance frequency f0, Q value Qs, and resonance frequency fs of the known metal. The resonance characteristics may be measured multiple times in steps 2) and 5) and averaged. When measuring the conductivity of multiple types of samples 35, steps 3) to 6) are repeated.

[0025] (Effects, etc.) Figure 5 is an explanatory diagram showing the movement of the resonant waveform when the distance between the concave reflecting mirror 11 and the sample 35 changes due to differences in the film thickness of the sample 35. Figure 5(a) shows the case where the reflecting surface of the sample 35 is at the reference position, and Figure 5(b) shows the case where the reflecting surface of the sample 35 is located 200 μm closer to the reflecting surface 12 of the concave reflecting mirror 11 than the reference position. A 30 μm-thick copper sheet was used as the sample 35. In measuring the resonance characteristics in step 5 above, for example, if the resonant waveform is observed in the 2 GHz frequency range of 57 GHz to 59 GHz, as shown in Figure 5, several peaks indicating resonance are displayed, making it difficult to find the desired resonant waveform among them. Therefore, the frequency range is usually narrowed to, for example, 0.6 GHz (57.6 GHz to 58.3 GHz, range A indicated by the dashed line in Figure 5), and the measured resonant waveform is observed.

[0026] In the Fabry-Perot resonator 110, when the sample 35 is placed at the reference position as shown in FIG. 5A, the desired resonance is observed near a frequency of 58 GHz due to the relationship between the frequency of the input signal and the distance D between the center of the reflecting surface 12 and the reflecting surface of the sample 35. In contrast, when the sample 35 is moved 200 μm closer to the reflecting surface 12 of the concave reflecting mirror 11, the desired resonance frequency is observed at a frequency approximately 0.4 GHz higher, as shown in FIG. 5B. If the displayed frequency range is narrowed to range A indicated by the dashed line in FIG. 5B, the desired resonance will move outside of range A, as shown in FIG. 5B. This may prevent the operator from identifying the desired resonance or may mistakenly identify other unwanted resonances as the desired resonance. Adjusting the position of the concave reflecting mirror or the sample to display within the specified frequency range is not only time-consuming and inefficient, but errors in the adjustment may also result in errors in the measured conductivity, hindering accurate conductivity measurement.

[0027] In the Fabry-Perot resonator 110, the distance D between the center of the reflecting surface 12 and the reflecting surface of the sample 35 is constant regardless of the thickness of the sample 35, so that the desired resonance position does not move significantly, and efficient and accurate conductivity measurement is possible.

[0028] (Embodiment 2) In the first embodiment, a Fabry-Perot resonator 110 using one concave reflecting mirror 11 has been described. In the second embodiment, a Fabry-Perot resonator 120 using two concave reflecting mirrors will be described. FIG. 6 is a schematic diagram showing a cross section of the Fabry-Perot resonator 120 according to the second embodiment. As shown in FIG. 6, the Fabry-Perot resonator 120 has two concave reflecting mirrors 211 and 213 (a first concave reflecting mirror and a second concave reflecting mirror), a first holding housing 21A, a second holding housing 21B, and four springs 25 and spacers 245 arranged at the four corners between the first holding housing 21A and the second holding housing 21B. In the following description, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0029] The concave reflecting mirror 211 has a concave reflecting surface 212 (first reflecting surface), and the concave reflecting mirror 213 has a concave reflecting surface 214 (second reflecting surface). The reflecting surface 212 is a spherical surface having a central axis C1 and a radius R1 of 96 mm, and the reflecting surface 214 is a spherical surface having a central axis C2 and a radius R2 of 96 mm. The central axis C1 is parallel to the Z axis, and the central axis C2 is parallel to the Y axis. The surface of the sample 35 (a plane including the second surface of the first holding housing 21A) is located at the intersection of the central axis C1 of the reflecting surface 212 and the central axis C2 of the reflecting surface 214. The distances D1 and D2 between the centers of the reflecting surfaces 212 and 214 and the surface (reflecting surface) of the sample 35 are both 60 mm.

[0030] Concave reflecting mirror 211 has excitation hole 215 penetrating concave reflecting mirror 211 in the direction of central axis C1, and input waveguide 241 (signal input section) is arranged in excitation hole 215, while concave reflecting mirror 213 has excitation hole 216 penetrating concave reflecting mirror 213 in the direction of central axis C2, and output waveguide 242 (signal output section) is arranged in excitation hole 216. In the second embodiment, from the viewpoint of ease of manufacture, excitation holes 215, 216 are formed on central axes C1, C2, respectively, but they do not necessarily have to be formed on central axes C1, C2, and may be formed in concave reflecting mirrors 211, 213. In addition, in embodiment 2, from the viewpoint of ease of manufacturing, excitation holes 215 and 216 are formed in concave reflectors 211 and 213, respectively. However, it is also possible to form two excitation holes 215 and 216 in one of concave reflectors 211 and 213, and to place input waveguide 241 and output waveguide 242 in one of concave reflectors 211 and 213.

[0031] As shown in Fig. 6 , the first holding housing 21A that holds the sample 35 is arranged so that the angle θ1 between the normal N of a plane including the second surface of the first holding housing 21A (the surface facing the second holding housing 21B) and the central axis C1 is 45°, and the angle θ2 between the normal N and the central axis C2 is 45°. That is, when the sample 35 is sandwiched between the first holding housing 21A and the second holding housing 21B, the angle θ1 between the normal N of the surface (reflection surface) of the sample 35 and the central axis C1 is 45°, and the angle θ2 between the normal N and the central axis C2 is 45°. In this case, the intersection of the central axis C1 and the central axis C2 is located on the reflection surface of the sample 35. By arranging sample 35 relative to concave reflecting mirrors 211 and 213 in this way, the input signal input from input waveguide 241 is reflected by the surface of sample 35 in the direction of concave reflecting mirror 213, and resonance occurs between concave reflecting mirror 211 and concave reflecting mirror 213 via sample 35. When measuring the resonance characteristics of a reference metal in step 2) of the conductivity measurement described in embodiment 1, the input signal is reflected by the surface of the reference metal, and resonance occurs between concave reflecting mirror 211 and concave reflecting mirror 213 via the reference metal.

[0032] As shown in FIG. 6 , the spacer 245 is disposed between the concave reflecting mirrors 211, 213 and the first holding housing 21A. The spacer 245 is a holding member that reliably maintains a constant distance between the concave reflecting mirrors 211, 213 and the surface of the sample 35 (the reflecting surface, i.e., the plane including the second surface of the first holding housing 21A). As shown in FIG. 6 , the spacer 245 has two openings 246, 247 and a recess 248. The opening 246 is a hole through which the central axis C1 passes, and the opening 247 is a hole through which the central axis C2 passes. The first holding housing 21A and the second holding housing 21B, which sandwich the sample 35, are disposed in the recess 248. By securely positioning the first holding housing 21A and the second holding housing 21B in the recess 248 of the spacer 245, the distance between the center of the reflecting surfaces 212, 214 of the concave reflecting mirrors 211, 213 and the surface (reflecting surface) of the sample 35 is ensured to be constant regardless of the thickness of the sample 35.

[0033] In the second embodiment, an example has been described in which the concave reflecting mirrors 211, 213 and the sample 35 are arranged so that the angles θ1 and θ2 are 45°, but the angles θ1 and θ2 do not have to be 45°, and may be, for example, 30° as long as the angles θ1 and θ2 are the same.

[0034] 6, the Fabry-Perot resonator 120 does not use the sample holding plate 31 described in the first embodiment, but the sample holding plate 31 may be used as in the first embodiment. In this case, the wall portion 249 of the spacer 245 needs to be positioned so that the intersection of the central axis C1 of the reflecting surface 212 and the central axis C2 of the reflecting surface 214 located on the surface (reflecting surface) of the sample 35 is located on a plane including the inner surface (second surface) of the first sample holding plate 31A.

[0035] (Embodiment 3) In the first and second embodiments, a technique for positioning the sample 35 so that the distance D between the reflecting surface of the sample 35 and the center of the reflecting surface 12 of the concave reflecting mirror 11 is constant regardless of the thickness of the sample 35 has been described. When measuring conductivity using an open resonator, it is necessary to measure the resonance characteristics of both the reference and the sample 35 under conditions where the distance D is as close to identical as possible. Figure 7 is a graph showing the change in calculated specific conductivity as the distance D between the center of the reflecting surface 12 of the concave reflecting mirror 11 and the reflecting surface of the sample 35 changes. Figure 7 shows the change in measured specific conductivity when the distance D is changed by ±200 μm from the reference position, with a reference position of 60 mm. As can be seen from Figure 7, a change in distance D of 200 μm significantly changes the measured specific conductivity. For example, if a tolerance of ±2% is desired for the measured specific conductivity, the distance D must be set within a range of ±0.6 μm from the reference position of 60 mm. In the Fabry-Perot resonators 110 and 120 described in the first and second embodiments, although the distance D is set to a constant value, it is difficult to determine whether the distance D is actually set within the range of ±0.6 μm. In the third embodiment, a Fabry-Perot resonator will be described, which allows confirmation that the distance D is set within a constant range.

[0036] FIG. 8 is a schematic diagram showing a cross section of a Fabry-Perot resonator 130 according to the third embodiment. As shown in FIG. 8, the Fabry-Perot resonator 130 has a movable stage 47 between the sample holder 20 and the mounting base 10 of the Fabry-Perot resonator 110 according to the first embodiment. That is, the Fabry-Perot resonator 130 differs from the Fabry-Perot resonator 110 in that the sample holder 20 is disposed on the movable stage 47, in that the sample holder 20 is fixed to the mounting base 10. In the following description, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted. The movable stage 47 is disposed on the mounting base 10 and is movable parallel to the Z axis. The movable stage 47 is moved by a micrometer (not shown). By moving the movable stage 47 in the left-right direction, the sample 35 held on the sample holder 20 can be moved closer to or farther away from the concave reflecting mirror 11.

[0037] 9A and 9B are flowcharts illustrating a method for measuring electrical conductivity using a Fabry-Perot resonator 130 according to the third embodiment. First, a reference metal (reference) with a known electrical conductivity is attached to the sample holder 20. Prior to more precise measurements of the resonance characteristics (S3 to S5), the resonance characteristics of the reference are measured at a desired frequency (a first frequency, e.g., 110 GHz) to simply confirm that the measurement position (reflection surface) of the reference attached to the sample holder 20 is stable (S1). At this time, the measurement of the resonance characteristics is repeated, and it is determined whether the resonance frequency measured over a predetermined period is within the reference range (S2). If the resonance frequency measured over the predetermined period is not within the reference range (No in S2), the measurement of the resonance characteristics continues. If the resonance frequency measured over the predetermined period is within the reference range (Yes in S2), the method proceeds to more precise measurements of the resonance characteristics from step S3 onward. Specifically, for example, the resonance characteristics are measured multiple times per second, and the average value is used as one measurement value, and this is repeated for 10 seconds (10 times) or more, and measurement is continued until the variation in the measurement values ​​(i.e., the difference between the maximum and minimum values) over the last 10 seconds falls within a reference range (e.g., within 15 kHz). Note that by displaying the measurement results (transition of the resonance frequency) on a monitor, it becomes possible to easily check whether the measurement position of the reference attached to the sample holder 20 is stable.

[0038] Next, in step S3, the reference resonance characteristic (first resonance characteristic) is measured multiple times more precisely (by spacing the frequency measurement points closer together) at the first frequency. The number of times to measure the resonance characteristic in step S3 is not limited to two or more, and is preferably selected from two to five times. In the third embodiment, the number of times is three. Next, the process proceeds to step S4, where it is determined whether the variations in the multiple resonance frequencies measured in the multiple resonance characteristic measurements in step S3 are within a reference range. If it is determined that the values ​​of the multiple resonance frequencies are not within the reference range (No in S4), after a predetermined time has elapsed (S5), the process returns to step S3, where the reference resonance characteristic is measured multiple times, and the process proceeds to step S4 again. The predetermined time in step S5 is 30 seconds in the third embodiment, but may be set to 60 seconds, for example. Furthermore, if the determination in step S4 is "No" after the predetermined time of 30 seconds has elapsed in step S5, the predetermined time in step S5 may be set to 60 seconds, longer than 30 seconds, depending on the number of "No" determinations in step S4. If it is determined in step S4 that the variation in the resonant frequency is within the reference range (Yes in S4), measurement of the reference resonance characteristics at the first frequency is terminated. In the third embodiment, this reference range is set to ±3.3 kHz, the same as the reference range ((second predetermined range)) in measuring the resonance characteristics of sample 35 described later. However, it can be set depending on the allowable measurement error of the conductivity. Here, the resonant frequency and bandwidth for calculating the Q value may be average values ​​of measurements obtained from multiple measurements of the resonance characteristics.

[0039] Next, in order to measure the reference resonance characteristics for all desired frequencies, it is determined whether the resonance characteristics have been measured for all frequencies (S6), and if the measurements for all desired frequencies have not been completed (No in S6), the frequency to be measured is changed to the next frequency (e.g., 105 GHz), and the reference resonance characteristics are measured (S7). If the measurements for all desired frequencies have been completed (Yes in S6), the process proceeds to step S8.

[0040] In steps S8 and after shown in FIG. 9B , the sample 35, the conductivity of which is to be measured, is mounted in the sample holder 20, and the resonance characteristics (second resonance characteristics) of the sample 35 are measured. First, in step S8, the resonance characteristics of the sample 35 are measured at a first frequency to align the measurement position (reflecting surface) of the sample 35 with the measurement position (reflecting surface) of the reference measured in steps S3 to S5 (i.e., to match the distance D). The measured resonance frequency is then displayed on the monitor along with a target predetermined reference range. Here, the measured resonance frequency is determined by the distance D between the center of the reflecting surface 12 of the concave reflecting mirror 11 and the reflecting surface of the sample 35. Therefore, the distance D can be matched by matching the resonance frequency obtained in the measurement of the reference resonance characteristics with the resonance frequency obtained in the measurement of the resonance characteristics of the sample 35. Therefore, in the conductivity measurement of the third embodiment, the resonance frequency of the reference measured in steps S3 to S5 is set as the target resonance frequency, and the allowable range of variation for the target resonance frequency is set as the reference range (first predetermined range). As described above, when the distance D is 60 mm, the resonant frequency variation corresponding to the allowable tolerance of ±0.6 μm is approximately ±1 MHz when the target resonant frequency is 110 GHz, so in embodiment 3, ±1 MHz is set as the reference range.

[0041] 10 is a diagram showing the transition of the measured resonant frequency in the method for measuring conductivity using the Fabry-Perot resonator 130 according to embodiment 3. As shown in Fig. 10, the transition of the measured resonant frequency of the sample 35 is displayed on a graph together with the target resonant frequency and its reference range (S8).

[0042] Next, in step S9, it is determined whether the resonant frequency measured for the sample 35 is within the reference range. If it is not within the reference range (No in S9), the position of the sample 35 is adjusted by moving the movable stage 47 (S10), and the process returns to step S8, where the resonance characteristics of the sample 35 are measured at the adjusted position. If the resonant frequency of the sample 35 is within the reference range (Yes in S9), the process proceeds to step S11. In steps S8 to S10, the position of the sample 35 is adjusted by moving the movable stage 47, and when the resonant frequency of the sample 35 falls within the reference range as shown in FIG. 10, the adjustment of the position of the sample 35 by moving the movable stage 47 is completed.

[0043] Next, a method for measuring the conductivity after adjusting the position of the sample 35 will be described. As described above, the conductivity is calculated from the Q value, which is calculated from the resonant frequency and bandwidth obtained by measuring the resonance characteristics of the sample 35. As described above, in steps S8 to S10, the position of the sample 35 is adjusted by moving the movable stage 47, and the resonant frequency of the sample 35 is measured within a certain allowable reference range. Therefore, it is necessary to accurately measure the bandwidth in the next step of measuring the resonance characteristics of the sample 35.

[0044] First, in step S11, prior to more precise measurements of the resonance characteristics (S13 to S15), the resonance characteristics of the sample 35 mounted on the sample holder 20 are measured at a first frequency to simply confirm that the measurement position (reflection surface) of the sample 35 is stable. At this time, similar to the confirmation of the stability of the reference measurement position (reflection surface) in steps S1 and S2, the measurement of the resonance characteristics is repeated, and it is determined whether the resonance frequency measured over a predetermined period of time is within a reference range (S12). If the resonance frequency measured over a predetermined period of time is not within the reference range (No in S12), the measurement of the resonance characteristics continues. If the resonance frequency measured over a predetermined period of time is within the reference range (Yes in S12), the process proceeds to more precise measurements of the resonance characteristics from step S13 onward. Here, the predetermined period (10 seconds (10 times)) and the reference range (within 15 kHz) are the same as those used in the measurement of the reference resonance characteristics described above, but may be changed depending on the type and characteristics of the sample 35.

[0045] The resonance characteristics are measured by sweeping the frequency. The more precise the measurement, the longer the time required for one frequency sweep (e.g., about 1 second). (The more (more densely) the frequency measurement points are used, the longer the measurement time.) If the position of the sample 35 is not stable during this sweep, the resonance waveform (resonance frequency) will shift, resulting in an inaccurate bandwidth measurement and an inaccurate Q value. Figure 11 is a schematic diagram illustrating the change in the resonance waveform when the position of the sample fluctuates during the measurement of the resonance characteristics. Since the network analyzer 200 sweeps the frequency point by point, starting from the lowest point. For example, as shown in Figure 11, if the resonance frequency moves higher (lower) during the sweep, the measured bandwidth will be wider (narrower) than the actual correct bandwidth. As a result, an accurate Q value cannot be obtained. Therefore, the resonance characteristics must be measured when the position of the sample 35 (i.e., the resonance frequency) is stable. As described below, this level is on the order of several nanometers for the position of the sample 35, and the variation in the resonance frequency is within several kHz.

[0046] Next, we will explain the effect of the measured bandwidth (i.e., Q factor) on the calculated conductivity. For example, if the measured resonant frequency fs is 110 GHz and the bandwidth BW is approximately 1 MHz, the Q factor will be approximately 120,000. As shown in the example in Figure 11, if the resonant frequency shifts higher during the frequency sweep and the measured bandwidth is wider than the correct value, the calculated Q factor will be smaller. For example, if the Q factor is calculated as 123,000, which is actually 124,000, and converted to a specific conductivity of 1.01, the calculated value will be 0.963, approximately 4.7% smaller, significantly exceeding the allowable 2% tolerance. To keep the measurement error within -2%, the specific conductivity must be 0.991 or greater, and the corresponding Q factor will be 123,600 or greater. Therefore, to keep the conductivity measurement error below 2%, it is desirable to be able to measure the Q factor with a reproducibility of approximately ±400. For example, if the resonance frequency fs is 110 GHz and the bandwidth BW is about 1 MHz, the Q value will be about 120,000, so the error in the measured bandwidth BW will be about ±3.3 kHz (= 400 / 120,000) for 1 MHz. If the distance D between the concave reflecting mirror 11 and the sample 35 is 60 mm, the calculated resonance frequency is 109.4 GHz, so the stability of the distance corresponding to the bandwidth BW error of ±3.3 kHz is ±1.81 nm, and the resonance characteristics must be measured with the position of the sample 35 stable on the nanometer order.

[0047] 9B , a method for measuring the resonance characteristics with the sample 35 in a stable position when measuring conductivity using the Fabry-Perot resonator 130 will be described. As described above, if the resonance frequency measured for the sample 35 is within the reference range in step S12 (Yes in S12), the procedure proceeds to more precise measurement of the resonance characteristics in step S13 and subsequent steps. In step S13, the resonance characteristics of the sample 35 are measured multiple times. The number of measurements of the resonance characteristics in step S13 is not limited to two or more times, and is preferably selected from about two to five times, but in the third embodiment, the number is three.

[0048] Next, the process proceeds to step S14, where it is determined whether the values ​​of the multiple resonant frequencies measured in the multiple resonance characteristic measurements of step S13 are within a reference range (second predetermined range). In the third embodiment, this reference range is ±3.3 kHz, but as described above, the reference range can be set according to the allowable conductivity error. If it is determined that the values ​​of the multiple resonant frequencies are not within the reference range (No in S14), the process waits for a predetermined time to elapse (S15), returns to step S13, and multiple resonance characteristic measurements are performed on the sample 35, and then proceeds to step S14. The predetermined time in step S15 is 30 seconds in the third embodiment, but may be changed as appropriate, as in the case of step S5 above. If it is determined in step S14 that the variations in the multiple resonance frequencies are within the reference range (Yes in S14), it is determined that the position of the reflecting surface of the sample 35 is stable, and the measurement of the resonance characteristic of the sample 35 at the first frequency is terminated. Here, the resonant frequency and bandwidth for calculating the Q value may be average values ​​measured in multiple resonance characteristic measurements.

[0049] Next, in order to measure the resonance characteristics of the sample 35 for all desired frequencies, it is determined whether the resonance characteristics have been measured for all frequencies (S16), and if measurements for all desired frequencies have not been completed (No in S16), the frequency to be measured is changed to the next frequency (e.g., 105 GHz), and the resonance characteristics of the sample 35 are measured (S17). When measurements for all desired frequencies have been completed (Yes in S16), the measurement of the resonance characteristics of the sample 35 is completed.

[0050] (Effects, etc.) FIG. 13 shows the stability of specific conductivity measured by the conductivity measurement method using a Fabry-Perot resonator according to the third embodiment. Conductivity measurements were performed on two types of samples 35 (copper foil A (Ra = 0.15 μm, Rz = 1.2 μm) and copper foil B (Ra = 0.45 μm, Rz = 2.5 μm)) using a Fabry-Perot resonator for measuring the broadband region (23 to 110 GHz) and a Fabry-Perot resonator for measuring the D-band region (110 to 170 GHz). The graph shown in FIG. 13 shows the conductivity measurement results obtained by repeating three times the series of steps of placing the sample holding plate 31 holding the sample 35 in the sample holder 20, measuring the conductivity, and removing the sample holding plate 31 holding the sample 35 from the sample holder 20. In FIG. 13, the first measurement value is indicated by a black circle, the second measurement value by a triangle, and the third measurement value by a circle. As shown in FIG. 13, the conductivity measurement method using the Fabry-Perot resonator according to the third embodiment enables the conductivity of both copper foil A and copper foil B to be measured stably and with good reproducibility in the broadband and D-band frequency bands.

[0051] Other Embodiments In the first embodiment, an example has been described in which the sample 35 is placed between the first sample holding plate 31A and the second sample holding plate 31B, and the sample holding plate 31 holding the sample 35 is placed in the sample holder 20. The sample 35 only needs to be placed so that the distance D between the reflecting surface of the sample 35 and the center of the reflecting surface 12 of the concave reflecting mirror 11 is constant regardless of the thickness of the sample 35, and the sample 35 may be placed in the sample holder 20 without using the sample holding plate 31.

[0052] In the first embodiment, the Fabry-Perot resonator 110 is described, in which the distance D is kept constant by fixing the concave reflecting mirror 11 and the sample holder 20 to the fixing table 10. As described in the second embodiment, by disposing a spacer between the concave reflecting mirror 11 and the sample holder 20 (the first surface of the first holding housing 21A), the distance D can also be kept constant without fixing the sample holder 20 to the fixing table 10.

[0053] In the second embodiment, spacers 245 are disposed between the concave reflecting mirrors 211 and 213 and the sample holding plate 31 so that the distances D1 and D2 between the centers of the reflecting surfaces 212 and 214 of the concave reflecting mirrors 211 and 213 and the reflecting surface of the sample 35 are constant regardless of the thickness of the sample 35. The sample 35 only needs to be disposed so that the distances D1 and D2 between the reflecting surfaces of the sample 35 and the centers of the reflecting surfaces 212 and 214 of the concave reflecting mirrors 211 and 213 are constant regardless of the thickness of the sample 35. Instead of using the spacers 245, the sample holder 20 may be fixed directly to the fixing table as in the first embodiment. However, by using spacers and providing a location on the spacer where the sample 35 is to be placed (for example, the recess 248 in the second embodiment), it becomes possible to fix the distances D1 and D2 constant with a relatively simple configuration.

[0054] In the first embodiment, an example has been described in which the sample 35 is sandwiched between the sample holding plate 31 by itself. The sample 35 may be attached to a support and sandwiched between the sample holding plate 31 instead of being held by itself. For example, if the sample 35 is a metal foil that is extremely thin and cannot stand on its own, it is easier to position the reflecting surface of the sample 35 by sandwiching it between the sample holding plate 31 by attaching it to a support such as a glass film.

[0055] In the Fabry-Perot resonators according to the first to third embodiments, a waveguide is used for the signal input section and the signal output section. Depending on the frequency to be measured, a coaxial cable having a loop antenna at its tip can be used instead of the waveguide.

[0056] In the third embodiment, an example has been described in which, prior to more precise measurement of resonance characteristics, it is confirmed whether the measurement positions (reflection surfaces) of the reference and sample 35 are stable (steps S1 and S2 in FIG. 9A and steps S11 and S12 in FIG. 9B). If it can be determined that the measurement positions of the reference or sample 35 are stable, at least one of steps S1 and S2 or steps S11 and S12 may be omitted.

[0057] 9B, if the resonant frequency measured for the sample 35 is within the reference range (Yes in S11), the process proceeds to step S13. If it is sufficiently expected that the variations in the measured resonant frequencies will be within the reference range even when the resonant characteristics are repeatedly measured, the process may proceed to step S16 without performing steps S13 to S15.

[0058] In the third embodiment, an example in which conductivity is measured at a plurality of frequencies has been described. When conductivity is measured at a single frequency, steps S6, S7, S16, and S17 are omitted.

[0059] The open resonator of the present invention is suitable for measuring the conductivity of a sample with higher accuracy.

[0060] 10 Fixing base 11, 51, 211, 213 Concave reflecting mirror 12, 212, 214 Reflecting surface 15, 215 Excitation hole 16, 216 Excitation hole 20 Sample holder 21A, 21B Holding housing 24 Through hole 25 Spring 31, 31A, 31B Sample holding plate 32 Through hole 35, 55 Sample 41, 241 Input waveguide 42, 242 Output waveguide 245 Spacer 246, 247 Opening 47 Movable stage 248 Recess 249 Wall 50 Sample stage 100 Resonance characteristic measurement system 110, 120, 130, 150 Fabry-Perot resonator 200 Network analyzer 300 Controller C, C1, C2 Central axis D, D1, D2, L Distance R, R1, R2 Radius N Normal

Claims

1. An open-type resonator used to measure the conductivity of a sample, A first concave reflector having a concave first reflecting surface made of metal, A first sample holding housing having a first through-hole through which the central axis of the first reflective surface passes, a first surface, and a second surface facing the first surface, A second sample holding housing has a third surface facing the second surface and a fourth surface facing the third surface, without having a through hole at a position through which the central axis of the first reflective surface passes, and the second sample holding housing holds the sample between itself and the first sample holding housing by moving the position of the third surface relative to the second surface of the first sample holding housing, The apparatus comprises a holding member for maintaining a constant first distance between the surface of the sample held between the first sample holding housing and the second sample holding housing, and the surface of the sample facing the second surface of the first sample holding housing, the sample being held between the first sample holding housing and the second sample holding housing. Open resonator.

2. The present invention further comprises a first sample holding plate having a second through-hole through which the central axis of the first reflective surface passes, and a second sample holding plate that does not have a through-hole at the position through which the central axis of the first reflective surface passes, The sample is placed between the first sample holding plate and the second sample holding plate. The open-type resonator according to claim 1.

3. The holding member is a fixing base to which the first concave mirror and the first sample holding housing are fixed. The open-type resonator according to claim 1.

4. The holding member is a spacer positioned between the first concave mirror and the first surface of the first sample holding housing. The open-type resonator according to claim 1.

5. The holding member is a movable stage that holds the first sample holding housing and the second sample holding housing and is configured to move along the central axis. The open-type resonator according to claim 1.

6. The system further comprises a second concave reflecting mirror having a concave second reflecting surface made of metal, The second distance between the sample and the second reflective surface is equal to the first distance. The open-type resonator according to claim 1.

7. A method for measuring conductivity using an open-type resonator according to any one of claims 1 to 6, A step of placing a reference metal having a known conductivity between the first sample holding housing and the second sample holding housing, and measuring the first resonance characteristics, The process involves placing the sample between the first sample holding housing and the second sample holding housing, and measuring the second resonance characteristic. The method includes a step of calculating the conductivity of the sample using the known conductivity, the Q value obtained from the measured first resonance characteristic, and the Q value obtained from the measured second resonance characteristic. Method for measuring electrical conductivity.

8. A first concave reflector having a concave first reflecting surface made of metal, A first sample holding housing having a first through-hole through which the central axis of the first reflective surface passes, a first surface, and a second surface facing the first surface, A second sample holding housing has a third surface facing the second surface and a fourth surface facing the third surface, and the second sample holding housing holds the sample between itself and the first sample holding housing by the movement of the position of the third surface relative to the second surface of the first sample holding housing, The apparatus comprises a holding member for maintaining a constant first distance between the surface of the sample held between the first sample holding housing and the second sample holding housing, and the surface of the sample facing the second surface of the first sample holding housing, the sample being held between the first sample holding housing and the second sample holding housing, The holding member is a movable stage configured to hold a first sample holding housing and a second sample holding housing and to move along the central axis, in a method for measuring the conductivity of a sample using an open-type resonator, A step of placing a reference metal having a known conductivity between the first sample holding housing and the second sample holding housing, and measuring the first resonance characteristics, The process involves placing the sample between the first sample holding housing and the second sample holding housing, and measuring the second resonance characteristic. A step of calculating the conductivity of the sample using the known conductivity, the Q value obtained from the measured first resonance characteristic, and the Q value obtained from the measured second resonance characteristic, A step of displaying a first predetermined range of target frequencies determined based on the resonant frequency of the reference metal measured in the step of measuring the first resonance characteristics, and the resonant frequency of the sample measured in the step of measuring the second resonance characteristics, The process includes a step of adjusting the position of the sample so that the resonant frequency of the sample measured in the step of measuring the second resonance characteristic falls within the first predetermined range. Method for measuring electrical conductivity.

9. If the resonance frequency of the sample measured in the step of measuring the second resonance characteristic is within the first predetermined range, the step of measuring the second resonance characteristic of the sample multiple times, The process of measuring the second resonance characteristics of the sample multiple times, and determining whether the multiple resonance frequencies of the sample measured are within a second predetermined range, If, in the step of measuring the second resonance characteristics multiple times, the multiple resonance frequencies of the sample measured are not within the second predetermined range, the method further comprises the step of measuring the second resonance characteristics of the sample multiple times after a predetermined time has elapsed. The method for measuring conductivity according to claim 8.