JP4530907B2 - Method for measuring dielectric properties of dielectric thin films - Google Patents

Description

  The present invention relates to a dielectric property measurement method for a dielectric thin film sample, and more particularly to a dielectric property measurement method for a dielectric thin film used as an electronic component in a millimeter wave region of 30 GHz or more.

  In recent years, with the development and popularization of mobile communication technology, systems in the millimeter wave band have been developed for the purpose of high transfer. Research on VCOs and tunable filters using dielectric thin films in the millimeter wave band is also underway, and measuring the physical properties of dielectric thin films is an important issue for the design and development of dielectric thin films. It is.

  Here, it is known that the dielectric characteristics of the dielectric thin film in the microwave band can be measured with high accuracy by using, for example, a cavity resonator as shown in FIG. 4 (see Patent Document 1). That is, a dielectric substrate 2 provided with a dielectric thin film 1 on the surface is sandwiched between a pair of bottomed cylindrical conductors 3 having flanges to form a cavity resonator, and a side surface of one bottomed cylindrical conductor 3 is formed. Excavation and detection of the cavity resonator can be performed by opening holes at two locations and inserting the micro loop antennas 5a and 5b provided at the ends of the coaxial cables 4a and 4b from the respective holes. Then, the resonance frequency and no-load Q of this cavity resonator are measured, and the dielectric characteristics (relative dielectric constant, dielectric loss tangent) of the dielectric thin film are obtained from the resonance frequency and no-load Q.

Specifically, first, a state where the dielectric thin film 1 and the dielectric substrate 2 are not inserted, that is, a pair of bottomed cylindrical conductors 3 is formed so as to join the respective openings, and the cavity resonator is configured, It is necessary to measure the resonance frequency and no-load Q of the cavity resonator to determine the size and conductivity of the cavity resonator. Next, a pair of bottomed cylindrical conductors 3 are sandwiched with a dielectric substrate 2 (a laminated structure comprising the dielectric thin film 1 and the dielectric substrate 2) on which the dielectric thin film 1 is formed, and similarly. By measuring the resonant frequency and no-load Q of the cavity resonator, the dielectric properties (dielectric constant, dielectric loss tangent) of the dielectric thin film 1 can be obtained.
JP 2002-228600 A

  However, the dielectric property measurement of the dielectric thin film by the resonator method using the cavity resonator having the above structure is established up to the microwave band, and the above resonator method is used in the millimeter wave band (30 GHz). At present, high-precision dielectric property measurement of dielectric thin films has not been established.

The electric field intensity of the TE ₀₁₁ mode generated in the cavity resonator becomes maximum at the center plane in the height direction of the cavity resonator and becomes zero at both ends. Therefore, when measuring the dielectric properties of a dielectric thin film at around 10 GHz, a dielectric substrate having a dielectric thin film formed on the upper surface is placed at a place where the electric field in the cavity resonator is maximum (in the height direction of the cavity resonator). Since the electric field can be concentrated on the dielectric thin film 1 and the dielectric substrate 2 by being arranged on the center plane), highly accurate measurement is possible.

On the other hand, when trying to expand this frequency to a millimeter wave band of 30 GHz or more, it is necessary to make the cavity dimension smaller than in the case of 10 GHz and reduce the thickness of the dielectric thin film 1 and the dielectric substrate 2. There is a limit to making the substrate thinner, and the ratio between the cavity size and the dielectric substrate will be different. Then, there is a problem that the measurement frequency when the dielectric substrate is inserted is greatly lowered with respect to the resonance frequency of the TE ₀₁₁ mode of the cavity resonator in a state where the substrate is not inserted, and measurement becomes impossible.

  An object of the present invention is to provide a dielectric property measurement method for a dielectric thin film that can be accurately measured in a millimeter wave band of 30 GHz or more.

  As a result of repeated studies, the inventors have placed a dielectric substrate having a dielectric thin film formed on the upper surface thereof on a conductor plate, and further formed a bottomed cylindrical conductor having an opening on the opening. Is arranged so as to be in contact with the dielectric thin film, the cavity resonator is configured, the resonance frequency of the TE mode and the no-load Q of the cavity resonator are measured, and the dielectric thin film dielectric is measured from the resonance frequency and the no-load Q The inventors have found that the above problems can be solved by obtaining the characteristics, and have reached the present invention.

According to the present invention, a cavity resonator is formed by arranging a bottomed cylindrical conductor having an opening on a conductor plate so that the opening abuts against the conductor plate, and then TE mode of the cavity resonator is formed. Measuring the resonance frequency and no-load Q of the substrate, and determining the dimensions and conductivity of the cavity resonator from the resonance frequency and no-load Q, and forming a dielectric substrate formed with a dielectric thin film on the main surface. After the body thin film is placed on the conductor plate so that it faces downward, the bottom resonator is disposed so that the opening of the bottomed cylindrical conductor is in contact with the dielectric substrate. resonant frequency and the unloaded Q of the TE mode of the cavity resonator is measured, a step of determining dielectric properties of the dielectric substrate from the resonant frequency and the unloaded Q, as the dielectric thin film is directed upward The dielectric substrate is placed on the conductor plate, and the dielectric thin film After the bottomed cylindrical conductor is arranged so that the opening is in contact with the cavity resonator, a TE-mode resonance frequency and no-load Q of the cavity resonator are measured, and the resonance frequency and no-load are measured. Q, a method for measuring the dielectric properties of the dielectric thin film, including the step of obtaining the dielectric properties of the dielectric thin film using the dimensions and conductivity of the cavity resonator and the dielectric properties of the dielectric substrate .

  Here, it is preferable that a relative dielectric constant of the dielectric thin film is larger than a relative dielectric constant of the dielectric substrate. By doing so, the ratio of the stored energy of the dielectric thin film to the total stored energy can be increased, and the measurement accuracy can be improved.

The dielectric thin film is preferably 10 μm or less, and the TE mode is preferably a TE ₀₁₁ mode.

According to the present invention, since the dielectric substrate is disposed in contact with the conductor plate at the end face, the dielectric substrate is disposed at a position where the TE ₀₁₁ mode electric field strength inherent to the cavity resonator is small. The electric field energy stored in the inside is limited, and the decrease in the resonance frequency of the TE mode (TE ₀₁₁ mode), that is, the decrease in the measurement frequency of the dielectric constant is alleviated. If a dielectric thin film is formed on a dielectric substrate in this state, it is possible to easily measure in the millimeter wave band. Therefore, the present invention is effective in the millimeter wave band, and is particularly suitable when the resonance frequency is 30 GHz or more.

The dielectric property measuring method of the present invention will be described with reference to the drawings.
FIG. 1 is a longitudinal sectional view showing a state in which a dielectric substrate having a dielectric thin film as a measurement sample formed on the upper surface is arranged in a cavity resonator. Specifically, a dielectric substrate 2 formed with a dielectric thin film 1 serving as a measurement sample on the upper surface is placed on a conductor plate 6, and the bottomed cylindrical conductor 3 having an opening 31 is placed on the dielectric substrate. A cavity resonator is configured so that the opening 31 is in contact with the dielectric thin film 1 on the substrate 2. The dielectric characteristic measuring method of the present invention measures the resonance frequency and no-load Q of the TE mode (preferably the TE ₀₁₁ mode) of the cavity resonator having such a structure, and from this resonance frequency and no-load Q, the dielectric thin film 1 is measured. It is characterized in that the dielectric characteristics of the above are obtained.

As shown in FIG. 1, a through-hole is formed in the side wall of the bottomed cylindrical conductor 3, coaxial cables 4a and 4b are inserted from the outside toward the inside, and a loop antenna 5a is provided at the inner end of the through hole. 5b are formed. Here, the insertion depth of the loop antennas 5a and 5b into the cavity resonator is adjusted so that the insertion loss at the resonance frequency of the TE mode (preferably the TE ₀₁₁ mode) is about 30 dB. Then, for example, a signal whose frequency is swept from a transmitter such as a synthesized sweeper is injected from one coaxial cable 4a into the cavity resonator through the loop antenna 5a, so that the resonance electromagnetic wave in the TE mode (preferably the TE ₀₁₁ mode) is obtained. The world is excited. Further, the transmission signal of the cavity resonator is input from the other loop antenna 5b through the coaxial cable 4b to a measuring instrument such as a network analyzer, and the resonance frequency of the cavity resonator in which the measurement sample (dielectric thin film 1) is installed is measured. The load Q is measured, and the dielectric characteristics, that is, the relative dielectric constant and the dielectric loss tangent are obtained by calculation.

The relative dielectric constant ε ′ and the dielectric loss tangent tan δ of the dielectric thin film can be obtained by numerical analysis of the finite element method, the FDTD method, and the mode matching method. For example, when the analysis is performed by the mode matching method, the relative permittivity ε ′ is determined by the following: cavity radius R, height H, resonance frequency f ₀ , dielectric substrate thickness t ₁ , radius a, and dielectric thin film It is calculated from the thickness t ₂ using the following formula.

Here, detM is a determinant of the matrix M derived from the boundary condition of the electromagnetic field of the TE ₀₁₁ mode.

The dielectric loss tangent tan δ is calculated from the measured value of the no-load Q (Q _u ) of the cavity resonator using the following equation.

However, Q _d is the Q due to dielectric loss, _{Q c} is Q by conductor loss. The dielectric loss tangent of the dielectric thin film can be calculated by measuring in advance the conductor loss of the cavity resonator other than the measurement sample (dielectric thin film) and the dielectric loss tangent of the dielectric substrate.

  Specifically, for such a measurement, first, a state in which the dielectric substrate is not inserted, that is, the bottomed cylindrical conductor 3 having the opening 31 is placed on the conductor plate 6 is configured. It is necessary to measure the resonance frequency and no-load Q of the cavity resonator to be measured and to measure the size and conductivity of the cavity resonator. This method is defined in JIS R 1641: 2002. Next, the second dielectric substrate is inserted between the bottomed cylindrical conductor 3 and the conductor plate 6 to measure the resonance frequency and no-load Q with respect to the second dielectric substrate. It is necessary to measure the dielectric constant and dissipation factor. This is a so-called correction. Thereafter, the dielectric thin film 1 is formed on the dielectric substrate 2 by sputtering, vapor deposition, or the like, and the dielectric characteristics (relative dielectric constant and dielectric loss tangent) can be obtained by the measurement method of the present invention. The second dielectric substrate may be the dielectric substrate 1 on which the dielectric thin film 1 is formed. The dielectric substrate 1 on which the second dielectric substrate and the dielectric thin film 1 are formed. May be different materials of the same material.

  As described above, when the dielectric thin film 1 is not formed in advance on the upper surface of the dielectric substrate 2, the dielectric characteristics of the dielectric thin film 1 can be obtained by the above-described flow. When the dielectric thin film 1 is formed on the surface (upper surface or lower surface), the dielectric substrate 2 can be measured upside down.

  That is, first, as shown in FIG. 2, a dielectric substrate 2 formed with a dielectric thin film 1 as a measurement sample on the main surface is placed on a conductor plate 6 so that the dielectric thin film 1 faces downward. The bottomed cylindrical conductor 3 having the opening 31 is disposed on the dielectric substrate 2 so that the opening 31 is in contact with the dielectric substrate 2 to form a cavity resonator, and the TE of the cavity resonator is formed. The resonance frequency and no-load Q of the mode are measured, and the dielectric characteristics of the dielectric substrate 2 are obtained from the resonance frequency and the no-load Q. At this time, the electric field generated in the dielectric thin film 1 becomes almost zero, the influence of the dielectric thin film 1 can be ignored, and the relative dielectric constant and dielectric loss tangent of only the dielectric substrate 2 can be measured.

  Thereafter, the dielectric substrate 2 is turned upside down, and placed on the conductor plate 6 so that the dielectric thin film 1 faces upward as shown in FIG. Is arranged so that the opening 31 faces the dielectric thin film 1 on the dielectric substrate 2 to form a cavity resonator, and the TE mode resonance frequency and no-load Q of the cavity resonator are measured, and the resonance frequency is measured. Further, the dielectric characteristics (relative permittivity and dielectric loss tangent) of the dielectric thin film 1 may be obtained from the unloaded Q.

In the present invention, they may be arranged upside down .

  As a structure of the cavity resonator in the dielectric property measuring method of the dielectric thin film of the present invention, for example, when measurement is performed at a resonance frequency of 35 GHz, the diameter of the cavity resonator is about 10 mm to 13 mm and the height is 5 mm. To about 10 mm is used. In addition, as shown in FIG. 1, it is preferable that a bottomed cylindrical conductor has a flange.

  As the material of the dielectric substrate, sapphire, MgO, Si or the like is used. Further, the thickness of the dielectric substrate is determined by the relative dielectric constant and the measurement frequency, and the diameter is formed to be about 1.5 times larger than the diameter of the cavity. For example, when sapphire is used as the dielectric substrate, a thickness of about 0.5 mm to 1.0 mm is required at a resonance frequency of 35 GHz.

Examples of the dielectric thin film whose dielectric characteristics are measured include (BaSr) TiO ₃ , BaTiO ₃ , SrTiO _{3 and the} like. The thickness of this dielectric thin film is about 0.01 μm to 10 μm. Become. It is preferable that the dielectric thin film has a relative dielectric constant greater than that of the dielectric substrate. This is because the ratio of the stored energy of the dielectric thin film to the total stored energy can be increased, and the measurement accuracy can be improved.

  In the method for measuring dielectric properties of a dielectric thin film according to the present invention, the temperature dependence of the resonance frequency and no load Q is measured by changing the temperature of the cavity resonator, and the temperature dependence of the dielectric properties of the dielectric thin film is measured. Sex can also be sought.

  The calculation result of the resonance frequency of the cavity resonator (diameter 11.8676 mm, height 6.56 mm) designed as a cavity resonator as shown in FIG. 1 is 38.38 GHz without a substrate inserted. A chart assuming the case of measuring the relative dielectric constant of a 1 μm dielectric thin film deposited on a sapphire substrate (thickness 0.7 mm, relative dielectric constant 9.4) installed in this cavity resonator is obtained by a mode matching method. Calculated. The result is shown in FIG.

  FIG. 3 shows that there is a one-to-one correspondence between the frequency and the relative permittivity, and the relative permittivity can be obtained by measuring the frequency. It can also be seen that the change in frequency with respect to the change in relative permittivity is sufficiently large, so that the relative permittivity can be measured with high accuracy.

It is a longitudinal cross-sectional view of the cavity resonator used as an example of the dielectric property measuring method of this invention. It is a longitudinal cross-sectional view of the cavity resonator in the case of calculating | requiring the dielectric characteristic of a dielectric substrate . It is an example of the calculation result of the dielectric constant of the dielectric thin film with respect to the resonant frequency by the cavity resonator structure of this invention. It is the longitudinal cross-sectional view of the cavity resonator which has arrange | positioned the dielectric substrate which formed the dielectric thin film in the conventional upper surface in the center.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Dielectric thin film 2 ... Dielectric substrate 3 ... Bottomed cylindrical conductor 31 ... Opening part 4a, 4b ... Coaxial cable 5a, 5b ... Loop antenna 6 ... Conductor Board

Claims (4)

After configuring the cavity resonator by placing the bottomed cylindrical conductor having an opening on the conductor plate so that the opening abuts the conductor plate, the resonance frequency of the TE mode of the cavity resonator and The step of measuring the no-load Q and obtaining the dimensions and conductivity of the cavity resonator from the resonance frequency and the no-load Q, and the dielectric thin film on the dielectric substrate formed with the dielectric thin film on the main surface The cavity resonator is constructed by placing the conductor plate on the conductor plate so as to face and arranging the opening of the bottomed cylindrical conductor in contact with the dielectric substrate. the resonant frequency and the unloaded Q of the TE mode was measured, the resonant frequency and a step of determining the dielectric properties of the dielectric substrate from the unloaded Q, wherein the dielectric substrate as a dielectric thin film is directed upward Is placed on the conductor plate, and the opening is formed in the dielectric thin film. The bottomed cylindrical conductor is arranged so as to abut the cavity resonator, and then the TE-mode resonance frequency and no-load Q of the cavity resonator are measured. dimensions and conductivity of the cavity resonator, and by using the dielectric properties of the dielectric substrate, the dielectric characteristic measuring method of the dielectric thin film characterized by comprising a step of determining the dielectric properties of the dielectric film. 2. The dielectric thin film dielectric property measuring method according to claim 1, wherein a relative dielectric constant of the dielectric thin film is larger than a relative dielectric constant of the dielectric substrate. The method for measuring dielectric properties of a dielectric thin film according to claim 1 or 2 , wherein the thickness of the dielectric thin film is 10 µm or less. The method for measuring dielectric properties of a dielectric thin film according to any one of claims 1 to 3 , wherein the TE mode is a TE ₀₁₁ mode.

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