WO2022168215A1

WO2022168215A1 - Variable-capacitance element

Info

Publication number: WO2022168215A1
Application number: PCT/JP2021/004012
Authority: WO
Inventors: 宗西岡; 真悟山浦; 皓貴内藤; 研悟西本; 泰弘西岡
Original assignee: 三菱電機株式会社
Priority date: 2021-02-04
Filing date: 2021-02-04
Publication date: 2022-08-11
Also published as: JPWO2022168215A1; JP7229448B1

Abstract

A variable-capacitance element (1) is provided with: a sealed container (2) containing a gas; a first electrode (3) that is disposed inside of the sealed container (2) and is grounded; a second electrode (4) disposed inside of the sealed container (2) to face the first electrode (3); a first variable power supply (5) one end of which is connected to the second electrode (4) and another end of which is grounded, the first variable power supply (5) being configured to apply a direct-current voltage between the first electrode (3) and the second electrode (4) and capable of changing the direct-current voltage; and a discharge controller (6) that converts the gas contained in the sealed container (2) into a plasma state and is capable of changing the electron density of plasma (7). The impedance between the first electrode (3) and the second electrode (4) can be changed by adjusting the direct-current voltage with the first variable power supply (5) and adjusting the electron density of the plasma (7) with the discharge controller (6).

Description

Variable capacitance element

The present disclosure relates to variable capacitance elements.

In recent years, plasma variable-capacitance elements have been proposed as variable-capacitance elements that have both high power resistance and high-speed response. For example, in the variable capacitance element described in Non-Patent Document 1, plasma is formed between two parallel plate electrodes, and the electrostatic capacitance value between the parallel plate electrodes is made variable by adjusting the electron density of the plasma. .

The variable capacitance element described in Non-Patent Document 1 has a minimum Q value (Quality Factor) of "5" when the capacitance is scanned from the minimum value to the maximum value. On the other hand, the Q value of a varactor diode, which is a widely used variable capacitance element, is about 200 at the minimum. Thus, the plasma variable capacitance element described in Non-Patent Document 1 has a problem of high loss.

An object of the present disclosure is to solve the above problems, and to obtain a variable capacitance element that can operate with lower loss than conventional variable capacitance elements using plasma.

A variable capacitance element according to the present disclosure includes a sealed container in which gas is sealed, a first electrode provided inside the sealed container and grounded, and a first electrode provided inside the sealed container and A second electrode arranged to face the electrode, one end connected to the second electrode and the other end grounded, applying a DC voltage between the first electrode and the second electrode, A first variable power source capable of changing a DC voltage, and a discharge control unit capable of changing the electron density of the plasma by turning the gas enclosed inside the sealed container into a plasma state, wherein the first variable power source is a DC voltage. is adjusted, and the discharge controller adjusts the electron density of the plasma, whereby the impedance between the first electrode and the second electrode is variable.

According to the present disclosure, the DC voltage applied between the first electrode and the second electrode provided inside the sealed container is adjusted to bring the gas enclosed inside the sealed container into a plasma state, thereby By adjusting the electron density of , the impedance between the first electrode and the second electrode is variable. By adjusting the impedance between the first electrode and the second electrode, the variable capacitance element according to the present disclosure can operate with lower loss than conventional variable capacitance elements using plasma.

1 is a schematic cross-sectional view showing an outline of a configuration of a variable capacitance element according to Embodiment 1; FIG. FIG. 4 is an explanatory view showing a state between electrodes when a gas enclosed in a sealed container is brought into a plasma state; 2 is a circuit diagram showing an equivalent circuit of the variable capacitance element according to Embodiment 1; FIG. 4 is a graph showing the relationship between the capacitance value and the Q value in the variable capacitance element according to Embodiment 1; FIG. 7 is a schematic cross-sectional view showing the outline of the configuration of a variable capacitance element according to Embodiment 2; FIG. 11 is a schematic cross-sectional view showing the outline of the configuration of a variable capacitance element according to Embodiment 3; FIG. 11 is a schematic cross-sectional view showing the outline of the configuration of a variable capacitance element according to a fourth embodiment; FIG. 12 is a schematic cross-sectional view showing the outline of the configuration of a variable capacitance element according to Embodiment 5; 14 is a graph showing the relationship between the capacitance value and the Q value in the variable capacitance element according to Embodiment 5. FIG. FIG. 11 is a schematic cross-sectional view showing the outline of the configuration of a variable capacitance element according to Embodiment 6; FIG. 11 is a circuit diagram showing an equivalent circuit of a variable capacitance element according to Embodiment 6; FIG. 14 is a graph showing the relationship between the capacitance value and the Q value in the variable capacitance element according to Embodiment 6; FIG.

Embodiment 1.
FIG. 1 is a schematic cross-sectional view showing the outline of the configuration of the variable capacitive element 1 according to Embodiment 1, and schematically shows the cross section of the main part of the variable capacitive element 1. As shown in FIG. In FIG. 1 , the variable capacitance element 1 includes a sealed container 2 ,

electrodes

3 , 4 , a power supply 5 and a discharge controller 6 . An electrode 3 and an electrode 4 are provided inside the sealed container 2 . Furthermore, the sealed container 2 is filled with an easily ionized gas such as helium, neon, or argon.

The electrode 3 is a plate-like electrode, and is a first electrode provided inside the sealed container 2 and grounded. For example, the electrode 3 is electrically connected to the ground through a first wiring provided so as not to allow communication between the inside of the sealed container 2 and the outside air.

The electrode 4 is a second electrode provided inside the sealed container 2 and arranged to face the electrode 3 . The electrode 4 is a plate-like electrode, and forms a parallel plate electrode together with the electrode 3 inside the sealed container 2 . For example, the electrode 4 is electrically connected to one end of the power source 5 through a second wiring provided so as to prevent communication between the inside of the sealed container 2 and the outside air.

The power supply 5 has a negative terminal connected to the electrode 4 via a second wiring, and a positive terminal grounded. Power supply. Also, the power supply 5 can change the DC voltage applied between the

electrodes

3 and 4 .

The discharge control unit 6 can change the electron density of the plasma 7 by putting the gas enclosed inside the sealed container 2 into a plasma state. For example, the discharge control unit 6 applies electric power between the

electrodes

3 and 4 to discharge and ionize the gas, thereby creating a plasma state. Further, the discharge controller 6 can change the electron density of the plasma 7 by adjusting the power applied between the

electrodes

3 and 4 .

The variable capacitance element 1 varies the impedance between the

electrodes

3 and 4 by adjusting the DC voltage with the power supply 5 and adjusting the electron density of the plasma 7 with the discharge controller 6 .
That is, the variable capacitance element 1 not only adjusts the electron density of the plasma 7 by the discharge control unit 6, but also adjusts the DC voltage applied between the

electrodes

3 and 4 by the power source 5, so that the

electrodes

3 and 4 4 can be varied. As a result, the variable capacitance element 1 can realize variable capacitance using the plasma 7 with low loss.

The principle of the variable capacitance element 1 is as follows.
FIG. 2 is an explanatory view showing the state between the

electrodes

3 and 4 when the gas enclosed in the sealed container 2 is brought into a plasma state. When the gas enclosed in the sealed container 2 is brought into a plasma state, a bulk region 7a and

sheath regions

7b and 7c are formed between the

electrodes

3 and 4, as shown in FIG. The bulk region 7a is the main part of the plasma 7 and the ions of the gas are mainly formed in the bulk region 7a.

In plasma 7 , sheath region 7 b is a region formed near electrode 3 , and sheath region 7 c is a region formed near electrode 4 . The thickness of the

sheath regions

7b and 7c largely determines the capacitance value of the plasma-based capacitive element. The dielectric constant ε _sheath of the

sheath regions

7b and 7c can be expressed by the following formula ( ₁ ) using the vacuum dielectric constant ε0.

Equation (1) above assumes that the vacuum and dielectric constant are equivalent. This is because the relationship n _e <<n _i is established between the electron density n _e contained in the

sheath regions

7b and 7c and the ion density n _i of the gas, and furthermore, the ions are applied from the outside due to their inertia. This is because they do not move following a high frequency (RF) electric field.

Each thickness s of the

sheath regions

7b and 7c is represented by the following formula (2). However, in the following formula ( ₂ ), e indicates the elementary charge, and V0 indicates the sheath potential. For example, the sheath potential _V0 at the sheath region 7b near the electrode 3 is the potential difference between the electrode 3 and the interface between the bulk region 7a and the sheath region 7b.

The sheath potential V ₀ can be expressed by the following formula (3) by considering the DC voltage V _bias applied by the power supply 5 .

V _float in the above formula (3) can be represented by the following formula (4). In the following formula (4), kB is the Boltzmann constant, _T _e is the electron temperature, _me is the electron mass, and _mi is the ion mass. The bulk region 7a is a region in which the relationship n _e =n _i holds.

In the case of low-temperature plasma and no external magnetic field, the dielectric constant ε _bulk of the bulk region 7a can be expressed by the following equation (5). In the following equation (5), _νm is the electron collision frequency in the plasma 7, and ω is the angular frequency of the electromagnetic wave.

The thickness l of the bulk region 7a consists of a sheath width s1 that is the thickness of the sheath region 7b formed near the electrode 3, _a sheath width s2 that is the thickness of the sheath region 7c formed near the electrode ₄ , and Using the distance d between the electrode 3 and the electrode 4, it can be represented by the following formula (6).

Further, the electrostatic capacitance value C of the capacitive element formed by sandwiching the medium having the dielectric constant _εr between the

electrodes

3 and 4 is expressed by the following formula (7). However, A indicates the area of the electrode 3 and the area of the electrode 4, and it is assumed that the areas where the

electrodes

3 and 4 face each other are the same.

The impedance Z of the capacitive element is represented by the following formula (8). i is the imaginary unit.

The impedance Z _total between the

electrodes

3 and 4 can be obtained by using the above equations (1) to (8). FIG. 3 is a circuit diagram showing an equivalent circuit of the variable capacitance element 1, showing an equivalent circuit relating to the impedance Z _total . The impedance Z _total is equivalent to the impedance of a parallel plate capacitor in which the bulk region 7a and the

sheath regions

7b and 7c shown in FIG. 2 are sandwiched between two plate electrodes.

Z _total can be represented by the following formula (9). In the following equation (9), Z _s1 is the impedance of the sheath region 7b formed near the electrode 3; Z _bulk is the impedance of the bulk region 7a. Z _s2 is the impedance of the sheath region 7c formed near the electrode 4; That is, Z _s1 , Z _bulk and Z _s2 are impedances of parallel plate capacitors sandwiched between two plate-

like electrodes

3 and 4 .

Z _s1 , Z _bulk and Z _s2 can be represented by the following formulas (10), (11) and (12) respectively. In the following formulas (10), (11) and (12) below, A indicates the area of the electrode 3 and the area of the electrode 4, and the area where the electrode 3 and the electrode 4 face each other is There is the same.

Assuming that the impedance between the

electrodes

3 and 4 is a variable capacitive element having a series parasitic resistance, the capacitance value C _total and the series parasitic resistance value R _total of the variable capacitive element are given by the following equation (13) and the following formula (14), respectively. In the following formulas (13) and (14), Im( _Ztotal ) indicates the imaginary part of _Ztotal , and Re( _Ztotal ) indicates the real part of _Ztotal .

Furthermore, the Q value of the variable capacitance element can be expressed by the following equation (15).

As is clear from the above formulas (2), (5), and (6), the dielectric constant ε _bulk of the bulk region 7a and the sheath region 7a included in the above formulas (10) to (12) The sheath width s ₁ of 7b, the sheath width s ₂ of sheath region 7c and the thickness l of bulk region 7a are all functions of the electron density n _e contained in

sheath regions

7b and 7c. Therefore, the impedance between the

electrodes

3 and 4 becomes variable by the discharge control unit 6 adjusting the electron density _ne between the

electrodes

3 and 4 .

FIG. 4 is a graph showing the relationship between the capacitance value and the Q value in the variable capacitance element 1. The capacitance value C _total of the equivalent circuit model of the variable capacitance element 1 using the equivalent circuit model of FIG. The dependence on the Q value is shown for each DC voltage V _bias . In FIG. 4, the discharge controller 6 makes the electron density n _e variable in the range from 0(m ⁻³ ) to 10 ²⁰ (m ⁻³ ).

In calculating the relationship between the capacitance value C _total and the Q value, the angular frequency ω of the electromagnetic wave is set to ω=94.2 (Mrad/s), and the area A of the

electrodes

3 and 4 is set to A=10 ³ ( mm ² ), the distance d between the

electrodes

3 and 4 is d=10 ³ (mm), and the electron temperature Te is Te=1 (eV). The gas enclosed in the sealed container 2 is argon, the gas temperature is 0.1 (eV), the gas pressure is 266 (Pa), and the mass _{mi of argon ions is m i} ₌ 6.7×10 ⁻²⁶ (kg), and the collision frequency ν _m of electrons in the plasma 7 is ν _m =1.4×10 ¹⁰ (Hz).

In FIG. 4, curve A shows the relationship between the capacitance value C _total and the Q value when the DC voltage V _bias is 0 (V). If V _bias =0 (V), it means that no DC voltage is applied between the

electrodes

3 and 4 by the power supply 5 . That is, the relationship between the capacitance value C _total and the Q value indicated by the curve A corresponds to the conventional variable capacitance element described in Non-Patent Document 1.

Curve B shows the relationship between the capacitance value C _total and the Q value when the DC voltage V _bias is 30 (V). Curve C shows the relationship between the capacitance value C _total and the Q value when the DC voltage V _bias is 60 (V), and curve D shows the relationship when the DC voltage V _bias is 100 (V). and the _Q value.

As is clear from FIG. 4, the Q value of the variable capacitance element 1 is improved by applying V _bias =0 (V). For example, when the capacitance of the variable capacitance element 1 is C _total =10 (pF), the relationship between the capacitance value C _total and the Q value at V _bias =0 (V) indicated by the curve A is is about "2". On the other hand, in the relationship between the capacitance value C _total and the Q value at V _bias =100 (V) indicated by the curve D, the Q value is improved to about "15".

As described above, the variable capacitance element 1 according to Embodiment 1 includes the sealed container 2 in which gas is sealed, the electrode 3 provided inside the sealed container 2 and grounded, and the sealed container 2 and an electrode 4 provided inside the sealed container 2 and arranged opposite to the electrode 3, and an electrode 3 and an electrode 4 having one end connected to the electrode 4 and the other end grounded and provided inside the sealed container 2. A power source 5 that applies a DC voltage between the . In the variable capacitance element 1, the power supply 5 adjusts the DC voltage applied between the

electrodes

3 and 4, and the discharge control unit 6 adjusts the electron density of the plasma 7, thereby controlling the voltage between the

electrodes

3 and 4. can be adjusted, it is possible to operate with a lower loss than the conventional variable capacitance element using plasma.

Embodiment 2.
FIG. 5 is a schematic cross-sectional view showing the outline of the configuration of the variable capacitive element 1A according to the second embodiment, and schematically shows the cross section of the main part of the variable capacitive element 1A. In FIG. 5, the same components as those in FIG. 1 are assigned the same reference numerals, and descriptions thereof are omitted. The variable capacitance element 1A includes a sealed container 2A,

electrodes

3, 4, a power source 5 and a discharge control section 6A. The discharge control section 6A is configured with an electrode 8, an electrode 9 and a power supply 10. As shown in FIG.

In addition to the

electrodes

3 and 4,

electrodes

8 and 9 are provided inside the sealed container 2A. Furthermore, the sealed container 2A is filled with an easily ionized gas such as helium, neon, or argon.

The electrode 8 is a third electrode provided inside the sealed container 2A and arranged at a position orthogonal to the direction in which the

electrodes

3 and 4 face each other. For example, the electrode 8 is connected to the positive terminal of the power supply 10 via a third wiring provided so as not to allow communication between the inside of the sealed container 2A and the outside air.

The electrode 9 is a fourth electrode that is provided inside the sealed container 2A, has the

electrodes

3 and 4 interposed between it and the electrode 8, and is arranged to face the electrode 8. The electrode 9 is electrically connected to the negative terminal of the power supply 10 and to the ground through a fourth wiring provided so as not to allow communication between the inside of the sealed container 2A and the outside air.

The power supply 10 is a second variable power supply having a positive terminal connected to the electrode 8 via a third wiring and a negative terminal connected to the electrode 9 and ground via a fourth wiring. . The power supply 10 applies a DC voltage between the

electrodes

8 and 9 to bring the gas enclosed inside the sealed container 2A into a plasma state, and applies a DC voltage between the

electrodes

8 and 9. By changing, the electron density of the plasma 7 can be changed.

As described above, in the variable capacitance element 1A according to the second embodiment, the discharge control section 6A is provided inside the sealed container 2A and arranged at a position orthogonal to the direction in which the

electrodes

3 and 4 face each other. and an electrode 9 provided inside the sealed container 2A, interposed between the electrode 8 and the electrode 3 and the electrode 4, and arranged to face the electrode 8, and the negative electrode side is grounded, By applying a voltage between the

electrodes

8 and 9, the gas enclosed inside the sealed container 2A is brought into a plasma state, and by changing the power applied between the

electrodes

8 and 9, plasma is generated. 7 with a variable electron density power supply 10 . The variable capacitance element 1A adjusts the DC voltage applied between the

electrodes

3 and 4 by the power source 5, and adjusts the electron density of the plasma 7 by the discharge control unit 6A. can be adjusted, it is possible to operate with a lower loss than the conventional variable capacitance element using plasma.

Embodiment 3.
FIG. 6 is a schematic cross-sectional view showing the outline of the configuration of the variable capacitive element 1B according to the third embodiment, and schematically shows the cross section of the main part of the variable capacitive element 1B. In FIG. 6, the same components as in FIG. 1 are denoted by the same reference numerals, and descriptions thereof are omitted. The variable capacitance element 1B includes a sealed container 2, electrodes 3, electrodes 4, a power source 5 and a discharge control section 6B. The discharge control section 6B is configured with a coil 11 and a power source 12 .

The coil 11 is a coil spirally wound around the outer circumference of the sealed container 2, and the

electrodes

3 and 4 are electrically insulated. The power source 12 is a third variable power source that applies high-frequency power to both ends of the coil 11 to bring the gas sealed inside the sealed container 2 into a plasma state. Also, the power supply 12 is realized by an AC power supply, and the electron density of the plasma 7 can be changed by changing the high frequency power applied to both ends of the coil 11 .

As described above, in the variable capacitance element 1B according to the third embodiment, the discharge control section 6B includes the coil 11 spirally wound around the outer peripheral portion of the sealed container 2 while being insulated from the

electrodes

3 and 4. By applying high-frequency power to both ends of the coil 11, the gas enclosed inside the sealed container 2 is brought into a plasma state, and by changing the high-frequency power applied to both ends of the coil 11, the electron density of the plasma is changed. and a possible power source 12 . The variable capacitance element 1B adjusts the DC voltage applied between the

electrodes

3 and 4 by the power source 5, and adjusts the electron density of the plasma 7 by the discharge control unit 6B. can be adjusted, it is possible to operate with a lower loss than the conventional variable capacitance element using plasma.

Further, in the discharge control unit 6B, an electrode to which a high voltage is applied for the purpose of forming the plasma 7 is not provided inside the sealed container 2. Therefore, in the discharge control unit 6B, the electrodes are not destroyed due to the sputtering that scrapes the electrodes due to the collision of the ion gas generated by the ionization of the gas. Therefore, the variable-capacitance element 1B can be expected to have a longer life than the variable-capacitance element 1A having the discharge control section 6A.

Embodiment 4.
FIG. 7 is a schematic cross-sectional view showing the outline of the configuration of the variable capacitance element 1C according to the fourth embodiment, and schematically shows the cross section of the main portion of the variable capacitance element 1C. In FIG. 7, the same components as those in FIGS. 1 and 5 are denoted by the same reference numerals, and descriptions thereof are omitted. The variable capacitance element 1C includes a sealed container 2A,

electrodes

3, 4, a power supply 5, a discharge control section 6A, filter

elements

13 and 14. FIG.

The filter element 13 is a first filter element provided between the electrode 3 and the ground, and selectively passes, for example, high-frequency signals in a target frequency band. The filter element 13 is provided between the electrode 3 and the ground in the first wiring that is provided so as to prevent communication between the inside of the sealed container 2A and the outside air and electrically connects the electrode 3 and the ground. .

The filter element 14 is a second filter element provided between the electrode 4 and the negative terminal of the power source 5, and similarly to the filter element 13, for example, selectively filters a high-frequency signal in a target frequency band. let it pass. The filter element 14 is provided so as not to allow communication between the inside of the sealed container 2A and the outside air, and is connected between the electrode 4 and the power source in the second wiring that electrically connects the electrode 4 and the negative terminal of the power source 5. 5.

Filter element 13 and filter element 14 are electrically open for a high-frequency signal applied between

electrodes

3 and 4, and electrically short-circuited for a direct-current signal applied between

electrodes

3 and 4. is designed to be This is because the impedance of the coil with the inductance L is expressed by jωL, where j is the imaginary unit and ω is the angular frequency of the electromagnetic wave. It means you should.

As shown in FIG. 7, by arranging the filter element 13 and the filter element 14, a DC voltage is applied between the

electrodes

3 and 4 in view of the high frequency signal applied between the

electrodes

3 and 4. The power supply 5, which is the circuit for In other words, the impedance between the

electrodes

3 and 4 to which the desired high-frequency signal is applied is not affected by the power supply 5 that applies the DC voltage between the

electrodes

3 and 4 .

FIG. 7 shows that the filter element 13 and the filter element 14 are provided with respect to the variable capacitance element 1A shown in FIG. Alternatively, the filter element 13 and the filter element 14 may be provided. Even in the variable capacitance element 1C configured in this way, the influence of the power supply 5 on the impedance between the

electrodes

3 and 4 is reduced.

As described above, the variable capacitance element 1C according to the fourth embodiment includes the filter element 13 and the filter element 14, the electrode 3 is grounded through the filter element 13, and the electrode 4 is grounded through the filter element 14. It is connected to one end of the power supply 5 . Filter element 13 and filter element 14 can reduce the influence of power supply 5 that applies a DC voltage between

electrodes

3 and 4 on the impedance between

electrodes

3 and 4 .

Embodiment 5.
FIG. 8 is a schematic cross-sectional view showing the outline of the configuration of the variable capacitive element 1D according to the fifth embodiment, and schematically shows the cross section of the main part of the variable capacitive element 1D. In FIG. 8, the same components as those in FIG. 1 are assigned the same reference numerals, and descriptions thereof are omitted. The variable capacitance element 1D includes a sealed container 2A,

electrodes

3 , 4 , a power source 5 , a discharge control section 6A,

filter elements

15 and 16 .

The filter element 15 is a third filter element provided between the electrode 3 and the negative terminal of the power supply 5, and selectively passes, for example, high-frequency signals in a target frequency band. The filter element 15 is provided between the electrode 3 and the power source 5 in the third wiring that electrically connects the electrode 3 and the power source 5 so as not to allow communication between the inside of the sealed container 2A and the outside air. be provided.

The filter element 16 is a fourth filter element provided between the electrode 4 and the negative terminal of the power supply 5, and similarly to the filter element 15, for example, selectively filters a high-frequency signal in a target frequency band. let it pass. The filter element 16 is provided so as not to allow communication between the inside of the sealed container 2A and the outside air, and is connected between the electrode 4 and the power source in the second wiring that electrically connects the electrode 4 and the negative terminal of the power source 5. 5.

The electrode 3 of the variable capacitance element 1D is connected to the power supply 5 via the filter element 15, and the electrode 4 is connected to the power supply 5 via the filter element 16. FIG. As a result, the sheath region 7b formed in the vicinity of the electrode 3 and the sheath region 7c formed in the vicinity of the electrode 4 are applied as if the DC voltage V _bias included in the above formula (3) is applied. state.

FIG. 9 is a graph showing the relationship between the capacitance value C _total and the Q value in the variable capacitance element 1D. The configuration of the variable capacitance element 1D is represented by the equivalent circuit model shown in FIG. 4 shows the relationship between the electrostatic capacitance value C _total and the Q value when a DC voltage V _bias is applied to both of . In FIG. 9, the gas enclosed in the sealed container 2A is argon. the electron density n _e , the angular frequency ω of the electromagnetic wave, the area A of the

electrodes

3 and 4, the distance d between the

electrodes

3 and 4, the electron temperature Te, the gas temperature, the gas pressure, the mass of argon ions m _i , and , and the collision frequency ν _m of electrons in the plasma 7, the same values as in the calculation in FIG. 4 are used.

In FIG. 9, curve E shows the relationship between the capacitance value C _total and the Q value when the DC voltage V _bias is 100 (V) in the variable capacitance element 1D shown in FIG. Curve F shows the relationship between the capacitance value C _total and the Q value when the DC voltage V _bias is 100 (V) in the variable capacitance element 1 shown in FIG. ).
As is clear from FIG. 9, variable capacitive element 1D is provided with filter element 15 and filter element 16, and compared with variable capacitive element 1 shown in Embodiment 1, the minimum value of the Q value is " improved from 4 to 5. That is, the variable-capacitance element 1D operates with less loss than the variable-capacitance element 1 does.

FIG. 8 shows that the filter element 15 and the filter element 16 are provided with respect to the variable capacitance element 1A shown in FIG. Alternatively, the filter element 15 and the filter element 16 may be provided. Even the variable capacitance element 1D configured in this way operates with a lower loss than the variable capacitance element 1 .

As described above, the variable capacitance element 1D according to Embodiment 5 includes the filter element 15 and the filter element 16, and the electrode 3 is connected to one end of the power supply 5 via the filter element 15. Electrode 4 is connected to one end of power supply 5 via filter element 16 . Filter element 15 and filter element 16 allow variable capacitive element 1D to operate with a lower loss than variable capacitive element 1 .

Embodiment 6.
FIG. 10 is a schematic cross-sectional view showing the outline of the configuration of the variable capacitive element 1E according to the sixth embodiment, and schematically shows the cross section of the main part of the variable capacitive element 1E. In FIG. 10, the same components as those in FIG. 1 are assigned the same reference numerals, and descriptions thereof are omitted. The variable capacitance element 1E includes a sealed container 2 ,

electrodes

3 , 4 , a power supply 5 , a discharge controller 6 ,

electrodes

17 , 18 ,

dielectrics

19 and 20 .

The electrode 17 is a fifth electrode provided inside the sealed container 2 and arranged to face the electrode 3 on the side opposite to the side on which the electrode 3 faces the electrode 4 . For example, electrode 17 is a plate-like electrode having the same area as electrode 3 . The electrode 18 is a sixth electrode provided inside the sealed container 2 and arranged to face the electrode 4 on the side opposite to the side on which the electrode 4 faces the electrode 3 . For example, electrode 18 is a plate-like electrode having the same area as electrode 4 .
In addition, the electrode 3 is a plate-like electrode having the same area as the electrode 4 .

A dielectric 19 is a first dielectric provided between the

electrodes

3 and 17 . For example, the dielectric 19 is placed in physical contact with the surface of the electrode 3 that is not in contact with the plasma 7 . Dielectric 20 is a second dielectric provided between

electrodes

4 and 18 . For example, the dielectric 20 is placed in physical contact with the surface of the electrode 4 that is not in contact with the plasma 7 .

Although not shown in FIG. 10, the variable capacitance element 1E includes a circuit for applying a high frequency electric field to the

electrodes

17 and 18. That is, in the variable capacitive element 1E, the circuit applies a high-frequency electric field to the

electrodes

17 and 18, so that the structure sandwiched between the

electrodes

17 and 18 functions as a capacitive element.

FIG. 11 is a circuit diagram showing an equivalent circuit of the variable capacitance element 1E. ₁₁ , the equivalent circuit model shown in FIG. 4 and the electrode 18 with a dielectric 20 provided in series with a capacitance capacitor _C2 .

Capacitors C1 and _C2 can be represented by the following equations ( ₁₆ ) and (17). In the following equations (16) and (17), ε _r1 is the relative permittivity of the dielectric 19 and ε _r2 is the relative permittivity of the dielectric 20 . t ₁ is the thickness of dielectric 19 and t ₂ is the thickness of dielectric 20 .

FIG. 12 is a graph showing the relationship between the capacitance value C _total and the Q value in the variable capacitance element _. and the Q value are shown for each DC voltage V _bias . In FIG. 12, the discharge controller 6 makes the electron density n _e variable in the range from 0(m ⁻³ ) to 10 ²⁰ (m ⁻³ ). In FIG. 12, the gas enclosed in the sealed container 2 is argon. Further, the electron density n _e , the angular frequency ω of the electromagnetic wave, the area A of the

electrodes

3 and 4, the distance d between the

electrodes

3 and 4, the electron temperature Te, the gas temperature, the gas pressure, and the mass of argon ions m _i , and the collision frequency ν _m of electrons in the plasma 7, the same values as in the calculation in FIG. 4 are used.

Both dielectric 19 and dielectric 20 are quartz glass (relative permittivity 3.7). Also, the thickness t1 of the dielectric ₁₉ and the thickness t2 of the dielectric ₂₀ are varied within the range of 0 (mm) to 1 (mm). It is assumed that the thickness t1 of the dielectric ₁₉ and the thickness t2 of the dielectric ₂₀ are equal. In FIG. 12, curve A1 shows the relationship between the capacitance value C _total and the Q value when the DC voltage V _bias is 100 (V) and t ₁ =t ₂ is 0 (mm). . When t ₁ =t ₂ is 0 (mm), it means that the capacitors C ₁ and C ₂ do not exist in the variable capacitance element 1E. That is, the relationship between the capacitance value C _total and the Q value indicated by the curve A1 corresponds to 1 for the variable capacitance element shown in FIG.

Further, in FIG. 12, a curve B1 shows the relationship between the capacitance value C _total and the Q value when the DC voltage V _bias is 100 (V) and t ₁ =t ₂ is 0.1 (mm). is shown. A curve C1 shows the relationship between the capacitance value C _total and the Q value when the DC voltage V _bias is 100 (V) and t ₁ =t ₂ is 0.5 (mm). D1 indicates the relationship between the capacitance value C _total and the Q value when the DC voltage V _bias is 100 (V) and t ₁ =t ₂ is 1.0 (mm).

As is clear from FIG. 12, loading the capacitors C1 and _C2 _{reduces the variable width of the capacitance value C total} _, but improves the Q value. For example, when the capacitance C _total =10 (pF), the Q value is “15” in the relationship between the capacitance value C _total and the Q value at t ₁ =t ₂ =0 (mm) indicated by the curve A1. degree. On the other hand, in the relationship between the capacitance value C _total and the Q value at t ₁ =t ₂ =1.0 (mm) indicated by the curve D1, the Q value is improved to about "100".

FIG. 10 shows the variable capacitance element ₁ shown in _FIG . , the variable-capacitance element 1E is any one of the variable-capacitance element 1A shown in FIG. 5, the variable-capacitance element 1B shown in FIG. 6, the variable-capacitance element 1C shown in FIG. 7, and the variable-capacitance element 1D shown in FIG. _{Alternatively} , capacitors C1 and _C2 may be loaded. Even the variable-capacitance element 1E configured in this way operates with a lower loss than the variable-capacitance element 1 .

As described above, the variable capacitance element 1E according to Embodiment 6 is provided inside the sealed container 2, and the electrode 3 is arranged to face the electrode 3 on the side opposite to the side facing the electrode 4. between the electrode 17, the electrode 18 provided inside the sealed container 2 and facing the electrode 4 on the side opposite to the side where the electrode 4 faces the electrode 3, and the electrode 3 and the electrode 17 A first dielectric provided and a dielectric 20 provided between

electrodes

4 and 18 .
The variable capacitance element 1E adjusts the DC voltage applied between the

electrodes

3 and 4 by the power source 5, and adjusts the electron density of the plasma 7 by the discharge control unit 6, thereby controlling the voltage between the

electrodes

3 and 4. Since the impedance between the electrode 17 and the electrode 18 can be adjusted, it is possible to operate with lower loss than the conventional variable capacitance element using plasma.

It should be noted that it is possible to omit any component in each of the combinations of the embodiments, the modification of the components of each of the embodiments, or the configuration of each of the embodiments.

A variable capacitance element according to the present disclosure can be used, for example, in a plasma processing apparatus.

1, 1A, 1B, 1C, 1D, 1E variable capacitance element, 2, 2A sealed container, 3, 4, 8, 9, 17, 18 electrode, 5, 10, 12 power supply, 6 discharge control section, 7 plasma, 7a Bulk region, 7b, 7c Sheath region, 11 Coil, 13, 14, 15, 16 Filter element, 19, 20 Dielectric.

Claims

a sealed container in which gas is sealed;
a first electrode provided inside the sealed container and grounded;
a second electrode provided inside the sealed container and arranged to face the first electrode;
A first variable power supply having one end connected to the second electrode and the other end grounded, applying a DC voltage between the first electrode and the second electrode, and capable of changing the DC voltage When,
a discharge control unit capable of changing the electron density of the plasma by bringing the gas enclosed inside the sealed container into a plasma state;
with
The impedance between the first electrode and the second electrode is made variable by the first variable power source adjusting the DC voltage and the discharge control section adjusting the electron density of the plasma. A variable capacitance element characterized by:
The discharge control unit
a third electrode provided inside the sealed container and arranged at a position orthogonal to the direction in which the first electrode and the second electrode face each other;
A fourth electrode provided inside the sealed container, with the first electrode and the second electrode interposed between itself and the third electrode, and arranged to face the third electrode an electrode of
The negative electrode side is grounded, and a voltage is applied between the third electrode and the fourth electrode to bring the gas enclosed inside the sealed container into a plasma state, thereby connecting the third electrode and the fourth electrode. 2. The variable capacitance element according to claim 1, further comprising a second variable power supply capable of changing the electron density of the plasma by changing the voltage applied between the 4 electrodes.
The discharge control unit
a coil spirally wound around the outer periphery of the sealed container in a state of being insulated from the first electrode and the second electrode;
By applying high-frequency power to both ends of the coil, the gas enclosed inside the sealed container is brought into a plasma state, and by changing the high-frequency power applied to both ends of the coil, the electron density of the plasma can be changed. 3. The variable capacitance element according to claim 1, further comprising a third variable power supply.
a first filter element;
a second filter element;
with
the first electrode is grounded through the first filter element;
The variable power supply according to any one of claims 1 to 3, wherein the second electrode is connected to one end of the first variable power supply via the second filter element. capacitive element.
a third filter element;
a fourth filter element;
with
the first electrode is connected to one end of the first variable power supply via the third filter element;
The variable power supply according to any one of claims 1 to 3, wherein the second electrode is connected to one end of the first variable power supply via the fourth filter element. capacitive element.
a fifth electrode provided inside the sealed container and arranged opposite to the first electrode on the side opposite to the side on which the first electrode faces the second electrode;
a sixth electrode provided inside the hermetic container and arranged to face the second electrode on the side opposite to the side on which the second electrode faces the first electrode;
a first dielectric provided between the first electrode and the fifth electrode;
a second dielectric provided between the second electrode and the sixth electrode;
with
The fifth electrode including between the first electrode and the second electrode is controlled by the first variable power supply adjusting the DC voltage and the discharge control unit adjusting the electron density of the plasma. 4. The variable capacitance element according to any one of claims 1 to 3, wherein the impedance between the and the sixth electrode is variable.