A T-type impedance matching network and a control method thereof

Abstract

The application provides a T-type impedance matching network and a control method thereof, which are used for a low impedance load of an inductively coupled plasma device, and the impedance characteristics of the load under 13.56 MHz are resistance 0.1 Ω-2 Ω and inductive reactance 100 Ω-200 Ω. The network comprises a fixed capacitor, a first adjustable capacitor and a second adjustable capacitor; the slope of the control output impedance real part with the change is controlled, the real part change range is dominated, and the imaginary part is independently adjusted. The control method comprises the following steps: selecting the capacitance value according to the real part range, adjusting the matching real part, adjusting the matching imaginary part and not affecting the real part. The application realizes the fast and stable matching of the extremely low impedance load, the real part and the imaginary part are decoupled and controlled, and the matching range is wide.

Description

Technical Field

[0001] This invention relates to the field of radio frequency impedance matching technology, and specifically to a T-type impedance matching network and its control method. Background Technology

[0002] Inductively Coupled Plasma (ICP) devices are core equipment in fields such as semiconductor etching, thin film deposition, and spectral analysis. The efficient coupling and stable transmission of radio frequency (RF) energy are crucial to the process results. In ICP devices, impedance matching between the RF power supply and the plasma load is key to ensuring power transmission efficiency and reducing reflection losses. However, the impedance characteristics of the ICP load vary significantly with process conditions (such as gas type, pressure, and power). Especially in low-pressure, high-density plasma processes, the load exhibits extremely low resistive components (as low as 0.1Ω-2Ω) and high inductive reactance components (approximately 0.7μH-1.5μH, corresponding to an inductive reactance of approximately 100Ω-200Ω at 13.56MHz), resulting in a very high quality factor (Q).

[0003] Currently, conventional RF impedance matching networks mostly employ L-type or Γ-type topologies. These networks are simple in structure, low in cost, and can operate effectively within common impedance ranges. However, when the real part of the load impedance is extremely low (e.g., below 2Ω), L-type or Γ-type networks have the following inherent drawbacks: Limited matching range: The quality factor (Q) of L-type or Γ-type networks is determined by the impedance transformation ratio and cannot be adjusted independently. For loads with extremely low real parts and high Q values, the impedance transformation ratio is extremely large, causing the matching network to be unable to effectively transform such low impedances to the standard 50Ω source impedance, resulting in insufficient dynamic matching range.

[0004] The component parameters change drastically: In order to achieve matching with extremely low real parts, the parallel capacitors in the L-type or Γ-type network need to change nonlinearly over a wide range. This not only requires a very high adjustment range for the adjustable capacitor, but also results in poor control accuracy in the small capacitance range, making it difficult to achieve stable matching.

[0005] Strong coupling between real and imaginary parts: In L-type or Γ-type networks, adjusting any matching element will simultaneously change both the real and imaginary parts of the load impedance, resulting in a complex matching and debugging process with many iterations, making it difficult to meet the requirements of fast automatic matching.

[0006] To address the aforementioned issues, existing technologies employ T-networks for impedance matching. For example, US Patent 7453328B2 discloses a broadband high-power T-network tuner, which uses a fixed capacitor grounded and two series-connected variable capacitors for antenna tuning. However, this solution does not optimize parameters for the extremely low real part characteristics of plasma loads, nor does it reveal the functional division and control logic of the three capacitors during the matching process. Furthermore, existing T-networks lack a systematic parameter design method when applied to ICP devices, resulting in slow matching speeds and unclear adjustment strategies.

[0007] Therefore, there is an urgent need in this field for a T-type impedance matching network and its control method that can quickly, stably, and efficiently match extremely low resistance and high inductive loads in inductively coupled plasma devices, in order to overcome the problems of insufficient matching range and complex adjustment of existing L-type / Γ-type networks. Summary of the Invention

[0008] This invention aims to overcome the technical shortcomings of existing L-type or Γ-type impedance matching networks when applied to inductively coupled plasma devices. These shortcomings include the inability to effectively match loads with extremely low resistance components (0.1Ω-2Ω) and high inductive reactance components (100Ω-200Ω), insufficient matching range, strong coupling between real and imaginary parts, and complex adjustment. The invention provides a T-type impedance matching network and its control method to achieve fast, stable, and efficient matching of extremely low impedance loads.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: A T-type impedance matching network is disclosed for use with a low-impedance load in an inductively coupled plasma device. The load, operating at a frequency of 13.56 MHz, exhibits impedance characteristics of a resistive component between 0.1 Ω and 2 Ω, and an inductive component between 100 Ω and 200 Ω. The T-type impedance matching network includes a fixed capacitor. First adjustable capacitor and the second adjustable capacitor The connection relationship is as follows: the fixed capacitor One end of the fixed capacitor is connected to the output terminal of the radio frequency power supply; The other end is connected to the first adjustable capacitor. one end and the second adjustable capacitor One end is connected; the first adjustable capacitor The other end of the capacitor is grounded; the second adjustable capacitor The other end is connected to one end of the plasma load; the other end of the plasma load is grounded. In the network, a fixed capacitor... The capacitance value is configured to control the real part of the output impedance as the first adjustable capacitor changes. The slope of the change; the first adjustable capacitor The capacitance value is configured to dominate the range of variation of the real part of the output impedance; the second adjustable capacitor The capacitance value is configured to independently adjust the imaginary part of the output impedance.

[0010] Furthermore, the real part of the output impedance and the first adjustable capacitor The capacitance value satisfies the following relationship: ; In the formula: The resistive component of the source impedance; The capacitance value is fixed. The angular frequency of the radio frequency power supply; The real part of the output impedance; The first adjustable capacitor The capacitance value; and when As it increases from 0 to infinity, from Monotonically decreasing to 0; exist The initial slope at is: ; In the formula: The resistive component of the source impedance; The capacitance value is fixed. Represents the real part of the output impedance Infinitesimal change; Indicates the first adjustable capacitor The capacitance Infinitesimal change; express right The derivative of the capacitance, i.e., the real part of the output impedance, varies with the capacitance. The instantaneous rate of change of the change; This means that in the derivative expression, the independent variable is... Substitute, and get The derivative value at this point.

[0011] Furthermore, the imaginary part of the output impedance satisfies: ; ; In the formula: To be with fixed capacitor and the first adjustable capacitor The relevant intermediate values ​​do not vary with the second adjustable capacitor. change; The resistive component of the source impedance; The angular frequency of the radio frequency power supply; To determine the imaginary part of the output impedance, change the second adjustable capacitor. The capacitance value only linearly shifts the imaginary part of the output impedance without affecting the real part, thereby achieving decoupling control between the real and imaginary parts.

[0012] A control method for the above-mentioned T-type impedance matching network includes the following steps: S1. Select the fixed capacitor based on the target impedance real part range of the plasma load. The capacitance value is adjusted to regulate the real part of the output impedance as the first adjustable capacitor changes. The slope of the change; S2. Adjust the first adjustable capacitor. The capacitance value is such that the real part of the output impedance matches the real part of the load impedance; S3. Adjust the second adjustable capacitor. The capacitance value is adjusted to match the imaginary part of the output impedance with the imaginary part of the load impedance. The real part of the already matched output impedance remains unchanged.

[0013] As one specific implementation, the fixed capacitor The capacitance value is selected from 50pF, 100pF, 200pF, or 400pF; the first adjustable capacitor The capacitance adjustment range is 100pF to 1000pF; the second adjustable capacitor The capacitance value can be adjusted from 50pF to 500pF. Select a fixed capacitor. The capacitance values ​​are based on the following criteria: when it is necessary to cover a lower range of the real part of the load impedance or to speed up the matching process, choose 50pF or 100pF; when it is necessary to control the real part of the matching more precisely or to increase the matching resolution, choose 200pF or 400pF.

[0014] As can be seen from the above technical solutions, compared with the prior art, the beneficial effects of the present invention are: 1. This invention utilizes a T-shaped topology and a fixed capacitor. First adjustable capacitor Second adjustable capacitor Functional division of labor, especially When the output impedance varies from 0 to infinity, the real part of the output impedance can be obtained from the source impedance. The monotonically decreasing rate to 0 can fully cover the matching requirements of extremely low resistance components (0.1Ω-2Ω) loads, overcoming the shortcomings of insufficient matching range of L-type / Γ-type networks; 2. In the T-type impedance matching network of the present invention, the second adjustable capacitor The first adjustable capacitor independently adjusts the imaginary part of the output impedance without affecting the real part. The changes in the dominant real part do not interfere with each other, which greatly simplifies the matching and debugging process and facilitates rapid automatic matching. 3. This invention provides the mathematical relationship between the real and imaginary parts of the output impedance and the capacitance values ​​of each capacitor, as well as the initial slope formula, for fixed capacitors. The selection process provides a quantitative basis, avoids empirical debugging, and improves the applicability and reproducibility of the matching network. Attached Figure Description

[0015] Figure 1 This is a circuit topology diagram of the T-type impedance matching network of the present invention; Figure 2 For different fixed capacitors The real part of the output impedance at the value and the first adjustable capacitor The relationship curve between capacitance and capacitance; Figure 3 For different first adjustable capacitors The imaginary part of the output impedance and the second adjustable capacitor at the value The relationship curve between capacitance and capacitance. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. The illustrative embodiments and descriptions of this invention are for illustrative purposes only and are not intended to limit the invention.

[0017] Example 1: Structure and Connection Relationship of T-Type Impedance Matching Network like Figure 1 As shown, this embodiment provides a T-type impedance matching network for an inductively coupled plasma (ICP) generation device. The T-type impedance matching network includes a fixed capacitor. First adjustable capacitor and the second adjustable capacitor The specific connection method is as follows: The fixed capacitor One end is connected to the output of the RF power supply, which has a standard source impedance of 50Ω and an operating frequency of 13.56MHz; a fixed capacitor... The other end is connected to the first adjustable capacitor. One end and the second adjustable capacitor One end is connected; the first adjustable capacitor The other end is grounded. The second adjustable capacitor... The other end is connected to one end of the plasma load, and the other end of the plasma load is grounded.

[0018] In the T-type impedance matching network, the fixed capacitor First adjustable capacitor Second adjustable capacitor They each perform different impedance adjustment functions: Used to control the real part of the output impedance The slope changes, by choosing different... The capacitance value can adjust the speed and resolution of real part matching; Used to dominate the range of variation of the real part of the output impedance, when As the capacitance value gradually increases from 0 to infinity, the real part of the output impedance changes from the source impedance. (50Ω) monotonically decreases to 0, thus enabling it to cover loads with extremely low resistivity components (0.1Ω-2Ω); Used to independently adjust the imaginary part of the output impedance, changing... It linearly shifts only the imaginary part of the output impedance without affecting the real part, thus achieving decoupling control between the real and imaginary parts.

[0019] In this embodiment, the first adjustable capacitor is shown. Second adjustable capacitor The specific adjustment method adopts electromechanical adjustment, which changes the physical parameters by driving the mechanical structure through a motor, that is, by driving a variable capacitor through a stepper / servo motor: For example, a vacuum variable capacitor (VVC) seals the electrodes within a high-vacuum ceramic shell. The capacitance is changed by altering the overlap area between the internal metal piston and the fixed electrode (i.e., the relative area between the fixed and moving plates) driven by a motor. Its advantages include the ability to withstand extremely high voltages (withstanding voltages exceeding 10kV) and currents, a wide capacitance adjustment range (e.g., a adjustment ratio of 1:50 or even higher), and extremely high resolution (up to 10,000 steps or more). It is widely used in impedance matching circuits in semiconductor etching / deposition equipment.

[0020] The control and drive system includes: motor drive, where the control system issues commands (such as via RS485 serial communication) to drive capacitor regulation through stepper motors, servo motors, or PLCs (Programmable Logic Controllers). Closed-loop control involves the system continuously monitoring the voltage standing wave ratio (VSWR) or complex impedance, and using advanced control strategies such as PID algorithms, Newton's extreme value search control (ESC), or variable gain algorithms to calculate the optimal adjustment direction and step size, continuously adjusting until a match is achieved.

[0021] Example 2: Mathematical Relationship and Parameter Design Method of Output Impedance To quantitatively describe the impedance transformation characteristics of the matching network described above, this embodiment provides mathematical expressions for the real and imaginary parts of the output impedance.

[0022] Let the angular frequency of the radio frequency power supply be... ( , The source impedance is purely resistive. When the first adjustable capacitor The capacitance value is Fixed capacitor The capacitance value is The second adjustable capacitor The capacitance value is At that time, the equivalent impedance seen from the network output (i.e., the end connected to the plasma load) towards the power supply side. for: (1); In formula (1): For the second adjustable capacitor Capacitive reactance (series branch); Source impedance and fixed capacitance Serial combination; The first adjustable capacitor Admittance (parallel branch); This is the equivalent impedance after parallel branches.

[0023] After algebraic simplification, the real part of the output impedance is... It can be represented as: (2); In formula (2): This is the real part of the output impedance, in ohms. ); The resistive component of the source impedance is, in this embodiment, the resistive component. ; The first adjustable capacitor The capacitance value is expressed in farads (F). The capacitance value is a fixed value, measured in farads (F). The angular frequency of the radio frequency power supply. The unit is radians per second (rad / s).

[0024] From formula (2), it can be seen that: when hour, ;when hour, ; Follow Monotonically decreasing, and the rate of decrease is affected by... Control; in Nearby, taking the derivative of formula (2) yields the initial slope: (3); In formula (3): For the real part of the output impedance Capacity The derivative of represents the real part as . The instantaneous rate of change of change, in ohms per farad (Ω). ); This means that in the derivative expression, the independent variable is... Substitute, and get The derivative value at this point; The source impedance resistance component, ; The capacitance value (farad) is fixed.

[0025] Formula (3) shows that, The smaller the initial slope, the larger the absolute value of the slope, and the greater the real part of the output impedance. The faster the increase and decrease, the better it is for quickly matching extremely low real part loads; The larger the value, the smaller the absolute value of the initial slope, and the slower the real part decreases, making it suitable for fine-tuning or matching a relatively high real part.

[0026] Furthermore, the imaginary part of the output impedance This can be simplified to: (4); (5); In formulas (4) and (5): This represents the imaginary part of the output impedance, in ohms. ); For the second adjustable capacitor Capacitive reactance, in ohms ( ); Angular frequency (rad / s); The capacitance value (farad) of the second adjustable capacitor; To and and The relevant intermediate quantities are only provided by , , and Decision, and Irrelevant; For fixed capacitor Capacitive reactance, in ohms ( ); This is the capacitance value of the first adjustable capacitor, in farads (F). The source impedance resistance component, .

[0027] From formula (4), it can be seen that changing The capacitance value only causes a linear shift in the imaginary part, while and Irrelevant, therefore adjustment It does not affect the real part, thus achieving independent control of the real and imaginary parts.

[0028] Example 3: Capacitor Selection for ICP Extremely Low Impedance Loads For the typical load impedance of the ICP device in low-pressure, high-density plasma processes at a frequency of 13.56MHz: resistive component 0.1Ω-2Ω, inductive component 100Ω-200Ω, this embodiment provides a set of preferred capacitance parameters.

[0029] Fixed capacitor Choose 50pF, 100pF, 200pF, or 400pF. For example... Figure 2 As shown, when When = 50pF, the real part follows The increase is the fastest, covering a range of 0.1Ω-2Ω; The drop is slightly slower at 100pF, which is suitable for situations with a slightly higher real part or where a higher resolution is required. The drop is smoother at 200pF or 400pF, allowing for finer matching control.

[0030] First adjustable capacitor The adjustment range is selected as 100pF-1000pF. Within this range, according to Equation 1, when... =50pF, When the output impedance is adjusted from 100pF to 1000pF, the real part of the output impedance drops from about 5Ω to about 0.2Ω, completely covering the target real part range.

[0031] Second adjustable capacitor The adjustment range is selected as 50pF-500pF. For example... Figure 3 As shown, in =50pF, When fixed at a certain value (e.g., 400pF), adjust It allows the imaginary part of the output impedance to vary linearly within the range of approximately 50Ω-250Ω, and can match the inductive reactance component of 100Ω-200Ω.

[0032] Example 4: Control method for matching networks This embodiment provides a control method based on the above-described T-type impedance matching network, specifically including the following steps: Step S1: Select a fixed capacitor

[0033] Select based on the range of the real part of the target impedance of the plasma load. Capacity: If the real part of the load is extremely low (e.g., 0.1Ω-1Ω) or fast matching is required, choose the smaller value. (50pF or 100pF); If the real part of the load is relatively high (e.g., 1Ω-2Ω) or a higher matching resolution is required, choose a larger one. (200pF or 400pF).

[0034] Step S2: Adjust the first adjustable capacitor Matching real part Keep Adjust for a given initial value (e.g., 200pF) Simultaneously, the reflection coefficient or impedance of the output port is monitored in real time. According to the relationship in formula (2), As the load increases, the real part decreases. By using a lookup table or closed-loop control algorithm, the real part of the output impedance can be made equal to the real part of the load impedance. Because... The changes also have a certain impact on the imaginary part (reflected in) (In the middle), but this impact can be compensated for through subsequent step S3.

[0035] Step S3: Adjust the second adjustable capacitor Matching the imaginary part After the real part matching is completed, adjust From formulas (4) and (5), it can be seen that... It only linearly shifts the imaginary part of the output impedance, without changing the real part. Therefore, it allows for independent adjustment. The imaginary part of the output impedance is made equal to the imaginary part of the load impedance. At this point, the entire matching process is complete, and the RF power supply and the plasma load achieve conjugate matching.

[0036] In the above control process, if adjustment The imaginary part is matched, but the real part has a slight offset, which can be fine-tuned again. and After one or two iterations, convergence is usually achieved in one iteration due to the high degree of decoupling between the two.

[0037] Example 5: Typical Application Case Taking a 13.56MHz ICP etching apparatus as an example, the complex impedance of the plasma load under certain process conditions. The actual measurement is as follows: = 0.5Ω + j150Ω (j is the imaginary unit, satisfying...) In AC circuits, this indicates phase orthogonality. This expression fully describes the electrical characteristics of the plasma load at a specific operating frequency (e.g., 13.56MHz): resistance 0.5Ω (real part of the load impedance), inductive reactance 150Ω (imaginary part of the load impedance, which is related to phase orthogonality in AC circuits). The product of these components forms the reactance component. In the matching network design, the 50-ohm pure resistive output of the RF power supply needs to be transformed into an impedance that is conjugate matched to the load (i.e., To achieve maximum power transmission, the matching network and control method of this invention are employed: Select =50pF, to quickly cover the low real part.

[0038] set up The initial value is 200pF, adjusted The impedance is gradually increased from 100pF while the real part of the output impedance is measured. When... When adjusted to approximately 800 pF, the result is calculated according to Equation 1. ≈0.5Ω, matching the real part of the load.

[0039] Keep =800pF remains unchanged, adjust According to Equation 3, when When the voltage is reduced from 200 pF to about 85 pF, the imaginary part decreases from about 180 Ω to 150 Ω, achieving imaginary part matching.

[0040] The final matching network parameters are: =50pF, =800pF, =85pF. Actual testing showed a voltage standing wave ratio (VSWR) of less than 1.1 and a power transfer efficiency exceeding 95%.

[0041] Example 6: Comparison with the prior art The T-type matching network of this invention was compared with a conventional L-type network (fixed inductor + adjustable capacitor) under the same conditions. The load was 0.5Ω+. 150Ω, source impedance 50Ω.

[0042] L-type network: It is impossible to match the real part of 0.5Ω to 50Ω using any combination of capacitors and inductors. The minimum achievable real part is about 5Ω, and the matching fails.

[0043] Gamma-type network: requires extremely large capacitance values ​​(>2000pF) and strong coupling between real and imaginary parts during adjustment. After multiple iterations, it can barely match, but the reflection coefficient is >0.2.

[0044] The T-type network of this invention: According to the parameters in Example 5, it was successfully adjusted on the first attempt, and the reflection coefficient was <0.05.

[0045] The comparative results show that the present invention has significant advantages in matching extremely low real part loads.

[0046] Example 7: Driving and Controlling an Adjustable Capacitor Those skilled in the art should understand that the first adjustable capacitor Second adjustable capacitor Vacuum variable capacitors, air variable capacitors, or piezoelectric ceramic driven adjustable capacitors can be used. The matching network can be configured with a microcontroller (MCU) or FPGA, which drives the capacitor adjustment via a stepper motor or servo motor, and integrates an RF detector or vector impedance detection module to achieve closed-loop automatic matching. Steps S1-S3 in the control method can be programmed as an automatic matching algorithm and stored in the controller's memory.

[0047] Example 8: Extension to other operating frequencies Although this embodiment uses the 13.56MHz industrial, scientific, and medical frequency band as an example, the T-type matching network and parameter design method of this invention can also be extended to other frequencies (such as 2MHz, 27MHz, 40MHz, etc.). It only requires consideration of the angular frequency. Corresponding adjustments , , The numerical range should be such that formulas (3) and (4) cover the required impedance range. For example, for 27MHz, the range can be... , , The capacitance is reduced by about half year-on-year to maintain the same reactance characteristics.

[0048] The above-described embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A T-type impedance matching network, wherein the T-type impedance matching network is used for a low-impedance load in an inductively coupled plasma device, the load having impedance characteristics at an operating frequency of 13.56MHz: a resistive component of 0.1Ω-2Ω and an inductive reactance component of 100Ω-200Ω, characterized in that: The T-type impedance matching network includes a fixed capacitor. First adjustable capacitor and the second adjustable capacitor ; The fixed capacitor One end of the fixed capacitor is connected to the output terminal of the radio frequency power supply; The other end is connected to the first adjustable capacitor. one end and the second adjustable capacitor One end is connected; the first adjustable capacitor The other end of the capacitor is grounded; the second adjustable capacitor The other end is connected to one end of the plasma load; the other end of the plasma load is grounded. Wherein, the fixed capacitor The capacitance value is configured to control the real part of the output impedance as the first adjustable capacitor changes. The slope of the change; the first adjustable capacitor The capacitance value is configured to dominate the range of variation of the real part of the output impedance; the second adjustable capacitor The capacitance value is configured to independently adjust the imaginary part of the output impedance.

2. The control method for the T-type impedance matching network according to claim 1, characterized in that, The real part of the output impedance and the first adjustable capacitor The capacitance value satisfies: ； In the formula: The resistive component of the source impedance; The capacitance value is fixed. The angular frequency of the radio frequency power supply; The real part of the output impedance; The first adjustable capacitor The capacitance value; and when As it increases from 0 to infinity, from Monotonically decreasing to 0; exist The initial slope at is: ； In the formula: The resistive component of the source impedance; The capacitance value is fixed. Represents the real part of the output impedance Infinitesimal change; Indicates the first adjustable capacitor The capacitance Infinitesimal change; express right The derivative of the capacitance, i.e., the real part of the output impedance, varies with the capacitance. The instantaneous rate of change of the change; This means that in the derivative expression, the independent variable is... Substitute, and get The derivative value at this point.

3. The control method for the T-type impedance matching network according to claim 1, characterized in that, The imaginary part of the output impedance satisfies: ； ； In the formula: To be with fixed capacitor and the first adjustable capacitor The relevant intermediate values ​​do not change with the second adjustable capacitor. change; The resistive component of the source impedance; The angular frequency of the radio frequency power supply; To determine the imaginary part of the output impedance, change the second adjustable capacitor. The capacitance value only linearly shifts the imaginary part of the output impedance without affecting the real part.

4. The control method for the T-type impedance matching network according to claim 1, characterized in that, The fixed capacitor The capacitance value is 50pF, 100pF, 200pF, or 400pF; the first adjustable capacitor The capacitance adjustment range is 100pF to 1000pF; the second adjustable capacitor The capacitance adjustment range is 50pF to 500pF.

5. A control method for the T-type impedance matching network according to any one of claims 1-4, characterized in that, Includes the following steps: S1. Select the fixed capacitor based on the target impedance real part range of the plasma load. The capacitance value is adjusted to regulate the real part of the output impedance as the first adjustable capacitor changes. The slope of the change; S2. Adjust the first adjustable capacitor. The capacitance value is such that the real part of the output impedance matches the real part of the load impedance; S3. Adjust the second adjustable capacitor. The capacitance value is adjusted to match the imaginary part of the output impedance with the imaginary part of the load impedance. The real part of the already matched output impedance remains unchanged.

6. The control method for the T-type impedance matching network according to claim 5, characterized in that, Select a fixed capacitor The capacitance values ​​are based on the following criteria: when it is necessary to cover a lower range of the real part of the load impedance or to speed up the matching process, choose 50pF or 100pF; when it is necessary to control the real part of the matching more precisely or to increase the matching resolution, choose 200pF or 400pF.

Images