Micro-nano film thickness eddy current sensor multi-modular detection circuit and design method

Abstract

The invention provides a multi-modular detection circuit for a micro-nano film thickness eddy current sensor, and the circuit provides three types of basic modules which are respectively a signal generation module, two types of signal conversion modules, and two types of post-processing modules. The two signal conversion modules are respectively an LC parallel resonant circuit + amplifying circuit and an alternating current bridge + differential amplifying circuit; in the two post-processing modules, one post-processing module adopts a rectifying circuit and a peak detection circuit to realize single-channel output; the other circuit comprises a phase shift circuit, a phase sensitive detection circuit, a filter circuit, a voltage bias circuit, a post-stage amplification circuit and a coupling equation calculation module, and thickness-temperature synchronous measurement is realized. The invention further provides a detection circuit design method based on the detection circuit architecture, and proper modules are selected to be combined according to measurement requirements to form a micro-nano film thickness sensor detection circuit. According to the invention, the system implementation complexity and cost can be reduced, and the detection performance is improved.

Description

Technical Field

[0001] The present invention relates to the field of micro-nano detection technology, and in particular to a multi-modular detection circuit and a design method for a micro-nano thin film thickness eddy current sensor. Background Art

[0002] In the field of micro-nano detection technology applications, eddy current sensors can effectively solve the problem of online detection of small quantities such as nano-level metal film thickness and micron-level lubricant film thickness. However, due to the actual working conditions and the fact that the measured quantity itself is very weak, how to further improve the sensor detection performance, reduce the complexity of the measurement equipment and reduce the cost has become a bottleneck in the development of film thickness measurement technology. Summary of the invention

[0003] In view of this, the present invention provides a multi-modular detection circuit of a micro-nano thin film thickness eddy current sensor and a detection circuit design method of a micro-nano thin film thickness eddy current sensor based on the modules provided by the detection circuit, which can reduce the complexity and cost of system implementation and improve detection performance.

[0004] In order to solve the above technical problems, the present invention is implemented as follows.

[0005] A multi-modular detection circuit of a micro-nano film thickness eddy current sensor, comprising:

[0006] The detection circuit architecture includes three basic modules, namely, a signal generation module, two signal conversion modules, and two post-processing modules;

[0007] The signal generating module provides an excitation signal;

[0008] Of the two signal conversion modules, one signal conversion module uses an LC parallel resonant circuit + an amplifier circuit, and the other signal conversion module uses an AC bridge + a differential amplifier circuit; the voltage signal output by the signal conversion module contains output impedance information of the eddy current coil as a sensor sensitive element;

[0009] Among the two post-processing modules:

[0010] A post-processing module realizes thickness measurement, including a rectifier circuit and a peak detection circuit connected in series to realize single-channel output;

[0011] Another post-processing module realizes thickness-temperature synchronous measurement, and includes a phase shift circuit, a phase-sensitive detection circuit, a filter circuit, a voltage bias circuit, a post-stage amplifier circuit and a coupling equation calculation module; the phase-sensitive detection circuit performs multiplication operation on the excitation signal output by the signal generation module and the excitation signal phase-shifted by π / 2 by the phase shift circuit with the output signal of the signal conversion module to separate the real part and the imaginary part, and then sequentially processes through the filter circuit, the voltage bias circuit and the post-stage amplifier circuit to output the real part and the imaginary part of the DC voltage signal;

[0012] Within the measuring range, the real and imaginary components of the output voltage show a certain linear relationship with the measured film thickness and temperature respectively, and a coupling equation group of the real and imaginary parts of the output voltage and the film thickness and ambient temperature is established; the coupling equation calculation module substitutes the real and imaginary components of the DC voltage signal output by the post-amplifier circuit into the coupling equation group to solve it, obtain the synchronous measurement results of the film thickness and ambient temperature, and realize dual-channel output.

[0013] According to the measurement requirements, the signal conversion module and the post-processing module are selected and combined with the signal generation module to form a micro-nano film thickness sensor detection circuit.

[0014] Preferably, the coupling equation is:

[0015]

[0016] Where th is the film thickness, T is the ambient temperature, U Re (th,T) is the real part of the output voltage, U Im (th,T) is the imaginary part of the output voltage, U Re0 is the real part of the output voltage under no-load condition, U Im0 is the imaginary part of the output voltage under no-load condition; based on the coupled equations, the coefficient matrix is ​​obtained by linear fitting A calibrated relationship between film thickness and ambient temperature can be obtained.

[0017] Preferably, the signal conversion module using the LC parallel resonant circuit includes a voltage divider resistor R0, a parallel capacitor C P and eddy current coil; parallel capacitor C P After being connected in parallel with the eddy current coil, a voltage dividing resistor R0 is connected in series;

[0018] The number of turns of the eddy current coil is selected to be 100 turns, and the diameter-to-height ratio is selected to be 4; the inner diameter of the coil is 3 mm, and the diameter of the wire is 100 μm;

[0019] Based on the selected eddy current coil, when the excitation frequency is 1MHz, the parallel capacitor C P The value range is 500pF~600pF.

[0020] Preferably, for the thickness measurement range of 100-1500nm, the average impedance of the resonant circuit measured by the impedance analyzer is 1.85kΩ, and the optimal value of the corresponding voltage divider resistor is 4.36kΩ; according to the actual possible resistance values, the voltage divider resistor value range is selected to be 4.0kΩ to 4.5kΩ.

[0021] Preferably, the thickness measurement range of 100 to 1500 nm is divided into three intervals: [100, 400] nm, [400, 1000] nm, and [1000, 1500] nm; the optimal voltage divider resistance value is determined for each interval, which are 2.7 kΩ, 4.0 kΩ, and 3.3 kΩ, respectively, and the voltage divider resistance value range is determined for each interval.

[0022] Preferably, the signal conversion module using the AC bridge includes an eddy current coil, a reference coil and two sampling resistors Rs; the sampling resistor Rs has a value range of 200Ω-400Ω.

[0023] Preferably, the signal generating module uses an active square wave crystal oscillator as an excitation source with an output frequency of 1 MHz, and removes high-order harmonics through a fourth-order Butterworth low-pass filter composed of an operational amplifier to obtain a 1 MHz sinusoidal output fundamental wave.

[0024] The present invention also provides a design method for a micro-nano film thickness sensor detection circuit, which adopts the architecture of the multi-modular detection circuit of the micro-nano film thickness eddy current sensor. The method comprises:

[0025] According to the measurement requirements and temperature environment, a signal conversion module and a post-processing module provided by the detection circuit are selected and combined with the signal generation module to form a micro-nano film thickness sensor detection circuit;

[0026] The parameters of the eddy current coil in the signal conversion module are designed: first, the inner diameter of the coil and the diameter of the wire are fixed, and the diameter-to-height ratio of the coil and the number of coil turns are determined by simulation; during simulation, the diameter-to-height ratio of the coil is first fixed to 1, and the sensitivity change of the coil impedance at different numbers of turns with respect to the thickness of the metal film to be measured is calculated, and the result that the greater the number of coil turns, the greater the sensitivity is obtained; the preferred value of the number of coil turns is selected according to the required sensitivity; then the number of coil turns is fixed, and the sensitivity change of the coil impedance at different diameter-to-height ratios with respect to the thickness of the metal film to be measured is calculated, and the result that the greater the diameter-to-height ratio, the greater the sensitivity is obtained; based on the relationship between the number of coil turns and the sensitivity and the relationship between the diameter-to-height ratio and the sensitivity, the diameter-to-height ratio is selected under the premise of ensuring the measurement sensitivity, combined with the actual physical space limitations and the device miniaturization goal; and the coil height is determined according to the diameter-to-height ratio and the inner diameter of the coil;

[0027] According to the selected eddy current coil, other parameters in the signal conversion module are determined.

[0028] Preferably, when an LC parallel resonant circuit is used as the signal conversion module, the voltage divider resistor R0 in the LC parallel resonant circuit is determined as follows:

[0029] The matching voltage-dividing resistor R0 is the voltage-dividing resistor corresponding to the average value of the resonant circuit impedance during the measurement process, which is the optimal value of the voltage-dividing resistor. According to the actual possible resistance values, the voltage-dividing resistor value range is determined around the optimal value of the voltage-dividing resistor, and the value of the voltage-dividing resistor R0 is selected within the value range;

[0030] Alternatively, the thickness measurement range is divided into a plurality of intervals; the optimal voltage-dividing resistance value is determined for each interval, and then the voltage-dividing resistance value range is determined for each interval according to the actual possible resistance value; the value of the voltage-dividing resistance R0 is selected according to the voltage-dividing resistance value range corresponding to the interval where the thickness of the measured object is located;

[0031] When an AC bridge is used as a signal conversion module, the sampling resistor Rs in the AC bridge is determined as follows: based on the selected eddy current coil parameters, the sampling resistor Rs that maximizes the sensitivity is determined.

[0032] Beneficial effects:

[0033] (1) The present invention is based on a multi-module architecture design, which can flexibly adjust the combination of detection circuit sub-modules to meet various measurement scenarios and reduce the complexity and cost of system implementation.

[0034] (2) The post-processing module proposed in the present invention includes a module form that integrates a temperature decoupling algorithm. The scheme characterizes the thickness and temperature by the real part and the imaginary part respectively. At this time, the voltage value corresponding to the thickness and temperature is not affected by the other quantity, reducing the interference of the ambient temperature on the detection performance. At the same time, the scheme further clearly characterizes the temperature and has the feasibility of synchronous perception of the temperature characteristic component.

[0035] (3) When designing the parameters of the eddy current coil, the present invention performs parameter decoupling simulation and value selection according to the different levels of influence of the number of turns, inner diameter, height, and diameter-to-height ratio on sensitivity. First, the inner diameter of the coil and the diameter of the wire are determined by directly selecting the parameter value, and then the preferred number of coil turns is determined by simulation of a given diameter-to-height ratio, and then the diameter-to-height ratio is re-determined based on the preferred number of coil turns. This parameter selection method and sequence enables the detection circuit to achieve the best measurement sensitivity.

[0036] (4) In a preferred embodiment, when selecting the parameters of the voltage divider resistor R0 of the LC parallel resonant circuit, the present invention divides the thickness measurement range into segments, and obtains the resistance value range corresponding to the segment according to the actual measurement thickness range, thereby further improving the linearity and sensitivity of the detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 A schematic diagram of a single-output detection circuit of an eddy current sensor based on an LC parallel resonance structure provided in an embodiment of the present invention;

[0038] Figure 2 A schematic diagram of a single-output detection circuit of an eddy current sensor based on an AC bridge structure provided in an embodiment of the present invention;

[0039] Figure 3 A schematic diagram of the principle of a dual-output detection circuit of an eddy current sensor based on an LC parallel resonance structure and an integrated decoupling algorithm provided in an embodiment of the present invention.

[0040] Figure 4 A schematic diagram of the principle of a dual-output detection circuit of an eddy current sensor based on an AC bridge structure and integrated with a decoupling algorithm provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0041] The present invention provides a multi-modular detection circuit and design method of a micro-nano film thickness eddy current sensor. The film thickness sensor described in the present invention is based on the eddy current detection principle and is mainly used for detecting the thickness of micro-nano metal films or lubricating oil films. The detection circuit design is mainly used to convert the output impedance change of the eddy current coil (sensor sensitive element) into an output voltage, and achieve high-precision stable output.

[0042] The basic idea of ​​the multi-modular detection circuit of the micro-nano thin film thickness eddy current sensor of the present invention is: first, based on the multi-module architecture design concept, a flexibly selectable / adjustable detection circuit sub-module combination is designed for various measurement scenarios, and the detection circuit sub-module combination can be flexibly selected according to actual detection needs to meet various measurement scenarios and reduce the complexity and cost of system implementation; secondly, the optimal value range and method design are proposed for the main electrical parameters in the signal conversion module, so that the measurement sensitivity of the detection circuit reaches the best state; in addition, in view of the adverse effect of ambient temperature on the detection accuracy of weak signals, an optional detection circuit of the present invention can integrate a decoupling algorithm module based on phase-sensitive detection, which can reduce the interference of ambient temperature fluctuations on the sensor output in hardware and synchronously perceive the temperature characteristic components.

[0043] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0044] For the thin film thickness sensor detection circuit, firstly, a signal generation module is required to provide a stable excitation signal for the entire circuit; secondly, different signal conversion circuits need to be designed according to the different requirements of the measurement object and measurement needs for sensitivity and range in different scenarios; in addition, different post-processing modules are used to measure whether the ambient temperature is stable. Therefore, the present invention divides the entire detection circuit into modules, and designs multiple optional forms for users to build detection circuits for use according to modules that cannot adopt a unified circuit structure due to different requirements.

[0045] Based on the above analysis, the present invention designs a basic module of a multi-modular detection circuit of a micro-nano thin film thickness eddy current sensor, including a signal generation module, two signal conversion modules, and two post-processing modules.

[0046] (1) Signal generation module

[0047] The signal generation module provides a stable sinusoidal excitation signal for the eddy current coil and the like.

[0048] In a preferred embodiment of the present invention, the signal generating module uses an active square wave crystal oscillator as an excitation source with an output frequency of 1 MHz, and removes high-order harmonics through a fourth-order Butterworth low-pass filter composed of an operational amplifier to obtain a 1 MHz sinusoidal output fundamental wave.

[0049] (2) Signal conversion module

[0050] The present invention provides two signal conversion modules. A signal conversion module such as Figure 1 and Figure 3 As shown, the structure of LC parallel resonant circuit + amplifier circuit is adopted; another signal conversion module is as follows Figure 2 and Figure 4 As shown, the structure of AC bridge + differential amplifier circuit is adopted. The output voltage signal of the signal conversion module contains the output impedance information of the eddy current coil as the sensor sensitive element.

[0051] See also Figure 1 , Figure 3 The LC parallel resonant circuit in the signal conversion module includes a voltage divider resistor R0 and a parallel capacitor C P and eddy current coil; parallel capacitor C P After being connected in parallel with the eddy current coil, a voltage dividing resistor R0 is connected in series.

[0052] When designing the LC parallel resonant circuit, the coil parameters of the eddy current coil, the parallel capacitance C P The voltage divider resistor R0 needs to be specially designed. The specific design method is:

[0053] ① Parameter selection of eddy current coil

[0054] The core sensitive element of the eddy current sensor is the eddy current coil, which is also part of the demodulation circuit. Its parameter design determines the design of the circuit module. Therefore, it is necessary to first optimize the coil parameters. The coil is wound with copper wire, and its size parameters include the number of coil turns, coil inner diameter, coil height, diameter-to-height ratio (ratio of radial width to height), and wire diameter.

[0055] When designing coil parameters, the present invention fixes the inner diameter of the coil to 3 mm, the wire diameter to 100 μm, and uses COMSOL simulation to determine the diameter-to-height ratio and number of turns, which have a greater impact on sensitivity and are more coupled. Specifically, in the simulation model, the diameter-to-height ratio of the coil is first fixed to 1, and after calculating the coil impedance at different numbers of turns with respect to the sensitivity of the measured metal film thickness, it can be obtained that the greater the number of coil turns, the greater the sensitivity; according to the required sensitivity, the preferred value of the number of coil turns is selected, for example, 100 turns. Then, the number of coil turns is fixed to the preferred value of 100 turns, and after calculating the coil impedance at different diameter-to-height ratios with respect to the sensitivity of the measured metal film thickness, it can be obtained that the greater the diameter-to-height ratio, the greater the sensitivity. Considering the limitations of the actual physical space and the miniaturization of the device, the diameter-to-height ratio is selected as 4 under the premise of ensuring the measurement sensitivity. Thus, the coil height can be determined according to the inner diameter of the coil and the diameter-to-height ratio.

[0056] The parameter selection method and sequence of the present invention performs parameter decoupling simulation and numerical value selection sequence according to the different influence levels of the number of turns, inner diameter, height, and diameter-to-height ratio on sensitivity, so as to achieve the best measurement sensitivity of the detection circuit.

[0057] ② Parallel capacitor C in LC parallel resonant circuit P Determination of parameters

[0058] The value of the parallel capacitor is related to the inductance of the coil. For the LC parallel resonant signal conversion circuit, the resonance condition must be met during design. When the coil inductance is determined and the excitation frequency is 1MHz, according to the resonance condition, C = 1 / 4π 2 f 2 L, the parallel capacitance C in the signal conversion circuit can be calculated P If the capacitance value deviates from the resonant capacitance value, the measurement sensitivity will decrease, and the greater the deviation, the greater the impact on the sensitivity. In this embodiment, based on the coil selection, the inductance of the determined coil is, for example, 46.05μH, and the value of the parallel capacitance in the signal conversion circuit can be calculated to be 550.06pF. Since the value of the actual capacitor device has been standardized, the selection of a parallel capacitance value of 500pF to 600pF can meet the resonant measurement requirements.

[0059] ③ Determination of the parameters of the voltage divider resistor R0 in the LC parallel resonant circuit

[0060] Another key parameter of the LC parallel resonant circuit is the voltage divider resistor, whose value will also affect the circuit measurement sensitivity. As the voltage divider resistor increases, the thickness sensitivity first increases and then decreases. When the voltage divider resistance is approximately equal to the average value of the resonant circuit impedance during the measurement process, the thickness sensitivity reaches the maximum value. Therefore, the voltage divider resistor R0 of the present invention is matched to the voltage divider resistor corresponding to the average value of the resonant circuit impedance during the measurement process as the optimal value of the voltage divider resistor. According to the actual possible resistance value, the voltage divider resistor value range is determined around the optimal value of the voltage divider resistor.

[0061] For the thickness measurement range of 100 to 1500nm, the average impedance of the resonant circuit measured by the impedance analyzer is 1.85kΩ, so the optimal value of the voltage divider resistor should also be 4.36kΩ. Considering that the actual resistance value has been standardized, the voltage divider resistor value of 4.0kΩ to 4.5kΩ can meet the measurement requirements.

[0062] However, the linearity within the large range is poor, only 0.9. In order to further improve the linearity and sensitivity, in a preferred embodiment, a method of adjusting the voltage-dividing resistor in segments is adopted. It is sufficient to ensure that the linear correlation coefficient in each interval reaches 0.99. Based on this, the preferred scheme divides the thickness measurement range of 100 to 1500 nm into three intervals: [100, 400] nm, [400, 1000] nm, and [1000, 1500] nm. Each interval has an optimal voltage-dividing resistor value, which is 2.7 kΩ, 4.0 kΩ, and 3.3 kΩ, respectively. The voltage-dividing resistor value range is determined for each interval. At this time, the sensitivity of each interval is increased by 11.7%, 0.79%, and 18.95% respectively compared to the sensitivity before segmentation. Then, when selecting the voltage-dividing resistor R0 for the thin film thickness sensor detection circuit, the corresponding resistance value range is obtained according to the range interval where the film thickness to be measured is located, and the voltage-dividing resistor R0 is selected within this range.

[0063] See also Figure 2 , Figure 4 The AC bridge in the signal conversion module includes an eddy current coil, a reference coil and two precision low-temperature drift sampling resistors Rs with equal resistance.

[0064] When designing an AC bridge, the design method of the coil parameters of the eddy current coil is the same as above; the sensor sensitivity increases first and then decreases with the increase of the sampling resistance, and there is an optimal value of the bridge arm resistance to maximize the sensitivity. Therefore, based on the selected eddy current coil parameters, when the excitation frequency is 1MHz, the sampling resistance Rs that maximizes the sensitivity is determined, and the optimal value range of the bridge arm resistance that matches the coil selected by the present invention is 200Ω~400Ω.

[0065] The output signal of the AC bridge circuit is extracted and amplified by the INA849DR to realize differential signal extraction. The amplification factor can be adjusted according to the measurement requirements by adjusting the peripheral resistors matching the chip.

[0066] (3) Post-processing module

[0067] The present invention provides two post-processing modules. One post-processing module implements thickness measurement, such as Figure 1 and Figure 2 As shown, it includes a rectifier circuit and a peak detection circuit connected in series to achieve single-channel output. Another post-processing module realizes thickness-temperature synchronous measurement, such as Figure 3 and Figure 4 As shown, it includes a phase shift circuit, a phase-sensitive detection circuit, a filter circuit, a voltage bias circuit, a post-amplifier circuit and a coupling equation calculation module. As a function expansion module, the coupling equation calculation module can be flexibly selected according to measurement requirements.

[0068] ① Consider thickness measurement only

[0069] See also Figure 1 , Figure 2 The post-processing module is used to extract the characteristic quantity of the AC signal output by the signal conversion module and realize stable output. When only considering thickness measurement, the input signal of the post-processing module (i.e., the output signal of the signal conversion module) first passes through the rectifier circuit to flip the negative half-cycle of the input signal to the positive half-cycle, and then the peak detection circuit extracts the voltage peak of the rectified signal to realize single-channel output.

[0070] In practice, a rectifier circuit based on AD818 can be used to flip the negative half-cycle of the input signal to the positive half-cycle, and then connected to a peak detection circuit of OPA350EA to extract the peak value of the AC voltage output by the signal conversion module to represent the measured thickness.

[0071] ② Consider thickness-temperature simultaneous measurement

[0072] When the post-processing module integrates the temperature decoupling algorithm module, it includes a phase shift circuit, a phase-sensitive detection circuit, a filter circuit, a voltage bias circuit, a post-stage amplifier circuit and a coupling equation calculation module. First, the excitation signal output by the signal generation module is phase-shifted by π / 2 through the phase shift circuit and output to the two multipliers in the phase-sensitive detection circuit; the two multipliers also obtain the excitation signal before phase shift from the signal generation module; the multiplier multiplies the excitation signal and the excitation signal with a phase shift of π / 2 with the output signal of the signal conversion module respectively to separate the real part and the imaginary part of the output voltage signal of the signal conversion module, and then the real part and the imaginary part of the DC voltage signal are output through the processing of the filter circuit, the voltage bias circuit and the post-stage amplifier circuit in turn to characterize the measured value.

[0073] In practice, a reference signal with a phase difference of 90° with the excitation signal can be generated through the phase shift circuit composed of the AD818 chip. Using the AD835 analog multiplier, the output signal of the signal conversion module is multiplied with the excitation signal and the reference signal with a phase shift of 90°, and the real and imaginary parts of the output voltage signal can be obtained. Then, the ADR3425 is used to provide a bias reference voltage, and two OPA2188s are used to form a DC voltage follower and a subtractor, respectively, so that the output voltage is forward biased, and finally the amplifier module based on the AD8221 outputs a DC voltage signal.

[0074] Within the measuring range, the real and imaginary parts of the output voltage show a certain linear relationship with the thickness and temperature of the measured metal film, respectively, and a coupled equation group of the real and imaginary parts of the output voltage and the thickness and temperature can be established.

[0075]

[0076] Where th is the film thickness, T is the ambient temperature, U Re (th,T) is the real part of the output voltage, U Im (th,T) is the imaginary part of the output voltage, U Re0 is the real part of the output voltage in the no-load state (the measured thickness is 0), U Im0 is the imaginary part of the output voltage under no-load condition, which is caused by the imbalance of the AC bridge. Based on this coupled equation group, the coefficient matrix is ​​obtained by linear fitting: A calibrated relationship between film thickness and ambient temperature can be obtained.

[0077] The equation group and the coefficient matrix obtained by fitting are stored in the coupling equation calculation module. The coupling equation calculation module substitutes the real and imaginary components of the DC voltage signal output by the post-stage amplifier circuit into the coupling equation group, and the film thickness and ambient temperature can be solved by the real and imaginary parts of the output voltage. The present invention adopts a decoupling method, and the thickness and temperature are respectively characterized by the real and imaginary parts. At this time, the voltage values ​​corresponding to the thickness and temperature are not affected by the other quantity, thereby achieving the purpose of reducing temperature interference. The real and imaginary parts are used to characterize the thickness and temperature, which not only reduces the temperature interference, but also further clearly characterizes the temperature. If the decoupling is not performed, the amplitude of the output voltage is directly used to characterize the thickness, and the output value is seriously disturbed by the temperature. Therefore, the scheme is used to reduce the influence of temperature fluctuations on the measurement accuracy, and the film thickness and ambient temperature can be measured synchronously, realizing the synchronous measurement of dual-channel output.

[0078] The modules are divided into basic modules and function expansion modules. A unified interface is designed, which can be flexibly adjusted according to actual measurement needs.

[0079] In actual use, according to the measurement requirements and temperature environment, a signal conversion module and a post-processing module provided above are selected and combined with the signal generation module to form a film thickness sensor detection circuit. Among them, the selection of the signal conversion module is mainly based on sensitivity and range considerations. The LC parallel resonant circuit is more sensitive than the AC bridge circuit, and the AC bridge circuit is more accurate than the LC parallel resonant circuit. One of the two signal conversion circuits is selected according to the actual sensitivity or accuracy requirements. The post-processing module with peak detection is mainly for single thickness measurement scenarios with stable temperature environments, while the circuit with decoupling module is mainly for measurement scenarios with large temperature changes and a large impact on thickness measurement.

[0080] The above specific embodiments only describe the design principle of the present invention. The shapes and names of the components in the description may be different and are not limited. Therefore, those skilled in the art in the field of the present invention may modify or replace the technical solutions recorded in the above embodiments; and these modifications and replacements do not deviate from the creative purpose and technical solutions of the present invention and should all fall within the protection scope of the present invention.

Claims

1. A multi-modular detection circuit for a micro-nano film thickness eddy current sensor, characterized in that: include: The detection circuit provides three types of basic modules, namely, signal generation module, two types of signal conversion modules, and two types of post-processing modules; The signal generating module provides an excitation signal; Of the two signal conversion modules, one signal conversion module uses an LC parallel resonant circuit + an amplifier circuit, and the other signal conversion module uses an AC bridge + a differential amplifier circuit; the voltage signal output by the signal conversion module contains output impedance information of the eddy current coil as a sensor sensitive element; Among the two post-processing modules: A post-processing module realizes thickness measurement, including a rectifier circuit and a peak detection circuit connected in series to realize single-channel output; Another post-processing module realizes thickness-temperature synchronous measurement, including a phase shift circuit, a phase-sensitive detection circuit, a filter circuit, a voltage bias circuit, a post-stage amplifier circuit and a coupling equation calculation module; The phase-sensitive detection circuit performs multiplication operation on the excitation signal output by the signal generation module and the excitation signal phase-shifted by π / 2 by the phase shift circuit and the output signal of the signal conversion module to separate the real part and the imaginary part, and then sequentially processes through the filtering circuit, the voltage bias circuit and the post-stage amplifier circuit to output the real part and the imaginary part of the DC voltage signal; Within the measuring range, the real and imaginary parts of the output voltage show a certain linear relationship with the measured film thickness and temperature respectively, and the coupling equations of the real and imaginary parts of the output voltage and the film thickness and ambient temperature are established; The coupling equation calculation module substitutes the real and imaginary components of the DC voltage signal output by the post-amplifier circuit into the coupling equation group for solution, obtains the synchronous measurement results of the film thickness and the ambient temperature, and realizes dual-channel output. According to the measurement requirements, the signal conversion module and the post-processing module are selected and combined with the signal generation module to form a micro-nano film thickness sensor detection circuit.

2. The multi-modular detection circuit according to claim 1, characterized in that: The coupling equation is: Where th is the film thickness, T is the ambient temperature, U Re (th,T) is the real part of the output voltage, U Im (th,T) is the imaginary part of the output voltage, U Re0 is the real part of the output voltage under no-load condition, U Im0 is the imaginary part of the output voltage under no-load condition; based on the coupled equations, the coefficient matrix is ​​obtained by linear fitting A calibrated relationship between film thickness and ambient temperature can be obtained.

3. The multi-modular detection circuit according to claim 1, characterized in that: The signal conversion module using the LC parallel resonant circuit includes a voltage divider resistor R0 and a parallel capacitor C P and eddy current coil; parallel capacitor C P After being connected in parallel with the eddy current coil, a voltage dividing resistor R0 is connected in series; The number of turns of the eddy current coil is selected to be 100 turns, and the diameter-to-height ratio is selected to be 4; the inner diameter of the coil is 3 mm, and the diameter of the wire is 100 μm; Based on the selected eddy current coil, when the excitation frequency is 1MHz, the parallel capacitor C P The value range is 500pF~600pF.

4. The multi-modular detection circuit according to claim 3, characterized in that: For the thickness measurement range of 100-1500nm, the average impedance of the resonant circuit measured by the impedance analyzer is 1.85kΩ, and the optimal value of the corresponding voltage divider resistor is 4.36kΩ; according to the actual possible resistance values, the voltage divider resistor value range is selected to be 4.0kΩ~4.5kΩ.

5. The multi-modular detection circuit according to claim 3, characterized in that: The thickness measurement range of 100-1500 nm is divided into three intervals: [100,400] nm, [400,1000] nm, and [1000,1500] nm. The optimal voltage divider resistance value is determined for each interval, which are 2.7 kΩ, 4.0 kΩ, and 3.3 kΩ respectively, and the voltage divider resistance value range is determined for each interval.

6. The multi-modular detection circuit according to claim 3, characterized in that: The signal conversion module using the AC bridge includes an eddy current coil, a reference coil and two sampling resistors Rs; the sampling resistor Rs has a value range of 200Ω-400Ω.

7. The multi-modular detection circuit according to claim 1, characterized in that: The signal generation module uses an active square wave crystal oscillator as an excitation source, with an output frequency of 1 MHz. A fourth-order Butterworth low-pass filter composed of an operational amplifier removes high-order harmonics to obtain a 1 MHz sinusoidal output fundamental wave.

8. A design method for a micro-nano film thickness sensor detection circuit, characterized in that: Using the architecture of the multi-modular detection circuit of the micro-nano film thickness eddy current sensor as claimed in claim 1, the method comprises: According to the measurement requirements and temperature environment, a signal conversion module and a post-processing module provided by the detection circuit are selected and combined with the signal generation module to form a micro-nano film thickness sensor detection circuit; The parameters of the eddy current coil in the signal conversion module are designed: first, the inner diameter of the coil and the diameter of the wire are fixed, and the diameter-to-height ratio of the coil and the number of coil turns are determined by simulation; during simulation, the diameter-to-height ratio of the coil is first fixed to 1, and the sensitivity change of the coil impedance at different numbers of turns with respect to the thickness of the metal film to be measured is calculated, and the result that the greater the number of coil turns, the greater the sensitivity is obtained; the preferred value of the number of coil turns is selected according to the required sensitivity; then the number of coil turns is fixed, and the sensitivity change of the coil impedance at different diameter-to-height ratios with respect to the thickness of the metal film to be measured is calculated, and the result that the greater the diameter-to-height ratio, the greater the sensitivity is obtained; based on the relationship between the number of coil turns and the sensitivity and the relationship between the diameter-to-height ratio and the sensitivity, the diameter-to-height ratio is selected under the premise of ensuring the measurement sensitivity, combined with the actual physical space limitations and the device miniaturization goal; and the coil height is determined according to the diameter-to-height ratio and the inner diameter of the coil; According to the selected eddy current coil, other parameters in the signal conversion module are determined.

9. The method according to claim 8, characterized in that When the LC parallel resonant circuit is used as the signal conversion module, the voltage divider resistor R0 in the LC parallel resonant circuit is determined as follows: The matching voltage-dividing resistor R0 is the voltage-dividing resistor corresponding to the average value of the resonant circuit impedance during the measurement process, which is the optimal value of the voltage-dividing resistor. According to the actual possible resistance values, the voltage-dividing resistor value range is determined around the optimal value of the voltage-dividing resistor, and the value of the voltage-dividing resistor R0 is selected within the value range; Alternatively, the thickness measurement range is divided into a plurality of intervals; the optimal voltage-dividing resistance value is determined for each interval, and then the voltage-dividing resistance value range is determined for each interval according to the actual possible resistance value; the value of the voltage-dividing resistance R0 is selected according to the voltage-dividing resistance value range corresponding to the interval where the thickness of the measured object is located; When an AC bridge is used as a signal conversion module, the sampling resistor Rs in the AC bridge is determined as follows: based on the selected eddy current coil parameters, the sampling resistor Rs that maximizes the sensitivity is determined.

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