JP7390814B2 - Capacitive sensor, diaphragm vacuum gauge, and capacitive sensor manufacturing method - Google Patents

Description

The present invention relates to a capacitive sensor, a diaphragm vacuum gauge, and a method for manufacturing a capacitive sensor that detects a physical quantity by converting a physical quantity of an object to be measured into a capacitance.

2. Description of the Related Art Conventionally, there are capacitive sensors that detect and measure physical quantities by utilizing changes in capacitance. Capacitive sensors are used, for example, as pressure sensors. When a capacitive sensor becomes a pressure sensor and is used in a diaphragm vacuum gauge, the sensor element has a sensor diaphragm (diaphragm) with a movable electrode, and the displacement of the sensor diaphragm based on the size of a physical quantity is measured. The detection principle is to convert it into a signal. The sensor diaphragm bends and changes its position under the pressure of the medium to be measured. The sensor diaphragm deflects in response to the pressure it is subjected to. The pressure sensor has a fixed electrode that faces the sensor diaphragm and forms an electrode portion in pair with a movable electrode. The distance between the electrodes changes due to the displacement of the sensor diaphragm due to pressure, which changes the capacitance at the electrodes. Therefore, the pressure of the medium to be measured can be detected from the capacitance. Such pressure sensors are often used in industrial applications including semiconductor equipment because they have little dependence on gas type.

Here, the sensor element of the capacitance type sensor has a detection side electrode part and a reference side electrode part for detecting pressure, which is a physical quantity, and detects it by a potential difference based on the capacitance between the two electrode parts. There is a capacitive sensor that improves accuracy (for example, see Patent Document 1).

Japanese Patent Application Publication No. 2005-351744

When detecting pressure, a sinusoidal AC voltage (for example, sensor drive frequency f, amplitude A) is applied as a signal to the sensor element. The current flowing through the sensor element is amplified by a charge amplification circuit and becomes a signal corresponding to the magnitude of the physical quantity. This signal is detected (rectified) by a detection circuit. The detected signal is further smoothed by a low-pass filter to obtain a DC signal. The DC signal is converted into a digital signal by, for example, an AD converter.

Here, the AD converter has a voltage range that can be input as a signal. Therefore, the gain, which is the amplification factor of the signal, is set so as not to exceed the voltage range. At this time, it is necessary to set the gain in consideration of variations occurring in sensor elements and the like. For example, in a sensor element of a capacitance type sensor, variations in capacitance occur between a detection side electrode part and a reference side electrode part due to manufacturing variations that occur during manufacturing. If the variation is large, the voltage range may be exceeded. For example, to prevent the signal from exceeding the voltage range, the gain must be set small. The lower the gain, the lower the S/N ratio.

In order to solve these problems, it is an object of the present invention to provide a capacitive sensor, a diaphragm vacuum gauge, and a method for manufacturing a capacitive sensor that can improve signal gain.

In order to achieve such an object, the capacitive sensor of the present invention includes a movable electrode that is displaced together with a sensor diaphragm whose position changes depending on the physical quantity to be measured, and a fixed electrode that is provided opposite to the movable electrode. A sensor element that has a plurality of electrode parts for detection and reference, and a capacitance regulator that adjusts the capacitance of at least one of the detection electrode part and the reference electrode part . The device adjusts the capacitance so that when the physical quantity is zero, the difference between the AC signals passing through the detection electrode section and the reference electrode section becomes the set potential. .

According to the present invention, the capacitance adjuster adjusts the capacitance of at least one of the detection electrode section and the reference electrode section, so that variations in capacitance in each electrode section are absorbed, The signal gain can be increased and the S/N ratio can be increased.

1 is a diagram showing the appearance of a diaphragm vacuum gauge having a capacitive sensor according to Embodiment 1. FIG. 3 is a diagram showing a configuration of main parts of a sensor section according to Embodiment 1. FIG. 1 is a diagram showing a configuration centered on a circuit section of a capacitive sensor according to Embodiment 1. FIG. 7 is a diagram showing a configuration of main parts of a sensor section according to Embodiment 2. FIG.

Hereinafter, capacitive sensors and the like according to embodiments will be described with reference to drawings and the like. In each drawing, the same reference numerals are the same or equivalent, and are common throughout the entire embodiment described below. Further, in the drawings, the size relationship of each component may differ from the actual one. The forms of the constituent elements shown in the entire specification are merely examples, and are not limited to the forms described in the specification. In particular, the combinations of components are not limited to those in each embodiment, and components described in other embodiments can be applied to other embodiments. Regarding multiple devices of the same type that are distinguished by subscripts, if there is no need to distinguish or specify them, the subscripts may be omitted from the description.

Embodiment 1.
FIG. 1 is a diagram showing the appearance of a diaphragm vacuum gauge having a capacitance type sensor according to a first embodiment. The diaphragm vacuum gauge 1 has a sensor section 100 of a capacitive sensor detecting section 10, which will be described later, at the bottom and a circuit section 200 of the capacitive sensor detecting section 10 at the top. The sensor unit 100 is a sensor portion of the capacitive sensor detection unit 10 that is a capacitive sensor that actually detects a physical quantity. Further, the circuit section 200 of the capacitive sensor detection section 10 has, for example, a circuit board, and outputs a signal sent to the sensor section 100 and outputs a signal related to capacitance sent from the sensor section 100 to a value of a physical quantity ( This is the part that performs processing such as conversion to measured values). Here, in the following, unless otherwise specified, it is assumed that the capacitive sensor detection unit 10 detects the pressure of the medium to be measured as a physical quantity.

FIG. 2 is a diagram showing the configuration of main parts of the sensor section according to the first embodiment. In the first embodiment, the sensor section 100 includes a sensor chip that is a capacitance type sensor element. The sensor section 100 includes a base 101, a sensor diaphragm 102, a movable sensor electrode (first electrode) 104, a fixed sensor electrode (second electrode) 105, a movable reference electrode 106, and a fixed reference electrode 107. In the sensor section 100 of the first embodiment, the sensor diaphragm 102 is pressed by the pressure of the medium to be measured, and the position of the sensor diaphragm 102 is changed. The capacitance between the movable electrode and the fixed electrode changes depending on the position of the sensor diaphragm 102. Therefore, the pressure of the medium to be measured is converted into capacitance.

The base 101 supports a sensor diaphragm 102 that serves as a pressure receiving section. The sensor diaphragm 102 is made of an insulating material having heat resistance and corrosion resistance, such as sapphire or alumina ceramic. However, it is not limited to this. The sensor diaphragm 102 is supported by a support portion 101a of the base 101, which has a recessed portion at the center in a plan view. The sensor diaphragm 102 is movable in a movable region 102a inside the support portion 101a. The movable region 102a has, for example, a circular shape in a plan view because pressure is evenly applied to the movable region 102a to cause displacement. Capacity chamber 103 is a space between sensor diaphragm 102 and base 101 in movable region 102a. In the diaphragm vacuum gauge 1, the capacity chamber 103 is a space in a vacuum state.

The movable sensor electrode 104 is formed in the movable region 102a of the sensor diaphragm 102 inside the capacitance chamber 103. Furthermore, the fixed sensor electrode 105 is installed on the base 101 inside the capacitance chamber 103 to face the movable sensor electrode 104 . The sensor unit 100 of the first embodiment further includes a movable reference electrode 106 and a fixed reference electrode 107. The movable reference electrode 106 is formed around the movable sensor electrode 104 (at the periphery of the sensor diaphragm 102 ) in the movable region 102 a of the sensor diaphragm 102 inside the capacitance chamber 103 . The fixed reference electrode 107 is formed on the base 101 around the fixed sensor electrode 105 inside the capacitance chamber 103 . The movable reference electrode 106 and the fixed reference electrode 107 are placed facing each other. Here, between the movable sensor electrode 104 and the movable reference electrode 106, the movable sensor electrode 104 is bent more easily, so its displacement is larger than that of the movable reference electrode 106. Here, the set of the movable sensor electrode 104 and the fixed sensor electrode 105 becomes a detection-side electrode section 108 for detection, which will be described later. Further, the set of the movable reference electrode 106 and the fixed reference electrode 107 becomes a reference-side electrode section 109 for reference, which will be described later. Therefore, two sensor signals are output.

FIG. 3 is a diagram showing a configuration centered on the circuit section of the capacitive sensor according to the first embodiment. The circuit section 200 includes a signal generator 210, a charge amplifier 220, a detection circuit 230, a smoother 240, and an AD converter 250.

The signal generator 210 applies a sinusoidal AC voltage, which is an AC signal, to the sensor unit 100 . In particular, the signal generator 210 in the first embodiment includes a signal generator 211 and a capacitance adjuster 212.

The signal generator 211 includes a dedicated IC circuit, oscillates at a predetermined oscillation frequency, and generates a sinusoidal AC signal. Further, the capacitance adjuster 212 changes the signal generated by the signal generator 211 to adjust the capacitance of the detection side electrode section 108. Here, among the signals generated by the signal generator 211, a DC voltage component is superimposed on the signal sent to the detection side electrode section 108. Therefore, a DC voltage is applied to the detection side electrode section 108 in addition to the voltage related to the AC signal. Here, the signal from the signal generator 210 is not particularly limited as long as it includes an AC signal component.

The charge amplifier 220 performs amplification according to the capacitance in the sensor section 100. In the charge amplifier 220, a detection side capacitor 222A and a reference side capacitor 222B are arranged in the feedback sections of the detection side amplifier 221A and the reference side amplifier 221B, respectively. The detection side amplifier 221A outputs a current amplified according to the capacitance of the detection side electrode section 108 of the sensor section 100 as a detection signal. Further, the reference side amplifier 221B outputs a current amplified according to the capacitance of the reference side electrode section 109 of the sensor section 100 as a reference signal. Then, the difference amplifier 223 outputs a difference signal obtained by amplifying the difference between the detection signal and the reference signal.

The noise removal section 260 includes bandpass filters 261A to 261C. The bandpass filters 261A to 261C are filters that pass signals in a set frequency band and remove noise in the detection signal, reference signal, and difference signal from the charge amplifier 220. Furthermore, the detection circuit 230 detects (rectifies) the detection signal, reference signal, and difference signal that have passed through the noise removal section 260. The detection circuit 230 includes rectifier circuits 231A to 231C. Further, the rectifier circuits 231A to 231C perform half-wave rectification or full-wave rectification of the signals that have passed through the band-pass filters 261A to 261C. Here, the rectifier circuit 231A rectifies the difference signal. Further, the rectifier circuit 231B rectifies the detection signal. Then, the rectifier circuit 231C rectifies the reference signal.

The smoother 240 includes low-pass filters (LPF) 241A to 241C, smoothes the signal detected by the detection circuit 230, and outputs an averaged DC signal to the AD converter 250 described above. Here, the low-pass filter 241A smoothes the difference signal and outputs it as a DC signal V1. Furthermore, the low-pass filter 241B smoothes the detection signal and outputs it as a DC signal V2. Then, the low-pass filter 241C smoothes the reference signal and outputs it as a DC signal V3.

The AD converter 250 converts a DC signal, which is an analog signal obtained by detecting the pressure of the medium to be measured, into a digital signal containing binary data representing a numerical value based on the magnitude of the signal. , output to an external processing device. Here, although not particularly limited, it is assumed that the AD converter 250 of the first embodiment is a ΔΣ type AD converter. A ΔΣ type AD converter is a converter that can perform high-speed and high-precision conversion by performing differential and integral calculations on an input DC signal.

The capacitive sensor detection section 10 included in the diaphragm vacuum gauge 1 of the first embodiment includes a capacitance regulator 212 in a signal generator 210 . When the capacitance regulator 212 applies a DC voltage component to the detection side electrode section 108, a Coulomb force is generated between the movable sensor electrode 104 and the fixed sensor electrode 105 of the detection side electrode section 108. Charges of opposite signs are accumulated between the movable sensor electrode 104 and the fixed sensor electrode 105, and a Coulomb force that attracts each other is generated, thereby changing the distance between the movable sensor electrode 104 and the fixed sensor electrode 105. The capacitance adjuster 212 of the first embodiment changes the distance between the movable sensor electrode 104 and the fixed sensor electrode 105 to adjust the capacitance of the detection side electrode section 108.

Here, in the sensor section 100, the capacitance at the detection side electrode section 108 is assumed to be CX [pF]. Further, the capacitance in the reference side electrode section 109 is set as CR [pF]. The capacitance regulator 212 generates a Coulomb force that attracts each other between the movable sensor electrode 104 and the fixed sensor electrode 105 of the detection side electrode section 108. Therefore, the capacitance adjuster 212 can only adjust the distance between the electrodes in a direction that increases the capacitance. Therefore, in the sensor unit 100, the capacitance CX before adjustment and the capacitance CR are set to satisfy the relationship CX<CR, including manufacturing variations. Furthermore, in the charge amplifier 220, the feedback capacitance of the detection side capacitor 222A is Cfx [pF]. Further, the feedback capacitance of the reference side capacitor 222B is assumed to be Cfr[pF]. Furthermore, the amplitude of the signal is assumed to be E·sin(wt) [V]. At this time, the detection signal VX[V] from the detection side amplifier 221A is expressed by equation (1). Further, the reference signal VR[V] from the reference side amplifier 221B is expressed by equation (2). Here, sin(wt) has a value of −1 or more and 1 or less.

VX=E・sin(wt)×CX/Cfx…(1)
VR=E・sin(wt)×CR/Cfr…(2)

Furthermore, if the amplification factor of the differential amplifier 223 is Gain, the differential signal Vout[V] of the differential amplifier 223 is expressed by equation (3). sin(wt) is

Vout=(VX-VR)×Gain
=E×sin(wt)×(CX/Cfx−CR/Cfr)×Gain
...(3)

As described above, there is a possibility that the capacitances of the detection-side electrode section 108 and the reference-side electrode section 109 are different due to manufacturing variations. For example, assume that the capacitance CX in the detection side electrode section 108 is 40 [pF] at zero pressure when no pressure is applied, and the capacitance CR in the reference side electrode section 109 is 50 [pF]. shall be. Furthermore, when the maximum measurable pressure (hereinafter referred to as FS pressure) is applied, the capacitance CX increases to 41 [pF], and the capacitance CR at the reference side electrode section 109 remains at 50 [pF]. shall be. If the feedback capacitance Cfx of the detection side capacitor 222A is 103 [pF], the feedback capacitance Cfr of the reference side capacitor 222B is 100 [pF], and the amplitude E is 2 [V], the detection at zero pressure The difference between the signal VX and the reference signal VR is −0.223 [V] when sin(wt)=1, which is the maximum amplitude. Furthermore, the difference between the detection signal VX and the reference signal VR when the FS pressure is applied is -0.204 [V]. Hereinafter, the description will be made assuming that sin(wt)=1.

The gain of the differential amplifier 223 needs to be set so as not to exceed the voltage within the input voltage range of the AD converter 250. When the input voltage range of the AD converter 250 is ±2.5 [V], taking the voltage range into account and assuming that the gain is 11 times and setting the Gain to 11, the difference signal Vout at zero pressure is -2.456 [V]. Further, the difference signal Vout when the FS pressure is applied becomes -2.433 [V].

At this time, the difference between the differential signal Vout when the pressure is zero and the differential signal Vout when the FS pressure is applied is approximately Δ0.214 [V]. This voltage is about 4% of the input voltage range of the AD converter 250 of ±2.5 [V]. Pressure must be measured in a narrow voltage range, and the S/N ratio is low.

Therefore, the capacitive sensor detection section 10 of the diaphragm vacuum gauge 1 of the first embodiment includes a capacitance regulator 212 to adjust the capacitance in the detection side electrode section 108. The capacitance regulator 212 changes the distance between the movable sensor electrode 104 and the fixed sensor electrode 105 by applying a DC voltage between the electrodes of the detection side electrode section 108 and generating a Coulomb force. Adjust the capacitance of Here, the capacitance CX is adjusted to 51.5 [pF]. Assuming that other conditions remain the same, the difference between the detection signal VX and the reference signal VR at zero pressure is 0.0000 [V]. Furthermore, the difference between the detection signal VX and the reference signal VR when the FS pressure is applied is 0.0194 [V].

In this case, even if the gain of the differential amplifier 223 is increased to 125 times, the differential signal Vout at zero pressure will be 0.000 [V]. Further, the difference signal Vout when the FS pressure is applied is 2.427 [V]. Therefore, it does not exceed the input voltage range of AD converter 250 of ±2.5V. The difference between the differential signal Vout when the pressure is zero and the differential signal Vout when the FS pressure is applied is Δ2.427 [V]. This is a voltage that is 49% larger than the input voltage range of ±2.5 [V] of the AD converter 250, and is about 11% larger than the voltage when the signal amplitude is the same as described above. The S/N ratio is doubled.

Regarding the manufacturing method of the capacitive sensor detection section 10, when performing capacitance adjustment, the capacitance sensor detection section 10 is brought into a zero pressure state in which no pressure from the object to be measured is applied on the production line. . Then, a capacitance change step is performed in which the capacitance type sensor detection unit 10 is operated to change the DC voltage applied by the capacitance regulator 212. Then, the capacitance is adjusted by repeatedly changing the capacitance and performing a voltage determination step of determining a DC voltage that makes the difference signal Vout zero. Capacitance adjustment is performed for each capacitive sensor detection section 10 on the production line.

As described above, the capacitive sensor detection section 10 of the diaphragm vacuum gauge 1 of the first embodiment has the capacitance regulator 212, applies a DC voltage to change the distance between the electrodes, and The capacitance in section 108 can be adjusted. Therefore, variations in capacitance between the elements placed in the detection signal path and the reference signal path are suppressed, and the difference signal Vout at zero pressure and the difference signal when FS pressure is applied are It is possible to widen the difference with Vout. Therefore, the gain in the differential amplifier 223 can be increased, and the S/N ratio can be increased. At this time, by adjusting the capacitance in the detection side electrode section 108 of each capacitive sensor detecting section 10 on the production line, variations in capacitance that occur in each capacitive sensor detecting section 10 are performed. The capacitance can be adjusted according to the Here, there is a limit to the Coulomb force that can be generated between the electrodes. Additionally, voltage is required to generate Coulomb force. If too much voltage is applied, the electrodes may stick. Considering the above, adjusting the capacitance is particularly effective in the case of the capacitive sensor detecting section 10 that detects minute pressure changes.

Embodiment 2.
FIG. 4 is a diagram showing the configuration of main parts of the sensor section according to the second embodiment. In FIG. 4, the same reference numerals as in FIG. 2 have the same functions as those described in the first embodiment.

In the capacitive sensor detection section 10 of the first embodiment described above, the capacitance regulator 212 adjusts the DC voltage to the signal sent to the detection side electrode section 108 among the AC signals generated by the signal generator 211. The components were superimposed.

The capacitive sensor detection section 10 of the second embodiment further includes a DC voltage application electrode section 112 having a movable DC application electrode 110 and a fixed DC application electrode 111. Then, the capacitance regulator 212 applies a DC voltage to the DC voltage application electrode section 112 to generate a Coulomb force and bend the sensor diaphragm 102 . Thereby, the distance between the electrodes of the detection side electrode section 108 changes, and the capacitance can be adjusted.

Embodiment 3.
In the first embodiment described above, as for the capacitance adjustment method, the capacitance is adjusted so that the difference signal Vout becomes 0. By adjusting the capacitance based on the difference signal Vout, it is possible to make settings that take into account variations in capacitance between the detection side capacitor 222A and the reference side capacitor 222B of the charge amplifier 220, but the present invention is not limited to this. It's not a thing.

For example, the detection signal of the detection side electrode section 108 and the reference signal of the reference side electrode section 109 in the sensor section 100 may be compared, and the capacitance in the detection side electrode section 108 may be adjusted separately. .

Furthermore, in the first embodiment described above, the capacitance in the detection side electrode section 108 is adjusted by the capacitance regulator 212 so that the difference signal Vout becomes 0 in the capacitance type sensor detection section 10 at zero pressure. Although a process related to adjustment is performed, the present invention is not limited to this. For example, assume that the input voltage range of AD converter 250 is ±2.5 [V]. At this time, the reference potential when no measurement is being performed is set as -2 [V], and when the pressure is zero, for example, a DC signal V1 of -2 [V] is sent to the AD converter 250. The amplitude adjustment may be performed such that the difference signal Vout is outputted. Therefore, pressures ranging from zero pressure to FS pressure can be measured over a wide voltage range.

In the first to third embodiments described above, the capacitive sensor detection unit 10 that measures pressure as a physical quantity has been described, but the object to be measured and the physical quantity are limited to pressure, such as weight and acceleration. isn't it. Further, the capacitive sensor detection section 10 can be applied not only to the diaphragm vacuum gauge 1 but also to other measuring devices.

Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the contents of the above embodiments. The configuration, details, etc. of the present invention may be modified in various ways within the scope of the technical idea of the present invention by those skilled in the art.

Reference Signs List 1 diaphragm vacuum gauge, 10 capacitive sensor detection unit, 100 sensor unit, 101 base, 101a support unit, 102 sensor diaphragm, 102a movable area, 103 capacity chamber, 104 movable sensor electrode, 105 fixed sensor electrode, 106 movable Reference electrode, 107 Fixed reference electrode, 108 Detection side electrode section, 109 Reference side electrode section, 200 Circuit section, 210 Signal generator, 211 Signal generator, 212 Capacity regulator, 220 Charge amplifier, 221A Detection side amplifier, 221B Reference side amplifier, 222A detection side capacitor, 222B reference side capacitor, 223 differential amplifier, 230 detection circuit, 231A, 231B, 231C rectifier circuit, 240 smoother, 241A, 241B, 241C low-pass filter, 250 AD converter, 260 noise removal part, 261A, 261B, 261C band pass filter.

Claims (7)

A sensor element having a plurality of electrode parts for detection and reference, each of which is a set of a movable electrode that is displaced together with a sensor diaphragm whose position changes according to a physical quantity to be measured, and a fixed electrode provided opposite to the movable electrode. ,
a capacitance adjuster that adjusts the capacitance of at least one of the electrode section for detection and the electrode section for reference ;
The capacitance regulator adjusts the static voltage so that the difference between the AC signals passing through the detection electrode section and the reference electrode section when the physical quantity is zero becomes a set potential. Capacitive sensor that adjusts capacitance . The capacitance adjuster applies a DC voltage to the electrode section to generate a Coulomb force between the movable electrode and the fixed electrode, thereby bending the sensor diaphragm to adjust the distance between the electrodes. Capacitive sensor described in . 3. The capacitance type sensor according to claim 2 , wherein the capacitance adjuster applies the DC voltage in a superimposed manner to the signal sent to the electrode section. The sensor element further includes the electrode section for applying a DC voltage,
4. The capacitive sensor according to claim 3 , wherein the capacitance adjuster applies the DC voltage to the electrode section for applying the DC voltage. a charge amplifier that amplifies a signal that has passed through the electrode section for detection and the electrode section for reference;
a detection circuit having a rectifier circuit that detects the signal;
The capacitive sensor according to claim 1 , further comprising a smoother that smoothes the signal from the detection circuit. A diaphragm vacuum gauge comprising the capacitance type sensor according to any one of claims 1 to 5 . A sensor element has a plurality of electrode parts for detection and reference, which are made up of a movable electrode that is displaced together with a sensor diaphragm whose position changes according to the physical quantity to be measured, and a fixed electrode provided opposite to the movable electrode. A method for manufacturing a capacitive sensor comprising:
When the physical quantity is zero, a DC voltage is applied to the electrode portion to generate a Coulomb force between the movable electrode and the fixed electrode, and the distance between the electrodes is adjusted by bending the sensor diaphragm. , a capacitance changing step of changing the capacitance of the electrode section for detection;
a voltage determining step of repeating the capacitance changing step and determining the DC voltage such that the difference between the AC signals passing through the electrode section for detection and the electrode section for reference becomes a set potential; A method for manufacturing a capacitive sensor having the following.

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