JP6787636B2 - Vacuum measurement sensor - Google Patents

Description

The present invention relates to a vacuum measurement sensor.

A Pirani type pressure gauge (for example, Non-Patent Document 1) is known as a vacuum measurement sensor for measuring the pressure in the vacuum device. Further, Patent Document 1 discloses a pyrani type pressure gauge including a thin film temperature sensor provided on a thermally separated thin film (for example, a cantilever) and a thin film heater for heating the thin film temperature sensor. There is. The pyrani type pressure gauge measures the vacuum pressure by detecting the gas heat transfer near the thin film temperature sensor, which changes in response to the change in gas pressure (vacuum pressure, etc.) near the thin film temperature sensor, as a temperature change. measure.

In Patent Document 2, diaphragm electrodes made of a pair of conductive thin films facing each other with an internal space separated from each other are arranged with their peripheral edges fixed to a substrate, and a plurality of sets of diaphragm electrodes having different areas of the conductive thin films are provided. Disclosed is a diaphragm type vacuum gauge in which the spaces between the diaphragm electrodes are communicated with each other and sealed in a high vacuum, and then electrically insulated from the substrate.

JP-A-2007-51963 Japanese Unexamined Patent Publication No. 6-109568

F. T. Zhang et al., “A micro-pirani vacuum gauge based on micro-hotplate technology,” Sens. Actuators A, Phys., Vol.126, no.2, p.300-305, Feb. 2006.

However, the Pirani type vacuum gauge has a problem that the sensitivity changes because the thermal conductivity differs depending on the type of gas to be measured, and the pressure value differs depending on the type of gas.

Although the diaphragm type pressure gauge does not depend on the type of gas, it cannot measure a wide range of vacuum pressure with one diaphragm electrode because it utilizes the displacement of the diaphragm electrode. Therefore, the diaphragm type pressure gauge has a problem that it is difficult to miniaturize it because it is necessary to provide a plurality of sets of diaphragm electrodes in order to measure the vacuum pressure in a wide measurement range.

An object of the present invention is to provide a vacuum measurement sensor capable of measuring a vacuum pressure in a desired range regardless of the type of gas.

The vacuum measurement sensor according to the present invention includes a reference pressure chamber having an opening on one surface and a detection unit provided so as to close the opening, and the reference pressure chamber is held at a saturated vapor pressure, and the detection is performed. The unit is characterized by having a pressure detecting cantilever that elastically deforms due to a pressure difference between the inside and outside of the reference pressure chamber.

According to the present invention, since the vacuum pressure is measured based on the difference between the saturated vapor pressure in the reference pressure chamber and the pressure in the vacuum chamber, the vacuum pressure can be measured regardless of the type of gas in the vacuum chamber. Can be done. Further, the vacuum pressure in a desired range can be measured by changing the saturated vapor pressure in the reference pressure chamber depending on the medium.

It is a perspective view which shows typically the structure of the vacuum measurement sensor which concerns on this embodiment. It is a vertical cross-sectional view which shows typically the structure of the vacuum measurement sensor which concerns on this embodiment, (A) is a figure which shows the state before measurement, (B) is a figure which shows the state at the time of measurement. It is a circuit diagram which shows the structure of the detection circuit applied to the vacuum measurement sensor which concerns on this embodiment. It is a schematic diagram which shows the structure of an experimental apparatus. It is a graph which shows the resistance change characteristic with respect to pressure of the vacuum measurement sensor used in an experiment. It is a graph which shows the result of having measured the pressure in the reference pressure chamber of the vacuum measurement sensor used in an experiment. It is a graph which shows the result of having measured the pressure of the vacuum chamber in an experimental apparatus, (A) is a Pirani type pressure gauge, (B) is the measurement result in a vacuum measurement sensor. It is a graph which shows the relationship between the Pirani type vacuum gauge and the vacuum measurement sensor in the result of FIG. It is a list which shows the measurable pressure of a vacuum gauge. It is a perspective view which shows typically the structure of the modification of the vacuum measurement sensor which concerns on this embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(overall structure)
The vacuum measurement sensor 10 shown in FIG. 1 includes a reference pressure chamber 12 and a detection unit 14. The reference pressure chamber 12 is a closed container having an opening on one side. The detection unit 14 is provided so as to close the opening of the reference pressure chamber 12.

The detection unit 14 has a frame 18. Although not shown, the frame 18 includes a substrate, an insulating layer, a silicon (Si) layer, a piezoresistive layer, and an electrode layer. The frame 18 is detachably fixed to the open end of the reference pressure chamber 12 while maintaining airtightness. The detection unit 14 has a pressure detection cantilever 16 at substantially the center of the frame 18. The pressure detecting cantilever 16 is composed of a silicon layer and a piezoresistive layer.

The pressure detecting cantilever 16 has a so-called cantilever structure formed in a state where a gap 20 is provided between the cantilever 16 and the frame 18 except for one end. One end of the pressure detecting cantilever 16 is integrated with the frame 18. The pressure detecting cantilever 16 has a flat plate-shaped pressure receiving portion 17 and a pair of hinge portions 19 integrally formed on one side surface of the pressure receiving portion 17.

The gap 20 between the frame 18 and the pressure detecting cantilever 16 is preferably less than or equal to the mean free path of the gas at the measured pressure. The mean free path depends on the pressure, and the higher the pressure, the smaller the mean free path. Therefore, it is preferable that the mean free path or less at the maximum pressure in the target measurement pressure range. The frame 18 has electrodes 24 and 25 integrated with a pair of hinge portions 19 of the pressure detecting cantilever 16.

In order to manufacture the detection unit 14, an insulating layer made of SiO ₂ is first formed on a substrate made of Si, and then a silicon layer is formed on the insulating layer, whereby a substrate, an insulating layer, and a silicon layer are laminated. Form the SOI of the structure. The thickness of each layer of SOI (Si / SiO ₂ / Si) can be 0.3 μm / 1 μm / 250 μm in order from the top. Next, impurities are doped onto the silicon layer to form a piezoresistive layer in which a part of the silicon layer is an N-type or P-type semiconductor.

Next, the electrode is patterned on the piezoresistive layer on the SOI, and then the silicon layer and the piezoresistive layer are partially etched to form the gap 20. Finally, the pressure detection cantilever 16 is formed by etching the substrate and the insulating layer in a rectangular shape (22 in the figure) from the bottom surface side.

As shown in FIG. 2A, the reference pressure chamber 12 is a closed container except for the gap 20, and contains the medium 28. The medium 28 is a liquid or solid with a known saturated vapor pressure. As the liquid, water, ethanol, acetone, heptanol, silicone oil and the like can be used. As the solid, ice, iodine or the like can be used. The internal space 26 of the reference pressure chamber 12 is filled with a medium and the vapor of the medium. The pressure in the reference pressure chamber 12 is the saturated vapor pressure of the medium 28.

The vacuum measurement sensor 10 is connected to the vacuum chamber 30 on the opposite side of the reference pressure chamber 12 with the detection unit 14 interposed therebetween. The pressure detection cantilever 16 is elastically deformed with one end as the center of rotation due to the pressure difference between the vacuum chamber 30 and the reference pressure chamber 12. When the pressure in the vacuum chamber 30 is low with respect to the pressure in the reference pressure chamber 12, the pressure detection cantilever 16 elastically deforms so as to fall toward the vacuum chamber 30 (FIG. 2B). The pressure detection cantilever 16 is elastically deformed to change the resistance value of the piezoresistive layer. The resistance change characteristic of the pressure detecting cantilever 16 with respect to the pressure difference has been measured in advance and is known.

As shown in FIG. 3, the vacuum measurement sensor 10 is electrically connected to the detection circuit. The detection circuit 31 has a bridge circuit 33 and a lock-in amplifier 38. In the bridge circuit 33, the branch side in which the vacuum measurement sensor 10 and the temperature compensation cantilever 32 are connected in series and the branch side in which the variable resistor 34 and the fixed resistor 36 are connected in series are connected in parallel to the lock-in amplifier 38. Has been done.

Although not shown, the temperature compensation cantilever 32 has the same resistance change characteristics with respect to temperature as the pressure detection cantilever 16, and includes a substrate, an insulating layer, a silicon (Si) layer, a piezoresistive layer, and an electrode layer. Consists of. Since the temperature compensation cantilever 32 is integrated with the substrate, it does not elastically deform due to the pressure difference between the inside and outside of the reference pressure chamber 12.

The lock-in amplifier 38 is connected to a connection point 35 of the pressure detection cantilever 16 and the temperature compensation cantilever 32, and a connection point 37 of the variable resistor 34 and the fixed resistor 36. A predetermined AC voltage is applied to the bridge circuit 33 through the lock-in amplifier 38. The variable resistor 34 is adjusted so that the voltage values of the connection point 35 and the connection point 37 are equal to each other in a state where the pressure detection cantilever 16 is not elastically deformed.

When the pressure detection cantilever 16 is elastically deformed, the resistance value of the piezoresistive layer changes, so that the voltage value at the connection point 35 fluctuates. The lock-in amplifier 38 receives the fluctuation of the voltage value of the connection point 35 as the potential difference between the connection point 35 and the connection point 37. The lock-in amplifier 38 removes noise from the potential difference by a low-pass filter and outputs it as a vacuum measurement signal. The potential difference is a value corresponding to the difference between the resistance value of the pressure detection cantilever 16 and the resistance value of the temperature compensation cantilever 32.

(Operation and effect)
Next, the operation and effect of the vacuum measurement sensor 10 will be described. First, the gas in the reference pressure chamber 12 is sufficiently exhausted. By exhausting, the inside of the reference pressure chamber 12 is filled with the steam of the medium 28. Next, the temperature in the reference pressure chamber 12 is measured, and the saturated vapor pressure of the medium 28 is calculated. The means for measuring the temperature in the reference pressure chamber 12 is not particularly limited. For example, the temperature inside the reference pressure chamber 12 may be measured based on the temperature characteristics of the temperature compensating cantilever 32 measured in advance.

Subsequently, the inside of the vacuum chamber 30 is evacuated using a vacuum pump. In the vacuum chamber 30, when the pressure drops with respect to the pressure in the reference pressure chamber 12 and a high vacuum is obtained, the pressure detection cantilever 16 is elastically deformed so as to fall toward the vacuum chamber 30 side according to the pressure difference. The fluctuation of the resistance change characteristic caused by the elastic deformation of the pressure detection cantilever 16 is output from the lock-in amplifier 38 as a vacuum measurement signal. Based on the vacuum measurement signal, the pressure difference between the vacuum chamber 30 and the reference pressure chamber 12 is calculated. The vacuum pressure in the vacuum chamber 30 is obtained from the difference between the saturated vapor pressure in the reference pressure chamber and the calculated pressure difference. As described above, the vacuum measurement sensor 10 can measure the vacuum pressure in the vacuum chamber 30.

Since the vacuum measurement sensor 10 of the present embodiment measures the vacuum pressure based on the difference between the saturated vapor pressure in the reference pressure chamber 12 and the pressure in the vacuum chamber 30, it depends on the type of gas in the vacuum chamber 30. It is possible to measure a wide range of vacuum pressure without using it.

The vacuum measurement sensor 10 can select the measurement range of the vacuum pressure by changing the saturated vapor pressure according to the medium 28 housed in the reference pressure chamber.

The vacuum measurement sensor 10 can widen the measurement range of the vacuum pressure by reducing noise and improving the resolution by using the bridge circuit 33 and the lock-in amplifier 38.

(Evaluation)
The experimental device shown in FIG. 4 was actually manufactured, and the vacuum measurement sensor 10 was evaluated. The vacuum measurement sensor 10 is connected to the vacuum chamber 30 on the opposite side of the reference pressure chamber 12 with the detection unit 14 interposed therebetween. The reference pressure chamber 12 is connected to the exhaust pipe 46 through the pipe 42 and the bypass valve 44. The exhaust pipe 46 connects the vacuum chamber 30 to the vacuum pump. Pirani type vacuum gauges 48 and 50 are provided in the pipe 42 and the exhaust pipe 46, respectively. Water is stored in the reference pressure chamber 12 as a medium 28. The volume of the reference pressure chamber 12 was 18 cm ³ , and the volume of water contained was 0.5 ml.

The pressure detection cantilever 16 has a length × width of 75 μm × 50 μm and a thickness of 300 nm. The gap 20 was set to 2 μm. FIG. 5 shows the resistance change characteristic of the pressure detection cantilever 16 with respect to the pressure difference. In this figure, the horizontal axis shows the pressure difference (Pa), and the vertical axis shows the resistance value change rate (× 10 ^-3 ). It was confirmed that the rate of change in resistance increased as the pressure difference increased. Therefore, the pressure difference between the vacuum chamber 30 and the reference pressure chamber 12 can be measured based on the resistance value change rate of the pressure detection cantilever 16.

In the experimental apparatus of FIG. 4, the reference pressure chamber is from the time when the vacuum pump is started to open the bypass valve 44, the inside of the vacuum chamber 30 and the reference pressure chamber 12 is exhausted, and after 1 minute, until the bypass valve 44 is closed. The pressure change in 12 was measured. The result is shown in FIG. In this figure, the horizontal axis represents time (S) and the vertical axis represents pressure (Pa) in the reference pressure chamber 12. The pressure in the reference pressure chamber 12 was once reduced to about 900 Pa, and then closed at the bypass valve 44 to stabilize at 1280 Pa after a certain period of time. The pressure of 1280 Pa is the saturated vapor pressure at the environmental temperature (11 ° C.) at which the pressure change is measured. From this result, it was confirmed that the vacuum measurement sensor 10 can stably maintain the pressure in the reference pressure chamber 12 at the saturated vapor pressure.

From a state where the pressure in the reference pressure chamber 12 is saturated vapor pressure, in this case 1280 Pa, the inside of the vacuum chamber 30 is exhausted by a vacuum pump, and the pyrani type vacuum gauge 50 and the vacuum measurement sensor 10 are used in the vacuum chamber 30. The pressure change was measured. The result is shown in FIG. In this figure, the horizontal axis represents time (S), the vertical axis of FIG. 7A is pressure (Pa), and the vertical axis of FIG. 7B is the resistance value change rate (× 10 ^-3 ). From this figure, it can be said that the resistance value change rate of the vacuum measurement sensor 10 is decreasing like the pressure measured by the Pirani type pressure gauge 50, and has a correlation with the pressure measured by the Pirani type pressure gauge 50.

FIG. 8 shows the relationship between the pressure difference between the vacuum chamber 30 and the reference pressure chamber 12 and the resistance value change rate measured by the vacuum measurement sensor 10. In this figure, the horizontal axis shows the pressure difference (Pa), and the vertical axis shows the resistance value change rate (× 10 ^-3 ). The pressure difference between the vacuum chamber 30 and the reference pressure chamber 12 was measured by Pirani type vacuum gauges 48 and 50. From this figure, it was confirmed that the pressure difference between the vacuum chamber 30 and the reference pressure chamber 12 and the resistance value change rate measured by the vacuum measurement sensor 10 are on the same linearity. From this result, it can be said that the vacuum measurement sensor 10 can measure the vacuum pressure in the range of 200 to 1200 Pa.

The vacuum measurement sensor 10 can measure the vacuum pressure in the measurement range of 1 × 10 ^-3 Pa to × 10 ³ Pa by appropriately selecting the medium 28. Therefore, as shown in FIG. 9, the vacuum measurement sensor 10 can measure a vacuum pressure in a wider range than the conventional pressure gauge by itself.

(Modification example)
The present invention is not limited to the above embodiment, and can be appropriately modified within the scope of the gist of the present invention.

The vacuum measurement sensor 10 may measure the temperature in the reference pressure chamber 12 by a temperature sensor provided in the reference pressure chamber 12 in advance, for example, a thermocouple.

As shown in FIG. 10, the vacuum measurement sensor 56 may include a temperature compensation cantilever 32 in the detection unit 57. In the case of this figure, the temperature compensating cantilever 32 is provided at a position symmetrical with the pressure detecting cantilever 16. The temperature compensation cantilever 32 has the same resistance change characteristics with respect to temperature as the pressure detection cantilever 16, and includes a substrate, an insulating layer, a silicon (Si) layer, a piezoresistive layer, and an electrode layer. Since the temperature compensation cantilever 32 is integrated with the substrate, it does not elastically deform due to the pressure difference between the inside and outside of the reference pressure chamber 12. The temperature compensation cantilever 32 is electrically connected to the bridge circuit 33 through the electrodes 58 and 59. The temperature compensation cantilever 32 can perform temperature compensation of the pressure detection cantilever 16 and can measure the temperature in the reference pressure chamber 12.

10 Vacuum measurement sensor 12 Reference pressure chamber 14 Detection unit 16 Pressure detection cantilever 18 Frame 20 Gap 24, 25 Electrodes 28 Medium 30 Vacuum chamber 31 Detection circuit 32 Temperature compensation cantilever 33 Bridge circuit 34 Variable resistance 35 Connection point 36 Fixed resistance 37 Connection point 38 Lock-in amplifier 58, 59 electrodes

Claims (5)

A reference pressure chamber with an opening on one side,
It is provided with a detection unit provided so as to close the opening.
The reference pressure chamber is held at a saturated vapor pressure and is maintained.
The detection unit is a vacuum measurement sensor characterized by having a pressure detection cantilever that elastically deforms due to a pressure difference between the inside and outside of the reference pressure chamber. The vacuum measurement sensor according to claim 1, wherein a medium having a known saturated vapor pressure is housed in the reference pressure chamber. The vacuum measurement sensor according to claim 1 or 2, wherein the detection unit is connected to a vacuum chamber on the side opposite to the reference pressure chamber. Claims 1 to 1, wherein the gap between the pressure detecting cantilever and the frame holding the pressure detecting cantilever in the reference pressure chamber is equal to or less than the mean free path at the maximum pressure in the measurement pressure range. The vacuum measurement sensor according to any one of 3. The vacuum measurement sensor according to any one of claims 1 to 4, wherein the detection unit further includes a temperature compensation cantilever having a resistance change characteristic with respect to a temperature similar to that of the pressure detection cantilever.

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