JP6144540B2 - Pressure sensor - Google Patents

Description

  The present invention relates to a pressure sensor that detects minute pressure fluctuations based on a pressure difference.

  Conventionally, as a pressure sensor for detecting pressure fluctuation (also referred to as “differential pressure sensor”), for example, a substrate having a through hole or a recess, a storage container having a vent hole, and a storage container disposed in the storage container, There is known a pressure sensor including a piezoelectric element that is cantilevered by a substrate so as to vibrate in a recess (see, for example, Patent Document 1).

  According to the pressure sensor having the above configuration, according to the magnitude of the differential pressure between the pressure fluctuation transmitted through the ventilation hole into the storage container and the pressure inside the through hole or the recess following the transmitted pressure fluctuation. The piezoelectric element is deformed. As a result, the pressure sensor can detect a pressure fluctuation transmitted to the storage container based on a voltage change generated in the piezoelectric element.

JP-A-4-208827

  By the way, in this type of pressure sensor (including the pressure sensor disclosed in Patent Document 1), the specification is determined according to the application, and the sensor is designed to satisfy the specification. At this time, factors that determine the specifications of the pressure sensor include, for example, the shape of the piezoelectric element, the volume of the through hole or the recess, the shape of the gap between the piezoelectric element and the through hole or the recess, and the inside and outside of the through hole or the recess. The flow rate that goes in and out can be raised.

  Further, as one element that determines the performance of the pressure sensor, for example, there is a frequency band in which pressure fluctuation can be detected. The upper limit frequency of pressure fluctuation that can be detected by the pressure sensor is considered to be in the vicinity of the resonance frequency of the piezoelectric element. On the other hand, as for the lower limit frequency, it has been found that the lower limit frequency tends to be lowered as the volume of the through hole or recess is increased and the flow rate between the inside and outside of the through hole or recess is reduced. When the pressure sensor has a large volume of the through hole or the recess and the gap between the inside of the through hole or the recess and the outside is narrow, the pressure fluctuation in the through hole or the recess is in contrast to the pressure fluctuation outside the through hole or the recess. This is because the delay time becomes longer.

That is, even if the pressure outside the through hole or the recess fluctuates very slowly, the pressure inside the through hole or the recess fluctuates more than this pressure fluctuation. For this reason, the differential pressure | voltage between an external pressure and the pressure inside a through-hole or a recessed part is obtained, and the output of a pressure sensor can be obtained.
In order to realize such a pressure sensor that can detect a very slow pressure fluctuation and has a small configuration, it is necessary to configure the gap between the through hole or the recess and the outside very narrow.

  However, in order to form a very narrow gap between the inside and outside of the through hole or recess, the piezoelectric element and the substrate having the through hole or recess are formed with very high dimensional accuracy, and then with very high positional accuracy. It is necessary to bond or bond each other. For example, if the piezoelectric thin film or the like is used to form a single body with a substrate having a through hole or a recess, internal stress remains when the cantilever structure is formed with the piezoelectric thin film, resulting in bending in the thickness direction. There are many. For this reason, even if the gap between the inside or outside of the through hole or the recess in the surface direction of the cantilever can be made very small, the gap in the thickness direction becomes large and the lower limit frequency cannot be lowered.

  Even if there is no deformation of the piezoelectric thin film, the flow rate of air from the outside differs depending on the presence or absence of the through holes or the side walls of the recesses when the external pressure increases and when it decreases. That is, like the pressure sensor 100 shown in FIG. 17, the piezoelectric element 110 is deformed toward the inside of the through hole or the recess 120 when the external pressure is increased, and is deformed to the opposite side when the pressure is decreased. If the pressure change width is the same, the tip of the piezoelectric element 110 is displaced up and down by the same amount. However, the flow rate between the through-holes or the recesses 120 and the outside air is larger when the pressure is lower than when the pressure is increased, depending on the presence or absence of the side walls of the through-holes or the recesses 120, for example, as shown in FIG. For this reason, as shown in FIGS. 18A and 18B, the larger the flow rate, the shorter the time during which the differential pressure between the outside air and the inside of the through hole or the recess 120 is maintained. And then. Since the output of the pressure sensor 110 is proportional to the differential pressure between the outside air and the inside of the through hole or the recess, even if the amount of change in the outside air pressure is the same, the output of the pressure sensor decreases as the flow rate increases. For this reason, the conventional pressure sensor has a problem that the sensitivity of the sensor differs depending on whether the external pressure increases or decreases.

  Therefore, the present invention has an object to provide a small pressure sensor that can lower the lower limit frequency of the detectable pressure fluctuation and can equalize the detection sensitivity of the sensor when the external pressure fluctuation rises and falls. And

In order to solve the above-mentioned problem, a first feature of the pressure sensor of the present invention is a pressure sensor for detecting pressure fluctuations, which is arranged to seal the cavity with a sensor body having a cavity, and a tip portion. A cantilever that is supported in a cantilever shape so as to form a gap for allowing air to flow in and out of the cavity between the sensor body and the cantilever to bend and deform according to a pressure difference between the inside and outside of the cavity, and the cantilever The gist of the invention is to include a displacement measuring unit that measures a displacement according to the bending deformation of the gas, and a flow rate control unit for suppressing the amount of air flowing through the gap from being changed by the deformation of the cantilever.
According to this feature, even if the cantilever is deformed, the flow rate of the pressure transmission medium inside and outside the cavity does not increase abruptly, so the differential pressure inside and outside the cavity can be maintained for a long time, and high sensitivity can be achieved even with very slow pressure fluctuations. It becomes possible to detect. Furthermore, since the flow rate of the pressure transmission medium flowing inside and outside the cavity can be made constant even when the pressure fluctuation rises or falls, the sensitivity of the pressure sensor when the pressure rises and falls can be made constant. Furthermore, even if a large pressure fluctuation is applied and the displacement of the cantilever increases, the increase in the flow rate of the pressure transmission medium can be suppressed, so that the linearity of the sensor output signal can be maintained over a wide range of pressure fluctuations.

Furthermore, a second feature of the pressure sensor according to the present invention is that the flow rate control unit is installed on the outer side of the cavity and in the vicinity of the outer end of the gap, and has a side wall extending along the thickness direction of the cantilever. The main point is that it consists of parts.
According to this feature, the flow rate control unit can be formed with a very simple structure, so that the pressure sensor can be manufactured at low cost. Even if the cantilever is deformed up and down at the time of manufacture, the flow rate of the pressure transmission medium does not increase greatly regardless of the amount of deformation, so that the sensitivity of the pressure sensor when the atmospheric pressure increases or decreases can be made equal.

Furthermore, a third feature of the pressure sensor according to the present invention is that the side surface of the wall section is vertically cut along a trajectory due to deformation of the tip of the cantilever when the pressure inside the cavity is larger than the pressure outside. The gist of the invention is that it is formed in an arc shape in a plan view.
According to such a feature, the flow rate of the pressure transmission medium can be kept substantially constant regardless of the deformation amount of the cantilever, so that the sensitivity of the pressure sensor when the atmospheric pressure increases or decreases can be made equal.

Furthermore, the fourth feature of the pressure sensor according to the present invention is that the cantilever is covered with a cover part having a vent hole in a part thereof.
According to such a feature, it is possible to prevent the cantilever from being damaged by contact from the outside.

Furthermore, the fifth feature of the pressure sensor of the present invention is that a waterproof and moisture permeable film is provided so as to cover the vent hole.
According to this feature, water droplets do not enter the pressure sensor, and damage due to adhesion of water droplets, damage due to electrical short-circuiting, and the like can be prevented. Further, even in an environment where water droplets are applied to the pressure sensor, only the pressure transmission medium can flow inside and outside the pressure sensor, so that an accurate pressure change can be detected.

Furthermore, the sixth feature of the pressure sensor of the present invention is summarized in that the vent hole is provided at a position shifted from directly above the cantilever.
According to such a feature, it is possible to prevent dust floating from the outside from entering the inside of the pressure sensor, preventing damage to the atmospheric pressure measurement cantilever and lowering of sensitivity due to adhesion of dust or the like.

Further, according to a seventh feature of the pressure sensor of the present invention, the wall portion has a second side surface extending to the inner side of the cavity, and the second side surface has an internal pressure outside the cavity. The gist of the present invention is that it is formed in an arc shape in a longitudinal sectional view along a trajectory due to deformation of the tip of the cantilever when the pressure is larger than the pressure at the top.
According to such a feature, since the flow rate of the pressure transmission medium when the pressure outside the cavity is larger than the pressure inside the cavity is constant regardless of the amount of deformation of the cantilever, the sensitivity of the pressure sensor can be further increased. .

  The present invention can provide a small pressure sensor that can reduce the lower limit frequency of the detectable pressure fluctuation, and can equalize the detection sensitivity of the sensor when the external pressure fluctuation increases and decreases.

It is a top view of the pressure sensor concerning a first embodiment of the present invention. It is sectional drawing of the pressure sensor which concerns on 1st embodiment of this invention. It is explanatory drawing which shows the output and pressure change of the pressure sensor which concerns on 1st embodiment of this invention. It is explanatory drawing which shows operation | movement of the pressure sensor which concerns on 1st embodiment of this invention. It is explanatory drawing which shows the relationship between the differential pressure added to the pressure sensor which concerns on 1st embodiment of this invention, and the flow volume inside and outside a cavity. It is explanatory drawing which shows the flow of the pressure transmission medium which goes in and out of the cavity of the pressure sensor which concerns on 1st embodiment of this invention. It is explanatory drawing which shows the manufacturing process of the cantilever for atmospheric pressure measurement of the pressure sensor which concerns on 1st embodiment of this invention. It is sectional drawing of the pressure sensor which concerns on 2nd embodiment of this invention. It is sectional drawing of the pressure sensor which concerns on the modification 1 of this invention. It is sectional drawing of the pressure sensor which concerns on 3rd embodiment of this invention. It is sectional drawing of the pressure sensor which concerns on the modification 2 of this invention. It is explanatory drawing which shows the structure of the pressure measurement cantilever and the reference cantilever of the pressure sensor which concerns on the modification 3 of this invention, (a) is a top view, (b) is sectional drawing along an AA sectional line. Are shown respectively. It is a circuit diagram which shows the structure of the displacement measurement part of the pressure sensor shown in FIG. It is sectional drawing of the pressure sensor which concerns on the modification 4 of this invention. It is sectional drawing of another pressure sensor which concerns on the modification 4 of this invention. It is sectional drawing of the pressure sensor which concerns on the modification 5 of this invention. It is explanatory drawing which shows the mode of the airflow in the conventional pressure sensor. It is explanatory drawing which shows the relationship between the pressure change added to the conventional pressure sensor, and the output of the pressure sensor at that time.

Hereinafter, embodiments of a pressure sensor according to the present invention will be described with reference to the drawings.
(First embodiment)
(overall structure)
FIG. 1 is a plan view showing a configuration of a pressure sensor 1 according to the first embodiment of the present invention. FIG. 2 is a cross-sectional view of the pressure sensor 1 taken along line AA shown in FIG.

  As shown in FIGS. 1 and 2, the pressure sensor 1 according to the first embodiment is a sensor that detects pressure fluctuations in a predetermined frequency band (for example, 0.05 Hz to 10 kHz), and includes a sensor body 3, A barometric pressure measuring cantilever 4 disposed on the upper part of the sensor body 3, a lid portion 12 disposed so that one end faces the atmospheric pressure measuring cantilever 4, and a displacement for measuring the atmospheric pressure measuring cantilever 4. The displacement measuring unit 5 and the flow rate control unit 11 disposed on the top of the lid 12 are included.

  The sensor main body 3 is a box-shaped member in which a cavity 10 that is a gap portion is formed. The sensor body 3 includes, for example, a first portion 31 made of a resin material constituting the cavity 10, a silicon support layer 2 a to be described later, and an oxide layer 2 b such as a silicon oxide film. And a second portion 32.

The atmospheric pressure measurement cantilever 4 is formed, for example, by processing the SOI substrate 2 in which the silicon support layer 2a, the oxide layer 2b such as a silicon oxide film, and the silicon active layer 2c are thermally bonded. Specifically, the atmospheric pressure measurement cantilever 4 is formed of a silicon active layer 2c constituting the SOI substrate 2 and is formed in a U shape in plan view from the flat silicon active layer 2c. The gap 13 is cut out.
As a result, the atmospheric pressure measurement cantilever 4 has a cantilever structure in which the base end portion 4a is a fixed end and the distal end portion 4b, which is the end facing the lid portion 12, is a free end.

The atmospheric pressure measurement cantilever 4 is disposed so as to surround the upper surface of the cavity 10 formed in the sensor body 3. That is, the atmospheric pressure measuring cantilever 4 substantially closes the opening of the cavity 10.
The atmospheric pressure measuring cantilever 4 is cantilevered by being fixed to the sensor body 3 integrally with the second portion 32 via the base end portion 4a. Thereby, the cantilever 4 for atmospheric pressure measurement can be bent and deformed according to the pressure difference between the inside and the outside of the cavity 10 with the base end portion 4a as the center.

A through-hole 15 having a U-shape in plan view is formed in the atmospheric pressure measurement cantilever base end portion 4a so that the atmospheric pressure measurement cantilever 4 is easily bent and deformed. However, the shape of the through hole 15 is not limited to the U-shape as long as it can easily be bent and deformed by the atmospheric pressure measuring cantilever 4.
The lid 12 is positioned above the cavity 10 and is disposed around the atmospheric pressure measurement cantilever 4 via the gap 13. The lid 12 is composed of a silicon active layer 2c.

  The flow control unit 11 (wall portion) is disposed on the upper surface of the lid 12 and in the vicinity of the outer periphery of the gap 13. The flow rate control unit 11 has a U-shaped shape in plan view, and in particular, the side wall on the inner side of the U-shaped side extends substantially perpendicular to the surface of the lid 12 (in the thickness direction of the atmospheric pressure measuring cantilever 4). Shape). That is, the U-side sidewall flow rate control unit 11 is made of a MEMS resist (for example, a dry film or SU-8) that can realize an insulating high aspect.

The displacement measuring unit 5 includes a piezoresistor 20 whose electric resistance value changes in accordance with a deflection amount (displacement amount) of the atmospheric pressure measuring cantilever 4 and a detection circuit 22 that extracts the electric resistance value change. As shown in FIG. 1, the piezoresistors 20 are arranged in pairs on both sides of the through hole 15 in the short direction of the atmospheric pressure measurement cantilever 4.
The pair of piezoresistors 20 are electrically connected to each other via a wiring portion 21 made of a conductive material.

  The overall shape including the wiring portion 21 and the piezoresistor 20 can be a U shape in plan view as shown in FIG. 1, for example. The piezoresistor 20 is electrically connected to a detection circuit 22 that measures the displacement of the atmospheric pressure measuring cantilever 4 based on a change in the electric resistance value of the piezoresistor 20.

In the displacement measuring unit 5 configured as described above, a current generated when a predetermined voltage is applied to the piezoresistor 20 through the detection circuit 22 wraps around the through hole 15 so that the wiring unit 21 is connected to the piezoresistor 20. To the other piezoresistor 20 via.
For this reason, the detection circuit 22 can take out the change in the electric resistance value of the piezoresistor 20 that changes in accordance with the displacement (flexure deformation) of the atmospheric pressure measurement cantilever 4 as an electrical output signal.

Therefore, the displacement measuring unit 5 can measure the displacement of the atmospheric pressure measuring cantilever 4 based on the output signal (sensor output) of the detection circuit 22. That is, the displacement measuring unit 5 can extract the change in atmospheric pressure outside the cavity 10 as an output signal because the atmospheric pressure measuring cantilever 4 is deformed based on the differential pressure between the inside and outside of the cavity 10.
The piezoresistor 20 is formed by doping a silicon active layer 2c with a dopant (impurity) such as phosphorus by various methods such as an ion implantation method and a diffusion method.

In addition, the pair of piezoresistors 20 is configured to be electrically connected only by the wiring portion 21. For this reason, although not shown, the silicon active layer 2 c located around the atmospheric pressure measuring cantilever 4 is etched so that both the piezoresistors 20 are not conductive except at the wiring portion 21.
Note that a piezoelectric thin film may be used instead of the piezoresistor 20. In this case, an electromotive force is generated according to the stress applied to the base end portion 4b of the barometric pressure measurement cantilever 4, and the displacement of the atmospheric pressure measurement cantilever 4 can be detected by detecting the electromotive force.

(Pressure sensor operation)
Next, the operation of the pressure sensor 1 when the pressure sensor 1 according to the present embodiment detects a minute pressure fluctuation will be described with reference to FIGS. 3 and 4. Here, FIG. 3 is a diagram schematically showing an example of the output of the pressure sensor 1 shown in FIG. 1, in which (A) shows the change over time of the pressure inside and outside the cavity, and (B) shows the change over time of the output of the pressure sensor. Each represents a change. 4 is a cross-sectional view schematically showing an example of the operation of the pressure sensor shown in FIG. 1. (A) is a cross-sectional view of the pressure sensor in the initial state, and (B) is a pressure outside the cavity. (C) is a sectional view of the pressure sensor when the pressure inside and outside the cavity returns to the same pressure. In FIG. 4, illustration of the detection circuit 22 constituting the pressure sensor 1 is omitted.

First, as in period A shown in FIG. 3A, the difference between the pressure outside the cavity 10 (hereinafter “external pressure Pout”) and the pressure inside the cavity 10 (hereinafter “internal pressure Pin”) is zero. In some cases, as shown in FIG. 4A, the pressure measuring cantilever 4 is not bent and deformed.
Here, as in the period B after time t1 shown in FIG. 3A, for example, when the external pressure Pout rises stepwise, a differential pressure is generated between the outside and the inside of the cavity 10, so that FIG. ), The barometric pressure measuring cantilever 4 is bent and deformed toward the inside of the cavity 10.

Since the piezoresistor 20 is distorted in accordance with the bending deformation of the atmospheric pressure measuring cantilever 4 and the electric resistance value changes, the output signal of the pressure sensor 1 increases as shown in FIG.
Further, after the increase of the external pressure Pout, the pressure transmission medium gradually flows from the outside to the inside of the cavity 10 through the gap 13. For this reason, as shown in FIG. 3A, the internal pressure Pin rises with time, with a response that is slower than the fluctuation of the external pressure Pout while being delayed from the external pressure Pout.

As a result, the internal pressure Pin gradually approaches the external pressure Pout, so that the pressure between the outside and the inside of the cavity 10 is in a balanced state, and the bending of the atmospheric pressure measuring cantilever 4 gradually decreases, as shown in FIG. The output signal gradually decreases.
When the internal pressure Pin becomes the same as the external pressure Pout as in the period C after time t2 shown in FIG. 3A, the bending deformation of the atmospheric pressure measuring cantilever 4 is eliminated as shown in FIG. 4C. To return to the original state. Further, as shown in FIG. 3B, the output signal of the pressure sensor 1 also returns to zero.

Thus, by monitoring the fluctuation of the output signal based on the displacement of the atmospheric pressure measuring cantilever 4, the pressure fluctuation outside the cavity 10 can be detected.
In particular, since the barometric pressure measuring cantilever 4 can be formed by a semiconductor process technique using the silicon active layer 2c of the SOI substrate 2, it can be easily made thinner (for example, several tens to several hundreds of nm) than a conventional piezoelectric element. Therefore, it is possible to detect minute pressure fluctuations with high accuracy.

(Function of flow control unit)
Next, the function of the flow control unit 11 will be described below.
FIG. 5 is a diagram showing the relationship between the pressure difference inside and outside the gap 13 and the flow rate of the pressure transmission medium that flows inside and outside the cavity 10 due to the pressure difference. Here, the horizontal axis in FIG. 5 indicates differential pressure = external pressure Pout−internal pressure Pin, and the vertical axis indicates the volume (flow rate) per unit time of the pressure transmission medium flowing into the cavity 10. In FIG. 5, the solid line indicates the case where the flow rate control unit 11 is provided in the pressure sensor (pressure sensor 1 according to the present embodiment), and the broken line indicates the case where the flow rate control unit 11 is not provided in the pressure sensor (conventional pressure sensor). The relationship between differential pressure and flow rate is shown.

  As shown in FIG. 5, regardless of the presence or absence of the flow rate control unit 11, the flow rate of the pressure transmission medium flowing inside and outside the cavity 10 increases as the differential pressure departs from zero and draws a gradually saturated curve. However, the increasing tendency of the flow rate with respect to the differential pressure differs depending on the presence or absence of the flow control unit 11. Specifically, in the case of a configuration in which the flow rate control unit 11 is not provided, the flow rate that flows out of the cavity 10 is much higher when the differential pressure increases in the negative direction than when the differential pressure increases in the positive direction. Become bigger. This is due to the deformation of the atmospheric pressure measurement cantilever 4 as shown in FIG. That is, when the differential pressure is in the negative direction (Pout <Pin), the atmospheric pressure measuring cantilever 4 is deformed outside the cavity 10, and when the differential pressure is in the positive direction (Pout> Pin), it is deformed inside the cavity 10. When a differential pressure in the positive direction is generated (when the atmospheric pressure measuring cantilever 4 is deformed inward of the cavity 10), the pressure transmission medium flows through the inner wall of the cavity 10 and the atmospheric pressure measuring cantilever 4. On the other hand, when a differential pressure in the negative direction is generated (the atmospheric pressure measuring cantilever 4 is deformed to the outside of the cavity 10), the pressure transmission medium flows between the atmospheric pressure measuring cantilever 4 and the lid 12. Here, the flow rate of the pressure transmission medium flowing in and out of the cavity 10 does not increase suddenly due to the inner wall of the cavity 10 when a positive differential pressure is generated, but a negative differential pressure is generated. In this case, as the gap between the atmospheric pressure measurement cantilever 4 and the lid portion 12 is opened, it rapidly increases. That is, in the pressure sensor 1 provided with the flow rate control unit 11, the flow rate of the pressure transmission medium flowing inside and outside the cavity 10 is different depending on whether the differential pressure is positive or negative. Therefore, the sensitivity of the pressure sensor differs depending on whether the differential pressure is positive or negative. .

  On the other hand, when the flow rate control unit 11 is provided in the pressure sensor 1, as shown in FIG. 6B, in the case where a differential pressure in the negative direction is generated (when the atmospheric pressure measurement cantilever 4 is deformed to the outside of the cavity 10). The pressure transmission medium flows through the space between the pressure measuring cantilever 4 and the flow rate control unit 11 provided on the top of the lid 12. In other words, the pressure sensor 1 including the flow rate control unit 11 is controlled by the flow rate control unit 11 even if the gap between the lid 12 and the pressure measurement cantilever 4 increases as the pressure measurement cantilever 4 is deformed to the outside of the cavity 10. Since the flow amount of the pressure transmission medium can be regulated, an increase in the flow rate can be prevented as compared with a pressure sensor that does not have the flow rate control unit 11 as shown in FIG. For this reason, in the pressure sensor 1 according to the present embodiment, the flow rate of the pressure transmission medium does not change greatly regardless of whether the differential pressure is positive or negative. Therefore, the sensitivity of the pressure sensor is maintained regardless of whether the differential pressure is positive or negative. Can do.

Furthermore, the pressure sensor 1 is provided with the flow rate control unit 11 so that the differential pressure range in which the differential pressure and the flow rate maintain linearity is widened as shown by the solid line in FIG. For this reason, the pressure sensor 1 can widen the differential pressure range in which the sensitivity has linearity.
Further, the pressure sensor 1 has a pressure difference of zero because the pressure cantilever 4 for measuring pressure is not flat even when the pressure difference is zero, even when the pressure sensor 1 is deformed. Sensitivity can be kept equal regardless of whether it is positive or negative.

(Production method)
Next, a method for manufacturing the pressure sensor 1 will be described. Here, FIG. 7 is a diagram schematically showing a manufacturing process of the pressure sensor 1 shown in FIG.
First, phosphorus M1 is doped on the surface of the silicon active layer 2c of the SOI substrate 2 by an ion implantation method. At this time, phosphorus M1 is implanted with unnecessary regions of the silicon active layer 2c masked. Furthermore, phosphorus M1 is not implanted so as to have a uniform concentration in the thickness direction of the silicon active layer 2c, but is implanted so that the concentration in the vicinity of the surface of the silicon active layer 2c is the highest (FIG. 7 ( A)).

Next, chromium and gold M2 are vapor-deposited on the upper surface of the silicon active layer 2c and patterned (FIG. 7B).
Next, the silicon active layer 2c is etched using the chromium and gold M2 patterned in FIG. 7B as a mask (FIG. 7C).

Next, unnecessary regions of chromium and gold M2 on the surface of the silicon active layer 2c are etched (FIG. 7D).
Next, a dry resist film M3 is pasted on the upper surface of the silicon active layer 2c, developed, and exposed to produce a structure in which the inner periphery of the gap around the cantilever for atmospheric pressure measurement is removed (FIG. 7E).

Thereafter, a resist M4 is applied to the surface of the silicon support layer 2a, development and exposure processing are performed, and the silicon support layer 2a and the oxide layer 2b are etched (FIG. 7F). Thereby, the cantilever 4 for atmospheric pressure measurement is formed.
Further, the resist on the upper surface of the dry resist film M3 is removed, alignment with the concave portion formed in the first portion 31 of the sensor body 3 is performed, and the first portion 31 of the sensor body 3 is joined or adhered (illustration). (Omitted).
Finally, the pressure sensor 1 is formed by electrically connecting the pressure measuring cantilever 4 and the displacement measuring unit 5 formed on the SOI substrate 2 (not shown).

  By manufacturing the pressure sensor 1 by the above manufacturing method, a cavity can be provided on the back surface side of the atmospheric pressure measurement cantilever 4 and a gap can be formed with a very narrow dimension around the atmospheric pressure measurement cantilever 4. In addition, since the flow control unit 11 having a vertical wall structure can be formed near the outer periphery of the gap, an output signal with high linearity can be obtained in a wide pressure range. Further, even if the atmospheric pressure measurement cantilever 4 cannot be formed flat due to internal stress generated during the manufacturing process, an output signal with the same sensitivity characteristic can be obtained when the atmospheric pressure increases or decreases.

  In the manufacturing process, the impurity is not limited to phosphorus M1, but may be an impurity used for the impurity semiconductor, such as boron or arsenic. Alternatively, impurities may be implanted into the entire surface of the SOI substrate and electrodes may be formed in appropriate surrounding areas so that only necessary areas function as piezoresistors. In this case, it is necessary to form the groove 16 in the silicon active layer 2c so that the piezoresistors do not conduct with each other.

  And the pressure sensor 1 of 1st embodiment is applicable to the following various uses. The pressure sensor 1 of 1st embodiment is applicable to the navigation apparatus for motor vehicles, for example. In this case, for example, the automobile navigation device can detect the pressure difference based on the height difference using the pressure sensor 1, so that the automobile on which the automobile navigation device is mounted is an elevated road and an elevated road. It is possible to accurately determine which of the two is running. That is, the automobile navigation device including the pressure sensor 1 can provide more accurate navigation information to the user by reflecting the above determination on the navigation result.

  Furthermore, the pressure sensor 1 of the first embodiment can be applied to a portable navigation device, for example. In this case, the portable navigation device using the pressure sensor 1 can detect the pressure difference based on the height difference using the pressure sensor 1, for example, so that the device carrier is located on the floor in the building. It is possible to accurately determine whether or not it is being reflected in the navigation result. Further, the portable navigation device can also determine detailed vertical movements such as whether an elevator is used for floor movement or whether stairs are used from the pressure change. For this reason, the portable navigation device can accurately measure the energy consumption of the device carrier by the floor movement.

In addition, the portable navigation device can detect the level difference with high accuracy even with a large pressure change such as movement of an elevator or a small pressure change such as moving up and down stairs.
As described above, the pressure sensor 1 of the first embodiment can be applied to various applications, and can obtain an output signal with high linearity regardless of the vertical movement of the atmospheric pressure fluctuation.

(Second embodiment)
Hereinafter, the pressure sensor 1 according to a second embodiment of the present invention will be described.
In addition, about the structure and function equivalent to the pressure sensor 1 which concerns on above-mentioned 1st embodiment, a code | symbol is made the same and description is abbreviate | omitted.
FIG. 8 is a cross-sectional view showing the configuration of the pressure sensor 1 according to the second embodiment of the present invention.

As shown in FIG. 8, the pressure sensor 1 includes a sensor body 3 having a cavity 10, an atmospheric pressure measurement cantilever 4, a displacement measurement unit 5, and a flow rate control unit 11.
The difference of the pressure sensor 1 according to this embodiment from the first embodiment is that a pressure measuring cantilever 4 is provided inside the sensor body 3.

The sensor body 3 includes a first portion 31 having a substantially concave shape, a second portion 32 composed of an oxide layer 2 b and a silicon support layer 2 a of an SOI substrate, and a wiring substrate 33. Further, a space substantially closed by the sensor body 3 constitutes the cavity 10.
Moreover, the pressure sensor 1 includes a flow rate control unit 11 having a concave side wall in the vicinity of the outer periphery of the gap 13 around the atmospheric pressure measurement cantilever 4 as in the first embodiment.

  Here, the SOI substrate on which the atmospheric pressure measuring cantilever 4 is formed is mounted on the wiring substrate 33 and connected to the wiring 3e formed on the substrate. Similarly, the detection circuit 22 mounted on the wiring board 33 and the atmospheric pressure measurement cantilever 4 are electrically connected via the wiring 3e.

  The wiring board 33 is provided with a vent hole 34 penetrating the wiring board 33, and the SOI substrate 2 constituting the atmospheric pressure measuring cantilever 4 is installed above the vent hole 34. Further, a waterproof moisture permeable film 35 is provided between the vent hole 34 and the SOI substrate 2.

  The waterproof and moisture permeable film 35 is a porous resin film that does not transmit water droplets, but is made of a material that is permeable to water vapor or a pressure transmission medium. Therefore, since the pressure transmission medium can circulate in and out of the cavity 10 via the waterproof moisture permeable film 35 and the gap 13 around the atmospheric pressure measurement cantilever 4, the pressure sensor 1 is similar to the first embodiment described above. The pressure fluctuation outside the cavity 10 can be detected.

Further, as in the first embodiment described above, the flow rate of the pressure transmission medium moving through the gap 13 does not change greatly regardless of whether the pressure measuring cantilever 4 is deformed up or down by the fluid control unit 11. For this reason, an output signal with high linearity can be obtained even in a wide pressure range.
Since the fluid control unit 11 having a concave side wall has a shape that is difficult to manufacture by a semiconductor process or the like, a member molded from a resin or the like is bonded or bonded to the SOI substrate 2 on which the atmospheric pressure measurement cantilever 4 is formed. Also good.

  Further, the pressure sensor 1 is provided with the waterproof moisture-permeable film 35, so that water does not enter the cavity and can be used for atmospheric pressure measurement even in a usage environment in which water droplets adhere to the outside of the pressure sensor 1. Breakage of the cantilever 4 and a short circuit of the displacement measuring unit 5 can be prevented. Moreover, since the atmospheric pressure measurement cantilever 4 has a structure covered with the waterproof and moisture permeable film 35 and the like, the atmospheric pressure measurement cantilever 4 can be prevented from being damaged by external contact or the like.

(Modification 1)
The pressure sensor 1 according to the second embodiment may have a configuration in which the air hole 34 of the wiring board 33 and the pressure measuring cantilever 4 are not arranged on the same straight line. Here, FIG. 9 shows an example (modified example 1) of the pressure sensor 1 having a configuration not arranged on the same straight line. In the pressure sensor 1 shown in FIG. 9, the atmospheric pressure measurement cantilever 4 and the vent hole 34 are arranged in a non-linear manner in the vertical direction. Further, in the pressure sensor 1 shown in FIG. 9, the flow rate control unit 11 is processed in an arc shape in a sectional view along the locus of the tip when the cantilever 4 is deformed when a differential pressure in the positive direction is generated. . Therefore, the pressure sensor 1 is configured in this manner, so that dust or the like floating outside the cavity 10 can be directly contacted with the pressure measuring cantilever 4 before the silicon support layer without providing a waterproof and moisture permeable film. By colliding with the side walls of the holes or grooves provided in 2a, it is possible to suppress a decrease in sensitivity due to breakage of the atmospheric pressure measurement cantilever 4 or adhesion of dust. In addition, since the flow rate control unit 11 has the above-described shape, the gap between the pressure measurement cantilever 4 and the flow rate control unit 11 can be kept constant even if the pressure measurement cantilever 4 is deformed by a differential pressure. . For this reason, since the differential pressure range in which the flow rate flowing inside and outside the cavity 10 can be made constant can be widened, the linearity of the output signal with respect to changes in atmospheric pressure can be ensured over a wide range.

  As described above, according to the pressure sensor 1 according to the present embodiment or the first modified example, the linearity of the output signal with respect to the atmospheric pressure change is maintained, and at the same time, even when the atmospheric pressure measurement cantilever is deformed, Can maintain the same sensitivity.

(Third embodiment)
Hereinafter, a pressure sensor 1 according to a third embodiment of the present invention will be described.
In addition, about the structure and function equivalent to the pressure sensor 1 which concerns on the above-mentioned 1st and 2nd embodiment, a code | symbol is made the same and description is abbreviate | omitted.
The pressure sensor 1 according to the present embodiment is different from the pressure sensors according to the first and second embodiments in that a cover portion 36 that covers the SOI substrate 2 is provided.

FIG. 10 is a cross-sectional view showing the configuration of the pressure sensor 1 according to the third embodiment of the present invention.
The pressure sensor 1 includes a sensor main body 3 having a cavity 10, an atmospheric pressure measurement cantilever 4, a displacement measurement unit 5, and a flow rate control unit 11.

  The sensor body 3 includes a first portion 31 having a substantially concave shape, an oxide layer 2b and a silicon support layer 2a of the SOI substrate 2, and a wiring substrate 33. A space substantially closed by these members is a cavity. 10 is configured. Furthermore, a substantially concave cover portion 36 is installed on the surface of the wiring board 33 that faces the surface on which the first portion 31 is installed. The atmospheric pressure measuring cantilever 4 is installed inside the concave shape of the cover portion 36.

  The cover portion 36 is made of a substantially concave metal or resin material, and a vent hole 36a is provided at a part of the upper end. The cover part 36 is preferably made of a material having low light transmittance and low thermal conductivity. For this reason, the cover part 36 can prevent destruction of the atmospheric pressure measurement cantilever 4 due to unintentional contact with the outside of the pressure sensor 1. Further, since the pressure transmission medium can enter and exit through the vent hole 36a, the pressure fluctuation outside the cavity is transmitted to the atmospheric pressure measurement cantilever 4 through the vent hole 36a. As in the first and second embodiments, the pressure fluctuation transmitted to the pressurization measuring cantilever 4 is converted into an output signal of the detection circuit 22. The output signal of the detection circuit 22 is output to the outside through the electrical wiring 3e and the terminal 3f provided on the substrate 33.

  Furthermore, as in the first and second embodiments described above, the flow rate of the pressure transmission medium that moves through the gap 13 does not change greatly regardless of whether the pressure control cantilever 4 is deformed up or down by the fluid control unit 11. For this reason, an output signal with high linearity can be obtained even in a wide pressure range.

Further, in the pressure sensor 1 according to the present embodiment, a waterproof and moisture permeable film may be provided in the vent hole 36a as in the second embodiment described above. With such a configuration, intrusion of water droplets and the like can be prevented, so that it is possible to prevent the detection circuit 22 and the electric wiring 3e provided on the substrate 33 due to water droplets from being short-circuited and the atmospheric pressure measurement cantilever 4 from being damaged. .
Since not only the pressure transmission medium but also dust and the like enter and exit through the vent hole 36a, the vent hole 36a is preferably provided at a position shifted from directly above the atmospheric pressure measurement cantilever 4.

(Modification 2)
In the pressure sensor 1 according to the third embodiment, the cover unit 36 and the flow rate control unit 11 may be configured integrally. An example (Modification 2) of the pressure sensor 1 having the integral structure is shown in FIG. In the pressure sensor 1 shown in FIG. 11, the cover part 36 configured integrally with the flow rate control part 11 is formed so as to cover the outer periphery of the second part 32 and the lid part 12. Furthermore, in the pressure sensor 1 according to this modification, the vent hole 36a provided in the cover portion 36 is covered with the waterproof and moisture permeable film 35 in order to prevent dust flowing in through the vent hole 36a. As a result, the pressure sensor 1 integrates the formation process of the flow rate control unit 11, the mounting process of the SOI substrate 2 and the flow rate control unit 11, and the mounting process of the substrate on which the SOI substrate is mounted and the cover unit. Therefore, it can be manufactured at a low cost.

(Modification 3)
In the pressure sensor 1 according to the third embodiment, it is preferable that the cover portion 36 is made of a material having low light transmittance and low thermal conductivity. If the piezoresistor 20 cannot be made of the above material, the electrical resistance value changes due to temperature change and light irradiation. For this reason, temperature change and light irradiation are mistaken for pressure fluctuation.

  Therefore, in the pressure sensor 1 (the pressure sensor 1 according to the modified example 3) including the cover portion 36 that does not use the above-described material, for example, as shown in FIGS. And the piezoresistor 20a connected to the reference cantilever 41 are provided. Unlike the atmospheric pressure measurement cantilever 4, the reference cantilever 41 has a configuration in which the rear oxide layer 2 b and the silicon support layer 2 a are not removed, and is not deformed by a differential pressure. For this reason, the electrical resistance value of the piezoresistor 20a of the reference cantilever 41 is changed only by temperature change or light irradiation almost simultaneously with the pressure measurement cantilever 4.

  As shown in FIG. 13, in the pressure sensor 1 according to this modification, the piezoresistor 20 of the atmospheric pressure measuring cantilever 4 and the piezoresistor 20a of the reference cantilever 41 constitute a Wheatstone bridge circuit. The output of this Wheatstone bridge circuit is to output the difference between the resistance value change of the piezoresistor 20 and the resistance value change of the piezoresistor 20a due to temperature change or light irradiation, so that the stress change due to the differential pressure is output as the resistance value change. Is possible.

  Therefore, since the pressure sensor 1 according to the present modification has such a configuration, even if the resistance value of the piezoresistor changes due to light or heat from the outside, the influence of light or heat can be removed from the output. Only the change in the resistance value of the piezoresistor due to the displacement of the atmospheric pressure measurement cantilever 4 can be taken out by the pressure.

  As described above, according to the pressure sensor 1 according to the third embodiment and the modifications 2 and 3, when the flow rate control unit 11 is provided in the vicinity of the outer periphery of the gap 13, it is possible to detect a slow pressure fluctuation with high sensitivity. At the same time, the linearity of the output signal can be maintained over a wide pressure range. Further, in the pressure sensor 1 according to the third embodiment and the second and third modifications, even when the cantilever is slightly deformed in the manufacturing process, the sensitivity when the atmospheric pressure change is increased or decreased can be maintained substantially equal. it can. Furthermore, in the pressure sensor 1 according to the third embodiment and the second and third modified examples, the atmospheric pressure measuring cantilever 4 and the flow rate control unit 11 can be collectively manufactured by a semiconductor process. It can be manufactured.

(Modification 4)
In the pressure sensor 1 according to the above-described embodiment, the flow rate control unit 11 is provided as a separate body on the top of the lid unit 12, but may be configured as shown in FIGS. 4). Specifically, in the case of the pressure sensor 1 shown in FIG. 14, the flow rate control unit 11 is configured such that the height position forming the cantilever 4 faces the wall portion of the sensor main body 3 through the gap 13 (the silicon activity of the sensor main body 3). The layer 2c is provided in the vicinity of a position in contact with the oxide layer 2b. That is, in the pressure sensor 1 shown in FIG. 12, the sensor body 3 (the silicon active layer 2 c) functions as the flow rate control unit 11.

In the case of the pressure sensor 1 shown in FIG. 15, the cantilever 4 is provided such that the tip is inclined toward the bottom surface of the cavity 10 in a state where there is no differential pressure (a state where the external pressure and the internal pressure are equal). That is, in the pressure sensor 1 shown in FIG. 15, the sensor body 3 (the SOI substrate 2) functions as the flow rate control unit 11.
Therefore, in the pressure sensor 1 according to the present modification, the sensor body 3 (the SOI substrate 2) functions as the flow rate control unit 11, and therefore, the manufacturing process is simplified as much as it is possible to save the trouble of providing the flow rate control unit separately. In addition, downsizing can be realized.

(Modification 5)
In the pressure sensor 1 according to the above-described embodiment, the flow rate of the pressure transmission medium when a differential pressure in the negative direction is generated (the atmospheric pressure measuring cantilever 4 is deformed to the outside of the cavity 10) is provided by providing the flow rate control unit 11. Although the configuration is exemplified, a configuration for stabilizing the flow rate of the pressure transmission medium when a differential pressure in the positive direction is generated may be further provided (Modification 5). Specifically, in the pressure sensor 1 according to this modification, as shown in FIG. 16, the SOI substrate 2 (second side surface) that faces the tip of the cantilever 4 through the gap 13 has a positive differential pressure. When the cantilever 4 is deformed when the cantilever occurs, it is processed into a circular arc shape in cross section along the locus of the tip.
Therefore, the flow rate of the pressure transmission medium becomes a constant amount regardless of the amount of deformation due to the differential pressure in the positive direction of the pressure sensor 1, so that the sensitivity of the pressure sensor 1 can be further enhanced.

1, 100 Pressure sensor 2 SOI substrate 3 Sensor body 4 Barometric pressure measurement cantilever (cantilever)
5 Displacement Measuring Unit 11 Flow Control Unit 12 Lid 13 Gap 20 Piezoresistor 22 Detection Circuit 35 Waterproof Moisture-permeable Film 36 Cover 110 Piezoelectric Element 120 Through Hole or Recess

Claims (6)

A pressure sensor for detecting pressure fluctuations,
A sensor body having a cavity;
The cavity is disposed so as to seal, and the tip is supported in a cantilever shape so as to form a gap for circulating air into and out of the cavity between the sensor body and the inside and outside of the cavity. A cantilever that bends and deforms according to the pressure difference;
A displacement measuring unit for measuring displacement according to the bending deformation of the cantilever;
The amount of air flowing through the gap, have a, a flow control unit for preventing the change by the deformation of the cantilever,
The flow rate control unit is installed on the outer side of the cavity and in the vicinity of the outer end of the gap, and includes a wall portion having a side surface extending along the thickness direction of the cantilever,
A pressure sensor comprising: a lid portion having one end disposed opposite the cantilever through the gap and having a surface substantially perpendicular to a side surface of the wall portion . The side surface of the wall portion is formed in an arc shape in a longitudinal sectional view along a locus due to deformation of a tip portion of the cantilever when a pressure inside the cavity is larger than a pressure outside the cavity. Item 2. The pressure sensor according to Item 1. The cantilever pressure sensor of claim 1 or 2, characterized by being covered with a cover portion having a part to vent. The pressure sensor according to claim 3 , wherein a waterproof and moisture permeable film is provided so as to cover the vent hole . The pressure sensor according to claim 3 or 4 , wherein the vent hole is provided at a position shifted from directly above the cantilever . The wall has a second side surface extending to the inside of the cavity,
The second side surface is formed in an arc shape in a longitudinal sectional view along a locus due to deformation of a tip portion of the cantilever when a pressure outside the cavity is larger than a pressure inside the cavity. Item 3. The pressure sensor according to Item 1 or 2 .

Images