JP2766257B2 - Structure of pressure sensor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a pressure sensor such as a depth gauge, a water pressure gauge or a barometer used by a diver or the like. 2. Description of the Related Art In recent years, scuba diving technology has made great strides, and along with this, the number of people who enjoy diving as a profession or enjoying diving as leisure has increased rapidly. These divers have sought diving equipment that can be used safely during diving. Recently, electronic equipment with a pressure sensor formed using a pressure sensor formed of a semiconductor has come to be seen. Hereinafter, an electronic timepiece will be described as an example of the electronic apparatus, and an electronic timepiece with a depth gauge will be described as an example of an electronic timepiece with a pressure sensor. In recent years, diver watches having an outer structure capable of withstanding a water pressure of several hundred atmospheres have become commercially available, and such diver watches have become indispensable to prevent diver accidents due to damage to the timepiece. I have. on the other hand,
A very important requirement along with the dive time is the dive depth for ensuring the safety of diving. Divers must always check the depth of the dive, calculate the associated air consumption, and adjust the ascent rate. Of course, going too deep is dangerous in itself and must be avoided. Although the diving depth has such an important meaning, at present, there are large measuring instruments which restrict the diver's behavior in the water, and have problems in terms of accuracy and stability. Some of them are commercially available or very expensive. For this reason, many divers rely on eye measurements and experience and are in a very dangerous state. A measuring instrument for measuring the depth of a dive is defined as a depth gauge. As a method of measuring the depth, a method of measuring the water pressure applied to the depth gauge and dividing the density of the water to obtain the water depth is first mentioned. Can be Although this method may require some corrections due to differences in the density of freshwater and seawater, it is most suitable as a diver depth meter because it measures physical quantities that directly affect the diver. [0006] Since the physical quantity directly affecting the diver is the pressure itself, there is an opinion that a water pressure gauge that displays the pressure as it is is more useful. The depth gauge referred to here includes a water pressure gauge and a barometer. [0007] The exterior of the diver watch is a very rugged hermetically sealed container, and there is almost no change in the internal volume at a depth of about 100 meters, so that the internal pressure is kept almost equal to the atmospheric pressure. If a small hole is provided in a part of such an exterior, and the small hole is sealed with a diaphragm and put into water, a stress-strain occurs in the diaphragm in proportion to the water pressure. The stress strain is converted into an electric signal by a strain gauge, and the signal is amplified.
It can be displayed as a depth by the indicating instrument,
The pressure measuring device used in the present invention is also realized by applying this principle. The diaphragm type semiconductor pressure converter described above is disclosed in Japanese Patent Application Laid-Open No. 56-154638. JP-A-56-15463
No. 8 discloses that a pressure-sensitive pellet made of a semiconductor single crystal in which a strain resistance layer is diffused and formed on a thin diaphragm is held in a holder, and an electrically insulating oil penetrates the pressure-sensitive pellet, and the oil is transferred to the holder. A configuration is described in which a cover is closed to cover the inside of the cover, and leakage of oil is prevented by surface tension of a small hole of the cover. [0009] However, in the case of a diaphragm type semiconductor pressure converter, Japanese Patent Application Laid-Open No. Sho 56-15463.
Use of a pressure-sensitive pellet made of a semiconductor single crystal in which a strain resistance layer is diffused and formed on a thin diaphragm as disclosed in Japanese Patent Publication No. 8 can be downsized and adopted for an electronic watch or the like. However, the protection member to be filled to protect the pressure-sensitive pellet is oil, and is a substance having a high fluidity as is well known. For this reason, a process for preventing oil leakage is required, and the structure becomes complicated. As one of the prevention structures, Japanese Patent Application Laid-Open No. 56-154
As described in Japanese Patent No. 638, it was considered to make a hole in the lid to prevent leakage by using surface tension.However, when the surface tension was dependent on the pressure, the pressure due to the surface tension was Due to the change over time due to the application to the surface or the evaporation of oil, only a pressure converter having a large measurement error can be obtained. Therefore, the pressure converter as disclosed in Japanese Patent Application Laid-Open No. 56-154638 is not practical. SUMMARY OF THE INVENTION The present invention is intended to improve the above-mentioned drawbacks, and is intended to improve the durability, enable high-precision and high-stability pressure measurement, and realize a high practical pressure which can be adopted for small equipment. The purpose is to provide a sensor. In order to achieve the above object, the gist of the present invention is to provide a pressure sensor formed of a semiconductor material for measuring pressure such as atmospheric pressure or water pressure. The sensor is covered with an elastic substance containing a light-shielding substance. Further, the elastic material is an elastic material having a small Young's modulus and a large Poisson's ratio. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of a pressure detector according to the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of a silicon diaphragm type pressure sensor for detecting water pressure used in the present invention, and FIG. 2 is a plan view thereof. The silicon diaphragm type pressure sensor is
A silicon single crystal plate 1 is a semiconductor material having a side of several millimeters square and a thickness of several hundred microns, and a semiconductor resistor 3 is formed on the surface of a diaphragm 2 formed by engraving one surface of the silicon single crystal plate.
Is formed by diffusion. Since the semiconductor resistor 3 exhibits a piezoresistive effect with respect to strain, the change ΔR in resistance value corresponding to the pressure difference ΔP is extremely large, and has a sensitivity several hundred times that of a normal metal foil strain gauge. Have. In addition, since the diaphragm made of a thin silicon plate has a number of very excellent features, such as a large elastic limit, small residual strain, less occurrence of material fatigue, and a small change with time, the silicon diaphragm type pressure sensor is Currently, it is practically used for various pressure measurements as the most useful pressure sensor. In FIG. 1, when a pressure difference occurs between the left and right surfaces of the diaphragm 2, distortion occurs in the diaphragm 2, and as a result, the resistance value of the semiconductor resistor 3 changes. As shown in FIG. 2, the semiconductor resistors 3 are formed at four locations on the periphery of the diaphragm 2 in the same direction, and their resistance values are substantially equal. The four semiconductor resistors 3 are bridge-connected as shown in the circuit diagram of FIG. 3, and an output voltage Vout given by the following equation is obtained by the pressure difference ΔP between the upper and lower surfaces of the diaphragm 2. Vout = (△ R / R) · E where R is the resistance value of each semiconductor resistor 3 when there is no pressure difference ΔP, and ΔR is each semiconductor resistor 3 corresponding to the pressure difference ΔP.
And E is the voltage of the power supply applied to the bridge. The silicon diaphragm type pressure sensor having such excellent characteristics seals a small hole provided in a part of the exterior of the diver watch and detects a pressure difference between both surfaces. One side of one side is in direct contact with the outside world. Since a diver's watch is naturally immersed in a liquid, comes into contact with corrosive substances generated by decomposition of sweat, and is exposed to ozone-rich air, the diver's watch cannot be used. Care must be taken to ensure that no chemical effects are applied to the silicon diaphragm type pressure sensor. Also, the seawater and sweat entering the small holes provided on the exterior are prevented from evaporating and salt crystals are deposited in the small holes, and the small holes themselves are not closed due to deposition of dirt. I have to The present invention proposes a structure of a pressure detecting portion that protects the diaphragm of the sensor from such chemical and physical influences and can always stably and accurately measure a pressure. FIG. 4 is an external plan view showing an embodiment of an electronic timepiece having a depth gauge function using the silicon diaphragm pressure sensor described above. The present embodiment relates to a digital display wristwatch using an electro-optical display element.
Minutes 35 seconds and time 0 hours 45
The minute and the water depth of 24.6 m are displayed. A pressure detection unit is provided on a part of the windshield 5 covering the display surface of the timepiece, and a cover plate 6 for mechanically protecting the pressure detection unit is fixed to the surface of the windshield 5. FIG. 5, FIG. 6, FIG. 7, and FIG. 8 are cross-sectional views of a pressure detecting section which can be used in the electronic timepiece of FIG. 4, respectively, and are specific embodiments of the present invention. In the four embodiments, the upper side of the drawing represents the outer surface of the watch exterior, and the lower side represents the inner surface of the watch exterior. The principle of the pressure sensor will be described with reference to FIG. 5. A cover plate 6 having mesh-like small holes is fixed to the outer surface of the windshield 5. An opaque paint 7 is partially applied to the inner surface of the windshield 5,
Digital display is being closed. A small through hole is provided in the lower windshield 5 below the cover plate 6, and the silicon diaphragm type pressure sensor 8 (hereinafter referred to as a sensor body) is hermetically fixed to an opening inside the windshield 5. . The four terminals of the resistance bridge of the sensor body 8 are connected to the four pattern wirings of the terminal board 10 by the fine wires 9.
10a, and further electrically connected to a signal processing circuit (not shown) via four pressure contact springs 11. On the pattern wiring surface of the terminal board 10, a diaphragm protective cover 12 for protecting the wiring of the sensor body 8 and the fine conductive wire 9 is fixed so that the pressure detecting function is not damaged during the watch manufacturing process or repair. Is protected. The diaphragm protection cover 12 has a small hole so that the size of the back pressure chamber of the sensor body 8 is not limited. The small hole provided in the windshield 5 is a pressure introducing hole for introducing the pressure outside the timepiece to the diaphragm of the sensor body 8.
A solid material having a very low Young's modulus, that is, a rubbery elastic material 13 is filled up to the outer opening of the windshield 5 in the engraved portion on the back surface which is a direct contact surface with the outside. Since the rubber-like elastic substance 13 has a very small Young's modulus, a large Poisson's ratio, and is confined in an area where deformation is small, the pressure applied to the small opening of the pressure introducing hole is reduced. Is transmitted with almost no attenuation to the diaphragm of the sensor body 8 at the deepest part. When a diver watch provided with a water pressure detecting section having such a structure is put in water, the pressure difference between the inside and outside of the watch exterior is passed through the mesh-like small holes of the cover plate 6 to the rubber-like elastic material 13 of the pressure introducing holes. Applied to the diaphragm of the sensor body 8. As a result, the diaphragm of the sensor body 8 is deformed to the inside of the timepiece, and the distortion causes an imbalance in the bridge resistance, and generates an electric signal corresponding to the water depth. As described above, the pressure introducing hole is formed in the rubber-like elastic material 13.
When filled, the seawater, sweat and air do not enter the pressure introduction hole, so that the sensor body 8 does not directly touch these substances, and the pressure is correctly transmitted.
An excellent pressure detection mechanism with extremely excellent weather resistance is realized. In the embodiment shown in FIG. 6, the sensor body 8 is not directly fixed to the windshield 5a, but is fixed to the sensor mount 14, and the sensor mount 14 is fixed to the windshield 5a. It has a structure to do. A small hole penetrates through the center of the sensor mount 14, and the sensor body 8 is hermetically fixed to an opening inside the sensor mount 14. Screws are provided on the outer periphery of the sensor mount 14 and are engaged with a cover plate 6a having internal threads to fix the sensor mount 14 to the windshield 5a. In this fixing, the sensor mount 14 is fixed to the windshield 5a. In this fixing, a waterproof packing 15 is compression-fixed between the sensor mounting base 14 and the parting paint 7 on the lower surface of the windshield 5, and has a waterproof function. The terminal wiring and the protection structure of the sensor body 8 are the same as those of the embodiment shown in FIG. The small hole of the sensor mounting base 14 is a pressure introducing hole, and is similar to the embodiment of FIG. 5 except that the windshield 5 in the embodiment of FIG. The contact surface side of the contact is filled with a rubber-like elastic substance 13. FIG. 7 shows that the sensor mount 14a is connected to the windshield 5b.
Is an embodiment inserted from the outer surface of the. The sensor mount 14a is press-fitted and fixed to the windshield 5b via a waterproof packing 15a. The central axis of the sensor mount 14a has a penetrating small hole whose diameter increases from the inside to the outside, and the sensor body 8 is hermetically sealed in an opening inside the sensor mount 14a. The elastic substance 13 is filled in the carved portion and a part of the small hole, which are the direct contact surfaces of the sensor body 8 with the outside. A cover plate 6b having a small hole different from the small hole of the sensor mount 14a is fixed to the outside of the sensor mount 14a. The terminal wiring and the protection structure of the sensor body 8 are the same as those in the embodiment of FIGS. In the present embodiment, the rubber-like elastic substance 13 is filled only in a part of the small hole, but this is because the shape of the small hole is different from that of the embodiment shown in FIGS. This is because there is no obstacle such as the pores themselves being blocked by crystals or dirt of salt. In the above-described embodiments of FIGS. 5, 6, and 7, the sensor is disposed in the inner opening formed by the pressure introducing hole. However, in the embodiment of FIG. 1 shows a case where the device is arranged in the opening of FIG. FIG. 8 shows a pressure sensor mounting structure according to an embodiment of the present invention. In the present embodiment, the sensor body 8 is housed in a recess of the sensor mounting base 14b, and is fixed so as to hermetically seal a small hole provided in the center from the outer surface. The four fixed conductive pins 16 are electrically connected to the fine conductive wires 9. The periphery of the sensor body 8 and the wiring portion of the ultrafine conductive wire 9 are filled with a rubber-like elastic material 13 so as to be in contact with the inner wall of the sensor mount 14b, and are physically and chemically protected. It is mechanically protected by a cover plate 6c fixed to the mounting base 14b. Further, since the sensor body 8 is made of a semiconductor material, when exposed to external light such as sunlight, there is a large danger that a current will flow through the semiconductor and cause leakage, but the sensor body 8 is covered. The elastic material 13 is formed so as to be optically protected by including a light-shielding pigment. The sensor mounting base 14b is inserted from the outside of the exterior, is press-fitted into the windshield 5c via a waterproof packing 15b, and the sensor body 8 is illustrated via a conductive pin 16 and a spring 11 pressed against one end thereof. Not electrically coupled with signal processing circuits. The case where the water pressure detecting unit is provided on the windshield of the timepiece has been described above with reference to the four embodiments. The water pressure detecting unit is provided with the windshields 5 to 5c and the paint shown in the drawing. Instead of the part 7, the back cover of the watch exterior or the exterior body (case body) may be replaced. In this case, space restrictions are likely to occur in the mounting portion, but on the other hand, there is an advantage that the display surface of the timepiece can be enlarged. FIG. 9 is an external plan view showing an embodiment of an analog display wristwatch with a depth gauge, and a pointer-type time display surface.
A pointer-type depth display section 18 is also provided in a part of 17. In the present embodiment, the water pressure detecting section is provided on the side surface of the case body (case body) 19 as understood from the position taken by the cover plate 6 in the drawing, and the pressure introducing hole is located at the 10 o'clock position of the watch. From the direction of the center of the watch in parallel with the paper. In this case, the sensor mount 13b is not the windshield 5c but the case body 19 as a matter of course. Next, the rubbery elastic substance will be described. In the present invention, the diaphragm portion of the silicon diaphragm type pressure sensor, the fixing portion of the sensor body and the base portion of the sensor, the pressure introduction hole, or the wiring drawn from the sensor are physically and chemically protected, and The following three items are particularly important as characteristics required for the rubber-like elastic substance used for the purpose of not impairing the detection capability of the water pressure detection unit. First, the material must be as flexible as possible and do not attenuate the pressure transmitted to the diaphragm. For that purpose, it is necessary that the material has a Young's modulus as small as possible and a Poisson's ratio as large as possible, and the property thereof is not affected by temperature and pressure. However, the area of the diaphragm of the silicon diaphragm type pressure sensor is as small as several square millimeters and its mechanical displacement is also small, so even though it is a rubber-like elastic material, the range of its elastic limit does not necessarily need to be large, such as agar. It may be nature. Second, it is necessary that the substance does not deteriorate even if it is constantly exposed to seawater, sweat, ozone, or the like. This characteristic is necessary not only for the problem of strength but also for keeping the sensitivity of the depth gauge stable for a long period of time. Third, it is necessary to have good filling properties. The pressure introduction hole provided on the outer surface of the diver watch has a small hole diameter and is relatively deep, but it must be filled with no gaps in every corner, and it is necessary to enclose the wiring of extremely fragile ultrafine conductive wire . Therefore, it is desirable that the material be a liquid having a high fluidity at the time of filling and lose its fluidity after the completion of filling to become a solid. As the substance having such characteristics, there are the rubber-like elastic substance and the agar-like substance as described above. In general, cholera may be a gel-like substance. The effect of using this substance is, of course, no need to take measures to prevent leakage of fluidity, and since there is no fluidity, unnecessary pressure such as surface tension is not applied, and correction is possible A pressure sensor that can obtain a constant pressure can be obtained. Silicone rubber is a material having the above-mentioned important properties, and is most suitable as the rubbery elastic material of the present invention. Silicone rubbers with various characteristics are manufactured according to various application fields.
The ordinary temperature-curable ones are suitable for the application of the present invention. With such a silicone rubber, a silicone rubber having a very soft hardness after curing and having the inherent characteristics of a silicon rubber excellent in heat resistance, cold resistance, weather resistance and the like has been obtained. The electronic timepiece with a depth gauge using a silicon diaphragm type pressure sensor has been described in detail above, particularly focusing on the structure of the water pressure detecting unit. As described above, in order to protect the pressure sensor, after filling, a solid substance having a low fluidity and a small Young's modulus and a large Poisson's ratio, for example, a rubber-like or agar-like elastic substance is used. As a result, there is no need to take measures against fluidity, and the effect of thermal expansion on measurement accuracy and errors due to unnecessary pressure such as surface tension can be eliminated. In addition to having a sufficient effect on intrusion, for example, the above-mentioned solid elastic substance can directly contact seawater, so that it is possible to use extraneous metal diaphragms and troublesome holes that use surface tension. It is no longer necessary to determine the setting conditions, which makes it possible to adopt it in small devices such as electronic watches, and has seen a great step forward in practical use. As is apparent from the above description, according to the present invention, when the sensor body is made of a semiconductor material, a current flows through the semiconductor when external light such as sunlight shines. Although the danger of leaks is very high, since the elastic material covering the sensor body contains a light-shielding material, it is optically protected even under extremely severe environmental conditions, so it is highly accurate and A pressure sensor that enables highly stable pressure measurement can be provided. Further, by covering the sensor body with the elastic substance, it becomes difficult for dust and seawater to enter the mounting table. Even if the sensor body is covered with the elastic substance, it hardly remains in the mounting table. Further, by filling the mounting base, the upper surface of the elastic substance becomes a substantially flat surface, so that the internal pressure to the pressure sensor due to the surface tension can be reduced to almost zero. This can also provide a portable device having a built-in pressure sensor with sufficiently improved long-term reliability. Therefore, not only can a device incorporating a semiconductor pressure sensor be used in the presence of external light, but also because it has a high degree of freedom in structure, it can be used in a small device without impairing the design. Thus, it has become possible to provide a highly practical pressure sensor.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of a diaphragm type pressure sensor according to the present invention. FIG. 2 is a plan view of the diaphragm type pressure sensor of FIG. FIG. 3 is a principle circuit diagram for explaining connection of a resistance bridge of the pressure sensor. FIG. 4 is a plan view of an electronic timepiece with a pressure sensor showing one embodiment of the present invention. FIG. 5 is a sectional view of a pressure sensor structure showing one embodiment of the present invention. FIG. 6 is a cross-sectional view of a pressure sensor structure showing one embodiment of the present invention. FIG. 7 is a cross-sectional view of a pressure sensor structure showing one embodiment of the present invention. FIG. 8 is a cross-sectional view of a pressure sensor structure showing one embodiment of the present invention. FIG. 9 is a plan view of an electronic timepiece with a pressure sensor showing one embodiment of the present invention. [Description of Signs] 5, 5a, 5b, 5c: Windshield 6, 6a, 6b, 6c ... Cover plate 7 ... Paint 8 ... Sensor body 9 ... Fine wire 10 ... Terminal board 11 ... Pressure contact Spring 12: Diaphragm protective cover 13: Elastic material 14, 14a, 14b, Sensor mounting base 15, 15a, 15b, Waterproof packing 16: Conductive pin

Claims (1)

(57) [Claims] A pressure sensor comprising a semiconductor material for measuring pressure such as atmospheric pressure or water pressure, wherein the pressure sensor is covered with an elastic material containing a light-shielding material. 2. The pressure sensor according to claim 1, wherein the elastic material has a small Young's modulus and a large Poisson's ratio.