Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
  • G01L9/00—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means
  • G01L9/0041—Transmitting or indicating the displacement of flexible diaphragms
  • G01L9/0072—Transmitting or indicating the displacement of flexible diaphragms using variations in capacitance
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
  • G01L9/00—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means
  • G01L9/0041—Transmitting or indicating the displacement of flexible diaphragms
  • G01L9/0072—Transmitting or indicating the displacement of flexible diaphragms using variations in capacitance
  • G01L9/0073—Transmitting or indicating the displacement of flexible diaphragms using variations in capacitance using a semiconductive diaphragm

Definitions

• the present invention relates to an improvement of a pressure sensor used to measure the pressure of fluid, in particular
• the present invention relates to a pressure sensor in which the linearity of pressure sensitivity characteristics is improved by configuring a thin-walled portion (diaphragm) so as to stagnate and deform rapidly at a low pressure stage while gradually stagnating at a high pressure state.
• a conventional tire pressure monitoring system that detects the air pressure of a tire mounted on a vehicle such as a car by using a pressure sensor and issues a warning when an abnormality occurs.
• Japanese Patent Laid-Open No. 2001-174357 joins a diaphragm which also serves as ceramic force and a base which also serves as ceramic force, and Techniques for converting capacitance changes to pressure are disclosed.
• air pressure sensors that use ceramics as detection pieces have problems in detection accuracy and improvement is desired.
• This pressure sensor has a structure in which a detection piece 110 made of silicon is assembled on a bottom plate 100 formed by sequentially laminating a lower electrode film 102, a dielectric thin film 103, and an electrode film 104 on a glass plate 101 as a base. ing.
• This pressure sensor utilizes, for pressure detection, the change in electrostatic capacity caused by the thin-walled portion (diaphragm) 110 a of the detection piece 110 being deformed by pressure and coming into direct contact with the dielectric thin film 103.
• An air pressure sensor of this type is disclosed, for example, in the Journal of the Institute of Electrical Engineers of Japan, Vol. 123-E “Tatch Mode Capacitive Pressure Sensor for Tire Pressure Monitoring System”.
• the diaphragm 110 a and the dielectric thin film 103 can be used.
• a gap of about 3 m at the smallest dimension Should be set to However, in the case of etching silicon, it is difficult to ensure high accuracy at such a minute size level that it is difficult to control the thickness accurately. As a result, manufacturing variations become large.
• silicon materials have problems in terms of the repeatability of elastic deformation from the physical properties of their crystal structure.
• silicon is detected by using quartz having physical properties more stable than silicon as a detection piece of a pressure sensor. It is possible to eliminate the poor repeatability in elastic deformation which is a drawback of the pressure sensor using a piece.
• the whole diaphragm in order to obtain sensitive sensor sensitivity, the whole diaphragm has been formed in the form of a parallel plate having a uniform thickness.
• the diaphragm in the case of a tactile mode pressure sensor, the diaphragm rapidly and largely stagnates and deforms at a specific pressure value and contacts the upper surface of the base.
• the movable range is limited to a small range, and the pressure range in which the sensor characteristics excellent in linearity can be obtained is limited to a narrow range (a range in which the pressure is low).
• FIGS. 7 (a) and 7 (b) are cross-sectional views for explaining the operation of the touch mode pressure sensor of the type in which the thickness of the diaphragm is uniform.
• This pressure sensor has a lower portion on a base 101 made of insulating material.
• a configuration in which a detection piece 110 is assembled on a bottom plate 100 in which an electrode film 102 and a dielectric film 103 are sequentially stacked is provided.
• An upper electrode 111 is formed on the lower surface of the diaphragm 11 Oa of the detection piece 110, and the upper electrode 111 is disposed opposite to the dielectric film 103 with a predetermined minute gap therebetween.
• FIG. 7 (a) shows the measurement start state in which the lower surface of the central portion of the diaphragm 110a is deformed downward and the lower surface of the central portion contacts the upper surface of the bottom plate. This is a state where the waist of the diaphragm 110a starts to break. Since the amount of stagnation further is substantially determined only by the rigidity of the joint structure of the diaphragm 110a and the base 101, the diaphragm is in a state where it is difficult to stagnate further to the bottom plate side beyond the state of (a). Therefore, when in the state of (a), even if a slightly higher pressure is applied, the diaphragm is greatly deformed and shifts to the state of (b).
• Patent Document 1 Japanese Patent Application Laid-Open No. 2001-174357
• Patent Document 2 Japanese Utility Model Application Publication No. 63-175833
• Patent Document 3 Japanese Patent Application Laid-Open No. 06-021740
• Non-Patent Document 1 The Journal of the Institute of Electrical Engineers of Japan 2003 Vol. 123— E “Tatch mode capacitive pressure sensor for tire pressure monitoring system”
• the present invention has been made in view of the above, and while the pressure to be measured is small, it stagnates and deforms rapidly while the pressure is reduced by configuring the diaphragm so as to gradually stagnate in a high pressure state. It is an object of the present invention to improve the linearity of sensitivity characteristics and to provide a pressure sensor capable of measuring with high sensitivity up to low pressure and high pressure by one type of pressure sensor.
• a base made of an insulating material, a lower electrode film and a dielectric film sequentially stacked on the surface of the base, and the dielectric film
• a detection piece provided with a thin portion at the opposite position and fixed on the surface of the base, and an upper electrode film formed on at least a part of the thin portion and in a positional relationship facing the lower electrode film.
• a pressure sensor provided with an airtight space of a minute gap between the lower surface of the detection piece and the dielectric film, characterized in that the thickness of the thin portion of the detection piece is not uniform over the entire surface. .
• the thin-walled part has a uniform-thickness area in a range of a predetermined width from one end thereof, and a uniform-thickness area in the range from the uniform-thickness area force to the other end of the thin-walled part. It is characterized by being a thickened area rather than a thick area.
• the thickened region has a step-like configuration in which the thickness of the thin-walled portion gradually increases linearly and linearly or at least one stepped portion. It is characterized by having.
• the invention according to claim 4 is characterized in that in claim 1, 2, or 3, the detection piece has a configuration in which a thick annular portion is integrated with the outer peripheral edge of the thin portion.
• the invention according to claim 5 is that in claim 1, 2, 3 or 4, the thin-walled portion of the detection piece has a flat surface on one side and an inclined surface or step-like surface on the other side. It is characterized by The invention of claim 6 is characterized in that, in claim 5, the flat surface of the thin portion of the detection piece is disposed to face the lower electrode film on the base.
• the detection piece and the base are made of the same type of piezoelectric crystal material, and the crystal axis of the detection piece and the crystal axis of the base are It is characterized in that the base is superposed on the detection piece in a state of coincidence.
• the invention according to claim 8 relates to any one of claims 1 to 7, wherein the base has a recess and an outer frame surrounding the outer periphery of the recess, and the base is provided on the inner bottom surface of the recess.
• the micro gap is formed between the thin portion and the dielectric film by having a configuration in which the lower electrode film and the dielectric film are laminated, and the bottom surface of the detection piece is supported by the upper surface of the outer frame of the base.
• the invention of claim 9 is characterized in that, in any one of claims 1 to 8, the detection piece is made of a quartz material.
• the invention according to claim 10 is characterized in that, in claim 9, the detection piece is a quartz plate force, and the radiation with respect to the main surface of the detection piece forms an angle other than 0 ° with respect to the quartz crystal axis Z.
• the piece is characterized by having the thin portion obtained by processing a quartz plate thinly by wet etching.
• the invention according to claim 11 is characterized in that, in claim 9 or 10, the quartz plate constituting the detection piece has a filling mode.
• the invention according to claim 12 is characterized in that in claim 9, 10, or 11, the crystal plate constituting the detection piece is an AT-cut quartz plate.
• the invention according to claim 13 is characterized in that the pressure sensor according to any one of claims 1 to 12 is a touch mode capacitive pressure sensor.
• the invention of claim 14 is characterized in that, in claim 3, the step portion is formed by adding a metal layer on a base of a thin portion.
• the invention of claim 1 is configured such that the thickness of the thin-walled part gradually increases in the form of a slope without being uniformly thick over the entire surface, or increases stepwise. Since the range of the predetermined width of one end force of the thin portion of the detection piece is a uniform thickness area, and the range of force toward the other end of the uniform thickness area of the thin portion is a thicker thickness area than the uniform thickness area.
• the thickness difference portion is formed in the thin-walled portion as a diaphragm, and a low thickness uniform thickness region functions at low pressure measurement, and a thick thickness increase region functions at high pressure measurement. In total, the linearity of pressure sensor sensitivity can be improved.
• the thickness of the thin portion tapers and linearly increases, so that the thickness becomes a continuous inclined structure, and when high pressure is measured, the waist of the thin portion Maintain the strength of the pressure sensor and improve the linearity of the pressure sensor sensitivity.
• the thickened region has a step-like structure having at least one step portion, the stiffness of the thin portion can be maintained at the time of high pressure measurement, and the linearity of the pressure sensor sensitivity can be improved.
• the detection piece since the detection piece has the structure in which the thick annular portion is integrated with the outer peripheral edge of the thin portion, the strength of the detection piece can be enhanced and the durability can be improved.
• the thin portion of the detection piece has a flat surface on one side and an inclined surface or a step on the other surface, so that the flat surface faces the bottom plate upper surface. This makes it possible to form a uniform gap airtight space and stabilize the performance of the pressure sensor.
• the detection piece and the base are constituted by the same kind of piezoelectric crystal material force, and the crystal axis of the detection piece and the crystal axis of the base are made to coincide with each other, It can be closely matched and the effects of thermal distortion can be avoided.
• the base has the recessed portion and the outer frame surrounding the outer periphery of the recessed portion, and in this case, the detection piece is mounted with the outer frame as the spacer. be able to.
• the detection piece is made of quartz material, its reproducibility due to mechanical deformation with little secular change is high (hysteresis is small).
• V a diaphragm of uniform plate thickness
• the radiation with respect to the main surface of the detection piece made of quartz forms an angle other than 0 ° with respect to the quartz crystal axis Z, and the quartz plate is thinly processed by wet etching.
• the material of the detection strip can be identified to realize anisotropic etching.
• the inclined surface can be easily formed on the thin portion.
• the quartz plate constituting the detection piece has a thickness smooth mode, so thickness control becomes easy.
• the pressure sensor is a touch mode capacitive pressure sensor, it can be used in an environment where a strong pressure is applied.
• step portion can be formed by adding a metal layer on the base of the thin portion, manufacturing is easy.
• FIG. 1 is a longitudinal sectional view showing the configuration of a touch mode capacitive pressure sensor according to an embodiment of the present invention, and (a), (b) and (c) show the change of the diaphragm.
• the touch mode capacitive pressure sensor (hereinafter referred to as a pressure sensor) 1 is a minute gap between the bottom plate 2, the detection piece 10 assembled on the bottom plate 2, and the upper surface of the bottom plate 2 and the lower surface of the detection piece 10. And a joining member 20 for joining the two in a state in which the airtight space S is interposed.
• the bottom plate 2 includes a base 3 made of an insulating material such as quartz, glass, ceramic, etc., a lower electrode film 4 and a dielectric film 5 sequentially formed on the base 3.
• the detection piece 10 is made of, for example, a quartz plate, and the dielectric film 5 on the lower electrode film 4 A facing thin portion (diaphragm) 11 and a thick annular portion 12 integrally surrounding an outer periphery of the thin portion 11 are formed.
• An upper electrode film 13 is formed on the lower surface of the thin portion 11 so as to face the lower electrode film 4.
• the pressure sensor 1 is used by being fixed and disposed at a suitable position in a tire of a vehicle such as a car while being assembled to a transponder.
• the transponder has an antenna coil, operates a pressure sensor by a current induced in the antenna coil by an electromagnetic wave output from an antenna on the vehicle side, and outputs measured pressure information as an electromagnetic wave to the vehicle side.
• the air pressure in the tire is applied to the thin-walled portion 11 of the pressure sensor 1 and stagnates and deforms the thin-walled portion 11 when a pressure exceeding the pressure in the airtight space S set to the atmospheric pressure is applied.
• this pressure sensor 1 When this pressure sensor 1 is incorporated into a tire, it is mainly used to monitor the decrease in air pressure in the tire.
• the linearity of pressure sensitivity characteristics is important in order to detect in real time that the air pressure has fallen below the allowable value and to display a warning alert immediately to the driver etc.
• the bonding member 20 doubles as a bonding means and a spacer, and forms an airtight space S for obtaining a reference pressure between the lower surface of the thin portion 11 and the upper surface of the bottom plate 2.
• the characteristic configuration of the pressure sensor 1 according to the present invention is that the thickness of the thin portion 11 of the detection piece is not uniform over the entire surface and the range of the predetermined width of the one end force of the thin portion 11 is the uniform thickness region 11a.
• the range from the thick area 11a toward the other end is a thick area l ib in which the thickness of the thin portion is larger than that of the uniform thickness area.
• the thickened region l ib has a tapered cross-sectional shape with a gradually increasing thickness.
• the thickened region l ib in the pressure sensor 1 is such that the main surface on the airtight space S side is flat (parallel to the upper surface of the bottom plate), the main surface on the opposite side to the airtight space is tapered, and straight It has a steep slope. That is, from the end portion A of the uniform thickness area 11a to the other end of the thin portion In the range up to B, the plate thickness is configured to gradually increase in an inclined manner. That is, in the uniform thickness region 11a, the upper and lower main surfaces are parallel, but in the thick region l ib, the upper main surface is not parallel to the lower main surface, and is expanded in a tapered shape It extends.
• the thin-walled portion 11 may be configured to have only the thickened area l ib without providing the uniform thickness area 11a. That is, the thickness may be gradually increased in a sloped shape or stepwise increased from one end edge to the other end edge of the thin portion.
• the pressure in the outer part (inside the tire) is equal to the pressure in the airtight space S, as shown in (a)
• the thin-walled part 11 is not deformed, but in the state where the measurement pressure is low, to (b)
• the waist (shape retention force) of the uniform thickness region 11a of the thin-walled portion 11 quickly disappears and bends, and contacts with the bottom plate upper surface (dielectric film 5).
• the thickened area l ib of the thin-walled part has a sufficient stiffness, it is gradually pushed to the bottom plate side as the measurement pressure increases.
• the measurement pressure changes uniformly in the state of FIG. It is possible to control the operation of the thin-walled part more smoothly and quantitatively.
• the lower electrode film 4 provided on the upper surface of the base 3 is extended toward the outer edge of the base while the lower extraction electrode (not shown) is extended to the outer surface of the base.
• the upper electrode lead electrode (not shown) of the electrode 13 is extended to the outer edge of the detection piece. It becomes possible to calculate the external pressure based on the change of the capacitance value C between the electrode films 4 and 13 oppositely disposed through the airtight space and the dielectric film 5 by supplying electricity from both extraction electrodes. That is, the capacitance value C of the capacitor formed between the electrode films 4 and 13 is
• the capacitance value C becomes large (small).
• the capacitance value C is large (small).
• the inside of the airtight space S is set to the same pressure as the atmospheric pressure.
• the external air pressure is the same as the air pressure in the air tight space S, as shown in FIG. 1 (a)
• the air pressure in the air tight space is balanced with the outside air, so the thin portion 11 is not deformed.
• the thin portion 11 deforms and approaches (contacts) the dielectric film 5 as shown in FIGS. 1 (b) and (c).
• the thin-walled portion is deformed, and the upper electrode film 13 contacts the dielectric film 5. It is possible to sense pressure by detecting a change in contact area with the dielectric film 5 as a capacitance value.
• FIG. 2 (a) is a cross-sectional view showing another embodiment of the pressure sensor of the present invention, and this pressure sensor 1 is characterized in that the detection piece 10 does not have the thick annular portion 12. It differs from the embodiment of FIG. This embodiment is effective in thinning the pressure sensor because the maximum thickness of the detection piece 10 can be reduced.
• Fig. 2 (b) is a modification of Fig. 2 (a), and the base 3 has a recess 3a and an outer frame 3b surrounding the outer periphery of the recess, and on the inner bottom surface of the recess 3a.
• a structure in which the lower electrode film 4 and the dielectric film 5 are stacked is provided.
• the bottom surface of the detection piece 10 is supported by the upper surface of the outer frame 3 b of the base, thereby forming a minute gap between the thin portion 11 and the dielectric film 5.
• This detection piece 1 Unlike 0 in the detection piece of (a), 0 does not have a uniform thickness region, and the entire thin-walled portion is a thick region 11 b.
• FIGS. 3 (a) and 3 (b) are cross-sectional views of a pressure sensor according to another embodiment of the present invention.
• the thickened region l ib of the thin portion 11 is It has at least one step portion 15 and has a structure in which the thickness gradually increases in a step-like manner.
• the thin portion 11 when the pressure in the outside (inside the tire) is equal to the pressure in the airtight space S, the thin portion 11 is not deformed as shown in FIG. 3A, but when the measurement pressure is low. As shown in Fig. 3 (b), the uniform thickness region 1 la of the thin-walled part 11 has a stiffness (shape retention strength), it quickly bends, and contacts the upper surface of the bottom plate (dielectric film 5).
• the thickened region l ib of the thin-walled part is thicker than the uniform thickness region 11a and has a sufficient stiffness, so it is gradually pressed to the bottom plate side as the measurement pressure increases.
• the measurement pressure is constant at and after the state of (b). In this case, it is possible to control the operation of the thin portion more smoothly and quantitatively. Therefore, highly accurate pressure measurement with less error is possible.
• the thickened region l ib has a step shape having a plurality of step portions 15a and 15b, and the thickness of the step portion 15b is set to be thicker than that of the step portion 15a. Therefore, as the measurement pressure becomes higher after the stage where the uniform thickness area 11a contacts the bottom plate upper surface, it is possible to control the movement of the thin portion more smoothly and quantitatively.
• the metal film is thickened by depositing a metal film on the main surface of the thin-walled portion of uniform thickness. Let us form a region l ib.
• the state in which the crystal axis of the detection piece and the crystal axis of the base coincide with each other Preferably, the base is superimposed on the detection piece.
• quartz is a material that is physically stable compared to silicon, and has high reproducibility due to mechanical deformation with less secular change (less hysteresis). Further, according to the quartz crystal, it is easy to strictly control the thickness of the thin-walled portion as a diaphragm, and it is possible to obtain a diaphragm having a uniform thickness without a difference in thickness of the thin-walled portion for each piece.
• first thin-walled portion 11 is formed by etching on a quartz plate, and then an electrode is attached to thin-walled portion 11 to conduct electricity. Compare to the target frequency (target thickness) by measuring the frequency. If the frequency does not match the target frequency, fine etching is performed until the target frequency is reached. As a result, it is possible to obtain a thin-walled portion having a uniform thickness without a thickness difference of the thin-walled portion for each piece.
• the characteristic frequency for finely adjusting the thickness of the thin-walled portion 10a of piezoelectric material such as quartz is known as the processing technology for ultra thin plate piezoelectric vibrators by the applicant, and it is possible to apply this technology as it is. it can.
• a quartz crystal material to be used a material having a smooth surface mode, for example, an AT-cut quartz plate is preferable.
• a method by wet etching is preferred. Production is also possible by dry etching such as gas etching, but wet etching is effective when productivity is taken into consideration.
• a material having such anisotropy it is preferable to use a quartz material, in particular an AT cut quartz plate. That is, while quartz is a stable substance against temperature changes, it has anisotropy with respect to the etching rate by wet etching, so uniform thickness regions 11a and 11a as shown in FIGS.
• the thin-walled portion 11 having the thickened area l ib can be easily manufactured.
• the advantage is that the inclined surface is easily formed on the etching surface due to the anisotropy. Yes, desired An inclined surface can be obtained.
• the detection piece 10 when the detection piece 10 is also configured to have a quartz plate force, it is preferable to configure the radiation with respect to the main surface of the detection piece to have an angle other than 0 ° with respect to the crystal crystal axis Z.
• the thickness is monitored by converting it to a frequency.
• the thin-walled portion can be processed with high accuracy.
• Fig. 5 (a) and (b) show a conventional touch mode pressure sensor using a detection piece that also has a silicon force with a thin portion with uniform thickness
• Fig. 1 that uses a detection piece made of AT cut quartz. It is a figure which compares the pressure one volume characteristic of a touch mode type pressure sensor of the present invention shown. Both pressure sensors have the same ability to saturate when the capacity reaches 80 pF.
• the pressure sensor of the present invention is excellent in linearity of pressure sensitivity in the process of reaching the saturation state, and has a higher pressure side. It has the potential to measure the pressure up to.
• the pressure sensor of the prior art maintains linearity until reaching the pressure of lOkgZcm 2 while the pressure sensor of the present invention reaches a state close to saturation when the measured pressure reaches 5kg / cm 2 . . Therefore, in the present invention, the same pressure sensor can be shared for tires with different air pressures. In other words, it is not necessary to manufacture and apply different pressure sensors to tires having different air pressures.
• the pressure sensor of the present invention can be applied to pressure measurement of general fluids other than measuring the pressure change of gas in a closed space such as a tire.
• FIG. 1 (a) (b) and (c) are longitudinal sectional views showing the configuration of a touch mode capacitive pressure sensor according to an embodiment of the present invention.
• FIG. 2 (a) is a cross-sectional view showing another embodiment of the pressure sensor of the present invention
• FIG. 2 (b) is an explanatory view of a modified embodiment thereof.
• FIG. 3 (a) and (b) are cross-sectional views of a pressure sensor according to another embodiment of the present invention.
• FIG. 4 is a cross-sectional view of a pressure sensor according to another embodiment of the present invention.
• FIG. 5 (a) and (b) are diagrams comparing pressure-volume characteristics of a conventional touch mode pressure sensor and a touch mode pressure sensor of the present invention.
• FIG. 6 An explanatory view of a conventional example.
• FIG. 7 (a) and (b) are cross-sectional views for explaining the operation of a touch mode pressure sensor of a type in which the thickness of the diaphragm is uniform.

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• 2005
  • 2005-05-10 JP JP2006513032A patent/JP5217163B2/ja not_active Expired - Fee Related
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• 2011
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