JP2006038787A - Flow sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flow sensor capable of measuring correctly flow rate of fluid flowing through conduits, which, preferably, is suitable for correct measurement of minute flow rate. <P>SOLUTION: In the flow sensor, having a base 10 and a sensor chip 100 adhered on the base, which has a concavity 100a on one side and is equipped with a heater 113 as well as an upstream-side temperature sensor 111 and a downstream-side temperature sensor 112 on the other lateral face, opposite to the concavity of the sensor chip concerned and also a first channel 11 and a second channel 12 configuring a channel of measured fluid together with the concavity of sensor chip adhered to the base, an aperture 11a at the sensor chip side of first conduit on the base is formed so as to correspond with the back side of the upstream-side temperature sensor in the concavity of the sensor chip or its vicinity. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a flow sensor for measuring a flow rate of a fluid flowing in a flow path, and particularly to a flow sensor excellent in measuring a minute flow rate.

  As a flow rate sensor for measuring the flow rate of a fluid, a thermal flow rate sensor that detects a flow rate of a fluid by detecting a change in electric power or a change in resistance due to heat deprived by the fluid is known. A flow sensor having a special structure suitable for measuring the flow rate of a corrosive fluid to be measured is also known (see, for example, Patent Document 1). As shown in FIGS. 8 and 9, the flow sensor described in Patent Document 1 includes a base 90 and a sensor chip 100 having a recess 100 a that is attached on the base and forms a part of a flow path. ing. The first flow path 91 and the second flow path 92 that form the flow path of the fluid to be measured cooperate with the recessed portion 100 a of the sensor chip 100 on the base 90 of the flow rate sensor 9, and the bottom surface of the recessed portion of the sensor chip 100. It is formed perpendicular to 100b. The sensor chip 100 is made of, for example, a stainless steel plate having a thickness of about 0.2 to 3 mm provided with a recess that forms a thin portion having a thickness of about 20 μm to 150 μm. An electrical insulating film is formed, and an upstream temperature sensor 111 and a downstream temperature sensor 112 for measuring a fluid flow rate are formed thereon, and a heater 113 is formed at a position between the temperature sensors 111 and 112. Has been. Further, electrode pads and metal thin films for wiring (not shown in FIGS. 8 and 9) are formed at appropriate positions of these temperature sensors 111 and 112 and the heater 113.

  In such a flow sensor 9, the heat generated by the heater 113 is mainly transmitted through the thin part of the sensor chip 100 and is conducted to the upstream temperature sensor formation region and the downstream temperature sensor formation region of the sensor chip 100. As the measurement fluid flows through the flow path, a temperature difference is generated between the upstream temperature sensor 111 and the downstream temperature sensor 112 according to the flow rate, and this temperature difference is taken out as output sensitivity to measure the flow rate. Yes. In addition, by using a stainless steel plate provided with a recessed portion that forms a thin portion in the sensor chip 100 and using a flow path on the opposite side of the sensor forming surface, it is long even if the fluid to be measured is a corrosive fluid. The flow rate can be measured over a period.

JP 2002-122454 A (page 3-4, FIG. 1)

  In the flow sensor described in Patent Document 1, as shown in FIGS. 8 and 9, the sensor chip side opening 91 a of the first flow path 91 is formed further upstream than the upstream temperature sensor 111 of the sensor chip 100. In addition, the sensor chip side opening 92 a of the second flow path 92 is formed further downstream of the downstream temperature sensor 112 of the sensor chip 100. Then, from the upstream side temperature sensor back side part to the downstream side temperature sensor back side part of the recessed part 100a of the sensor chip 100 forming a part of the flow path, the fluid to be measured is the bottom surface of the sensor chip recessed part (upper surface of the recessed part in the figure) 100b. (Refer to the center arrow in FIG. 8).

  However, when the fluid to be measured flows in parallel along the back side portion where the upstream temperature sensor 111 and the downstream temperature sensor 112 of the sensor chip recess portion 100a of the flow path are formed in this way, the upstream temperature sensor 111. However, the temperature of the downstream temperature sensor once rises but tends to decrease again. That is, the temperature of the upstream temperature sensor 111 is unlikely to change according to the increase or decrease of the flow rate, and the temperature of the downstream temperature sensor 112 is likely to reach a maximum temperature described later. Therefore, a temperature difference is unlikely to occur between the upstream temperature sensor 111 and the downstream temperature sensor 112. In particular, when the fluid to be measured has a very small flow rate, such a flow path structure has a problem that a temperature difference between the upstream temperature sensor 111 and the downstream temperature sensor 112 hardly occurs, and accurate flow rate measurement is difficult.

  An object of the present invention is to provide a flow sensor that accurately measures the flow rate of a fluid flowing in a flow path, and particularly suitable for accurately measuring a minute flow rate.

  In order to solve the above-mentioned problem, a flow sensor according to the present invention is a sensor chip having a base and a dent on one surface, which is attached on the base, on the side surface opposite to the dent of the sensor chip. A first flow path and a second flow path having a heater and a sensor chip including an upstream temperature sensor and a downstream temperature sensor and forming a flow path of the fluid to be measured in cooperation with the recess of the sensor chip. In the flow rate sensor in which the path is formed in the base, the sensor chip side opening of the first flow path is formed so as to correspond to the upstream side temperature sensor back side portion of the sensor chip recess or the vicinity thereof. It is characterized by.

  By forming the sensor chip side opening of the first flow path in this way, the flow of the fluid to be measured from this opening hits the upstream side temperature sensor back side portion or the vicinity thereof on the bottom surface of the sensor chip recess, and the flow rate As the temperature increases, the temperature sensor upstream of the sensor chip can be efficiently cooled. As a result, the temperature of the upstream temperature sensor changes greatly according to the increase or decrease of the flow rate. As a result, the temperature difference between the upstream temperature sensor and the downstream temperature sensor is likely to change according to the flow rate, the output sensitivity according to the flow rate is increased, and even if the flow rate is very small, the measurement according to the flow rate can be performed accurately. It becomes like this.

  According to a second aspect of the present invention, there is provided a flow rate sensor comprising a base and a sensor chip attached on the base and having a concave portion on one surface, and a heater on a side surface opposite to the concave portion of the sensor chip. And a first flow path and a second flow path that form a flow path of the fluid to be measured in cooperation with the recess portion of the sensor chip. In the flow sensor formed in the base, the upstream end surface of the sensor chip side opening of the second flow path is formed in the base so that it is upstream from the formation region of the downstream temperature sensor. It is characterized by.

  Since the sensor chip side opening of the second flow path is formed in this way, the flow velocity of the fluid to be measured is rapidly decreased in the downstream side temperature sensor back side portion of the bottom surface of the sensor chip recess and in the vicinity thereof. Even if the temperature increases, the temperature sensor on the downstream side of the sensor chip is hardly cooled. This makes it difficult for the downstream temperature sensor formation region to reach the maximum temperature, and the temperature difference between the upstream temperature sensor and the downstream temperature sensor is likely to change according to the flow rate, increasing the output sensitivity according to the flow rate, Even if the flow rate is very small, accurate flow rate measurement can be performed.

  The flow rate sensor according to claim 3 of the present invention is the flow rate sensor according to claim 1, wherein the opening area of the sensor chip side opening of the first flow path is substantially equal to the formation area of the upstream temperature sensor. It is characterized by having an equivalent or smaller size.

  With such a configuration, the fluid to be measured is ejected as a jet from the opening of the first channel toward the bottom surface of the sensor chip recess, and the bottom surface of the recess corresponding to the upstream temperature sensor of the sensor chip or its It hits the neighboring area directly. Therefore, the upstream temperature sensor of the sensor chip can be cooled more efficiently as the flow rate increases. As a result, the temperature difference between the upstream temperature sensor and the downstream temperature sensor is more likely to change according to the flow rate, increasing the output sensitivity according to the flow rate, so that even if the flow rate is very small, more accurate flow rate measurement can be performed. become.

  The flow rate sensor according to claim 4 of the present invention is the flow rate sensor according to claim 1 or 3, wherein the sensor chip side opening of the first flow path is near the bottom of the recess of the sensor chip. The protrusion part which the end surface protruded to is formed.

  The fluid to be measured flowing out from the sensor chip side opening of the first channel can be reliably applied to the bottom surface of the recess corresponding to the upstream temperature sensor of the sensor chip, and the upstream temperature sensor is reliably cooled as the flow rate increases. Will be able to.

  A flow rate sensor according to a fifth aspect of the present invention is the flow rate sensor according to any one of the first, third, and fourth aspects, wherein the first flow path is a sensor chip of the first flow path. A side opening is formed so as to form an acute angle with respect to the upstream direction of the flow path of the sensor chip recess, and the central axis of the first flow path is formed on the upstream side of the sensor chip or in the vicinity thereof It is characterized by being formed so as to intersect the region.

  Since the first flow path is formed in this way, the fluid to be measured flowing out from the sensor chip side opening of the first flow path is sprayed to the upstream side temperature sensor back side portion of the sensor chip recess or the vicinity thereof. After that, it flows smoothly downstream of the flow path without staying in the sensor chip recess. As a result, the fluid to be measured does not stay on the upstream side of the flow path in the recess of the sensor chip. As a result, the temperature difference between the upstream temperature sensor and the downstream temperature sensor is likely to change according to the flow rate, increasing the output sensitivity according to the flow rate, and enabling accurate flow measurement even at very small flow rates. .

  According to the flow rate sensor of the present invention, it is possible to accurately measure the flow rate of the fluid flowing in the flow path, and in particular, it is possible to accurately measure a minute flow rate.

  Hereinafter, a flow sensor according to an embodiment of the present invention will be described with reference to the drawings. As shown in FIGS. 1 and 2, the flow sensor 1 according to an embodiment of the present invention has a base 10 and a recess 100a that is deposited on the base by laser welding or the like and forms a part of a flow path. A sensor chip 100 is provided. The base 10 includes a first channel 11 and a second channel 12 that form a channel for the fluid to be measured in cooperation with the recess 100a of the sensor chip 100. The bottom surface 100b of the recess of the sensor chip (in FIG. 1). It is formed perpendicular to the upper surface of the recess. That is, by attaching the sensor chip 100 to the base 10, the fluid to be measured flows in the order of the first flow path 11 of the base 10, the recess 100 a of the sensor chip 100, and the second flow path 12 of the base 10. (See arrows in FIG. 1). In the present embodiment and its modifications, the fluid to be measured flowing through the flow path of the flow sensor is a gas such as a process gas used in a semiconductor manufacturing process.

  The sensor chip 100 is made of a stainless steel plate having a concave portion that forms a thin portion having a thickness of about 20 μm to 150 μm, and an electric insulating film is formed on the surface of the thin portion opposite to the flow path side. Further, an upstream temperature sensor 111 and a downstream temperature sensor 112 for flow rate measurement are formed, and a heater 113 is formed at a position sandwiched between the temperature sensors 111 and 112. In addition, electrode pads and wiring metal thin films (not shown) are formed at appropriate positions of the temperature sensors 111 and 112 and the heater 113.

  As shown in FIG. 2, the recess 100a of the sensor chip 100 has a so-called track shape in which both ends form a semicircular arc when viewed from above, and is formed by, for example, a photolithography technique, an etching technique, an end mill, or a composite technique thereof. ing. In the case of photolithography and etching techniques, first, a resist is applied to the entire back surface of a stainless steel wafer by spin coating or the like, or a dry film resist is applied, and an ultraviolet ray or electron beam is irradiated to form a mask pattern on the resist. Transfer exposure. Next, the exposed resist is developed with a developer, and unnecessary portions of the resist are removed. Then, a negative resist or a positive resist is selected depending on whether the exposed part is left or removed. The portion where the resist has been removed exposes the wafer, and the exposed portion is removed by wet etching or dry etching until the thickness reaches about 20 μm to 150 μm. Then, the remaining resist is peeled off, removed and washed to form the recess 100a. In the case of wet etching, it is immersed or sprayed in an etching solution and gradually dissolved. In the case of dry etching, it is formed by irradiating the back surface of the wafer with ions or electrons by sputtering, plasma, or the like and scraping it little by little.

On the other hand, the opposite side surface (the upper surface of the sensor chip 100 in FIG. 1) that is not in contact with the fluid to be measured of the recess 100a is mirror-polished, and an electric insulating film (not shown) is formed in a predetermined region. The electrical insulating film is formed of, for example, a thin silicon oxide (SiO ₂ ) film, silicon nitride film, alumina, polyimide film or the like having a thickness of about several thousand angstroms to several μm. The silicon oxide film is formed by, for example, sputtering, CVD, or SOG (spin on glass). The silicon nitride film is formed by sputtering, CVD, or the like.

  In addition to the upstream temperature sensor 111, the downstream temperature sensor 112, and the heater 113 including a plurality of electrode pads and a metal thin film for wiring, an ambient temperature sensor (not shown) includes a sensor device 110 on the surface of the electrical insulating film. It is formed by a well-known thin film molding technique. The sensor device 110 is formed, for example, by depositing a material such as platinum on the surface of the electrical insulating film and etching it into a predetermined pattern. In addition, the upstream temperature sensor 111, the downstream temperature sensor 112, the heater 113, and the ambient temperature sensor are electrically connected to the electrode pads through the wiring metal thin film, respectively. Although not shown in detail here, each electrode pad is an electrode of a printed wiring board provided in the vicinity of the sensor chip 100 after the periphery of the contact portion between the sensor chip 100 and the base 10 is welded with, for example, a laser. The terminal is connected via a bonding wire.

  The heater 113 is controlled to be higher by a certain temperature than the temperature detected by the ambient temperature sensor (by a known control circuit). The upstream temperature sensor 111 and the downstream temperature sensor 112 form a bridge circuit, and heat generated by the heater 113 is transmitted to the temperature sensors 111 and 112 through the thin portions of the sensor chip 100 by heat conduction, and flows into the fluid to be measured. Due to the accompanying forced convection (heat transfer), the heat balance in the temperature sensor 111, 112 is lost in the formation region of the upstream temperature sensor 111 and the formation region of the downstream temperature sensor 112, and the resistance values of the temperature sensors 111, 112 are mutually different. By changing differently, the difference in the resistance value change amount is detected as a temperature difference between the upstream temperature sensor 111 and the downstream temperature sensor 112, that is, a flow rate of the fluid to be measured.

  On the other hand, the base 10 is made of stainless steel like the sensor chip 100, and is formed of a long and rectangular plate body with a thickness of 5 mm, for example, as shown in FIGS. As described above, the first flow path 11 and the second flow path 12 that are two through holes forming a part of the flow path are formed in parallel in a direction perpendicular to the back surface 100b of the sensor chip recess. . The first flow path 11 and the second flow path 12 are formed by machining using, for example, a drill. Further, the sensor chip side opening 11a of the first flow path 11 is formed at a position corresponding to the upstream temperature sensor back side portion 101b (see FIG. 1) of the sensor chip recess 100a. And the sensor chip side opening part 11a of the 1st flow path 11 has circular shape by upper surface view (refer FIG. 2), and has the opening area containing the upstream temperature sensor 111 and its vicinity area | region. On the other hand, the sensor chip side opening 12a of the second flow path 12 has a track shape close to an ellipse in a top view, and the opening area is considerably larger than the opening area of the sensor chip side opening 11a of the first flow path 11. ing. And the upstream end surface 12b (refer FIG. 2) of the sensor chip side opening part 12a of the 2nd flow path 12 is formed in the upstream rather than the formation area of the downstream temperature sensor 112, and the sensor chip side opening part 12a The downstream end face 12c (see FIG. 2) is formed on the downstream side considerably from the formation region of the downstream temperature sensor 112. As a result, the fluid to be measured is ejected vigorously as a jet from the sensor chip side opening 11a of the first flow path 11 toward the upstream temperature sensor 111, and the jet from the sensor chip side opening 11a is recessed in the sensor chip. Is blown to the upstream temperature sensor back side portion 101b of the portion 100a or the vicinity thereof, flows along the heater back side portion 103b (see FIG. 1) of the sensor chip recess portion 100a, and a part thereof is the downstream temperature sensor back side portion 102b (FIG. 1), and the remainder flows into the second channel from the sensor chip side opening 12a of the second channel 12. As a result, the flow of the fluid to be measured becomes a slow flow in the downstream side temperature sensor back portion 102b.

  Since the sensor chip side opening 11a of the first flow path 11 is formed in this way, the upstream temperature sensor 111 is caused by the jetting action of the jet to the upstream temperature sensor 111 as the flow rate of the fluid to be measured increases. Can be cooled efficiently.

  In addition, since the sensor chip side opening 12a of the second flow path 12 is formed in this manner, the flow rate of the fluid to be measured in the downstream temperature sensor back side portion 102b of the sensor chip recess 100a is reduced, and the flow rate is reduced. Even if it increases, the downstream temperature sensor 112 becomes difficult to be cooled. As a result, the portion where the downstream temperature sensor 112 is formed is less likely to reach the maximum temperature, and the measurable flow rate range becomes wider than in the past. The maximum temperature referred to here is the following temperature, that is, the temperature of the downstream temperature sensor 112 rises as the flow rate increases, but the downstream temperature sensor 112 also increases the upstream temperature as the flow rate further increases. Similar to the sensor, it is cooled by the fluid to be measured and does not increase in temperature, but starts to decrease.

  As a result, the temperature difference between the upstream temperature sensor 111 and the downstream temperature sensor 112 is likely to change according to the flow rate, and the output sensitivity according to the flow rate is increased. Even if the flow rate is very small, accurate measurement according to the flow rate is achieved. Is possible.

  Subsequently, various modifications of the above-described embodiment will be described. First, a first modification of the above-described embodiment will be described with reference to FIG. In addition, the structure similar to embodiment mentioned above attaches | subjects a corresponding code | symbol, and abbreviate | omits detailed description.

  Unlike the above-described embodiment, the flow rate sensor 2 according to the first modified example press-fits an elongated cylindrical body 25 made of stainless steel into the first flow path 21, and the sensor chip side end of the elongated cylindrical body 25 is a sensor. A protruding portion 25a is formed by slightly protruding from the chip side opening 21a. And the front-end | tip of the protrusion part 25a is located in a slight gap, without contacting the upstream temperature sensor back side part 101b of the sensor chip | tip recessed part 100a. Instead of forming the protruding portion 25a in the first flow path 21 of the base 20 by press-fitting the elongated cylindrical body 25 to the position described above, the sensor chip side joint surface of the base 20 is formed. For example, it may be formed so as to leave only a cylindrical protrusion by machining using an end mill or the like.

  By having such a structure, the jet flow flowing out from the first flow path 21 can be efficiently blown to the upstream side temperature sensor back side portion 101b of the sensor chip recess 100a, and the upstream side temperature sensor is increased according to the increase in the flow rate. 111 can be cooled effectively. As a result, the temperature difference between the upstream temperature sensor 111 and the downstream temperature sensor 112 can be increased in accordance with the increase in the flow rate, thereby enabling accurate flow measurement even at a very small flow rate.

  Next, a second modification of the present embodiment described above will be described with reference to FIG. In the flow rate sensor 3 according to the second modified example, the first flow path 31 forms an acute angle with respect to the upstream direction of the flow path of the sensor chip recess 100a toward the upstream side of the opening 31a of the first flow path 31. 4 (see angle α, which is an acute angle smaller than 90 ° in FIG. 4), and the central axis of the first flow path 31 is the formation position of the upstream temperature sensor 111 of the sensor chip 100 (upstream temperature sensor back side portion) 101b) (see the central axis CL in FIG. 4).

  By forming the first flow path 31 in this way, the fluid to be measured flowing out from the sensor chip side opening 31a of the first flow path 31 hits the upstream temperature sensor back side portion 101b of the bottom surface 100b of the sensor chip recess. After that, it flows smoothly downstream without staying there. As a result, the fluid to be measured does not stay on the upstream side of the recess 100a of the sensor chip. As a result, the temperature difference between the upstream temperature sensor 111 and the downstream temperature sensor 112 is likely to change according to the flow rate, and the output sensitivity according to the flow rate is enhanced, so that accurate flow measurement can be performed even with a minute flow rate. become.

  Then, the 3rd modification of embodiment mentioned above is demonstrated based on FIG. In the flow rate sensor 4 according to the third modified example, the second flow path 42 formed in the base 40 is formed so as to extend along the bottom surface 100b of the recessed portion of the sensor chip 100 unlike the above-described embodiment and the modified example. Has been. And by providing the step part 42s between the downstream temperature sensor 112 and the heater 113, the flow path cross-sectional area of this 2nd flow path 42 is rapidly increased downstream from the step part 42s. As a result, even if the fluid to be measured has the same flow rate, the flow velocity rapidly decreases downstream from this step portion, and the flow velocity of the fluid to be measured in the downstream temperature sensor back side portion 102b of the bottom surface 100b of the sensor chip recess also decreases. In addition, the downstream temperature sensor 112 is less likely to be cooled. In addition, the first channel 41 of the base 40 is formed so that the opening area of the sensor chip side opening 41a is substantially the same as the formation area of the upstream temperature sensor 111, as in the above-described embodiment. The fluid to be measured flowing out from the sensor chip side opening 41a of the first flow path 41 is jetted and sprayed to the upstream temperature sensor back side portion 101b of the bottom surface 100b of the sensor chip recess, thereby effectively cooling the upstream temperature sensor 111. be able to. These make it difficult for the downstream temperature sensor 112 to reach the maximum temperature, and the temperature difference between the upstream temperature sensor 111 and the downstream temperature sensor 112 easily changes according to the flow rate, and the output sensitivity according to the flow rate. This makes it possible to accurately measure the flow rate even at a minute flow rate.

  Since the evaluation test simulation for comparing the flow rate detection characteristics of the flow rate sensor 1 according to the embodiment shown in FIG. 1 and the flow rate sensor described as the conventional example was performed, the simulation result will be described. FIG. 6 is a flow rate detection characteristic diagram showing the simulation results. In this detection characteristic diagram, the horizontal axis indicates the flow rate flowing through the flow path of each flow sensor, and the vertical axis indicates the measured temperature and upstream temperature of the downstream temperature sensor. The temperature difference of the measured temperature of the sensor is shown. In addition, it shows that the detection sensitivity according to the increase / decrease in flow volume is excellent, so that this temperature difference is large in the whole flow area.

  As is apparent from the simulation results, it was found that the flow rate sensor according to the present embodiment has a detection sensitivity that is twice or more higher in all flow ranges than the conventional flow rate sensor. The detection sensitivity differs greatly between the two, especially at a very small flow rate. When the fluid to be measured has a very small flow rate, it can be seen that the flow sensor in this embodiment can be used for extremely high sensitivity measurement. It was.

  In the above-described embodiment and its modification, the sensor chip side opening area of the first flow path is slightly larger than the formation area of the upstream side temperature sensor of the sensor chip. Without limitation, the sensor chip side opening area of the first flow path may have, for example, an opening area equivalent to the formation area of the upstream temperature sensor, or the upstream temperature of the sensor chip 100 as shown in FIG. It may be large enough to include the sensor 111 and its vicinity. Even in such a configuration, the fluid to be measured flowing out from the sensor chip side opening 51a of the first flow channel 51 is sprayed to the upstream temperature sensor back side portion 101b of the sensor chip recess portion 100a and the vicinity thereof, as shown in FIG. And it becomes possible to cool the upstream temperature sensor 111 more than the conventional flow sensor 9 shown in FIG. As a result, a temperature difference between the upstream temperature sensor 111 and the downstream temperature sensor 112 can be sufficiently generated in any flow rate range, and accurate flow rate measurement is possible.

  In the configuration shown in FIG. 7, the first flow path 51 and the second flow path 52 are formed symmetrically in the drawing with respect to the heater forming portion of the sensor chip 100. Further, the upstream temperature sensor 111 and the downstream temperature sensor 112 on the sensor chip are also formed symmetrically with respect to the heater forming portion of the sensor chip 100 in the drawing. By having such a symmetric structure, even when the fluid under measurement flows backward (when the fluid under measurement flows from the opposite direction of the arrow in the figure), the flow rate of the fluid under measurement flowing back can be measured. .

  As described above, the basic principle of the flow sensor according to the present invention is that the flow of the fluid to be measured is positively applied to the bottom surface of the sensor chip recess corresponding to the upstream temperature sensor formation region of the sensor chip, and the downstream temperature sensor This is because the flow velocity is lowered at the bottom surface of the sensor chip recess corresponding to the formation region. In addition, by changing the cross-sectional area of the flow path of the base, the flow rate of the fluid to be measured corresponding to the upstream side temperature sensor back side portion of the sensor chip recess is made higher than the flow rate of the downstream temperature sensor back side portion of the sensor chip recess. Thus, the forced convection transmission in the upstream temperature sensor increases as the flow velocity in the upstream temperature sensor increases, and the forced convection transmission in the downstream temperature sensor decreases as the flow velocity in the downstream temperature sensor decreases.

  As a result, the upstream temperature sensor is easily cooled, the downstream temperature sensor is less likely to be cooled, the downstream temperature sensor formation region is less likely to reach the maximum temperature, and the flow rate between the upstream temperature sensor and the downstream temperature sensor is low. The detected temperature difference according to the value can be increased.

  Further, as a modification, a sensor chip having a hollow part forming a thin part is provided with a heater or a temperature sensor, and the sensor chip side opening of the base so that the fluid to be measured having a high flow rate directly hits the upstream temperature sensor The opening was arranged so as to correspond to the upstream side temperature sensor back side portion of the sensor chip recess.

  Further, as a further modification, in order to apply the fluid to be measured to the upstream side temperature sensor back side portion of the sensor chip recess, a protruding portion is provided at the sensor chip side opening of the first flow path of the base, and the fluid to be measured flows out. The heat transfer by forced convection of the upstream temperature sensor is promoted by making the part closer to the temperature sensor.

  Further, the flow rate of the fluid to be measured in the vicinity of the downstream temperature sensor is lowered by changing the flow channel structure of the second flow channel that is the downstream flow channel of the base.

  These modifications also promote heat transfer by forced convection in the upstream temperature sensor backside portion of the sensor chip recess, and reduce heat transfer by forced convection in the downstream temperature sensor backside portion of the sensor chip recess, The output sensitivity can be improved by increasing the temperature difference with respect to the flow rate change between the upstream temperature sensor and the downstream temperature sensor.

  In the above-described embodiment and the first and third modifications thereof, the first flow path is configured to be generally reduced as compared with the sensor chip recess and the second flow path. Instead of restricting the first flow path as a whole in this way, only the outlet that is the sensor chip side opening may be restricted. In any way, it is possible to spray a jet on the upstream side temperature sensor rear side portion of the sensor chip recess and the vicinity thereof.

  The material of the base and the sensor chip is not limited to stainless steel, and any material such as a corrosion-resistant material such as sapphire or ceramics, or silicon or glass may be used if the fluid is non-corrosive.

  The heater (heat generating part) formed on the sensor chip is not limited to a metal thin film resistor such as a platinum thin film part, and any element capable of generating heat such as polysilicon or thermistor may be used. Absent. Also, the temperature sensors that form the upstream temperature sensor, downstream temperature sensor, and ambient temperature sensor are not limited to platinum thin film resistors, but include polysilicon, thermistors, thermopiles, and surface acoustic wave devices. Any temperature sensor that can output temperature information electrically can be used.

  Further, the heater and the temperature sensor formed on the sensor chip may be a two-element type instead of the three-element type as described above. Specifically, as described above, the heater may be formed independently as a three-element type between the upstream temperature sensor and the downstream temperature sensor, and each of the two temperature sensors may self-heat as a heater 2. It may be formed as an element type.

  In addition, the shape of the recess of the sensor chip may be an elongated rectangular shape, or may be a deformed elliptical shape having a semicircular shape at both ends, which is called a track shape as described above.

  Moreover, although the fluid to be measured has been described as a gas in the above-described embodiment and its modifications, the fluid to be measured is not necessarily limited to this and may be a liquid. Even if the fluid to be measured is a liquid, the liquid can be sufficiently cooled by positively applying the liquid to the upstream side temperature sensor back side part of the sensor chip recess part and the vicinity thereof, and the second of the base By devising the shape and arrangement of the flow path, the downstream side temperature sensor back portion of the sensor chip recess can be hardly cooled, and the above-described effects of the present invention can be sufficiently exhibited.

  As described above, the flow sensor according to the present embodiment is excellent in measuring minute flow rates, but is not necessarily limited to this, and can measure flow rates in various flow ranges. Moreover, although it is suitable for the flow measurement of corrosive fluid because of its structure, it is not necessarily limited to such fluid flow measurement.

It is a fragmentary sectional view of the flow sensor concerning one embodiment of the present invention. It is the top view which looked at the flow sensor shown in FIG. 1 from the sensor chip upper surface side. It is a fragmentary sectional view showing the 1st modification of the flow rate sensor shown in Drawing 1. It is a fragmentary sectional view showing the 2nd modification of a flow sensor shown in Drawing 1. It is a fragmentary sectional view showing the 3rd modification of a flow sensor shown in Drawing 1. In the Example of this invention, it is a flow rate detection characteristic view which compared the detection characteristic of the flow sensor of this embodiment with the conventional flow sensor by simulation. It is a fragmentary sectional view of the flow sensor included in the scope of the present invention. It is the fragmentary sectional view which showed the conventional flow sensor. It is the top view which looked at the conventional flow sensor shown in FIG. 8 from the sensor chip upper surface side.

Explanation of symbols

1, 2, 3, 4 Flow rate sensor 9 Flow rate sensor 10 Base 11 First flow path 11a Sensor chip side opening 12 Second flow path 12a Sensor chip side opening 12b Upstream end face 12c Downstream end face 20 Base 21 First flow Path 21a Sensor chip side opening 25 Elongated cylindrical body 25a Protruding part 31 First flow path 31a Opening 40 Base 41 First flow path 41a Sensor chip side opening 42 Second flow path 42s Step section 51 First flow path 51a Sensor Chip side opening 52 Second flow path 52a Sensor chip side opening 90 Base 91 First flow path 91a Sensor chip side opening 92 Second flow path 92a Sensor chip side opening 100 Sensor chip 100a (sensor chip) recess 100b (Sensor chip) Recessed portion bottom surface 101b Upstream temperature sensor backside portion 102b Downstream temperature Capacitors rear portion 103b heater rear portion 110 sensor device 111 upstream temperature sensor 112 downstream temperature sensor 113 heater

Claims (5)

Base and
A sensor chip deposited on the base and having a recess on one surface, the sensor chip including a heater on the opposite side of the sensor chip from the recess and an upstream temperature sensor and a downstream temperature sensor; Have
In the flow sensor in which the first flow path and the second flow path that form the flow path of the fluid to be measured in cooperation with the recess of the sensor chip are formed in the base,
The flow rate sensor, wherein the sensor chip side opening of the first flow path is formed to correspond to the upstream side temperature sensor back side portion of the sensor chip recess or the vicinity thereof. Base and
A sensor chip deposited on the base and having a recess on one surface, the sensor chip including a heater on the opposite side of the sensor chip from the recess and an upstream temperature sensor and a downstream temperature sensor; Have
In the flow sensor in which the first flow path and the second flow path that form the flow path of the fluid to be measured in cooperation with the recess of the sensor chip are formed in the base,
The flow rate sensor according to claim 1, wherein the upstream end surface of the sensor chip side opening of the second flow path is formed on the base so as to be on the upstream side of the formation region of the downstream temperature sensor.   2. The flow sensor according to claim 1, wherein an opening area of the sensor chip side opening of the first flow path is approximately equal to or smaller than a formation area of the upstream temperature sensor.   4. The flow rate according to claim 1, wherein a projecting portion whose end surface protrudes to the vicinity of the bottom surface of the recess of the sensor chip is formed in the sensor chip side opening of the first flow path. Sensor. The first flow path is formed so as to form an acute angle from the sensor chip side opening of the first flow path to the flow path upstream direction of the recess of the sensor chip, and the central axis of the first flow path 5. The flow rate sensor according to claim 1, wherein the flow rate sensor is formed so as to intersect with a formation surface of the upstream side temperature sensor of the sensor chip or a region in the vicinity thereof. .

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