JPH04230808A - Diaphragm sensor - Google Patents

Abstract

PURPOSE:To reduce the heat conduction from a heating part to a thermometric resistor and to prevent the adhesion of dust to the utmost by forming a slit part between the heating part and the thermometric resistor along the longitudinal direction thereof. CONSTITUTION:A thin-walled diaphragm part 23 is formed to the surface of a semiconductor substrate 21 and a heater 7 is formed thereon and thermometric resistors 8, 9 are formed on both sides of the heater 7 and, further, slit parts 24l, 24r are provided on both sides of the heater 7. Since the heat conduction from the heater 7 to the resistors 8, 9 through the member of the diaphragm part 23 is reduced by this constitution, the temp. rise of the resistors 8, 9 becomes low as compared with conventional resistors. Therefore, the output error due to the adhesion of dust becoming large in proportion to the temps. of the resistors 8, 9 and the output error due to the drift of the TCR mismatching between the upstream resistor 8 and the downstream resistor 9 becomes small. Further, since air does not enter the space part under the diaphragm part 23 and flows along the surface of the diaphragm part, the adhesion of dust becomes min.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diaphragm sensor used as a flow rate detection element.

0002

2. Description of the Related Art FIG. 5 is a perspective view showing an example of a conventional microbridge type flow sensor for detecting the flow velocity of a fluid. In the figure, 1 is a semiconductor substrate made of silicon, and in the center of this semiconductor substrate 1, a through hole, that is, a cavity 4, which communicates openings 2 and 3 on both sides is formed by anisotropic etching. A bridge portion 5 is formed above this gap portion, which is spatially isolated from the semiconductor substrate 1 in a bridge shape and is thermally insulated from the semiconductor substrate 1 as a result. On the surface of this bridging portion 5, a thin film heater element 7 and thin film temperature sensing resistance elements 8, 9 sandwiching the heater element 7 are arranged and formed using a normal thin film forming technique. Also,
A thin film resistance temperature measuring element 1 is mounted on the corner of the semiconductor substrate 1.
0 is formed. Note that 11 is a slit-shaped central opening formed in the center of each opening 2 and 3 on the semiconductor substrate 1, and the silicon portion exposed by these openings 2 and 3 and the central opening 11 is filled with a solution such as KOH. By performing anisotropic etching, a cavity 4 having an etched cross-sectional shape of an inverted trapezoid is formed, and the heater element 7 and the temperature sensing resistance elements 8 and 9 are thermally insulated from the semiconductor substrate 1 by the cavity 4. A supported bridge portion 5 is formed.

FIGS. 6(a) and 6(b) are explanatory diagrams showing the operation of the microbridge type flow sensor shown in FIG. 5. FIG. 6(a) shows the temperature distribution of each element, and FIG.
shows a cross section taken along line B-B' in FIG. In addition, in the figure, 6
is a protective film for protecting elements such as the heater element 7 formed on the semiconductor substrate 1, and is made of a material such as silicon nitride having low thermal conductivity.

[0004] Here, when the heater element 7 is controlled at a certain higher temperature th than the ambient temperature (for example, 63°C: ambient temperature reference), the temperatures t3 and t4 of the resistance temperature sensing elements 8 and 9 (for example, 35°C: (ambient temperature reference) are approximately equal as shown in FIG. 6(a). At this time, when the gas moves in the direction of the arrow 12 as shown in FIG. 5, for example, the upstream temperature measuring resistance element 8 is cooled and its temperature decreases by ΔT3. On the other hand, the temperature of the temperature measuring resistance element 9 on the downstream side increases by ΔT4. As a result, a temperature difference occurs between the upstream temperature measuring resistance element 8 and the downstream temperature measuring resistance element 9. Therefore, by incorporating the temperature measuring resistance elements 8 and 9 into a Wheatstone bridge circuit and converting the temperature difference into voltage, a voltage output corresponding to the gas flow rate can be obtained, and as a result, the gas flow rate can be detected. can do.

As described above, the conventional microbridge type flow sensor has a thin film bridge structure with extremely low heat capacity formed by thin film technology and anisotropic etching technology, and has an extremely fast response speed, high sensitivity, and low heat capacity. It has excellent advantages such as low power consumption and good mass production.

[0006]

[Problems to be Solved by the Invention] However, in the conventional microbridge type flow sensor, when a part of the semiconductor substrate 1 is removed by anisotropic etching to form the cavity 4, it is particularly difficult to The openings 2 and 3 on both the left and right sides were relatively large. For this reason, the gas flow also enters the cavity 4, and dirt (dust) contained in the gas may adhere to the periphery of the openings 2 and 3 or enter the cavity 4. There was a problem in that the sensor characteristics were adversely affected. Further, there was a problem in that low flow velocity (low flow rate) measurements could not be performed accurately and stably.

[0007]

[Means for Solving the Problems] In order to solve such problems, a first diaphragm sensor according to the present invention includes a diaphragm portion formed in a thin shape on a part of a substrate, and a diaphragm portion formed on this diaphragm portion. It is composed of a heat generating part, a temperature measuring resistor part formed on both sides of the heat generating part, and a slit part formed along the longitudinal direction between the heat generating part and the temperature measuring resistor part. be. Further, the second diaphragm sensor according to the present invention has a slit section provided at the longitudinal end of the heat generating section in addition to the first diaphragm sensor. Moreover, the third diaphragm sensor according to the present invention includes:
In addition to the first diaphragm sensor or the second diaphragm sensor, a slit portion is provided on the outer periphery of the temperature measuring resistor portion.

[0008]

[Operation] The first diaphragm sensor in the present invention has the following features:
By arranging the resistance temperature detectors symmetrically on both sides with the heat generating part in between, and by providing a slit section along the longitudinal direction between the heat generating part and the resistance temperature detector, the resistance temperature detectors on both sides can be connected to the heat generating part. Heat conduction through the diaphragm member to the body is reduced. Moreover, the second diaphragm sensor in the present invention is
By providing the slit portion at the longitudinal end of the heat generating portion, heat conduction from the heat generating portion to the thick portion of the substrate through the diaphragm member is reduced. Further, in the third diaphragm sensor of the present invention, by providing the slit portion on the outer circumferential portion of the temperature-measuring resistor portion, heat conduction through the diaphragm member to the thick portion of the substrate of the temperature-measuring resistor portion is reduced.

[0009]

Embodiments Hereinafter, embodiments of the present invention will be explained in detail with reference to the drawings. FIG. 1 is a diagram showing the configuration of an embodiment of a diaphragm sensor according to the present invention. FIG. 1(a) is a plan view of the main part seen from above, and FIG. FIG. In the figure, reference numeral 21 denotes a semiconductor substrate made of silicon, for example, and this semiconductor substrate 21
An opening 22 with a trapezoidal cross section that does not communicate with the front surface side is formed in the central part of the back side of the semiconductor substrate 21 by, for example, anisotropic etching. A diaphragm portion 23 is integrally formed. Furthermore, a thin film heater element 7 is formed at the center of the surface of the diaphragm portion 23 using a normal thin film forming technique. Furthermore, this heater element 7
Thin film resistance temperature measuring elements 8 and 9 are symmetrically arranged and formed on both sides of the sensor by a conventional thin film forming technique at a predetermined distance apart. Furthermore, band-shaped slits 24l and 24r are provided between the heater element 7 and the temperature-measuring resistance elements 8 and 9 on both sides of the heater element 7, passing through the thin wall portion of the diaphragm portion 23 along its longitudinal direction. Furthermore, slit portions 25l and 25r, which are formed by intermittently connecting a plurality of square holes passing through the thin wall portion of the diaphragm portion 23, are bored on the outside of the temperature sensing resistance elements 8 and 9 on both sides along the longitudinal direction. . Similarly, slits 24u and 24d passing through the thin wall portion of the diaphragm portion 23 are formed on both ends of the heater element 7 in the longitudinal direction. Slit portions 25u and 25d passing through the thin wall portion of the diaphragm portion 23 are also provided in the diaphragm portion 23. In addition, these slit parts 24l, 24r, 24u, 24d, 25l, 25
r, 25u, and 25d can be easily formed by ordinary photolithography and wet or dry etching techniques.

According to such a configuration, the semiconductor substrate 21
A thin diaphragm part 23 is formed on the surface of the diaphragm part 23, and a heater element 7 and temperature measuring resistance elements 8 and 9 are formed and arranged symmetrically on both sides of the heater element 7 on both sides of the heater element 7. Slit portions 24l, 2 are provided along the longitudinal direction on both sides of the
By providing 4r, heat conduction from the heater element 7 to the temperature-measuring resistance elements 8 and 9 through the members of the diaphragm section 23 is extremely reduced.
, 9 is lower than that of the conventional method. Therefore, the output error due to adhesion of dust increases in proportion to the temperature of the resistance temperature measurement elements 8 and 9, and the TCR between the upstream resistance temperature measurement element 8 and the downstream temperature measurement resistance element 9 increases in proportion to the temperature. Output errors due to mismatch drift are reduced. Particularly in the case of a gas with low thermal conductivity, the temperature of the element resistance of the temperature measuring resistance elements 8 and 9 can be set lower. In addition, since there is no excess heat supplied from the heater element 7, which operates to reduce the temperature difference formed by the gas flow between the resistance temperature measurement element 8 and the resistance temperature measurement element 9, in the low flow velocity region, The sensitivity can also be improved. Further, although the heater element 7 is slightly thermally deformed when energized, the influence (stress) is not transmitted to the temperature measuring resistance elements 8 and 9, and the cause of errors can be significantly reduced. Further, slit portions 25l, 25r, 25u, 2 are provided on the outside of the temperature sensing resistance elements 8, 9, respectively.
By providing 5d, these slit parts 25l,
The thermal insulation between the thick portions of the semiconductor substrate 21 on the outside of 25r, 25u, and 25d is extremely good, and the sensitivity can be improved. Furthermore, slit portions 24u, 24d and slit portions 25u, 2 are provided along the width direction on both end sides of the heater element 7 and the resistance temperature sensing elements 8, 9, respectively.
5d provides extremely good thermal insulation between the heater element 7 and the thick portion of the semiconductor substrate 21, reducing the power consumption of the heater element 7. Thermal insulation between the thick wall portion and the thick portion is extremely good, and the sensitivity can be improved.

FIG. 2 shows the resistance value characteristics of the temperature measuring resistor in the diaphragm sensor, and FIG.
Heater element 7 and resistance temperature measuring elements 8 and 9 shown in
Resistance values of the resistance temperature measurement elements 8 and 9 when the heater current is increased in a structure in which the heater element 7 and the resistance temperature measurement elements 8 and 9 are partially separated by a slit Figure (b) shows the change when the heater current is increased in the structure according to this embodiment in which slits 24l and 24r are provided between the heater element 7 and the resistance temperature sensing elements 8 and 9 to completely separate them. It shows the resistance value change of the temperature measuring resistance elements 8 and 9. As the current applied to the heater element 7 increases, the resistance values of the resistance temperature measurement elements 8 and 9 increase;
In a structure in which the diaphragm 23 is not separated from the diaphragm 23 or is partially separated by a slit, as the heater current increases, mechanical deformation of the diaphragm 23 due to the generated heat is transmitted to the temperature sensing resistance elements 8 and 9. ), when a certain limit point P is exceeded, mechanical distortion is also given to the resistance temperature measurement elements 8 and 9, giving an error to the resistance values of the resistance temperature measurement elements 8 and 9, and furthermore, when this limit point P is exceeded, The position of the resistance value and the resistance value characteristics above the limit point P are not constant, and there is some deviation in the degree of this effect between the temperature measuring resistance elements 8 and 9 on both sides of the heater element 7. The balance between the resistance elements 8 and 9 is unstable, that is, the zero point is not stable. In actual usage conditions, when the heater current necessary to obtain the required sensitivity is applied, this limit point is often exceeded, and especially in intermittent drive, the zero point fluctuates each time, making it difficult to make accurate measurements. I can't. Therefore, the condition is that it is used below the limit point P, which is not affected by mechanical distortion. On the other hand, in the structure according to this embodiment in which the heater element 7 is completely separated by the slit parts 24l and 24r,
As the heater current increases, mechanical deformation of the diaphragm portion 23 due to the generated heat is not transmitted to the temperature measuring resistance elements 8, 9, so that stable resistance value characteristics can be obtained. Therefore, with a structure in which the slit parts 24l and 24r are completely separated, more stable measurement becomes possible, and in particular, the stability of the zero point can be greatly improved.

FIG. 3 is a diagram showing the configuration of another embodiment of the diaphragm sensor according to the present invention, in which FIG. 3(a) is a plan view of the main part seen from above, and FIG. It is a cross-sectional view along a line, and the same parts as in the previous figure are given the same reference numerals. In the figure, the difference from FIG. 1 is that the semiconductor substrate 21
The heater element 7, the temperature-measuring resistance element 8, the temperature-measuring resistance element 9, and their slit portions 24l, 24r, 2 are arranged so that the gas flow direction 12 is set on the opposite sides of the
It is constructed by arranging 4u, 24d, 25l, 25r, 25u, and 25d.

[0013] Even in such a configuration, effects exactly similar to those described above can be obtained. Note that the diaphragm portion 23 may be formed in either a square or rectangular shape.

In the above embodiment, etching was performed from the back side of the semiconductor substrate 21 to form the opening 22. For example, FIGS. 4(a) and 4(b) show a diagram corresponding to FIG. As shown in , a plurality of slits 31 are formed in the diaphragm portion 23 , and each of these slits 31 is used to perform anisotropic etching or isotropic etching from the top surface using the etching characteristics of the crystal axis. A hollow space 31 may be formed below.

Furthermore, in the above-mentioned embodiments, the case where a semiconductor substrate made of silicon, for example, was used as the substrate was explained, but the present invention is not limited to this, and for example, a metal substrate such as aluminum or stainless steel may be used. The diaphragm part is made of SiO2, Si3, etc.
It goes without saying that the same effect can be obtained by forming an insulating film such as N4.

In addition, in the above-mentioned embodiments, the case where anisotropic etching was used to form the diaphragm portion was explained, but it is also possible to use an etching method such as isotropic etching using a mixed solution of hydrofluoric acid and nitric acid. Needless to say, it can be formed in the same way.

Furthermore, the method for forming the diaphragm part is not limited to etching, but can also be formed by machining with an end mill or laser, or the substrate and diaphragm part may be manufactured separately and then bonded together. Of course, it can be formed.

[0018]

As described above, according to the diaphragm sensor according to the present invention, a thin diaphragm portion is provided on a part of the substrate, and the diaphragm portion has a heat generating portion and a temperature measuring resistor portion on both sides of the heat generating portion. By providing a In addition, thermal insulation from the substrate becomes extremely good, and flow rate detection with high sensitivity and low power consumption becomes possible. In addition, by providing a slit section along the longitudinal direction between the heat generating section and the temperature measuring resistor section, heat conduction from the heat generating section to the temperature measuring resistor section through the members of the diaphragm section becomes extremely small. , the temperature rise in the RTD part due to the heat generated by the heat generating part is lower than before, and the output error due to dust adhesion increases in proportion to the temperature of the RTD part, and increases in proportion to the temperature. It is possible to reduce the output error due to TCR mismatch drift between the temperature-measuring resistor parts, and especially in the case of gases with low thermal conductivity, the temperature of the temperature-measuring resistor part can be set lower, and furthermore, the excess heat is supplied from the heat-generating part. Since the flow rate is eliminated, the sensitivity in the low flow rate region can be improved. Further, although the heat generating part deforms slightly when energized, the stress caused by this deformation is not transmitted to the temperature measuring resistor part, so the causes of errors can be significantly reduced. Further, by providing the slit portion at the longitudinal end of the heat generating portion, thermal insulation between the heat generating portion and the thick portion of the substrate becomes extremely good, and power consumption of the heat generating portion is reduced. Further, by providing the slit portion on the outer circumference of the temperature-measuring resistance portion, thermal insulation from the thick portion of the substrate becomes extremely good, and sensitivity can be improved. In addition, unlike conventional bridge structures, diaphragm structures in which all end faces are fixed by thick substrates may crack if there is a lot of residual stress when forming the diaphragm part, but the slit part By providing this, an extremely excellent effect can be obtained in that stress can be dispersed and a highly reliable diaphragm sensor can be formed.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an embodiment of a diaphragm sensor according to the present invention.

FIG. 2 is a diagram illustrating resistance value characteristics of a temperature-measuring resistor portion of a diaphragm sensor according to the present invention.

FIG. 3 is a diagram showing the configuration of another embodiment of the diaphragm sensor according to the present invention.

FIG. 4 is a diagram showing a configuration according to still another embodiment of the diaphragm sensor according to the present invention.

FIG. 5 is a diagram showing the configuration of a conventional microbridge type flow sensor.

FIG. 6 is a diagram illustrating the operation of a microbridge type flow sensor.

[Explanation of symbols]

7 Heater element 8. Temperature measuring resistance element 9 Temperature measuring resistance element 21 Semiconductor substrate 22 Opening 23 Diaphragm part 24l Slit part 24r Slit part 24u Slit part 24d Slit part 25l Slit part 25r Slit part 25u Slit part 25d Slit part 31 Slit 32 Space part

Claims (3)

[Claims] 1. A diaphragm section formed thin with a space provided in a part of a substrate, a heat generating section formed in the diaphragm section, and a temperature measuring resistor section formed on both sides of the heat generating section. A diaphragm sensor comprising: a slit portion formed along the longitudinal direction between the heat generating portion and the temperature measuring resistor portions on both sides. 2. The diaphragm sensor according to claim 1, wherein a slit portion is provided at a longitudinal end of the heat generating portion. 3. The diaphragm sensor according to claim 1, wherein a slit portion is provided at an outer peripheral portion of the temperature measuring resistor portion.