JP2014016219A - Gas flow sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas flow sensor capable of suppressing reduction in detection accuracy while suppressing adhesion of foreign matters.SOLUTION: A gas flow sensor has a protection layer 20 for suppressing adhesion of foreign matters which is formed on an outermost surface of a thin-film section 3 formed on a semiconductor substrate. The protection layer 20 is formed of any one material of chromium nitride, diamond-like carbon, and titanium nitride, or formed of a composite material including any one of them.

Description

  The present invention relates to a gas flow rate sensor that measures the flow rate and flow rate of a gas.

  In general, a gas flow rate sensor has a configuration in which a detection unit for measuring the flow rate and flow rate of a gas is provided on a diaphragm formed on a semiconductor substrate, and the detection unit is covered with an insulating layer formed of a silicon oxide film or the like. ing.

  At this time, there are many foreign substances such as dust in the flow path where the gas flow sensor is arranged, and if the foreign substances adhere to the insulating layer arranged on the outermost surface of the thin film portion, the foreign substances are There has been a problem that the heat capacity of the attached portion changes and affects the output of the sensor.

  In view of this, there has been proposed a sensor element that is provided with an anti-adhesion surface coating as a protective layer so that adhesion of foreign substances can be suppressed (see, for example, Patent Document 1).

  A gas flow sensor in which a protective layer is formed on the outermost surface of the thin film portion is also known (see, for example, Patent Document 2).

JP 2000-169795 A Special table 2009-529695

  However, in any of the above prior arts, since a layer based on a fluorine-based material is used as a protective layer in any of the above-described techniques, there is a problem that thermal conductivity is low and thermal response is poor (slow). It was. As described above, when the thermal responsiveness of the protective layer is poor, the detection unit is difficult to dissipate heat, so that the detection accuracy of the sensor may be reduced.

  Therefore, an object of the present invention is to obtain a gas flow rate sensor that can suppress the adhesion of foreign substances and can suppress the decrease in detection accuracy.

  In order to achieve the above object, according to a first aspect of the present invention, there is provided a gas flow sensor in which a protective layer that suppresses adhesion of foreign matters is formed on the outermost surface of a thin film portion formed on a semiconductor substrate. Is made of any one material of chromium nitride, diamond-like carbon and titanium nitride or a composite material containing any one material.

  A second feature of the present invention is that the thin film portion includes a detection unit that measures a flow rate and a flow rate of gas, and an insulating layer is interposed between the protective layer and the detection unit. And

  The gist of the third feature of the present invention is that the protective layer has an electrical resistivity smaller than that of the silicon oxide film.

  The gist of the fourth feature of the present invention is that the protective layer has a surface tension smaller than that of the silicon oxide film.

  The fifth feature of the present invention is summarized as that the protective layer has a friction coefficient smaller than that of the silicon oxide film.

  According to the present invention, since the protective layer is formed of a material having higher thermal conductivity than the conventional protective layer, the thermal responsiveness can be increased (accelerated), and adhesion of foreign matters can be suppressed, It is possible to obtain a gas flow sensor that can suppress a decrease in detection accuracy.

It is a top view of the gas flow sensor concerning a 1st embodiment of the present invention. It is the sectional view on the AA line of FIG. It is sectional drawing which expanded and showed the thin film part of FIG. It is the figure which showed the test result of the protective layer used for the gas flow sensor concerning 1st Embodiment of this invention. It is the figure which showed the test result of the protective layer used for the gas flow sensor concerning 2nd Embodiment of this invention. It is sectional drawing which expanded and showed the thin film part of the gas flow sensor concerning 3rd Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[First embodiment]
FIGS. 1-4 is the figure which showed the gas flow sensor 1 concerning 1st Embodiment of this invention.

  As shown in FIGS. 1-3, the gas flow sensor 1 of this embodiment is provided with the semiconductor substrate 2 in which the thin film part 3 was formed.

  The thin film portion 3 includes a diaphragm 30 formed by providing a recess 4 on one side of the semiconductor substrate 2 by etching or the like and providing a support thin film on the opening side of the recess 4. And in this embodiment, while forming the detection part 11 which measures the flow velocity and flow volume of gas in the hollow diaphragm 30, the detection part 11 is covered with the protective layer 20 from the outside. That is, the thin film portion 3 of the present embodiment includes the diaphragm 30 and the detection portion 11 and the protective layer 20 laminated on the diaphragm 30, and the protective layer 20 is formed on the outermost surface of the thin film portion 3.

  The detection part 11 is arrange | positioned at the both sides of the heater part 5 in the flow direction (left-right direction of FIG. 1) of the heater part 5 provided in the center part of the thin film part 3, and the flow path where the gas flow sensor 1 is arrange | positioned. Two thermal elements (temperature sensitive resistors) 6 and 7 are provided.

  Both end portions of the heater unit 5 are connected to electrode pads 5 a formed on the semiconductor substrate 2, while both end portions of the thermal elements 6 and 7 are electrode pads 6 a formed on the semiconductor substrate 2. , 7a. For the heater section 5 and the thermal elements 6 and 7, for example, a resistor made of platinum (Pt) can be used.

  The semiconductor substrate 2 is mounted on a circuit board 10 on which a plurality of electrode pads 8 are formed. The electrode pads 5a, 6a, 7a provided on the semiconductor substrate 2 side and the plurality of electrode pads 8 provided on the circuit board 10 side are electrically connected by wires 9 (wire bonding).

  The heater unit 5 generates heat when a current flows through the electrode pad 5a. Since the resistance values of the thermosensitive elements 6 and 7 change according to heat, it is possible to detect the distribution of heat generated by the heater unit 5 in the flow direction of the flow path via the electrode pads 6a and 7a. As described above, the detection unit 11 can measure the flow velocity and flow rate of the gas flowing through the flow path from the distribution of heat detected by the thermal elements 6 and 7.

  Here, in this embodiment, the protective layer 20 disposed on the outermost surface of the thin film portion 3 is formed of chromium nitride (CrN).

  Since chromium nitride (CrN) is a material having a higher thermal conductivity than a conventional fluorine-based material such as Teflon (registered trademark), there is an advantage that the thermal response can be further improved (accelerated). Teflon (registered trademark) has a thermal conductivity of about 0.25 W / m · k, whereas chromium nitride (CrN) has a thermal conductivity of about 9 W / m · k.

  As is clear from the test results shown in FIG. 4, chromium nitride (CrN) has an electrical resistivity compared to a silicon oxide film (SiO 2) which is the outermost surface layer of a thin film portion of a general gas flow sensor. It has a characteristic of being low (1 Ωcm or less). Therefore, there is an advantage that the amount of charge on the surface of the protective layer 20 can be made very small, and the adsorption of foreign matter due to electrostatic attraction can be suppressed.

  After the standard size dust test, 123 adhesion of dust was confirmed in the silicon oxide film (SiO2), whereas chromium nitride (CrN) had 6 adhesion of dust. Note that the scale per photo shown in FIG. 4 is about 100 microns between the left end and the right end.

  Thus, in this embodiment, since chromium nitride (CrN) was used as the protective layer 20, the adsorption | suction of the foreign material by the electrostatic attraction force of the protective layer 20 can be suppressed. Therefore, it is possible to suppress the change in the heat capacity due to the foreign matter staying, and to suppress the influence on the output of the sensor.

  As described above, according to the gas flow sensor 1 of the present embodiment, the protective layer 20 formed on the outermost surface of the thin film portion 3 is formed of chromium nitride (CrN). Therefore, it is possible to increase the heat responsiveness (accelerate) as compared with the conventional protective layer as well as to suppress the adhesion of foreign matters, and thus to easily dissipate the detection unit 11. Therefore, for example, it is possible to suppress the detection unit 11 from measuring the flow rate and the flow velocity before the distribution of heat generated by the heater unit 5 returns to the original state, and it is possible to suppress the detection accuracy from being lowered. .

  Moreover, in this embodiment, since the electrical resistivity of the protective layer 20 is smaller than that of the silicon oxide film, the amount of charge on the surface of the protective layer 20 can be reduced, and the adsorption of foreign matters due to electrostatic attraction can be suppressed. Therefore, the adhesion of foreign matter to the protective layer 20 can be reduced, and the change in the heat capacity due to the foreign matter remaining can be suppressed and the influence on the output of the sensor can be suppressed.

[Second Embodiment]
FIG. 5 is a diagram showing test results of the protective layer 20 used in the gas flow sensor 1 according to the second embodiment of the present invention.

  The main difference between the gas flow sensor 1 of the present embodiment and the gas flow sensor 1 of the first embodiment is that diamond-like carbon (DLC) is used as the material of the protective layer 20.

  Since diamond-like carbon (DLC) is a material having higher thermal conductivity than a conventional fluorine-based material, for example, Teflon (registered trademark), the thermal responsiveness is increased (accelerated) as in the first embodiment. ) Has the advantage of being able to. Therefore, the detection part 11 can be made to radiate heat easily, and it can suppress that the detection accuracy of a sensor falls. Teflon (registered trademark) has a thermal conductivity of about 0.25 W / m · k, whereas diamond-like carbon (DLC) has a thermal conductivity of about 0.5 to 40 W / m · k.

  As is clear from the test results shown in FIG. 5, diamond-like carbon (DLC: 48.2 mN / m) has a smaller surface tension than silicon oxide film (SiO2: 57.1 mN / m), and water There is a characteristic that the contact angle with respect to is large. Therefore, water droplets can be easily repelled on the surface of the protective layer 20, and there is an advantage that adsorption of foreign matters after the water droplet dropping can be reduced.

  Furthermore, diamond-like carbon (DLC) has a characteristic that the coefficient of friction is smaller (0.1 or less) than the silicon oxide film (SiO 2). Therefore, it is possible to further suppress foreign matters such as dust from adhering to the protective layer 20.

  In addition, the test result of the surface tension and the friction coefficient in this embodiment is a state in which no treatment is performed on the surface of the protective layer 20.

  Also according to this embodiment described above, the same operations and effects as those of the first embodiment can be achieved.

  Moreover, in this embodiment, since the surface tension of the protective layer 20 is smaller than that of the silicon oxide film (SiO 2), it is possible to easily repel water droplets on the surface of the protective layer 20 and to reduce the adsorption of foreign matters after the water droplets are dropped. be able to. Therefore, it is possible to suppress the adhesion of foreign matter to the protective layer 20, and it is possible to suppress the change in the heat capacity due to the foreign matter staying and to affect the output of the sensor.

  Furthermore, in this embodiment, since the friction coefficient of the protective layer 20 is also smaller than that of the silicon oxide film (SiO 2), the adhesion of foreign matters such as dust to the protective layer 20 can be further suppressed.

[Third embodiment]
FIG. 6 is a diagram showing a third embodiment of the present invention. The same components as those in the first embodiment are denoted by the same reference numerals, and redundant description is omitted.

  The main difference between the gas flow sensor 1 of the present embodiment and the gas flow sensor 1 of the first embodiment is that an insulating layer 15 is interposed between the protective layer 20 and the detection unit 11.

  That is, in the said 1st Embodiment, there exists a possibility that the insulation of the detection part 11 may fall by using the protective layer 20 formed with the material with low electrical resistivity. Therefore, in the present embodiment, the detection unit 11 is provided by interposing the insulating layer 15 formed of, for example, a silicon oxide film (SiO 2) or a silicon nitride film (SiN) between the protective layer 20 and the detection unit 11. In this way, it is possible to prevent the deterioration of the insulation property.

  Also according to this embodiment described above, the same operations and effects as those of the first embodiment can be achieved.

  In the present embodiment, the thin film portion 3 includes the detection unit 11 that measures the flow rate and flow rate of the gas, and the insulating layer 15 is interposed between the protective layer 20 and the detection unit 11. For this reason, it is possible to prevent the insulation of the detection unit 11 from being lowered, and the safety of the gas flow sensor 1 can be improved.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments, and various modifications can be made.

  For example, in the above embodiment, the protective layer is formed of chromium nitride (CrN) or diamond-like carbon (DLC), but may be formed of titanium nitride (TiN).

  Titanium nitride (TiN) is a material having a higher thermal conductivity than a conventional fluorine-based material, for example, Teflon (registered trademark), and therefore can further improve (accelerate) thermal responsiveness. Teflon (registered trademark) has a thermal conductivity of about 0.25 W / m · k, whereas titanium nitride (TiN) has a thermal conductivity of about 29 W / m · k.

  The protective layer may be formed of a composite material containing any one material of chromium nitride (CrN), diamond-like carbon (DLC), and titanium nitride (TiN).

2 Semiconductor substrate 3 Thin film part 5 Heater part 6 Thermal element 7 Thermal element 11 Detection part 15 Insulating layer 20 Protective layer

Claims (5)

In the gas flow rate sensor in which a protective layer that suppresses adhesion of foreign substances is formed on the outermost surface of the thin film portion formed on the semiconductor substrate,
A gas flow rate sensor characterized in that the protective layer is formed of any one material of chromium nitride, diamond-like carbon, and titanium nitride or a composite material containing any one material. The thin film portion includes a detection unit that measures the flow rate and flow rate of gas,
The gas flow sensor according to claim 1, wherein an insulating layer is interposed between the protective layer and the detection unit.   The gas flow rate sensor according to claim 1, wherein the protective layer has an electrical resistivity smaller than that of the silicon oxide film.   The gas flow rate sensor according to claim 1, wherein the protective layer has a surface tension smaller than that of the silicon oxide film.   The gas flow rate sensor according to claim 1, wherein the protective layer has a friction coefficient smaller than that of the silicon oxide film.