JP4906422B2 - Thermal gas flow sensor and internal combustion engine controller using the same - Google Patents

Description

  The present invention relates to a thermal gas flow sensor in which a heating resistor is constituted by a semiconductor thin film.

  Thermal gas flowmeters are used as mass gas as flowmeters for intake air quantity installed in electronically controlled fuel injection devices for internal combustion engines such as automobiles, and for various gases used in semiconductor manufacturing and hydrogen / oxygen flowmeters used in fuel cells. It is mainstream because the amount can be detected directly.

  Of these, gas flowmeters manufactured by semiconductor micromachining technology have attracted attention because they can be reduced in cost and driven with low power.

  As such a conventional gas flow meter using a semiconductor substrate, for example, as described in Patent Document 1 and Patent Document 2, it has been conventionally used as a heating resistor because of the advantages of heat resistance and material cost. A material using polycrystalline silicon instead of platinum is known.

Japanese Patent No. 2880651 Japanese Patent No. 3698679

  By the way, when polysilicon, metal, or the like is used for the heating resistor, the sensor durability characteristics are affected by the change with time of the resistance value of the heating resistor or the like, so it is necessary to suppress the change with time.

Here, since the protective film that electrically insulates the resistor such as the heating resistor is manufactured by a semiconductor process in the same manner as the resistor, H ₂ O (moisture) is contained in the protective film during the film forming process. And H ₂ O is adsorbed on the protective film even after film formation.

Among the resistance value fluctuation factors such as heating resistors, water (H ₂ O), hydrogen (H ₂ ), etc. present in the protective film or attached to the outermost surface will reduce the energy during heating. Receive and dissociate. When the heating resistor is formed on the diaphragm portion, when water or hydrogen is dissociated from the protective film, the film stress changes, and the resistance value fluctuates due to the resistance piezo effect.

  For this reason, the flow rate detection accuracy of the thermal gas flow rate sensor has been lowered.

  An object of the present invention is to realize a thermal gas flow rate sensor in which a resistance value change with time of a heating resistor or a resistance temperature detector is reduced and detection accuracy is improved, and a control device for an internal combustion engine using the same. .

  The thermal gas flow sensor of the present invention has a heating resistor and a temperature detection resistor on a diaphragm formed on a substrate, and the surface of the heating resistor and the temperature detection resistor formed on the diaphragm. The surface protective film for protecting the film is an oxynitride film (SiON film) or a polysilicon film.

  Further, the control device for an internal combustion engine of the present invention includes an air flow rate measuring means for measuring an air flow rate supplied to the internal combustion engine, and a means for controlling the air flow rate based on the flow rate measured by the flow rate measuring means. The air flow rate measuring means has a heating resistor and a temperature detection resistor on the diaphragm formed on the substrate, and protects the surface of the heating resistor and the temperature detection resistor formed on the diaphragm. The surface protective film is an oxynitride film (SiON film) or a polysilicon film.

  It is possible to realize a thermal gas flow rate sensor in which resistance value changes with time of a heating resistor and a resistance temperature detector are reduced and detection accuracy is improved, and a control device for an internal combustion engine using the same.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. In addition, embodiment shown below is an example at the time of applying this invention to a thermal-type air flow sensor.

  FIG. 1 is a plan view of a detection element 1 of a thermal air flow sensor to which the first embodiment of the present invention is applied, and FIG. 2 is a cross-sectional view taken along the line AA ′ of FIG.

  1 and 2, the detection element 1 includes a protective film 30a, 30b, 31a, insulating films 31b, 30c, a heating resistor 3, and a flat substrate 32 made of a material having good thermal conductivity such as silicon or ceramic. The temperature detection resistor 4, the contact portion 33, the strength reinforcing protective film 37, and the lead-out wiring portion 34 are formed.

  Thereafter, the flat substrate 32 is etched from the back surface with an alkali etch such as KOH or TMAH solution to form a space 35 below the insulating film 30c, and a thin portion (diaphragm) 2 is formed on the flat substrate 32.

  On the surface of the thin-walled portion 2, a heating resistor 3 is formed as a heating element heated to a predetermined temperature difference from the temperature of the measured air flow, and temperature detection resistors 4, 14 are formed on both sides of the heating resistor 3 as temperature detection means. is doing. The heating resistor 3 is a resistor made of a polysilicon thin film, a platinum thin film, a molybdenum film, or the like. By utilizing the fact that the resistance value of these resistors varies depending on the temperature, the temperature detecting resistors 4, 14 are used. Detect the temperature of the place where is located.

  Wiring portions 18 to 23 and pads 8 to 13 connected to the wiring portions 18 to 23 are formed so that signal lines can be drawn from the heating resistor 3 and the temperature detection resistors 4 and 14.

  The heating resistor portion 3 and the temperature detection resistors 4 and 14 are connected to the contact portions 24 to 29 via the wiring portions 18 to 23. Then, signals can be taken out to the outside using the pads 8 to 13. The heating resistor 3 and the temperature detection resistors 4 and 14 are covered with protective films 30a, 30b, and 31a and insulating films 31b and 30c.

  The protective films 31a and 31b are formed of a dense film such as silicon nitride. Here, since the silicon nitride films of the protective films 31a and 31b are dense, water absorption and water desorption are unlikely to occur. However, the outermost protective film 30a in contact with the air flow to be measured is an insulating film such as a silicon oxide film formed by a low-pressure CVD method or a plasma method, and thus lacks denseness.

FIG. 3 is a diagram for explaining desorption of water (H ₂ O) from the protective film 30a, and FIG. 4 is a diagram for explaining desorption of water (H ₂ O) from the outermost surface of the protective film 30a. It is. As shown in FIGS. 3 and 4, when the heating resistor 3 is heated, desorption of water from the film 30 a or from the outermost film is observed.

FIG. 5 is a diagram showing the relationship between the temperature at which the protective film 30a is analyzed by TSD (degassing analysis) and the amount of water desorption. As shown in FIG. 5, it was found that a large amount of adsorbed water (H ₂ O) and contained water (H ₂ O) were detached from the protective film. In particular, with regard to adsorbed water, it has been found that a large amount of desorption is observed at 80 ° C. to 300 ° C. corresponding to the temperature during heating of the heating resistor.

The protective film 30a receives the heat energy when the heating resistor generates heat, and H ₂ O is desorbed from the protective film 30a or from the outermost surface. At this time, it has been confirmed that the energy required for desorption coincides with the activation energy value when the resistance changes with time.

In other words, the film stress of the diaphragm 2 fluctuates due to desorption of H ₂ O from the outermost surface protective film 30a when the resistance aging changes, and the resistance value of the heat generating resistor 3 fluctuates due to the resistance piezo effect. To do.

Accordingly, the protective film 30a is preferably a film made of a material that has a small content of H ₂ O and does not adsorb. Specifically, an oxynitride film (SiON film) or a polysilicon film is preferable. It is conceivable to use a silicon nitride film or the like for the protective film 30a. However, in the case of a silicon nitride film, the content of H ₂ O or the like is reduced, but it is a hard film. Will be more likely to occur.

As described above, in the thermal air flow sensor in which the heating resistor is provided in the diaphragm and the air flow rate is measured using the electric resistance value, the diaphragm outermost surface film is formed of a SiON film or a polysilicon film, thereby forming H _2. The content of O or the like can be reduced to reduce the occurrence of cracks, and resistance value fluctuations of the heating resistor and the resistance temperature detector can be reduced.

  That is, according to the first embodiment of the present invention, it is possible to realize a thermal gas flow sensor with reduced resistance value aging of the heating resistor and the resistance temperature detector and improved detection accuracy.

  FIG. 6 is a plan view of the detection element 1 of the thermal air flow sensor according to the second embodiment of the present invention. The sectional view of the detection element of the thermal air flow sensor according to the second embodiment has almost the same structure as that of the thermal air flow measuring apparatus according to the first embodiment, and the material of the protective film 30a. Is an oxynitride film (SiON film) or a polysilicon film, but in the second embodiment, slits 30d are formed in portions other than on the diaphragm 2 in order to reduce film stress.

  That is, the slits 30d are provided between the wiring parts 15 and 16, between the wiring parts 16 and 17, between the wiring parts 17 and 7, between the wiring parts 7 and 6, and between the wiring parts 6 and 5. Is formed. By forming these slits 30d, the film stress of the protective film 30a is further reduced, and the resistance value fluctuations of the heating resistor and the resistance temperature detector are reduced.

  Next, specific examples of the thermal flow sensor of the present invention including a drive circuit will be described with reference to FIGS. 7 is a plan view of the detection element 71 of the thermal flow sensor of the present invention, FIG. 8 is a cross-sectional view taken along line BB ′ of FIG. 7, and FIG. 9 is a detection of the thermal flow sensor of the present invention. FIG. 10 is a drive circuit diagram for operating the thermal flow sensor of the present invention.

  The detection element 38 of the thermal type flow measuring device of the present invention is formed as follows. That is, a silicon oxide film 74, a silicon nitride film 73, and a silicon oxide film 72 are formed on a flat substrate 75 made of a material having good thermal conductivity such as silicon or ceramic, and a polysilicon thin film is laminated thereon, By patterning the polysilicon thin film, a heating resistor 66, an intake air temperature detection resistor 68, temperature difference detection resistors 39, 40, 64, 65, and the like are formed. Then, a silicon oxide film 69, a silicon nitride film 70, and a silicon oxide film 71 are formed as a protective film, an aluminum thin film is laminated thereon, and the aluminum thin film is patterned to form wirings and pads.

  Further, by etching the flat substrate 75 from the back surface, a space is formed below the silicon oxide film 74, and a diaphragm (thin portion) 67 is formed on the flat substrate 75. The diaphragm 67 has a heating resistor 66 as a heating element heated to a predetermined temperature difference from the temperature of the measurement air flow, and temperature difference detection resistors 39, 40, 64, 65 as temperature difference detecting means on both sides of the heating resistor 66. Is forming.

  One end of the heating resistor 66 is connected to the pad 48 through the lead wire 45, the other end is connected to the fixed resistor 59, and the connection point between the heating resistor 66 and the fixed resistor 59 is connected to the pad 58. . The other end of the fixed resistor 59 is connected to the pad 58.

  The temperature difference detection resistors 39, 40, 64, 65 are connected by lead wires 41, 42, 43, 44, 60, 61, 62 to form a bridge circuit, and the temperature difference detection resistors 39, 40, 64 are connected. , 65 are connected to pads 46, 47, 49, 55, respectively. Here, since the heater temperature of the heating resistor 66 operates at a high temperature of 80 ° C. or higher, evaporation or desorption occurs when adsorbed water such as water or contained water in the film exists.

  Next, a drive circuit for operating the detection unit 38 of the present invention will be described. This drive circuit includes a differential amplifier 76 that amplifies the output voltage of a bridge circuit composed of a heating resistor 66, a fixed resistor 59, an intake air temperature detection resistor 68, and fixed resistors 63 and 58 of the detection element 38, and a temperature difference detection resistor. A differential amplifier 78 that amplifies the output voltage of the bridge circuit composed of 39, 40, 64, and 65 and outputs a sensor output, and a transistor that is controlled by the output of the differential amplifier 78 and passes a current to the heating resistor 66 77.

  This drive circuit controls the current flowing through the heating resistor 66 so that the output voltage of the bridge circuit constituted by the heating resistor 66, the fixed resistor 59, the intake air temperature detection resistor 68, and the fixed resistors 59, 58 becomes zero. .

  Here, the heating resistor 66, the intake air temperature detection resistor 68, and the fixed resistors 59 and 58 are formed of a polysilicon thin film as described above, and the resistance value of each resistor changes according to the temperature of each resistor. For this reason, the output voltage of this bridge circuit varies depending on the resistance values of the heating resistor 66, the fixed resistor 59, the intake air temperature detecting resistor 68, the fixed resistors 59 and 58 and the temperature of each resistor. Is selected so that the output of the bridge circuit becomes zero when the temperature of the heating resistor 66 and the temperature of the intake air temperature detection resistor 68 have a predetermined temperature difference.

  In this way, the drive circuit operates so that the temperature of the heating resistor 66 and the temperature of the intake air temperature detection resistor 68 have a predetermined temperature difference. Further, the temperature of both sides of the heating resistor 66 is detected by a bridge circuit constituted by the temperature difference detection resistors 39, 40, 64, 65, and the output voltage of this bridge circuit is amplified by the differential amplifier 78, whereby the air flow rate is increased. The sensor output corresponding to is obtained.

  FIG. 11 is a schematic configuration diagram of a main part of an internal combustion engine controller to which the above-described thermal air flow sensor according to the present invention is applied.

  In FIG. 11, the intake air 116 sucked from the air cleaner 100 includes a main pipe 118 provided with a thermal air flow sensor 117, an intake duct 103, a throttle body 104, and an injector (fuel injection valve) 105 to which fuel is supplied. The air is drawn into the engine cylinder 107 through the intake manifold 106. The gas 108 generated in the engine cylinder 107 is discharged to the outside through the exhaust manifold 109.

  The thermal air flow sensor 117 is installed between the air cleaner 100 in the engine room and the throttle body 104. An air flow signal output from the thermal air flow sensor 117, an intake air temperature signal, a throttle valve angle signal output from the throttle angle sensor 111, and an oxygen concentration signal output from the oximeter 112 provided in the exhaust manifold 109 The engine speed signal output from the engine speed meter 113 is transmitted to the control unit 114.

  The control unit 114 sequentially calculates the transmitted signal to obtain an optimal fuel injection amount and an idle air control valve opening, and controls the injector 105 and the idle air control valve 115 using these values.

According to the control apparatus for an internal combustion engine to which the thermal air flow sensor 117 according to the present invention is applied, the diaphragm outermost surface film of the thermal air flow sensor 117 is formed of a SiON film or a polysilicon film, so that H ₂ O or the like is formed. Therefore, the generation of cracks can be reduced, and the resistance value fluctuation of the heating resistor and the resistance temperature detector can be reduced.

  Thereby, since the flow rate detection accuracy is improved, the control accuracy of the internal combustion engine can also be improved.

  In addition, although the example mentioned above is an example at the time of applying this invention to a thermal air flow sensor, it is applicable also to the sensor which measures not only air but other gas flow rates, such as hydrogen and oxygen.

1 is a plan view of a detection element 1 of a thermal air flow sensor to which a first embodiment of the present invention is applied. It is sectional drawing along the AA 'line of FIG. It is a diagram illustrating the elimination of water (H 2 _O) from the protective film. It is a diagram illustrating the elimination of water (H 2 _O) from the outermost surface of the protective film. It is a figure which shows the relationship between the temperature which analyzed the protective film by TSD (degassing analysis) etc., and the desorption amount of water. It is a top view of the detection element of the thermal air flow rate sensor which is the 2nd Embodiment of this invention. It is a top view of the detection element of the thermal type flow sensor of the present invention. It is sectional drawing along the BB 'line of FIG. It is a top view of the part relevant to the heating resistor of the detection element of the thermal type flow measuring sensor of the present invention. It is a drive circuit diagram which operates the thermal type flow sensor of the present invention. It is a principal part schematic block diagram of the internal combustion engine control apparatus with which the thermal type air flow sensor by this invention is applied.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Detection element, 2 ... Thin part, 3 ... Heating resistor, 4 ... Temperature detection resistor, 5-7 ... Wiring part, 8-13 ... Pad part, 14 ˜17... Wiring portion, 18 to 23... Electrode lead wiring, 24 to 29... Contact portion, 30a, 30b, 31a .. protective film, 30d .. slit, 30c, 31b. Membrane, 32 ... Flat substrate, 33, 36 ... Contact part, 34 ... Lead-out wiring part, 35 ... Hollow part, 37 ... Strength reinforcing protective film, 38 ... Detection element, 39 ... Temperature difference Detection resistor, 40-45 ... lead-out wiring, 46-57 ... pad part, 58-63 ... lead-out wiring, 64, 65 ... temperature difference detection resistor, 66 ... heater resistance, 67. ..Diaphragm, 68 .. Intake air temperature detection resistance, 69, 71, 72, 74 Silicon oxide film, 70, 73 ... silicon nitride film, 75 ... flat substrate, 76, 78 ... differential amplifier, 77 ... transistor

Claims (5)

In a thermal gas flow sensor having a heating resistor and a temperature detection resistor on a diaphragm formed on a substrate,
A thermal gas flow sensor, wherein the outermost protective film of the surface protective film for protecting the surfaces of the heating resistor and the temperature detecting resistor formed on the diaphragm is a polysilicon film.   2. The thermal air flow rate measuring device according to claim 1, wherein the surface protective film covers the entire surface of the diaphragm.   3. The thermal gas flow sensor measuring apparatus according to claim 2, wherein the surface protective film covers the surface of the substrate in a larger area than the diaphragm.   4. The thermal gas flow sensor measuring device according to claim 3, wherein a slit is formed in a region of the surface protective film that is not located on the diaphragm. In a control apparatus for an internal combustion engine, comprising: an air flow rate measuring unit that measures an air flow rate supplied to the internal combustion engine; and a unit that controls the air flow rate based on the flow rate measured by the flow rate measuring unit.
The air flow rate measuring unit has a heating resistor and a temperature detection resistor on a diaphragm formed on the substrate, and protects the surface of the heating resistor and the temperature detection resistor formed on the diaphragm. The control apparatus for an internal combustion engine, wherein the outermost protective film of the surface protective film is a polysilicon film.

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