DE102008021896B4 - Device for determining a measured variable of a gas - Google Patents

Abstract

Apparatus for determining a measured quantity of a gas with a substrate (5) and a thermal sensor element (8) thermally connected to the substrate (5), wherein a heat transfer surface (13) of the thermal sensor element (8) for transferring the heat of the thermal sensor element (8) on the substrate (5) is smaller than an area extent (14) of the thermal sensor element (8) along the substrate (5), and wherein the thermal sensor element (8) along its surface extent (14) at least partially from the substrate (5 ) is spaced and the substrate (5) with its heat transfer surface (13) touched, characterized in that the thermal sensor element (8) on its the substrate (5) facing side (18) in the region of its heat transfer surface (13) a plurality of integral with The sensor element (8) formed heat transfer elements (19) extending between recesses (20) and of the thermal Projecting sensor element (8) and the substrate (5) touch.

Description

The The invention relates to a device for determining a measured variable of a Gas with a substrate and one with the substrate in thermal Connecting thermal sensor element.

Such a device is known from DE 41 12 601 A1 known. In the known device is an air flow sensor, which is used for example in the automotive industry for engine control.

Of the known air quantity sensor has an electrically insulated substrate on, on which several, designed as a thermal sensor elements thermosensitive resistors are arranged. There is between the substrate and the resistors a heat insulating layer from a lower thermal conductivity arranged material that extends along the entire Resistance expansion extends. By means of one with the resistors in Connected control circuit can one of the resistors Heating current supplied which heats this resistance to a temperature greater than the ambient temperature determined by the other resistor is. From the supplied Heating current can then be determined, the gas flow.

In the from the US 5,321,382 A known flow sensor, the heating resistor is applied over the entire surface of an upper and lower insulating layer. Since the heat transfer surface of the thermal sensor element is to be regarded as the surface with which the sensor element rests on the ground, in which from the US 5,321,382 A the known embodiment, the heat transfer area as large as the surface area of the thermal sensor element along the substrate.

The US 2004/0020286 A1 shows in 4 an embodiment in which a plurality of sensor elements are arranged on a base. The sensor elements are each provided with a cantilevered portion extending over the surface of the base.

To the Capture fast changes the amount of air, the known air quantity sensor under the Heating serving a dilution of the substrate. Further is the portion of the substrate on which the heater is used Resistance is located only by a narrow bridge with the remaining substrate connected.

One Disadvantage of the known gas quantity sensor is that the response time of the air quantity sensor despite being made to shorten the response time activities occasionally too long.

One Another disadvantage of the gas quantity sensor is that the time that the acting as a temperature sensor Resistance needed, to adjust its temperature to the ambient temperature, occasionally is too long. If the evaluation of the heating current takes place at a time, to which as a temperature sensor serving resistance not yet in thermal equilibrium with environment, it can lead to incorrect measurements.

outgoing From this prior art, the invention is therefore the task based on an improved response time and accuracy To provide device.

These The object is achieved by a device having the features of the independent claim. In it dependent claims Advantageous embodiments and developments are given.

The inventive device is characterized in that the thermal sensor element to its side facing the substrate in the region of its heat transfer surface several has integral with the sensor element formed heat transfer elements, which extend between recesses and of the thermal Project sensor element and touch the substrate.

When Heat transfer surface is in the following, those with the substrate in direct or indirect thermal Contact standing surface understood the thermal sensor element via which a transmission the heat from the thermal sensor element to the substrate. The area extent the thermal sensor element, however, denotes the projection surface of the thermal sensor element on the substrate surface at one taking place at right angles to the surface of the substrate Projection of the sensor element on the substrate surface of the Substrate. These are caused by elevations and depressions surface enlargements or surface reductions not considered. In the case of a flat, parallel to the substrate arranged thermal Sensor element corresponds to the surface area the thermal sensor element of its surface.

Due to the smaller design of the heat transfer surface of the thermal sensor element compared to its surface area, the unwanted heat transfer between the thermal sensor element and the substrate is reduced, so that the thermal sensor element from the Subst rat thermally decoupled and maintains its temperature approximately. As a result, the response time of the device according to the invention is significantly reduced.

The Temperature of the thermal sensor element also corresponds with the measured variable to be determined of the device according to the invention, whereby the device according to the invention a higher Measurement accuracy compared to a poorly thermally insulated thermal sensor element having.

at the inventive device is the thermal sensor element along its surface area At least partially spaced from the substrate and touches the Substrate with its heat transfer surface. These Arrangement of the thermal sensor element with respect to the substrate allows a good heat insulation respectively thermal decoupling of both device components, since the direct Thermal contact between both is reduced and heat transfer only in the area of the contact area takes place of the thermal sensor element and the substrate. In In this context, it is particularly preferred that between the thermal sensor element and the substrate an air or gas-filled cavity is present, the thermal decoupling of the thermal sensor element and the substrate significantly improved.

at inventive device has the thermal sensor element facing the substrate at its Side in the region of its heat transfer surface at least a heat transfer element which protrudes from the thermal sensor element and the substrate touched. By the formation of a between the thermal sensor element and the substrate existing heat transfer element arises the at least partially spaced arrangement of the thermal sensor element from the substrate, leaving the heat insulation the thermal sensor element is particularly good. The heat transfer element For example, it may be integrally formed with the thermal sensor element or a material different from the material of the thermal sensor element be made.

Preferably are the heat transfer elements along the surface area arranged distributed regularly the thermal sensor element. hereby becomes a particularly stable construction of the device according to the invention guaranteed since the thermal sensor element is connected to the substrate at regular intervals is. Furthermore, the heat transfer takes place on the substrate at a plurality of selected substrate areas, such that a temperature-induced material degradation or fatigue of the Substrate by increased heat transfer is avoided on a single substrate area and consequently the Life of the device according to the invention is particularly long.

at another embodiment is a heat insulating element for thermally insulating the thermal sensor element from the substrate present between the substrate and the thermal sensor element, and the heat insulating element touch that thermal sensor element along at least part of the heat transfer surface of the thermal sensor element. That in addition between the substrate and the thermal sensor element can be arranged heat insulating causes a additional thermal insulation of both components, allowing a heat transfer correspondingly reduced by the thermal sensor element to the substrate and As a result, the response time of the device according to the invention is increased. The heat insulating element can, for example, along the entire surface extent of the thermal Extend sensor element or even partial areas between the fill thermal sensor element and the substrate.

Farther can the heat insulating the thermal sensor element along the entire heat transfer surface of the touch the thermal sensor element. This will ensure that the already low heat transfer further reduced by the thermal sensor element on the substrate is because these two device components only in indirect thermal contact stand.

at a further preferred embodiment is the thermal sensor element structured such that the of Sub strat surface facing away of the thermal sensor element compared to the surface area of the thermal sensor element is increased. This causes the contact area the thermal sensor element is enlarged with the environment, so that a higher sensitivity the thermal sensor element and thus the device according to the invention is achieved with the environment. In the case of the design of the thermal Sensor element as a temperature sensor can small temperature fluctuations of the environment detected particularly quickly become.

Preferably, a protective layer is formed for sealing the substrate, the thermal sensor element and / or the heat insulating element on the substrate, the thermal sensor element and / or the heat insulating element. The additional protective layer causes a protection of the device according to the invention from environmental influences that adversely affect the stability and sensitivity of the device according to the invention can.

at a further preferred embodiment are the thermal sensor element, the heat transfer element and / or the heat insulating element produced by lithography process. This type of production the individual device components is particularly simple, inexpensive and with well-known from the prior art measures realizable.

Preferably are the substrate of glass, the thermal sensor element of molybdenum and the thermal insulating made of silicon dioxide. The use of glass and silica as a substrate and heat insulating element material allows a particularly cost-effective Production of the device according to the invention. molybdenum has a high thermal conductivity on, making this material especially good as a base material for the thermal Sensor element is suitable.

In a further preferred embodiment if the device is a gas flow measuring gas quantity sensor, a designed as a heating element or temperature sensor thermal Has sensor element. This embodiment of the device according to the invention is used for example in the automotive industry.

Further Advantages and characteristics of the invention will become apparent from the following Description forth, in the embodiments the invention with reference to the drawing will be explained in detail. Show it:

1 a plan view of a gas quantity sensor;

2 a cross section through a first embodiment of a heating arm of the gas quantity sensor 1 along the line II-II;

3 a plan view of another embodiment of the heating of the gas quantity sensor 1 ;

4A - 4D four process stages of a method for producing the heating arm of the gas quantity sensor 2 ; and

5A - 5D four process stages of a method for producing the heating arm of the gas quantity sensor 3 ,

In 1 is a device 1 represented, which is set up to detect a measured variable.

At the in 1 illustrated device 1 it is a gas flow sensor, which is a gas flow 2 in a flow channel 3 measures. The flow channel 3 is through the in 1 shown as dashed lines walls 4 limited. The gas quantity sensor 1 has a substrate 5 on that in the flow channel 3 protrudes and one with the substrate 5 integrally formed Heizarm 6 and one with the substrate 5 integrally formed temperature measuring arm 7 having. On the heating arm 6 there is a heating element 8th , and on the temperature arm 7 is a temperature sensor 9 arranged. The heating element 8th and the temperature sensor 9 are thermal sensor elements used for quantitative detection of the gas flow 2 be used. The heating element 8th and the temperature sensor 9 are via tracks 10 with a control circuit 11 connected, which is adapted to the operation of the gas quantity sensor 1 to ensure. The gas quantity sensor 1 also has contacts 12 via which the gas quantity sensor 1 is electrically contacted with, for example, an engine control of a motor vehicle.

At the in 2 illustrated embodiment of the heating arm 6 of the gas quantity sensor 1 is the heating element 8th directly on the substrate 5 arranged so that both sensor components are in direct thermal contact with each other. To heat dissipation from the heating element 8th on the substrate 5 to prevent is a heat transfer surface 13 of the heating element 8th less than a surface area 14 of the heating element 8th along the substrate 5 educated. In the embodiment shown corresponds to the heat transfer surface 13 the contact surface 15 of the heating element 8th and the substrate 5 , The area extent 14 of the heating element 8th along the substrate 5 denotes a cross-sectional area of the heating element 8th parallel to the substrate 5 ,

The compared to the area expansion 14 of the heating element 8th lower heat transfer area 13 causes a heat loss over the contact surface 15 both sensor components 5 . 8th is reduced or suppressed, so that the heating element 8th directly supplied heating power not by an unwanted heat dissipation to the substrate 5 is reduced. Therefore, the airflow sensor points 1 a fast response time.

The heating element 8th has a rectangular section 16 on top of that, from a surface 17 of the substrate 5 spaced apart. On the substrate 5 facing bottom 18 of the heating element 8th are heat transfer elements 19 arranged from the heating element section 16 to the substrate 5 to project out. End faces of the heat transfer elements 19 form the heat transfer surface 13 of the heating element 8th and touch the surface 17 of the substrate 5 , The heat transfer elements 19 are integral with the heating element 8th educated.

The heat transfer elements 19 form bridge-like structures, between which recesses 20 are formed. The heat transfer along side surfaces of the recesses 20 is greatly diminished because the cavities filled with air or gas 20 the heating element 8th in the region of their side surfaces thermally from the substrate 5 isolate.

One from the substrate 5 remote surface 21 of the heating element 8th has structures formed as depressions 22 on. It is also possible that the structures 22 are designed as surveys. By structuring the surface 21 of the heating element 8th becomes a contact surface of the gas quantity sensor 1 Enlarged with the environment, allowing a better coupling of the heating element 8th is ensured to the environment and the sensitivity of the gas quantity sensor 1 is improved. The surface structures 22 of the heating element 8th are along the surface extent 14 of the heating element 8th arranged distributed regularly, but they can also be formed irregularly or partially differently structured.

The regularly distributed structures 22 the surface 21 of the heating element 8th offer the advantage that they can be produced in a particularly simple and cost-effective manner, for example by means of photolithographic processes.

The gas quantity sensor 1 also has a protective layer 23 on that the heating element 8th and the substrate 5 encapsulated by the environment. Here are the heating element 8th and the substrate 5 in the protective layer 22 poured in, both components of the gas quantity sensor 1 envelops.

The substrate 5 of the gas quantity sensor 1 consists of electrically insulating glass, while the heating element 8th is made of a material based on molybdenum, which has a high thermal conductivity. The protective layer 23 is made of silicon dioxide, which ensures sufficient electrical insulation and is particularly accurate processable.

An edge length of the approximately square cross-sectional area of the heat transfer element 19 is about 5-10 microns, while a spacing of the Heizelementabschnitts 16 from the substrate surface 17 is about 0.5 microns. One at right angles to the substrate surface 17 measured thickness expansion of the heating element 8th is about 1 micron, while a lateral extent of the formed as a conductor heating element 8th is about 5-10 microns.

3 shows a modified embodiment of the heating arm 6 of the gas quantity sensor 1 in 1 , In accordance with the in 2 illustrated gas quantity sensor 1 is a heating element 24 on a heat insulating element 25 arranged, in turn, on a substrate 26 is appropriate. The heat insulating element 25 thus forms an intermediate element between the heating element 24 and the substrate 26 ,

The heating element 24 is formed as an elongated conductor, which is serpentine, parallel to a substrate surface 27 extends. The conductor has mutually parallel first sections 28 on that over second sections 29 connected to each other. The second sections 29 run transversely to the first sections 28 and are about four times shorter. This causes the heating element 24 on the one hand has a sufficiently large contact surface with the environment, on the other hand, however, acting as a heat dissipation surface surface of the heating element 24 is reduced accordingly, so that a heat transfer to the substrate 26 in comparison to a flat configuration of the heating element 24 is correspondingly smaller.

That between the heating element 24 and the substrate 26 arranged heat insulating element 25 consists of a variety of elongated, mutually parallel webs 30 , The bridges 30 have an approximately rectangular cross-section and extend transversely to the first sections 28 of the heating element 24 , This is the heating element 24 with approximately rectangular or square contact surfaces 31 on the heat insulating element 25 on. The outline of the contact surfaces 31 is in 3 represented by a dashed line. The contact surfaces 31 form heat transfer surfaces 32 of the heating element 24 , about the heat of the heating element 24 to the substrate 26 is directed. In the area of between the jetties 30 existing gaps 33 sits the heating element 24 not on the surface 27 of the substrate 26 on, but is spaced from this. Through these cavities, a particularly good thermal insulation of the heating element 24 from the substrate 26 guaranteed.

Preferably, the substrate is 26 made of glass, the heat insulating layer 25 made of silicon dioxide and the heating element 24 made of a material based on molybdenum. Dimensions of the heating element 24 correspond approximately to the dimensions of the heating element 8th in 2 ,

The following are two methods of making the in 2 and 3 illustrated gas quantity sensors 1 described.

4A shows a first process stage of the method for producing the Heizarms 6 of the gas quantity sensor 1 in 2 ,

On the substrate 5 is a sacrificial layer 34 applied from a nickel-chromium-containing material. This can be done, for example, by sputtering or vacuum vapor deposition. After that, the sacrificial layer becomes 34 suitably structured so that the sacrificial layer 34 , as in 4B represented, through openings passing through the sacrificial layer 35 with to the surface 17 of the substrate 5 approximately perpendicular side walls 36 having. For this purpose, the sacrificial layer becomes 34 first coated with photoresist, which is then exposed through a reticle having a suitable pattern. This is followed by the sacrificial shift 34 etched so selectively that the openings 35 in the sacrificial layer 34 arise. The etching step can be carried out, for example, by means of wet-chemical etching. Thereafter, the heating element 8th by vapor deposition as another coating on the substrate 5 and the sacrificial layer 34 applied. This is in the in 4C shown third process stage shown. After that, the surface becomes 21 of the heating element 8th properly structured with depressions or elevations before the sacrificial layer 34 is selectively removed by wet-chemical etching, so that the recesses 20 between the heating element 8th and the substrate 5 arise. Finally, according to 4D the protective layer 23 applied to the heating element 8th and the substrate 5 seals against an environment.

In the following, the method for producing the in 3 shown Heizarms 6 of the gas quantity sensor 1 explained. First, the heat insulating element 25 according to 5A on the substrate 26 applied. Thereafter, the heat insulating member 25 structured by means of non-detailed photolithography processes such that the elongated webs 30 form, between which the spaces between 33 be formed by wet chemical etching. Thereafter, according to 5B a sacrificial layer 37 Applied to the interstices 33 fills up and the jetties 30 encloses. Then the sacrificial layer becomes 37 Etched until the bridges 30 lie free. Next is according to 5C the heating element 24 layered on the footbridges 30 and the sacrificial layer 37 applied by steaming and suitably structured so that its in 3 shown serpentine-like design arises. For this purpose, for example, a coating of the heating element 24 with photoresist as well as exposure and selective etching of the heating element 24 necessary. Next is the in between spaces 33 located sacrificial layer 37 selectively removed by wet chemical etching. The gaps 33 stay free. Finally, according to 5D a protective layer 38 applied to the substrate 26 , the thermal insulation element 25 and the heating element 24 encloses.

In conclusion, be it should be noted that features and properties that are in the Described in connection with a particular embodiment may also be combined with another embodiment can, except if for reasons the compatibility is excluded.

1

contraption

2

gas flow

3

flow channel

4

walls

5

substratum

6

heating arm

7

Temperaturmessarm

8th

heating element

9

temperature sensor

10

conductor tracks

11

control circuit

12

contacts

13

Heat transfer surface

14

surface area

15

contact area

16

heating element

17

substrate surface

18

bottom

19

Heat transfer element

20

recess

21

heating element

22

structure

23

protective layer

24

heating element

25

thermal insulating

26

substratum

27

substrate surface

28

first section

29

second section

30

web

31

contact area

32

Heat transfer surface

33

gap

34

sacrificial layer

35

Opening sacrificial layer

36

Side wall sacrificial layer

37

sacrificial layer

38

protective layer

Claims (8)

Device for determining a measured variable of a gas with a substrate ( 5 ) and one with the substrate ( 5 ) in thermal communication thermal sensor element ( 8th ), wherein a heat transfer surface ( 13 ) of the thermal sensor element ( 8th ) for transferring the heat of the thermal sensor element ( 8th ) on the substrate ( 5 ) less than a surface area ( 14 ) of the thermal sensor element ( 8th ) along the substrate ( 5 ), and wherein the thermal sensor element ( 8th ) along its surface area ( 14 ) at least partially from the substrate ( 5 ) is spaced and the substrate ( 5 ) with its heat transfer surface ( 13 ), characterized in that the thermal sensor element ( 8th ) at its the substrate ( 5 ) facing side ( 18 ) in the region of its heat transfer surface ( 13 ) a plurality of integral with the sensor element ( 8th ) formed heat transfer elements ( 19 ), which extends between recesses ( 20 ) and of the thermal sensor element ( 8th ) and the substrate ( 5 ) touch. Device according to claim 1, characterized in that the heat transfer elements ( 19 ) along the surface area ( 14 ) of the thermal sensor element ( 8th ) are distributed regularly. Device according to one of claims 1 or 2, characterized in that the thermal sensor element ( 8th ) is structured such that the from the substrate ( 5 ) facing away from the surface of the thermal sensor element ( 8th ) compared to the area ( 14 ) of the thermal sensor element ( 8th ) is enlarged. Device according to one of claims 1 to 3, characterized in that a protective layer ( 23 ) for sealing the substrate ( 5 ), and / or the thermal sensor element ( 8th ) on the substrate ( 5 ) and / or the thermal sensor element ( 8th ) is trained. Device according to one of claims 1 to 4, characterized in that the thermal sensor element ( 8th ) comprises a conductor track. Device according to one of claims 1 to 5, characterized in that the thermal sensor element ( 8th ) and / or the heat transfer elements ( 19 ) are produced by lithography process. Device according to one of claims 1 to 6, characterized in that the substrate ( 5 ) of glass and the thermal sensor element ( 8th ) are made of molybdenum. Device according to one of claims 1 to 7, characterized in that the device ( 1 ) a gas flow measuring gas quantity sensor and the thermal sensor element ( 8th ) a heating element or a temperature sensor of the gas quantity sensor ( 1 ).