DE102008006831A1 - Hot-film sensor - Google Patents

Abstract

Hot-film sensor having a sensor element (2) formed by an electrical conductor structure and a substrate (1) on which the sensor element (2) is arranged, wherein in the substrate (1) under the sensor element (2) extended cavity (3) for reducing the heat transfer from the sensor element (3) to the substrate (1) is formed. According to the invention, the substrate (1) is formed by a flexible film made of an electrically insulating material, in which the cavity (3) extended below the sensor element (2) is formed on the rear side (1b) facing away from the sensor element (2) Thickness of the substrate (1) on the sensor element (2) facing front (1a) is left.

Description

The The invention relates to a hot film sensor with a through a sensor structure formed sensor element according to the preamble of claim 1.

Hot-film sensors and arrays of hot film sensors become the Measurement of flows of fluids used, for example for Measurement of air flow on aircraft components such as wings, Tail or the like in the wind tunnel or the test flight. there becomes a thin conductor pattern forming a sensor element suitable geometry on a thin, electric and thermal insulating substrate produced and with an electronic heating and evaluation connected. The sensor is set up for measurement an elevated relative to the fluid temperature, wherein the heating electronics are intended to control the voltage (CV operation), the current (CC operation) or the temperature (CT operation) constant to keep. The discharged from the flow of the surrounding fluid Heat is used to characterize the flow, especially their speed. The light principle as such has been used for a long time, for example, on the Field of meteorological hot wire anemometer or air mass sensors of internal combustion engines.

The hot film sensors used to measure flows Work more effectively and accurately, the more heat in the flowing fluid is transmitted and the less by conduction of heat across the substrate in the measured (test) carrier is delivered. A substrate with low heat conduction can be further improved by a cavity (depression, cavity or recess) is introduced, which the heat conduction locally further reduced.

From the EP 0 958 487 B1 , of the DE 199 61 129 A1 , of the US Pat. No. 6,698,283 B2 , of the US 5 237 867 A or the JP 2003 021547 A hot-film sensors are known in which sensor elements formed by an electrical conductor structure are arranged on a substrate, wherein in the substrate an extended under the sensor element cavity for reducing the heat transfer from the heating element to the substrate and thus to the underlying (trial) carrier is formed. In the EP 0 958 478 B1 the substrate is formed by a relatively massive support of glass, for example with a thickness of 0.5 mm, in which a cavity-forming, through the entire thickness of the support continuous window is recessed. A coating, which ultimately serves as a membrane carrying the actual sensor element, is formed by a plurality of partial layers, wherein a silicon nitride layer is embedded between two silicon carbide layers. The Indian DE 199 61 129 A1 described hot film sensor is constructed in a similar manner, wherein a base film carrying the actual sensor element is disposed on a plate-like substrate, in which a cavity forming the cavity is also provided as a window passing through the entire thickness of the plate-like substrate. In the from the US Pat. No. 6,698,283 B1 and the US 5 237 867 A known hot-film sensors, a plate-like substrate is also used, which consists of semiconductor silicon and also has a window extending through its entire thickness, over which the actual sensor element is arranged on an insulating film forming a membrane. The from the JP 2003 021547 A known hot film sensor is constructed in a similar manner. From the US 5,484,517 For example, a hot film sensor is known in which the sensor element is deposited on a substrate formed by a polyimide film which has a constant thickness. Finally, out of the DE 44 17 679 C1 a hot film sensor is known in which electrically connected to the actual sensor element sensor leads are sunk in wells of a carrier film so that they do not represent elevations in the film surface.

The The object of the invention is an improved hot film sensor to create the most accurate and unadulterated Measurement of fluid flows allowed.

The Task is by a hot film sensor with the features of claim 1.

advantageous Embodiments and developments of the invention Hot film sensors are specified in the subclaims.

By The invention will be a hot film sensor with a through a electrical conductor structure formed sensor element and a substrate, on which the sensor element is arranged, wherein in the substrate an under the sensor element extended cavity for reduction the heat transfer from the sensor element to the substrate is formed, created. According to the invention the substrate by a flexible foil of an electrically insulating Material formed in which extended under the sensor element Cavity on the rear side facing away from the sensor element is formed, wherein a reduced thickness of the substrate at the Sensor element facing the front of the same is left.

According to advantageous Embodiments of the invention has the flexible forming the substrate Film has a thickness of 10 to 1000 microns, in particular a thickness from 25 to 250 μm.

The rear side of the substrate, which faces away from the sensor element, has preferably emerged Cavity formed a depth of 20% to 80% of the thickness of the film forming the substrate.

According to one advantageous embodiment of the invention Hot film sensor is on the sensor element forming Ladder structure and the substrate provided a passivation layer, which forms a smooth surface.

According to one advantageous development of the invention, it is provided that the passivation layer formed over the sensor element Area with a higher heat transfer and one formed over the remaining substrate Has area with lower heat transfer.

According to one Embodiment thereof may be provided that the Passivation layer in the formed over the sensor element Range of a material with higher thermal conductivity and in the over the other substrate formed Range of a material with lower thermal conductivity consists.

there can the material of higher thermal conductivity, which is provided above the sensor element, a higher Have stiffness than that over the rest Substrate provided material of lower thermal conductivity.

The the conductor element forming the sensor element can be used as a meander, Spiral or be designed as a double spiral.

According to one Further development of the hot-film sensor according to the invention It is envisaged that the conductor structure with electrical contacts connected from the front to the back of the substrate are performed.

According to advantageous Embodiments of the invention Hot film sensors may include a number of sensor elements in a 1-dimensional or in a 2-dimensional arrangement the flexible film forming the substrate is co-located be, wherein in each case under the sensor elements extensive cavities on the side facing away from the sensor element back of the substrate forming flexible film are formed.

The The flexible film forming the substrate may advantageously be made Polyimide or be prepared from polyetheretherketone.

According to one Further development of the hot-film sensor according to the invention is the back of the substrate through an additional insulation in the form of another film or coating or by an adhesive layer electrically isolated.

in the Below, embodiments of the invention are based on explained the drawing.

It demonstrate:

1 a highly magnified perspective view of a hot-film sensor according to an embodiment of the invention;

2 a perspective cross-sectional view of the hot-film sensor according to the embodiment of 1 ;

3 a plan view of the hot film sensor according to the embodiment of 1 ;

4 a rear view of the hot-film sensor according to the embodiment of 1 ;

5 in the plan view, another embodiment of the hot film sensor according to the invention; and

6 in plan view, a hot-film array as a still further embodiment of the invention.

In the 1 to 4 a hot film sensor according to an embodiment of the invention is shown in which a sensor element formed by an electrical conductor structure 2 on a substrate 1 is arranged. The substrate 1 is formed by a flexible film of an electrically insulating material, for example by a polyimide film or by a film of thermoplastic polyetheretherketone (PEEK). In the substrate formed by the flexible film 1 is one under the sensor element 2 extended cavity 3 designed to reduce the heat transfer from the sensor element 2 to the substrate 1 and thus to the underlying (trial) carrier. This cavity 3 in the form of a cavity, recess or depression is at the sensor element 2 facing away back 1b formed of the substrate, so that a reduced thickness of the substrate 1 at the sensor element 2 facing front 1a of the same remains.

The the substrate 1 forming flexible film may for example have a thickness of 10 to 1000 .mu.m, in particular a thickness of 25 to 250 .mu.m, and those at the sensor element 2 facing away back 1b of the substrate 1 trained cavity 3 For example, a depth of 20% to 80% of the thickness of the substrate 1 have forming film.

On the the sensor element 2 forming conductor structure and the substrate 1 is a passivation layer 4 provided a smooth Oberflä kitchen. In the in the 1 to 4 illustrated embodiment has the passivation layer 4 one above the sensor element 2 trained area 4a with higher heat transfer and one above the rest of the substrate 1 trained area 4b with lower heat transfer. This is the passivation layer 4 in the above the sensor element 2 trained area 4a made of a material with higher thermal conductivity and in the above the rest of the substrate 1 trained area 4b made of a material with lower thermal conductivity. The higher heat transfer in the area 4a above the sensor element 2 may additionally or alternatively also by a smaller thickness of the passivation layer 4 in this area 4a be effected.

Furthermore, the material of higher thermal conductivity, in the range 4a above the sensor element 2 is intended to have a higher rigidity than that over the rest of the substrate 1 provided material of lower thermal conductivity.

The the sensor element 2 forming conductor structure is with electrical contacts 5a . 5b connected to that in the 1 to 4 shown embodiment of the front 1a to the back 1b of the substrate 1 are performed.

• 1. Es wird eine Maskierungsschicht auf die Rückseite 1b des Substrats 1 aufgebracht und fotolithographisch strukturiert. In einem Sauerstoffplasma, dem auch etwas Fluor beigemengt sein kann, wird die Kavität 3 in das Substrat 1 geätzt. Danach wird die Maskenschicht entfernt.
• 2. Es wird ein Prozess wie unter 1. durchgeführt, aber die Ätzung wird in einer geeigneten Weise als Nassätzung ausgeführt.
• 3. Bei dicken Substraten 1 und großen Strukturen kann die Kavität 3 auch durch einen Feinfräser erzeugt werden.
• 4. Die Kavität 3 wird durch Laserablation erzeugt.
• 5. Die Kavität kann erzeugt werden durch Laminieren von mindestens zwei Folien, wobei in eine dieser Folien die Geometrie der Kavität eingeschnitten wurde, während die andere als geschlossene Deckfolie dient. Das Zuschneiden dieser Folie kann durch einen Schneidplotter, Laserschneiden, Wasserstrahlschneiden oder Plasmaätzen erfolgen.

The cavity 3 can be generated by various methods, for example:

• 1. There will be a masking layer on the back 1b of the substrate 1 applied and patterned photolithographically. In an oxygen plasma, which may also be mixed with some fluorine, the cavity 3 in the substrate 1 etched. Thereafter, the mask layer is removed.
• 2. A process is carried out as in 1., but the etching is carried out in a suitable manner as wet etching.
• 3. For thick substrates 1 and big structures can be the cavity 3 also be produced by a fine milling cutter.
• 4. The cavity 3 is generated by laser ablation.
• 5. The cavity can be produced by laminating at least two films, wherein in one of these films, the geometry of the cavity was cut, while the other serves as a closed cover sheet. The cutting of this film can be done by a cutting plotter, laser cutting, water jet cutting or plasma etching.

The hot film sensor with the finished substrate 1 becomes with the sensor element 2 upwards and the cavity 3 attached to the bottom of the (trial) carrier to be measured.

The production of the substrate 1 by a flexible film, such as a film of polyimide, allows attachment to curved or rounded surfaces, such as on components of wings, tail units or other flow around bodies, in particular of aircraft.

Of the described hot film sensor is characterized by a low Height out so that flow characteristics up or in the immediate vicinity of the carrier surface to be examined can be determined without the carrier would have to be changed, for example by Applying incisions without affecting the flow to be studied is significantly affected.

The sensor has protection against environmental influences and electrical insulation over the sensor element 2 the passivation layer described 4 , By structuring the passivation layer in the manner described above, after which over the sensor element 2 a passivation layer 4a with higher thermal heat transfer and passivation on the remaining areas 4b is provided with lower thermal heat transfer, an increase of locally at the location of the sensor element 2 reached to the flow of heat.

So that the flow to be measured is not influenced by the geometry of the sensor, the sensor has a small thickness and a smooth surface. In particular, the electrical contacts 5a . 5b are through the substrate 1 on the back to supply lines or connections 7a . 7b carried out. If the (trial) beam to be measured is made of a conductive material, such as aluminum, the back side becomes 1b of the substrate 1 on which the supply lines or connections 7a . 7b then run, by an additional insulation in the form of another film or coating or by an adhesive layer of the substrate 1 electrically isolated what is in 1 by the partially shown, dashed coating with the reference numeral 6 is indicated.

The the sensor element 2 forming conductor structure may be formed as a meander, spiral or as a double spiral.

5 shows in plan view another embodiment of the hot film sensor according to the invention, in which the said conductor structure is formed as a double spiral. As a result, line crossings are avoided in the supply and results in a largely independent direction sensitivity of the sensor element 2 ,

There may be a number of sensor elements 2 in a 1-dimensional or 2-dimensional arrangement on a common substrate formed by a flexible film 1 intended be, where among the respective sensor elements 2 wells 3 of the type described at the sensor element 2 facing away back 1b the substrate 1 forming flexible film are provided. Such a design allows high resolution flow measurement with small "pixels" and high sensor resistance. This makes it possible, with the same sensitivity of the sensor elements 2 to use lower currents for measurement than with conventional sensors.

The cavity 3 under the sensor element 2 may have an area of the order of 0.1 to 10 mm ² and a depth of 10 to 200 μm.

6 shows as a further embodiment of the invention, a hot-film array with three rows of 16 sensors. The individual sensors are arranged as a two-dimensional array. It is also possible for a plurality of arrays to be distributed on more than one film substrate. The above-described structured passivation with a passivation layer 4a higher thermal conductivity and a passivation layer 4b lower thermal conductivity is particularly advantageous in that even more thermally conductive materials with higher stiffness can be used. These then only need individual islands in a matrix of a softer and / or stress-free passivation layer 4b form with lower thermal conductivity. The coated sensor film remains relatively flexible and stress-free and can thus be handled better than if a tighter and / or more rigid thin film is applied to the entire surface. Otherwise, in the case of a high voltage thin film, the sensor film would throw or roll so much that it could no longer be mounted on a curved surface or handled further without the coating 4 locally flake or cracks may occur.

The invention provides a hot film sensor whose heat loss to the (trial) carrier is significantly reduced, resulting in improved sensor sensitivity and improved time response of the sensor. Due to the small thickness and the smooth surface of the sensor, the flow to be measured is little disturbed and there is the possibility of mounting on curved or curved surfaces. Due to a carrying out the electrical contacts 5a . 5b To the back, the sensor has a smooth surface, so that the size to be measured is not affected.

1

substratum

1a

front

1b

back

2

sensor element

3

cavity

4

passivation

4a

passivation higher thermal conductivity

4b

passivation lower thermal conductivity

5a

Contact

5b

Contact

6

additional insulation

7a

connection

7b

connection

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• EP 0958487 B1 [0004]
• - DE 19961129 A1 [0004, 0004]
• - US 6698283 B2 [0004]
• - US 5237867 A [0004, 0004]
• - JP 2003021547 A [0004, 0004]
• EP 0958478 B1 [0004]
• - US 6698283 B1 [0004]
• US 5484517 [0004]
• - DE 4417679 C1 [0004]

Claims (14)

Hot film sensor having a sensor element formed by an electrical conductor structure ( 2 ) and a substrate ( 1 ) on which the sensor element ( 2 ), wherein in the substrate ( 1 ) one under the sensor element ( 2 ) extended cavity ( 3 ) for reducing the heat transfer from the sensor element ( 3 ) to the substrate ( 1 ), characterized in that the substrate ( 1 ) is formed by a flexible foil of an electrically insulating material, in which the under the sensor element ( 2 ) extended cavity ( 3 ) at the sensor element ( 2 ) facing away from the back ( 1b ), wherein a reduced thickness of the substrate ( 1 ) at the sensor element ( 2 ) facing front ( 1a ) is left over. Hot-film sensor according to claim 1, characterized in that the substrate ( 1 ) forming flexible film has a thickness of 10 to 1000 .mu.m, in particular a thickness of 25 to 250 microns. Hot film sensor according to claim 1 or 2, characterized in that the on the the sensor element ( 2 ) facing away from the back ( 1b ) of the substrate ( 1 ) formed cavity ( 3 ) a depth of 20% to 80% of the thickness of the substrate ( 1 ) has forming film. Hot film sensor according to claim 1, 2 or 3, characterized in that on which the sensor element ( 2 ) forming conductor structure and the substrate ( 1 ) a passivation layer ( 4 ) is provided which forms a smooth surface. Hot film sensor according to claim 4, characterized in that the passivation layer ( 4 ) one above the sensor element ( 2 ) trained area ( 4a ) with higher heat transfer and one above the remaining substrate ( 1 ) trained area ( 4b ) with lower heat transfer. Hot film sensor according to claim 5, characterized in that the passivation layer ( 4 ) in the above the sensor element ( 2 ) trained area ( 4a ) of a material with higher thermal conductivity and in the above the remaining substrate ( 1 ) trained area ( 4b ) consists of a material with lower thermal conductivity. Hot film sensor according to claim 6, characterized in that the material of higher thermal conductivity, the above the sensor element ( 2 ) has a higher rigidity than that over the remaining substrate ( 1 ) provided lower thermal conductivity material. Hot film sensor according to one of claims 1 to 7, characterized in that the sensor element ( 2 ) forming conductor structure is designed as a meander, spiral or as a double spiral. Hot film sensor according to one of claims 1 to 8, characterized in that the conductor structure with electrical contacts ( 5a . 5b ) connected from the front ( 1a ) to the back ( 1b ) of the substrate ( 1 ) are performed. Hot-film sensor according to one of claims 1 to 9, characterized in that a number of sensor elements ( 2 ) in a 1-dimensional or in a 2-dimensional arrangement on which the substrate ( 1 ) are arranged together, wherein in each case under the sensor elements ( 2 ) extensive cavities ( 3 ) at the sensor element ( 2 ) facing away from the back of the substrate ( 1 ) are formed flexible film. Hot-film sensor according to one of claims 1 to 10, characterized in that the substrate ( 1 ) is formed by a flexible film of polyimide or polyetheretherketone. Hot film sensor according to one of claims 1 to 11, characterized in that the rear side ( 1b ) of the substrate ( 1 ) by an additional insulation ( 6 ) is electrically isolated in the form of another film or coating or by an adhesive layer. Hot film sensor according to one of the preceding claims, characterized in that a plurality of sensor elements ( 2 ) are arranged as a two-dimensional array. Hot film sensor according to claim 13, characterized in that one or more arrays of sensor elements on a plurality of substrates ( 1 ) are arranged distributed.