Sensor chip with additional heating element, method for preventing a sensor chip from being soiled, and use of an additional heating element on a sensor chip

Abstract

In the case of a sensor chip according to the related art, impurities in a flowing medium may be deposited in the area of a sensor area and may permanently soil it, resulting in a negative effect on the measurement response of the membrane.

Description

BACKGROUND INFORMATION

[0001] The present invention is directed to a sensor chip according to the preamble of claim 1 and use of an additional heater on a sensor chip according to the preamble of claim 2 and a method of preventing contamination on a sensor chip according to the preamble of claim 3.

[0002] German Patent Application 196 01 791 A1 describes a sensor chip having a sensor area composed of a frame element, a recess, and a membrane, for example. An unwanted influence on the measuring signal of the sensor chip in the sensor area may occur repeatedly due to contamination, e.g., oil, to which the sensor chip is exposed. Contamination with oil in the sensor area or in the immediate area around the sensor area alters the thermal conductivity at the surface of the sensor chip and thus affects the measuring signal. In addition, oil deposited on the sensor chip forms an adhesive for particles contained in a flowing medium. These trapped particles further increase the unfavorable effect.

[0003] U.S. Pat. No. 5,705,745 describes a sensor chip having a membrane on which are arranged temperature resistors and heating resistors, the membrane being surrounded by a thermally conductive element, which may also be U-shaped. The thermally conductive element is not heated. The thermally conductive element is also situated at least partially in the area of the membrane.

[0004] U.S. Pat. No. 4,888,988 describes a sensor chip having a membrane, a metallic conductor being situated around the membrane but not in the area of the membrane. This conductor is the common grounded neutral conductor of the measuring arrangement on the sensor chip. The cross section of this grounded neutral conductor has even been increased selectively to prevent an increase in temperature. An elevated temperature of the grounded neutral conductor would also have an extremely deleterious effect on the measurement according to this method.

[0005] German Patent Application 198 01 484 A1 describes a sensor chip having a membrane, electric conductors being situated around the membrane with an electric current flowing through them. These conductors are temperature sensors which are used for the measurement method and/or the measurement procedure.

[0006] German Patent Application 2 900 210 A1 and U.S. Pat. No. 4,294,114 describe a sensor chip having a temperature-dependent resistor on a carrier, another resistor directly adjacent to the temperature-dependent resistor also being applied to the carrier.

[0007] German Patent Application 4 219 454 and U.S. Pat. No. 5,404,753 describe a sensor chip having a reference temperature sensor at a distance from a sensor area.

[0008] German Patent Application 3 135 793 A1 and U.S. Pat. No. 4,468,963 describe a sensor chip having another resistor upstream and/or downstream from the sensor resistor, but the additional resistor influences the measuring signal.

ADVANTAGES OF THE INVENTION

[0009] The sensor chip according to the present invention and the use of an additional heater on a sensor chip according to the present invention and the method according to the present invention for preventing contamination of a sensor chip having the characterizing features of claims 1, 2, and 3, respectively, has the advantage over the related art that contamination of the sensor area of the sensor chip is reduced or prevented in a simple way.

[0010] Advantageous refinements of and improvements on the sensor chip and the aforementioned use and the aforementioned method as characterized in claims 1, 2, and 3, respectively, are possible through the measures characterized in the dependent claims.

[0011] An additional heater situated at a distance of up to 1 mm from the membrane is advantageous, so that the precipitates which are intentionally formed there are far enough away from the sensor area and are unable to influence the measurement response of the sensor area.

[0012] The additional heater advantageously is in a U shape enclosing the sensor area in an advantageous manner.

DRAWING

[0013] Exemplary embodiments of the present invention are shown in simplified form in the drawing and are explained in greater detail in the following description.

[0014] FIG. 1 shows a sensor chip according to the related art;

[0015] FIG. 2 a shows a first exemplary embodiment of a sensor chip according to the present invention; FIG. 2b shows a second embodiment, and FIG. 2c shows a third embodiment;

[0016] FIGS. 3 a and 3b show a sensor chip designed according to the present invention and a control circuit; and

[0017] FIG. 4 shows a temperature profile of an additional heater and a sensor area of a sensor chip designed according to the present invention.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0018] FIG. 1 shows a sensor chip according to the related art which is improved according to the present invention according to the descriptions of FIGS. 2a through 2c. The production method and the use of such a sensor chip are described in detail in German Patent Application 196 01 791 A1, which is herewith explicitly to be included as part of the present disclosure.

[0019] The sensor chip has a frame element 3 made of silicon for example. Frame element 3 has a recess 5. A dielectric layer 21, e.g., made of SiO2, for example, is applied to the frame element. Layer 21 may extend over entire frame element 3 or only over an area of recess 5. This area forms a membrane area 7 which partially or entirely delimits recess 5 on one side.

[0020] At least one, e.g., three metal strips 19 are applied on the side of membrane area 7 facing away from recess 5. Metal strips 19 form electric heaters and/or measuring shunts, for example, forming a sensor area 17 together with membrane area 7. Sensor area 17 is preferably covered with a protective layer 23. Protective layer 23 may also extend only over metal strips 19.

[0021] Membrane area 7 is then formed in part by dielectric layer 21 producing a measuring signal, a membrane 33 and in part by protective layer 21. The sensor chip has a surface 27 which is in direct contact with a flowing medium.

[0022] FIG. 2 a shows a top view of a first exemplary embodiment of a sensor chip 1 designed according to the present invention. Sensor chip 1 has a sensor area 17 having a length 1 across a main direction of flow 42. For example, metal strips 19 which form at least one electric heating resistor 35 and at least one temperature sensor 37, for example, are situated in sensor area 17. Temperature sensor 37 is also an electric resistor, for example. In this case there will be one heating resistor 35 and two temperature sensors 37. Metal strips 19 are mostly situated in sensor area 17 and are the prerequisite for a measurement method for determining at least one parameter, e.g., the temperature and flow rate of the flowing medium. Sensor area 17 is therefore connected to a control and regulating circuit. Sensor area 17 may be formed by membrane 33 described above, for example. Sensor chip 1 is situated in a flowing medium for determination of at least one parameter, the flowing medium flowing in the main direction of flow 42, on or over sensor chip 1, i.e., surface 27. The flowing medium may contain impurities which may result in contamination of sensor chip 1. These include, for example, salts dissolved in water or oil. To prevent these impurities from being deposited in the area of sensor area 17, at least partially an additional heater 39 is situated upstream from sensor area 17, for example, is connected to a current source (not shown), and is heated by its ohmic resistance. Additional heater 39 is situated at a defined distance, e.g., up to 1 mm away from sensor area 17.

[0023] No control circuit is necessary to regulate the temperature of additional heater 39. An amperage determined by the design, i.e., by the cross section is sufficient. Additional heater 39 is not used for a measurement method for determining a parameter of the flowing medium, i.e., it is not a component of this measurement zone.

[0024] Additional heater 39 here is in the form of a straight line, for example, which extends across, e.g., perpendicular to, the main direction of flow 42, e.g., extending beyond a length 1 of sensor area 17. Additional heater 39 may also have a spiral shape. Due to additional heater 39, contamination of sensor chip 1 occurs in the area of additional heater 39, but at a definite distance away from sensor area 17 so that the measurement response of sensor area 17 is not affected. This contamination is thus displaced from sensor area 17 into the area around additional heater 39.

[0025] The temperature of additional heater 39 is set so that there is a sharp temperature transition in the area of additional heater 39, so that thermal gradient eddies are produced, more or less filtering the liquid or the oil out of the flowing medium, i.e., the heavier components of the flowing medium are deposited on surface 27 in the area of additional heater 39 but not in sensor area 17.

[0026] FIG. 2 b shows a top view of another exemplary embodiment of sensor chip 1 according to the present invention. In contrast with FIG. 2a, additional heater 39 is U shaped. The U shape of additional heater 39 is in turn situated on sensor chip 1 at a definite distance away upstream from sensor area 17, the two legs of the U shape running across main direction of flow 42.

[0027] FIG. 2 c shows a top view of another exemplary embodiment of a sensor chip 1 according to the present invention. Additional heater 39 again has a U shape which at least partially encloses sensor area 17. Additional heater 39 runs on downstream and upstream sides, for example, definitely at a distance from sensor area 17 and on an end face of membrane 33.

[0028] Additional heater 39 is designed, for example, so that it has a length greater than that of sensor area 17, for example, at least upstream or downstream from sensor area 17. Therefore, sensor area 17 is protected from contamination over its entire length 1.

[0029] Resistors 35, 37 and/or additional heater 39 are preferably designed as printed conductors.

[0030] Sensor chip 1 is designed in the form of a chip, for example and has surface 27 past which the flowing medium flows. Sensor area 17 and additional heater 39 are situated together on surface 27.

[0031] FIG. 3 a shows a sensor chip 1 designed according to the present invention, having a sensor area 17 and a first control circuit 54 which is electrically connected to sensor area 17 by electric conductors 51, e.g., bond wires. First control circuit 54 has a first power source 45, e.g., a current or voltage source, or it is connected electrically to such a source by which at least one heating resistor 35 or at least one temperature sensor 37 is heated electrically in sensor area 17.

[0032] Additional heater 39 is connected to a separate second power source 48, for example, via electric conductors 51. There is no electric connection between first control circuit 54 and second power source 48. First control circuit 54 thus supplies a measuring signal, e.g., for an engine controller which is independent of operation of additional heater 39, i.e., the operation of additional heater 39 has no effect on the measuring signal. First power source 45 may also heat additional heater 39, e.g., via a voltage splitter, but the control signal of first power source 45 to additional heater 39 is still independent of the measurement method or signals to sensor area 17.

[0033] Sensor chip 1 supplies a measuring signal, e.g., for regulating an internal combustion engine. Additional heater 39 for example is heated only when the engine is not in operation, because only after shutdown of the engine does the most frequent contamination of sensor chip 1 occur due to backflow, e.g., from crankcase venting, containing contaminants such as oil. First control circuit 54 may deliver the signal for the heating operation of additional heater 39, for example, by closing a switch 60, for example, so that second power source 48 heats additional heater 39.

[0034] This control signal for heating additional heater 39 when the engine is not in operation may also be supplied by a second control circuit 57. Second control circuit 57 is the engine regulating unit, for example (FIG. 3b).

[0035] FIG. 4 shows a temperature profile of additional heater 39 and sensor area 17. FIG. 4 shows an X/Y diagram, a length in main direction of flow 42 being plotted on the X axis and a temperature on the surface of sensor chip 1 being plotted on the Y axis.

[0036] Additional heater 39 is located, for example, upstream from sensor area 17. Between additional heater 39 and sensor area 17 there is a distance which is different from zero. For example, the resistors in sensor area 17 generate a trapezoidal temperature curve having a maximum temperature TM.

[0037] Additional heater 39 has a maximum temperature TZ which varies according to a parabolic curve, for example, which is equal to or greater than temperature TM.

[0038] Arrows 62 show the flow pattern of the medium near surface 27. Additional heater 39 creates a more or less abrupt increase in temperature at surface 27, i.e., a thermal gradient which is large and differs from zero. Oncoming particles near surface 27 are more or less sucked by a partial vacuum to surface 27 upstream from or at the initial area of additional heater 39, and then rise upward in the area of the additional heater, i.e., removing themselves from surface 27. Due to this flow pattern, thermal gradient eddies 65 are created in the area of additional heater 39. Particles of dirt or oil therefore adhere to surface 27 of sensor chip 1 in the area of additional heater 39, so that the flowing medium is cleaned in the area near the surface, and sensor area 17 has little or no contamination.

Claims

1. A sensor chip for measuring at least one parameter of a flowing medium, having a sensor area for at least one measurement method, wherein at least one additional heater (39) is situated on the sensor chip (1) at a distance from the sensor area (17), and the sensor area (17) is operated independently of the additional heater (39).

2. A use of at least one additional heater (39) for forming thermal gradient eddies (65) in a flowing medium in the area of the additional heater (39), the additional heater (39) for determining at least one parameter of a flowing medium being situated on a sensor chip (1) and at a distance from a sensor area (17) of the sensor chip (1).

3. A method of preventing contamination on a sensor chip (1) which has a sensor area (17) and is situated in a flowing medium, wherein at least one additional heater (39) is heated electrically due to its ohmic resistance so that thermal gradient eddies are formed in the area of the additional heater (39), resulting in precipitation of the contaminants in the flowing medium in the area of the additional heater (39), away from the area of the sensor area (17).

4. The sensor chip as recited in claim 1, wherein the sensor area (17) is electrically connected to a first control circuit (54) which generates a measuring signal which is independent of the operation of the additional heater (39).

5. The sensor chip as recited in claim 4, wherein the first control circuit (54) controls a first energy source (45), and the additional heater (39) is electrically connected to a separate second energy source (48).

6. The sensor chip as recited in claim 1, 4 or 5, wherein the additional heater (39) is at least partially at a distance of up to 1 mm away from the sensor area (17).

7. The sensor chip as recited in one or more of claims 1 or 4 through 6, wherein the additional heater (39) is U shaped.

8. The sensor chip as recited in claim 7, wherein the U shape at least partially encloses the sensor area (17).

9. The sensor chip as recited in claim 1, wherein the flowing medium has a main direction of flow (42) and the additional heater (39) is situated at least partially in the main direction of flow (42), upstream from the sensor area (17).

10. The sensor chip as recited in claim 1, wherein the sensor area (17) has a membrane (33).

11. The sensor chip as recited in claim 1, wherein at least one heating resistor (35) and at least one temperature sensor (37) are situated in the sensor area (17) which (35, 37) are situated mostly in the sensor area (17).

12. The sensor chip as recited in claim 1, wherein the flowing medium has a main direction of flow (42); and the additional heater (39) is situated at least partially in the main direction of flow (42) downstream from the sensor area (17).

13. The sensor chip as recited in claim 1, wherein the flowing medium has a main direction of flow (42); and the sensor area (17) has a length (1) across the main direction of flow (42); and the additional heater (39) is situated across the main direction of flow (42) and is longer than the length (1).

14. The sensor chip as recited in claim 11, wherein the resistors (35) or the temperature sensor (37) are designed as printed conductors.

15. The sensor chip as recited in one or more of claims 1, 6 or 7, wherein the additional heater (39) is designed as a printed conductor.

16. The sensor chip as recited in claim 1, wherein the sensor chip (1) has at least one surface (27) past which the flowing medium flows; and the sensor area (17) and the additional heater (39) are situated together on a surface (27).

17. The method as recited in claim 3, wherein the sensor chip (1) supplies a measuring signal for a control unit of an internal combustion engine; and the additional heater (39) is heated only when the engine is not in operation.

18. The method as recited in claim 17, wherein the signal for the heating operation of the additional heater (39) is supplied by a first control circuit (54) of the sensor chip (1).

19. The method as recited in claim 17, wherein the signal for heating operation of the additional heater (39) is supplied by a second control circuit (57).

20. The method as recited in claim 17, wherein the second control circuit (57) is an engine regulating unit.