Capacitive sensor

• US 6,690,569 B1
• Filed: 09/03/2002
• Issued: 02/10/2004
• Est. Priority Date: 12/08/1999
• Status: Expired due to Term

• Current Assignee: Sensirion Holding AG
• Original Assignee: Sensirion AG (Sensirion Holding AG)
• Inventors: Mayer, Felix, Lechner, Moritz
• Primary Examiner(s): Reichard, Dean A.
• Assistant Examiner(s): Nguyen, T. Ha
• Application Number:
  US10/130,969
• Time in Patent Office: 525 Days
• Field of Search: 361/303, 361/286, 361/322, 361/302, 361/305, 361/277, 361/280, 361/283.1, 361/283.4, 361/281, 361/287, 361/329, 361/278, 361/283.3
• US Class Current: 361/303
• CPC Class Codes: G01N 27/225 by using hygroscopic materials

Abstract

A sensor, in particular a humidity sensor, comprises a measuring layer (4), the dielectric properties of which depend on a parameter to be measured, e.g. of the humidity of the environmental air. Electrodes (2, 3) are arranged on a substrate (1) side by side for capacitively measuring the measuring layer (1). A protective layer (8) of a non-oxidizing material, in particular a layer of silicon oxide or gold, is arranged between the electrodes (2, 3) and the measuring layer (4). This layer prevents an oxidation of the electrodes (2, 3) and increases the live time and reliability of the sensor.

Claims

1. A sensor comprising

a measuring layer having dielectric properties that depend on a parameter to be measured,

a semiconductor chip,

interdigital electrodes lying on the semiconductor chip side by side for capacitively measuring the measuring layer, and

a protective layer of gas proof, non-oxidizing material arranged between the electrodes and the measuring layer.

2. The sensor of claim 1 wherein the protective layer has a thickness between 1 and 100 nm.

3. The sensor of claim 1 wherein the interdigital electrodes are of aluminum.

4. The sensor of claim 1 wherein the interdigital electrodes are of copper, titanium, tungsten or polysilicon.

5. The sensor of claim 1 wherein the protective layer consists at least partially of a noble metal.

6. The sensor of claim 5 wherein the protective layer consists of a first layer of a noble metal and a second layer of a non-oxidizing dielectric.

7. The sensor of claim 1 wherein the measuring layer comprises a polymer.

8. The sensor of claim 1 wherein it is a humidity sensor and that the dielectric constant of the measuring layer depends on the environmental humidity.

9. The sensor of claim 5 wherein said noble metal is gold.

10. The sensor of claim 1 wherein the protective layer consists at least partially of a non-oxidizing dielectric.

11. The sensor of claim 10 wherein the non-oxidizing dielectric is silicone oxide.

12. A sensor comprising

a measuring layer having dielectric properties that depend on a parameter to be measured,

a semiconductor chip,

interdigital electrodes lying on the semiconductor chip side by side for capacitively measuring the measuring layer, and

a protective layer of gas proof, non-oxidizing material arranged between the electrodes and the measuring layer,

wherein an opening spanned by a membrane is arranged in the semiconductor chip, wherein the interdigital electrodes are arranged on or within the membrane and the measuring layer is arranged at the membrane.

13. The sensor of claim 12 wherein a compensation layer is arranged on a side of the membrane opposite to the measuring layer, wherein the compensation layer has substantially the same thermal expansion properties as the measuring layer.

14. The sensor of claim 12 wherein the membrane consists of silicon oxide or silicon nitride.

15. The sensor of claim 12 wherein the measuring layer is located on an inner side of the membrane facing the opening and the membrane forms the protective layer.

16. The sensor of claim 13 wherein the compensation layer is of the same material as the measuring layer and has substantially the same thickness as the measuring layer.

17. The sensor of claim 15 further comprising a circuit arranged on said semiconductor chip, wherein the membrane and the circuit are arranged on a first side of the semiconductor chip and wherein the membrane forms a barrier between the first side and the opening.

18. The sensor of claim 12 further comprising a heating element arranged on the membrane.

19. A method for producing a sensor comprising the steps of

applying interdigital electrodes to a semiconductor chip,

applying a protective layer of gas proof, non-oxidizing material layer on the interdigital electrodes, and

applying a measuring layer, having dielectric properties that depend on a parameter to be measured, over the protective layer.

20. The method of claim 19 wherein the protective layer is applied on the interdigital electrodes by galvanic deposition of a noble metal.