Micromechanical Sensor, Sensor Array and Method

• US 20090277271A1
• Filed: 07/04/2006
• Published: 11/12/2009
• Est. Priority Date: 07/08/2005
• Status: Active Grant

• Current Assignee: Valtion Teknillinen Tutkimuskeskus
• Original Assignee: Valtion Teknillinen Tutkimuskeskus
• Inventors: Oja, Aarne, Tappura, Kirsi, Helle, Hannu, Tuppurainen, Jussi, Alastalo, Ari, Mattila, Tomi, Seppa, Heikki
• Granted Patent: US 8,136,403 B2
• Time in Patent Office: Days
• US Class Current: 73/627
• CPC Class Codes: B81B 2201/0292 Sensors not provided for in B81B2201/0207 - B81B2201/0285
• CPC Class Codes: G01N 2291/0255 (Bio)chemical reactions, e.g. on biosensors
• CPC Class Codes: G01N 2291/0256 Adsorption, desorption, surface mass change, e.g. on biosensors
• CPC Class Codes: G01N 2291/106 one or more transducer arrays
• CPC Class Codes: G01N 29/022 Fluid sensors based on microsensors, e.g. quartz crystal-microbalance [QCM], surface acoustic wave [SAW] devices, tuning forks, cantilevers, flexural plate wave [FPW] devices microdevices per se B81B
• CPC Class Codes: G01N 29/036 by measuring frequency or resonance of acoustic waves
• CPC Class Codes: G01N 29/2462 Probes with waveguides, e.g. SAW devices
• CPC Class Codes: G01N 29/30 Arrangements for calibrating or comparing, e.g. with standard objects

Abstract

The present invention relates to a micromechanical sensor for analyzing liquid samples and an array of such sensors. The invention also concerns a method for sensing liquid samples and the use of longitudinal bulk acoustic waves for analyzing liquid phase samples micromechanically. The sensor comprises a body and a planar wave guide portion spaced from the body. At least one electro-mechanical transducer element are used for excitation of longitudinal bulk acoustic waves to the wave guide portion in response to electrical actuation and for converting acoustic waves into electrical signals. The wave guide portion is provided with a sample-receiving zone onto which the sample can be introduced. By means of the invention, the sensitivity of micromechanical liquid sensors can be improved.

Claims

1. A micromechanical sensor for analyzing samples, comprising,

a body,

a planar wave guide portion spaced from the body,

at least one electro-mechanical transducer element located on a lateral side of the wave guide portion for excitation of acoustic waves to the wave guide portion in response to electrical actuation, and

a sample-receiving zone on one surface of the wave guide portion for receiving a sample,

wherein the at least one of the transducer element is adapted to excite longitudinal bulk acoustic waves to the wave guide portion.

2. A micromechanical sensor according to claim 1, further comprising at least one transducer element for converting longitudinal bulk acoustic waves carried by the wave guide portion into electrical signals.

3. A micromechanical sensor according to claim 2, wherein the transducer elements for transmitting and converting of acoustic waves comprise a single element adapted to perform the functions of transmitting and converting.

4. A micromechanical sensor according to any of claims 1, 2 or 3, wherein the body and the wave guide portion are made of a semiconductor material, such as silicon.

5. A micromechanical sensor according to claim 4, in that the wave guide portion and at least part of the transducer elements contained in the sensor are fabricated from the semiconductor layer of a semiconductor-on-insulator structure.

6. A micromechanical sensor according to claim 5, wherein the semiconductor-on-insulator comprises a silicon semiconductor layer and the insulator layer is a buried oxide (BOX) layer, such as a SiO₂ layer.

7. A micromechanical sensor according to claim 5, wherein the transducer elements contained in the sensor comprise piezoelectric material, such as AlN or ZnO, arranged between the wave guide portion and the semiconductor layer of the transducer elements for piezoelectric actuation and detection of the acoustic waves.

8. A micromechanical sensor according to claim 5, wherein there is a narrow gap between the wave guide portion and the semiconductor layer of the transducer elements contained in the sensor for capacitive transduction of the acoustic waves.

9. A micromechanical sensor according to any of claims 1-3, wherein the wave guide portion is anchored to the body by at least one insulating anchor element between the body and the wave guide portion.

10. A micromechanical sensor according to claim 9, wherein the sample-receiving zone comprises a molecule-specific layer applied on the wave guide portion.

11. A micromechanical sensor according to claim 8, wherein the sample-receiving zone comprises a buffer layer arranged between the wave guide portion and the molecule-specific layer.

12. A micromechanical sensor according to claim 1, wherein at least part of the wave guide portion outside the sample-receiving zone and/or at least part of the transducer elements contained in the sensor are provided with hydrophobic coating.

13. A micromechanical sensor according to claim 12, wherein the sample-receiving zone comprises a hydrophilic surface.

14. A micromechanical sensor according to claim 13, wherein the sample-receiving zone faces away from the body.

15. A micromechanical sensor according to claim 14, wherein the body and the wave guide portion are provided with openings for introduction of samples on the sample-receiving zone from the direction of the body.

16. A micromechanical sensor according to any the claims 1-3, wherein the sample-receiving zone faces the body and the body is provided with an opening for introduction of samples on the sample-receiving zone.

17. A micromechanical sensor according to claim 15 or 16, wherein an insulator torus is provided around the opening of the body between the body and the wave guide portion for assisting the introduction of the sample on the sample-receiving zone.

18. A micromechanical sensor according to any of claims 1-3, wherein the wave guide portion is of length λ

in a longitudinal direction and linear isolator anchor elements are provided symmetrically between the wave guide portion and the body parallel to each other and essentially at distance λ

/2 from each other.

19. A micromechanical sensor according to claim 17, wherein the surfaces of the openings in the semiconductor portions of the device and/or the insulator anchor elements are provided with hydrophilic or hydrophobic coatings for assisting the introduction of the sample on the sample-receiving zone.

20. A micromechanical sensor according to any of claims 1 to 3, wherein there are provided electrical contacts to the transducer elements contained in the sensor from a side of the sensor that is opposite to the side of sample introduction.

21. A micromechanical sensor according to any of claims 1 to 3, wherein the transducer elements contained in the sensor comprise semiconductor electrodes, which are patterned for enabling electro-mechanical transduction of longitudinal bulk acoustic waves.

22. A micromechanical sensor according to claims 1-3, wherein the at least one transducer element extends on two lateral sides of the wave guide portion for excitation of longitudinal bulk acoustic waves in two perpendicular directions parallel to the sample-receiving surface of the wave guide portion.

23. A micromechanical sensor according to claims 1-3, wherein the wave guide portion is 10-30 μ

m thick.

24. A micromechanical sensor according to any of claims 1-3, wherein the length of the wave guide portion in the lateral directions is 400-4000 mm.

25. A micromechanical sensor according to any of claims 1-3, wherein the sample-receiving zone is open to the exterior of the sensor.

26. A micromechanical sensor according to claims 1-3, wherein the sensor is packed in a hermetically sealed casing having electrical contact terminals coupled to the transducer elements contained in the sensor.

27. A micromechanical sensor according to any of claims 1-3, wherein it is incorporated in an integrated circuit (IC) structure comprising the actuation and/or readout electronics coupled to the transducer elements contained in the sensor.

28. A micromechanical sensor according to any of claims 1-3, wherein it is incorporated in an integrated circuit (IC) structure comprising an integrated reference sensor and circuitry for comparing the output signals of the sensor and the reference sensor.

29. An array of micromechanical sensors, which array comprises a body and a plurality of sensors elements, each of the sensor elements comprising

a planar wave guide portion spaced from the body,

at least one electro-mechanical transducer element, which are located on a lateral side of the wave guide portion for excitation of acoustic waves to the wave guide portion in response to electrical actuation and for converting acoustic waves into electrical signals, and

a sample-receiving zone on one surface of the wave guide portion for receiving a sample,

wherein the transducer element of at least one of the sensor elements is adapted to excite longitudinal bulk acoustic waves to the wave guide portion.

30. An array of micromechanical sensors according to claim 29, wherein it at least one of the sensor elements comprises a micromechanical sensor according to any of claims 1-3.

31. An array of micromechanical sensors according to claim 29, wherein the array further comprises electrical conductors microfabricated on the array for contacting each of the transducer elements electrically outside the array element.

32. An array of micromechanical sensors according to claim 29, wherein the array comprises electrical contacts to one transducer element of each sensor element for simultaneous excitation of sensors and electrical contacts for individual reading of each sensor element.

33. An array of micromechanical sensors according to claim 29, wherein at least one of the sensor elements is a reference sensor coupled to a frequency comparator together with at least one of the longitudinal bulk acoustic wave sensors.

34. A method for sensing samples micromechanically, the method comprising the steps of

introducing a sample on a sample-receiving zone of a planar micromechanical wave guide,

transmitting acoustic waves into the wave guide by using a transducer by electro-mechanical coupling of the transducer and the wave guide, and

converting the acoustic waves into electrical signals for wave guide for sensing the impact of the sample on the vibrational behaviour of the wave guide,

wherein the step of transmitting acoustic waves comprises using as said acoustic waves longitudinal bulk acoustic waves.

35. A method according to claim 34, wherein the method is performed using a micromechanical sensor according to any of claims 1-3.

36. A method according to claim 34, wherein the step of transmitting acoustic waves comprises transmitting longitudinal waves in two lateral directions in such a mode that the displacement of the wave guide in the vicinity of the sample-receiving zone is minimized in the direction normal to the surface of the wave guide.

37. A method according to claim 34, wherein the step of introducing the sample on the sample-receiving zone comprises conveying a liquid sample through a semiconductor layer, on which the planar micromechanical wave guide is situated.

38. (canceled)

39. A method of sensing a liquid sample comprising:

providing a semiconductor in mechanical contact with the liquid sample; and

providing longitudinal bulk acoustic waves to the semiconductor to excite the semiconductor.