Flexural plate wave sensor and array

• US 20030200823A1
• Filed: 12/19/2002
• Published: 10/30/2003
• Est. Priority Date: 03/20/2000
• Status: Active Grant

• Current Assignee: Charles Stark Draper Laboratory Incorporated
• Original Assignee: Charles Stark Draper Laboratory Incorporated
• Inventors: Williams, John R., Cunningham, Brian T.
• Granted Patent: US 6,851,297 B2
• Time in Patent Office: Days
• US Class Current: 73/865
• CPC Class Codes: G01N 2291/02466 Biological material, e.g. blood
• 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 2291/0427 Flexural waves, plate waves, e.g. Lamb waves, tuning fork, cantilever
• 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 29/22 Details , e.g. general constructional or apparatus details
• CPC Class Codes: Y10T 29/42 Piezoelectric device making
• CPC Class Codes: Y10T 29/49007 Indicating transducer

Abstract

A method for manufacturing a flexural plate wave sensor includes the steps of depositing an etch-stop layer over a substrate, depositing a membrane layer over the etch stop layer, depositing a piezoelectric layer over the membrane layer, forming a first transducer on the piezoelectric layer and forming a second transducer on the piezoelectric layer, spaced from the first transducer. The method further includes the steps of etching a cavity through the substrate, the cavity having substantially parallel interior walls, removing the portion of the etch stop layer between the cavity and the membrane layer to expose a portion of the membrane layer, and depositing an absorptive coating on the exposed portion of the membrane layer.

Claims

1. A method for manufacturing a flexural plate wave sensor comprising the steps of:

depositing an etch-stop layer over a substrate;

depositing a membrane layer over said etch stop layer;

depositing a piezoelectric layer over said membrane layer;

forming a first transducer on said piezoelectric layer;

forming a second transducer on said piezoelectric layer, spaced from said first transducer;

etching a cavity through the substrate, the cavity having substantially parallel interior walls;

removing the portion of the etch stop layer between the cavity and the membrane layer to expose a portion of the membrane layer; and

depositing an absorptive coating on the exposed portion of the membrane layer.

2. The method of claim 1 further comprising the steps of etching a hole in the piezoelectric and forming a ground contact on the silicon membrane layer

3. A flexural plate wave sensor comprising:

a base substrate;

an etch stop layer disposed over said base substrate;

a membrane layer disposed over said etch stop layer;

a cavity disposed in said base substrate and said etch stop layer, thereby exposing a portion of said membrane layer, said cavity having substantially parallel interior walls;

an absorptive coating disposed on the exposed portion of said membrane layer within said cavity;

a piezoelectric layer disposed over said membrane layer;

a first transducer disposed on said piezoelectric layer; and

a second transducer disposed on said piezoelectric layer, spaced from said first transducer.

4. The flexural plate wave sensor of claim 3 wherein said first and second transducers are interdigitated transducers.

5. The flexural plate wave sensor of claim 3 wherein said first and second transducers are formed from TiPtAu.

6. The flexural plate wave sensor of claim 3 wherein said first and second transducers are formed from aluminum.

7. The flexural plate wave sensor of claim 3 wherein said piezoelectric layer is formed from a material selected from the group consisting of aluminum nitride, zinc oxide and lead zirconium titanate.

8. The flexural plate wave sensor of claim 3 wherein said etch stop layer is formed from silicon dioxide.

9. The flexural plate wave sensor of claim 3 wherein said membrane layer is formed from silicon.

10. The flexural plate wave sensor of claim 3 wherein said base substrate is formed from silicon.

11. A flexural plate wave sensor array comprising:

a substrate; and

a plurality of flexural plate wave sensors, each sensor including a cavity formed in the substrate, a thin film membrane layer spanning the cavity, a piezoelectric layer disposed on the thin film membrane layer, a transducer disposed on the piezoelectric layer and a plurality of discrete absorptive coatings disposed on said thin film membrane layer within said cavity;

wherein said cavity of each of said sensors includes interior walls which are substantially parallel to each other and to the interior walls of adjacent sensors.