Surface-micromachined absolute pressure sensor and a method for manufacturing thereof

• US 20040020303A1
• Filed: 05/09/2003
• Published: 02/05/2004
• Est. Priority Date: 11/10/2000
• Status: Active Grant

• Current Assignee: Valtion Teknillinen Tutkimuskeskus
• Original Assignee: Vaisala Oyj, Valtion Teknillinen Tutkimusekeskus
• Inventors: Blomberg, Martti
• Granted Patent: US 6,931,935 B2
• Time in Patent Office: Days
• US Class Current: 73/718
• CPC Class Codes: G01L 9/0073 using a semiconductive diaphragm

Abstract

The present publication discloses a capacitive pressure sensor structure, in particular for measurement of absolute pressure, and a method for manufacturing the sensor. The sensor comprises at least one fixed electrode (3), and at least one movable electrode (6, 7) electrically isolated from said fixed electrode (3) and spaced apart (10) from said fixed electrode (3). According to the invention, a portion of said movable electrode (6, 7) is formed from a porous polycrystalline silicon layer (6) that in a finished component remains as an integral portion of said flexibly movable electrode (6, 7).

Claims

1. A capacitive pressure sensor structure, in particular for measurement of absolute pressure, the sensor comprising

at least one fixed electrode (3), and

at least one movable electrode (6, 7) electrically isolated from said fixed electrode (3) and spaced apart (10) from said fixed electrode (3),

characterized in that

a portion of said movable electrode (6, 7) is formed from a porous polycrystalline silicon layer (6) that in a finished component remains as an integral portion of said flexibly movable electrode (6, 7).

2. The absolute pressure sensor structure of claim 1, characterized in that at the edges of the partially-vacuumed volume (10) is left a portion of the material of the sacrificial layer (4) by way of not carrying the etching-away of said material to completion in the lateral direction.

3. The sensor structure of any one of foregoing claims, characterized in that the structure remaining under said porous polycrystalline layer (6) is stiffened by providing thereunder a uniform silicon layer (5) having openings (13) made thereto.

4. The sensor structure of any one of foregoing claims, characterized in that columnar pads (14) are formed within the partially-vacuumed displacing volume (10) of the reference element by way of leaving certain portions of the sacrificial layer unetched.

5. The sensor structure of any one of foregoing claims, characterized in that to the center of the flexible diaphragm (6, 7) is made a thicker area (12) that serves to stiffen the structure at its central area.

6. The sensor structure of any one of foregoing claims, characterized in that over the flexible, porous polycrystalline silicon layer (6) is deposited a polycrystalline silicon layer (7) so that the composite layered structure becomes impervious to gases.

7. The sensor structure of any one of foregoing claims, characterized in that the sensor structure constitutes a plurality of single sensor elements connected in parallel or series with each other.

8. The sensor structure of any one of foregoing claims, characterized in that the sensor structure is manufactured using silicon micromechanical techniques.

9. The sensor structure of any one of foregoing claims, characterized in that the sensor structure is an absolute pressure sensor.

12. The method of any one of foregoing claims, characterized in that the structure remaining under said porous polycrystalline layer (6) is stiffened by providing thereunder a uniform silicon layer (5) having openings (13) made thereto.

13. The method of any one of foregoing claims, characterized in that columnar pads (14) are formed within the partially-vacuumed displacing volume (10) of the reference element by way of leaving certain portions of the sacrificial layer unetched.

14. The method of any one of foregoing claims, characterized in that to the center of the flexible diaphragm (6, 7) is made a thicker area (12) that serves to stiffen the structure at its central area.

15. The method of any one of foregoing claims, characterized in that over the flexible, porous polycrystalline silicon layer (6) is deposited a polycrystalline silicon layer (7) such that makes the composite layered structure impervious to gases.

16. The method of any one of foregoing claims, characterized in that the sensor structure constitutes a plurality of single sensor elements connected in parallel or series with each other.

17. The method of any one of foregoing claims, characterized in that the sensor structure is manufactured using silicon micromechanical techniques.

18. The method of any one of foregoing claims, characterized in that the solid material (4) (of the sacrificial layer) from the interior of the cavity that in a finished sensor is taken to a partial vacuum is removed via a porous polycrystalline silicon layer (6).

19. The method of any one of foregoing claims, characterized in that the sealing of a sensor element is carried out by depositing onto said porous polycrystalline silicon layer another polycrystalline silicon layer in a process that leaves the partial vacuum of said deposition process into the interior of the sensor element.

10. A method of manufacturing a capacitive pressure sensor structure, in particular a sensor for measurement of absolute pressure, the sensor comprising

at least one fixed electrode (3), and

at least one movable electrode (6, 7) electrically isolated from said fixed electrode (3) and spaced apart (10) from said fixed electrode (3),

characterized in that

a portion of said movable electrode (6, 7) is formed from a porous polycrystalline silicon layer (6) that in a finished component remains as an integral portion of said flexibly movable electrode (6, 7).

11. The method of claim 10, characterized in that at the edges of the partially-vacuumed volume (10) is left a portion of the material of the sacrificial layer (4) by way of not carrying the etching-away of said material to completion in the lateral direction.