Sealed capacitive sensor

• US 7,938,014 B2
• Filed: 02/21/2008
• Issued: 05/10/2011
• Est. Priority Date: 02/25/2005
• Status: Active Grant

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Kierse, Oliver, Hunt, William, Hynes, Eamon, Meehan, Peter G., O'Dowd, John
• Primary Examiner(s): Kirkland, III; Freddie
• Application Number:
  US12/070,849
• Publication Number:
  US 20080210013A1
• Time in Patent Office: 1,174 Days
• Field of Search: 737/18, 737/24, 737/80, 257/737
• US Class Current: 73/780
• CPC Class Codes: G01L 1/142 using capacitors
• CPC Class Codes: G01L 1/148 using semiconductive material, e.g. silicon
• CPC Class Codes: G01L 9/0072 using variations in capacitance
• CPC Class Codes: G01L 9/0073 using a semiconductive diaphragm
• CPC Class Codes: G01L 9/0075 using a ceramic diaphragm, e.g. alumina, fused quartz, glass
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2224/73257 Bump and wire connectors
• CPC Class Codes: H01L 2924/00014 the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details

Abstract

A sealed capacitive sensor includes a substrate having a diaphragm forming a first plate of a capacitor; a second fixed plate of the capacitor spaced from the diaphragm and defining a predetermined dielectric gap and a sealing medium connecting together the substrate and fixed plate in an integrated structure and hermetically sealing the gap.

Claims

1. A sealed capacitive sensor comprising:

a substrate having a diaphragm forming a first plate of a capacitor supported via supports;

a second fixed plate of the capacitor spaced from the diaphragm and defining a dielectric gap and bearing an active electronic circuit associated with the capacitive sensor; and

a frit sealing medium directly connecting together the substrate and fixed plate in a structure and hermetically sealing the gap, wherein the substrate further comprises a conductor buried in the substrate, such that the buried conductor traverses the sealing medium.

2. The sealed capacitive sensor of claim 1 in which the substrate includes ceramic.

3. The sealed capacitive sensor of claim 1 in which the substrate includes silicon.

4. The sealed capacitive sensor of claim 1 in which the fixed plate includes silicon.

5. The sealed capacitive sensor of claim 1 in which the frit includes a glass frit.

6. The sealed capacitive sensor of claim 1 in which at least one of the first and fixed plates includes a metal layer.

7. The sealed capacitive sensor of claim 1 in which the first and fixed plates comprise silicon.

8. The sealed capacitive sensor of claim 7 in which the silicon plates are doped.

9. The sealed capacitive sensor of claim 1 in which the fixed plate bears on a separate chip, an active electronic circuit associated with the capacitive sensor.

10. The sealed capacitive sensor of claim 9 in which there is an insulation layer between the active electronic circuit and the fixed plate.

11. The sealed capacitive sensor of claim 1 in which the fixed plate is electrically accessed through a wire bonding lead.

12. A sealed capacitive sensor comprising:

a substrate having a diaphragm forming a first plate of a capacitor supported via supports;

a fixed plate of the capacitor spaced from said diaphragm and defining a dielectric gap, the fixed plate comprising a recess on a first surface which is opposite the diaphragm and which defines at least a part of the gap dimension, and further comprising a second recess on a second surface of the fixed plate opposite the first surface, the second recess housing an active electric circuit associated with said capacitive sensor;

a frit sealing medium directly connecting together said substrate and fixed plate in a structure and hermetically sealing said gap; and

a cover covering the second surface of the fixed plate, and second sealing medium for connecting the cover to the fixed plate and hermetically sealing the second recess.

13. The sealed capacitive sensor of claim 12 in which the second sealing medium includes a frit.

14. The sealed capacitive sensor of claim 12 in which the second sealing medium includes a glass frit.

15. A sealed capacitive sensor comprising:

a substrate having a diaphragm forming a first plate of a capacitor supported via supports;

a fixed plate having a first surface and a second surface opposite the first surface, the first surface spaced from the diaphragm and defining a dielectric gap of the capacitor such that the diaphragm and the first surface form a variable capacitor, the fixed plate bearing an active electronic circuit associated with the capacitive sensor;

an over mold covering the second surface of the fixed plate and attached to the substrate above the supports; and

a frit sealing medium directly connecting together the substrate and the first surface of the fixed plate in a structure and hermetically sealing the gap.

16. The sealed capacitive sensor of claim 15, wherein the over mold covering comprises a glob top that provides a second seal for the gap.

17. The sealed capacitive sensor of claim 16 in which the substrate includes ceramic.

18. The sealed capacitive sensor of claim 16 in which the substrate includes silicon.

19. The sealed capacitive sensor of claim 15, wherein the over mold covering comprises plastic.

20. The sealed capacitive sensor of claim 19 in which the substrate includes ceramic.