Micromachined comb capacitive accelerometer

• US 20060156819A1
• Filed: 12/19/2005
• Published: 07/20/2006
• Est. Priority Date: 12/29/2004
• Status: Active Grant

• Current Assignee: Commissariat a L'Energie Atomique (French Alternative Energies and Atomic Energy Commission)
• Original Assignee: Commissariat a L'Energie Atomique (French Alternative Energies and Atomic Energy Commission)
• Inventors: Robert, Philippe
• Granted Patent: US 7,322,240 B2
• Time in Patent Office: Days
• US Class Current: 73/514.320
• CPC Class Codes: G01P 15/0802 Details
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 15/18 in two or more dimensions

Abstract

Comb capacitive accelerometer comprising a substrate (5), a first electrode free to move (2) with respect to the said substrate (5) provided with a set of mobile fingers (7), a first electrode (4A, 4B) fixed with respect to the said substrate (5) and provided with a set of fixed fingers (8A, 8B), each of the mobile fingers (7) being arranged between two contiguous fixed fingers (8A, 8B) so as to form a first microstructure with interdigitised combs (20), accelerometer in which at least one second mobile electrode (40) associated with at least one second fixed electrode (42) to form at least one second microstructure with interdigitised combs (22) superposed on the first microstructure with interdigitised combs (20).

According to the invention, the said second mobile electrode (40) and the said second fixed electrode (42) are etched in the same substrate (5) as the said first mobile electrode (2) and the said first fixed electrode (4).

Claims

1. Comb capacitive accelerometer comprising a substrate (5), a first electrode free to move (2) with respect to the said substrate (5) provided with a set of mobile fingers (7), a first electrode (4A, 4B) fixed with respect to the said substrate (5) and provided with a set of fixed fingers (8A, 8B), each of the mobile fingers (7) being arranged between two contiguous fixed fingers (8A, 8B) so as to form a first microstructure with interdigitised combs (20), accelerometer in which at least one second mobile electrode (40) associated with at least one second fixed electrode (42) to form at least one second microstructure with interdigitised combs (22) superposed on the first microstructure with interdigitised combs (20), characterised in that the said second mobile electrode (40) and the said second fixed electrode (42) are etched in the same substrate (5) as the said first mobile electrode (2) and the said first fixed electrode (4).

2. Accelerometer according to claim 1, in which each of the said first and second mobile electrodes (2, 40) is composed of a mobile central mass (6) from which a plurality of mobile fingers (7) extends laterally, and the first and second fixed electrodes (4, 42) are each formed of two parts arranged symmetrically about the said central mobile masses (6) and each comprising a plurality of fixed fingers (8) extending laterally towards the said central masses (6) such that each mobile finger (7) is arranged between two fixed contiguous fingers (8A, 8B).

3. Accelerometer according to claim 2, in which the mobile fingers (7) of the first and second mobile electrodes (2, 40) and the fixed fingers (8A, 8B) of the first and second fixed electrodes (4, 42) are fixed.

4. Accelerometer according to claim 2, in which the mobile fingers (7) of the first and second mobile electrodes (2, 40) and the fixed fingers (8A, 8B) of the first and second fixed electrodes (4, 42) are dissociated.

5. Accelerometer according to claim 4, in which the mobile fingers (7) of the first and second mobile electrodes (2, 40) and the fixed fingers (8A, 8B) of the first and second fixed electrodes (4, 42) are aligned vertically.

6. Accelerometer according to claim 4, in which the mobile fingers (7) of the first and second mobile electrodes (2, 40) and the fixed fingers (8A, 8B) of the first and second fixed electrodes (4, 42) are offset from each other vertically.

7. Accelerometer according to claim 4, in which the constituents (7), (8), (6) of the first microstructure with interdigitised combs (20) are rotated by an angle of 90°

from the elements (7), (8), (6) forming the second microstructure with interdigitised combs (22).

8. Accelerometer according to any one of the previous claims, in which the mobile masses (6) of the said first and second mobile electrodes (2, 40) are fixed.

9. Accelerometer according to any one of claims 1 to 7, in which the mobile masses (6) of the said first and second mobile electrodes (2, 40) are dissociated.

10. Accelerometer according to any one of claims 1 to 9, in which the said first and second mobile electrodes (2, 40) are connected at their ends to the substrate through flexible rods (12).

11. Accelerometer according to the previous claim, in which the flexible rods (12) of the first mobile electrode (2) are fixed to the flexible rods (12) of the second mobile electrode (40).

12. Accelerometer according to claim 10, in which the flexible rods (12) of the first mobile electrode (2) are dissociated from the flexible rods (12) of the second mobile electrode (40).

13. Accelerometer according to claim 10, in which the said flexible rods (12) are etched directly in the substrate (5).

14. Process for manufacturing a comb capacitive accelerometer on a first substrate (5) comprising a buried sacrificial layer (24) according to any one of the previous claims, characterised in that it comprises the following steps:

formation of a mask on the first substrate (5) on two opposite faces of the said substrate, to define a first microstructure with interdigitised combs (20) superposed on a second microstructure with interdigitised combs (22), on each side of the said buried superficial layer (24),

etching of the first microstructure with interdigitised combs (20) comprising fixed fingers (8) and mobile fingers (7), a mass (6) and return arms (12), on one face of the first substrate, stopping on the buried sacrificial layer (24),

formation of a cavity on one face of a second substrate (26),

sealing the face of the first substrate (5) comprising the first microstructure with interdigitised combs (20) onto the face of the second substrate (26) facing the cavity in the second substrate,

etching of the second microstructure with interdigitised combs (22) comprising fixed fingers (8) and mobile fingers (7), a masse (6) and return arms (12), stopping on the buried sacrificial layer (24),

elimination of at least part of the buried sacrificial layer (24).

15. Manufacturing process according to claim 14, in which the buried sacrificial layer is eliminated (24) at the level at which the buried sacrificial layer is exposed by etching steps.

16. Manufacturing process according to claim 15, in which the buried sacrificial layer (24) is eliminated by dry etching.

17. Manufacturing process according to claim 14, in which the buried sacrificial layer (24) is also eliminated at the buried sacrificial layer connecting the fingers of the first microstructure (20) and the fingers of the second microstructure (22).

18. Manufacturing process according to claim 17, in which the buried sacrificial layer (24) is eliminated at the masses (6).

19. Manufacturing process according to claim 18, in which the buried sacrificial layer (24) is eliminated by etching with hydrofluoric acid HF in the liquid or vapour state.

20. Manufacturing process according to claim 14, characterised in that it also comprises a step thinning the exposed face of the substrate (5), between the sealing step and the etching step, stopping before reaching the buried oxide layer (24).

21. Manufacturing process according to claim 20, in which the thinning step is done by KOH etching.

22. Manufacturing process according to any one of claims 14 to 21, in which the substrate (5) is an SOI type substrate comprising a buried sacrificial oxide layer SiO₂ (24).