Accelerometer sensor of crystalline material and method for manufacturing the same

• US 5,578,755 A
• Filed: 12/02/1994
• Issued: 11/26/1996
• Est. Priority Date: 12/03/1993
• Status: Expired due to Term

• Current Assignee: Robert Bosch GmbH
• Original Assignee: Robert Bosch GmbH
• Inventors: Offenberg, Michael
• Primary Examiner(s): CHAPMAN JR, JOHN E
• Application Number:
  US08/348,700
• Time in Patent Office: 725 Days
• Field of Search: 73/514.32, 73/514.36, 73/514.38, 73/514.21, 73/514.24, 361/280, 361/283.1
• US Class Current: 73/514.32
• CPC Class Codes: B81B 2201/0235 Accelerometers
• CPC Class Codes: B81B 2203/0118 Cantilevers
• CPC Class Codes: B81B 2203/0136 Comb structures
• CPC Class Codes: B81B 3/0035 Constitution or structural means for controlling the movement of the flexible or deformable elements
• CPC Class Codes: B81B 3/0078 Constitution or structural means for improving mechanical properties not provided for in B81B3/007 - B81B3/0075
• CPC Class Codes: B81B 3/0086 Electrical characteristics, e.g. reducing driving voltage, improving resistance to peak voltage
• CPC Class Codes: B81C 1/00595 Control etch selectivity
• CPC Class Codes: B81C 2201/0107 Sacrificial metal
• CPC Class Codes: B81C 2201/0109 Sacrificial layers not provided for in B81C2201/0107 - B81C2201/0108
• CPC Class Codes: B81C 2201/016 Passivation
• CPC Class Codes: G01P 15/0802 Details
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 2015/0814 for translational movement of the mass, e.g. shuttle type

Abstract

In an accelerometer sensor of crystalline material, whose components are composed partly of monocrystalline and partly of polycrystalline material, a band-shaped seismic mass preferably is composed of polycrystalline material, whose suspension by means of suspension segments of monocrystalline material at the end regions permits a movement in the longitudinal direction upon the occurrence of an acceleration. Parallel plates extend from this mass at right angles to their longitudinal direction and, together with additional plates, which run parallel to said plates and are anchored at a base, form a capacitor arrangement and are composed, in particular, of monocrystalline material. At least the monocrystalline material is doped to attain an electric conductivity. When lightly doped, the long and thin plates and suspension segments have a high conductivity, given a very small mechanical prestressing, and can easily be isotropically undercut. The polycrystalline formation of the seismic mass can be designed to be very wide and large by etching away an underlying sacrificial oxide.

Claims

1. An accelerometer sensor composed of crystalline material, comprising:

a seismic mass, suspended by suspension segments, permitting a movement in a first direction in response to an acceleration;

a plurality of parallel plates extending from the seismic mass at right angles to the first direction;

a plurality of additional plates coupled on a first end to a base, the additional plates being parallel to the parallel plates, and forming a capacitor arrangement with the parallel plates;

wherein the seismic mass is composed of polycrystalline material, the parallel plates and the suspension segments are composed of monocrystalline material, and the monocrystalline material and polycrystalline material being doped to attain an electric conductivity.

2. The accelerometer sensor according to claim 1, wherein each one of the monocrystalline material and the polycrystalline material includes silicon.

3. The accelerometer sensor according to claim 1, wherein the base is composed of monocrystalline silicon.

4. The accelerometer sensor according to claim 1, wherein each of the suspension segments includes an unattached end, wherein each of the suspension segments extends at right angles to the first direction of the seismic mass, and wherein each of the suspension segments is coupled at its unattached end to the base or an epitaxy applied to the base.

5. The accelerometer sensor according to claim 1, wherein the additional plates are coupled to the base in coupling regions only at the first end that is distant from the seismic mass, the coupling regions being composed of polycrystalline material.

6. The accelerometer sensor according to claim 1, wherein the plurality of parallel plates coupled to the seismic mass and the plurality of additional plates coupled to the base are interleaved.

7. The accelerometer according to claim 1, wherein the parallel plates and the suspension segments are formed from an epitaxy layer of monocrystalline material, and further comprising at least one integrated circuit disposed on the epitaxy layer.