Micromechanical rotation speed sensor

• US 5,959,206 A
• Filed: 11/18/1997
• Issued: 09/28/1999
• Est. Priority Date: 05/31/1995
• Status: Expired due to Fees

• Current Assignee: Litef GmbH (Northrop Grumman Corporation)
• Original Assignee: Litef GmbH (Northrop Grumman Corporation)
• Inventors: Hafen, Martin, Ryrko, Bruno F., Breng, Uwe, Handrich, Eberhard
• Primary Examiner(s): Williams, Hezron
• Assistant Examiner(s): MOLLER, RICHARD ALAN
• Application Number:
  US08/952,756
• Time in Patent Office: 679 Days
• Field of Search: 73/502.02, 73/503.03, 73/504.04, 73/504.12, 73/504.14, 73/504.15, 73/504.16, 73/510
• US Class Current: 73/504.12
• CPC Class Codes: G01C 19/5656 the devices involving a micromechanical structure

Abstract

A micromechanical rate-of-rotation sensor based on the coriolis principle includes two plate-like oscillators electrostatically driven to oscillate out-of-phase. The oscillators are arranged one above another in alignment to oscillate via plate-like support structures separated from one another by a very small drive capacitor gap. By suitable selection of the natural frequency of the support structure parts, due to a significantly-larger distance between the oscillators, it is possible to achieve larger amplitudes of oscillation and, hence, a high oscillation quality, unlimited by the drive capacitor gap (which is narrow for reasons of good stimulation at small excitation voltages). The two oscillator structures in each case preferably comprise two electrically mutually insulated bonded parts suspended via springs within a frame and configured so that essentially only rotational oscillator movements are possible with linear movements of the oscillators in the ±z spatial direction largely suppressed.

Claims

1. In a micromechanical rate-of-rotation sensor of the type that is based on the coriolis principle and includes two plate-like oscillators driven electrostatically to oscillate out-of-phase, the improvement comprising, in combination:

a) said two oscillators being arranged one above the other in two plane-like layers; and

b) said oscillators are arranged to be driven to oscillate perpendicular to their plate-like planes.

2. A rate-of-rotation sensor as recited in claim 1, characterized in that said oscillators are connected on two opposite sides in each case to a part of a plate-like support structure arranged one above another, via which said electrostatic driving of oscillation is performed.

3. A rate-of-rotation sensor as recited in claim 1, characterized in that said oscillators are connected on one side in each case to a part of a plate-like support structure arranged one above another, via which said electrostatic driving of oscillation is performed.

4. A rate-of-rotation sensor as recited in claim 2 characterized in that:

a) the natural frequency of said support structure is different from, and preferably higher than, that of said oscillators; and

b) said support structure parts of each oscillator are configured so that their reaction forces mutually cancel one another.

5. A rate-of-rotation sensor as recited in claim 2 characterized in that the thickness of each oscillator extending out from said support structure is less than that of said support structure so that the possible amplitude of oscillation of each oscillator is significantly larger than the possible exciter amplitude, through said drive capacitor gap, for the electrostatic stimulation of oscillation in the region of said support structure.

6. A rate-of-rotation sensor as recited in claim 1 characterized in that each oscillator is connected on one piece to a support structure, via in each case at least one oscillation spring articulation strut of low thickness.

7. A rate-of-rotation sensor as recited in claim 6, characterized in that said support structure is secured on at least one side, in each case on the outer side facing away from said oscillator, via a spring strut, in a frame surrounding the arrangement of oscillator and support structure.

8. A rate-of-rotation sensor as recited in claim 7, characterized in that said individual spring struts comprise leaf spring elements for insuring rotational deflection movements of said oscillators and largely suppress linear movements of said oscillator.

9. A rate-of-rotation sensor as recited in claim 1 characterized in that said oscillators, together with parts connected in one piece thereto of a support structure, the spring struts and the frame, are formed by means of anisotropic etching from two layers of wafers which, for the purpose of insulation, are oxidized on the respectively mutually connected surfaces and are connected to one another by wafer bonding to form a double oscillator structure.

10. A rate-of-rotation sensor as recited in claim 9, characterized in that said wafers are 100! Si wafers.

11. A rate-of-rotation sensor as recited in claim 9, characterized in that said double oscillator structures, arranged one above another in alignment, is arranged, sealed off hermetically at the upper and lower side by cover plates bonded to said frames, inside the housing which is thus formed and which is evacuated or flooded with inert gas under low pressure.

12. A rate-of-rotation sensor as recited in claim 11, characterized in that said cover plates consist of glass and are connected in a hermetically sealed manner by anodic bonding along said frames.

13. A rate-of-rotation sensor as recited in claim 11 characterized in that said cover plates are coated on the inside with flat metal fields which, on the one hand, are assigned to the two oscillators as oscillation reading out or resetting capacitor surfaces and, on the other hand, are assigned to the spaced-apart support structure parts as stimulation electrodes or for reading out movements induced by rates of rotation.

14. A rate-of-rotation sensor as recited in claim 13, characterized in that:

a) said metal fields can be contacted electrically via through-plated holes in said cover plates; and

b) said holes are closed on the outside by bonded on, conductive closure islands.

15. A rate-of-rotation sensor as recited in claim 14, characterized in that said conductive closure islands are formed by highly doped Si material and connected in a hermetically sealed manner to said cover plates by means of anodic bonding or Si fusion bonding.

16. A rate-of-rotation sensor as recited in claim 7 characterized in that:

a) said frames comprise a pair of frame parts that include at least on one outer side of the layer arrangement, attachments for electrical connection; and

b) said attachments are offset from wafer layer to wafer layer.

17. A rate-of-rotation sensor as recited in claim 7 characterized in that said frame parts are printed on two opposite sides with mounting attachments arranged one above another in alignment.

18. A rate-of-rotation sensor as recited in claim 7, characterized in that when said support structure is held on one side, apart from a spring strut assigned in each case to each oscillator, the said support structure is also provided with further holding and connecting struts arranged in an offset manner, for the purpose of connecting to the respective frame.

19. A rate-of-rotation sensor as recited in claim 10 characterized in that said spring struts are formed, by means of anisotropic etching, in planes of the respective wafer layer, as leaf spring struts arranged at an angle to the possible deflection directions.

20. A rate-of-rotation sensor as recited in claim 19, characterized in that each wafer layer is provided with two leaf spring struts of equal angular position opposed to an imaginary center line to produce a strut arrangement that mutually aligns and crosses itself from layer to layer and, as a whole, forms a crossed-spring articulation.