Frequency compensated oscillator design for process tolerances

• US 9,985,598 B2
• Filed: 06/02/2015
• Issued: 05/29/2018
• Est. Priority Date: 10/03/2003
• Status: Active Grant

• Current Assignee: Robert Bosch GmbH
• Original Assignee: Robert Bosch GmbH
• Inventors: Lutz, Markus, Partridge, Aaron
• Primary Examiner(s): Gannon, Levi
• Application Number:
  US14/728,930
• Publication Number:
  US 20150263695A1
• Time in Patent Office: 1,092 Days
• Field of Search: 331154, 331156
• CPC Class Codes: H03H 2009/02299 Comb-like, i.e. the beam comprising a plurality of fingers or protrusions along its length
• CPC Class Codes: H03H 2009/0233 comprising perforations
• CPC Class Codes: H03H 2009/02496 Horizontal, i.e. parallel to the substrate plane
• CPC Class Codes: H03H 3/0072 of microelectro-mechanical resonators or networks micromembranes or microbeams B81B2203/01; manufacture of microstructural devices in general B81C
• CPC Class Codes: H03H 3/0076 for obtaining desired frequency or temperature coefficients
• CPC Class Codes: H03H 3/0077 by tuning of resonance frequency
• CPC Class Codes: H03H 9/2447 Beam resonators H03H9/2468 takes precedence
• CPC Class Codes: H03H 9/2457 Clamped-free beam resonators
• CPC Class Codes: H03H 9/2463 Clamped-clamped beam resonators
• CPC Class Codes: Y10T 29/49016 Antenna or wave energy "plumbing" making

Abstract

A continuous or distributed resonator geometry is defined such that the fabrication process used to form a spring mechanism also forms an effective mass of the resonator structure. Proportional design of the spring mechanism and/or mass element geometries in relation to the fabrication process allows for compensation of process-tolerance-induced fabrication variances. As a result, a resonator having increased frequency accuracy is achieved.

Claims

1. A method of forming a resonator, comprising:

subjecting a spring-mass mechanism, with an effective mechanical mass and stiffness and including at least one of a void and an indentation in a first section of the spring-mass mechanism, to a single fabrication process, wherein;

the single fabrication process is at least one of a planar process, a surface micromachining process, a gas flow process, and an etching process;

the subjecting of the spring-mass mechanism to the single fabrication process includes simultaneously subjecting indiscriminately as a whole to the single fabrication process both (a) a first section at least partially defined by the at least one of the void and the indentation and (b) a second separate section of the spring-mass mechanism;

due to the simultaneous indiscriminate subjection to the single fabrication process of both the first and second sections as a whole, the single fabrication process acts on exposed surface area of the first section and on exposed surface area of the second section of the spring-mass mechanism to simultaneously remove material from both the first section and the second section;

due to a first ratio of (a) the exposed surface area of the first section to (b) the exposed surface area of the second section, the removal of the material from the first section by the subjection to the single fabrication process is automatically at a greater rate than the removal of the material from the second section by the subjection to the single fabrication process; and

the automatic greater rate of removal of the material from the first section than the rate of removal of the material from the second section is automatically at a second ratio due to which, the single fabrication process maintains a third ratio between the effective mechanical stiffness to the effective mechanical mass from prior to the subjecting of the spring-mass mechanism to the process until after completion of the process.

2. The method of claim 1, wherein the spring-mass mechanism includes a spring structure and a mass structure connected to the spring structure, the first section is the mass structure, and the second section is the spring structure.

3. The method of claim 2, wherein:

the spring-mass mechanism includes the void and the indentation;

the indentation includes a plurality of indentations in an outer edge of the mass structure; and

the void is formed in a body of the mass structure.

4. The method of claim 1, wherein the spring-mass mechanism includes a plurality of mass structures and a spring structure that are interconnected, the spring-mass mechanism includes the void, and the void is in a body of at least one of the plurality of mass structures.

5. The method of claim 1, wherein:

the spring-mass mechanism includes a plurality of mass structures and a spring structure that are interconnected, the spring-mass mechanism includes the void and the indentation;

the indentation includes a plurality of indentations in an outer edge of at least one of the mass structures; and

the void is formed in a body of at least one of the mass structures.

6. The method of claim 1, further comprising:

calculating dimensions of the at least one of the void and the indentation as a function of a difference between an initial design width and an expected deviation from the initial design width resulting from the process.

7. The method of claim 1, wherein the spring-mass mechanism includes a spring beam and a mass formed by a plurality of stacked beams, a width of the spring is greater than a width of each of the stacked beams, the void is formed by an interconnection of at least two of the stacked beams.

8. The method of claim 1, wherein the single fabrication process is an exposure of the first and second sections as a whole to an etching gas.

9. The method of claim 1, wherein the single fabrication process is an exposure of the first and second sections as a whole to a wet etch.

10. The method of claim 1, wherein the single fabrication process is an exposure of the first and second sections as a whole to a dry etch.

11. The method of claim 1, wherein the single fabrication process is an exposure of the first and second sections as a whole to a plasma etch.

12. The method of claim 1, wherein the single fabrication process is an exposure of the first and second sections as a whole to a vapor etch.

13. The method of claim 1, wherein the single fabrication process is the planar process.

14. The method of claim 1, wherein the single fabrication process is the surface micromachining process.

15. The method of claim 1, wherein the single fabrication process is the gas flow process.

16. The method of claim 1, wherein the single fabrication process is the etching process.

17. A method, comprising:

subjecting at least a section of a resonator structure, with an effective mechanical mass and stiffness and including at least one of a void and an indentation, to a single fabrication process, wherein;

the single fabrication process is at least one of a planar process, a surface micromachining process, a gas flow process, and an etching process;

the subjecting of the resonator structure to the single fabrication process includes simultaneously indiscriminately subjecting to the single fabrication process, as a whole, the at least the section of the resonator structure, which includes exposed surface area;

due to the simultaneous indiscriminate subjection of the at least the section of the resonator structure as a whole to the single fabrication process, the single fabrication process indiscriminately acts on all of the exposed surface area of the at least the section of the resonator structure to simultaneously indiscriminately remove material across the exposed surface area of the at least the section of the resonator structure;

the exposed surface area is at least partially defined by the at least one of the void and the indentation; and

due to a first ratio of the exposed surface area to non-exposed area of the at least the section of the resonator structure, the removal of the material by the subjection to the single fabrication process is automatically in a manner that maintains a second ratio between the effective mechanical stiffness to the effective mechanical mass from prior to the subjecting of the resonator structure to the process until after completion of the process.

18. The method of claim 17, wherein the resonator structure includes the void and the indentation, the void extends lengthwise in the resonator structure, and the indentation includes a plurality of indentations in an outer edge of the resonator structure.

19. The method of claim 17, wherein the resonator structure includes the void, and the void extends lengthwise in the resonator structure.

20. The method of claim 17, wherein the resonator structure includes a plurality of mass structures.

21. The method of claim 20, wherein the resonator structure includes the void in a body of at least one of the mass structures.

22. The method of claim 17, wherein the automatic maintenance of the second ratio is due to a structure of the at least one of a void and an indentation that causes the indiscriminate subjection to the single fabrication process to cause the removal of the material to be such that a ratio of a reduction of a width of a beam structure to a reduction of a mass to automatically remain approximately constant throughout the removal of the material.