Frequency compensated oscillator design for process tolerances

• US 9,800,222 B2
• Filed: 06/02/2015
• Issued: 10/24/2017
• Est. Priority Date: 10/03/2003
• Status: Expired due to Term

• Current Assignee: Robert Bosch GmbH
• Original Assignee: Robert Bosch GmbH
• Inventors: Lutz, Markus, Partridge, Aaron
• Primary Examiner(s): Williams, Thomas J
• Assistant Examiner(s): Sy, Mariano
• Application Number:
  US14/728,805
• Publication Number:
  US 20150263699A1
• Time in Patent Office: 875 Days
• Field of Search: 267136, 188378-380, 331116 M, 331154, 331175, 331176, 331183, 310309, 310367, 438706, 438709, 438735, 7351436, 73105
• 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 resonator comprising:

a substrate;

an anchor; and

a spring-mass mechanism having an effective mechanical stiffness, an effective mechanical mass, and a geometry that defines the effective mechanical stiffness and mass;

wherein;

the geometry includes at least one of a void and a plurality of indentations in a first portion of the spring-mass mechanism, the at least one of the void and plurality of indentations being dimensioned so that, when the spring-mass mechanism, after the spring-mass mechanism is formed, is subjected to a process that removes material from the spring-mass mechanism, a greater surface area of the first portion is exposed to the process than a remaining portion of the spring-mass mechanism, the difference in exposure resulting in a change in at least one of the effective mechanical stiffness and the effective mechanical mass produced in the first portion by the removal of the material that offsets a change in at least one of the effective mechanical stiffness and the effective mechanical mass produced in the remaining portion by the removal of the material, thereby providing a predetermined ratio between the effective mechanical stiffness and the effective mechanical mass upon completion of the process;

the spring-mass mechanism includes a spring beam and a mass;

a first end of the spring beam is connected to the anchor, which anchors the spring beam to the substrate in a manner in which the spring beam is movably suspended over the substrate;

a second end of the spring beam is connected to the mass;

the mass is formed by a plurality of stacked beams that are interconnected to each other;

a width of the spring beam is greater than a width of each of the stacked beams; and

the void is formed by an interconnection of at least two of the stacked beams.

2. The resonator of claim 1, wherein:

the width of the spring beam is defined by a process used to form the spring beam from a constituent material and to form the mass;

the effective mechanical stiffness defines a limitation on the movability of the spring beam and is defined at least in part by the width of the spring beam;

the resonator has a resonance frequency that is a function of a ratio of the effective mechanical stiffness to the effective mechanical mass; and

the geometry is defined such that modification of the width of the spring beam by the process results in a modification in widths of the plurality of stacked beams of the mass to an extent that little change to the ratio occurs by the modifications, by virtue of a proportion of a change to the effective mechanical mass that occurs with each change to the width of the spring beam by virtue of the geometry.

3. The resonator of claim 2, wherein the width of the sprint hear results from a design width and a total deviation from the design width due to imperfections in the process.

4. The resonator of claim 3, wherein:

the total deviation is defined by a nominal undercut and a tolerance of undercut; and

the nominal undercut is accounted for in a design procedure defining the design width.

5. The resonator of claim 4, wherein the net effect of the tolerance of undercut associated with the process, as applied proportionally to the width of the spring beam and the effective mechanical mass, results in little change to the ratio defined by a change in the effective mechanical stiffness and a change in the effective mechanical mass.

6. The resonator of claim 2, wherein the spring beam and the mass are formed from the same constituent material.

7. The resonator of claim 2, wherein the process includes at least one etch step selected from a group of etch steps including wet etch, plasma etch, and vapor etch.

8. The resonator of claim 1, wherein:

the resonator has a resonance frequency f that is defined as

9. The resonator of claim 1, wherein a first side of the mass is attached to the spring beam, which is anchored to the substrate via the anchor, and a second side of the mass, opposite the first side, is not attached to the spring beam and is not separately anchored to the substrate.

10. The resonator of claim 1, wherein the plurality of beams of the mass element are uniformly formed with widths that are ⅓

of the width of the spring beam.