# US 8,464,418 B2 · Method for temperature compensation in MEMS resonators with isolated regions of distinct material > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,464,418 B2 - Document ID: US8464418B2 - Status: Granted - Kind: B2 - Application number: 12/638,919 - Filed: 2009-12-15 - Published: 2010-04-15 - Granted: 2013-06-18 - Earliest claimed: 2007-03-09 - Assignees: Silicon Laboratories Inc. - Applicants: Emmanuel P. Quevy; David H. Bernstein - Inventors: Emmanuel P. Quevy; David H. Bernstein - Web page: https://patentgrep.com/patent/US8464418B2 ## CPC - B81C 1/0069: {Thermal properties, e.g. improve thermal insulation} - B81C 1/00349: {Creating layers of material on a substrate} - B81C 1/00523: {Etching material} - H03H 3/0076: {for obtaining desired frequency or temperature coefficients} - H03H 9/2405: {of microelectro-mechanical resonators} - H03H 9/2457: {Clamped-free beam resonators} - G02B 6/358: {Latching of the moving element, i.e. maintaining or holding the moving element in place once operation has been performed; includes a mechanically bistable system} - H03H 2009/02496: {Horizontal, i.e. parallel to the substrate plane} - H03H 2009/2442: {Square resonators} - Y10T 29/42: Piezoelectric device making - Y10T 29/49005: Acoustic transducer - Y10T 29/49165: by forming conductive walled aperture in base - B81C: PROCESSES OR APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OR TREATMENT OF MICROSTRUCTURAL DEVICES OR SYSTEMS (making microcapsules or microballoons B01J13/02; processes or apparatus specially adapted for the manufacture or treatment of piezoelectric, electrostrictive or magnetostrictive elements per se H10N30/01) - H03H: IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS (waveguides, resonators, lines or other devices of the waveguide type H01P) - G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS - Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION ## Abstract MEMS resonators containing a first material and a second material to tailor the resonator's temperature coefficient of frequency (TCF). The first material has a different Young's modulus temperature coefficient than the second material. In one embodiment, the first material has a negative Young's modulus temperature coefficient and the second material has a positive Young's modulus temperature coefficient. In one such embodiment, the first material is a semiconductor and the second material is a dielectric. In a further embodiment, the quantity and location of the second material in the resonator is tailored to meet the resonator TCF specifications for a particular application. In an embodiment, the second material is isolated to a region of the resonator proximate to a point of maximum stress within the resonator. In a particular embodiment, the resonator includes a first material with a trench containing the second material. ## Claims ### Claim 1 A method of forming a MEMS resonator device, comprising: forming a first structural material on a substrate; forming a trench in the first structural material; forming in the trench, a second structural material having a different Young's modulus temperature coefficient than the first structural material; patterning a resonator comprising both the first and second structural materials; and anchoring the patterned resonator to an anchor; where the second material is confined to a region of the resonator having a longest dimension that is shorter than a distance between the anchor and a point of the resonator furthest from the anchor. ### Claim 2 (depends on 1) The method of claim 1, wherein forming the first and second structural materials on the substrate further comprises depositing films at a temperature below 500° C. ### Claim 3 (depends on 1) The method of claim 1, wherein forming the first structural material comprises depositing a polycrystalline silicon germanium alloy and wherein forming the second structural material comprises depositing silicon dioxide. ### Claim 4 (depends on 1) The method of claim 1, wherein forming the first structural material comprises depositing an silicon dioxide and wherein forming the second structural material comprises depositing a polycrystalline silicon germanium alloy. ### Claim 5 (depends on 1) The method of claim 1, wherein the trench in the first structural material is defined through lithography and etch to have a dimension required to compensate the temperature coefficient of frequency of the resonator. ### Claim 6 (depends on 1) The method of claim 1, wherein forming the second structural material in the trench further comprises: filling the trench with the second structural material to form a void-free structure; and removing the second structural material from the top surface of the first structural material with at least one of an etch back and chemical-mechanical polish. ### Claim 7 (depends on 1) The method of claim 1, wherein the second structural material in the trench forms a spacer on the sidewalls of the trench and patterning the resonator removes the first structural material from a portion of the spacer to form a spacer ring attached to a sidewall of the resonator. ### Claim 8 (depends on 7) The method of claim 7, further comprising isotropically etching the second structural material to remove the portions of the ring not attached to the sidewall of the resonator. ### Claim 9 (depends on 1) The method of claim 1, where the first material has a negative Young's modulus temperature coefficient and the second material has a positive Young's modulus temperature coefficient. ### Claim 10 (depends on 1) The method of claim 1, where the first material is a semiconductor and the second material is a dielectric. ### Claim 11 (depends on 1) The method of claim 1, where the top surface of the first material is planar with the top surface of the second material. ### Claim 12 (depends on 1) The method of claim 1, where the resonator is a beam; and where the region of the resonator to which the second material is confined includes a point of maximum flexural stress within the resonator when the resonator is made to resonate. ### Claim 13 (depends on 1) The method of claim 1, where the resonator is a beam; and where the region of the resonator to which the second material is confined includes a point of maximum stress within the resonator and excludes a point of maximum displacement when the resonator is made to resonate. ### Claim 14 (depends on 1) The method of claim 1, where the resonator is a bulk mode resonator; and where the region of the resonator to which the second material is confined is an isolated block completely surrounded by the first material. ### Claim 15 (depends on 1) The method of claim 1, where the second material stiffens the resonator region to which the second material is confined as a function of temperature to tune a temperature coefficient of frequency of the resonator in a manner at least partially decoupled from the resonator temperature coefficient. ### Claim 16 (depends on 1) The method of claim 1, where an edge of the second material farthest from the anchor is disposed a first distance from the anchor, the first distance being less than a distance between the anchor and a point of maximum displacement during resonance. ### Claim 17 (depends on 16) The method of claim 16, further comprising forming the plurality of trenches in the first structural material such that the plurality of trenches are arranged in a radial array about the anchor. ### Claim 18 (depends on 16) The method of claim 16, where the first material has a negative Young's modulus temperature coefficient and the second material has a positive Young's modulus temperature coefficient. ### Claim 19 (depends on 16) The method of claim 16, where the top surface of the first material is planar with the top surface of the second material. ### Claim 20 A method of forming a MEMS resonator, comprising: forming a first structural material on a substrate; forming a trench in the first structural material; forming in the trench, a second structural material having a different Young's modulus temperature coefficient than the first structural material; and patterning a resonator comprising both the first and second structural materials; where the second material is isolated to a region of the resonator proximate to a point of maximum stress within the resonator during operation. ### Claim 21 A method of forming a MEMS resonator, comprising: forming a first structural material on a substrate; forming a trench in the first structural material; forming in the trench, a second structural material having a different Young's modulus temperature coefficient than the first structural material; and patterning a resonator comprising both the first and second structural materials; where the resonator is a bulk-mode resonator, and where the method further comprises: forming a plurality of trenches in the first structural material, the plurality of trenches being arranged in a radial array; and forming the second structural material in the plurality of trenches.