# US 10,479,674 B2 · Oscillation frequency measuring system and method for a MEMS sensor > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,479,674 B2 - Document ID: US10479674B2 - Status: Granted - Kind: B2 - Application number: 15/639,203 - Filed: 2017-06-30 - Published: 2017-10-19 - Granted: 2019-11-19 - Earliest claimed: 2013-06-28 - Assignees: STMicroelectronics S.r.l. - Applicants: Stmicroelectronics S.R.L. - Inventors: Alfio Russo; Massimo Cataldo Mazzillo; Ferenc Nagy - Web page: https://patentgrep.com/patent/US10479674B2 ## CPC - B81C 1/0015: {Cantilevers (switches using MEMS H01H1/0036; electrostatic relays using micromechanics H01H59/0009; microelectro-mechanical resonators H03H9/02244)} - G01H 3/06: by electric means - G01H 9/00: Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means - B81C 2203/075: the electronic processing unit being integrated into an element of the micromechanical structure - 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) - G01H: MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES ## Abstract A MEMS sensor has at least a movable element designed to oscillate at an oscillation frequency, and an integrated measuring system coupled to the movable element to provide a measure of the oscillation frequency. The measuring system has a light source to emit a light beam towards the movable element and a light detector to receive the light beam reflected back from the movable element, including a semiconductor photodiode array. In particular, the light detector is an integrated photomultiplier having an array of single photon avalanche diodes. ## Claims ### Claim 1 A device, comprising: a semiconductor substrate having a first surface; a light emitting device extending in the semiconductor substrate to a first distance from the first surface; a light detector extending in the semiconductor substrate to a second distance from the first surface, the second distance being smaller than the first distance; a movable element coupled to the semiconductor substrate and extending over the first surface of the substrate, the movable element having a surface that faces the first surface of the semiconductor substrate, the light emitting device, and the light detector, the surface of the moveable element being configured to reflect light from the light emitting device to the light detector. ### Claim 2 (depends on 1) The device of claim 1, further comprising a suspension structure physically coupled to the first surface of the semiconductor substrate and to the surface of the movable element, wherein the suspension structure extends in a direction transverse to the semiconductor substrate and to the movable element. ### Claim 3 (depends on 2) The device of claim 2, further comprising an adhesive layer between the suspension structure and the first surface of the semiconductor substrate. ### Claim 4 (depends on 1) The device of claim 1, wherein the semiconductor substrate includes: a semiconductor base substrate layer; a first semiconductor layer on the base substrate layer; and a second semiconductor layer on the first semiconductor layer, the device further comprising a first insulating layer on the second semiconductor layer; and a second insulating layer on the first insulating layer, a surface of the second semiconductor layer corresponding to the first surface of the semiconductor substrate. ### Claim 5 (depends on 4) The device of claim 4 wherein the light emitting device is formed in the first semiconductor layer and the light detector is formed in the second semiconductor layer. ### Claim 6 (depends on 5) The device of claim 5, further comprising an optical confinement structure at least partially surrounding the light emitting device in the semiconductor substrate, the optical confinement structure separates the light emitting device from the light detector within the semiconductor substrate. ### Claim 7 (depends on 6) The device of claim 6 wherein the optical confinement structure comprises a metal-filled trench that extends through the first insulating layer and the first and second semiconductor layers of the semiconductor substrate into the base substrate layer. ### Claim 8 (depends on 1) The device of claim 1 wherein the light detector is an integrated photomultiplier including an array of single-photon avalanche diodes. ### Claim 9 (depends on 1) The device of claim 1 wherein the movable element includes a light-reflective tip that extends at an inclined angle from the surface of the movable element toward the first surface of the semiconductor substrate, wherein in operation the tip reflects light emitted by the light emitting device toward the light detector. ### Claim 10 (depends on 1) The device of claim 1, further comprising an electronic detection circuit coupled to the light detector, the electronic detection circuit in operation provides a measure of an oscillation frequency of the movable element based on an output signal received from the light detector. ### Claim 11 A device, comprising: a MEMS sensor including: a movable element; and an integrated measuring system coupled to the movable element, the integrated measuring system including: a semiconductor substrate having a first surface; a light source that emits a light beam towards the movable element, the light source extending in the semiconductor substrate to a first distance from the first surface; and a light detector that receives the light beam reflected back from the movable element, the light detector extending in the substrate to a second distance from the first surface, the second distance being smaller than the first distance; and an electronic detection circuit, operatively coupled to the light detector, the electronic detection circuit being configured to provide a measure of an oscillation frequency of the movable element based on an output signal received from the light detector. ### Claim 12 (depends on 11) The device according to claim 11 wherein the electronic detection circuit includes: a leading edge discriminator that receives the output signal and provides a first processed signal including pulses corresponding to respective peaks in the received output signal having an amplitude higher than a discrimination threshold; and a time measuring stage that receives the first processed signal and measures a time interval occurring between corresponding peaks detected in consecutive oscillation periods. ### Claim 13 (depends on 12) The device according to claim 12 wherein the output signal has a first peak and a second peak due to the reflected light beam within each oscillation period, and the time measuring stage includes a digital counter that measures a time interval between corresponding pairs of first peaks or second peaks detected in consecutive oscillation periods. ### Claim 14 (depends on 11) The device according to claim 11 wherein the light detector is an integrated photomultiplier including an array of single-photon avalanche diodes. ### Claim 15 (depends on 14) The device according to claim 14 wherein the single-photon avalanche diodes operate as independent photon counters, and are biased at a reverse-biasing voltage having an absolute value higher than a breakdown voltage of the single-photon avalanche diodes, and wherein the light source includes a forward-biased integrated light emitting diode. ### Claim 16 A method, comprising: forming a light source in a semiconductor substrate having a first surface, the light source extending into the semiconductor substrate to a first distance from the first surface; forming a light detector in the semiconductor substrate, the light detector extending into the semiconductor substrate to a second distance from the first surface, the second distance being smaller than the first distance; and physically coupling a movable element to the semiconductor substrate, the movable element extending over the first surface of the substrate, and having a surface that faces the light emitting device and the light detector. ### Claim 17 (depends on 16) The method of claim 16 wherein attaching the movable element to the semiconductor substrate comprises: attaching a first end of a suspension structure to the surface of the movable element; and attaching a second end of the suspension structure, opposite to the first end, to the semiconductor substrate, the suspension structure extending transverse to the first surface of the substrate and to the surface of the movable element. ### Claim 18 (depends on 16) The method of claim 16, further comprising: forming the semiconductor substrate by forming a first semiconductor layer on a semiconductor base substrate layer; and forming a second semiconductor layer on the first semiconductor layer; forming a first insulating layer on the second semiconductor layer; and forming a second insulating layer on the first insulating layer, the second semiconductor layer including the first surface of the semiconductor substrate. ### Claim 19 (depends on 18) The method of claim 18 wherein forming the light source includes forming the light source in the first semiconductor layer, and forming the light detector includes forming the light detector in the second semiconductor layer. ### Claim 20 (depends on 16) The method of claim 16, further comprising: forming an optical confinement structure at least partially surrounding the light source in the semiconductor substrate, the optical confinement structure separating the light source from the light detector within the semiconductor substrate.