# US 2017/0285064 A1 · Mems accelerometric sensor having high accuracy and low sensitivity to temperature and aging > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2017/0285064 A1 - Document ID: US20170285064A1 - Status: Published application - Kind: A1 - Application number: 15/265,111 - Filed: 2016-09-14 - Published: 2017-10-05 - Earliest claimed: 2016-03-31 - Assignees: STMicroelectronics S.r.l. - Applicants: STMicroelectronics S.R.L. - Inventors: Alessandro Tocchio; Gabriele Gattere - Web page: https://patentgrep.com/patent/US20170285064A1 ## CPC - G01P 15/125: by capacitive pick-up - B81B 3/0021: {Transducers for transforming electrical into mechanical energy or vice versa (dynamo-electric machines H02K99/00; electrostatic machines H02N1/00; piezoelectric devices H10N30/00)} - B81B 2201/0235: Accelerometers - B81B 2203/0181: See-saws - B81B 2203/04: Electrodes - G01P 2015/0814: {for translational movement of the mass, e.g. shuttle type} - G01P 2015/0831: {the mass being of the paddle type having the pivot axis between the longitudinal ends of the mass, e.g. see-saw configuration} - G01P: MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT (measuring or recording blood flow A61B5/02, A61B8/06; monitoring speed or deceleration of electrically-propelled vehicles B60L3/00; vehicle lighting systems adapted to indicate speed B60Q1/54; determining position or course in navigation, measuring ground distance in geodesy or surveying G01C; combined measuring devices for measuring two or more variables of movement G01C23/00; measuring velocity of sound G01H; measuring velocity of light G01J7/00; measuring direction or velocity of solid objects by reception or emission of radiowaves or other waves and based on propagation effects, e.g. Doppler effect, propagation time, direction of propagation, G01S; measuring speed of nuclear radiation G01T; measuring acceleration of gravity G01V; {measuring or recording the speed of trains B61L23/00; speed indicators incorporated in motor vehicles B60K35/00; measuring frequency or phase G01R; traffic control G08G}) - B81B: MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES (piezoelectric, electrostrictive or magnetostrictive elements per se H10N30/00, H10N35/00) ## Abstract A MEMS accelerometric sensor includes a bearing structure and a suspended region that is made of semiconductor material, mobile with respect to the bearing structure. At least one modulation electrode is fixed to the bearing structure and is biased with an electrical modulation signal including at least one periodic component having a first frequency. At least one variable capacitor is formed by the suspended region and by the modulation electrode in such a way that the suspended region is subjected to an electrostatic force that depends upon the electrical modulation signal. A sensing assembly generates, when the accelerometric sensor is subjected to an acceleration, an electrical sensing signal indicating the position of the suspended region with respect to the bearing structure and includes a frequency-modulated component that is a function of the acceleration and of the first frequency. ## Claims ### Claim 1 An accelerometric sensor, comprising: a bearing structure; a suspended region of semiconductor material, mobile with respect to the bearing structure; at least one first modulation electrode which is fixed to the bearing structure and is configured to be biased, in use, with an electrical modulation signal including at least one periodic component having a first frequency; at least one first variable capacitor formed by said suspended region and by said first modulation electrode, in such a way that the suspended region is subjected to a first electrostatic force that depends upon said electrical modulation signal; and a sensing assembly configured to generate, when the accelerometric sensor is subjected to an acceleration, an electrical sensing signal, which indicates the position of the suspended region with respect to the bearing structure and includes a frequency-modulated component, which is a function of said acceleration and of said first frequency. ### Claim 2 (depends on 1) The accelerometric sensor according to claim 1, further comprising: at least one second variable capacitor which is formed by said suspended region and by said first modulation electrode or is formed by said suspended region and by a second modulation electrode, which is fixed to the bearing structure and is configured to be biased with said electrical modulation signal; and wherein the suspended region is subjected, in use, to a second electrostatic force that depends upon said electrical modulation signal, said first and second variable capacitors being configured in such a way that the respective capacitances vary as a function of the movement of the suspended region with opposite signs. ### Claim 3 (depends on 2) The accelerometric sensor according to claim 2, wherein said first modulation electrode forms a first fixed surface and a second fixed surface parallel to one another; and wherein the suspended region comprises a main body and an elongated element, which projects towards the outside of the main body so as to extend between the first and second fixed surfaces, said elongated element forming a first mobile surface and a second mobile surface, which face the first and second fixed surfaces, respectively. ### Claim 4 (depends on 2) The accelerometric sensor according to claim 2, wherein the accelerometric sensor forms an out-of-plane acceleration sensor and comprises said second modulation electrode, which forms said second variable capacitor; and wherein the suspended region is set overlying said first and second modulation electrodes and is anchored to the bearing structure by means of elastic suspension elements configured so as to enable rotation of the suspended region about an axis of rotation, which is parallel to a surface of main extension of the suspended region. ### Claim 5 (depends on 2) The accelerometric sensor according to claim 2, wherein the suspended region delimits at least one cavity; and wherein said first modulation electrode extends in said cavity and forms said second variable capacitor. ### Claim 6 (depends on 5) The accelerometric sensor according to claim 5, wherein the accelerometric sensor forms an in-plane acceleration sensor, wherein the suspended region is anchored to the bearing structure by means of elastic suspension elements configured so as to enable a translation of the suspended region with respect to the bearing structure, along an axis of translation. ### Claim 7 (depends on 6) The accelerometric sensor according to claim 6 further comprising a generator configured to generate said electrical modulation signal and for biasing said first modulation electrode. ### Claim 8 (depends on 7) The accelerometric sensor according to claim 7, wherein the suspended region and the elastic suspension elements form a mechanical system, the frequency response of which has a peak at a second frequency; and wherein said first frequency is comprised in the frequency range such that the modulus of said frequency response is at least equal to the d.c. value of the modulus of said frequency response increased approximately by 3 dB. ### Claim 9 (depends on 8) The accelerometric sensor according to claim 8, further comprising a processing circuit including said generator, and: a conversion interface coupled to the sensing assembly and configured to generate, on the basis of the electrical sensing signal, an electrical signal to be filtered that comprises a number of respective components, one of said respective components being a function of said frequency-modulated component; a filter coupled to an output of the conversion interface and configured to filter a d.c. component of the electrical signal to be filtered; and a demodulator coupled to an output of the filter and configured to generate an output signal that indicates said acceleration and is at a frequency lower than the frequency of said frequency-modulated component. ### Claim 10 (depends on 9) The accelerometric sensor according to claim 9, wherein the suspended region and the bearing structure are formed in a first die of semiconductor material, and the processing circuit is formed in a second die of semiconductor material. ### Claim 11 (depends on 9) The accelerometric sensor according to claim 9, wherein the suspended region, the bearing structure, and the processing circuit are formed in a first die of semiconductor material. ### Claim 12 (depends on 9) The accelerometric sensor according to claim 9, wherein said sensing assembly is of a capacitive type; and wherein said electrical sensing signal is a capacitive-variation signal. ### Claim 13 A portable electronic device, comprising: an accelerometric sensor including, a fixed region; a suspended region of semiconductor material that is moveable in a translational or rotational direction relative to fixed region; a first modulation electrode attached to fixed region and configured receive an electrical modulation signal including at least one periodic component having a first frequency; a first variable capacitor formed by the suspended region and the first modulation electrode to provide a first electrostatic force to the suspended region based on the electrical modulation signal; and a sensing structure configured to generate, responsive to the first suspended region experiencing an acceleration that causes movement of the suspended region in the translational or rotational direction, an electrical sensing signal that indicates the position of the suspended region relative to the fixed region and includes a frequency-modulated component that is a function of the acceleration and a function of the first frequency of the electrical modulation signal; and a processing unit electrically coupled to the accelerometric sensor. ### Claim 14 (depends on 13) The portable electronic device of claim 13 further comprising an input/output device coupled to the processing unit, the input/output device including a keypad and a display. ### Claim 15 (depends on 14) The portable electronic device of claim 14, wherein the processing unit includes at least one of cellphone, personal digital assistant, portable computer, photographic-camera, video-camera, and wearable device circuitry. ### Claim 16 (depends on 13) The portable electronic device of claim 13, wherein the processing unit further comprises: a capacitance-to-voltage converter configured to receive the electrical sensing signal and configured to generate an output voltage signal having a value indicating a value of the first variable capacitor and thereby a deviation of the suspended region along the translational or rotational direction; a high-pass filter coupled to the capacitance-to-voltage converter to receive the output voltage signal and configured to filter the output signal to remove selected contributions from the output voltage signal and to provide a filtered output signal; and a demodulator coupled to the high-pass filter to receive the filtered output signal and configured to receive the electrical modulation signal, the demodulator configured to generate a demodulated output signal indicating the deviation of the suspended region but having a frequency that is different than a frequency of the output voltage signal from the capacitance-to-voltage converter. ### Claim 17 A method for detecting an acceleration, comprising: biasing a first modulation electrode with an electrical modulation signal having a first frequency, the first modulation electrode being fixed relative to a bearing structure; capacitively coupling the first modulation electrode to a suspended region so as to generate a first electrostatic force that is applied to the suspended region, the first electrostatic force being based on the electrical modulation signal; and generating an electrical sensing signal responsive to the bearing structure and suspended region experiencing an acceleration, the suspended region being moveable relative to the bearing structure and the electrical sensing signal indicating a position of the suspended region relative to the bearing structure and the electrical signal including a frequency-modulated component that is a function of the acceleration and a function of the first frequency of the electrical modulation signal. ### Claim 18 (depends on 17) The method according to claim 17, further comprising: generating, on the basis of the electrical sensing signal, an electrical signal to be filtered, the electrical signal to filtered including a number of respective components, one of said respective components being a function of said frequency-modulated component; and filtering a d.c. component of the electrical signal to be filtered to thereby generate an electrical signal to be demodulated. ### Claim 19 (depends on 18) The method according to claim 18 further comprising generating, starting from the electrical signal to be demodulated, a demodulated output signal that indicates said acceleration and is at a frequency lower than the frequency of said frequency-modulated component. ### Claim 20 (depends on 14) The method according to claim 14, wherein biasing said first modulation electrode comprises generating said electrical modulation signal so that said first frequency is in a frequency range with a modulus of a frequency response having a peak at a second frequency is at least equal to a d.c. value of the modulus of said frequency response increased by approximately 3 dB.