# US 2014/0191344 A1 · Mems process and device > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2014/0191344 A1 - Document ID: US20140191344A1 - Status: Published application - Kind: A1 - Application number: 14/203,131 - Filed: 2014-03-10 - Published: 2014-07-10 - Earliest claimed: 2007-08-17 - Assignees: Wolfson Microelectronics plc - Applicants: Wolfson Microelectronics plc - Inventors: Anthony Bernard Traynor; Richard Ian Laming; Tsjerk H. Hoekstra - Web page: https://patentgrep.com/patent/US20140191344A1 ## CPC - H04R 19/04: Microphones (H04R19/01 takes precedence) - 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 3/0072: {For controlling internal stress or strain in moving or flexible elements, e.g. stress compensating layers} - B81B 3/0094: {Constitution or structural means for improving or controlling physical properties not provided for in B81B3/0067 - B81B3/0091} - H04R 19/00: Electrostatic transducers - H04R 19/005: {using semiconductor materials} - H04R 23/00: Transducers other than those covered by groups H04R9/00 - H04R21/00 {(diaphragms for transducers of the distributed-mode type H04R7/045)} - H04R 31/00: Apparatus or processes specially adapted for the manufacture of transducers or diaphragms therefor {(manufacture of microstructural arrangements of deformable or non-deformable structures in general B81C1/00182)} - H10D 99/00: Subject matter not provided for in other groups of this subclass - B81B 2201/00: Specific applications of microelectromechanical systems - B81B 2201/0235: Accelerometers - B81B 2201/0257: Microphones or microspeakers - B81B 2201/0264: Pressure sensors - H04R 2499/11: Transducers incorporated or for use in hand-held devices, e.g. mobile phones, PDA's, camera's - H04R: LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS (producing sounds with frequency not determined by supply frequency G10K) - B81B: MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES (piezoelectric, electrostrictive or magnetostrictive elements per se H10N30/00, H10N35/00) - H10D: INORGANIC ELECTRIC SEMICONDUCTOR DEVICES ## Abstract A method of fabricating a micro-electrical-mechanical system (MEMS) transducer comprises the steps of forming a membrane on a substrate, and forming a back-volume in the substrate. The step of forming a back-volume in the substrate comprises the steps of forming a first back-volume portion and a second back-volume portion, the first back-volume portion being separated from the second back-volume portion by a step in a sidewall of the back-volume. The cross-sectional area of the second back-volume portion can be made greater than the cross-sectional area of the membrane, thereby enabling the back-volume to be increased without being constrained by the cross-sectional area of the membrane . The back-volume may comprise a third back-volume portion. The third back-volume portion enables the effective diameter of the membrane to be formed more accurately. ## Claims ### Claim 1 A micro-electrical-mechanical system (MEMS) capacitive microphone comprising: a substrate; a membrane formed relative to a first side of the substrate; and a back-volume formed in the substrate relative to a second side of the substrate; wherein the back-volume comprises a first back-volume portion and a second back-volume portion having a boundary therebetween defined by a discontinuity in a sidewall of the substrate; and wherein the cross sectional area of the second back-volume portion is greater than the cross sectional area of the first back-volume portion. ### Claim 2 (depends on 1) A MEMS capacitive microphone as claimed in claim 1, wherein the discontinuity comprises a discontinuity in the cross-sectional area of the back volume in a plane parallel to the substrate. ### Claim 3 (depends on 1) A MEMS capacitive microphone as claimed in claim 1, wherein the discontinuity comprises a discontinuity in a rate of change of cross-sectional area of the back volume in a plane parallel to the substrate with distance from the membrane. ### Claim 4 (depends on 1) A MEMS capacitive microphone as claimed in claim 1, wherein the discontinuity is curved. ### Claim 5 (depends on 1) A MEMS capacitive microphone as claimed in claim 1, wherein the discontinuity comprises a change in the gradient of the sidewall. ### Claim 6 (depends on 1) A MEMS capacitive microphone as claimed in claim 1, wherein the discontinuity comprises two or more changes in the gradient of the sidewall. ### Claim 7 (depends on 1) A MEMS capacitive microphone as claimed in claim 1, wherein the first back-volume portion has a cross-sectional area that is smaller than the cross-sectional area of the membrane in a plane where the first back-volume portion and the membrane meet. ### Claim 8 (depends on 1) A MEMS capacitive microphone as claimed in claim 1, wherein the cross-sectional area of the second back-volume portion is greater than the cross-sectional area of the membrane. ### Claim 9 (depends on 1) A MEMS capacitive microphone as claimed in claim 1, wherein the first back-volume portion has substantially vertical walls. ### Claim 10 (depends on 1) A MEMS capacitive microphone as claimed in claim 1, wherein the first back-volume portion has sloped walls. ### Claim 11 (depends on 1) A MEMS capacitive microphone as claimed in claim 1, wherein the second back-volume portion has substantially vertical walls. ### Claim 12 (depends on 1) A MEMS capacitive microphone as claimed in claim 1, wherein the second back-volume portion has sloped walls. ### Claim 13 (depends on 1) A MEMS capacitive microphone as claimed in claim 1, wherein the back-volume further comprises a third back-volume portion. ### Claim 14 (depends on 13) A MEMS capacitive microphone as claimed in claim 13, wherein the third back-volume portion is positioned between the first back-volume portion and the membrane. ### Claim 15 (depends on 13) A MEMS capacitive microphone as claimed in claim 13, wherein the third back-volume portion has a cross sectional area or diameter that is larger than the cross-sectional area or diameter of the first back-volume portion, but smaller than the cross-sectional area or diameter of the membrane. ### Claim 16 (depends on 1) A MEMS capacitive microphone as claimed in claim 1, wherein the discontinuity comprises a kink in the sidewall of the back-volume. ### Claim 17 (depends on 1) A MEMS capacitive microphone as claimed in claim 1, wherein the discontinuity comprises a step in the sidewall of the back-volume. ### Claim 18 (depends on 17) A MEMS capacitive microphone as claimed in claim 17, wherein the step comprises substantially a right angled step in the sidewall of the back-volume. ### Claim 19 (depends on 1) A MEMS capacitive microphone as claimed in claim 1, wherein the shape of the second portion of the back-volume is similar in shape to the substrate of the MEMS capacitive microphone. ### Claim 20 (depends on 19) A MEMS capacitive microphone as claimed in claim 19, wherein the second portion of the back-volume and the substrate are circular in shape, or rectangular in shape, or square in shape. ### Claim 21 (depends on 1) A MEMS capacitive microphone as claimed in claim 1, wherein the shape of the first portion of the back-volume is similar in shape to the membrane of the MEMS capacitive microphone. ### Claim 22 (depends on 21) A MEMS capacitive microphone as claimed in claim 21, wherein the first portion of the back volume and the membrane are circular in shape, or rectangular in shape, or square in shape. ### Claim 23 (depends on 1) A MEMS capacitive microphone as claimed in claim 1, wherein the shape of the first portion of the back-volume is matched to the shape of the membrane and/or wherein the shape of the second portion of the back-volume is matched to the shape of the substrate of the MEMS capacitive microphone. ### Claim 24 (depends on 1) A portable telephone device comprising a micro-electrical-mechanical system (MEMS) capacitive microphone as claimed in claim 1. ### Claim 25 (depends on 1) A communications device comprising a micro-electrical-mechanical system (MEMS) capacitive microphone as claimed in claim 1. ### Claim 26 (depends on 1) A computer device comprising a micro-electrical-mechanical system (MEMS) capacitive microphone as claimed in claim 1. ### Claim 27 A micro-electrical-mechanical system (MEMS) capacitive microphone comprising: a substrate; a membrane formed relative to a first side of the substrate; and a back-volume comprising means for enabling the effective height of the MEMS capacitive microphone to be reduced for a given volume of back-volume. ### Claim 28 A micro-electrical-mechanical system (MEMS) capacitive microphone comprising: a substrate; a membrane; and a back-volume, wherein the back-volume comprises first and second back-volume portions distinguishable by a discontinuity in a sidewall of the back-volume; and wherein the cross sectional area of the second back-volume portion is greater than the cross sectional area of the first back-volume portion.