# US 2024/0201070 A1 · Photoacoustic gas sensor, and method for producing same > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2024/0201070 A1 - Document ID: US20240201070A1 - Status: Published application - Kind: A1 - Application number: 18/288,918 - Filed: 2022-04-29 - Published: 2024-06-20 - Earliest claimed: 2021-04-29 - Assignees: Technische UniversitäT Dortmund - Applicants: Technische UniversitäT Dortmund - Inventors: Stefan PALZER - Web page: https://patentgrep.com/patent/US20240201070A1 ## CPC - G01N 21/1702: {with opto-acoustic detection, e.g. for gases or analysing solids} - G01N 2021/1704: {in gases} - G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q) ## Abstract A method for producing a photoacoustic gas sensor for a target gas, having the steps of a) providing a wafer made of silicon, having a front face and a rear face. The wafer having a buried insulating layer within the silicon. The method including b) providing a suspended thermal emitter having a first cavity on the rear face of the wafer. The method including c) providing a sound-sensitive element on the front face of the wafer, the sound-sensitive element having a second cavity in which the target gas is enclosed. The additionally relates to a photoacoustic gas sensor for a target gas. ## Claims ### Claim 1 Method for producing a photoacoustic gas sensor for a target gas, comprising the following steps: a) Provision of a wafer made of silicon having a front side and a back side, wherein the wafer includes a buried insulation layer within the silicon; b) Implementation of a suspended thermal emitter including a first cavity on the back side of the wafer; c) Implementation of an acoustically sensitive element on the front side of the wafer, wherein the acoustically sensitive element includes a second cavity in which the target gas is contained, wherein steps b) and c) are implemented by means of photolithographic processes and etching processes in such a manner that the first cavity and the second cavity are separated from one another solely by the buried insulation layer. ### Claim 2 (depends on 1) Method according to claim 1, wherein step a) comprises a provision of a silicon-on-insulator wafer and/or a provision of a {100}Si wafer, and/or wherein the wafer comprises a first insulation layer on the back side, a second insulation layer on the front side, and the buried insulation layer between the first insulation layer and the second insulation layer and within the silicon. ### Claim 3 (depends on 2) Method according to claim 2, wherein the first insulation layer, the second insulation layer and/or the buried insulation layer comprises silicon dioxide, silicon carbide, and/or sapphire. ### Claim 4 (depends on 1) Method according to claim 1, wherein step a) comprises provision of a wafer with a distance of 500 μm to 2000 μm between the buried insulation layer and the back side, or wherein step a) comprises provision of a wafer —2 with a distance of 500 μm to 2000 μm between the buried insulation layer and the first insulation layer. ### Claim 5 (depends on 1) Method according to claim 1, wherein step b) comprises implementation of a suspended radiation source and/or of a suspended micromechanical hotplate on the back side of the wafer. ### Claim 6 (depends on 1) Method according to claim 1, wherein step b) comprises implementation of an IR emitter. ### Claim 7 (depends on 1) Method according to claim 1, wherein the wafer provided in step a) includes a first insulation layer on the back side comprises the following steps: Application of a heating structure to the first insulation layer by means of photolithographic processes, and Creation of the first cavity between the first insulation layer and the buried insulation layer in the region of the applied heating structure by means of chemical and/or physical etching processes. ### Claim 8 (depends on 1) Method according to claim 1, wherein step c) comprises implementation on the front side of the wafer of a microphone in which the target gas is contained. ### Claim 9 (depends on 1) Method according to claim 1, wherein the wafer provided in step a) includes a second insulation layer on the front side, and step c) comprises the following steps: Partial removal of the second insulation layer by means of chemical and/or physical etching processes, Application of a cover plate to the front side of the wafer by means of photolithographic processes, wherein the cover plate has a perforated structure in the region of the removed second insulation layer, Creation of the second cavity between the cover plate and the buried insulation layer in the region of the perforated structure by means of chemical etching processes, and Sealing of the second cavity under target gas atmosphere by the application of a sealing layer to the cover plate under target gas atmosphere. ### Claim 10 Photoacoustic gas sensor for a target gas, comprising a thermal emitter, a measuring volume designed as a first cavity and an acoustically sensitive element, wherein a gas and/or gas mixture to be analyzed can flow through the measuring volume, wherein the acoustically sensitive element includes a second cavity in which the target gas is contained, and wherein the first cavity and the second cavity are separated from one another solely by a buried insulation layer of a silicon wafer used for production. ### Claim 11 (depends on 10) Photoacoustic gas sensor according to claim 10, wherein no adhesive layer is present between the first cavity and the second cavity.