US-12618792-B2 - Gas sensor

Abstract

A gas sensor includes a base member, a first insulating film, a second insulating film, a heater section, a flat section, and a gas detection section. The base member is provided with a cavity. The first insulating film includes beam portions connected to a peripheral portion of the cavity of the base member and a first-insulating-film membrane portion held over the cavity by the beam portions. The second insulating film is laminated on an upper side of the first insulating film. The heater section is provided on an upper side of the first-insulating-film membrane portion. The flat section is provided between the first-insulating-film membrane portion and the second insulating film and disposed closer to a center of the first-insulating-film membrane portion than the heater section and forms a flat surface. The gas detection section is disposed on at least the second insulating film over the flat section.

Inventors

• Makoto Shibata
• Shizuko Ono
• Takumi Matsuo

Assignees

• TDK CORPORATION

Dates

Publication Date

20260505

Application Date

20231208

Priority Date

20221215

Claims (12)

1. 1 . A gas sensor comprising: a base member provided with a cavity; a first insulating film including: a plurality of beam portions connected to a cavity peripheral portion as a peripheral portion of the cavity of the base member; and a first-insulating-film membrane portion held over the cavity by the beam portions; a second insulating film laminated on an upper side of the first insulating film; a heater section provided on an upper side of the first-insulating-film membrane portion; a flat section provided between the first-insulating-film membrane portion and the second insulating film, disposed closer to a center of the first-insulating-film membrane portion than the heater section when viewed from above, and forming a flat surface facing upward; and a gas detection section disposed on at least the second insulating film over the flat section and having an area smaller than that of the flat surface.
2. 2 . The gas sensor according to claim 1 , wherein the flat section has a thermal conductivity higher than that of the second insulating film.
3. 3 . The gas sensor according to claim 1 , wherein the flat section has the same material as the heater section.
4. 4 . The gas sensor according to claim 1 , wherein the heater section includes a bending portion repeatedly bending with an amplitude of ½ or less of a length of a side of the first-insulating-film membrane portion having a substantially rectangular shape.
5. 5 . The gas sensor according to claim 1 , wherein the heater section has a symmetrical shape with respect to a reference line extending in a horizontal direction through the center of the first-insulating-film membrane portion.
6. 6 . The gas sensor according to claim 1 , wherein the heater section is connected to the flat section.
7. 7 . The gas sensor according to claim 1 , wherein the gas detection section includes at least a pair of electrodes in contact with a semiconductor material, and gas is detected based on resistance change between the electrodes.
8. 8 . The gas sensor according to claim 1 , wherein the gas detection section includes a Pt wire in contact with a catalyst material, and gas is detected based on resistance change of the Pt wire.
9. 9 . The gas sensor according to claim 1 , wherein the gas detection section includes at least a pair of electrodes in contact with a thermistor film, and gas is detected based on resistance change between the electrodes.
10. 10 . The gas sensor according to claim 9 , wherein the thermistor film is in contact with a catalyst material.
11. 11 . The gas sensor according to claim 1 , further comprising a heater wiring section connecting a heater terminal provided in the cavity peripheral portion and the heater section through an upper side of at least one of the beam portions.
12. 12 . The gas sensor according to claim 1 , further comprising a detection wiring section connecting a detection terminal provided in the cavity peripheral portion and the gas detection section through an upper side of at least one of the beam portions.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS The present application claims priority from Japanese Patent Application No. 2022-200511 filed on Dec. 15, 2022, and Japanese Patent Application No. 2023-150361 filed on Sep. 15, 2023, the entire contents of which are hereby incorporated by reference. BACKGROUND The present disclosure relates to a gas sensor. A gas sensor is a device that detects gases existing in an atmosphere and converts information on their type, concentration, etc., into electrical signals for output. Such a gas sensor is installed in home appliances, industrial equipment, environmental monitoring equipment, etc. and is used to detect the concentration of specific gases that affect humans, the environment, etc. Various detection methods are known for gas sensors, depending on the type of gas to be detected, concentration range, accuracy, operating principle, constituent material, etc. Among them, a gas sensor combining a detection section and a heater for controlling the temperature around the detection section is being developed as a sensor capable of reducing errors caused by temperature effects. For example, as one of the gas sensors according to the prior art, there is a gas sensor with a heater wire disposed on the outer periphery of a membrane and a detection electrode disposed on the inner part of the membrane (see, for example, Patent Document 1). In such a gas sensor, it is difficult to transmit heat from the heater wire to the central part of the membrane, which may increase the non-uniformity of temperature distribution around the detection electrode and adversely affect detection stability. Meanwhile, a technique is also proposed in which a heater wire and a detection electrode are stacked in layers in a membrane (see, for example, Patent Document 2). In such a technique, it is difficult to form the detection electrode as an upper layer on a flat surface due to the unevenness of the pattern shape of the heater wire as a lower layer, so there are problems that local distortions tend to occur in the shape of the detection electrode, which destabilizes the detection signal and reduces detection responsiveness. Moreover, in the technique of stacking the heater wire and the detection electrode in layers, it is conceivable to planarize an intermediate layer by CMP, etc., but if such a measure is taken, there are problems that lead to an increase in process lead time and cost. Patent Document 1: JP6960645 (B2)Patent Document 2: JP6877397 (B2) SUMMARY It is desirable to provide a gas sensor capable of being manufactured in a simple process and demonstrating good detection stability and detection responsiveness. A gas sensor according to the present disclosure comprises: a base member provided with a cavity;a first insulating film including: a plurality of beam portions connected to a cavity peripheral portion as a peripheral portion of the cavity of the base member; anda first-insulating-film membrane portion held over the cavity by the beam portions; a second insulating film laminated on an upper side of the first insulating film;a heater section provided on an upper side of the first-insulating-film membrane portion;a flat section provided between the first-insulating-film membrane portion and the second insulating film, disposed closer to a center of the first-insulating-film membrane portion than the heater section when viewed from above, and forming a flat surface facing upward; anda gas detection section disposed on at least the second insulating film over the flat section and having an area smaller than that of the flat surface. BRIEF DESCRIPTION OF THE DRAWING(S) FIG. 1 is a schematic plan view of a gas sensor according to First Embodiment of the present disclosure; FIG. 2 is a schematic cross-sectional view of the gas sensor shown in FIG. 1 along II-II; FIG. 3 is a schematic cross-sectional view of the gas sensor shown in FIG. 1 along III-III; FIG. 4 is a schematic cross-sectional view of the gas sensor shown in FIG. 1 along IV-IV; FIG. 5 is a partially enlarged view illustrating the shapes of a heater section, a gas sensor section, and the like in the gas sensor shown in FIG. 1; FIG. 6 is a partially enlarged view illustrating the shapes of a heater section, a flat section, and the like in the gas sensor shown in FIG. 1; FIG. 7 is an enlarged cross-sectional view of a section of the gas sensor shown in FIG. 2 disposed on the upper side of a cavity; FIG. 8 is a schematic plan view of a gas sensor according to Second Embodiment of the present disclosure; FIG. 9 is a schematic cross-sectional view of the gas sensor shown in FIG. 8 along IX-IX; FIG. 10 is a schematic cross-sectional view of the gas sensor shown in FIG. 8 along X-X; FIG. 11 is a partially enlarged view illustrating the shapes of a heater section, a gas sensor section, and the like in the gas sensor shown in FIG. 8; FIG. 12 is an enlarged cross-sectional view illustrating a section of the gas sensor shown