CN-116888464-B - Gas sensor

Abstract

The invention provides a gas sensor with high response speed and high sensitivity to oxygen. A gas sensor (100) comprises a substrate (10), a first pad electrode (12A) and a second pad electrode (12B), nanowires (14) made of a specific metal, and an oxide layer (16) made of a high-resistance semiconductor of an oxide of a metal different from the metal constituting the nanowires (14). A first pad electrode (12A) and a second pad electrode (12B) are formed on a substrate (10). The nanowire (14) connects the first pad electrode (12A) and the second pad electrode (12B), and is formed on the substrate (10). The oxide layer (16) is formed in contact with the nanowires (14). By the nanowire (14)/oxide layer (16) contact, a high speed response and high sensitivity to oxygen is achieved.

Inventors

• ZHEN DAOFENG
• PAN ZHONGHUI

Assignees

• 国立研究开发法人科学技术振兴机构

Dates

Publication Date

20260505

Application Date

20220215

Priority Date

20210225

Claims (9)

1. 1. A gas sensor, comprising: A substrate having an insulating surface; a first pad electrode and a second pad electrode formed on the insulating surface of the substrate; A nanowire connecting the first pad electrode and the second pad electrode and formed on the insulating surface of the substrate, the nanowire being composed of one or more selected from platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), osmium (Os), iridium (Ir), and alloys thereof, and An oxide layer in contact with the nanowire, the oxide layer being composed of a high-resistance semiconductor of an oxide of a metal different from the metal constituting the nanowire, the oxide layer satisfying at least one or both of (I) being located between the insulating surface of the substrate and the nanowire in contact with a lower surface of the nanowire, (II) being located on the nanowire in contact with an upper surface of the nanowire, When an electric current is caused to flow between the first pad electrode and the second pad electrode, and oxygen is detected based on a change in an electric signal detected between the first pad electrode and the second pad electrode, a first conductive path, which is a path through which carriers pass in the nanowire, and a second conductive path, which is a path through which carriers are injected from the nanowire into the oxide layer, move in the oxide layer, and return again to the nanowire, are formed.
2. 2. The gas sensor according to claim 1, wherein, The nanowire has a linewidth of 5nm or more and 150nm or less.
3. 3. The gas sensor according to claim 1, wherein, The thickness of the nanowire is 1nm or more and 20nm or less.
4. 4. The gas sensor according to claim 1, wherein, The length of the nanowire is more than 80 nm.
5. 5. The gas sensor according to claim 1, wherein, The high-resistance semiconductor constituting the oxide layer is one or more selected from cerium oxide, tin oxide, zirconium oxide, zinc oxide, tungsten oxide, iron oxide, nickel oxide, cerium-zirconium oxide, titanium oxide, cobalt oxide, niobium oxide, tantalum oxide, rhodium oxide, and hafnium oxide.
6. 6. The gas sensor according to claim 1, wherein, The thickness of the oxide layer is 5nm or more.
7. 7. The gas sensor according to claim 1, wherein, The nanowires are in ohmic contact with the oxide layer.
8. 8. The gas sensor according to claim 1, wherein, The substrate is any one of a glass substrate, an alumina substrate, a zirconia substrate, and a silicon substrate having a silicon oxide film formed on a surface thereof.
9. 9. The gas sensor according to claim 1, wherein, The first pad electrode and the second pad electrode are composed of the same kind of metal as the nanowire.

Description

Gas sensor Technical Field The present invention relates to a gas sensor in which nanowires made of a specific metal are combined with an oxide made of a high-resistance semiconductor. Background Currently, various gas sensors are used for electric appliances, vehicles, ships, airplanes, etc. for maintaining daily life. For example, in an automobile, it is necessary to control a mixture ratio of air and fuel supplied to an engine so as to improve combustion efficiency of the engine and to make exhaust gas meet environmental standards, and an oxygen sensor using a solid electrolyte (for example, zirconia) as described in patent literature 1 is used for the control system. As an oxygen sensor, a resistive oxygen sensor using an oxide semiconductor as described in patent document 2 is known. Further, non-patent document 1 describes a gas sensor in which a first pad electrode and a second pad electrode, and a platinum nanowire connecting these pad electrodes are formed on a glass substrate. In this gas sensor, hydrogen gas is detected based on a change in resistance detected between the first pad electrode and the second pad electrode in a state where a constant voltage is applied between the first pad electrode and the second pad electrode. Prior art literature Patent literature Patent document 1, japanese patent application laid-open No. 2015-137998; patent document 2 Japanese patent laid-open No. 2003-149889. Non-patent literature Non-patent literature 1：F.Yang et al.,The Surface Scattering-Based Detection of Hydrogen in Air Using a Platinum Nanowire,Nano Lett.12(2012)2924-2930 Disclosure of Invention Problems to be solved by the invention An oxygen sensor using a solid electrolyte as described in patent document 1 has problems in that a reference gas is required, sensitivity to oxygen is insufficient, and response speed is slow (response time is about tens of seconds). Further, the resistive oxygen sensor using an oxide semiconductor as described in patent document 2 has a response speed of 10 seconds or less even in the case of extremely high temperatures such as 900 ℃ and 600 ℃, but has a response time of several hundred seconds or more even in the case of relatively low temperatures such as 300 ℃ and has a slow response speed, and is not satisfactory for the industrial needs. In addition, in the gas sensor using the platinum nanowire described in non-patent document 1, hydrogen gas can be detected, but oxygen gas is not detected. That is, no verification was made regarding the sensor characteristics such as the response speed and sensitivity to oxygen. In view of the above, an object of the present invention is to provide a gas sensor having a high response speed to oxygen and a high sensitivity. Solution for solving the problem The present inventors have conducted intensive studies in order to solve the above-mentioned problems, and have found out as follows. The present inventors have conceived a gas sensor formed by combining nanowires made of a specific metal such as platinum (Pt) and an oxide layer made of a specific high-resistance semiconductor. By disposing the nanowire in contact with the oxide layer made of the high-resistance semiconductor, a second conductive path is formed in addition to the first conductive path through which carriers (oxygen vacancies, electrons, etc.) pass through the nanowire, and the second conductive path is a path through which carriers (oxygen vacancies, electrons, etc.) are injected from the nanowire into the oxide layer, move in the oxide layer, and return to the nanowire again. The present inventors have found that the presence of these two conduction paths can provide a remarkable effect of a high response speed to oxygen and a high sensitivity. The main structure of the present invention completed based on the above findings is as follows. [1] A gas sensor, comprising: A substrate having an insulating surface; a first pad electrode and a second pad electrode formed on (on or above) the insulating surface of the substrate; A nanowire connecting the first pad electrode and the second pad electrode and formed on the insulating surface (on or above) of the substrate, and composed of one or more selected from platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), osmium (Os), iridium (Ir), and alloys thereof, and An oxide layer in contact with the nanowire, the oxide layer being composed of a high-resistance semiconductor of an oxide of a metal different from the metal constituting the nanowire, the oxide layer satisfying at least one or both of (I) being located between the insulating surface of the substrate and the nanowire, in contact with a lower surface of the nanowire, (II) being located on (on: upper) the nanowire, in contact with an upper surface of the nanowire, A current is caused to flow between the first pad electrode and the second pad electrode, and a gas is detected based on a change in an electrical signal detected between the first pad electro