CN111289584B - Capacitive gas sensor and preparation method thereof - Google Patents
Capacitive gas sensor and preparation method thereof Download PDFInfo
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- CN111289584B CN111289584B CN202010258867.2A CN202010258867A CN111289584B CN 111289584 B CN111289584 B CN 111289584B CN 202010258867 A CN202010258867 A CN 202010258867A CN 111289584 B CN111289584 B CN 111289584B
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Abstract
The invention discloses a capacitive gas sensor, which comprises a shielding layer, support columns, interdigital electrodes positioned above the support columns and a sensitive layer filled between the interdigital electrodes, wherein the shielding layer is arranged on the support columns; the shielding layer is positioned below and around the gas sensor, and when the gas diffuses to the upper surface of the gas sensor, the shielding layer reacts with the sensitive layer chemically or physically, so that the capacitance between the interdigital electrodes changes. According to the capacitive gas sensor and the preparation method, the influence of the electric field between the interdigital electrodes on an external circuit can be shielded, and the sensitivity of the sensor is remarkably improved by changing the height of the sensitive layer and increasing the air gap between the support columns.
Description
Technical Field
The invention relates to a capacitive gas sensor, in particular to a capacitive gas sensor and a preparation method thereof.
Background
Conventional gas sensors use interdigitated electrodes and a gas sensitive layer between the interdigitated electrodes to detect ambient gas. The sensing layer is filled between the interdigital electrodes in the gas sensor, and when the gas diffuses to the sensing layer, the sensing layer can react with the gas physically or chemically, so that the capacitance between the interdigital electrodes is changed, and the capacitance change can reflect the characteristics of the concentration of the gas and the like.
As shown in fig. 1-2, a top view of a prior art gas sensor is shown in fig. 1, and the electric field distribution between the interdigital electrodes is shown in fig. 2. Adjacent interdigital electrodes are respectively a sensor one-end electrode 1 and a sensor other-end electrode 2; the external gas contacts the fork value electrodes along the outer side of the sensor, and the external gas is diffused into a sensitive layer between the fork value electrodes to generate capacitance change. As shown in the electric field profile of fig. 2, the area between the electrodes where the electric field is strongest for the conventional interdigitated electrodes resembles a plate capacitor. However, the time and distance required for the outside air to diffuse to the position between the inter-cross value capacitors are long, and the diffusion amount of the outside air gradually decreases when the outside air diffuses to the position between the inter-cross value electrodes due to the long diffusion distance required for the air to diffuse to the sensitive layer between the inter-cross value electrodes, thereby resulting in poor detection sensitivity. Meanwhile, the prior art fork electrode structure generates a large amount of fringe electric field, and the downward fringe electric field can affect the circuit below the sensor and generate parasitic capacitance.
Disclosure of Invention
According to the capacitive gas sensor and the preparation method, the influence of the electric field between the interdigital electrodes on an external circuit can be shielded, and the sensitivity of the sensor is remarkably improved by changing the height of the sensitive layer and increasing the air gap between the support columns.
In order to achieve the above purpose, the present invention adopts the following technical scheme: a capacitive gas sensor comprises a shielding layer, support columns, interdigital electrodes positioned above the support columns and a sensitive layer filled between the interdigital electrodes; the shielding layer is positioned below and around the gas sensor.
Further, the interdigital electrode has a top dimension smaller than a bottom dimension.
Further, the cross section of the interdigital electrode in the vertical direction is trapezoidal.
Further, the height of the interdigital electrode is smaller than or equal to the dimension of the middle position of the interdigital electrode in the horizontal direction.
Further, the height of the sensitive layer is greater than the height of the interdigital electrode.
Further, an air gap and/or a sensitive layer is arranged between the support columns.
A method of making a capacitive gas sensor comprising the steps of:
s01: depositing and patterning a shielding layer on a substrate to form a bottom shielding layer;
s02: depositing a dielectric isolation layer on the bottom shielding layer and patterning to form support columns;
s03: depositing and patterning a sensitive layer I to form a groove above the support column;
s04: filling interdigital electrodes in the grooves;
s05: and etching and filling metal in the sensitive layer I to form a shielding layer positioned around the interdigital electrode.
Further, the step S03 is preceded by coating a two-dimensional insulating layer between the support columns to form an air gap between the support columns.
Further, the two-dimensional insulating layer includes a sheet-like insulating material having a dimension in a two-dimensional direction that is greater than 1.2 times the dimension of the air gap.
Further, the step S05 further includes depositing a sensitive layer ii on the interdigital electrode, such that the height of the sensitive layer is greater than the height of the interdigital electrode; and shielding layers positioned around the interdigital electrodes are formed in the sensitive layers I and II.
The invention has the following beneficial effects: the invention adopts the interdigital electrode with smaller height relative to the plane size, and generates a large amount of fringe electric fields outside the sensor so as to enhance the electric field and capacitance change of the gas contact area outside the sensor; according to the invention, the shielding layer is added below the sensor, so that an electric field between the interdigital electrodes is mainly distributed on one side of the sensor facing gas, and the influence of the electric field on a lower circuit is shielded; the interdigital electrodes have the characteristic that the top size is smaller than the bottom size, and the height of the sensitive layer is larger than that of the interdigital electrodes, so that gas is fully diffused to a region with a stronger electric field between the interdigital electrodes, and the detection sensitivity of the sensor is improved; according to the invention, the air gap is formed between the support columns, and the sensitivity of the sensor depends on the relative change proportion of the capacitance, so that the whole capacitance of the sensor can be reduced through the air gap, and the detection sensitivity of the sensor is further improved.
Drawings
FIG. 1 is a top view of an interdigitated electrode of the prior art;
FIG. 2 is a schematic diagram of the electric field distribution of an interdigital electrode in the prior art;
FIG. 3 is an overall schematic diagram of a capacitive sensor according to the present invention;
FIG. 4 is a schematic diagram of the shape and electric field distribution of the interdigital electrode of the present invention;
fig. 5 is a schematic illustration of the formation of an air gap in the present invention.
In the figure: the sensor comprises a sensor electrode at one end, a sensor electrode at the other end, a sensitive layer 3, a support column 4, an air gap 5, a shielding layer 6, a sheet-shaped two-dimensional insulating material 11 and a two-dimensional insulating layer 12.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the following detailed description of the specific embodiments of the present invention will be given with reference to the accompanying drawings.
The invention provides a capacitive gas sensor, as shown in figure 3, which comprises a shielding layer 6, support columns 4, interdigital electrodes positioned above the support columns 4 and a sensitive layer 3 filled between the interdigital electrodes; when the gas diffuses to the upper surface of the gas sensor, a chemical or physical reaction with the sensitive layer 3 occurs, so that the capacitance between the interdigital electrodes changes. Adjacent interdigital electrodes in the top view of the interdigital electrodes are a sensor end electrode 1 and a sensor other end electrode 2 respectively.
The shielding layer 6 is positioned below and around the gas sensor, namely comprises a bottom shielding layer and a surrounding shielding layer, the bottom shielding layer enables an electric field between the interdigital electrodes to be mainly distributed on one side of the sensor facing to external gas, namely the upper surface of the sensor in the drawing, and the bottom shielding layer can shield the influence of the electric field generated by the interdigital electrodes on a lower circuit; the surrounding shielding layer surrounds the sensor, so that the influence of the side on the performance of the sensor is reduced, the problems of noise and the like of the sensor are reduced, and the signal-to-noise ratio and the related performance of the sensor are improved.
The sensitive layer in the present invention generally refers to a material having a certain chemical or physical reaction with a gas, such as a metal oxide, etc.
As shown in fig. 2 and 4, the area between the electrodes where the electric field is strongest in the conventional fork-valued electrode resembles a plate capacitor. However, the time required for the external gas to diffuse to the position between the fork-value capacitors is long, and the gas concentration is attenuated, so that the speed and sensitivity of the sensor for detecting the gas are reduced. The invention adopts the interdigital electrode with smaller height relative to the plane size, and generates a large amount of fringe electric fields outside the sensor so as to enhance the electric field and capacitance change of the gas contact area outside the sensor; when the external gas is firstly diffused to the sensitive layer outside the interdigital electrode and is not contacted with the interdigital electrode, the sensitive layer is controlled and influenced by the fringe electric field, and the gas can be detected by the electric field outside the interdigital electrode, so that the sensor has higher sensitivity, higher response speed and better performance.
As shown in fig. 4, the top dimension of the interdigital electrode is smaller than the bottom dimension; specifically, the cross section of the interdigital electrode in the vertical direction can be trapezoidal, or the cross section in the vertical direction is a triangle with small top and large bottom, or the cross section in the vertical direction is an arc triangle, and the like, and the size of the interdigital electrode in the vertical direction is one direction or more than one direction in the horizontal direction only needs to be ensured to be larger than the size of the bottom. The top size of the interdigital electrode is smaller, namely the interdigital electrode facing to the gas side is smaller, so that the gas can be fully diffused to a region with a stronger electric field between the interdigital capacitors, and the sensitivity of detection sensing is enhanced. Because the horizontal cross section sizes corresponding to the interdigital electrodes at different heights are not identical, the height of the interdigital electrode can be specifically smaller than or equal to the horizontal dimension of the middle position of the interdigital electrode, wherein the middle position refers to the horizontal cross section size corresponding to the half height of the interdigital electrode, and can be the maximum dimension on the horizontal cross section.
With continued reference to fig. 3, in the present invention, the height of the sensitive layer is greater than the height of the interdigital electrode, and the sensitive layer higher than the interdigital electrode faces gas, when the gas diffuses into the sensor and does not reach the interdigital electrode, the gas reacts with the sensitive layer, and the change of the sensitive layer can cause the change of the capacitance of the interdigital electrode.
With continued reference to fig. 3, the air gaps 5 and/or the sensitive layers are provided between the support columns in the present invention, and specifically, the gaps between the support columns may be partially air gaps, partially filled with the sensitive layers, may be all air gaps, or may be all sensitive layers. The invention realizes the isolation between the bottom shielding layer and the interdigital electrode through the support column, and the support column is used for supporting the interdigital electrode. The invention forms an air gap between the support columns, so that the sensitivity of the sensor can be improved, because the sensitivity of the sensor depends on the relative change proportion of the capacitance, namely delta C/C, the dielectric constant of air is smaller than that of a sensitive layer, the integral capacitance C of the sensor can be reduced through the air gap between the support columns, and the same capacitance change can cause a larger proportion of relative change.
The invention provides a method for preparing a capacitive gas sensor, which comprises the following steps:
s01: depositing and patterning a shielding layer on a substrate to form a bottom shielding layer;
s02: and depositing and patterning a dielectric isolation layer on the bottom shielding layer to form support columns.
After the support columns are formed, a two-dimensional insulating layer can be coated between the support columns to form air gaps between the support columns, all gaps between the support columns can be formed into the air gaps, only part of the gaps can be formed into the air gaps, and the sensitive layer I can be directly deposited in all the gaps between the support columns. The process of forming the air gap 5 may be as follows: as shown in fig. 5, a two-dimensional insulating layer 12 is coated between the support columns 4 to form air gaps 5 between the support columns; the two-dimensional insulating layer 12 includes a sheet-shaped two-dimensional insulating material 11, for example, a sheet-shaped graphene oxide or the like, and the size of the individual sheet-shaped insulating material 11 in the two-dimensional direction is greater than 1.2 times the size of the air gap; the specific method for coating the two-dimensional insulating layer can be carried out by adopting the processes of immersed film forming, spin coating, dispensing and the like in the prior art; the invention preferably selects the sheet insulating material with the size which is about 1.5 times of the size of the air gap in the two-dimensional direction for sealing the air gap.
S03: and depositing and patterning the sensitive layer I to form a groove above the support column. When air gaps are not completely formed among the support columns, a sensitive layer I is deposited on the upper surface of the two-dimensional insulating layer, the upper surface of the support columns and among the support columns which are not formed with the air gaps in the step, namely, the air gaps are partially formed among the support columns at the moment, and the sensitive layer I is partially filled; when no air gap exists between the support columns, a sensitive layer I is deposited on the upper surfaces of the support columns and between the support columns in the step, namely, the part between the support columns is the sensitive layer I; when the air gap is formed between the support columns, the sensitive layer I is deposited on the upper surfaces of the support columns and the upper surfaces of the two-dimensional insulating layers in the step, namely, the air gap is formed between the support columns.
S04: filling interdigital electrodes in the grooves; the specific interdigital electrode material can be any material in the prior art, and two adjacent interdigital electrodes in the interdigital electrode are two ends of a capacitor.
S05: and depositing a sensitive layer II on the interdigital electrode, and forming shielding layers around the interdigital electrode in the sensitive layer I and the sensitive layer II. In the invention, the sensitive layer I and the sensitive layer II are the same in material, the sensitive layer II and the sensitive layer I jointly form the sensitive layer, and the sensitive layer II is deposited, so that the sensitive layer height is larger than the height of the interdigital electrode and covers the interdigital electrode; the gas diffused to the upper surface of the interdigital electrode can react with the sensitive layer higher than the interdigital electrode, thereby enhancing the sensitivity of the sensor.
The foregoing description is only of the preferred embodiments of the present invention, and the embodiments are not intended to limit the scope of the invention, so that all changes made in the structure and details of the invention which may be regarded as equivalents thereof are intended to be included within the scope of the invention as defined in the following claims.
Claims (6)
1. A method of making a capacitive gas sensor comprising the steps of:
s01: depositing and patterning a shielding layer on a substrate to form a bottom shielding layer;
s02: depositing a dielectric isolation layer on the bottom shielding layer and patterning to form support columns; coating a two-dimensional insulating layer between the support columns to form an air gap between the support columns;
s03: depositing and patterning a sensitive layer I to form a groove above the support column; when air gaps are not completely formed among the support columns, a sensitive layer I is deposited among the upper surface of the two-dimensional insulating layer, the upper surface of the support columns and the support columns which are not formed with the air gaps, namely, the air gaps are partially formed among the support columns at the moment, and the sensitive layer I is partially filled; when no air gap exists between the support columns, a sensitive layer I is deposited on the upper surfaces of the support columns and between the support columns in the step, namely, the part between the support columns is the sensitive layer I; when the air gaps are formed between the support columns completely, depositing a sensitive layer I on the upper surfaces of the support columns and the upper surfaces of the two-dimensional insulating layers in the step, namely, the air gaps are formed between the support columns at the moment;
s04: filling interdigital electrodes in the grooves;
s05: and etching and filling metal in the sensitive layer I to form a shielding layer positioned around the interdigital electrode.
2. A method of manufacturing a capacitive gas sensor according to claim 1, characterized in that the two-dimensional insulating layer comprises a sheet-like insulating material having a dimension in two dimensions that is greater than 1.2 times the dimension of the air gap.
3. The method of manufacturing a capacitive gas sensor according to claim 1, wherein step S05 further comprises depositing a sensitive layer ii on the interdigitated electrodes such that the height of the sensitive layer is greater than the height of the interdigitated electrodes; and shielding layers positioned around the interdigital electrodes are formed in the sensitive layers I and II.
4. A method of making a capacitive gas sensor according to claim 1 wherein the interdigital electrode has a top dimension that is smaller than a bottom dimension.
5. A method of manufacturing a capacitive gas sensor according to claim 1, characterized in that the cross section of the interdigital electrode in the vertical direction is trapezoidal.
6. The method of manufacturing a capacitive gas sensor according to claim 1, wherein the height of the interdigital electrode is equal to or less than the dimension of the intermediate position of the interdigital electrode in the horizontal direction.
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Citations (3)
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| CN105264365A (en) * | 2013-01-11 | 2016-01-20 | 精量电子（法国）公司 | Capacitive sensor integrated onto semiconductor circuit |
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| CN110455899A (en) * | 2019-07-16 | 2019-11-15 | 广州钰芯传感科技有限公司 | A kind of electrochemical gas sensor and its device packaging method |
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| CN105264365A (en) * | 2013-01-11 | 2016-01-20 | 精量电子（法国）公司 | Capacitive sensor integrated onto semiconductor circuit |
| CN109983328A (en) * | 2016-11-23 | 2019-07-05 | 罗伯特·博世有限公司 | Gas sensor and method for probe gas |
| CN110455899A (en) * | 2019-07-16 | 2019-11-15 | 广州钰芯传感科技有限公司 | A kind of electrochemical gas sensor and its device packaging method |
Non-Patent Citations (2)
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| A novel airgap formation scheme by GO nanosheet gap sealing process with extreme low effective dielectric constant;Xiaoxu Kang 等;《Microelectronic Engineering》;20200113;第223卷;第111218（2-6）页第2-4节 * |
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