CN113495088A

CN113495088A - Gas sensor

Info

Publication number: CN113495088A
Application number: CN202110187406.5A
Authority: CN
Inventors: 简志轩; 骆玠錞; 黄柏恺; 蔡明志; 何羽轩
Original assignee: Nuvoton Technology Corp
Current assignee: Nuvoton Technology Corp
Priority date: 2020-04-01
Filing date: 2021-02-18
Publication date: 2021-10-12
Also published as: TW202138802A; TWI747223B

Abstract

A gas sensor includes a substrate, a plurality of electrodes, and at least one sensing structure. The electrodes are disposed on the substrate and spaced apart from each other by a distance, wherein each electrode has a first thickness. The sensing structure is arranged between the electrodes and is in direct contact with the electrodes, wherein the sensing structure has a second thickness which is 0.01-1.1 times of the first thickness.

Description

Gas sensor

Technical Field

The present invention relates to a gas sensing technology, and more particularly, to a gas sensor with good sensitivity.

Background

Due to the advances of science and technology in recent years, intelligent devices are popularized, and products after the science and technology are more and more oriented to three directions, namely intellectualization, automation and cloud end; the smart phone is as small as a basic smart phone, and a plurality of sensors are integrated in the smart phone, so that the smart phone can bring the efficiency of the sensors to the maximum and bring full-automatic driving experience to people.

Various types of sensors have been used in various fields, and for example, gas sensors generally employ a sensing material formed on an electrode structure by coating the entire surface of the electrode structure, so that the electrode is completely covered in a sensing region.

However, although the current gas sensor has a significant rate of change (variation) in transient response (transient response), there is also a non-negligible error disturbance that affects the sensitivity of the sensor (sensitivity).

Disclosure of Invention

The invention provides a gas sensor, which can improve the sensitivity of the gas sensor and greatly reduce the use amount of sensing materials on the gas sensor.

The invention provides a gas sensor, which comprises a substrate, a plurality of electrodes and at least one sensing structure. The electrodes are disposed on the substrate and spaced apart from each other by a distance, wherein each electrode has a first thickness. The sensing structure is arranged between the electrodes and is in direct contact with the electrodes, wherein the sensing structure has a second thickness which is 0.01-1.1 times of the first thickness.

In an embodiment of the invention, the second thickness of the sensing structure is smaller than the first thickness.

In an embodiment of the invention, the second thickness of the sensing structure is less than half of the first thickness.

In an embodiment of the invention, the second thickness of the sensing structure is higher than the first thickness.

In an embodiment of the invention, the sensing structure partially covers the plurality of electrodes.

In an embodiment of the invention, the first distance is between 1 μm and 1000 μm.

In an embodiment of the invention, the sensing structures may be a plurality of sensing structures, and the plurality of sensing structures are separated from each other by a second distance, and the second distance is less than or equal to the width of each electrode.

In an embodiment of the invention, a variation rate of the second distance is ± 20%.

In an embodiment of the invention, the electrode includes a interdigital electrode.

In an embodiment of the invention, the substrate includes a Printed Circuit Board (PCB), and the electrode is a circuit of the PCB.

Based on the above, the present invention increases the change rate of the gas sensor by reducing the film thickness of the region not affected by the gas in the sensing structure, in other words, the film thickness of the region affected by the gas is relatively increased, thereby improving the sensitivity of the gas sensor. Moreover, due to the reduction of the thickness of the film layer, compared with the traditional sensing material of the whole surface covering type, the usage amount of the sensing material can be greatly reduced.

In order to make the aforementioned and other features and advantages of the invention more comprehensible, embodiments accompanied with figures are described in detail below.

Drawings

Fig. 1 is a schematic top view of a gas sensor according to an embodiment of the present invention.

Fig. 2A is a schematic cross-sectional view of a gas sensor taken along line a-a' of fig. 1.

Fig. 2B is a cross-sectional schematic view of another gas sensor, taken along line a-a' of fig. 1.

FIG. 3A is a graph of the total variation rate (total variation) versus the variation rate of the area of electrically affected gas.

FIG. 3B is a graph of the total rate of change versus the rate of change of the area of the electrical property affected by the gas as a function of the thickness parameter.

Fig. 4 is a schematic top view of a gas sensor in accordance with another embodiment of the present invention.

Fig. 5 is a schematic cross-sectional view of a gas sensor of the line a-a' of fig. 4.

Fig. 6 is a schematic top view of a gas sensor according to yet another embodiment of the present invention.

[ notation ] to show

100. 400, 600 gas sensor

102 substrate

104 electrodes

106. 402, 602 sensing structure

106a, 106b areas

d1 first distance

d2 second distance

t1 first thickness

t2 second thickness

ta, tb thickness

w is width

Detailed Description

The following provides more than one embodiment for implementing various features of the invention. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to limit the scope or application of the invention. In addition, the relative thicknesses, distances, and locations of various regions or layers may be reduced or exaggerated for clarity. Additionally, the use of similar or identical reference symbols in the drawings indicates the presence of similar or identical elements or features.

Referring to fig. 1, a gas sensor 100 includes a substrate 102, a plurality of electrodes 104, and at least one sensing structure 106. The electrodes 104 are disposed on the substrate 102 and separated from each other by a first distance d1, and the sensing structure 106 directly contacts the electrodes 104. The gas sensor 100 is, for example, a resistive sensor or a capacitive sensor. The sensing principle of the resistive sensor mainly utilizes the fact that when the sensing structure 106 which is conductive and connected with the electrode 104 adsorbs gas, the resistance of the sensing structure 106 changes correspondingly, so that measurement is performed; the sensing principle of the capacitive sensor is that when the sensing structure 106 adsorbs gas molecules, the dielectric coefficient changes and the capacitance value changes to perform measurement. The electrodes 104 are, for example, fork-shaped electrodes, and thus the first distance d1 represents the spacing between the fingers of different fork-shaped electrodes. In the present embodiment, the first distance d1 is, for example, between 1 μm and 1000 μm. If the electrodes 104 are normal bulk electrodes, the spacing between the two bulk electrodes is the first distance d1, and so on. In one embodiment, the substrate 102 may be a Printed Circuit Board (PCB), and the electrode 104 is a circuit of the PCB.

In fig. 2A, each electrode 104 has a first thickness t1, the sensing structure 106 is between the electrodes 104, and the sensing structure 106 has a second thickness t2, wherein the second thickness t2 is smaller than the first thickness t1, and the second thickness t2 is, for example, more than 0.01 times the first thickness t 1. In one embodiment, the first thickness t1 is, for example, around 100 μm; the second thickness t2 is, for example, 1 μm or more. Since the region 106a of the sensing structure 106, which is electrically affected by the gas, is substantially fixed on the surface of the sensing structure 106, and the region 106b, which is not affected by the gas, is under the sensing structure, the sensing structure 106 between the two electrodes 104 is an equivalent resistance composed of Ra and Rb, wherein Ra represents the resistance of the region 106a and Rb represents the resistance of the region 106b, so the total resistance R is_totalRa × Rb/(Ra + Rb). And Rb Ra/t, t represents the thickness parameter, i.e., t tb/ta, where ta represents the thickness of the area 106a and tb represents the thickness of the area 106b, and t is proportional to tb because ta is almost a fixed value.

Assuming that the thickness of the region 106b is 10 times the thickness of the region 106a (t is 10), the trend of the total variation rate (total variation) obtained by simulation with respect to the variation rate of the region 106a is shown in fig. 3A, in which the value of the Y axis (total variation rate) is equal to Δ R_total/R_totalX 100; the value of the X-axis (rate of change of region 106 a) is equal to Δ Ra/Ra × 100. As can be seen from fig. 3A, when the rate of change of the area 106a is 10%, the total rate of change is less than 1. Once t becomes smaller (i.e., the thickness of the region 106B becomes smaller), the overall rate of change will be as small as 10% for the region 106a as shown in FIG. 3B, but the overall rate of change can be from smallIncreasing to more than 3 (t-2) in 1 (t-10), the foot is raised by 400%. In other words, the thinner the thickness of the region 106b, the higher the overall rate of change. The increase in the total rate of change can reduce the influence of error interference on the sensing result, thereby improving the sensitivity of the gas sensor 100. In one embodiment, the sensing structure 106 may be formed between the electrodes 104 by an Aerosol Jet Printing process or the like. Since the thickness of the sensing structure 106 (the second thickness t2) is significantly thinner than that required conventionally, the material usage is reduced accordingly, thereby achieving the effect of reducing the cost. In addition, the present embodiment can achieve the effect of improving the sensitivity without additionally providing a heater under the substrate 102.

FIG. 2B is a cross-sectional view of another gas sensor along line A-A' of FIG. 1, wherein the difference from FIG. 2A is that the second thickness t2 of the sensing structure 106 is less than half of the first thickness t1, such as the second thickness t2 of the sensing structure 106 is equal to the thickness of the region 106a, and the second thickness t2 can be more than 0.01 times the first thickness t 1.

Fig. 4 is a schematic top view of a gas sensor according to another embodiment of the present invention, wherein the same or similar components are denoted by the reference numerals in fig. 1, and the description of the same components can refer to the related contents, which are not repeated herein.

In fig. 4, sensing structure 402 of gas sensor 400 partially covers electrode 104. As can be seen from the cross-sectional view (fig. 5), the second thickness t2 of the sensing structure 402 is slightly higher than the first thickness t1, and the second thickness t2 is, for example, 1.1 times or less of the first thickness t 1. In one embodiment, the first thickness t1 is above 1 μm, for example, and the second thickness t2 is around 1.1 μm, for example. Furthermore, from a cross-section of the line A-A', because the sensing structures 402 partially cover the electrodes 104, the second distance d2 between the sensing structures 402 is less than the width w of each electrode 104. In another embodiment, when the second thickness t2 of the sensing structure 402 is equal to the first thickness t1 of the electrode 104 in height (t2/t1 equals 1), the second distance d2 is equal to the width w of the electrode 104.

Fig. 6 is a schematic top view of a gas sensor according to still another embodiment of the invention, in which the same or similar components are denoted by the reference numerals in fig. 1, and the description of the same components can refer to the above-mentioned related contents, which are not repeated herein.

In fig. 6, gas sensor 600 has several sensing structures 602 that partially cover electrodes 104. Therefore, the second distance d2 separating the sensing structures 602 is smaller than (or equal to) the width w of the electrode 104, wherein the variation rate of the second distance d2 is, for example, ± 20%.

In summary, the present invention reduces the film thickness of the region not affected by the gas in the sensing structure, maintains the thickness of the region affected by the gas, and can increase the total change rate of the gas sensor, thereby improving the sensitivity of the gas sensor. Moreover, since the thickness of the sensing structure is reduced, compared with the traditional whole-surface covering type sensing structure, the material usage amount can be greatly reduced, and the cost is reduced.

Although the present invention has been described with reference to the above embodiments, it should be understood that various changes and modifications can be made therein by those skilled in the art without departing from the spirit and scope of the invention.

Claims

1. A gas sensor, comprising:

a substrate;

the electrodes are arranged on the substrate, are separated by a first distance and have a first thickness; and

at least one sensing structure between the electrodes and directly contacting the electrodes, wherein the sensing structure has a second thickness, and the second thickness is 0.01 times to 1.1 times the first thickness.

2. The gas sensor of claim 1, wherein the second thickness of the sensing structure is less than the first thickness.

3. The gas sensor of claim 2, wherein the second thickness of the sensing structure is less than half of the first thickness.

4. The gas sensor of claim 1, wherein the second thickness of the sensing structure is higher than the first thickness.

5. The gas sensor according to claim 4, wherein the sensing structure partially covers the plurality of electrodes.

6. The gas sensor according to claim 1, wherein the first distance is between 1 μ ι η and 1000 μ ι η.

7. The gas sensor according to claim 1, wherein the at least one sensing structure is a plurality of sensing structures, and the plurality of sensing structures are separated from each other by a second distance, and the second distance is less than or equal to a width of each of the electrodes.

8. The gas sensor according to claim 7, wherein the rate of change of the second distance is ± 20%.

9. The gas sensor of claim 1, wherein the plurality of electrodes comprises interdigitated electrodes.

10. The gas sensor of claim 1, wherein the substrate comprises a printed circuit board and the plurality of electrodes are circuitry of the printed circuit board.