TWI607214B - Gas sensor manufacturing method - Google Patents

Description

Gas sensor manufacturing method

The invention relates to a method for fabricating a gas sensor, in particular to a method for fabricating a metal layer directly forming a gas sensor by an evaporation method.

In general, the detection of the concentration of ammonia through a gas sensor can be used as an indicator for monitoring environmental pollution, the freshness of food, or monitoring the user's breathing to reflect the health of the user. Ammonia-detecting gas sensors have been extensively studied and are widely used in rapidly emerging wearable devices.

Referring to FIG. 1 , a conventional gas sensor is fabricated by sequentially forming a sensing layer 11 on a conductive substrate 10 and immersing the conductive substrate 10 having the sensing layer 11 in a plurality of polyphenylene. In the organic solvent of the polystyrene ball (PS ball) 12, the polystyrene microspheres 12 are formed on the sensing layer 11 at intervals. Then, a metal layer 13 is deposited on the sensing layer 11 and the polystyrene microspheres 12, and then a portion of the metal layer on the polystyrene microspheres 12 is adhered by a tape (not shown). 13. A portion of the metal layer 13 and the polystyrene microspheres 12 are torn away from the sensing layer 11 to create a plurality of the sensing layers 11 to expose the sensing holes 14.

When the gas sensor is produced in a conventional manner, not only the manufacturing process is complicated, but also when the conductive substrate 10 having the sensing layer 11 is immersed in an organic solvent to form the polystyrene microspheres 12, the organic solvent easily breaks the feeling. The measurement of the layer 11 results in a poor yield of the gas sensor that is subsequently completed.

Accordingly, it is an object of the present invention to provide a method of fabricating a gas sensor.

Therefore, the method for fabricating the gas sensor of the present invention comprises a preparation step, a sensing unit forming step, and a metal layer forming step.

The preparation step is to prepare a conductive substrate.

The sensing unit forming step is to form a sensing unit on the conductive substrate.

The metal layer forming step is to form a metal layer on the sensing unit that is continuous and thick enough to generate a plurality of sensing holes by evaporation, and expose the surface of the sensing unit from the sensing holes.

The effect of the present invention is that by evaporating the metal layer directly on the sensing unit, the metal layer can generate a plurality of sensing holes for exposing the surface of the sensing unit, without immersing the component as in the prior art. The organic solvent or etching step can effectively simplify the overall process and eliminate the use of organic solvents to prevent the sensing unit from being damaged.

Before the present invention is described in detail, it should be noted that in the following description, similar elements are denoted by the same reference numerals.

Referring to FIG. 2 , a gas sensor 2 according to a first embodiment of the present invention includes a conductive substrate 21 , a sensing unit 22 formed on the conductive substrate 21 , and a metal formed on the sensing unit 22 . The layer 23 has a plurality of surfaces of the metal layer 23 exposing the sensing holes 231 to the surface of the sensing unit 22.

Specifically, the sensing unit 22 of the gas sensor 2 of the first embodiment is constituted by a single layer of the active layer 221. The material of the active layer 221 to which the first embodiment is applied is selected from a conductive polymer, and the material of the active layer 221 can still be changed by sensing different gases. Preferably, the active layer 221 of the first embodiment is made of a conductive polymer material capable of sensing ammonia. The metal layer 23 is mainly used for conducting electricity. Therefore, the material of the metal layer 23 is selected to be electrically conductive. The sensing holes 231 of the metal layer 23 pass the gas to be sensed, and the active layer 221 is sensed.

In detail, the mechanism for sensing the gas of the gas sensor 2 of the first embodiment is to measure the current change of the gas sensor 2, that is, before the sensing gas is performed, After a voltage is applied between the metal layer 23 and the conductive substrate 21, the gas is allowed to enter the sensing unit 22 through the sensing holes 231, since the sensing unit 22 can be combined with the gas to be measured, thereby affecting The current value of the gas sensor 2 and the different concentrations of gas cause the gas sensor 2 to generate different current values, thereby knowing the relationship between the gas concentration and the current of the gas sensor 2.

It should be noted that the gas sensor 2 is not limited to the structural aspect of the first embodiment, and the structure of the sensing unit 22 may be changed to constitute a second embodiment as described below.

Referring to FIG. 3, the gas sensor 3 of the second embodiment of the present invention has substantially the same structure as the gas sensor 2 of the first embodiment, except that the sensing unit 22 of the second embodiment is composed of Made of a three-layer film structure. The sensing unit 22 includes a hole injection layer 222 formed on the conductive substrate 21, a hole transport layer 223 formed on the hole injection layer 222, and a layer formed on the hole transport layer 223. Light emitting layer 224.

Specifically, the main purpose of the three-layer structure of the sensing unit 22 of the second embodiment is to change the light-emitting layer 224 to emit light of different intensity when the gas to be sensed enters the sensing unit 22, The material may be selected from a hole injecting material, a hole transporting material, and a light emitting layer material which are commonly used in general organic light emitting diodes (OLEDs).

In detail, the mechanism for sensing the gas by the gas sensor 3 of the second embodiment is to measure the light intensity of the gas sensor 3, that is, before the sensing gas is performed, before the metal layer 23 is performed. After a voltage is applied between the conductive substrate 21 and the gas, the gas is transmitted through the sensing holes 231 to the sensing unit 22. At this time, the gas molecules cause the conductivity of the sensing unit 22 to decrease, affecting the load. The sub-recombination efficiency further reduces the luminous intensity of the luminescent layer 224, thereby knowing the relationship between the gas of different concentrations and the light intensity of the gas sensor 3.

In order to clearly explain the manufacturing method of the gas sensor of the embodiments of the present invention, the gas sensor 2 of the first embodiment and the second embodiment are respectively described below with a specific example 1 and a specific example 2. The method of manufacturing the gas sensor 3. <Specific example 1>

Referring to FIG. 4, a specific example 1 of the method for fabricating the gas sensor of the present invention is used to fabricate the gas sensor 2 of the first embodiment, and the active layer 221 is composed of a polythiophene conjugated polymer. (poly(3-hexythiophene-2,5-diyl), P3HT) is taken as an example. However, the material of the active layer 221 may vary depending on the type of the sensor body.

The method for fabricating the gas sensor includes a preparation step 41, a pre-processing step 42, a sensing unit forming step 43, and a metal layer forming step 44.

First, the preparation step 41 is to prepare an indium tin oxide (ITO) glass substrate as the conductive substrate 21 and as the lower electrode of the gas sensor 2.

Next, the pre-processing step 42 is to irradiate the surface of the conductive substrate 21 with ultraviolet light under ozone conditions to increase the hydrophilicity and work function of the conductive substrate 21.

The sensing unit forming step 43 is to use a chlorobenzene as a solvent and a polythiophene conjugated polymer (P3HT) as a solute, and to prepare a sensing solution having a concentration by weight of 4.5% by weight, and then to apply the sensing solution. The surface of the conductive substrate 21 is applied by spin coating to form a coating layer. Next, the coating layer was dried at a temperature of 200 ° C to obtain the active layer 221. Here, the method of applying the sensing solution is not limited to the spin coating method, and may be a solution process such as a doctor blade coating method or an inkjet coating method.

The metal layer forming step 45 directly deposits a metal thin film having a thickness of not more than 10 nm on the active layer 221 by vapor deposition, and directly forms the sensing holes 231 by the non-dense property of the metal after vapor deposition. This metal layer 23 is used. It is to be noted that in order to ensure that the aluminum film is in a continuous state and the sensing holes 231 can be produced by itself, the thickness of the aluminum film formed by the evaporation of the vapor is between 7 nm and 10 nm. In other words, the metal layer 23 can automatically form a continuous aluminum film with the sensing holes 231 by controlling the thickness of the evaporated aluminum film, and as one of the gas sensors 2 electrode.

In the first embodiment, an aluminum film having a thickness of 10 nm is directly vapor-deposited on the active layer 221 by an evaporation method, and the sensing holes 231 are directly formed as the metal layer 23. It is to be noted that the number and size of the sensing holes 231 automatically generated by forming an aluminum thin film having a thickness of 10 nm by thermal evaporation may vary depending on the vapor deposition rate. <Specific example 2>

A specific example 2 of the method for fabricating the gas sensor of the present invention is for fabricating the gas sensor 3 according to the second embodiment, and the implementation condition of the specific example 2 is substantially the same as the specific example 1. The difference is that the sensing unit forming step 43 of the specific example 2 is to form a three-layer structure to constitute the sensing unit 22.

In detail, the sensing unit forming step 42 of the specific example 2 is a commercial poly(3,4-ethylenedioxythiophene: poly(styrenesulfonate), PEDOT:PSS. )) a conductive polymer is used as the material of the hole injection layer 222, and the conductive polymer is formed on the conductive substrate 21 by spin coating, and then dried at a temperature of 200 ° C to form the hole injection. Layer 222. Next, TFB (poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(p-butylphenyl)))))) was used as the solute and p-xylene ( P-xylene) as a solvent, a solution having a concentration by weight of 2.3 wt% was prepared and formed on the hole injection layer 222 by spin coating, and then dried at a temperature of 180 ° C to constitute the hole Transport layer 223. Finally, F8BT (poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(1,4-benzo-{2,1',3}-thiadiazole)]) was selected as the solute, and P-xylene was used as a solvent to prepare a solution having a concentration by weight of 1.8 wt%, and was formed on the hole transport layer 223 by spin coating, followed by drying at a temperature of 130 ° C. The light emitting layer 224. Here, the method of applying the solution is not limited to the spin coating method, and may be carried out by a solution process such as a doctor blade method or an inkjet coating method. <Data Analysis>

Referring to FIG. 5, FIG. 5 shows an AFM diagram of the metal layer 23 of the gas sensor 2 produced in the specific example 1. As can be seen from the AFM chart of FIG. 5, the aluminum root film having a thickness of 10 nm was deposited to have a square root roughness of 12 nm, and the diameter of the sensing holes 231 (arrows) was observed to be about 0.1 to 0.5 μm. From this, it can be seen that the aluminum thin film having a thickness of 10 nm is vapor-deposited, and the sensing holes 231 can be generated by themselves.

Referring to FIG. 6 and FIG. 7, FIG. 6 shows a current-voltage characteristic curve of the gas sensor 2 prepared in the specific example 1, that is, the metal layer 23 (upper electrode) is grounded, and the conductive substrate is given. 21 (lower electrode) is a bias voltage for measuring the current-voltage characteristic curve of the gas sensor 2 itself. As can be seen from Fig. 6, the initial current (I ₀ ) of 2 V applied to the gas sensor 2 was 20 μA. It is to be noted that the subsequent sensing of ammonia is performed by applying 2 V to the gas sensor 2. Next, the gas sensor 2 is placed in a chamber with nitrogen as a background gas, and ammonia at a concentration of 1 ppm, 5 ppm, and 10 ppm is injected at different times (the columnar body in FIG. 7 represents the time of injecting ammonia). The gas sensor 2 is caused to sense. As can be seen from Fig. 7, when the ammonia is injected, the current of the gas sensor 2 drops significantly, and the larger the concentration of ammonia, the more obvious the current drop. Further, when the ammonia concentrations of 1 ppm, 5 ppm, and 10 ppm were respectively injected in FIG. 7, the current changes (∆I) generated by the gas sensor 2 were 0.58 μA, 2.08 μA, and 2.49 μA, respectively.

Referring to FIGS. 8 and 9, will sense a change in current sensing different concentrations of ammonia ([Delta] I) divided by the initial current (I ₀₎ to give the current rate of change (ΔI / I _0), which is defined as the sensing The response is sent, and the relationship between each concentration of ammonia is plotted as shown in Fig. 8, and the respective concentrations are logarithmically presented as shown in the larger view of Fig. 8. It can be seen that the current change rate (∆I/I ₀ ) has a considerable linearity for different concentrations of ammonia, and therefore, the unknown ammonia concentration can be sensed by the linear relationship. Then, in order to know whether there is still a certain degree of linearity during different sensing periods, the current variation slop of sensing for 10 seconds and sensing for 60 seconds is further calculated, and each concentration is taken as a logarithmic value, and The relationship between the two is shown in Figure 9. As can be seen from Fig. 9, the relationship between the two still has considerable linearity, and even if only 10 seconds of sensing, the current change can be clearly obtained.

Referring to FIG. 10, FIG. 10 shows an AFM diagram of the metal layer 23 of the gas sensor 3 produced in the specific example 2. As can be seen from the AFM diagram of FIG. 10, the aluminum thin film having a thickness of 10 nm can be self-generated to generate the sensing holes 231.

Referring to FIG. 11 , when the gas sensor 3 is used for sensing, the metal layer 23 of the gas sensor 3 is grounded, and after the conductive substrate 21 is biased, the ammonia concentration of 10 ppm and 100 ppm is sensed. The luminous intensity of the gas sensor 3 is measured by the side of the conductive substrate 21. As can be seen from Fig. 11, the brightness of the gas sensor 3 drops significantly after the ammonia injection, and the brightness gradually becomes stable after about 30 seconds to 50 seconds. In detail view, sensing the concentration of ammonia in 10ppm, its brightness dropped from 10cd / m ² to 5cd / m ^2; when sensing the concentration of ammonia and 100ppm, which is close to the luminance decreased to 0cd / m ^2, The gas sensor 3 is made to be in a dark state.

Referring to Figure 12, in order to verify the cause of the decrease in brightness, the light-emitting spectral intensity (PL intensity) is measured by sensing the ammonia with a single layer of the light-emitting layer 224 (F8BT). 12 shows the photoexcitation fluorescence spectrum intensity of the luminescent layer 224 sensing the concentration of 10 ppm and 100 ppm of ammonia, respectively, after measuring the luminescent layer 224 (F8BT) in a single layer for 10 minutes in a nitrogen atmosphere.

Referring to FIG. 13, the intensity spectrum of each of the light-excited fluorescence spectra of the wavelength of 544 nm of FIG. 12 is further selected to plot the intensity spectrum of the photoexcited fluorescence spectrum of FIG. It can be seen that only the concentration of 100 ppm of ammonia causes the intensity of the photoexcited fluorescence spectrum of the light-emitting layer 224 to decrease slightly. Therefore, it can be seen that the reason why the brightness of the gas sensor 3 is lowered in FIG. 11 is not from the light-emitting layer 224. The fluorescence quench should be due to a decrease in the recombination of the carrier in the luminescent layer 224.

Referring to FIG. 14, it can be further verified from this observation that it is apparent from FIG. 14 that when the gas sensor 3 senses ammonia having a concentration of 10 ppm, the current value thereof is significantly decreased, thereby knowing that when ammonia is used When entering the gas sensor 3, the conductivity of the hole is significantly reduced, and the number of composite carriers in the light-emitting layer 224 is reduced, resulting in a decrease in the luminance of the light.

In summary, the method for fabricating the gas sensor of the present invention directly deposits the metal layer 23 on the sensing unit 22 by the metal layer forming step 45, so that the metal layer 23 generates a plurality of self-generating portions for the sensing. The sensing hole 231 exposed on the surface of the unit 22 not only simplifies the overall process, but also prevents the sensing unit 22 from being immersed in the organic solvent and is destroyed as compared with the prior art manufacturing method, so that the object of the present invention can be achieved.

However, the above is only the embodiment of the present invention, and the scope of the invention is not limited thereto, and all the simple equivalent changes and modifications according to the scope of the patent application and the patent specification of the present invention are still Within the scope of the invention patent.

2‧‧‧ gas sensor
23‧‧‧metal layer
21‧‧‧Electrical substrate
231‧‧‧Sense hole
22‧‧‧Sensor unit
3‧‧‧ gas sensor
221‧‧‧ active layer
41‧‧‧Preparation steps
222‧‧‧ hole injection layer
42‧‧‧Pretreatment steps
223‧‧‧ hole transport layer
43‧‧‧Sensor unit formation steps
224‧‧‧Lighting layer
44‧‧‧ Metal layer formation steps

Other features and effects of the present invention will be apparent from the following description of the drawings, wherein: FIG. 1 is a flow diagram illustrating a method of making a conventional gas sensor; FIG. 2 is a side view showing A gas sensor according to a first embodiment of the present invention; FIG. 3 is a side view showing a gas sensor according to a second embodiment of the present invention; FIG. 4 is a flow chart illustrating the gas sensor of the present invention. Figure 5 is an atomic force microscope (AFM) diagram illustrating the surface pattern of the gas sensor of the first embodiment; Figure 6 is a current versus voltage diagram illustrating the specific The current sensor corresponding to the specific voltage applied by the gas sensor prepared in Example 1; FIG. 7 is a current versus time diagram illustrating the current of the gas sensor produced in the specific example 1 for sensing different concentrations of ammonia. Figure 8 is a graph of current change rate versus concentration, illustrating the current change rate of the gas sensor produced in the specific example 1 for sensing different concentrations of ammonia; Figure 9 is a slope versus concentration diagram illustrating specific The gas sensor prepared in Example 1 senses the change in the slope of different concentrations of ammonia; FIG. 10 is an atomic force microscope diagram illustrating the surface pattern of the gas sensor fabricated in the specific example 2; FIG. 11 is a brightness For the time relationship diagram, the gas sensor produced in the specific example 2 is used to sense the change in brightness of different concentrations of ammonia over time; FIG. 12 is a photoluminescence intensity (PL Intensity) versus wavelength of light. The relationship diagram illustrates the wavelength distribution of different concentrations of ammonia in a light-emitting layer of the gas sensor produced in the specific example 2; FIG. 13 is a graph showing the intensity of the spectrum of the photoexcited fluorescence versus time, and an auxiliary explanatory diagram. 12 photoexcitation fluorescence spectral intensity at different concentrations of ammonia at a wavelength of 544 nm; and FIG. 14 is a current versus time diagram illustrating the gas sensor produced in the specific example 2 at a sensing concentration of 10 ppm ammonia Current change

41‧‧‧Preparation steps

42‧‧‧Pretreatment steps

43‧‧‧Sensor unit formation steps

44‧‧‧ Metal layer formation steps

Claims (9)

A method for fabricating a gas sensor includes the following steps: a preparation step of preparing a conductive substrate; a sensing unit forming step of forming a sensing unit on the conductive substrate; and a metal layer forming step for vapor deposition The method forms a continuous metal layer on the sensing unit that is thick enough to generate a plurality of sensing holes, and exposes the surface of the sensing unit from the sensing holes. The method of fabricating the gas sensor according to claim 1, wherein the metal layer forming step is to form the metal layer having a thickness of 7 nm to 10 nm by thermal evaporation. The method of manufacturing the gas sensor according to claim 1, wherein the sensing unit is formed by forming an active layer made of a conductive polymer material on the conductive substrate to form the sensing unit, and the metal layer is formed. The step is to form the metal layer on the active layer. The method for fabricating a gas sensor according to claim 1, wherein the sensing unit is formed by forming a hole injection layer on the conductive substrate, forming a hole transport layer on the hole injection layer, and A light-emitting layer is formed on the hole transport layer to jointly form the sensing unit. The metal layer forming step is to form the metal layer on the light-emitting layer. The method for fabricating a gas sensor according to claim 3, wherein the sensing unit forming step forms the active layer by a solution process and dries the active layer. The method of fabricating a gas sensor according to claim 4, wherein the sensing unit forming step is to form the hole injection layer, the hole transport layer, and the light emitting layer by a solution process. The method of fabricating a gas sensor according to claim 5 or 6, wherein the solution process comprises a spin coating method, a knife coating method, and an inkjet coating method. The method for fabricating a gas sensor according to claim 1, further comprising a pretreatment step performed after the preparing step, irradiating the conductive substrate with ultraviolet light under ozone conditions. The method of fabricating a gas sensor according to claim 3, wherein the active layer of the sensing unit forming step is composed of a polythiophene conjugated polymer.