Sensitive device and method of forming the same

A sensitive device includes a plurality of first conductive nanostructures, a conductive layer and at least one electrode. The conductive layer covers the first conductive nanostructures. An intrinsic melting point of the conductive layer is higher than that of the first conductive nanostructures. At least one of the conductive layer and the first conductive nanostructures is sensitive to gas. The electrode is electrically connected to at least one of the first conductive nanostructures and the conductive layer.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Chinese Application Serial Number 201610988314.6, filed Nov. 10, 2016, which is herein incorporated by reference.

BACKGROUND

Technical Field

The present disclosure relates to a sensitive device and the method of forming the same.

Description of Related Art

Gas sensor can absorb gas through a gas sensitive device. Variation of physical or chemical property (such as electrical resistance variation) is generated as the gas sensitive device absorbs gas, and hence the gas sensor can detect gas using the variation of property. With the improvement of material technology, conductive nanomaterial is widely used in many fields. Because the conductive nanomaterial has an excellent electrical conductivity, some gas sensors also include conductive nanomaterial to serve as sensitive device. However, forming the gas sensor with the conductive nanomaterial still faces with some difficulties to be overcome.

SUMMARY

Some embodiments of the present disclosure can effectively use conductive nanomaterial as a sensitive device of a gas sensor.

According to some embodiments of the present disclosure, a sensitive device includes a plurality of first conductive nanostructures, a conductive layer and at least one electrode. The conductive layer covers the first conductive nanostructures. An intrinsic melting point of the conductive layer is higher than that of first conductive nanostructures. At least one of the conductive layer and the first conductive nanostructures is sensitive to gas. The electrode is electrically connected to at least one of the first conductive nanostructures and conductive layer.

According to some embodiments of the present disclosure, a method of forming a sensitive device includes forming a plurality of conductive nanostructures on a substrate; covering a group of the conductive nanostructures with a conductive layer, and exposing another group of the conductive nanostructure, wherein at least one of the conductive nanostructures and the conductive layer is sensitive to gas; performing a thermal process to the conductive layer and the conductive nanostructures, wherein the exposed group of conductive nanostructures are melted by the thermal process, and the covered group of conductive nanostructures are not melted by the thermal process; and forming at least one electrode to electrically connect to at least one of the conductive layer and the covered group of conductive nanostructures.

In the foregoing embodiments, when the conductive nanostructures and conductive layer undergo a thermal process, the conductive layer can prevent the conductive nanostructures from being melted or even broken by the thermal process. This is due to the fact that the intrinsic melting point of the conductive layer covering the conductive nanostructures is higher than that of the conductive nanostructures. As a result, the embodiments of the present disclosure can effectively use conductive nanomaterial to form the sensitive device of the gas sensor, and is advantageous to satisfy high temperature operations of the gas sensor as well.

DETAILED DESCRIPTION

FIG. 1is a top view of a sensitive device in accordance with some embodiments of the present disclosure.FIG. 2is a cross-sectional view of the sensitive device taken along line2-2inFIG. 1. As shown inFIGS. 1 and 2, the sensitive device includes a plurality of first conductive nanostructures100, a conductive layer200and electrodes300. The conductive layer200is disposed on the first conductive nanostructures100. In other words, the first conductive nanostructures100are covered with the conductive layer200. The electrodes300are electrically connected to at least one of the first conductive nanostructures100and the conductive layer200. In other words, in some embodiments, the electrodes300may be electrically connected to the first conductive nanostructures100, but not be connected to the conductive layer200; in some embodiments, the electrodes300may be electrically connected to the conductive layer200, but not connected the first conductive nanostructures100; in some other embodiments, the electrode300may be electrically connected to the first conductive nanostructures100and the conductive layer200.

At least one of the first conductive nanostructures100and the conductive layer200is sensitive to gas. It is understood that, in this context, a device is “sensitive to gas” refers to that a resistance or other electric properties of the device vary when the device absorbs the gas. In other words, in some embodiments, the first conductive nanostructures100are sensitive to gas, and hence variation of the resistance or the other electric properties can be generated when the first conductive nanostructures100absorb gas; in some embodiments, the conductive layer200is sensitive to gas, and hence variation of the resistance or the other electric properties can be generated when the conductive layer200absorbs gas; in some embodiments, the first conductive nanostructures100and the conductive layer200are sensitive to gas, so that the resistance or the other electric properties of them are varied due to absorption of gas. Based on such characteristics, the gas sensor can use the electrodes300to detect the variation of the resistance or other electric properties of the first conductive nanostructures100, conductive layer200or combinations thereof, so that gas detection can be enabled. As a result, the first conductive nanostructures100, conductive layer200and electrodes300can in combination serve as the sensitive device of the gas sensor.

Due to the fact that a scale of the first conductive nanostructures100is nanoscale, a specific surface area of the first conductive nanostructures100is larger than that of large-sized conductive structures (for example, the scale of the conductive structures is micrometer-scaled or even millimeter-scaled), so as to benefit gas absorption, and hence gas detection ability can be improved. Moreover, the large specific surface area of the first conductive nanostructures100is advantageous to increase electric conductivity. In some embodiments, the first conductive nanostructures100may be conductive nanowires or conductive nanorods.

Due to the fact that the scale of the first conductive nanostructures100is nanoscale, the first conductive nanostructures100are susceptible to high temperature, so that the first conductive nanostructures100may be broken as they melt due to the high temperature. Therefore, in some embodiments, an intrinsic melting point of the conductive layer200is higher than that of the first conductive nanostructures100. Because the conductive layer200covers the first conductive nanostructures100and has higher melting point than that of the first conductive nanostructures100, the conductive layer200can prevent the first conductive nanostructures100from melting due to the high temperature. Therefore, when the first conductive nanostructures100and the conductive layer200are together in the high temperature ambience, the conductive layer200can prevent the underlying first conductive nanostructures100from melting in high temperature ambience. As a result, the sensitive device can be operated in high temperature ambience, and hence is satisfactory for a high temperature operation. Furthermore, because the conductive layer200can help the first conductive nanostructures100to resist against the high temperature, the conductive layer200can protect the first conductive nanostructures100when forming steps of the sensitive device include a high temperature treatment (for example, annealing process).

In some embodiments, the first conductive nanostructures100may include sliver, so that the first conductive nanostructures100may be silver nanowires. In some embodiments, material of the conductive layer200can include metallic oxide, and the metallic oxide may be ITO, IZO, AZO, AlO, INO, GAO or combinations thereof. Due to the fact that the melting point of the metallic oxide is higher than that of the silver nanowires, the metallic oxide can prevent the underlying silver nanowires from melting in high temperature. As a result, the metallic oxide and the silver nanowires can be operated in high temperature ambience, so the gas detection ability is not affected by the high temperature. Furthermore, the metallic oxide may be sensitive to the gas, so that resistance or other electric properties thereof may vary as it absorbs gas. Furthermore, even though the silver nanowires are covered with the metallic oxide and are therefore hard to absorb the gas on surfaces thereof, the sensitive device can still use the metallic oxide to absorb the gas, and then uses a gas sensitive property of the metallic oxide to achieve gas detection.

In some embodiments, the first conductive nanostructures100are wrapped in the conductive layer200. In other words, the surfaces of the first conductive nanostructures100can contact the conductive layer200, and are enclosed by the conductive layer200. Therefore, the conductive layer200with high melting point can protect the first conductive nanostructures100with low melting point in a more comprehensive manner, so as to prevent the first conductive nanostructures100with low melting point from melting due to the high temperature.

In some embodiments, the sensitive device can also include a substrate400. The substrate400can carry the first conductive nanostructures100. In other words, the first conductive nanostructures100are disposed on the substrate400and are covered with the conductive layer200. In other words, the first conductive nanostructures100are located between the substrate400and the conductive layer200. In some embodiments, the sensitive device can also include a plurality of second conductive nanostructures500. The first conductive nanostructures100and the second conductive nanostructures500are arranged on the different regions of the substrate400, and the second conductive nanostructures500are not covered by the conductive layer200. In other words, during the process of forming the sensitive device, the second conductive nanostructures500are free from protection of the conductive layer200, and therefore, when formation of the sensitive device includes thermal process (for example, annealing process), the second conductive nanostructures500may melt or even be broken due to the high temperature. For example, the intrinsic melting point of the conductive layer200can be higher than that of the second conductive nanostructures500, and the temperature of the thermal process in the forming steps of the sensitive device is between the intrinsic melting point of the conductive layer200and that of the second conductive nanostructures500. As a result, during the thermal process, the conductive layer200and the first conductive nanostructures100which are covered by the conductive layer200are not melted, while the second conductive nanostructures500are melted.

In some embodiments, the second conductive nanostructures500and the first conductive nanostructures100are made of the same material. For example, the first conductive nanostructures100and the second conductive nanostructures500are silver nanowires. The first conductive nanostructures100are silver nanowires wrapped in the conductive layer200, and the second conductive nanostructures500are silver nanowires uncovered by the conductive layer200. Due to the fact that the intrinsic melting point of the silver nanowires is lower than that of the conductive layer200, the first conductive nanostructures100wrapped by the conductive layer200are not melted, while the second conductive nanostructures500uncovered by the conductive layer200are melted during the thermal process. Therefore, the gas detection ability of the second conductive nanostructures500is inferior to that of the first conductive nanostructures100, so that the second conductive nanostructures500can be referred to as disabled gas sensitive structures; on the other hand, the gas detection ability of the first conductive nanostructures100is higher than that of the second conductive nanostructures500, so that the first conductive nanostructures100can be referred to as enabled gas sensitive structures. Because the enabled gas sensitive structures and the disabled gas sensitive structures are respectively located inside and outside the conductive layer200, the conductive layer200can isolate the enabled gas sensitive structures from the disabled gas sensitive structures. Therefore, a location of the enabled gas detective structures can be defined using a patterning process of the conductive layer200.

In some embodiments, the sensitive device can include two electrodes300. The electrodes300are respectively located at two opposite ends of the conductive layer200, so as to electrically connect to the first conductive nanostructures100, the conductive layer200or both. As a result, the gas sensitive device can obtain the variation of the resistance or the other properties of the first conductive nanostructures100, the conductive layer200or combinations thereof by the two electrodes300, so as to assist the gas detection. In some embodiments, the material of the electrodes300may include aluminum or copper.

FIGS. 3-6are a method of forming sensitive device in accordance with some embodiments of the present disclosure. As shown inFIG. 3, a plurality of conductive nanostructures600can be formed on the substrate400. For example, solution containing nanowires can be coated on the substrate400to form a plurality of conductive nanostructures600on the substrate400.

Thereafter, as shown inFIG. 4, a group of the conductive nanostructures600can be covered with the conductive layer200, and thus another group of the conductive nanostructures600are uncovered with the conductive layer200. For example, in some embodiments, a metallic oxide layer can be blanket formed over the conductive nanostructures600, and then the blanket metallic oxide layer is patterned to expose the group of the conductive nanostructures600. In some embodiments, methods of forming the metallic oxide layer include deposition, such as physical vapor deposition (PVD) or chemical vapor deposition (CVD). In some embodiments, the metallic oxide layer can be formed using coating metallic oxide solution on the substrate400. In some embodiments, the patterning process of the metallic oxide layer can include photolithography and etching operations.

Then, as shown inFIG. 5, the conductive layer200and foregoing the conductive nanostructures600can be provided with heat H for preforming thermal process. Due to the fact that the intrinsic melting point of the conductive layer200is higher than that of the conductive nanostructures600, the conductive nanostructures600uncovered by the conductive layer200are melted by the thermal process, and then the second conductive nanostructures500, as discussed previously, can be formed; on the other hand, the conductive nanostructures600covered with the conductive layer200are not melted by the thermal process, and then the first conductive nanostructures100, as discussed previously, can be formed. In some embodiments, the temperature of the thermal process is higher than the intrinsic melting point of the conductive nanostructures600but lower than the intrinsic melting point of the conductive layer the conductive layer200, so that the conductive nanostructures600uncovered by the conductive layer200can be melted while the conductive layer200is not melted.

The first conductive nanostructures100which are protected by the conductive layer200are not melted, and the second conductive nanostructures500which are not protected by the conductive layer200are melted. As such, after the thermal process, the gas sensitive ability of the first conductive nanostructures100is higher than that of the second conductive nanostructures500. Therefore, the first conductive nanostructures100which are not melted can be referred to as the enabled gas detective structures, and the second conductive nanostructures500which are melted can be referred to as disabled gas sensitive structures. Due to the fact that the conductive layer200can isolate the enabled gas sensitive structures from the disabled gas sensitive structures, the location of the enabled gas sensitive structures can be defined by the foregoing patterning process of the conductive layer200. Stated differently, location, shape and size of a region of the substrate400occupied by the enabled gas sensitive structures can be defined by that of the conductive layer200. In some embodiments, the second conductive nanostructures500can be removed from the substrate400as well. In other words, the disabled gas sensitive structures can be removed, and the enabled gas sensitive structures and the conductive layer200can be remained on the substrate400.

In some embodiments, the thermal process performed inFIG. 5may be the annealing process. The annealing process can at least relieve accumulated internal stress which is caused by defects (for example, grain boundary, dislocation or point defects), so atoms of the conductive material are capable of rearranging lattice sites to decrease defect density of the conductive material. Decreasing defect density of the first conductive nanostructures100and the conductive layer200is advantageous to improve the gas sensitive ability. In other words, the annealing process is advantageous to improve the gas sensitive ability of the first conductive nanostructures100and the conductive layer200, and the conductive layer200can also prevent the first conductive nanostructures100from being damaged by the annealing process. Therefore, the embodiments of the present disclosure can effectively use the conductive nanomaterial to manufacture the sensitive device with the great gas detective ability.

Then, as shown inFIG. 6, the electrodes300can be formed to electrically connect to at least one of the conductive layer200and the first conductive nanostructures100covered by the conductive layer200. For example, the two electrodes300can be formed at the two opposite ends of the conductive layer200. In some embodiments, the method of forming the electrodes300may be physical vapor deposition (PVD) or chemical vapor deposition (CVD). For example, the electrodes300can be formed using physical vapor deposition of metallic material at the two opposite ends of the conductive layer200.