WO2015080551A1

WO2015080551A1 - A method of adhering sensing membranes in a sensing device

Info

Publication number: WO2015080551A1
Application number: PCT/MY2014/000120
Authority: WO
Inventors: Aun Shih Teh; Khairul Anuar; Daniel Chia Sheng Bien; Wai Yee Lee
Original assignee: Mimos Bhd
Current assignee: Mimos Bhd
Priority date: 2013-11-27
Filing date: 2014-05-27
Publication date: 2015-06-04
Anticipated expiration: 2016-05-27

Abstract

The present invention discloses a method for adhering a sensing membrane (10) to a sensing substrate (12), and more particularly, the method utilises nanoparticles (14) as an intermediary to physical modify or improve the surface area of the sensing substrate (12) before layering a sensing membrane (10) on the sensing substrate (12). The nanoparticles (14) are formed in pillar structures on sensing substrate (12) as physical protrusions that are capable of interrupting the flatness and uniformity of the sensing membrane (10) and the sensing substrate (12) that thereby anchors the adhesion of the sensing membranes (10) to the sensing substrate (12).

Description

A ETHOD OF ADHERING SENSING MEMBRANES IN A SENSING

DEVICE

TECHNICAL FIELD OF THE INVENTION

This invention is related to the field of sensing films or membranes for detecting target anaiytes, and more particularly a method of adhering sensing membranes in a sensing device.

BACKGROUND OF THE INVENTION

A large number of sensing films or membranes is used in chemical or gas sensors for detecting target anaiytes, where the sensing response can be typically transduced into analytical useful signals, in view of the advancement in technology, vigorous researches and developments are in progress to produce improved sensors that are more sensitive in sensing processes and provide more accurate results. Portability and reliability of the sensors are also some other factors for improving sensors while allowing continuous operation.

One of the critical aspects during the development of sensors is fo make sure that ttiey are sufficiently robust to enable continuous use and lead towards having long operation lifetimes. In some instances these sensors are subjected io harsh conditions such as immersion in solution or exposure to elevated temperatures. Such exposure results in the degradation of the sensing film or membrane and in many cases, the sensing film or membrane peels of from the attached surface, which causes a variation in sensing performance and eventually failure of the sensing device. One such area for improvement is the adhesion of the sensing material to the substrate o the surface of the sensor device.

A number of prior arts have been found using nanomateriais to improve the adhesion of the sensing material to the substrate of the sensor device. However, the use of nanomateriais is far more sensitive as compared to conventional surface adhesion improvements, in one of the prior arts, conventional nanowire based gas sensors suffer from selectivity and reversibility issues. This is because they react based on changes in the electrical properties of the catalyst upon exposure to gas, while different gases when adsorbed may induce similar changes. Prior art US 200S0025875 A1 discloses a synthesis of nanochannels within membranes where the nanochanneis are prepared using known methods for nanopore/nanotube synthesis such as mechanical, radiological, gaivanostatic, electrical, electrochemical, photochemical, or chemical methods. However, the prior art only produces individual channels on the membrane instead of plilar structures, which the channels only anchor the adherence between two layer of membrane.

Prior art US 8241697 B2 discloses enzyme immobilization compositions and methods for forming sensors comprising such compositions and apparatus for forming arrays of immobilized iayers on an array of sensors by dispensing such compositions onto a substrate. The prior art utilizes oxide surfac and siiane silano! as adhesion promoter instead of nanomatehais. Further, th prior art does not disclose any means to modify the membrane surface in order to improve the membrane adhesion.

Therefore, it is an aim of this present invention to address the aforesaid technical disadvantages by introducing a method for adhering a membrane to a sensing substrate that utilises nanoparticles as an intermediary to physical modify or improve the surface area of the sensing substrate before layering a sensing membrane on the sensing substrate. The nanoparticles are formed in pillar structures on sensing substrate as physical protrusions that are capable of interrupting the flatness and uniformity of the sensing substrate that thereby anchors the adhesion of the sensing membranes to the sensing substrate. SUMMARY OF THE PRESENT INVENTION

The present invention relates to a method for adhering a sensing membrane to a sensing substrate comprising the steps of providing a sensing substrate, depositing at least a catalyst material on the sensing substrate, subjecting the catalyst material to chemical vapour deposition to form nanoparticies on the sensing substrate, function a iking the nanoparticies, depositing at least a layer of sensing membrane across the sensing substrate having the deposition of nanoparticies, characterized in that the nanoparticies are formed in pillar structures that enhances bonding strengths between at least a layer of sensing membrane and the sensing substrate, which anchors the adhesion between the layer of sensing membrane to the sensing substrate.

It is an object of the present invention to provide a method for adhering a sensing membrane to a sensing substrate that includes the step of producing nanoparticies in pillar structures on sensing substrate as physical protrusions that are capable of interrupting the flatness and uniformity of the sensing membranes and the sensing substrate, thereby anchoring the adhesion of the layers of sensing membranes to the sensing substrate. it is another object of the present invention to provide a method for adhering a sensing membrane to a sensing substrate that includes the step of producing nanoparticies in pillar structures on sensing substrate that is capable of redistributing the stress of the sensing membrane across the pillar structures and reducing the overall sensing membrane stress level in the event of expansion and contraction, as a result of the absorption and adsorption of target anafytes, during the sensing operation in a sensing device. it is further an object of the present invention to provide a method for adhering a sensing membrane to a sensing substrate that includes the steps of functionaSizing the nanoparticies to further reinforce the bonding strength between the layers of sensing membranes and the sensing substrate, which enhances the adhesion. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1a illustrates the isometric view of a Iayer of sensing membrane embedded within an array of pillar structures of nanoparticies. Figure 1b illustrates the cross sectional view of a layer of sensing membrane embedded within an array of pillar structures of nanoparticles.

Figure 1c illustrates the cross sectional view of a layer of sensing membrane S embedded within an array of pillar structures of nanoparticles in a field effect transistor based sensing device.

Figure 2a illustrates carbon nanoiube bundles within a pillar structure formed on the sensing substrate.

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Figure 2b illustrates zinc oxide nanowire bundles within a pillar structure formed on the sensing substrate.

Figure 2c illustrates silicon nanowire bundles within a pillar structure formed5 on the sensing substrate.

Figure 3 illustrates the attachment of functional groups for further bonding between the pillar structures of the nanoparticles and the layer of sensing membrane.

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Figure 4 illustrates the formation of pillar structures of the nanoparticles on a sensing substrate m a field effect transistor based sensing device.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

5 The above mentioned and othe features and objects of this inventio will become more apparent and better understood by reference to the following detailed description. It should be understood that the detailed description made known below is not intended to be exhaustive or limit the invention to the precise form disclosed as the invention may assume various alternative0 forms. On the contrary, the detailed description covers all the relevant modifications and alterations made to the present invention, unless the claims expressly stat otherwise. As mentioned earlier, in order to produce a sensor that is sufficiently robust to enable continuous use and that has a long operational lifetime, the physical conditions of a sensing substrate in the sensor is one of the areas to be explored. In the present invention, a method is disclosed for adhering a sensing membrane (10) to a sensing substrate (12). More particularly, the method utilise nanoparticies (14) as an intermediary to physical modify or improve the surface area of the sensing substrate (12) before layering a sensing membrane (10) on the sensing substrate (12). The present invention comprises the steps of providing a sensing substrate ( 2), depositing at least a catalyst materia! (16) on the sensing substrate (12), subjecting the catalyst material (16) to chemical vapour deposition to form nanoparticies (14) on the sensing substrate (12) in pillar structures, functionaSizing the nanoparticies (14), depositing at least a layer of sensing membrane (10) across the sensing substrate (12) having the deposition of nanoparticies (14), wherein the formation of nanoparticies (14) in pillar structures enhances bonding strengths between the at least a layer of sensing membrane (10) and the sensing substrate (12), which anchors the adhesion of the layers of membrane (10) to the sensing substrate (12).

The catalyst material (16) is deposited on the sensing substrate (12) in dots array, The dots array is deliberatel formed sparsely across the sensing substrate (12) so that they do not interfere with the device's sensing function. The catalyst material (18) is deposited on the sensing substrate (12) using in situ deposition. It should be noted that the method of depositing the catalyst material (16) is not limited to in situ deposition but other general and known methods may also be used. Upon depositing the catalyst material (16) onto the sensing substrate (12), the catalyst material (16) is subjected to chemical vapour deposition to form nanoparticies (14). The nanoparticies (14) form a pillar structure within the pre-patterned catalyst material (16) as the growth of the nanoparticies (14) is confined only to where the catalyst material (16) is positioned. The preferred method of growth of The nanoparticies (14) utilising the pre-patterned catalyst material (16) is chemicai vapour deposition, in which in-situ grown nanoparticles (14) can be formed at designated positions that am targeted for the membrane {10} in the sensing device. It should be noted that other methods can also be used if it is capable of producing rsanoparticies (14) in pillar structure within the designated positions. The growth of the pillar structures of the nanoparticles (14) may also be tailored according to Its specific application. One of the physical requirements that may be tailored is the density of the nanopartic!es (14) as it is dependent on the catalyst material (16) and the deposition conditions. According to the specific conditions and applications, the array may also be tailored based on its spacing in between the dots of the catalyst material (16).

As illustrated in figures 1 a and 1 b, the pillar structures of nanoparticles (14) are formed to interrupt the smoothness and flatness of the surface of the layer of sensing membrane (10), which results in a redistribution of stress between the layer of sensing membrane (10) and the pillar structures of nanoparticles (14). in the case that more than a layer of sensing membrane (10) is deposited onto the sensing substrate (12). the pillars also help alleviate the stress in between the layers of membranes ( 0), in the event of an expansion or contraction during the sensing operation, which is a result of the absorption and adsorption of target analytes.

The nanoparticle (14), as disclosed in the present invention, is preferred but is not limited to be any one or a combination of carbon nanotubes, zinc oxide nanowlres or silicon nanowires. Figures 2a. 2b and 2c illustrate carbo nanotube bundles, zinc oxide nanowire bundles and silicon nanowire bundles within a pillar structure formed on the sensing substrate (12) respectively.

Upon growing the nanoparticles (14), the subsequent step is to functionaiize the nanoparticles (14). The purpose of the step of functiona!izing the nanoparticles (14) is to increase the bonding strength between the structures of the nanoparticles (14). The functional groups that covalently attach to the outer surface of the pillars of the nanoparticles (14) are capable of modifying the stacking properties of the structures of the nanoparticles ( 4). Further, the functiona!ization also promotes mechanical, chemical, dispersive, electrostatic or diffusive adhesion between the sensing membrane {10} and the sensing substrate 12}_t and between the layer of sensing membranes (10). The iarge surface area of the nanoparticle (14) bundles also plays an important role in the fuoctionalizafion as it provides more functionaSizing sites that further anchors the adhesion between the sensing membrane {10} and the sensing substrate (12), and between the layers of sensing membranes (10). The functional group mentioned and used herein is any one or a combination of COOH and ~GH. However, it should be noted that other functional group may be used, provided that the utilization of the functional groups assist in increasing the bonding strength between the structures of the nanoparticles (14) and in promoting the adhesion between the sensing membrane (10) and the sensing substrate {12}, and between the layers of sensing membranes (10). The attachment of functional groups for further bonding between the pillar structures of the nanoparticles (14) is illustrated in figure 3.

Subsequently, at least a layer of sensing membrane (10) is deposited across the sensing substrate (12) having the deposition of nanoparticles (14). The layer of sensing membrane (10) is deposited using any one or a combination of methods such as spin-coating, for example wafer spinning, drop-casting, dip-coating, spraying such as spray forming, spray casting or spray deposition, printing, physical vapour deposition and chemical vapour deposition, in case the sensing material is polymeric, a low temperature curing process is applied to ensure th conformity of the layer of sensing membrane (10) and aiso its adhesion to the sensing substrate (12). Numerous layers of sensing membranes (10) may be deposited onto the sensing substrate (12) depending on the application of the sensing device. The sensing membrane (10) may be made of materials such as but not limited to metal, metal oxides, dielectrics, polymers and organic materials.

Also disclosed is a method of adhering a sensing membrane (10) to a sensing substrate {12} in an ion-selective field effect transistor based sensing device (17), and an ion-selective field effect transistor based sensing device (17) made using the method disclosed herein, as illustrated in Figure 1c and more particularly in Figure 4. Generally, a sensing membrane in the transistor acts as the ga e material in which target analytes (in this instance H+ Ions) are adsorbed by the sensing membrane. This causes a potential shift that then modifies the gate voltage, which modulates the field effect transistor channel current and thus resulting in the sensor response.

Firstly, a sensing substrate (12) having channels (19) for the flow of current is fabricated. The sensing substrate (12) herein refers to a partial or base device structure of the ion-selective field effect transistor based sensing device (17). An oxide layer (21 ) is then deposited on the sensing substrate (12) using in situ deposition as a gate material and aiso as a protective iayer for the nanoparticle deposition process. Subsequently, at least a catalyst material (16) is pre-patterned and deposited on the oxide Iayer (21) using lithography. The catalyst material (16), which is metal in this case, is etched to form dot arrays on the oxide layer (21). The catalyst material (18) is then subjected to chemical vapour deposition process, which results in the formation of pillar structures of the nanoparticles (14). The nanoparticle (14) is preferred but is not limited to be any one of a combination of carbon nanotubes, zinc oxide nanowires or silicon nanowires.

After that, functionalization process is performed to attach functional groups to the pilla structures of the nanoparticles (14). The functional group mentioned and used herein is any one or a combination of COOH and ~OH. Further, the oxide iayer (21) above the channels {19} is patterned according to the area above the channels (19) and the patterned area is etched away to enable elect ica! connection to the sensing device (17), The sensing membrane (10) is then deposited onto across the sensing substrate { 2} having the deposition of nanoparticles (14) using any one or a combination of spin-coating, drop- casting, dip-coating, spraying, printing, physical vapor deposition or chemical vapour deposition. The sensing membrane {10} may be made of materials such as but not limited to metal, metal oxides, dielectrics, polymers and organic materials. Thereafter, the sensing membrane (10) is patterned according to the area above the channels (19) and the patterned area Is etched to remove the sensing membrane (10) from the sensing substrate (12).

The method disclosed herein produces nanopartlcles (14) In the form of piliar structures that enhances bonding strengths between the at least a layer of sensing membrane (10) and the sensing substrate (12), which anchors the adhesion between the iayer of sensing membrane (10) to the sensing substrate (12) in a sensing device (17). The pillar structures of the nanoparticies (14) also redistribute the stress of the sensing membrane (10) across the sensing substrate (12) and reducing the overall sensing membrane (10) stress level in the event of expansion and contraction, as a result of the absorption and adsorption of target analytes, during the sensing operation in the sensing device (17). The invention described herein is susceptible to variations, modifications and/or additions other than those specifically described and it is to be understood that the Invention includes all such variations, modifications and/or additions which fail within the scope of the following claims.

Claims