Patent Publication Number: US-2016244709-A1

Title: Patterned Magnetic Thin Film with Rolled-Up Hollow Structure

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claim priority to TAIWAN application Numbered 104105891, filed Feb. 24, 2015, which is herein incorporated by reference in its&#39; integrity. 
     TECHNICAL FIELD 
     The present invention generally relates to a patterned magnetic thin film, and more particularly, to an integration of patterned magnetic thin film with rolled-up hollow structure. 
     BACKGROUND OF RELATED ART 
     Cancer seriously affects human being. Cancer is a class of diseases which occurs as cell become immortalized. Most early symptoms of cancer are unable to be observed easily. But in terminal cancer, cancer cells may spread out to other parts through blood. It is worth to develop a new treatment to detect cancer cell early so as to inhibit it degradation. 
     Animals are formed by numerous and tiny units, such cell, vessel, and so on. In recent, scientists try to creating devices using microelectromechanical technology for in vitro applications, such as cell culture, and detecting and sensing thereof, to realize the in vivo environment. 
     The benefit of applying magnetic film for biologic application is to reduce cell damage during the collection/detection process, furthermore, improve drug test on particular cell and/or cell cluster. In prior art, most magnetic films are restricted to 2D planar structures which can be modified by functional group or defined with specific patterns thereon, for increasing collection and detection. However, the amount of collected cells are limited by planar space and magnetic property of cells. Furthermore, 2D planar magnetic thin film is not useful for separating particular cells from cell cluster. 
     In prior art, it has developed thin film with three-dimensional (3D) structure to improve the efficiency of detection, but in conventional manufacturing process, 3D structure must firstly be prepared on the substrate, and then followed by other material covered onto the 3D structure; therefore, it is complicated to prepare 3D magnetic thin film by conventional process. 
     In order to solve the problem of the conventional arts, there is a need to provide simple apparatus for improving detection and preparing. The present invention remains normal 2D characteristics but improves detection property by forming 3D structure. 
     SUMMARY 
     An object of the present invention is to provide a patterned thin film with tube-shaped structure to generate particular stray field and collect large amount of cells. 
     Another object of the present invention is to provide a method for preparing a patterned thin film with tube-shaped structure. The rolled-up structure was then obtained due to the different thermal expansion coefficient of material. 
     According to one embodiment, the patterned thin film with tube-shaped structure includes at least one substrate. The substrate includes at least one tube-shaped supportive layer rolled up onto the substrate. The tube-shaped thin film further includes a pattern portion having magnetic material for attracting an object into the hollow portion of the tube-shaped thin film. Wherein the thermal expansion coefficient of the magnetic material and the tube-shaped supportive layer are different. 
     According to one embodiment, the method of preparing the patterned thin film with tube-shaped structure includes following steps: preparing a substrate; covering a supportive layer onto the substrate; defining a pattern portion onto the supportive layer; depositing magnetic material onto the pattern portion; opening a concavity on at a side of the supportive layer; and removing the substrate by etching. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The components, characteristics and advantages of the present invention may be understood by the detailed description of the preferred embodiments outlined in the specification and the drawings attached. 
         FIG. 1  illustrates a flow chart of preparing the patterned magnetic thin film with 3D tube-shaped structure according to an embodiment of the present invention. 
         FIG. 2A  illustrates a sectional view of the substrate, supportive layer and magnetic material according to an embodiment of the present invention. 
         FIG. 2B  illustrates a sectional view of opening a concavity at a side of the supportive layer according to an embodiment of the present invention. 
         FIG. 2C  illustrates a sectional view of rolled-up structure according to an embodiment of the present invention. 
         FIG. 3A  illustrates a diagram of supportive layer without pattern according to an embodiment of the present invention. 
         FIG. 3B  illustrates a diagram of the supportive layer with pattern according to an embodiment of the present invention. 
         FIG. 3C  illustrates a diagram of concavities at three sides of the supportive layer according to an embodiment of the present invention. 
         FIG. 3D  illustrates a diagram of etching substrate and forming rolled-up structure according to an embodiment of the present invention. 
         FIG. 4A-4B  illustrate diagrams of the patterned magnetic thin film with rolled-up structure according to an embodiment of the present invention. 
         FIG. 5A  illustrates a diagram of the magnetic thin film with single periodic pattern before rolling-up according to an embodiment of the present invention. 
         FIG. 5B  illustrates a diagram of the magnetic thin film with single periodic pattern with rolled-up structure according to an embodiment of the present invention. 
         FIG. 6A  illustrates a diagram of the magnetic thin film with M periodic pattern before rolling-up according to an embodiment of the present invention. 
         FIG. 6B  illustrates a diagram of the magnetic thin film with M periodic pattern with rolled-up structure according to an embodiment of the present invention. 
         FIG. 7A-7B  illustrate diagrams of the patterned magnetic thin film with rolled-up structure according to an embodiment of the present invention. 
         FIG. 8A  illustrates a diagram of the objective cells collected by the magnetic thin film with rolled-up structure according to an embodiment of the present invention. 
         FIG. 8B  illustrates the curve of number of collected cells versus collection time of the tube-shaped with patterned magnetic thin film according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Some preferred embodiments of the present invention will now be described in greater detail. However, it should be recognized that the preferred embodiments of the present invention are provided for illustration rather than limiting the present invention. In addition, the present invention can be practiced in a wide range of other embodiments besides those explicitly described, and the scope of the present invention is not expressly limited except as specified in the accompanying claims. The layout of components may be more complicated in practice. 
       FIG. 1  illustrate a flow chart of preparing a patterned magnetic thin film with rolled-up hollow structure according to an embodiment of the present invention. The method provides at least one substrate, such as silicon material, for following steps: 
     Step  202 : A supportive layer  104  is covered over the substrate  102 .  FIG. 2A  illustrates a sectional view of the substrate  102 , a supportive layer  104  and a magnetic material  106  of the present invention. The supportive layer  104  includes but is not limited to SiO 2  or Si 3 N 4 , in the preferred embodiment, the supportive layer  104  is SiO 2 . The supportive layer  104  is formed over the substrate  102  by coating, printing or other process. In the preferred embodiment, the supportive layer  104  is covered over the substrate  102  by coating. The thickness of the supportive layer  104  is can be about 10-100 nm, more particularly, about 100 nm. 
     Step  204 : A micro-pattern is defined on the supportive layer  104 .  FIGS. 3A-3D  illustrate processes of patterning portion  110  formed on the supportive layer  104 . It is well understood that the present invention must coat a photoresist agent on the surface of the supportive layer  104  in order to define a pattern. Either positive resist or negative resist can be adapted for defining patterns based on the specific requirements. In the preferred embodiment, a positive resist polymethylmethacrylate (PMMA) is covered on the supportive layer  104  by spin coating, then continues following steps. 
     Lithography is an important part in process of semiconductor and micro electro mechanism (MEM), most of the patterned area can be defined by lithography. Lithographic technique includes extreme ultraviolet lithography (EUV), X-ray lithography, electron projection lithography (EPL), ion projection lithography (IPL), and so on. Electron-beam lithography (often abbreviated as e-beam lithography) is the practice of scanning a focused beam of electrons to draw custom shapes on a surface covered with an electron-sensitive film called a resist. The electron beam changes the solubility of the resist, enabling selective removal of either the exposed of non-exposed regions of the resist by immersing it in a solvent. In the preferred embodiment, the pattern portion  110  are created onto the substrate  102  that spin-coated with e-beam resist polymethyl methacrylate (PMMA). Then, the pattern portion  110  will be appeared on the substrate  102  in developer, such as 3:1 mixture of 2-propanol and methyl isobutyl ketone. The pattern portion  110  includes any micro patterns, such as but not limited to linear, wave-shaped (as shown in  FIG. 3B ), or fishbone-shaped (as shown in  FIGS. 4A-4B ). It is well understood that the lithographic technique is not limited to e-beam lithography, but can be varied or modified by the person in the art in the light of the need in use. Besides, in step  204 , the method further includes dehydration baking, priming, soft baking and hard baking to enhance precision and reliability of the pattern portion  110 . 
     Step  206 : A magnetic material  106  is deposited onto the pattern portion  110 . A required material can be coated onto the supportive layer  104 , such as but not limited to magnetic material, conductive material, non-conductive material or semiconductive material, after defining the pattern portion. In one embodiment, the magnetic material  106 , coated onto the surface of the supportive layer  104 . In the preferred embodiment, the magnetic material  106  is deposited onto the surface of the supportive layer  104  by e-beam evaporation. In the preferred embodiment, the magnetic material  106  comprises a first layer of non-magnetic material as adhesive layer, a second layer of magnetic layer as sensing layer and a third layer as protective layer. Non-magnetic material includes but not limited to Cr, Ti, Al; magnetic metal includes but not limited to Fe, Co, Ni, or nickel-, iron- and cobalt-based alloys; protective layer includes but not limited to Cr, Ti, Al or polymer (not shown in drawings). We used the e-beam evaporation system to deposit (1) about 5-20 nm thick Cr as the adhesive layer, preferable 10 nm; (2) second layer of Ni 80 Fe 20  ranges from 30 nm to several micrometers as the sensing layer, preferable 90 nm; and (3) about 5-20 nm thick Cr as the protective layer, preferable 10 nm, in sequence. Accordantly, 2D patterned thin film with will be done through above steps. It is well understood that different magnetic material  106  can be deposited with interlaced format and repeatability to modulate the magnetic strength. 
     In another embodiment, particular functional groups can be modified onto the surface of the supportive layer  104 , such as but not limited protein or DNA, for trapping or attracting particular cells. 
     Step  208 : A concavity  108  is opened on at a side of the supportive layer  104 .  FIG. 2B  illustrates a sectional view of the concavity  108  formed at a side of the supportive layer  104 .  FIG. 3C  illustrate a perspective view of the opening  108  formed at a side of the supportive layer  104 . First, required concavities are defined onto the supportive layer  104  and the magnetic material  106  by lithography, and then the concavities are etched by buffered oxide etchant (BOE). As shown in  FIG. 3C , each of left, right and front side of the supportive layer  104  and the magnetic material  106  has a concavity, respectively, for forming rolled-up thin film  120  (also called tube-shaped thin film or ring-structure thin film). It is well understood that the height and width of concavities  108  can be modified or varied based on the requirements by a skilled person in the art. In the embodiment, the width of the concavity  108  is 50 micrometers. The length of the two concavities  108 , formed at the right and left sides of the supportive layer  104  and the magnetic material  106 , determines the diameter of the tube-shaped thin film  120 . As shown in  FIG. 4A , it illustrates a front view of tube-shaped thin film  120  by SEM, the diameter of the tube-shaped thin film is 80 micrometers. The length of the two concavities  108 , formed at the front and back sides of the supportive layer  104  and the magnetic material  106 , determines the length of the tube-shaped thin film  120 . As shown in  FIG. 4B , it illustrates a front view of tube-shaped thin film  120  by SEM, the length of the tube-shaped thin film is 135 micrometers. 
     Step  210 : The substrate is subsequently etched. The substrate  102 , after step  208 , is immersed into etchant, such as tetramethylammonium hydroxide (TMAH) for removing parts of the substrate  102  to form the tube-shaped thin film  120 . Referring to  FIG. 2C , the supportive layer  104  and the magnetic material  106  bend away or curl towards a side of the substrate  102  in etching process, due to the difference in thermal expansion coefficient between the supportive layer  104  and the magnetic material  106  in etching process. In the embodiment, the etchant includes but is not limited to TMAH (N(CH 3 ) 4   + OH − ). 
     Step  212 : The magnetic material  106  and the supportive layer  104  can roll up owing to stress induced by the difference in thermal expansion between different layers being released after substrate etched. If the thermal expansion coefficient of the supportive layer  104  is greater than that of the magnetic material  106 , they will bent towards a side of the supportive layer  104  (away from a side of the magnetic material  106 ), thereby rolling downward (not shown in figures.) If the thermal expansion coefficient of the supportive layer  104  is smaller than the magnetic material  106 , they will bent towards a side of the magnetic material  106  (away from a side of the supportive layer  104 ), thereby rolling upward and forming the tube-shaped thin film  120 , as shown in  FIGS. 2C and 3D . In the preferred embodiment, the thermal expansion coefficient of Cr, Ni 80 Fe 20  and SiO 2  are 6.2 (10 −6 /mK), 12.8 (10 −6 /mK) and 0.5 (10 −6 /mK), respectively, so the supportive layer  104  will bent towards a side of Ni 80 Fe 20 . The difference of thermal expansion coefficient between the magnetic  106  and the supportive layer  104  is about 4.8-12.3 (10 −6 /mK). Furthermore, the present invention can develop tube-shaped structure with multiple thin film. Beside, multiple 3D tube-shaped thin films can be prepared onto the same substrate. 
     On the other hand, diameter and turns can be modulated by external factors, such as etching time and temperature. In one embodiment, etching rate rises as temperature from 60° C. to 150° C., and thus the number of turns (N) of the tube-shaped thin film  120  will be made. In one embodiment, the number of turns (N) is 3 under temperature between 90° C.-110° C.; in contrary, the number of turns (N) is 1 under temperature between 60° C.-80° C. Accordantly, the number of turns (N) are proportional to the temperature. It is well understood that the desired operating temperature is based on the depositing material chosen in thin film material layer. 
     The pattern portion  110  defined onto the supportive layer  104  includes various type, such as simple linear or wave-shaped. In one embodiment, another type, such as elliptical or oval shape with width-to-length ratio being 1:2-1:10, are perpendicular to the simple linear or wave-shaped type to form particular type with high magnetic anisotropy, such as fishbone-shaped type, to enhance the sensitivity of magnetic detection. Type of the pattern portion  110  can be arranged regularly or randomly, type and its arrangement of the pattern portion  110  can be modified or varied based on the requirements, as shown in  FIG. 7A-7B .  FIG. 7A  illustrates the simple linear type, and the  FIG. 7B  illustrates the elliptical type, with width-to-length ratio 1:5, being perpendicular to the simple linear type. 
       FIG. 5A  illustrates a magnetic thin film with single periodic type before rolling up.  FIG. 6A  illustrates a magnetic thin film with seven periodic type before rolling up. The pattern portion  110  of the supportive layer  104  includes M periodic type, as shown in  FIGS. 3C, 5A and 6A . After depositing the magnetic material  106  onto the pattern portion  110  of the supportive layer  104 , the tube-shaped thin film  120  will be made through heating and etching, thereby enhancing magnetic collection and sensitivity thereof, as shown in  FIGS. 3D, 5B and 6B .  FIG. 5B  illustrates a side views of tube-shaped thin film with single periodic type,  FIG. 6B  illustrates a side view of tube-shaped thin film with multiple periodic patterns. 
     In one embodiment, the magnetic material includes but is not limited to Cr coated on Ni 80 Fe 20 . Magnetic objects, such as magnetic cell, magnetic molecule and magnetic bead, can be collected and attracted by the stray field of the 3D magnetic film  120  due to the patterned magnetic film  120  has particular magnetic anisotropy. 
     The number of the magnetic objects attracted are depended on the diameter and length of the tube-shaped thin film  120 . In one embodiment, magnetically labeled cancer cells are collected into the hollow portion of tube-shaped thin film  120 , the diameter of the hollow portion is 60 micrometers. As shown in  FIG. 8A , (a), (b) and (c) illustrate diagrams of magnetic cells collected by the tube-shaped thin film  120  after 200, 1000 and 1800 seconds, respectively.  FIG. 8B  illustrates the curve of number of collected cells versus collection time, the maximum number of collected cells in  FIG. 8B  is about 150. In another embodiment, the similar size and amount of cell cluster can be collected into the tube-shaped thin film  120  by modulating the size of diameter of the tube-shaped thin film  120 , for analysis. 
     Rolled-up structure can be as a scaffold for 3D cell culture. On the other hand, the rolled-up thin film can capture a particular cell from cell cluster. 
     Table 1 presents the switching field variation of 2D magnetic thin film and 3D magnetic thin film trapping a magnetic cell. The Hc 1  indicates coercivity of a cell attached, the Hc 0  indicates coercivity of no cell attached, wherein Hc 1  minus Hc 0  equals the switching field variation. Long and short axes in Table 1 respectively indicate the magnetic field applied along the long axis or short axis of device. According to the Table 1, the switching field variation of 3D magnetic thin film are greater than those of 2D magnetic thin film as magnetic field applied in either axis, in other words, the variation of magnetic signal of 3D thin film are greater than those of 2D thin film, and thus 3D magnetic thin film is better to as magnetic sensor or biosensor. That is, rolled-up magnetic thin film can be served as biosensor to enhance signal and sensitivity, and reduce deviation. 
     
       
         
           
               
               
               
               
             
               
                   
                   
               
               
                   
                 switching field 
                 2D sensor 
                 3D sensor 
               
               
                   
                 variation (%) 
                 with a cell 
                 with a cell 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Long axis 
                 12 
                 62.5 
               
               
                   
                 Short axis 
                 20.2 
                 41.4 
               
               
                   
                   
               
            
           
         
       
     
     As description above, the present invention provides a patterned magnetic thin film with 3D rolled-up structure. The 3D rolled-up thin film can be served as biosensor to dissolve disadvantage of conventional 2D sensor due to its magnetic thin film having patterns with high magnetic anisotropy. In addition, the 3D rolled-up thin film also increase the amount of collected cells and detective direction as a result of its rolled-up structure which can enhance the signal. 
     Various terms used in this disclosure should be construed broadly. For example, if an element “A” is said to be coupled to or with element “B,” element A may be directly coupled to element B or be indirectly coupled through, for example, element C. When the specification states that a component, feature, structure, process, or characteristic A “causes” a component, feature, structure, process, or characteristic B, it means that “A” is at least a partial cause of “B” but that there may also be at least one other component, feature, structure, process, or characteristic that assists in causing “B.” If the specification indicates that a component, feature, structure, process, or characteristic “may”, “might”, or “could” be included, that particular component, feature, structure, process, or characteristic is not required to be included. If the specification refers to “a” or “an” element, this does not mean there is only one of the described elements. 
     The foregoing descriptions are preferred embodiments of the present invention. As is understood by a person skilled in the art, the aforementioned preferred embodiments of the present invention are illustrative of the present invention rather than limiting the present invention. The present invention is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims, the scope of which should be accorded the broadest interpretation so as to encompass all such modifications and similar structures.