Abstract:
An electronic device including a bio-polymer material and a method for manufacturing the same are disclosed. The electronic device of the present invention comprises: a substrate; a first electrode disposed on the substrate; a bio-polymer layer disposed on the first electrode, wherein the bio-polymeric material is selected from a group consisting of wool keratin, collagen hydrolysate, gelatin, whey protein and hydroxypropyl methylcellulose; and a second electrode disposed on the biopolymer material layer. The present invention is suitable for various electronic devices such as an organic thin film transistor, an organic floating gate memory, or a metal-insulator-metal capacitor.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefits of the Taiwan Patent Application Serial Number 101101562, filed on Jan. 13, 2012, the subject matter of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an electronic device including a bio-polymer material and a method for manufacturing the same. More specifically, the present invention relates to an organic thin film transistor including a bio-polymer material, an organic floating gate electrode memory including a bio-polymer material, and a metal-insulator-metal capacitor including a bio-polymer material; and a method for manufacturing the same. 
         [0004]    2. Description of Related Art 
         [0005]    As well known to those skilled in the art, transistors are applied in a wide variety of electronics to serve as switches for electric current. Different from mechanical valves, transistors are controlled by electric signals and the switch-speed of the transistors can be very fast. Transistors, for example, may be classified into bipolar junction transistors (BJTs) and field effect transistors (FETs). The field effect transistor comprises N-type organic thin film transistors (OTFT) and P-type organic thin film transistors, etc. 
         [0006]    Usually, N-type or P-type of organic thin film transistors can be classified into top contact organic thin film transistors and bottom contact organic thin film transistors. As shown in  FIG. 1A , a top contact organic thin film transistor comprises: a substrate  10 ; a gate electrode  11  locating on the substrate  10 ; a gate dielectric layer  12  disposed on the substrate  10  and covering the gate electrode  11 ; an organic semiconductor layer  13  covering the gate dielectric layer  12 ; and a source electrode  14  and a drain electrode  15  disposed on the organic semiconductor layer  13 . 
         [0007]    In addition, as shown in  FIG. 1B , the bottom contact OTFT comprises: a substrate  10 ; a gate electrode  11  disposed on the substrate  10 ; a gate dielectric layer  12  disposed on the substrate  10  and covering the gate electrode  11 ; a source electrode  14  and a drain electrode  15  disposed on the gate dielectric layer  12 ; and an organic semiconductor layer  13  covering the gate dielectric layer  12 , the source electrode  14 , and the drain electrode  15 . 
         [0008]    In the conventional method for forming a gate dielectric layer, the dielectric material is sputtered on the substrate and the gate electrode to form the gate dielectric layer. However, the instrument for the sputtering process is very expensive and the process is complex. In addition, the common materials used in N-type or P-type organic semiconductor layers of the OTFT are pentacene, fullerene (C60), PTCDI-C8 (N,N′-Dioctyl-3,4,9,10-perylenedicarboximide), or F 16 CuPc etc. Although pentacene, fullerene, PTCDI-C8, or F 16 CuPc have good hole/electron field-effect mobility theoretically, they cannot match well with the dielectric material, so the hole/electron field-effect mobility thereof is low. For example, when silicon nitride is used as a material of the gate dielectric layer in the P-type pentacene OTFT, the hole field-effect mobility of the pentacene is lower than 0.5 cm 2 /V-sec; however, the hole field-effect mobility of pentacene is estimated to be 35-50 cm 2 /V-sec theoretically. Even when aluminum nitride is used as the material of the gate dielectric layer in the P-type pentacene OTFT, the hole field-effect mobility of the pentacene is about 1 cm 2 /V-sec. Hence, it is desirable to provide a material for the gate dielectric layer to match well with pentacene, fullerene, PTCDI-C8, or F 16 CuPc. 
         [0009]    The consumable electronic system is indispensably in this century. New organic electronic elements have the advantage of low weight, non-volatile property, and convenient portability so as to apply to extensive flexible electronic products. More specifically, these organic electronic elements are suitable for portable electronic products, such as cell phones, digital cameras, flash disks, etc. 
         [0010]    One of the main techniques of organic electronic elements is conventional floating gate electrode non-volatile memory. As shown in  FIG. 2 , the floating gate electrode non-volatile memory comprises: a substrate  20 ; a gate electrode  21  disposed on the substrate  20 ; a gate dielectric layer  22  disposed on the substrate  10  and covering the gate electrode  21 ; a floating gate electrode  26  covers the gate dielectric layer  22 ; a dielectric layer  27  covers the floating gate electrode  26 ; an organic semiconductor layer  23  covers the dielectric layer  27 ; a source electrode  24  and a drain electrode  25  disposed on the organic semiconductor layer  23 . As described above, the floating gate electrode  26  is used to store charge, and the material thereof can be metal, nanoparticle, or oxide. 
         [0011]    In addition, metal-insulator-metal (MIM) capacitors are widely applied on digital and radio frequency (RF) circuit designs. Currently, several dielectric materials with high dielectric constant are developed to increase the capacitor density of the MIM capacitors and decrease the leakage current thereof. As shown in  FIG. 3 , a conventional MIM capacitor comprises: a substrate  30 ; a first electrode  31  disposed on the substrate  30 ; an insulating layer  32 , disposed on the substrate  30  and covering the first electrode  31 ; and a second electrode  33  disposed on the insulating layer  32 . Herein, the conventional dielectric material used in the insulating layer of the MIM capacitor can be TiN, TiO 2 , SiO 2 , and SiN. However, when the aforementioned dielectric material is serves as the insulating layer of the MIM capacitor, there are two disadvantage: first, the insulating layer is formed on the metal layer by use of a sputtering process or vacuum deposition equipment, which may cause the production cost and the process complexity to be increased; second, the MIM capacitor doesn&#39;t have flexibility, so the MIM capacitor cannot be applied to manufacture flexible electronic products. 
         [0012]    Therefore, it is desirable to develop an electronic device including a novel bio-polymer material and a method for manufacturing the same, in order to prepare an efficient electronic device in a simple and cheap way, and apply to an organic thin film transistor, an organic floating gate electrode memory, or a metal-insulator-metal capacitor. 
       SUMMARY OF THE INVENTION 
       [0013]    The object of the present invention is to provide an electronic device including a bio-polymer material and a method for manufacturing the same, to prepare an electronic device with low cost. 
         [0014]    To achieve the object, the electronic device of the present invention including a bio-polymer material comprises: a substrate; a first electrode disposed on the substrate; a bio-polymer layer disposed on the first electrode; and a second electrode disposed over the biopolymer material layer. 
         [0015]    In the electronic devices of the present invention, the bio-polymer layer preferably has a single-layered structure or a multi-layered structure. The thickness of the overall bio-polymer layer can be adjusted by the number of the individual layers added, so as to obtain higher electron mobility or to reduce the leakage current. 
         [0016]    In the present invention, the substrate can be a plastic substrate, a glass substrate, a quartz substrate, a silicon substrate, or a paper substrate. Preferably, the substrate is a plastic substrate. Using a plastic substrate to manufacture an electronic device, the electronic device has flexibility. 
         [0017]    The material of the first electrode and the second electrode are independently selected from a group consisting of Al, Cu, Cr, Ag, Pt, Au, ZnO, and ITO. Preferably, the material is Au. 
         [0018]    The material of the bio-polymer layer is not limited; it can be selected from bio-polymer protein material or cellulose polymer material. The bio-polymer protein material group may consist of wool keratin, collagen hydrolysate, gelatin, and whey protein; and cellulose polymer material can be hydroxypropyl methylcellulose and so on. Preferably, the material of the bio-polymer layer is selected from a group consisting of wool keratin, collagen hydrolysate, and gelatin; herein, the wool keratin can add glycerol selectively. The aforementioned bio-polymer materials have the advantage of low production cost, non-toxic environmentally, flexibility, etc. In the electronic device including a bio-polymer material of the present invention, the bio-polymer layer can be a dielectric layer or a gate dielectric layer. 
         [0019]    According to the electronic device including a bio-polymer material of the present invention, the present invention can provide an organic thin film transistor. Herein, the bio-polymer material layer is a gate dielectric layer; the first electrode is a gate electrode disposed between the substrate and the gate dielectric layer, and the gate dielectric layer covers the gate electrode; and the second electrode comprises a source electrode and a drain electrode locating over the gate dielectric layer. 
         [0020]    In the electronic device including a bio-polymer material of the present invention, the electronic device further comprises an organic semiconductor layer, wherein the organic semiconductor layer covers the gate dielectric layer. Preferably, the electronic device is a top contact organic thin film transistor; the organic semiconductor layer covers the entire surface of the gate dielectric layer, and the source electrode and the drain electrode locate on the organic semiconductor layer. 
         [0021]    The material of the organic semiconductor layer is not limited; it can be selected from any material that has been used in P-type and N-type organic semiconductor layers in the art. Preferably, the material of a P-type organic semiconductor layer is pentacene or pentacene derivatives; the material of an N-type organic semiconductor layer is fullerene (C60), F 16 CuPc, or perylene derivatives. The perylene derivatives can be PTCDI-C8 (N,N′-Dioctyl-3,4,9,10-perylenedicarboximide). 
         [0022]    In the electronic device including a bio-polymer material of the present invention, the electronic device further comprises an organic semiconductor layer, wherein the organic semiconductor layer covers the gate dielectric layer, the source electrode, and the drain electrode. Preferably, the electronic device is a bottom contact organic thin film transistor, the organic semiconductor layer covers the gate dielectric layer, the source electrode, and the drain electrode, and the source electrode and the drain electrode locate on the gate dielectric layer. 
         [0023]    In the electronic device including a bio-polymer material of the present invention, the present invention can provide an N-type organic thin film transistor. Herein, the electronic device further comprises a buffering layer disposed on the gate dielectric layer, and the material of the buffering layer is not limited, preferably is pentacene. The thickness of the buffering layer can range from 1 nm to 20 nm, preferably ranging from 1 nm to 10 nm, and more preferably ranging from 1 nm to 3 nm. 
         [0024]    In the present invention, the N-type organic thin film transistor can be a top contact structure; the organic semiconductor layer, the source electrode, and the drain electrode are disposed over the buffering layer. The N-type organic thin film transistor can be a bottom contact structure; the organic semiconductor layer disposes over the buffering layer, and the buffering layer covers the gate dielectric layer, the source electrode, and the drain electrode. 
         [0025]    According to the electronic device including a bio-polymer material of the present invention, the present invention can provide an organic floating gate electrode memory. Herein, the electronic device further comprises a floating gate electrode disposed between the gate dielectric layer and the organic semiconductor layer, and the floating gate electrode locates on the gate-dielectric layer. The material of the floating gate electrode is made of nanoparticle, oxide, or alloy selected from a group consisting of Al, Cu, Cr, Ag, Pt, Au, Zn, In or Sn. Preferably, the material is gold nanoparticle. 
         [0026]    In the electronic device including a bio-polymer material of the present invention, the electronic device further comprises a dielectric layer disposed between the floating gate electrode layer and the organic semiconductor layer, and the dielectric layer covers the floating gate electrode. 
         [0027]    In the electronic device including a bio-polymer material of the present invention, the bio-polymer layer can be an insulating layer. 
         [0028]    According to the electronic device including a bio-polymer material of the present invention, the present invention can provide a metal-insulator-metal capacitor. Herein, the first electrode disposes between the substrate and the insulating layer; the insulating layer covers the first electrode; and the second electrode is disposed over the insulating layer. 
         [0029]    Moreover, the present invention provides a method for manufacturing an electronic device including a bio-polymer material, comprising the following steps: (A) providing a substrate; (B) forming a first electrode on the substrate; (C) coating the substrate having the first electrode formed thereon with a bio-polymer solution to obtain a bio-polymer layer on the substrate and the first electrode; and (D) forming a second electrode over the bio-polymer layer. 
         [0030]    In the method for manufacturing an electronic device including a bio-polymer material of the present invention, the bio-polymer layer is a gate dielectric layer; the first electrode is a gate electrode; and the second electrode comprises a source electrode and a drain electrode. 
         [0031]    The step (C) comprises the flowing steps: (C1) providing a bio-polymer solution; (C2) coating the substrate having the gate electrode formed thereon with the bio-polymer solution, or dipping the substrate having the gate electrode formed thereon into the bio-polymer solution; and (C3) drying the bio-polymer solution which is coated on the substrate to obtain a gate dielectric layer on the substrate and the electrode. 
         [0032]    In the manufacturing method of the present invention, the step (D) further comprises forming an organic semiconductor layer over the gate dielectric layer. 
         [0033]    According to the manufacturing method of the present invention, the present invention provides a method for manufacturing a top contact organic thin film transistor. In the step (D), the semiconductor layer covers the entire surface of the gate dielectric layer, and the source electrode and the drain electrode are disposed on the organic semiconductor layer so as to obtain a top contact organic thin film transistor. 
         [0034]    According to the manufacturing method of the present invention, the present invention provides a method for manufacturing a bottom contact organic thin film transistor. In the step (D), the source electrode and the drain electrode are disposed on the gate dielectric layer, and the organic semiconductor layer covers the gate dielectric layer, the source electrode, and the drain electrode so as to obtain a bottom contact organic thin film transistor. 
         [0035]    According to the manufacturing method of the present invention, the present invention provides a method for manufacturing an N-type organic thin film transistor. In the step (D), a buffer layer is formed on the gate dielectric layer before forming the organic semiconductor layer. 
         [0036]    According to the manufacturing method of the present invention, the present invention provides a method for manufacturing an organic floating gate electrode memory. In the step (D), a floating gate electrode is formed on the gate dielectric layer before forming the organic semiconductor layer. Furthermore, in the step (D): after forming the floating gate electrode, a dielectric layer is formed on the floating gate electrode; the dielectric layer disposes between the floating gate electrode and the semiconductor layer and covers the floating gate electrode. 
         [0037]    According to the manufacturing method of the present invention, the present invention provides a method for manufacturing a metal-insulator-metal capacitor, comprising the following steps: (a) providing a substrate; (b) forming a first electrode on the substrate; (c) coating the substrate having the first electrode formed thereon with a bio-polymer solution to obtain a insulating layer on the substrate and the first electrode; and (d) forming a second electrode on the insulating layer. 
         [0038]    According to the method for manufacturing a metal-insulator-metal capacitor, the step (c) comprises the flowing steps: (c1) providing a bio-polymer solution; (c2) coating the substrate having the first electrode formed thereon with the bio-polymer solution, or dipping the substrate having the first electrode formed thereon into the bio-polymer solution; and (c3) drying the bio-polymer solution which is coated on the substrate to obtain an insulating layer on the substrate and the first electrode. 
         [0039]    According to the embodiment examples of the present invention, the electronic device and the method for manufacturing the same comprises: forming an electronic element, which includes a bio-polymer protein material, on a substrate having the first electrode formed thereon with a bio-polymer protein solution. Compared with the conventional method for forming a gate dielectric layer or an insulating layer by a sputtering method or vacuum vapor deposition method, the manufacturing method of the present invention can obtain a gate dielectric layer or an insulating layer via the solution process. Therefore, the manufacturing process is quite easy and the production cost is low. Moreover, the temperature of manufacturing process is lower than the conventional method so as to apply on large-area production. In addition, bio-polymer protein belongs to non-polluting environmental material, and it has a low production cost. For example, wool keratin is dissolved from wool waste, recycling the wool waste to apply on an electronic device, thus, the wool waste is assigned a high economic value again; collagen hydrolysate is hydrolyzed from animal by-products, making this material cheap and easily accessible; and gelatin has a much lower material cost, and it is also easily accessible commercially. 
         [0040]    Furthermore, according to the embodiment examples of the present invention, compared with SiO 2  and Al 2 O 3 , bio-polymer protein matches well with pentacene. While using the bio-polymer protein material of the present invention as the material of the gate dielectric layer, and matching pentacene as the material of the P-type organic semiconductor layer, one can obtain a P-type OTFT with upraised field-effect mobility. For example, using wool keratin, collagen hydrolysate, and gelatin to form a gate dielectric layer in P-type OTFT separately, its hole field-effect mobility is about 3.5 cm 2 /V-sec, 8.5 cm 2 /V-sec, and 6.9 cm 2 /V-sec respectively. These results show wool keratin, collagen hydrolysate, and gelatin can match well with the material of the organic semiconductor layer, so the hole field-effect mobility can be increased greatly. Further, adding glycerol into the wool keratin can elevate the hole field-effect mobility to about 3.85 cm 2 /V-sec, assigning the wool keratin that is dissolved from wool waste a higher economic value. 
         [0041]    In addition, compared with a conventional silicon-based floating gate electrode memory, the organic floating gate electrode memory including the bio-polymer of the present invention as the material of the dielectric layer has the properties of being flexible, lightweight, low priced, environmentally friendly, low operating voltage, etc. Therefore, the organic floating gate electrode memory can be integrated into organic electronic products to achieve the purposes of lighter weight, low production cost, and convenient carrying. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0042]      FIG. 1A  is a perspective view of a conventional top contact OTFT; 
           [0043]      FIG. 1B  is a perspective view of a conventional bottom contact OTFT; 
           [0044]      FIG. 2  is a perspective view of a conventional organic floating gate electrode memory; 
           [0045]      FIG. 3  is a perspective view of a conventional MIM capacitor; 
           [0046]      FIGS. 4A to 4D  are cross-sectional views illustrating the process for manufacturing a top contact OTFT in Embodiment 1 of the present invention; 
           [0047]      FIG. 5A  is a curve showing the transfer characteristics of the OTFT of Embodiment 1 of the present invention; wherein ABS(I D ) represents the absolute value of the drain current (|I D |); 
           [0048]      FIG. 5B  is a curve showing the output characteristics of the OTFT of Embodiment 1 of the present invention; 
           [0049]      FIG. 6A  is a curve showing the transfer characteristics of the OTFT of Embodiment 2 of the present invention; wherein ABS(I D ) represents the absolute value of the drain current (|I D |); 
           [0050]      FIG. 6B  is a curve showing the output characteristics of the OTFT of Embodiment 2 of the present invention; 
           [0051]      FIG. 7A  is a curve showing the transfer characteristics of the OTFT of Embodiment 3 of the present invention; wherein ABS(I D ) represents the absolute value of the drain current (|I D |); 
           [0052]      FIG. 7B  is a curve showing the output characteristics of the OTFT of Embodiment 3 of the present invention; 
           [0053]      FIG. 8A  is a curve showing the transfer characteristics of the OTFT of Embodiment 4 of the present invention; wherein ABS(I D ) represents the absolute value of the drain current (|I D |); 
           [0054]      FIG. 8B  is a curve showing the output characteristics of the OTFT of Embodiment 4 of the present invention; 
           [0055]      FIG. 9A  is a curve showing the transfer characteristics of the OTFT of Embodiment 5 of the present invention; wherein ABS(I D ) represents the absolute value of the drain current (|I D |) and ABS(I G ) represents the absolute value of the gate leakage current (|I G |); 
           [0056]      FIG. 9B  is a curve showing the output characteristics of the OTFT of Embodiment 5 of the present invention; 
           [0057]      FIG. 10A  is a curve showing the transfer characteristics of the OTFT of Embodiment 6 of the present invention; wherein ABS(I D ) represents the absolute value of the drain current (I D |) and SQRT(I D ) represents the square root of the drain current (I D   1/2 ); 
           [0058]      FIG. 10B  is a curve showing the output characteristics of the OTFT of Embodiment 6 of the present invention; 
           [0059]      FIGS. 11A to 11C  are cross-sectional views illustrating the process for manufacturing a bottom contact OTFT in Embodiment 7 of the present invention; 
           [0060]      FIGS. 12A to 12D  are cross-sectional views illustrating the process for manufacturing a top contact N-type OTFT in Embodiment 8 of the present invention; 
           [0061]      FIG. 13A  is a curve showing the transfer characteristics of the top contact N-type OTFT of gelatin and PTCDI-C8 of Embodiment 8 of the present invention; wherein ABS(I D ) represents the absolute value of the drain current (|I D |), ABS(I G ) represents the absolute value of the gate leakage current, and SQRT(I D ) represents the square root of the drain current (I D   1/2 ); 
           [0062]      FIG. 13B  is a curve showing the output characteristics of the top contact N-type OTFT of gelatin and PTCDI-C8 of Embodiment 8 of the present invention; 
           [0063]      FIG. 14A  is a curve showing the transfer characteristics of the top contact N-type OTFT of wool keratin and PTCDI-C8 of Embodiment 8 of the present invention; wherein ABS(I D ) represents the absolute value of the drain current (|I D |), ABS(I G ) represents the absolute value of the gate leakage current, and SQRT(I D ) represents the square root of the drain current (I D   1/2 ); 
           [0064]      FIG. 14B  is a curve showing the output characteristics of the top contact N-type OTFT of wool keratin and PTCDI-C8 of Embodiment 8 of the present invention; 
           [0065]      FIG. 15A  is a curve showing the transfer characteristics of the top contact N-type OTFT of collagen hydrolysate and fullerene of Embodiment 8 of the present invention; wherein ABS(I D ) represents the absolute value of the drain current (I D |) and SQRT(I D ) represents the square root of the drain current (I D   1/2 ); 
           [0066]      FIG. 15B  is a curve showing the output characteristics of the top contact N-type OTFT of collagen hydrolysate and fullerene of Embodiment 8 of the present invention; 
           [0067]      FIG. 16A  is a curve showing the transfer characteristics of the top contact N-type OTFT of gelatin and fullerene of Embodiment 8 of the present invention; wherein ABS(I D ) represents the absolute value of the drain current (|I D |) and SQRT(I D ) represents the square root of the drain current (I D   1/2 ); 
           [0068]      FIG. 16B  is a curve showing the output characteristics of the top contact N-type OTFT of gelatin and fullerene of Embodiment 8 of the present invention; 
           [0069]      FIG. 17A  is a curve showing the transfer characteristics of the top contact N-type OTFT of collagen hydrolysate and F 16 CuPc of Embodiment 8 of the present invention; wherein ABS(I D ) represents the absolute value of the drain current (|I D |), ABS(I G ) represents the absolute value of the gate leakage current, and SQRT(I D ) represents the square root of the drain current (I D   1/2 ); 
           [0070]      FIG. 17B  is a curve showing the output characteristics of the top contact N-type OTFT of collagen hydrolysate and F 16 CuPc of Embodiment 8 of the present invention; 
           [0071]      FIG. 18A  is a curve showing the transfer characteristics of the top contact N-type OTFT of gelatin and F 16 CuPc of Embodiment 8 of the present invention; wherein ABS(I D ) represents the absolute value of the drain current (|I D |), ABS(I G ) represents the absolute value of the gate leakage current, and SQRT(I D ) represents the square root of the drain current (I D   1/2 ); 
           [0072]      FIG. 18B  is a curve showing the output characteristics of the top contact N-type OTFT of gelatin and F 16 CuPc of Embodiment 8 of the present invention; 
           [0073]      FIGS. 19A to 19D  are cross-sectional views illustrating the process for manufacturing a bottom contact N-type OTFT in Embodiment 9 of the present invention; 
           [0074]      FIG. 20  is a perspective view of a top contact organic floating gate electrode memory in Embodiment 10 of the present invention; 
           [0075]      FIG. 21  is a curve showing the transfer characteristics of the top contact organic floating gate electrode memory of collagen hydrolysate of Embodiment 10 of the present invention; wherein ABS(I D ) represents the absolute value of the drain current (|I D |); 
           [0076]      FIG. 22  is a curve showing the transfer characteristics of the top contact organic floating gate electrode memory of gelatin of Embodiment 10 of the present invention; wherein ABS(I D ) represents the absolute value of the drain current (|I D |); 
           [0077]      FIG. 23  is a perspective view of a bottom contact organic floating gate electrode memory in Embodiment 11 of the present invention; 
           [0078]      FIGS. 24A to 24C  are cross-sectional views illustrating the process for manufacturing a MIM capacitor in Embodiment 12 of the present invention; 
           [0079]      FIG. 25  is a curve showing the capacitance-voltage characteristics of the MIM capacitor of collagen hydrolysate of Embodiment 12 of the present invention; 
           [0080]      FIG. 26  is a curve showing the capacitance-voltage characteristics of the MIM capacitor of wool keratin of Embodiment 12 of the present invention; and 
           [0081]      FIG. 27  is a curve showing the capacitance-voltage characteristics of the MIM capacitor of gelatin of Embodiment 12 of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0082]    The present invention has been described in an illustrative manner, and it is to be understood that the terminology used is intended to be in the nature of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings. Therefore, it is to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. 
       Preparation Embodiment 1 
     Preparation of a Wool Keratin Solution 
       [0083]    First, the wool was cleaned with Clearwater, and then the cleaned wool was soaked in a the solution composed of ethanol and acetone. Second, the ethanol and acetone were washed out by deionized water, and the dried wool was soaked in a the solution composed of thioethyl alcohol, urea, and sodiumdodecylsulfate (SDS) to extract the wool keratin. Finally, the solution having the wool keratin dissolved therein was dialysed by a dialysis membrane to obtain a wool keratin solution. 
       Preparation Embodiment 2 
     Preparation of a Collagen Hydrolysate Solution 
       [0084]    The collagen hydrolysate power extracted from pigskin was purchased from Ken Le Ad Development CO., LTD., and then was dissolved in deionized water to obtain a collagen hydrolysate solution with about 2-4% concentration. 
       Preparation Embodiment 3 
     Preparation of a Gelatin Solution 
       [0085]    The gelatin power was purchased from Sigma-Aldrich, and then was dissolved in deionized water to obtain a gelatin solution with various concentrations. 
       Preparation Embodiment 4 
     Preparation of a Whey Protein Solution 
       [0086]    The whey power was purchased from NOW Foods Bloomingdale (Ill., USA), and then was dissolved in deionized water to obtain a whey protein solution with various concentrations. 
       Preparation Embodiment 5 
     Preparation of a Hydroxypropyl Methylcellulose Solution 
       [0087]    The hydroxypropyl methylcellulose power was purchased from Sigma-Aldrich Co. LLC, and then was dissolved in deionized water to obtain a gelatin solution with various concentrations. 
       Example 1 
     Top Contact OTFT Including Wool Keratin 
       [0088]      FIGS. 4A to 4D  are illustrating the process for manufacturing a top contact OTFT including wool keratin. 
         [0089]    As shown in  FIG. 4A , a substrate  40  was provided, and the substrate  40  was cleaned by deionized water through a sonication process. In the present embodiment, the substrate  30  was a transparent plastic substrate made of PET. Next, the substrate  40  was placed inside a vacuum chamber (not shown in the figure), and a metal was evaporated onto the substrate  40  by using a mask (not shown in the figure) to form a patterned metal layer, which was used as a gate electrode  41 . In the present example, the metal used in the gate electrode  41  was Au, and the thickness of the gate electrode  41  was about 65 nm. In addition, the condition of the evaporation process for forming the gate electrode  41  is listed below: Pressure: 5×10 −6  torr, Evaporation rate: 1 Å/s. 
         [0090]    Then, the substrate  40  having the gate electrode  41  formed thereon was dipped into the wool keratin solution for 15 mins to coat the substrate  40  having the gate electrode  41  with the wool keratin solution. After the coating process, the substrate  40  coated with the wool keratin solution was dried at 60° C. to form a wool keratin film, and the wool keratin film was used as a gate dielectric layer  42 , as shown in  FIG. 4B . In the present embodiment, the gate dielectric layer  42  formed by the wool keratin film has a thickness of 400 nm. 
         [0091]    In addition, the coating process and the drying process can be performed several times to form a wool keratin film with multi-layered structure. 
         [0092]    As shown in  FIG. 4C , through a heat evaporation process, pentacene was deposited on the gate dielectric layer  42  at room temperature by use of a shadow metal mask to form an organic semiconductor layer  43 . In the present embodiment, the thickness of the organic semiconductor layer  43  is about 60 nm. In addition, the condition of the heat evaporation process for forming the organic semiconductor layer  43  is listed below: Pressure: 2×10 −6  torr, Evaporation rate: 0.3 Å/s. 
         [0093]    Finally, the same evaporation process and condition for forming the gate electrode  41  was performed to form a patterned metal layer, which was used as a source electrode  44  and a drain electrode  45 , on the organic semiconductor layer  43  by using another mask (not shown in the figure), as shown in  FIG. 4D . In the present embodiment, the material of the source electrode  44  and the drain electrode  45  was Au, and the thickness of the source electrode  44  and the drain electrode  45  was about 65 nm. 
         [0094]    As shown in  FIG. 4D , after the aforementioned process, a top contact OTFT of the present embodiment was obtained, which comprises: the substrate  40 ; the gate electrode  41  disposed on the substrate  40 ; the gate dielectric layer  42  disposed on the substrate  40  and covering the gate electrode  41 , wherein the gate dielectric layer  42  comprises wool keratin; the organic semiconductor layer  43  covering the entire surface of the gate dielectric layer  42 ; and the source electrode  44  and the drain electrode  45 , respectively disposed on the organic semiconductor layer  43 . 
       Example 2 
     Top Contact OTFT Including Wool Keratin 
       [0095]    The processes, procedures, and conditions were the same as described in Example 1, except that the material of the wool keratin solution obtained in Example 1 and glycerol was added together to form the film of the gate dielectric layer  42 . 
       Example 3 
     Top Contact OTFT Including Collagen Hydrolysate 
       [0096]    The processes, procedures, and conditions were the same as described in Example 1, except that the material of the collagen hydrolysate solution obtained in Example 2 was used to form the film of the gate dielectric layer  42 . 
       Example 4 
     Top Contact OTFT Including Gelatin 
       [0097]    The processes, procedures, and conditions were the same as described in Example 1, except that the material of the gelatin solution obtained in Example 3 was used to form the film of the gate dielectric layer  42 . 
       Example 5 
     Top Contact OTFT Including Whey Protein 
       [0098]    The processes, procedures, and conditions were the same as described in Example 1, except that the material of the whey protein solution obtained in Example 4 was used to form the film of the gate dielectric layer  42 . 
       Example 6 
     Top Contact OTFT Including Hydroxypropyl Methylcellulose 
       [0099]    The processes, procedures, and conditions were the same as described in Example 1, except that the material of the hydroxypropyl methylcellulose solution obtained in Example 5 was used to form the film of the gate dielectric layer  42 . 
       Evaluation of the Characteristics of the OTFT 
       [0100]    A current-voltage test was performed on the P-type top contact OTFT of Examples 1 to 6. The results of the transfer characteristics of the OTFT are shown in  FIGS. 5A ,  6 A,  7 A,  8 A,  9 A, and  10 A respectively, and the results of the output characteristics under different gate voltages (V G ) are shown in  FIGS. 5B ,  6 B,  7 B,  8 B,  9 B, and  10 B respectively. In  FIGS. 5A ,  6 A,  7 A,  8 A,  9 A and  10 A, ABS(I D ) represents the absolute value of the drain current (|I D |), ABS(I G ) represents the absolute value of the gate leakage current, and SQRT(I D ) represents the square root of the drain current (I D   1/2 ). The output characteristics in  FIG. 5B , the V G  from top to bottom are 0, −1, −2, −3, and −4 V respectively. The output characteristics in  FIG. 6B , the V G  from top to bottom are 0, −1, −2, and −3 V respectively. The output characteristics in  FIG. 7B , the V G  from top to bottom are 0, −1, −2, −3, and −4 V respectively. The output characteristics in  FIG. 8B , the V G  from top to bottom are 0, −1, −2, and −3 V respectively. The output characteristics in  FIG. 9B , the V G  from top to bottom are −4, −3, −2, −1, and 0 V respectively. The output characteristics in  FIG. 10B , the V G  from top to bottom are −3, −2, −1, and 0 V respectively. 
         [0101]    The current on-to-off ratio (I ON/OFF ), the subthreshold swing (S.S.), the hole field-effect mobility and the threshold voltage (V TH ) are listed in the following Table 1. 
         [0000]    
       
         
               
               
               
               
               
               
               
             
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Example 1 
                 Example 2 
                 Example 3 
                 Example 4 
                 Example 5 
                 Example 6 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Channel width 
                 600 
               
               
                 (μm) 
               
               
                 Channel length 
                 50 
               
               
                 (μm) 
               
               
                 Thickness of the 
                 600 
               
               
                 organic 
               
               
                 semiconductor 
               
               
                 layer (nm) 
               
             
          
           
               
                 On-to-off ratio 
                 9 × 10 4   
                 1.2 × 10 3   
                 2.6 × 10 4   
                 3.8 × 10 3   
                 9 × 10 2   
                 8 × 10 2   
               
               
                 (I ON /I OFF ) 
               
               
                 Subthreshold swing 
                 −0.155 
                 −0.158 
                 −0.162 
                 −0.240 
                 −0.173 
                 −0.3 
               
               
                 (V/decade) 
               
               
                 hole field-effect 
                 3.50 
                 3.85 
                 8.5 
                 6.87 
                   
                 2.6 
               
               
                 mobility 
               
               
                 (cm 2 /V-sec) 
               
               
                 threshold voltage 
                 −0.504 
                 −0.216 
                 −0.78 
                 −0.56 
                 −0.36 
                 −0.7 
               
               
                 (V th ) 
               
               
                   
               
             
          
         
       
     
         [0102]    According to the results shown in  FIG. 5A  to  FIG. 10B  and Table 1, the field-effect mobility of the gate dielectric layer made of the wool keratin (Example 1), wool keratin combined glycerol (Example 2), collagen hydrolysate (Example 3), gelatin (Example 4) and hydroxypropyl methylcellulose (Example 6) are 3.50 cm 2 /V-sec, 3.85 cm 2 /V-sec, 8.5 cm 2 /V-sec, 6.87 cm 2 /V-sec, 6 cm 2 /V-sec, and 2.6 cm 2 /V-sec respectively. Accordingly, the gate dielectric layers including collagen hydrolysate (Example 3) and gelatin (Example 4) show better efficiency. In addition, by adding glycerol into the wool keratin, the hole field-effect mobility is higher than using the wool keratin only. 
       Example 7 
     Bottom Contact OTFT 
       [0103]      FIGS. 11A to 11D  illustrate the process for manufacturing a bottom contact OTFT. 
         [0104]    As shown in  FIG. 11A , a substrate  40  was provided, and a gate electrode  41  and a gate dielectric layer  42  were formed on the substrate  40  sequentially. In the present Example, the material of the substrate  40  and gate electrode  41  and the manufacturing method were the same as described in Example 1, and the material of the gate dielectric layer  42  is selected from wool keratin, wool keratin combined with glycerol, collagen hydrolysate, gelatin, whey protein or hydroxypropyl methylcellulose. In the present Example, the thickness of the gate electrode  41  is about 65 nm, and the thickness of the gate dielectric layer is about 400 nm. 
         [0105]    Then, the same manufacturing process and condition as described in Example 1 for forming the gate electrode was used, and to form a patterned metal layer on the gate dielectric layer  42 . The patterned metal layer was used as a source electrode  44  and a drain electrode  45 , as shown in  FIG. 11B . In the present Example, the material of the source electrode  44  and the drain electrode  45  was Au, and the thickness of the source electrode  44  and the drain electrode  45  was about 65 nm. 
         [0106]    Finally, the same manufacturing process and condition as described in Example 1 for forming the organic semiconductor layer was used, and to form an organic semiconductor layer  43  on the gate dielectric layer  42 , source electrode  44 , and drain electrode  45 , as shown in  FIG. 11C . In the present Example, the material of the organic semiconductor layer  43  was pentacene, and the thickness of the organic semiconductor layer  43  was about 60 nm. 
         [0107]    As shown in  FIG. 11C , after the aforementioned process, a bottom contact OTFT of the present embodiment was obtained, which comprises: the substrate  40 ; the gate electrode  41  disposed on the substrate  40 ; the gate dielectric layer  42  disposed on the substrate  40  and covering the gate electrode  41 , wherein the gate dielectric layer  42  comprises a bio-polymer; the source electrode  44  and the drain electrode  45  disposed on the gate dielectric layer  42 ; and the organic semiconductor layer  43  covering the gate dielectric layer  42 , the source electrode  44  and the drain electrode  45 . 
       Example 8 
     Top Contact N-Type OTFT 
       [0108]      FIGS. 12A to 12D  illustrate the process for manufacturing a top contact N-type OTFT. 
         [0109]    As shown in  FIG. 12A , a substrate  40  was provided, and a gate electrode  41  and a gate dielectric layer  42  were formed on the substrate  40  sequentially. In the present Example, the material of the substrate  40  and gate electrode  41  and the manufacturing method were the same as described in Example 1, and the material of the gate dielectric layer  42  is selected from wool keratin, wool keratin combined glycerol, collagen hydrolysate, gelatin, whey protein or hydroxypropyl methylcellulose. 
         [0110]    As shown in  FIG. 12B , through a heat evaporation process, pentacene was deposited on the gate dielectric layer  42  at room temperature by use of a shadow metal mask to form a buffer layer  5 . In the present Example, the thickness of the buffer layer  5  is about 3 nm. In addition, the condition of the heat evaporation process for forming the buffer layer  5  is listed below: Pressure: 1×10 −6  torr, Evaporation rate: 0.03 nm/s. 
         [0111]    Then, the same manufacturing process and condition as described in Example 1 for forming the organic semiconductor layer was used, and to form an organic semiconductor layer  43  on the buffer layer  5 , as shown in  FIG. 12C . 
         [0112]    Finally, the same manufacturing process and condition as described in the Example 1 for forming the gate electrode was used, and to form a patterned metal layer on the organic semiconductor layer  43 . The patterned metal layer was used as a source electrode  44  and a drain electrode  45 , as shown in  FIG. 12D . 
         [0113]    As shown in  FIG. 12D , after the aforementioned process, a top contact N-type OTFT of the present embodiment was obtained, which comprises: the substrate  40 ; the gate electrode  41  disposed on the substrate  40 ; the gate dielectric layer  42  disposed on the substrate  40  and covering the gate electrode  41 , wherein the gate dielectric layer  42  comprises a bio-polymer; the buffer layer  5  covering the entire surface of the gate dielectric layer  42 ; the organic semiconductor layer  43  covering the entire surface of the buffer layer  5 ; and the source electrode  44  and the drain electrode  45 , respectively disposed on the organic semiconductor layer  43 . 
       Evaluation the Characteristics of the N-Type OTFT 
       [0114]    A transfer characteristics test was performed on the N-type top contact OTFT of which gelatin and wool keratin were used to obtain the gate dielectric layer  42  and PTCDI-C8 was used to obtain the organic semiconductor layer  43  (the steps of forming the buffer layer  5  were omitted). The results of the transfer characteristics of the OTFT are shown in  FIGS. 13A and 14A  respectively, and the results of the output characteristics are shown in  FIGS. 13B and 14B  respectively. In  FIGS. 13A and 14A , ABS(I D ) represents the absolute value of the drain current (|I D |)ABS(I G ) represents the absolute value of the leakage current (|I G |), and SQRT(I D ) represents the square root of the drain current (I D   1/2 ). The output characteristics in  FIGS. 13B and 14B , both of the V G  from top to bottom are 3, 2, 1, and 0V respectively. The current on-to-off ratio (I ON/OFF ), the subthreshold swing (S.S.), the hole field-effect mobility and the threshold voltage (V TH ) are listed in the following Table 2. 
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Gelatin 
                 Wool keratin 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Current on-to-off ratio (I ON /I OFF ) 
                 1.0 × 10 4   
                 4.5 × 10 3   
               
               
                 Subthreshold swing (mV/decade) 
                 0.152 
                 0.145 
               
               
                 Hole field-effect mobility (cm 2 /V-sec) 
                 1.70 
                 0.55 
               
               
                 Threshold voltage (V th ) 
                 0.46 
                 0.55 
               
               
                 Slope 
                 0.000292 
                 0.000388 
               
               
                   
               
             
          
         
       
     
         [0115]    Another transfer characteristics test was performed on the N-type top contact OTFT of which collagen hydrolysate and gelatin were used to obtain the gate dielectric layer  42  and fullerene was used to obtain the organic semiconductor layer  43 . The results of the transfer characteristics of the OTFT are shown in  FIGS. 15A and 16A  respectively, and the results of the output characteristics are shown in  FIGS. 15B and 16B  respectively. In  FIGS. 15A and 16A , the definition of ABS(I D ) and SQRT(I D ) are the same as described in Example 6. The output characteristics in  FIGS. 15B and 16B , both of the V G  from top to bottom (judges by the I D  value while V D =8) are 8, 6, 0, 4, and 2V respectively. The electron field-effect mobility of the OTFT that used collagen hydrolysate and gelatin to form the gate dielectric layer are 5.3 cm 2 /V-sec and 4 cm 2 /V-sec respectively. 
         [0116]    Still another transfer characteristics test was performed on the N-type top contact OTFT of which collagen hydrolysate and gelatin were used to obtain the gate dielectric layer  42  and F 16 CuPc (COPPER1,2,3,4,8,9,10,11,15,16,17,18,22,23,24,25-HEXADECAFLUO RO-PHTHALOCYANINE, SIGMA-ALDRICH 14916871) was used to obtain the organic semiconductor layer  43  (the steps of forming the buffer layer  5  were omitted). The results of the transfer characteristics of the OTFT are shown in  FIGS. 17A and 18A  respectively. In  FIGS. 17A and 18A , ABS(I D ) represents the absolute value of the drain current (|I D |), ABS(I G ) represents the absolute value of the gate leakage current, (|I G |) and SQRT(I D ) represents the square root of the drain current (| D   1/2 ). The results of the output characteristics are shown in  FIGS. 17B and 18B  respectively. The output characteristics in  FIG. 17B , the V G  from top to bottom are 4, 3, 2, 1, and 0V. The output characteristics in  FIG. 18B , the V G  from top to bottom are 5, 3.75, 2.5, 1.25, and 0V. The electron field-effect mobility of the OTFT that was used collagen hydrolysate and gelatin to form the gate dielectric layer are 0.23 cm 2 /V-sec and 0.35 cm 2 /V-sec respectively. 
       Example 9 
     Bottom Contact N-Type OTFT 
       [0117]      FIGS. 19A to 19D  illustrate the process for manufacturing a bottom contact N-type OTFT. 
         [0118]    As shown in  FIG. 19A , a substrate  40  was provided, and a gate electrode  41  and a gate dielectric layer  42  were formed on the substrate  40  sequentially. In the present Example, the material of the substrate  40  and gate electrode  41  and the manufacturing method were the same as described in Example 1, and the material of the gate dielectric layer  42  is selected from wool keratin, wool keratin combined glycerol, collagen hydrolysate, gelatin, whey protein or hydroxypropyl methylcellulose. 
         [0119]    As shown in  FIG. 19B , the same manufacturing process and condition as described in Example 1 for forming the gate electrode was used, and to form a patterned metal layer on the gate dielectric layer  42 . The patterned metal layer was used as a source electrode  44  and a drain electrode  45 . 
         [0120]    Then, pentacene was deposited on the gate dielectric layer  42 , the source electrode  44 , and the drain electrode  45  to form a buffer layer  5 , as shown in  FIG. 19C . 
         [0121]    Finally, the same manufacturing process and condition as described in Example 1 for forming the organic semiconductor layer was used, and to form an organic semiconductor layer  43  on the buffer layer  5 , as shown in  FIG. 19D . 
         [0122]    As shown in  FIG. 19D , after the aforementioned process, a bottom contact N-type OTFT of the present embodiment was obtained, which comprises: the substrate  40 ; the gate electrode  41  disposed on the substrate  40 ; the gate dielectric layer  42  disposed on the substrate  40  and covering the gate electrode  41 , wherein the gate dielectric layer  42  comprises a bio-polymer; the source electrode  44  and the drain electrode  45  disposed on the gate dielectric layer  42 ; the buffer layer  5  covering the gate dielectric layer  42 , the source electrode  44 , and the drain electrode  45 ; and the organic semiconductor layer  43  covering the entire surface of the buffer layer  5 . 
       Example 10 
     Top Contact Organic Floating Gate Electrode Memory 
       [0123]    As shown in  FIG. 20 , a gate electrode  41 , a gate dielectric layer  42 , an organic semiconductor layer  43 , a source electrode  44 , and a drain electrode  45  were formed on the substrate  40  sequentially. In the present Example, a metal (Au) was evaporated onto the gate dielectric layer  42  by using a mask (not shown in the figure) to form a patterned metal layer, which was used as a floating gate  46 . Then, the same manufacturing process and condition as described in the Example 1 for forming the gate dielectric layer  42  was used, and to form a bio-polymer film on the floating gate  46 . The patterned metal layer was used as a dielectric layer  47 . 
         [0124]    Accordingly, the top contact organic floating gate electrode memory of the present embodiment comprises: the substrate  40 ; the gate electrode  41  disposed on the substrate  40 ; the gate dielectric layer  42  disposed on the substrate  40  and covering the gate electrode  41 , wherein the gate dielectric layer  42  comprises a bio-polymer; the floating gate  46  covering the gate dielectric layer  42 ; the dielectric layer  47  covering the floating gate  46 ; the organic semiconductor layer  43  covering the dielectric layer  47 ; and the source electrode  44  and the drain electrode  45  disposed on the organic semiconductor layer  43 . 
       Evaluation of the Characteristics 
       [0125]    A transfer characteristic test was performed on the top contact organic floating gate electrode memory of which collagen hydrolysate and gelatin were used to obtain the dielectric layer  47 . The results of the transfer characteristics are shown in  FIGS. 21 and 22 , and ABS(I D ) represents the absolute value of the drain current (|I D |). 
       Example 11 
     Bottom Contact Organic Floating Gate Electrode Memory 
       [0126]    As shown in  FIG. 23 , a gate electrode  41 , a gate dielectric layer  42 , a source electrode  44 , a drain electrode  45 , and an organic semiconductor layer  43 , were formed on the substrate  40  sequentially. In the present Example, a metal (Au) was evaporated onto the gate dielectric layer  42  by using a mask (not shown in the figure) to form a patterned metal layer, which was used as a floating gate  46 . Then, the same manufacturing process and condition as described in Example 1 for forming the gate dielectric layer  42  was used, and to form a bio-polymer film on the floating gate  46 . The bio-polymer film was used as a dielectric layer  47 . 
         [0127]    Accordingly, the top contact organic floating gate electrode memory of the present embodiment comprises: the substrate  40 ; the gate electrode  41  disposed on the substrate  40 ; the gate dielectric layer  42  disposed on the substrate  40  and covering the gate electrode  41 , wherein the gate dielectric layer  42  comprises a bio-polymer; the floating gate  46  covering the gate dielectric layer  42 ; the dielectric layer  47  covering the floating gate  46 ; the source electrode  44  and the drain electrode  45  disposed on the dielectric layer  47 ; and the organic semiconductor layer  43  covering the dielectric layer  47 , the source electrode  44 , and the drain electrode  45 . 
       Example 12 
     MIM Capacitor 
       [0128]      FIGS. 24A to 24C  illustrate the process for manufacturing a MIM capacitor. 
         [0129]    As shown in  FIG. 24A , a substrate  140  was provided, and a first electrode  141  was formed on the substrate  140 . In the present Example, the same manufacturing process and condition as described in the Example 1 for forming the gate electrode  41  was used to form the first electrode  141 ; the substrate  140  is a plastic substrate and the material of the first electrode  141  is Au. 
         [0130]    Then, the same manufacturing process and condition as described in Example 1 for forming the gate dielectric layer  42  was used, and to form a bio-polymer film covering the first electrode  141 . The bio-polymer film was used as an insulating layer  142 , as shown in  FIG. 24B . 
         [0131]    Finally, the substrate  140  was placed inside a vacuum chamber (not shown in the figure) under 5×10 −6  torr for evaporation to form a second electrode  143 , as shown in  FIG. 24C . 
         [0132]    As shown in  FIG. 24C , after the aforementioned process, a MIM capacitor of the present embodiment was obtained, which comprises: the substrate  140 ; the first electrode  141  disposed on the substrate  140 ; the insulating layer  142  disposed on the substrate  140  and covering the first electrode  141 , wherein the insulating layer  142  comprises a bio-polymer; and the second electrode  143  disposed on the insulating layer. 
       Evaluation of the Characteristics 
       [0133]    A dielectric property test was performed on the MIM capacitor of which collagen hydrolysate, wool keratin, and gelatin were used to obtain the insulating layer  142 . The results of the capacitance (nF/cm 2 )-voltage property are shown in  FIGS. 25 ,  26 , and  27 . These experimental results prove that the bio-polymer material is an excellent dielectric material. 
         [0134]    Although the present invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the invention as hereinafter claimed.