Abstract:
In an antenna and a semiconductor device including the antenna, an object is to reduce the distance between electrodes of a capacitor as much as possible, reduce the area of the electrode of the capacitor as much as possible, and prevent the suppression of response sensitivity and a response range of the semiconductor device. The present invention relates to an antenna including an antenna coil provided over a first region of a base and a capacitor which uses a second region of the base as a dielectric body and which has electrodes provided for opposite planes of the second region of the base, wherein the second region of the base is thinner than the first region of the base, and also relates to a semiconductor device including the antenna.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     An aspect of the present invention to be disclosed relates to a semiconductor device having a wireless communication function (also referred to as an ID tag). 
     2. Description of the Related Art 
     In recent years, an RFID system where data are exchanged between an ID tag (also referred to as an RFID tag, an IC tag, an electronic tag, or a wireless tag) and a reader/writer (or a reader) has been popular. Since data are exchanged using an antenna provided for each of an ID tag and a reader/writer in this RFID system, communication is possible even when the ID tag is set apart from the reader/writer by several centimeters to several meters. Moreover, due to an advantage of high resistance against dust, static electricity, and the like, the RFID system has come to be used for a variety of fields including production management in factories, logistics, access control, and the like. 
     In a case of data communication in this RFID system, the resonant frequency of the antennas of both the ID tag and the reader/writer needs to correspond to the transmitted carrier frequency with a certain degree of accuracy. Here, the resonant frequency f of the antenna is expressed by the following Formula (1) where L is the inductance of an antenna coil and C is the capacitance of a capacitor.
 
 f= ½π√( LC )  (Formula 1)
 
     According to Formula 1, the resonant frequency f can be adjusted to a desired value by increasing or decreasing the inductance L of the antenna coil or the capacitance C of the capacitor (see Patent Document 1). 
     On the contrary, in a case where the resonant frequency f is determined in advance, the product of the inductance L of the antenna coil and the capacitance C of the capacitor needs to be set at a certain value. 
     The inductance L is proportional to the square of the number of windings of the coil N L  and the cross-sectional area thereof S L , and is inversely proportional to the length d L  of the coil in its axial direction. In other words, it can be said that the inductance L largely depends on the number of windings of the coil N L . However, once the area of the ID tag is determined, the area occupied by the antenna coil is also determined. That is to say, when the area occupied by the antenna coil is determined, the number of windings of the coil N L  is also determined necessarily. Therefore, it is difficult to adjust the resonant frequency f to a desired value by the number of windings of the coil N L . 
     Meanwhile, the capacitance C of the capacitor is proportional to the area S C  of an electrode, and is inversely proportional to the distance d C  between the electrodes. 
     As the capacitor of the ID tag, for example, a parallel-plate capacitor in which each of a top surface and a bottom surface of a dielectric body is provided with an electrode formed using a parallel-plate conductive material is given (see Patent Document 2). 
     REFERENCES 
     
         
         [Patent Document 1] Japanese Published Patent Application No. 2007-306601 
         [Patent Document 2] Japanese Published Patent Application No. 2002-42083 
       
    
     SUMMARY OF THE INVENTION 
     A conductive material used for an electrode of a capacitor causes an interruption of an electromagnetic wave including a signal transmitted from a reader/writer. Therefore, when the electrode of the capacitor has a large area, the electromagnetic wave is interrupted so as to cause the suppression of response sensitivity or a response range of a semiconductor device. Accordingly, the area of the electrode of the capacitor needs to be reduced as much as possible. 
     As described above, the capacitance C of the capacitor is proportional to the area S C  of the electrode and is inversely proportional to the distance d C  between the electrodes. That is to say, in a case of forming a semiconductor device with a desired resonant frequency f, in order to reduce the area S C  of the electrode of the capacitor, the distance d C  between the electrodes also needs to be reduced. 
     In view of the aforementioned, it is an object of an aspect of the present invention to be disclosed to reduce the distance between the electrodes of the capacitor as much as possible. 
     It is an aspect of the present invention to be disclosed to reduce the area of the electrode of the capacitor as much as possible. 
     It is an aspect of the present invention to be disclosed to prevent the suppression of response sensitivity and a response range of a semiconductor device. 
     In an aspect of the present invention to be disclosed, the thickness of a dielectric body of the capacitor is reduced. This allows the distance between the electrodes of the capacitor to be reduced. 
     An aspect of the present invention to be disclosed is an antenna including an antenna coil provided over a first region of a base, and a capacitor which uses a second region of the base as a dielectric body and which has electrodes provided for opposite planes of the second region of the base, wherein the second region of the base is thinner than the first region of the base. 
     An aspect of the present invention to be disclosed is a semiconductor device including a first antenna coil provided over a first region of a base, a capacitor which uses a second region of the base as a dielectric body and which has electrodes provided for opposite planes of the second region of the base, and a chip including a semiconductor integrated circuit and a second antenna coil, wherein the second region of the base is thinner than the first region of the base. 
     An aspect of the present invention to be disclosed is a method of manufacturing an antenna including an antenna coil and a capacitor, which includes the steps of rotating a roller having a projection portion while pressing the roller onto a base with a first thickness, providing the base with a dielectric body of the capacitor having a second thickness smaller than the first thickness by pressing the projection portion onto a first plane of the base, providing the base with an opening, forming a first conductive material over a first plane of a region with the second thickness, inside the opening, and over the first plane of the base, forming a second conductive material over the first plane of the base and a second plane thereof on an opposite side, and heating the first conductive material and the second conductive material so as to form the antenna coil and an electrode of the capacitor. 
     In an aspect of the present invention to be disclosed, the base is a film containing any of polyethylene terephthalate, polyethylene naphthalate, polyether sulfone, and polyimide. 
     In an aspect of the present invention to be disclosed, each of the first conductive material and the second conductive material includes at least one of silver (Ag), gold (Au), copper (Cu), nickel (Ni), platinum (Pt), palladium (Pd), tantalum (Ta), molybdenum (Mo), and titanium (Ti). 
     In an aspect of the present invention to be disclosed, the distance between the electrodes of the capacitor can be reduced by reducing the thickness of the dielectric body of the capacitor. By reducing the distance between the electrodes of the capacitor, the area of the electrode of the capacitor can be reduced. The reduction in the area of the electrode of the capacitor leads to the prevention of the suppression of response sensitivity and a response range of a semiconductor device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIGS. 1A and 1B  are a top view and a cross-sectional view of a semiconductor device, respectively; 
         FIGS. 2A to 2C  are cross-sectional views illustrating a manufacturing process of a semiconductor device; 
         FIGS. 3A to 3C  are cross-sectional views illustrating a manufacturing process of a semiconductor device; 
         FIGS. 4A to 4C  are cross-sectional views illustrating a manufacturing process of a semiconductor device; 
         FIGS. 5A and 5B  are top views of semiconductor devices and  FIG. 5C  is a block diagram thereof; and 
         FIG. 6  is a top view of a semiconductor device. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiment of the present invention disclosed in this specification will be hereinafter described with reference to the accompanying drawings. Note that the invention disclosed in this specification can be carried out in a variety of different modes, and it is easily understood by those skilled in the art that the modes and details of the invention disclosed in this specification can be changed in various ways without departing from the spirit and scope thereof. Therefore, the present invention is not construed as being limited to description of the Embodiment. Note that, in the drawings hereinafter shown, the same portions or portions having similar functions are denoted by the same reference numerals, and repeated description thereof will be omitted. 
     This Embodiment is explained with reference to  FIGS. 1A and 1B ,  FIGS. 2A to 2C ,  FIGS. 3A to 3C ,  FIGS. 4A to 4C ,  FIGS. 5A to 5C , and  FIG. 6 . 
       FIG. 1A  is a top view of a semiconductor device  100 , and  FIG. 1B  is a cross-sectional view along A-A′ of  FIG. 1A . The semiconductor device  100  shown in  FIGS. 1A and 1B  includes a base  101  having a first thickness, an antenna including an antenna coil  102  and a capacitor  103 , and a semiconductor integrated circuit chip  117 . The capacitor  103  includes as a dielectric body a region  113  which corresponds to a part of the base  101 . The opposite planes of the region  113  are provided with an electrode  111  and an electrode  112  of the capacitor  103 . The antenna coil  102  is provided over the base  101  and is electrically connected to the capacitor  103 . The semiconductor integrated circuit chip  117  is a circuit formed using a semiconductor substrate or a circuit formed using a semiconductor thin film. 
     In  FIG. 1B , the antenna coil  102 , and the electrode  111  and the electrode  112  of the capacitor  103  correspond to one continuous conductive layer. However, regions provided for the opposite planes of the dielectric body (the region  113  corresponding to a part of the base  101 ) in the conductive layer function as the electrodes (the electrode  111  and the electrode  112 ) of the capacitor  103 . Further, a region of the conductive layer which does not overlap with the dielectric body functions as the antenna coil  102 . 
     A second thickness, which corresponds to the thickness of the dielectric body of the capacitor  103 , i.e., the region  113  of the base  101 , is smaller than the first thickness corresponding to the thickness of the region of the base  101  where the antenna coil  102  is formed. By reducing the thickness of the dielectric body of the capacitor  103 , the distance between the electrode  111  and the electrode  112  of the capacitor  103  can be reduced. By reducing the distance between the electrode  111  and the electrode  112  of the capacitor  103 , the areas of the electrode  111  and the electrode  112  of the capacitor  103  can be reduced. The reduction in the area of each of the electrode  111  and the electrode  112  of the capacitor  103  leads to the prevention of the suppression of response sensitivity and a response range of the semiconductor device  100 . 
     As the base  101 , for example, a flexible film of polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polyether sulfone (PES), polyimide (PI), or the like can be used. 
     The first thickness corresponding to the thickness of the region of the base  101  where the antenna coil  102  is formed is preferably 1 μm or more and 300 μm or less, more preferably 1 μm or more and 50 μm or less. When the base  101  with such a thickness is used, the semiconductor device  100  can be manufactured so as to be thin and capable of being bent. 
     The second thickness corresponding to the thickness of the region  113  of the base  101  (the dielectric body of the capacitor  103 ), i.e., the distance d C  between the electrode  111  and the electrode  112  of the capacitor  103  may be determined based on the resonant frequency f of the antenna and the number of windings of the coil N L . 
     In this Embodiment, a polyethylene naphthalate film with a thickness of 25 μm is used as the base  101 . 
     Each of the antenna coil  102 , and the electrode  111  and the electrode  112  of the capacitor  103  may be formed of a conductive material including at least one metal element of silver (Ag), gold (Au), copper (Cu), nickel (Ni), platinum (Pt), palladium (Pd), tantalum (Ta), molybdenum (Mo), and titanium (Ti). 
     In  FIG. 1A , the semiconductor integrated circuit chip  117  is disposed so as not to overlap with the antenna coil  102 ; however, the semiconductor integrated circuit chip  117  may be disposed so as to overlap with the antenna coil  102  as shown in  FIG. 6 . 
     A method of manufacturing the semiconductor device  100  of this Embodiment is described below. 
     First, the base  101  having the first thickness is prepared (see  FIG. 2A ). 
     Next, a roller  107  having a projection portion  108  is rotated while being pressed onto the base  101 , so that the projection portion  108  is pressed onto a first plane of the base  101 . Accordingly, the base  101  is provided with a depression portion  106  (see  FIG. 2B ). The region  113  of the base  101  where the depression portion  106  is formed has reduced thickness. The region  113  of the base  101  with the reduced thickness serves as the dielectric body of the capacitor  103 . Note that the thickness of the base in the region with the reduced thickness corresponds to the second thickness. Note that the depression portion  106  may be formed by irradiation with a laser beam instead of using the roller  107  having the projection portion  108 . 
     Next, the base  101  is provided with an opening  109  (see  FIG. 2C ). The opening  109  is formed by irradiation with a laser beam having a wavelength which is absorbed by the base  101 . Typically, a laser beam of an ultraviolet region, a visible region, or an infrared region is selected as appropriate for the irradiation. 
     As a laser oscillator which can deliver the aforementioned laser beam, an excimer laser oscillator such as a KrF oscillator, an ArF oscillator, or an XeCl laser is given. Alternatively, as the laser oscillator, a gas laser oscillator including gas such as He, He—Cd, Ar, He—Ne, HF, or CO 2  is given. Further, as the laser oscillator, a solid-state laser oscillator including a crystal such as YAG, GdVO 4 , YVO 4 , YLF, YAlO 3 , or the like doped with Cr, Nd, Er, Ho, Ce, Co, Ti, or Tm, or a solid-state laser oscillator including glass, ruby, or the like is given. In the case of using the solid-state laser oscillator, it is preferable to use any of the fundamental wave to the fifth harmonic as appropriate. Further alternatively, a semiconductor laser oscillator including GaN, GaAs, GaAlAs, InGaAsP, or the like can be used. 
     In this Embodiment, the base  101  is irradiated with a UV laser beam with a wavelength of 266 nm, whereby the opening  109  having a circular shape with a diameter of 50 μm when seen from above is formed. The opening  109  is formed with respect to the first plane of the base  101  provided with the depression portion  106  and a second plane thereof on the side opposite to the first plane. The shape of the opening  109  does not have to be circular but may be triangular or rectangular. The width of the cross section of the opening can be determined as appropriate. The number of the openings  109  may be one or two or more. The shape and the number of the openings  109  may be determined as appropriate so that conductive materials formed for the opposite planes of the base  101  are electrically connected to each other favorably through the opening. 
     The opening  109  may be formed by a punch press process using metallic molding or by a cutter knife or the like. 
     A supporting base  116  having a base  115  and an adhesive  114  is attached to the second plane of the base  101  by a mechanical or manual means (see  FIG. 3A ). 
     Next, a conductive material  104  is formed inside the depression portion  106 , inside the opening  109 , and over the first plane of the base  101  (see  FIG. 3B ). Note that the inside of the depression portion  106  is filled with the conductive material  104  in  FIG. 3B ; however, as shown in  FIG. 3C , the inside of the depression portion  106  does not have to be filled with the conductive material  104 . 
     As the conductive material  104 , a material including a conductive particle and an organic resin is used. Specifically, a conductive paste in which conductive particles each having a diameter of several nanometers to several tens of micrometers are dissolved or dispersed in an organic resin is used. As the conductive particle, a dispersive nanoparticle, a microparticle of silver halide, or a metal particle of one or more of silver (Ag), gold (Au), copper (Cu), nickel (Ni), platinum (Pt), palladium (Pd), tantalum (Ta), molybdenum (Mo), titanium (Ti), and the like can be used. In addition, as the organic resin included in the conductive paste, one or more organic resins selected from among organic resins which serve as a binder, a solvent, a dispersing agent, and a coating material for the metal particle can be used. Organic resins such as an epoxy resin and a silicone resin are typically given. Further, in forming the conductive layer, baking is preferably performed after the conductive paste is extruded. 
     The conductive material  104  can be formed by a screen printing method, a gravure printing method, an inkjet printing method, a rotary screen printing method, or the like. 
     In this Embodiment, a silver paste is formed as the conductive material  104  by a screen printing method. 
     After the formation of the conductive material  104 , a first heating step is performed. The first heating step is performed for hardening the organic resin included in the conductive material  104 . In this Embodiment, the first heating step is performed for 10 minutes at 90° C. Note that the first heating step is performed in order to prevent the peeling of the conductive material  104  in a later step of forming a conductive material  110  over the second plane of the base  101 . Therefore, if there is no risk of the peeling of the conductive material  104 , the first heating step does not have to be performed. 
     Next, the supporting base  116  having the base  115  and the adhesive  114  is separated from the second plane of the base  101  (see  FIG. 4A ). 
     After the separation of the supporting base  116 , the conductive material  110  is formed over the second plane of the base  101  (see  FIG. 4B ). The conductive material  110  may be either the same as or different from the conductive material  104 . However, the conductive material  110  is formed in contact with the conductive material  104  formed in the opening  109 . Note that a method for forming the conductive material  110  can be the same as a method for forming the conductive material  104 . 
     Next, a second heating step is performed so as to remove the organic resin included in the conductive material  104  and the conductive material  110 , whereby the resistance of the conductive material  104  and the conductive material  110  is reduced. In the aforementioned manner, the antenna coil  102 , and the electrode  111  and the electrode  112  of the capacitor  103  are formed using the conductive material  104  and the conductive material  110 . 
     Note that in  FIG. 4B , the conductive material  104  in the opening  109  and the conductive material  110  formed over the second plane of the base  101  are illustrated to be continuous. In the case where the conductive material  104  and the conductive material  110  are formed using the same material, the conductive material  104  and the conductive material  110  are continuous. In the case where the conductive material  104  and the conductive material  110  are formed using different materials from each other, the conductive material  104  and the conductive material  110  are not necessarily continuous. As long as the conductive material  104  in the opening  109  and the conductive material  110  formed over the second plane of the base  101  function as the antenna coil  102  and the electrode  112 , and the conductive material  104  and the conductive material  110  are electrically connected to each other, they may be either continuous or discontinuous. 
     In this manner, the antenna coil  102  and the capacitor  103  are provided for the base  101  (see  FIG. 4C ). Note that  FIG. 4C  corresponds to  FIG. 1B . 
     As shown in  FIG. 1A , the semiconductor device  100  includes the semiconductor integrated circuit chip  117  provided with the antenna (also referred to as an on-chip antenna), and the base  101  provided with the antenna coil  102  (also referred to as a booster antenna) and the capacitor  103 . 
     A semiconductor integrated circuit provided in the semiconductor integrated circuit chip  117  includes a plurality of elements such as a transistor which forms a memory portion or a logic portion. As the transistor which forms the memory portion or the logic portion, a field effect transistor is given. Further, a storage element in the memory portion may be formed with the use of the field effect transistor. 
       FIG. 5A  is an expanded view of an antenna coil  124  (on-chip antenna) and a semiconductor integrated circuit  123  included in the semiconductor integrated circuit chip  117  shown in  FIG. 1A . 
     In  FIG. 5A , the antenna coil  124  is a rectangular loop antenna with one winding; however, one embodiment of the present invention is not limited to this structure. The shape of the loop antenna is not limited to a rectangle and may be a shape with a curve line, e.g., a circular shape. In addition, the number of windings is not limited to one and may be plural. When the number of windings of the antenna coil  124  is 1, the parasitic capacitance generated between the semiconductor integrated circuit  123  and the antenna coil  124  can be reduced. 
     In  FIG. 5A , the antenna coil  124  is placed to surround the periphery of the semiconductor integrated circuit  123 , and except for portions corresponding to power feeding points  128  illustrated by dashed lines, the antenna coil  124  is arranged in a region different from the semiconductor integrated circuit  123 . 
     However, one embodiment of the present invention is not limited to the structure shown in  FIG. 5A ; as illustrated in  FIG. 5B , the antenna coil  124  may be arranged so as to at least partly overlap with the semiconductor integrated circuit  123  in addition to the portions corresponding to the power feeding points  128  indicated by the dashed lines. 
     Note that in the case where the antenna coil  124  is arranged in a region different from the semiconductor integrated circuit  123  as illustrated in  FIG. 5A , the parasitic capacitance generated between the semiconductor integrated circuit  123  and the antenna coil  124  can be reduced. 
     Next, operation of the semiconductor device  100  of this Embodiment will be described.  FIG. 5C  is an example of a block diagram illustrating a structure of the semiconductor device of this Embodiment. 
     The semiconductor device  100  shown in  FIG. 5C  includes the antenna coil  102  as a booster antenna, the semiconductor integrated circuit  123 , and the semiconductor integrated circuit chip  117 . The semiconductor integrated circuit chip  117  includes the antenna coil  124  as the on-chip antenna. 
     When the antenna coil  102  receives an electromagnetic wave transmitted from a reader/writer  121 , an alternate current is generated in the antenna coil  102 , whereby a magnetic field is generated around the antenna coil  102 . Then, a loop-like portion of the antenna coil  102  is electromagnetically coupled with the antenna coil  124  having a loop-like shape, so that induced electromotive force is generated in the antenna coil  124 . 
     The semiconductor integrated circuit  123  receives a signal or electric power from the reader/writer  121  by using the induced electromotive force. When current flows through the antenna coil  124  in accordance with a signal generated in the semiconductor integrated circuit  123  so that induced electromotive force is generated in the antenna coil  124 , a signal can be transmitted to the reader/writer  121  over a reflected wave of an electric wave transmitted from the reader/writer  121 . 
     Note that the antenna coil  102  mainly has a loop-like portion which is coupled electromagnetically with the antenna coil  124  and a portion which receives an electric wave from the reader/writer  121 . The shape of the antenna coil  102  in the portion which mainly receives the electric wave from the reader/writer  121  may be any shape as long as the electric wave can be received. 
     In the semiconductor device of this Embodiment, the on-chip antenna is used and a signal or electric power can be exchanged between the booster antenna and the on-chip antenna without contact; therefore, unlike the case where an external antenna is connected to a semiconductor integrated circuit, the semiconductor integrated circuit and the antenna are less likely to be disconnected due to external force, and generation of initial failure in the connection can also be suppressed. In addition, since the booster antenna is used in this Embodiment, unlike the case where only the on-chip antenna is used, the advantage of an external antenna can also be offered. In other words, the area of the semiconductor integrated circuit does not significantly limit the size or shape of the on-chip antenna, the frequency band of electric waves which can be received is not limited, and the communication distance can be increased. 
     Although this Embodiment describes the antenna coil  102  as the booster antenna, the antenna coil  102  may be used as the on-chip antenna. In the case of using the antenna coil  102  as the on-chip antenna, the capacitor is provided in connection with the antenna coil  124  shown in  FIG. 5A  and  FIG. 5B . The thickness of the base in the region which serves as the dielectric body of the capacitor may be reduced by using the roller  107  having the projection portion  108  or the laser beam. 
     The semiconductor integrated circuit can be directly formed over a flexible substrate. Alternatively, the semiconductor integrated circuit may be transferred from a formation substrate (for example, a glass substrate) to another substrate (for example, a plastic substrate). 
     In this Embodiment, the distance between the electrodes of the capacitor can be reduced by reducing the thickness of the dielectric body of the capacitor. By reducing the distance between the electrodes of the capacitor, the area of the electrode of the capacitor can be reduced. The reduction in the area of the electrode of the capacitor leads to the prevention of the suppression of response sensitivity and a response range of a semiconductor device. 
     This application is based on Japanese Patent Application serial no. 2010-139426 filed with Japan Patent Office on Jun. 18, 2010, the entire contents of which are hereby incorporated by reference.