Patent Publication Number: US-2006009251-A1

Title: RF device on insulating substrate and method of manufacturing RF device

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an RF device having an antenna and a signal processing circuit, for handling tag information, sensor information, security information, etc., a method of manufacturing such an RF device, a method of inspecting such an RF device, an RF apparatus, and a method of manufacturing such an RF apparatus.  
      2. Description of the Related Art  
      Recently, RF (Radio-Frequency) devices such as RF tags or noncontact IC cards are quickly being put to practical use. RF tags comprise an antenna, a memory, and a signal processing circuit, and tag information stored in the memory is transmitted to and from a dedicated reader/writer for merchandise management and security control.  
      As shown in  FIG. 1  of the accompanying drawings, an RF tag has antenna  302  mounted on substrate  301  and IC chip  303  mounted on substrate  301  in electrical connection to antenna  302 . Substrate  301  is usually made of inexpensive insulating plastics such as PET (Poly-Ethylene Terephthalate) or the like. Antenna  302  is made of a material having a relatively small electric resistance such as aluminum or the like, and is patterned substrate  301  by printing. IC chip  303  is thermally compressed to antenna  302  by ACF (Anisotropic Conductive Film) or the like.  
      In the RF tag shown in  FIG. 1 , IC chip  303  is directly mounted on substrate  301  with antenna  302  disposed thereon. Another RF tag has an IC chip mounted on a substrate (referred to as “inlet”) that is mounted on another substrate with an antenna disposed thereon. The IC chip is thermally compressed to interconnections on the inlet by ACF. The inlet is joined to the substrate by thermal compression or crimping, thereby connecting the interconnections on the inlet to the antenna.  
      The operating principles of a conventional RF tag will be described below.  
      As shown in  FIG. 2  of the accompanying drawings, reader/writer  311  has controller  312 , transmitter/receiver  313 , and antenna  314 . A signal generated by controller  312  is sent to transmitter/receiver  313 , which sends the signal as a radio wave from antenna  314 . RF tag  315  has antenna  316  and IC chip  317  which includes transmitter/receiver  318  and memory  319 . Antenna  316  of RF tag  315  detects the radio wave transmitted from antenna  314  of reader/writer  311 , and sends signal information of the detected radio wave to transmitter/receiver  318  of IC chip  317  to read information from and write information in memory  319 . A signal read from memory  319  is sent to transmitter/receiver  318 , which sends the signal as a radio wave from antenna  316  back to reader/writer  311 . Reader/writer  311  sends the returned information to a computer (not shown). The computer uses the information for merchandise management and security control. The RF tag usually does not have a battery, and obtains necessary electromotive forces from the radio wave that is received by antenna  316 .  
      A noncontact IC card operates according to operating principles which are essentially the same as the operating principles of the RF tag. However, RF tags and noncontact IC cards are used in different categories. Specifically, RF tags are used as tags on merchandise, and noncontact IC cards are used as authentication tools for ID cards and cash mediums for prepaid IC cards, for example.  
      As shown in  FIG. 3  of the accompanying drawings, IC card  321  comprises device  322  and auxiliary member  324  that are sandwiched between two substrates  323  bonded together for making IC card  321  portable. Auxiliary member  324  has a central opening with device  322  accommodated therein. Device  322  comprises an IC chip mounted on a thin PET film with an antenna disposed on its surface. Device  322  alone is too low in mechanical strength to be used as a card. Therefore, two substrates  322  each made of a plastics material such as polycarbonate or ABS (Acrylonitrile-Butadiene-Styrene copolymer) are bonded to device  322  to make IC card  321  as thick as about 1 mm, thereby protecting device  322 . When IC card  321  is carried by the user, device  322  is prevented from being damaged. Such an IC card is disclosed in JP-2002-279383-A and JP-2000-251037-A, for example.  
      Device  322  has a convex region where the IC chip is mounted, due to the thickness of the IC chip. If device  322  is simply sandwiched between substrates  323 , then they would not be sufficiently joined together. Consequently, auxiliary member  324  is added as a spacer to provide flat surfaces to IC card  321 . The surfaces of IC card  321  can thus be printed with clear patterns for increasing the commercial value thereof. Auxiliary member  324  is also able to increase the mechanical strength of IC card  321 .  
      Another form of RF tag comprise a circuit including a transmitter/receiver, a memory, etc., and an antenna which are integrally incorporated in a single IC chip. For example, there is known an RF tag (ME-Y1002 manufactured by Hitachi Maxell) having a signal processing circuit, a memory, and an antenna that are mounted on a square silicon chip having sides each 2.5 mm long. In the RF tag, the signal processing circuit and the memory are fabricated according to the ordinary CMOS (Complementary Metal Oxide Semiconductor) silicon process. After the signal processing circuit and the memory are produced, the antenna is formed on the silicon chip by copper plating. The antenna is of a spiral shape having a pitch that is slightly larger than 10 μm and extends to outermost peripheral edges of the silicon chip. Since the antenna is placed on the small silicon chip, the RF tag has a short communication range of 2.5 mm or less.  
      JP-H08-77317-A and JP-H10-162112-A, for example, disclose a technology for integrally forming a small antenna and a signal processing circuit on a silicon chip. These publications indicate that an IC card can be reduced in size and the cost required for mounting the components on the silicon chip can be lowered.  
      As described above, RF devices such as RF tags or the like are classified into two types, i.e., a type wherein a circuit and an antenna are formed on separate substrates (hereinafter referred to as “separate type”) and a type wherein a circuit and an antenna are integrally formed on a substrate (hereinafter referred to as “integral type”). A process of determining when to use an antenna based on required electromotive forces is revealed in, for example, PHILIPS “I-CODE Coil Design Guide”, September 2002, and Steve C. Q. Chen, et. al., “OPTIMIZATION OF INDUCTIVE RFID TECHNOLOGY”, 2001, IEEE, p. 82-87.  
      The conventional RF devices such as RF tags or the like suffer the following problems:  
      The separate-type RF device is problematic in that they are of low durability. Specifically, since the separate-type RF device is of such a structure that an IC chip mounted on a substrate with an antenna disposed thereon, junctions between these components are not highly reliable. If the terminal of the IC chip and the antenna arb connected to each other by ACF, then because the components are thermally expanded at different rates when the RF device is in a high-temperature environment and thermally contracted at different rates when the RF device is in a low-temperature environment, significant thermal stresses are developed in the components. For example, RF tags are attached to various products and placed in various different environments. They may be kept at low temperatures when placed in containers on airplanes or they may be kept at high temperatures when carried on pallets on factory production lines. Therefore, the RF tags are liable to undergo thermal stresses, which tend to break the junctions between the components thereof. The junctions between the components of RF tags can also be broken when products with the RF tags attached thereto are vibrated or shocked during shipment or when the RF tags are subjected to bending stresses while being applied to clothes or paper products. Actually, an introduction test conducted on conventional separate-type RF tags reported that they had a failure rate of nearly 10%.  
      Separate-type RF devices are highly costly to manufacture. Inasmuch as RF tags are expected to replace existing bar codes in the future, their manufacturing cost should desirably be reduced to several yen per RF tag. IC chips for use in RF devices are fabricated according to the so-called semiconductor process, a certain reduction in the cost of the IC chips can be expected by reducing the chip size and shortening the fabrication process, as is the case with the cost of DRAMs. However, smaller-size IC chips are likely to suffer an increase in the cost of mounting them. For example, for mounting a square IC chip having sides each of 0.3 mm (μ chip manufactured by Hitachi, Ltd.) on an antenna, a production facility having a very high handling capability is needed. In view of the yield and other factors, it is a task that cannot easily be achieved to reduce the manufacturing cost of separate-type RF devices.  
      Another drawback of separate-type RF devices is that when they are incorporated in IC cards, they have a poor appearance. Attempts to improve the appearance tend to incur expenses. Specifically, as shown in  FIG. 3 , since an RF device has a convex region due to an IC chip, when the RF device is incorporated in an IC card, the IC card has surface irregularities, which are not only unpleasing to the eye, but also make it difficult to form high-resolution printed patterns thereon. In order to reduce the surface irregularities, the RF device needs to have an auxiliary member having a certain thickness. However, adding the auxiliary member increases the number of components of the RF device and the manufacturing cost thereof.  
      Integral-type RF tags are disadvantageous in that they have a low communication capability. RF tags have a large merit in that they can send and receive signals in a noncontact fashion, and are more convenient to use if their communication range is wider. However, conventional integral-type RF tags have a circuit and an antenna that are disposed on the surface of a silicon substrate, and since the silicon substrate is a conductor, radio waves emitted from the antenna are blocked by the silicon substrate. Therefore, radio waves cannot be sent and received through the surface on which the antenna is mounted. Another problem is that a current induced in the silicon substrate tends to increase noise and hence lower communication sensitivity.  
      Heretofore, because silicon substrates are expensive to manufacture, RF devices are designed such that as many RF devices as possible can be obtained from a single silicon wafer. It is thus necessary to reduce the area of the antenna of an integral-type RF tag in order to lower the cost thereof. For example, the RF tag referred to above (ME-Y1002 manufactured by Hitachi Maxell) has an antenna mounted on a square silicon chip having sides each 2.5 mm long. JP-H08-77317-A employs a small antenna on a silicon chip.  
      The communication capability of an antenna is largely affected by the size of the antenna. An antenna having a larger size has a higher sensitivity. If electromotive forces generated from radio waves received by an RF tag are used as electric power for energizing the RF tag, then increasing the size of the antenna of the RF tag is effective to increase magnetic fluxes passing through the antenna for thereby generating larger electromotive forces, which can increase the strength of radio waves radiated from the antenna. Consequently, the size of the antenna of an RF tag is a parameter that is most effective to increase the communication range of the RF tag. With IC chips having silicon substrates, however, the antenna size cannot be increased due to the cost limitation. As described above, the RF tag referred to above (ME-Y1002 manufactured by Hitachi Maxell) has a small chip size having sides each 2.5 mm long and has a short communication range of 2.5 mm or less. This communication range is much smaller than the communication range of separate-type RF tags which is several tens cm.  
      Separate-type RF devices have an antenna disposed on the surface of an inexpensive PET substrate. Therefore, it is not necessary to make serious attempts to reduce the size of the antennas of separate-type RF devices from the standpoint of cost. Instead, separate-type RF devices may be designed freely within the limitations posed by the outer profile of a card to be employed, for example, so as to achieve a sufficient communication capability.  
      Specifically, the antenna of a separate-type RF device may be formed within a rectangular area having a longitudinal length of 7 cm and a transverse length of 5 cm.  
     SUMMARY OF THE INVENTION  
      It is an object of the present invention to provide an RF device which has excellent durability, communication capability, and appearance and which can be manufactured at a low cost, a method of manufacturing such an RF device, a method of inspecting such an RF device, an RF apparatus, and a method of manufacturing such an RF apparatus.  
      To achieve the above object, an RF device according to the present invention has an insulating substrate, a signal processing circuit, and an antenna for radio communications. The signal processing circuit is disposed on the insulating substrate. The antenna for radio communications is integrally formed with the signal processing circuit on the insulating substrate, and is connected to the signal processing circuit.  
      An RF apparatus according to the present invention has a plurality of RF devices described above, the RF devices being stacked together.  
      In a method of manufacturing an RF device according to the present invention, a signal processing circuit is formed on an insulating substrate according to a TFT fabrication process, and an antenna connected to the signal processing circuit is formed on the insulating substrate.  
      In a method of manufacturing an RF apparatus according to the present invention, an RF device is fabricated by the method of manufacturing an RF device according to the present invention, and a plurality of the RF devices are stacked and secured together.  
      In a method of inspecting an RF device according to the present invention, a conductive plate made of a conductive material and having an opening for alignment with a single RF device or a plurality of spaced RF devices is positionally adjusted with respect to an RF device sheet having a plurality of RF devices each comprising a signal processing circuit and an antenna disposed on an insulating substrate, to position the opening in alignment with the single RF device or the spaced RF devices. Then, the single RF device or the spaced RF devices are inspected by applying an inspecting signal by way of radio waves to the single RF device or the spaced RF devices.  
      According to the present invention, there is provided an apparatus for inspecting an RF device on an RF device sheet having a plurality of RF devices each comprising a signal processing circuit and an antenna disposed on an insulating substrate. The apparatus has a conductive plate and a reader/writer. The conductive plate is made of a conductive material and has an opening for alignment with a single RF device or a plurality of spaced RF devices. The opening is positioned in alignment with the single RF device or the RF devices to be inspected. The reader/writer applies an inspecting signal by way of radio waves to the single RF device or the spaced RF devices.  
      The above and other objects, features, and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings which illustrate examples of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a perspective view of a conventional RF tag;  
       FIG. 2  is a block diagram of a conventional RF tag and reader/writer;  
       FIG. 3  is an exploded perspective view of a conventional noncontact IC card;  
       FIG. 4  is a perspective view of an RF device according to a first embodiment of the present invention;  
       FIG. 5  is a block diagram of a circuit arrangement of the RF device according to the first embodiment;  
       FIGS. 6A through 6D  are graphs of coil wire widths represented by the horizontal axis and electromotive forces represented by the vertical axis, the graphs showing how the coil wire width affects the electromotive forces with respect to different numbers of coil turns and different coil profiles;  
       FIGS. 7A through 7C  are graphs of coil wire widths represented by the horizontal axis and electromotive forces represented by the vertical axis, the graphs showing how the coil wire width affects the electromotive forces with respect to different numbers of coil turns and different coil profiles;  
       FIGS. 8A through 8C  are fragmentary cross-sectional views showing successive steps of a method of manufacturing an RF device according to a second embodiment of the present invention;  
       FIG. 8D  is a perspective view of the RF device that is manufactured by the method according to the second embodiment of the present invention;  
       FIGS. 9A through 9F  are fragmentary cross-sectional views showing successive steps of a process of manufacturing a CMOS transistor of a signal processing circuit of the RF device according to the second embodiment of the present invention;  
       FIGS. 10A through 10C  are fragmentary cross-sectional views showing successive steps of a process of manufacturing an antenna of the RF device according to the second embodiment of the present invention;  
       FIGS. 11A and 11B  are fragmentary cross-sectional views showing successive steps of a process of manufacturing an antenna according to a first modification of the RF device according to the second embodiment of the present invention;  
       FIGS. 12A and 12B  are fragmentary cross-sectional views showing successive steps of a process of manufacturing an antenna according to a second modification of the RF devise according to the second embodiment of the present invention;  
       FIG. 13  is a perspective view of an RF device according to a third embodiment of the present invention;  
       FIG. 14  is a perspective view of an RF device according to a fourth embodiment of the present invention;  
       FIG. 15  is a perspective view of an RF device according to a fifth embodiment of the present invention;  
       FIG. 16  is a perspective view of an RF device according to a sixth embodiment of the present invention;  
       FIG. 17  is a perspective view of an RF device according to a seventh embodiment of the present invention;  
       FIG. 18  is a perspective view of an RF device according to an eighth embodiment of the present invention;  
       FIG. 19  is a perspective view of an RF device according to a ninth embodiment of the present invention;  
       FIGS. 20A through 20D  are cross-sectional views showing successive steps of a process of etching an insulating substrate of the RF device according to the ninth embodiment of the present invention;  
       FIG. 21  is an exploded perspective view of an RF apparatus according to a tenth embodiment of the present invention;  
       FIG. 22A  is a schematic view showing a process of laminating components of an RF apparatus according to a comparative example;  
       FIG. 22B  is a schematic view showing a process of laminating components of the RF apparatus according to the tenth embodiment;  
       FIG. 23  is a schematic view showing a process of manufacturing the RF apparatus according to the tenth embodiment;  
       FIG. 24  is a schematic view showing another process of manufacturing the RF apparatus according to the tenth embodiment;  
       FIGS. 25A and 25B  are perspective views showing successive steps of a process of inspecting an RF device according to an eleventh embodiment of the present invention; and  
       FIG. 26  is a schematic view showing a modified process of inspecting the RF device according to the eleventh embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      An RF device according to a first embodiment of the present invention will first be described below.  
      As shown in  FIG. 4 , the RF device according to the first embodiment of the present invention has insulating substrate  1  supporting rectangular signal processing circuit  2  and spiral antenna  3  that are integrally formed thereon. Insulating substrate  1  may comprise a glass substrate or a plastic substrate. In the illustrated embodiment, insulating substrate  1  comprises a glass substrate. Antenna  3  comprises a single wire wound in a rectangular spiral pattern. Generally, RF tag systems for use in a 13.56 Hz frequency band operate on the principle of electromagnetic induction for the RF tag to obtain electromotive forces from radio waves. Antenna  3  has opposite terminals connected to one side of rectangular signal processing circuit  2  that is disposed centrally on the surface of insulating substrate  1 . Antenna  3  has an outermost pattern edge disposed along the outer profile edge of insulating substrate  1 . Antenna  3  is made of Au, Cu, Al, Ni, Ag, solder, a conductive high-polymer material, or a laminated film of these materials, for example. Antenna  3  has an area of 1 cm 2  or more surrounded by the outermost pattern edge thereof.  
      A process of determining the area of antenna  3 , i.e., the specifications of antenna  3 , will be described below.  
      First, a process of calculating electromotive forces generated by an antenna from the antenna specifications will be described below. The calculating process may be of known nature, as disclosed in “I-CODE Coil Design Guide” or “OPTIMIZATION OF INDUCTIVE RFID TECHNOLOGY”, p. 82-87, which is referred to above. The process of calculating electromotive forces is generally performed through the following steps: 
          [1] The inductance of spiral (coil) antenna  3  is determined for resonance at the communication frequency.     [2] An antenna configuration for obtaining the above inductance is determined.     [3] Specifications of a reader/writer are determined, and mutual inductance thereof with antenna  3  is determined.     [4] Electromotive forces generated by the RF device are determined on the principles of electromagnetic induction.        

      Electromotive forces required to operate signal processing circuit  2  are of 2 V, for example, and antenna specifications are determined in order to obtain such electromotive forces.  
      [1] Determination of the Inductance of a Coil Antenna:  
      For determining the inductance of a coil antenna, the communication frequency F is set to 13.56 MHz, i.e., 1.356×10 7  Hz. The capacitance C pl  of the entire RF device is determined according to the following equation (1): 
 
 C   pl   =C   c   +C   con   +C   ic   (1) 
 
 where C c  represents the capacitance of the coil antenna, C con  the capacitance of the junction, and C ic  the capacitance of the signal processing circuit. If C c  is set to 2.00×10 −11  F, C con  to 2.00×10 −12  F, and C ic  to 3.00×10 −11  F, then capacitance C pl  of the entire RF device is calculated as 5.20×10 −11  F according to the equation (1). 
 
      The inductance of the coil antenna is set to cause a circuit which is a combination of signal processing circuit  2  and antenna  3  to resonate at the communication frequency. The inductance L o  of the coil antenna is determined according to the following equation (2):  
               L   O     =     1         (     2   ⁢   π   ⁢           ⁢   F     )     2     ·     C   pl                 (   2   )             
 
      The inductance L o  of the coil antenna is determined as 2.65×10 −6  H according to the equation (2). This value is used as a target inductance for determining antenna specifications.  
      [2] Determination of an Antenna Configuration:  
      Then, an antenna configuration for obtaining the target inductance L o  is determined. Based on antenna specifications, an inductance L cal  is determined, and antenna specifications are determined to equalize the inductance L cal  substantially to the target inductance L o . The inductance L cal  is determined according to the following equations (3) through (7):  
               L   cal     =         μ   0     π     ⁢       (       x   1     +     x   2     -     x   3     +     x   4       )     ·     N   c   p                 (   3   )                 x   1     =       a   avg     ·     ln   ⁡     [       2   ·     a   avg     ·     b   avg         d   ·     (       a   avg     +         a   avg   2     +     b   avg   2           )         ]                 (   4   )                 x   2     =       b   avg     ·     ln   ⁡     [       2   ·     a   avg     ·     b   avg         d   ·     (       b   avg     +         a   avg   2     +     b   avg   2           )         ]                 (   5   )                 x   3     =     2   ·     (       a   avg     +     b   avg     +         a   avg   2     +     b   avg   2           )               (   6   )                 x   4     =         a   avg     +     b   avg       4             (   7   )             
 
      Antenna specifications at the time the target inductance L o  is obtained are shown as follows: The number of coil turns: N c =5, the coil wire width: w=1.00×10 −3  m, the space between coil wires: g=6.00×10 −4  m, the coil wire thickness: t=3.00×10 −5  m, the horizontal width of the outermost coil profile: a 0 =7.60×10 −2  m, the vertical width of the outermost coil profile: b 0 =4.50×10 −2  m, the turn EXP: p=1.75, the magnetic permeability: μ 0 =1.2566×10 −6  H/m, the average of horizontal widths of the outer coil profile: a avg =a 0 −N c ×(w+g)−g=6.86×10 −2  m, the average of vertical widths of the outer coil profile: b avg =b 0 −N c ×(w+g)−g=3.76×10 −2  m, and the equivalent radius: d=2×(t+w)/π=6.56×10 −4  m. Putting these values into the equations (3) through (7), the inductance L cal  is determined as 2.69×10 −6  H, which is substantially equal to the value 2.65×10 −6  H of the target inductance L o .  
      [3] Calculation of a Mutual Inductance:  
      The mutual inductance between the coil antenna with the reader/writer is determined according to the following equation (8):  
             M   =         μ   0     ·     N   c     ·     N   r     ·     a   r   2     ·     (       a   avg     ·     b   avg       )         2   ·       (       a   r   2     +     r   2       )       3   2                   (   8   )             
 
      At this time, the specifications of the reader/writer are determined based on the product (SLRM900) described in the document “I-CODE Coil Design Guide” referred to above, as follows: The number of coil turns of the reader/writer: N r =1, the coil radius: a r =0.18 m, the communication range: r=0.5 m, and the current: I r =0.28 A (50 Ω, 4V). Putting these values into the equation (8), the mutual inductance is determined as M=1.75×10 −9 H/m.  
      [4] The Calculation of Generated Electromotive Forces:  
      A process of calculating electromotive forces generated in the RF device will be described below. Antenna  3  is made of aluminum, for example. Antenna  3  has a coil resistivity: ρp=2.655×10 −8  Ω·m. The coil resistance R SC  of antenna  3  is determined according to the following equation (9):  
               R   sc     =         ρ   ·     N   c     ·   2     ⁢     (       a   avg     +     b   avg       )         t   ·   w               (   9   )             
 
      The coil resistance R SC  is calculated as 9.40×10 −1  Ω. The Q of the coil is determined according to the following equation (10):  
               Q   sc     =       2   ⁢   π   ⁢           ⁢     f   ·     L   cal           R   sc               (   10   )             
 
      According to the equation (10), the Q of the coil is calculated as 244. The parallel equivalent circuit resistance R pc  of the coil is determined according to the following equation (11): 
 
 R   pc   =R   sc ·(1 +Q   sc   2 )  (11) 
 
      According to the equation (11), the parallel equivalent circuit resistance R pc  of the coil is calculated as 5.59×10 −4  Ω. The parallel equivalent circuit inductance L pc  of the coil is determined according to the following equation (12):  
               L   pc     =         L   sc     ·     Q   sc   2         1   +     Q   sc   2                 (   12   )             
 
      According to the equation (12), the parallel equivalent circuit inductance L pc  of the coil is calculated as 2.69×10 −6  H. If it is assumed that signal processing circuit  2  has an equivalent circuit resistance R ic =2.50×10 −4  Ω, then the parallel equivalent resistance R pl  of the entire circuit is determined according to the following equation (13):  
               R   pl     =         R   ic     ·     R   pc           R   ic     +     R   pc                 (   13   )             
 
      According to the equation (13), the parallel equivalent resistance R pl  of the entire circuit is calculated as 1.73×10 −4  Ω. The resonant frequency F r  is determined according to the following equation (14):  
               F   r     =     1     2   ⁢   π   ⁢         L   pc     ·     C   pl                     (   14   )             
 
      According to the equation (14), the resonant frequency F r  is calculated as 1.346×10 −7  Hz. Electromotive forces generated in the coil (antenna  3 ) of the RF device are calculated according to the following equation (15):  
             V   =       2   ⁢   π   ⁢           ⁢     f   ·   M   ·     I   r                 (     1   -     F     F   r         )     2     +       (     2   ⁢   π   ⁢           ⁢     f   ·       L   pc       R   pl           )     2                   (   15   )             
 
      According to the equation (15), the electromotive forces are calculated as 2.04 V. In this manner, the generated electromotive forces can be calculated on the basis of the antenna specifications.  
      The relationship between the outer profile and generated electromotive forces of the coil antenna will be reviewed according to the above calculating process.  
       FIGS. 6A through 6D  and  7 A through  7 C are graphs of coil wire widths represented by the horizontal axis and electromotive forces represented by the vertical axis, the graphs showing how the coil wire width affects the electromotive forces with respect to different numbers of coil turns and different coil profiles. In  FIGS. 6A through 6D  and  7 A through  7 C, N represents the number of coil turns.  FIGS. 6A through 6D  show data when the communication range of antenna  3  is 50 cm.  FIG. 6A  shows data when the coil profile is of a square shape having sides each 7 cm long.  FIG. 6B  shows data when the coil profile is of a square shape having sides each 5 cm long.  FIG. 6C  shows data when the coil profile is of a square shape having sides each 3 cm long.  FIG. 6D  shows data when the coil profile is of a square shape having sides each 2 cm long.  
       FIGS. 7A through 7C  show data when the communication range of antenna  3  is 5 cm long.  FIG. 7A  shows data when the coil profile is of a square shape having sides each 3 cm long.  FIG. 7B  shows data when the coil profile is of a square shape having sides each 1 cm long.  FIG. 7C  shows data when the coil profile is of a square shape having sides each 0.5 cm long.  
      For the specifications and the circuit resistances and capacitances of the reader/writer, the above values used to calculate the electromotive forces are employed as general values. The thickness of the wire of the antenna is set to 30 μm. Each of  FIGS. 6A through 6D  and  7 A through  7 C shows data produced by the number of turns for generating maximum electromotive forces, ±2 turns.  
      As shown in  FIGS. 6A through 6D  and  7 A through  7 C, when the coil wire width is changed for each number of coil turns, the electromotive forces take a peak value at a certain coil wire width. This indicates that the coil impedance changes with the coil wire width, and the electromotive forces take a peak value at a coil wire width for best matching, i.e., at a coil wire width where the resonant frequency is equal to the communication frequency.  
      It is also seen from  FIGS. 6A through 6D  and  7 A through  7 C that the generated electromotive forces are maximum at a certain number of coil turns for each coil profile. The generated electromotive forces increase as the number of coil turns increases. However, since the coil profile is given, as the number of coil turns increases, the effective area (a avg ×b avg ) of the antenna decreases. As a result, the generated electromotive forces take a maximum value at a certain number of coil turns.  
      With the RF device according to the first embodiment, electromotive forces required to operate signal processing circuit  2  are of 2 V, for example. As shown in  FIGS. 6A through 6D , if the communication range is 50 cm, the electromotive forces of 2 V are generated by the coil which has a square outer profile having sides each 3 cm or more long. Therefore, in order to achieve the communication range of 50 cm, the coil needs to have a square outer profile having sides each 3 cm or more long. As shown in  FIGS. 7A through 7C , if the communication range is 5 cm long, the coil needs to have a square outer profile having sides each 1 cm or more long. Consequently, the RF device can have a communication range of 5 cm or more by providing an antenna area of 1 cm 2  or greater. The communication range should be 50 cm or longer in view of how RF tags are actually used. However, RF devices with a communication range of 5 cm or more can enjoy benefits of noncontact communication means. Therefore, the antenna profile should preferably be of a square shape having sides each 1 cm long, i.e., the antenna should preferably have an area of 1 cm 2  or greater.  
      As shown in  FIG. 5 , signal processing circuit  2  comprises high-frequency interface circuit  11 , logic circuit  12 , and memory  13 . Antenna  3  is connected to high-frequency interface circuit  11 .  
      High-frequency interface circuit  11  comprises rectifying circuit  15 , clock generator  16 , demodulating circuit  17 , modulating circuit  18 , and booster circuit  19 . Rectifying circuit  15  rectifies a received radio wave and supplies a DC voltage to logic circuit  12 . Clock generator  16  generates a clock signal required to operate logic circuit  12  based on a received radio wave. For example, clock generator  16  generates a clock signal having a frequency ranging from several tens to several hundreds kHz from a received frequency of several MHz. Demodulating circuit  17  demodulates data from the received radio wave (carrier wave). Modulating circuit  18  modulates a carrier wave with data to be transmitted. Booster circuit  19  increases an electromotive force that is generated by rectifying circuit  15  to a higher voltage. Booster circuit  19  needs to increase the electromotive force when a nonvolatile EEPROM (Electrically Erasable and Programmable Read Only Memory) or an FeRAM (Ferroelectric Random Access Memory) which requires a high operating voltage is used as memory  13 .  
      Logic circuit  12  comprises decoding circuit  20 , encoding circuit  21 , serial I/O (Input/Output)  22 , command processing circuit  23 , and memory control circuit  24 . Decoding circuit  20  decodes received data according to a PPM (Pulse Position Modulation) process or the like. Encoding circuit  21  encodes data to be transmitted according to the Manchester process. Serial I/O  22  converts a data string between serial and parallel formats. Command processing circuit  23  serves to control the flow of signals. Memory control circuit  24  writes received data into memory  13  and reads data to be transmitted from memory  13 . Logic circuit  12  may also have a circuit for performing a parity check on data for the purpose of increasing the reliability of RF tags, and an anti-collision circuit for identifying a plurality of tags. Memory  13  comprises a ROM (Read Only Memory) or a nonvolatile write-once EEPROM or FeRAM depending on the purpose of RF tags. Alternatively, memory  13  may comprise a volatile memory such as a DRAM (Dynamic Random Access Memory) or an SRAM (Static Random Access Memory).  
      Operation and advantages of the RF device according to the first embodiment of the present invention will be described below.  
      As shown in  FIGS. 4 and 5 , the RF device according to the first embodiment has signal processing circuit  2  including high-frequency interface circuit  11 , logic circuit  12 , and memory  13 , and antenna  3 . Signal processing circuit  2  and antenna  3  are integrally mounted on insulating substrate  1 . Since no process is required for mounting a chip including a signal processing circuit on a substrate with an antenna formed thereon, the manufacturing cost of the RF device is relatively low. The RF device is highly durable because it does not have junctions which would be formed by the mounting process that are vulnerable to thermal stresses, bending stresses, vibrations, shocks, etc. Since the antenna is disposed on the insulating substrate, radio waves are not electromagnetically shielded by the substrate, allowing the RF device to have an excellent communication capability. The RF device produces low noise because no induced current flows through the substrate. However, an RF device disposed on a silicon substrate is unable to obtain the same communication quality as when a glass substrate is used because the silicon substrate is a conductor and hence shields radio waves and noise is produced due to an eddy current generated in the silicon substrate. The RF device where the signal processing circuit and the antenna are integrally formed needs to have an insulating substrate such as a glass substrate or the like in order to provide a sufficient communication range.  
      Inasmuch as the RF device incorporates an inexpensive insulating substrate such as a glass substrate or the like, it can be manufactured at a lower cost than if it employs an expensive insulating substrate such as a silicon substrate or the like. The area of the antenna of the RF device according to the present invention can easily be increased for better communication ability. Specifically, conventional RF devices on silicon substrates are not practical because their square size having sides each 1 cm long makes the substrate highly costly. If a silicon wafer having a diameter of 3 inches is used to produce RF device substrates, then only slightly less than 300 RF devices can be produced from that silicon wafer. Conversely, if a plurality of RF devices are to be fabricated from a square glass substrate having sides each 1 m long, then 10000 RF devices each having a square size having sides each 1 cm long can simultaneously be produced from that glass substrate. Inasmuch as the cost of the glass substrate and the cost of each RF device produced from the glass substrate and the cost of the fabrication process are much lower than if RF devices are formed on a silicon wafer, the fabrication of RF devices having a square size having sides each 1 cm long on the glass substrate is practical.  
      As no IC chips are mounted on the surface of the RF device, the surface of the RF device does not have surface irregularities which would be formed by IC chips, and can be printed highly at high resolution. No auxiliary member is required to make the surface of the RF device flat, so that the number of parts of the RF device is relatively small and the cost of the RF device is relatively low.  
      In the first embodiment, antenna  3  comprises a coil antenna having a spiral structure. However, antenna  3  may comprise an antenna having another structure, such as a dipole antenna, a patch antenna, etc. If radio waves that are used for communications are microwaves in the 900 MHz band or 2.45 GHz band, then antenna  3  comprises a dipole antenna having a length equal to ½ or ¼ wavelength. The antenna length that is required is 16.7 cm if it is ½ wavelength of the 900 MHz band, and 8.3 cm if it is ¼ wavelength of the 900 MHz band. The antenna length that is required is 6.1 cm if it is ½ wavelength of the 2.45 GHz band, and 3.1 cm if it is ¼ wavelength of the 2.45 GHz band. Therefore, if a dipole antenna is used, then the antenna length should desirably be more than 3 cm. That is, the antenna of the RF device according to the present embodiment should preferably have a square outer profile having sides each 1 cm or more long and a length of 3 cm or more. The length of 3 cm is a large value for a chip size and is not practical for a device on a silicon substrate.  
      A second embodiment of the present invention will be described below. The second embodiment is concerned with a method of manufacturing the RF device according to the first embodiment described above.  
       FIGS. 8A through 8C  show successive steps of a method of manufacturing an RF device.  FIG. 8C  shows the RF device which is manufactured.  FIGS. 9A through 9F  show details of the step shown in  FIG. 8B .  FIGS. 10A through 10C  show details of the step shown in  FIG. 8C .  
      As shown in  FIGS. 8A, 8B , and  8 D, rectangular signal processing circuit  2  is formed centrally on insulating substrate  1  by the thin-film transistor (TFT) fabrication technology, and two terminals  26  are formed on and along one side of signal processing circuit  2 . Insulating substrate  1  may comprise a glass substrate. In the method, a glass substrate for use in general liquid crystal displays is employed. Then, as shown in  FIGS. 8C and 8D , spiral antenna  3  is formed of a conductive material on insulating substrate  1  by plating or printing. Antenna  3  comprises a single conductor formed in a rectangular spiral pattern and has opposite ends connected respectively to terminals  26  on signal processing circuit  2 . Antenna  3  has an outermost turn extending along outer edges of insulating substrate  1 .  
      A process of forming signal processing circuit  2  as shown in  FIG. 8B  will be described below. Signal processing circuit  2  is structurally based on a CMOS transistor formed by the TFT fabrication technology. In the present embodiment, a process of forming a CMOS-TFT on a glass substrate will be described below with reference to  FIGS. 9A through 9F .  
      As shown in  FIG. 9A , barrier film  31  is formed on insulating substrate  1  of glass by sputtering, for example, and then amorphous silicon film  32  is formed on the surface of barrier film  31 . Amorphous silicon film  32  is deposited to a thickness ranging from 30 nm to 200 nm by CVD (Chemical Vapor Deposition) or sputtering. Then, as shown in  FIG. 9B , a laser beam is applied to the assembly as indicated by the arrows  33  to anneal amorphous silicon film  32  into polycrystalline silicon film  34 . The laser beam may be emitted from an excimer laser or a solid-state laser. Then, as shown in  FIG. 9C , polycrystalline silicon film  34  on barrier film  31  is processed into two separate patterns by photolithography, after which gate insulating film  35  is formed over barrier film  31  and two polycrystalline silicon films  34 . Gate insulating film  35  is deposited to a thickness ranging from 10 nm to 200 nm by CVD or sputtering.  
      Thereafter, as shown in  FIG. 9D , two gate electrodes  36  are formed on gate insulating film  35  in respective regions including regions directly above respective two polycrystalline silicon films  34 . Then, photoresist  37  is formed in a region where an n-channel TFT is to be formed, i.e., in the region including the region directly above one of two polycrystalline silicon films  34  in covering relation to one of gate electrodes  36  and gate insulating film  35 . Then, boron is injected from above as indicated by the arrows  38  into a region where a p-channel TFT is to be formed, forming p-type regions  39  in opposite end portions of other polycrystalline silicon film  34 . Boron is injected by ion doping, for example. Because of photoresist  37  functioning as a mask, no boron is injected into the region where the n-channel TFT is to be formed. Similarly, no boron is injected into the central portion of other polycrystalline silicon film  34  because gate electrode  36  functions as a mask in the region where the p-channel TFT is to be formed. After boron is injected, photoresist  37  is removed.  
      Then, as shown in  FIG. 9E , photoresist  37  is formed in the region where the p-channel TFT is to be formed, i.e., in the region including the region directly above polycrystalline silicon film  34  including the p-type regions  39  in covering relation to gate electrode  36  and gate insulating film  35 . Thereafter, phosphorus is injected from above as indicated by the arrows  40  into the region where the n-channel TFT is to be formed, forming n-type regions  41  in opposite end portions of polycrystalline silicon film  34 . Phosphorus is injected by ion doping, for example. Because of photoresist  37  functioning as a mask, no phosphorus is injected into the region where the p-channel TFT is to be formed. Similarly, no phosphorus is injected into the central portion of polycrystalline silicon film  34  because gate electrode  36  functions as a mask in the region where the n-channel TFT is to be formed. After phosphorus is injected, photoresist  37  is removed.  
      Then, as shown in  FIG. 9F , interlayer insulating films  42  and metal electrodes  43  are formed, thereby completing a CMOS circuit. Throughout the entire process of fabricating the CMOS circuit, the process temperature in the CVD or sputtering steps is set to 400° C. or lower, for example, in view of the heat resisting capability of the glass substrate.  
      A process of forming antenna  3  as shown in  FIG. 8C  will be described below with reference to  FIGS. 10A through 10C . Antenna  3  is formed by electrolytic plating. As shown in  FIG. 10A , conductive film  51  for use as an electrolytic plating feed layer is formed on insulating substrate  1 . Then, as shown in  FIG. 10B , photoresist  52  having an opening patterned as antenna  3  is formed on conductive film  51  by photolithography, and then plated film  53  is formed on conductive film  51  in the opening of photoresist  52  by electrolytic plating. Then, as shown in  FIG. 10C , photoresist  52  is removed, and unwanted portions of conductive film  51  which are not covered with plated film  53  are etched away. Conductive film  51  and plated film  53  which make up antenna  3  are formed of gold or copper, for example.  
      A plurality of RF devices may simultaneously be fabricated on single insulating substrate  1 . For simultaneously form a plurality of RF devices, a plurality of signal processing circuits  2  are formed on single insulating substrate  1 , and then a plurality of antennas  3  are formed on single insulating substrate  1 , thereby producing a plurality of sets of signal processing circuits  2  and antennas  3 . Then, insulating substrate  1  is cut off into pieces including those sets of signal processing circuits  2  and antennas  3 , whereupon a plurality of RF devices are simultaneously produced. A sheet-like substrate may be used as insulating substrate  1 , and signal processing circuits  2  and antennas  3  may be formed on the sheet-like substrate as it is delivered from a roll to a roll.  
      Advantages offered by the second embodiment will be described below. In the method of manufacturing an RF device according to the second embodiment, signal processing circuit  2  and antenna  3  can integrally be formed on single insulating substrate  1  as shown in  FIGS. 8A through 8D  through  FIGS. 10A through 10C . Since no device mounting steps are necessary, the RF device can be manufactured at a low cost. The RF device manufactured by the method according to the second embodiment is highly durable because it does not have junctions which would be formed by the mounting process that are vulnerable to thermal stresses, bending stresses, vibrations, shocks, etc. Since the signal processing circuit and the antenna are integrally formed on the inexpensive insulating substrate such as of glass, no mounting steps are required, and the RF device can be manufactured at a low cost. The antenna formed on the insulating substrate eliminates noise and antenna directivity, and can easily be produced in a large area for a better communication capability. According to the present embodiment, furthermore, since the antenna is fabricated by electrolytic plating, the antenna has a low resistance and causes a low loss of the received signal. Furthermore, the antenna can easily be formed in a desired shape. The antenna can be formed without causing damage to the signal processing circuit that has already been formed on the insulating substrate. The above advantages are available even if the antenna is formed by electroless plating, printing, conductive polymer patterning, or direct pattern writing.  
      In the method of manufacturing a CMOS transistor according to the second embodiment, after gate insulating film  35  is grown, a laser beam may be applied to the entire surface of gate insulating film  35  in order to reduce a fixed charge and an interfacial level that are present in the interface between polycrystalline silicon film  34  and gate insulating film  35 . The energy density of the applied laser beam should be lower than the energy density of the laser beam applied as indicated by the arrows  33  in  FIG. 9B  for annealing amorphous silicon film  32 . An RF device may be formed on a glass substrate of a display product such as a liquid crystal display unit, an EL display unit, or the like by the method of manufacturing the RF device according to the second embodiment. The RF device may be formed on the glass substrate of the display product before or after the process of manufacturing the display product. The RF device may be formed on either one of substrates on which a counter-electrode and a TFT are formed. Since the method of manufacturing the RF device according to the second embodiment can use a glass substrate, the method has a high affinity with the process of manufacturing the display product, and is free of process problems with respect to the process temperature and the chemical resistance, for example. For example, an RF device which integrally incorporates an authenticating function such as an ID authenticating function and an antenna may be combined with the display unit of a cellular phone, thereby increasing the functionality of the cellular phone. In such an application, the antenna should be made of a transparent conductor such as an ITO film or the like for preventing itself from obstructing images displayed by the display unit.  
      A first modification of the second embodiment of the present invention will be described below.  
      In the second embodiment described above, antenna  3  is formed by electrolytic plating as shown in  FIGS. 10A through 10C . According to the first modification of the second embodiment, antenna  3  is formed by electroless plating as shown in  FIGS. 11A and 11B . As shown in  FIG. 11A , base film  61  which serves as a base for selectively growing an electrolessly plated film is formed on the entire surface of insulating substrate  1  by sputtering, for example. Then, base film  61  is patterned to the shape of antenna  3  by photolithography. Base film  61  is formed of aluminum or nickel, for example. Then, as shown in  FIG. 11B , plated film  62  is formed on base film  61  by electroless plating. At this time, plated film  62  is selectively formed on base film  61 . Plated film  61  is formed of nickel, copper, or gold, for example. Other details of the first modification of the second embodiment are identical to those of the second embodiment described above.  
      In the first modification of the second embodiment, plated film  62  is formed as a single-layer film. However, plated film  62  may be formed as a film having two or more layers. If plated film  62  is formed as a film having two or more layers including a first layer of nickel, then since nickel has an electric resistance that is 30 to 40 times higher than copper and gold, the second layer may be formed as a copper or gold layer for thereby reducing the electric resistance of plated film  62 , i.e., antenna  3 .  
      A second modification of the second embodiment of the present invention will be described below.  
      In the second embodiment described above, antenna  3  is formed by electrolytic plating as shown in  FIGS. 10A through 10C . According to the second modification of the second embodiment, antenna  3  is formed by printing as shown in  FIGS. 12A and 12B . As shown in  FIG. 12A , a conductive paste  71  is placed on mask  72  having an opening patterned as antenna  3 . Mask  72  comprises, for example, a screen mask comprising a mesh of fine fibers woven in a grid-like pattern and an emulsifying layer that has an opening in a desired pattern, the emulsifying layer being disposed on the mesh. Conductive paste  71  placed on mask  72  can be pushed through the opening of the emulsifying layer and the mesh to the reverse side of mask  72 . Conductive paste  71  is a solder paste comprising a solvent with fine solder particles dispersed therein or a silver paste comprising a solvent with fine solder particles dispersed therein. From the standpoint of electric resistance, the silver paste is preferable. After the silver paste used as conductive paste  71  is baked to remove the solvent, the resistance of conductive paste  71  is essentially the same as the resistance of silver alone.  
      Then, as shown in  FIG. 12B , squeezee  73  is pressed against conductive paste  71  to push conductive paste  71  through the opening of mask  72  onto insulating substrate  1 , thereby applying printed pattern  74  of antenna  3  to insulating substrate  1 . Thereafter, the entire assembly is heated to remove the solvent contained in printed pattern  74 , thereby completing antenna  3 . The assembly is heated in an oven at a temperature of 200° C. for example. Other details of the second modification of the second embodiment are identical to those of the second embodiment described above.  
      In the second modification of the second embodiment, a screen mask is used as mask  72 . However, a metal mask comprising a metal plate with an opening defined in a desired pattern therein may be used as mask  72 . Antenna  3  may also be formed by a process other than the electrolytic plating process, the electroless plating process, and the printing process described above. For example, antenna  3  maybe formed by coating a substrate with a conductive polymer with fine metal particles dispersed therein and patterning the conductive polymer to an antenna shape. Alternatively, an antenna pattern may directly be plotted on a substrate.  
      Multifunctional designs of the RF device according to the first embodiment of the present invention will be described below. RF devices according to third through eighth embodiments of the present invention to be described below are such multifunctional RF devices.  
      First, an RF device according to a third embodiment of the present invention will be described below.  
      In the first embodiment described above, only signal processing circuit  2  is disposed centrally on insulating substrate  1 , as shown in  FIG. 4 . According to the third embodiment, as shown in  FIG. 13 , signal processing circuit  2  and memory circuit  81  are disposed adjacent to each other centrally on insulating substrate  1 .  
      Memory circuit  81  comprises a ROM for storing information of an RF tag in advance and a DRAM or an SRAM for reading and writing information at the time of signal processing. The ROM, the DRAM, and the SRAM are fabricated by the process of manufacturing a CMOS according to the second embodiment described above. Other structural details of the third embodiment are identical to those of the first embodiment described above.  
      In the third embodiment, since memory circuit  81  is integrally disposed on the glass substrate on which signal processing circuit  2  and antenna  3  are formed, the manufacturing cost of the RF device having desired functions can be reduced, and the mounting cost thereof can also be reduced. If the functionality of an RF device is to be increased using a conventional RF tag as described above, then a device fabricated by another process has to be further assembled regardless of whether the RF tag is of the integral type or the separate type, resulting in an increase in the manufacturing cost and an increase in the assembly size. Since different devices are separately designed and produced, it is expected that design and production losses such as a performance mismatch between the devices will be increased. According to the third embodiment, however, as the memory circuit is formed integrally with the antenna on the insulating substrate, it is easy to design total impedance matching between the antenna and the circuit (device). Because the memory circuit is formed in a relatively wide area surrounded by the spiral coil antenna on the surface of the insulating substrate, the size of the multifunctional RF device is relatively small. Other advantages of the third embodiment are identical to those of the first embodiment described above.  
      In the third embodiment, memory circuit  81  comprises a ROM and a DRAM or an SRAM. However, memory circuit  81  may comprise a nonvolatile memory such as an EEPROM or an FeRAM. The EEPROM has a floating gate disposed in a gate insulating film of an ordinary CMOS structure. The EEPROM retains a charge or information even after the EEPROM is turned off. The FeRAM comprises a ferrodielectric capacitor connected to a transistor. When a write voltage is applied to the FeRAM, the ferrodielectric material is polarized. Even when the FeRAM is turned off, the ferrodielectric material remains polarized. The ferrodielectric capacitor is formed by a sol-gel process or an aerosol process. The process temperature of the sol-gel process or the aerosol process is in the range from 200 to 400° C., lower than the allowable temperature limit of the glass substrate as the insulating substrate.  
      An RF device according to a fourth embodiment of the present invention will be described below.  
      In the first embodiment described above, only signal processing circuit  2  is disposed centrally on insulating substrate  1 , as shown in  FIG. 4 . According to the fourth embodiment, as shown in  FIG. 14 , signal processing circuit  2  and display unit  91  are disposed adjacent to each other centrally on insulating substrate  1 . Display unit  91  comprises an organic EL (ElectroLuminescence) display unit, an inorganic EL display unit, or a liquid crystal display unit. Display unit  91  is fabricated according to a conventional fabrication process. Other structural details of the fourth embodiment are identical to those of the first embodiment described above.  
      In the fourth embodiment, the glass substrate is employed, and display unit  91  is integrally formed on the glass substrate on which signal processing circuit  2  and antenna  3  are formed. The RF device with the display function is relatively small in size. The RF device with display unit  91  is capable of displaying a result of information processing after it has exchanged information with a reader/writer. For example, a prepaid card with a communication function, which is constructed as the RF device, can display information of the balance or the like. The manufacturing cost of the RF device is low because it employs an inexpensive glass substrate, and the mounting cost thereof is also low. Other advantages of the fourth embodiment are identical to those of the third embodiment described above.  
      An RF device according to a fifth embodiment of the present invention will be described below.  
      In the first embodiment described above, only signal processing circuit  2  is disposed centrally on insulating substrate  1 , as shown in  FIG. 4 . According to the fifth embodiment, as shown in  FIG. 15 , the RF device has antennas  101 ,  102  disposed adjacent to signal processing circuit  2  that is disposed centrally on insulating substrate  1 . Antennas  101 ,  102  have their lengths, sizes, etc. adjusted depending on frequencies to be handled. Antennas  101 ,  102  may be booster antennas which have a higher sensitivity for radio waves having a particular frequency. Antennas  101 ,  102  are not connected to signal processing circuit  2  by interconnection patterns. Other structural details of the fifth embodiment are identical to those of the first embodiment described above.  
      In the fifth embodiment, antennas  101 ,  102  are electrically connected to antenna  3  by a capacitive coupling or an electromagnetic inductive coupling for exchanging signals with signal processing circuit  2 . Since signal processing circuit  2  and antennas  3 ,  101 ,  102  are integrally formed on the insulating substrate which comprises an inexpensive glass substrate, the antennas can be designed with increased freedom without being limited by the area of the substrate, so that the RF device with higher functionality can be realized.  
      At present, RF tags are subject to various specifications including different frequency bands, e.g., a low frequency band near 125 kHz, a 13.56 MHz band, a 900 MHz band, and a 2.54 GHz band. Main frequency bands for RF tags differ from country to country. Since different antennas are used for different frequency bands, it is difficult for one RF tag to be compatible with a plurality of frequency bands. This poses a problem when RF tags are used in material distributions between many countries. According to the fifth embodiment, however, the plural antennas on the RF device makes the RF device compatible with a plurality of frequency bands, thereby solving the above problem. Other advantages of the fifth embodiment are identical to those of the third embodiment described above.  
      An RF device according to a sixth embodiment of the present invention will be described below.  
      In the first embodiment described above, only signal processing circuit  2  is disposed centrally on insulating substrate  1 , as shown in  FIG. 4 . According to the sixth embodiment, as shown in  FIG. 16 , signal processing circuit  2  and power supply device  111  are disposed centrally on insulating substrate  1 . Power supply device  111  comprises a solar cell, for example. The solar cell has a substrate comprising a P-type silicon layer and an N-type silicon layer. When light is applied to the substrate, holes having a positive charge tend to move to the P-type silicon layer and electrons having a negative charge tend to move to the N-type silicon layer. The solar cell is fabricated by the method of manufacturing a CMOS according to the second embodiment, for example. Other structural details of the sixth embodiment are identical to those of the first embodiment described above.  
      As described above, general RF devices produce electromotive forces from radio waves transmitted from a reader/writer and operate based on the produced electromotive forces. However, since the radio waves transmitted from the reader/writer are very weak, it is difficult for the RF devices have an increased communication range. As the RF devices function only when the radio waves transmitted from the reader/writer reach them, the RF devices are unable to actively send radio waves when the reader/writer is turned off. According to the sixth embodiment, since the signal processing circuit and the power supply device are integrally disposed on the insulating substrate, the operating voltage of the RF device is high, can output radio waves of high intensity, and can have an increased communication range. As the power supply voltage of the RF device does not depend on the received radio waves, the RF device is able to actively send radio waves even when the RF device is not receiving radio waves. The RF device with the power supply device can meet requirements for increased electric energy required by expanded functionality. Other advantages of the sixth embodiment are identical to those of the third embodiment described above.  
      In the sixth embodiment, the power supply device comprises a solar cell. However, the power supply device may comprise any sheet-like cell such as a secondary cell, e.g., a lithium-ion secondary cell, or a primary cell. The lithium-ion cell comprises a three-layer laminated assembly having an insulative porous separator sandwiched between two sheet-like electrodes. The three-layer laminated assembly is immersed in an electrolytic solution and sandwiched between glass substrates that are sealingly encased. The lithium-ion cell is charged in a contactless manner by converting received radio waves into electromotive forces. This charging process allows a stack of RF tags to be charged altogether at the same time.  
      An RF device according to a seventh embodiment of the present invention will be described below.  
      In the first embodiment described above, only signal processing circuit  2  is disposed centrally on insulating substrate  1 , as shown in  FIG. 4 . According to the seventh embodiment, as shown in  FIGS. 17A and 17B , signal processing circuit  2  and sensor circuit  121  are disposed centrally on insulating substrate  1 . As shown in  FIG. 17B , sensor circuit  121  comprises electrode  122  disposed on insulating substrate  1  and hollow body  123  disposed over electrode  122 . Hollow body  123  comprises a pair of upstanding side plates mounted on insulating substrate  1  and an upper plate having opposite ends joined to respective upper ends of the upstanding side plates. Electrode  122  is disposed between the upstanding side plates. Electrode  122  is spaced a distance G from the upper plate of hollow body  123 . Hollow body  123  comprises a thin silicon film or a thin metal film. Sensor circuit  121  is fabricated by the MEMS (Micro-Electro-Mechanical System) technology, for example. Other structural details of the seventh embodiment are identical to those of the first embodiment described above.  
      Operation of the RF device according to the seventh embodiment will be described below. When hollow body  123  of sensor circuit  121  flexes under downward pressure or acceleration, the distance G between the upper plate of hollow body  123  and electrode  122  changes. The change in the distance G is detected by measuring the electrostatic capacitance of a capacitor which is made up of the upper plate of hollow body  123  and electrode  122 . When the change in the distance G is detected, the downward pressure or acceleration applied to the upper plate of hollow body  123  is also detected.  
      According to the second embodiment, as described above, since sensor circuit  121 , signal processing circuit  2 , and antenna  3  are integrally mounted on insulating substrate  1 , information detected by sensor circuit  121  can be transmitted out of the RF device by radio waves. For example, sensor circuit  121  may comprise an air pressure sensor mounted on an automobile tire, and information detected as representing a tire air pressure by sensor circuit  121  may be transmitted from the RF device to a receiver in an automobile cabin where the information can be managed. According to the second embodiment, since sensor circuit  121 , signal processing circuit  2 , and antenna  3  are integrally mounted on insulating substrate  1 , they are highly failure-resistant in harsh environments on automobiles. Other advantages of the seventh embodiment are identical to those of the third embodiment described above.  
      In the seventh embodiment, a pressure sensor has been described as sensor circuit  121 . However, sensor circuit  121  may comprise a fingerprint sensor, an environment sensor such as a temperature sensor, a humidity sensor, or the like, a gas sensor, or an odor sensor. The pressure sensor may also be used as an acceleration sensor. The fingerprint sensor may be an optical sensor wherein an LED (Light-Emitting Diode) or the like applies light to a fingertip and light reflected by the fingertip is detected by a CCD (Charge-Coupled Device) or the like to determine the fingerprint based on changes in the detected light, or a pressure-sensitive sensor wherein the fingerprint is determined based on changes in the electrostatic capacitance between the fingertip and the sensor. The optical fingerprint sensor can be fabricated by the method of fabricating a CMOS according to the second embodiment, as a matrix of transistors and photodiodes formed on a glass substrate. The pressure-sensitive fingerprint sensor may be similar to the optical fingerprint sensor except that electrostatic capacitance detecting electrodes are formed instead of the photodiodes. The sensor circuit may be replaced with a mechanical input/output device such as a dip switch, a microphone, a speaker, a touch panel, or the like. The microphone may comprise a hollow thin film that can be vibrated under sound pressure applied thereto.  
      An RF device according to an eighth embodiment of the present invention will be described below.  
      In the first embodiment described above, antenna  3  and signal processing circuit  2  are electrically connected to each other on insulating substrate  1 , as shown in  FIG. 4 . According to the eighth embodiment, as shown in  FIGS. 18A and 18B , the RF device has isolated area  132  in which an interconnection pattern from antenna  3  to signal processing circuit  2  is partly removed, so that antenna  3  and signal processing circuit  2  are normally electrically disconnected from each other. The RF device also has removable conductive tape  131  which, when placed on insulating substrate  1 , electrically connects antenna  3  and signal processing circuit  2  to each other. When removable conductive tape  131  is removed or spaced from insulating substrate  1 , antenna  3  and signal processing circuit  2  are electrically disconnected from each other. When antenna  3  and signal processing circuit  2  are electrically disconnected from each other, the RF device is prevented from sending information to and receiving information from an external circuit, and is also prevented from erasing information from the RF device. The RF device can also have its tag function selectively tuned on and off by taking removable conductive tape  131  into and out of contact with insulating substrate  1 . Other structural details and advantages of the eighth embodiment are identical to those of the first embodiment described above.  
      An RF device according to a ninth embodiment of the present invention will be described below.  
      The RF device according to the ninth embodiment is a lower-profile version of the RF device according to the first embodiment. According to the first embodiment, antenna  3  and signal processing circuit  2  are disposed on single insulating substrate  1 . According to the ninth embodiment, as shown in  FIG. 19 , an insulating substrate comprises a stacked assembly of glass substrate  141  and flexible substrate  142 . Glass substrate  141  comprises a substrate made of non-alkali glass borosilicate containing boron oxide and alumina. Glass substrate  141  has a thickness of 200 μm or less, which makes the RF device flexible. If the thickness of glass substrate  141  exceeds 200 μm, then the EF device is not rendered flexible. If the thickness of glass substrate  141  is 0 μm, i.e., if the RF device has no glass substrate  141 , then signal processing circuit  2  and antenna  3  have their characteristics and reliability lost.  
      A method of manufacturing the RF device shown in  FIG. 19  will be described below with reference to  FIGS. 20A through 20D . The thickness of glass substrate  141  should preferably be reduced by etching after signal processing circuit  2  and antenna  3  have been formed on glass substrate  141 . As shown in  FIG. 20A , glass substrate  141  is prepared. At this time, glass substrate  141  has a thickness of 0.7 mm, for example. Then, circuit layer  151  including an antenna (not shown) and a signal processing circuit (not shown) is formed on glass substrate  141  by the process described above in the first embodiment. Then, protective film  152  is bonded by an adhesive (not shown) in covering relation to circuit layer  151 . Protective film  152  is made of polyethylene, for example. However, protective film  152  may be made of any of various materials that are highly resistant to hydrofluoric acid such as polypropylene, polycarbonate, PET, or PES (PolyEtherSulfone). Protective film  152  should preferably have a thickness of 200 μm or less. If the thickness of protective film  152  exceeds 200 μm, then it cannot easily be peeled off.  
      Then, as shown in  FIG. 20B , the stacked assembly of glass substrate  141 , circuit layer  151 , and protective film  152  is immersed in etching solution  153  for dissolving glass substrate  141 . Etching solution  153  comprises a mixture of hydrofluoric acid and hydrochloric acid. The addition of hydrochloric acid is effective in efficiently etching away boron oxide and alumina that are contained in non-alkali borosilicate glass that glass substrate  141  is made of. The reverse side of glass substrate  141  which is remote from circuit layer  151  is thus etched away to reduce the thickness of glass substrate  141 . The mixture of hydrofluoric acid and hydrochloric acid has an etching rate of 5 μm per minute with respect to non-alkali borosilicate glass. Therefore, when glass substrate  141  having a thickness of 0.7 mm is etched for 130 minutes, the thickness of glass substrate  141  is reduced to 50 μm. The etching rate can be increased if the temperature of etching solution  153  is increased. However, the temperature of etching solution  153  should preferably be 70° C. or less because the remaining thickness of glass substrate  141  cannot be controlled for good reproducibility if the temperature of etching solution  153  exceeds 70° C.  
      Then, as shown in  FIG. 20C , flexible film  142  is applied in covering relation to the etched surface of glass substrate  141 . Flexible film  142  comprises a PET film, for example, and has a thickness in the range from 10 μm to 2 mm, for example. If the thickness of flexible film  142  is smaller than 10 μm, then flexible film  142  is weak and liable to break. If the thickness of flexible film  142  exceeds 2 mm, then flexible film  142  is no longer flexible. Thereafter, as shown in  FIG. 20D , protective film  152  is mechanically peeled off. The process time required to peel off protective film  152  is about several minutes, for example. Other structural details and manufacturing process details of the ninth embodiment are identical to those of the first and second embodiments.  
      In the ninth embodiment, glass substrate  141  used as the insulating substrate is thinned down and applied to flexible film  142 , making the RF device flexible. Therefore, when the RF device is applied to flexible articles such as clothes or paper products or curved surfaces such as bottle surfaces, the RF device is less vulnerable to damage due to bending stresses. Other advantages of the ninth embodiment are identical to those of the first embodiment.  
      Except that the glass substrate and the flexible film are stacked together, the insulating substrate of the RF device according to the ninth embodiment has structural and operational details and advantages which are identical to those of the first embodiment. However, the insulating substrate of the RF device according to the ninth embodiment may have structural and operational details and advantages which are identical to those of the third through eighth embodiments.  
      Protective film  152  and circuit layer  151  may be bonded to each other by a thermoplastic adhesive. If protective film  152  and circuit layer  151  are bonded to each other by a thermoplastic adhesive, then protective film  152  can easily be peeled off in a short period of time by heating the thermoplastic adhesive. For example, if an adhesive which becomes solid at a temperature of 80° C. or lower and becomes liquid at a temperature higher than 80° C., then when the atmospheric temperature in the protective film peeling process is set to 100° C., the adhesive is liquefied, allowing the protective film to be peeled off easily within a short period of time. Protective film  152  may be made of a resin material which can be applied to circuit layer  151  and then hardened into a protective film.  
      An RF apparatus according to a tenth embodiment of the present invention will be described below.  
      As shown in  FIG. 21 , RF apparatus  167  according to the tenth embodiment comprises a plurality of laminated RF devices  165 ,  164 ,  163 ,  162 ,  162 . RF device  165  comprises the RF device according to the fourth embodiment, and has signal processing circuit  2 , antenna  3 , and display unit  91  on insulating substrate  1 . RF device  164  comprises the RF device according to the third embodiment, and has signal processing circuit  2 , antenna  3 , and memory circuit  81  on insulating substrate  1 . Memory circuit  81  comprises a DRAM or SRAM which can retain data only when it is supplied with electric energy, or a nonvolatile EEPROM or FeRAM which keeps on retaining data even when it is turned off.  
      RF device  163  has a CPU (Central Processing Unit)  166 , in place of signal processing circuit  2  according to the first embodiment, for instructing memory circuit  81  to record and read data, and also instructing display unit  91  to display data. Other structural details of RF device  163  are identical to those of the RF device according to the first embodiment. RF device  162  comprises the RF device according to the seventh embodiment, and has signal processing circuit  2 , antenna  3 , and sensor circuit  121  on insulating substrate  1 . Sensor circuit  121  comprises a pressure sensor, a temperature sensor, a humidity sensor, or the like. RF device  161  comprises the RF device according to the sixth embodiment, and has signal processing circuit  2 , antenna  3 , and power supply device  111  on insulating substrate  1 . Power supply device  111  comprises a solar cell, for example. RF apparatus  167  has a thickness of 1 mm, for example. Each of RF devices  161  through  165  may comprise a flexible RF device according to the ninth embodiment, for example. RF devices  161  through  165  have respective thicknesses adjusted such that the thickness of RF apparatus  167  is 1 mm. For example, RF devices  161  through  165  have respective thicknesses of 200 μm, or one of RF devices  161  through  165  has an unetched thickness of 0.7 mm and each of the other four RF devices has an etched thickness of 50 μm, such that the thickness of RF apparatus  167  is about 1 mm.  
      A method of manufacturing RF apparatus  167  according to the tenth embodiment will be described below.  
      The method of manufacturing RF apparatus  167  comprises the steps of fabricating RF devices  161  through  165  and the step of laminating RF devices  161  through  165  to securing them together. In manufacturing RF apparatus  167 , care should be taken not to develop warpage in the RF apparatus after the RF devices are bonded together. As shown in  FIGS. 22A and 22B , each of the RF devices to be laminated often has a certain degree of warpage. If the RF devices that are warped in the same direction are laminated as shown in  FIG. 22A , then the RF apparatus is also warped in the same direction as the RF devices are warped. Specifically, if the RF devices are stacked in downwardly convex orientations and bonded together, then the RF apparatus is also warped in the downwardly convex orientation. According to the tenth embodiment, as shown in  FIG. 22B , an uppermost RF device is oriented so as to be downwardly convex, and an RF device disposed beneath the uppermost RF device is oriented so as to be upwardly convex. In this manner, RF devices that are oriented so as to be downwardly and upwardly convex, respectively, are stacked alternately to have their warpage cancel each other. As a result, the RF apparatus manufactured by stacking the RF devices is free of warpage.  
      The RF devices are fastened together by an adhesive which is set at room temperature, e.g., a UV-curable adhesive which is curable by absorbing ultraviolet rays. For example, as shown in  FIG. 23 , flexible RF devices according to the ninth embodiment are laminated according to a roll-to-roll production process. Specifically, two sheets  182  each supporting a plurality of RF devices formed thereon are wound as rolls on respective cylindrical bobbins  181 . Sheets  182  are unreeled from respective bobbins  181 , and placed against each other with UV-curable adhesive  183  applied therebetween. Then, ultraviolet radiation  184  is applied to cure UV-curable adhesive  183  to bond two sheets  181  into laminated body  185 , which is wound into a roll on cylindrical bobbin  181 . In this manner, a plurality of RF devices are laminated and secured together, producing an RF apparatus.  
      Operation of RF apparatus  167  according to the tenth embodiment will be described below.  
      In  FIG. 21 , the electric energy stored by power supply device  111  of RF device  161  is supplied as radio waves to RF devices  162  through  165 , energizing the circuits of RF devices  162  through  165 . RF devices  162  through  165  may also generate electromotive forces from radio waves transmitted from a reader/writer, and may use both the electromotive forces thus generated and the electric energy supplied from RF device  161 . In RF device  162 , sensor circuit  121  operates to detect necessary information. The information detected by sensor circuit  121  is sent from antenna  3  of RF device  162  to RF device  163 . In RF device  163 , CPU  166  processes the information transmitted from RF device  162  through antenna  3 .  
      At this time, memory circuit  81  of RF device  164  is instructed to read and write information, if necessary. Memory circuit  81  stores ID information of the RF apparatus or information previously detected by sensor circuit  121 . Memory circuit  81  may comprise a nonvolatile memory such as an EEPROM or an FeRAM, so that information that is written in memory circuit  81  may be retained even after it is turned off. Alternatively, memory circuit  81  may comprise a DRAM or an SRAM, so that it can retain information only while it is being supplied with the electric energy from power supply device  111  of RF device  161 . Processed results are transmitted through antenna  3  to display unit  91  of RF device  165  and an external reader/writer (not shown). Display unit  91  displays data or an alarm in a visually recognizable fashion. The reader/writer stores the transmitted information in a computer for management.  
      As described above, the RF apparatus according to the tenth embodiment is constructed of a laminated assembly of RF devices having various functions, and allows signals to be exchanged between the RF devices as radio waves through the antennas. The RF apparatus can thus have higher functionality for higher added values. According to the tenth embodiment, since electric energy and signals are sent and received by way of radio waves between the RF devices of the RF apparatus, it is not necessary to provide junctions of metal or ACF between the RF devices. Therefore, the mount cost of the RF apparatus is relatively low, and the RF apparatus is free of junction failures due to thermal stresses or bending stresses which would otherwise be detrimental to junctions. RF device  161  with the solar cell mounted thereon is positioned in the uppermost layer of RF apparatus  167 , as shown in  FIG. 21 . Consequently, the solar cell is exposed to much solar radiation for higher electric generating efficiency. If an RF apparatus incorporates an RF device with a solar cell, therefore, the RF device with the solar cell should preferably be placed in the uppermost layer of the RF apparatus.  
      By laminating flexible RF devices according to the roll-to-roll process, the RF apparatus can achieve higher functionality efficiently in a relatively small number of man-hours. It is difficult to keep the RF devices in strict alignment with each other in the roll-to-roll process. However, since electric energy and signals are exchanged by way of radio waves between the RF devices according to the tenth embodiment, there is no need for direct contact between the RF devices, and hence the RF devices do not need to be strictly aligned with each other.  
      Furthermore, because the RF devices are bonded to each other by an adhesive such as an UV-curable adhesive that works at room temperature, it is not necessary to heat the adhesive to set. Accordingly, the RF devices are not deformed by heat, and are not warped as they do not need to be cooled after they are bonded. Since the glass substrate is used as the substrate of each of the RF devices, the ultraviolet radiation can penetrate the RF apparatus deep enough to reach its center.  
      In the tenth embodiment, an anaerobic adhesive may be used instead of the UV-curable adhesive to bond RF devices to each other. The anaerobic adhesive does not cause RF devices to warp as with the UV-curable adhesive though it takes some time to set the anaerobic adhesive and hence the anaerobic adhesive is not efficient to use. Alternatively, a sticky medium such as a double-sided tape or the like may be used. The sticky medium does not cause RF devices to warp as with the UV-curable adhesive and the anaerobic adhesive. Though the sticky medium such as a double-sided tape or the like makes it difficult to align the RF devices with each other, since electric energy and signals are exchanged by way of radio waves between the RF devices according to the present embodiment, the RF devices do not need to be strictly aligned with each other, and hence use of the sticky medium is sufficiently practical.  
      RF devices may further be bonded to each other mechanically by clips, screws, crimping, or the like.  FIG. 24  shows a process of mechanically securing RF devices with clips. As shown in  FIG. 24 , laminated body  191  has its end clamped and secured by clips  192 . The RF devices thus secured together can easily be removed, so that the RF apparatus can have its functions customized or any malfunctioning layers to be replaced.  
      Further alternatively, a plurality of RF devices may be bonded together by a tape whose adhesive force can be removed by exposure to ultraviolet radiation or heat. The RF devices thus bonded together can easily be removed, so that the RF apparatus can have its functions customized or any malfunctioning layers to be replaced.  
      According to the tenth embodiment, communications between the layers are performed by radio waves. However, some of the layers may be connected by metal or ACF so that the RF apparatus is of a hybrid structure wherein both radio or wireless communications and wired communications are performed. In the tenth embodiment, radio signals between the layers may possibly suffer interference. However, such signal interference may be suppressed by allocating appropriate frequencies or modulating processes to communications between the layers. Signals between the layers may be distinguished on a software basis by adding identification signals to the leading ends of signals that are transmitted from the respective layers. In the tenth embodiment, RF devices that are warped so as to be upwardly and downwardly convex, respectively, are stacked alternately. However, the present invention is not limited to such a stacking process. RF devices may be stacked in any fashion so as to minimize the warpage of the RF apparatus, and the number and order of stacked RF devices may be adjusted appropriately. Reinforcing plates may also be stacked in combination with RF devices for providing resistive forces against bending stresses developed in the RF apparatus. If each of the RF devices has a thickness of several tens μm, then any reactive forces of the RF devices are small even if they are warped. Therefore, the warpage of the RF devices can be corrected even if the reinforcing plates are relatively thin. Furthermore, spacers may be placed between RF devices. For example, dielectric members having a predetermined thickness may be placed between RF devices for adjusting the sensitivity of the antennas. In the tenth embodiment, single RF devices are stacked to produce a single RF apparatus. However, a plurality of sheet-like insulating substrates each supporting a matrix of RF devices thereon may be stacked to produce a single RF apparatus.  
      A method of inspecting an RF device according to an eleventh embodiment of the present invention will be described below.  
      According to the eleventh embodiment, when the RF devices or the RF apparatus according to the above embodiments is manufactured, they are inspected to see if they are acceptable or not.  
      As shown in  FIG. 25A , a matrix of RF devices are formed on glass substrate  221 . The RF devices may be manufactured by the method according to the second embodiment. The RF devices formed on glass substrate  221  are to be inspected. Selector  222  in the form of a conductive plate having opening  223  that is shaped and sized complementarily to one RF device is prepared. Then, glass substrate  221  is superposed on selector  222  to align opening  223  with an RF device to be inspected among the RF devices on glass substrate  221 . Opening  223  is now positioned behind the RF device to be inspected among the RF devices on glass substrate  221 , and the conductive plate is positioned behind the other RF devices. Then, as shown in  FIG. 25B , head  224  of a reader/writer is brought closely to the RF device to be inspected, and applies an inspection signal by way of radio waves.  
      In radio communications, when a conductor such as metal approaches an antenna, radio waves are blocked by the conductor, and substantially no communications can be performed. According to the eleventh embodiment, when selector  222  is brought closely to glass substrate  221 , all the RF devices except the RF device to be inspected fail to communicate. Therefore, no interference occurs between the RF device to be inspected and the other RF devices, and only the RF device to be inspected can be inspected with high accuracy. By successively moving opening  223  with respect to glass substrate  221 , the RF devices on glass substrate  221  are successively checked. The method of inspecting an RF device according to the eleventh embodiment can also be used to communicate with a certain RF device for writing initial data therein.  
      An RF device may be inspected by radio waves after it has been formed on an insulating substrate. Initial data such as ID data to be given in advance may be input to an RF device by radio waves. A plurality of sets of antennas and signal processing circuits may be formed on a single insulating substrate of glass and then the insulating substrate may be cut into a plurality of RF devices. In such a manufacturing process, if the above inspecting method is performed or the initial data are input after the insulating substrate is cut into RF devices, then the efficiency with which to handle RF devices is extremely low. According to the present embodiment, however, selector  222  is used to apply radio waves selectively to one RF device only. Therefore, RF devices that are still placed on a sheet or a roll may be inspected or supplied with initial data before the insulating substrate is cut to separate the RF devices. In this manner, the RF devices can be handled easily with increased efficiency.  
      A modification of the method of inspecting an RF device according to the eleventh embodiment will be described below.  
      In the eleventh embodiment, as shown in  FIG. 25A , RF devices disposed on a plate-shaped glass substrate are to be inspected. According to the modification of the eleventh embodiment, as shown in  FIG. 26 , flexible RF devices manufactured by a roll-to-roll process are to be inspected. In  FIG. 26 , a sheet supporting thereon RF devices  231  to be inspected is wound into a roll on cylindrical bobbin  232 . The sheet is unreeled and placed over selector  222  for inspecting RF devices  231 , and then wound into a roll on cylindrical bobbin  233  after RF devices  231  are inspected. When bobbins  232 ,  233  are rotated, the sheet is unreeled and wound to position a plurality of RF devices successively between opening  223  in selector  222  and head  224  for successively inspecting the RF devices. Other structural details and advantages of the modification of the eleventh embodiment are identical to those of the eleventh embodiment.  
      In the eleventh embodiment and its modification, one RF device is inspected at a time. However, a plurality of RF devices may simultaneously be inspected. When a plurality of RF devices are simultaneously inspected, they are spaced from each other to avoid interference therebetween. Selector  222  has a plurality of openings  223  positioned for alignment with the respective RF devices to be inspected. Openings  223  are then positioned in alignment with the respective RF devices to inspect the RF devices.  
      While preferred embodiments of the present invention have been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.