Abstract:
A semiconductor device includes: a transmission line including a capacitor section and an inductor section arranged on a semiconductor substrate, and a junction of the semiconductor substrate and one of the capacitor section and the inductance section, wherein a transmission characteristic of the transmission line is determined by a voltage applied to the junction.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a semiconductor device and a communication apparatus using the semiconductor device. 
         [0003]    2. Description of the Related Art 
         [0004]    In recent years, in the field of communication and the field of information processing, with the increase in processing speed, the development of a functional element which is smaller, has a wide application band or has excellent energy efficiency is demanded. 
         [0005]    In the field of a semiconductor device or a functional element, a material having negative dielectric constant or magnetic permeability was theoretically predicted in 1998, and thereafter, the effect was confirmed in an artificially constructed material, and much attention is suddenly paid to the material from the viewpoint of device application and system application. 
         [0006]    At present, a variable beam antenna, a variable filter or the like using a metamaterial of new material or structure is vigorously studied. Here, the metamaterial is an artificially formed left-handed material (substance) having negative dielectric constant or magnetic permeability in electromagnetic and optical properties. 
         [0007]    In the propagation of an electromagnetic wave in related art, the propagation direction of an electric field and a magnetic field is represented in a right handed transmission line (RH-TL). On the other hand, the metamaterial is called a left-handed material because the propagation direction is reversed by the effect of the negative dielectric constant and magnetic permeability, and the relation is represented in a left handed transmission line (LH-TL). 
         [0008]    As a functional element using the metamaterial, for example, an array antenna (leaky wave antenna) is known in which voltage is applied to liquid crystal formed as a stub inductor, and the phase is controlled so that the beam direction can be manipulated (see, for example, JP-A-2006-211328 (Patent Document 1)). 
       SUMMARY OF THE INVENTION 
       [0009]    In most of the related art functional elements, a structure of using a liquid crystal, ferroelectric substance, magnetic substance or the like is adopted, and a specific manufacturing method is required. Accordingly, they are not suitable for integration with semiconductor devices and other integrated circuit functions in realizing further miniaturization and higher performance. It is desirable that the metamaterial structure to be described here is simply integrated with a semiconductor LSI and its package to the utmost since application to a shield structure is also expected. 
         [0010]    On the other hand, in a high-frequency functional element which can be realized using the metamaterial structure, in view of the tendency to multi-band and wide band, when the frequency band is made variable, there is obtained a great merit that one element can deal with many bands. Here, as the high-frequency functional element, a transmission line, a filter, a balun (balanced to unbalanced transformer), an antenna and the like can be enumerated. 
         [0011]    From the above, the related art high-frequency functional element of combination of transmission lines using the liquid crystal, ferroelectric substance or the like is not suitable for simple and compact integration with an amplifier of semiconductor such as silicon (Si), a phase detector, a mixer or the like. 
         [0012]    Thus, it is desirable to provide a semiconductor device in which a transmission line of left-handed material or right-handed material having a variable transmission characteristic can be constructed on a semiconductor substrate in a simple structure and a communication apparatus using the semiconductor device. 
         [0013]    According to an embodiment of the present invention, there is provided a semiconductor device including a transmission line having a capacitor section and an inductor section arranged on a semiconductor substrate, and a junction of the semiconductor substrate and one of the capacitor section and the inductance section, and 
         [0014]    a transmission characteristic of the transmission line is determined by a voltage applied to the junction. 
         [0015]    The semiconductor device can be used for a communication apparatus, especially a communication apparatus for high-speed transmission of 30 GHz or higher. 
         [0016]    The transmission line electrically connected to the junction by using the property of semiconductor junction is formed on the semiconductor substrate, so that the left-handed or right-handled transmission line having a variable transmission characteristic can be directly formed on the semiconductor substrate in the simple structure. Here, that the transmission characteristic is determined by the voltage applied to the junction means that the transmission characteristic of the transmission line can be controlled by the voltage. 
         [0017]    According to the embodiment of the present invention, the transmission line of left-handed material or right-handed material having the variable transmission characteristic can be formed on the semiconductor substrate in the simple structure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  is a perspective view showing the outline of a structure of a semiconductor device according to a first embodiment of the invention. 
           [0019]      FIG. 2  is a view showing an equivalent circuit of the semiconductor device according to the first embodiment. 
           [0020]      FIG. 3  is a sectional view showing a sectional structure along line a-a′ of  FIG. 1 . 
           [0021]      FIG. 4  is a characteristic view showing an energy transmission efficiency (S parameter) with respect to a frequency f when voltage V 1  is changed. 
           [0022]      FIG. 5  is a view showing an example of a frequency characteristic of a high pass filter based on an equivalent circuit of a left-handed transmission line. 
           [0023]      FIG. 6  is a perspective view showing the outline of a structure of a transmission line according to a modified example of the first embodiment. 
           [0024]      FIG. 7  is a view showing an equivalent circuit of the transmission line according to the modified example of the first embodiment. 
           [0025]      FIG. 8  is a sectional view showing a sectional structure along line b-b′ of  FIG. 5 . 
           [0026]      FIG. 9  is a perspective view showing the outline of a structure of a semiconductor device according to a second embodiment of the invention. 
           [0027]      FIG. 10  is a view showing an equivalent circuit of the semiconductor device according to the second embodiment. 
           [0028]      FIG. 11  is a sectional view showing a sectional structure along line c-c′ of  FIG. 8 . 
           [0029]      FIG. 12  is a characteristic view showing an example of C-V characteristic representing a state of change in depletion layer capacitance C when an applied voltage V is changed. 
           [0030]      FIG. 13  is a view showing an example of frequency characteristic of a low pass filter based on an equivalent circuit of a right-handed transmission line. 
           [0031]      FIG. 14  is a perspective view showing the outline of a structure of a transmission line according to a modified example of the second embodiment. 
           [0032]      FIG. 15  is a view showing an equivalent circuit of the transmission line according to the modified example of the second embodiment. 
           [0033]      FIG. 16  is a sectional view showing a sectional structure along line d-d′ of  FIG. 12 . 
           [0034]      FIG. 17  is a perspective view showing the outline of a structure of a semiconductor device according to a third embodiment of the invention. 
           [0035]      FIG. 18  is a view showing an equivalent circuit of the semiconductor device according to the third embodiment. 
           [0036]      FIG. 19  is a view showing an example of a frequency characteristic of a band pass filter represented by the equivalent circuit of  FIG. 18 . 
           [0037]      FIG. 20  is a perspective view showing the outline of a structure of a semiconductor device according to a fourth embodiment of the invention. 
           [0038]      FIG. 21  is a view showing an equivalent circuit of the semiconductor device according to the fourth embodiment. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0039]    Hereinafter, modes for carrying out the present invention (hereinafter referred to as embodiments) will be described in detail with reference to the drawings. The description will be made in the following sequence. 
         [0040]    1. First embodiment (example of a high pass filter) 
         [0041]    2. Second embodiment (example of a low pass filter) 
         [0042]    3. Third embodiment (example of a band pass filter) 
         [0043]    4. Fourth embodiment (example of a balun) 
         [0044]    5. Operation and effect of the first to the fourth embodiments 
         [0045]    6. Modified example 
         [0046]    7. Application example 
       1. First Embodiment 
       [0047]      FIG. 1  is a perspective view showing the outline of a structure of a semiconductor device according to a first embodiment of the invention. A semiconductor device  10  according to the first embodiment has a structure having a so-called left-handed transmission line  12  of a metamaterial structure formed on a semiconductor substrate  11 , such as a silicon substrate, on which an active component or circuit, such as a MOS transistor or a bipolar transistor, can be formed. The transmission line  12  is, for example, a micro-strip transmission line to transmit an electromagnetic wave. 
         [0048]    The transmission line  12  includes a capacitor section  13 , an inductor section  14  and an MSM (Metal-Semiconductor-Metal) junction  15 . When a desired signal RF is inputted to the left end in the drawing, the transmission line  12  transmits the signal RF from the left to the right, and outputs it from the right end. As shown in  FIG. 2 , the equivalent circuit of the transmission line  12  is represented by an inductance L and a variable capacitance VC. The transmission line  12  has a structure generically called the left-handed transmission line. 
         [0049]      FIG. 3  is a sectional structure along line a-a′ of  FIG. 1 . The semiconductor substrate  11  is used as a dielectric substance. Thus, the semiconductor substrate  11  is a high resistance substrate (Si (Semi-insulating) substrate) doped with Fe or the like. Aground surface  16  is formed on the back surface of the semiconductor substrate  11 . An N −  or P −  region  17  is formed in a surface portion of the semiconductor substrate  11  so as to extend over two electrodes  131  and  132  forming the capacitor section  13 . 
         [0050]    By forming the N −  or P −  region  17  to extend over the two electrodes  131  and  132  forming the capacitor section  13  as stated above, a depletion layers  18  based on a metal Schottky junction is formed just below each of both the electrodes  131  and  132 . By this, an MSM junction  15  is formed just below the formation portion of the capacitor section  13 . 
         [0051]    In the MSM junction  15 , a voltage V 1  is applied between the electrodes  131  and  132  from the outside, and the width of the depletion layer  18  is changed by the voltage value of the voltage V 1 , so that the capacitance component of the capacitor section  13  can be changed. As a result, the capacitance value of the transmission line  12  can be made variable according to the voltage value of the voltage V 1 . 
         [0052]    The transmission line  12  of the embodiment as constructed above is the left-handed transmission line having the equivalent circuit shown in  FIG. 2 . The propagation constant of the transmission line  12  and the impedance characteristic easily become variable characteristics according to the voltage V 1  applied from the outside to the junction capacitance section shown in  FIG. 1 , that is, the MSM junction  15 . In other words, the transmission line  12  has the propagation constant and the impedance characteristic which can be changed according to the voltage V 1 .  FIG. 4  shows an energy transmission efficiency (so-called S parameter S 21 ) with respect to a frequency f when the voltage V 1  is changed. 
         [0053]    Besides, the transmission line  12  of the embodiment can be directly formed on the semiconductor substrate  11  such as a silicon substrate. Accordingly, the transmission line can be easily integrated with an active element or circuit such as a MOS transistor or a bipolar transistor. 
         [0054]      FIG. 5  shows a calculation example of frequency characteristic based on the equivalent circuit (see  FIG. 2 ) of the left-handed transmission line  12  formed on the semiconductor substrate  11 , such as the silicon substrate, as described above. As is apparent from the frequency characteristic, the left-handed transmission line  12  has basically the characteristic of a high pass filter. The propagation constant of the left-handed transmission line  12  can be controlled by the voltage V 1  applied from the outside. Accordingly, the cut-off frequency of the high pass filter can be made variable according to the voltage V 1 , and the high pass filter for all bands can be constructed. 
       Modified Example of the First Embodiment 
       [0055]    Although the capacitance component of the transmission line  12  is made variable in this embodiment, the inductance component can be made variable. 
         [0056]      FIG. 6  is a perspective view showing a schematic structure of a transmission line according to a modified example of the first embodiment. In  FIG. 6 , the same portion (corresponding portion) as that of  FIG. 1  is denoted by the same reference numeral and its duplicate description is omitted. 
         [0057]    A transmission line  12 A of the modified example is formed on a semiconductor substrate  11  such as a silicon substrate, and includes a capacitor section  13 A, an inductor section  14 A and an MSM junction  15 A. When a desired signal RF is inputted to the left end in the drawing, the transmission line  12 A transmits the signal RF from the left to the right, and outputs it from the right end. As shown in  FIG. 7 , an equivalent circuit of the transmission line  12 A is represented by a variable inductance VL and a capacitance C. 
         [0058]      FIG. 8  shows a sectional structure along line b-b′ of  FIG. 6 . The capacitor section  13 A includes two electrodes  131  and  132 , and a capacitance is formed between the electrodes  131  and  132 . An N −  or P −  region  17  is formed just below a portion constituting the inductance component of the inductor section  14 A. By this, the MSM junction  15 A is formed just below the formation portion of the inductor section  14 A. 
         [0059]    Besides, a contact section (not shown) is formed in the N −  or P −  region  17 , and can be electrically connected from the outside through the contact section. When a voltage V 2  is applied to the N −  or P −  region  17  and a conductor  141  just above the region, the inductance value of the inductance section  14 A can be made variable by the voltage value of the voltage V 2 . 
         [0060]    In the first embodiment and its modified example, with respect to an impurity (dopant) of the N −  or P −  region  17  required for forming the MSM junction  15 ,  15 A, it can be easily formed using a well-known diffusion method or an ion implantation method. 
         [0061]    Besides, in the first embodiment and its modified example, although the description is made while using the MSN junction as an example, the invention is not limited to the MSM junction. For example, it is needless to say that the so-called P-N junction may be used, and a structure in which a capacitance value or an inductance value can be changed can be realized. 
       2. Second Embodiment 
       [0062]    In the first embodiment, the transmission line having the structure called the left handed transmission line is used as an example. A transmission line called a right handed transmission line corresponding thereto can also be constructed in the same principle. The right-handed transmission line will be described below as the second embodiment. 
         [0063]      FIG. 9  is a perspective view showing the outline of a structure of a semiconductor device according to the second embodiment. A semiconductor device  20  of this embodiment has a structure in which a right-handed transmission line  22  is formed on a semiconductor substrate  21  such as a silicon substrate in which an active element or circuit such as a MOS transistor or a bipolar transistor can be formed. The transmission line  22  is, for example, a macro strip transmission line to transmit an electromagnetic wave. 
         [0064]    The transmission line  22  has a structure in which a capacitor section  23  and an inductor section  24  are alternately formed in series. When a desired signal RF is inputted to the left end in the drawing, the transmission line  22  transmits the signal from the left to the right, and outputs it from the right end. As shown in  FIG. 10 , an equivalent circuit of the transmission line  22  at this time is represented by an inductance L and a variable capacitance VC. The transmission line  22  has a structure called a right-handed transmission line. 
         [0065]      FIG. 11  shows a sectional structure along line c-c′ of  FIG. 9 . Similarly to the case of the first embodiment, aground surface  26  is formed on the back surface of the semiconductor substrate  21 . An N or P region  27  is formed in the surface portion of the semiconductor substrate  21 , so that a depletion layer  28  is formed just below a conductor  231  of the capacitor section  23 . By this, an MS junction  25  is formed just below the formation portion of the capacitor section  23 . A voltage V 3  is applied to the MS junction  25  from the outside, so that the capacitance component of the capacitor section  23  can be made variable by the voltage value of the voltage V 3 . 
       (Junction Capacitance by MS Junction) 
       [0066]    The junction capacitance C by MS junction is given by following expression (1) from the property of Schottky junction. 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       
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                                     V 
                                   
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                               ) 
                             
                             
                               1 
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                               2 
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
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         [0067]    Here, S denotes an area of the junction, e denotes an electron elementary charge, ∈0 denotes a material dielectric constant in vacuum, ∈s denotes a relative dielectric constant, d denotes a junction depletion layer thickness, Vd denotes a junction diffusion potential, and V denotes an applied voltage. 
         [0068]    As is apparent from the expression (1), the junction capacitance C is proportional to the square root of the applied voltage V. For example, when the electrode size is 100 μm×400 μm, the donor density Nd is 5×10 18  (cm −3 ) and V is −Vd, it can be estimated that the junction capacitance C is about 680 [pF] at maximum.  FIG. 12  shows an example of C-V characteristic in this case. The C-V characteristic represents the change of the depletion layer capacitance (junction capacitance) C when the applied voltage V is changed. 
         [0069]    The transmission line  22  of this embodiment constructed as stated above is the right-handed transmission line having the equivalent circuit shown in  FIG. 10 . The propagation constant of the transmission line  22  and the impedance characteristic are characteristics which can be easily changed according to the voltage V 3  applied from the outside to the junction capacitance section shown in  FIG. 9 , that is, the MS junction  25 . In other words, the transmission line  22  has the propagation constant and the impedance characteristic which can be changed according to the voltage V 3 . 
         [0070]      FIG. 13  shows a calculation example of a frequency characteristic based on the equivalent circuit (see  FIG. 10 ) of the right-handed transmission line  22  formed on the semiconductor substrate  21  such as the silicon substrate. As is apparent from the frequency characteristic, the right-handed transmission line  22  basically has the characteristic of a low pass filter. The propagation constant of the right-handed transmission line  22  can be controlled by the voltage V 3  applied from the outside. Accordingly, the cut-off frequency of the low pass filter can be changed according to the voltage V 3 , and the low pass filter for all bands can be constructed. 
       Modified Example of the Second Embodiment 
       [0071]    Although the capacitance component of the transmission line  22  is variable in this embodiment, the inductance component can be made variable. 
         [0072]      FIG. 14  is a perspective view showing a schematic structure of a transmission line according to a modified example of the second embodiment. In  FIG. 14 , the same portion as that of  FIG. 9  is denoted by the same reference numeral and its duplicate description is omitted. 
         [0073]    A transmission line  22 A of the modified example is formed on a semiconductor substrate  21  such as a silicon substrate, and includes a capacitor section  23 A, an inductor section  24 A and an MSM junction  25 A. When a desired signal RF is inputted to the left end in the drawing, the transmission line  22 A transmits the signal RF from the left to the right, and outputs it from the right end. As shown in  FIG. 15 , an equivalent circuit of the transmission line  22 A at this time is represented by a variable inductance VL and a capacitance C. 
         [0074]      FIG. 16  shows a sectional structure along line d-d′ of  FIG. 14 . An N or P region  27  is formed in a surface layer of the semiconductor substrate  21 , so that a depletion layer  28  is formed just below a conductor  241  of the inductor section  24 A. By this, the MS junction  25 A is formed just below the formation portion of the inductor section  24 A. When a voltage V 4  is applied to the MS junction  25 A, the inductance value of the inductor section  24 A can be made variable by the voltage value of the voltage V 4 . 
         [0075]    The two different transmission lines described above, that is, the left-handed transmission line  12  of the first embodiment and the right-handed transmission line  22  of the second embodiment are made base elements, and various types of circuits can be formed by combining these. 
       3. Third Embodiment 
       [0076]      FIG. 17  is a perspective view showing the outline of a structure of a semiconductor device according to a third embodiment of the invention. In  FIG. 17 , the same portion as that of  FIG. 1  and  FIG. 9  is denoted by the same reference numeral, and its duplicate description is omitted. 
         [0077]    A semiconductor device  30  of this embodiment has a structure in which the left-handed transmission line  12  of the first embodiment and the right-handed transmission line  22  of the second embodiment are connected in series to each other. The specific structures of the two transmission lines  12  and  22  are as described before. 
         [0078]    That is, the left-handed transmission line  12  includes a capacitor section  13  and an inductor section  14 , and an MSM junction  15  is formed in the capacitor section  23 , so that the capacitance component is variable. The right-handed transmission line  22  includes a capacitor section  23  and an inductor section  24 , and an MS section  25  is formed in the capacitor section  23 , so that the capacitance component is variable. 
         [0079]    A voltage V 11  applied to the MSM junction  15  of the left-handed transmission line  12  and a voltage V 12  applied to the MS section  25  of the right-handed transmission line  22  are changed in a reverse bias state, so that the width of the depletion layer of each of the MSM junction  15  and the MS section  25  can be controlled. As a result, the respective capacitance values of the left-handed transmission line  12  of the first embodiment and the right-handed transmission line  22  of the second embodiment can be made variable. 
         [0080]    As shown in  FIG. 18 , an equivalent circuit of the semiconductor device  30  of the embodiment at this time is an equivalent circuit model in which the equivalent circuit of  FIG. 2  is connected in series to the equivalent circuit of  FIG. 10 . By this, a band pass filter can be constructed. The band width of the band pass filter is variable according to each voltage value of the external voltages V 11  and V 12 . That is, the cut-off frequency on the low frequency side can be controlled by changing the voltage value of the external voltage V 11 , and the cut-off frequency on the high frequency side can be controlled by changing the voltage value of the external voltage V 12  respectively independently. 
         [0081]      FIG. 19  shows an example of frequency characteristic of the band pass filter represented by the equivalent circuit of  FIG. 18 . The cut-off frequency on the low frequency side and the cut-off frequency on the high frequency side can be respectively independently changed by the external voltage V 11  and the external voltage V 12 . Besides, in the frequency characteristic of  FIG. 19 , the attenuation characteristics on the low frequency side and the high frequency side can be changed by the structure of the number of stages of the capacitor sections  13  and  23  and the inductor sections  14  and  24  incorporated in the transmission lines  12  and  22 . 
         [0082]    Incidentally, as is easily estimated from the modified examples of the first embodiment and the second embodiment, as described in these modified examples, also when the inductance component is made variable, the band pass filter similar to the band pass filter of this embodiment can be formed. 
         [0083]    At this time, similarly to  FIG. 17 , a voltage is independently applied from the outside to the MS junction provided in the inductor formation portion of each of the transmission lines  12  and  22 . The band pass filter can be easily constructed in which the cut-off frequencies on the low frequency side and the high frequency side can be independently controlled. 
       4. Fourth Embodiment 
       [0084]      FIG. 20  is a perspective view showing the outline of a structure of a semiconductor device according to a fourth embodiment of the invention. In  FIG. 20 , the same portion as that of  FIG. 1  and  FIG. 9  is denoted by the same reference numeral and its duplicate description is omitted. 
         [0085]    A semiconductor device  40  of this embodiment has a structure in which the left-handed transmission line  12  of the first embodiment and the right-handed transmission line  22  of the second embodiment are connected so that the input terminal is common. By this connection relation, a balun (balanced to unbalanced transformer) can be constructed. The specific structure of each of the two transmission lines  12  and  22  is as described above. 
         [0086]    That is, the left handed transmission line  12  includes a capacitor section  13  and an inductor section  14 , and an MSM junction  15  is formed in the capacitor section  13 , so that the capacitance component can be changed. The right-handed transmission line  22  includes a capacitor section  23  and an inductor section  24 , and an MS section  25  is formed in the capacitor section  23 , so that the capacitance component can be changed. 
         [0087]    A voltage V 11  applied to the MSM junction  15  of the left-handed transmission line  12  and a voltage V 12  applied to the MS section  25  of the right-handed transmission line  22  are changed in the reverse bias state, so that the width of each depletion layer of the MSM junction  15  and the MS section  25  can be controlled. As a result, the capacitance value of each of the left-handed transmission line  12  and the right-handed transmission line  22  can be made variable. 
         [0088]    In the semiconductor device  40  of the balun structure, a signal RFin inputted to the input end common to the two transmission lines  12  and  22  is divided into two, and is outputted as signals RFout− and RFout+, whose phases are different from each other by 180 degrees, from the left-handed transmission line  12  and the right-handed transmission line  22 .  FIG. 21  shows an equivalent circuit at this time. Similarly to the case of the band pass filter, the band width of the balun is variable according to the voltage value of each of the external voltages V 11  and V 12 . As a result, the balun can be made to operate in a very wide band. 
       5. Operation and Effect of the First to the Fourth Embodiments 
       [0089]    As described in the first to the fourth embodiments, by using the property of the semiconductor junction and by forming the two kinds of the transmission lines  12  and  22  electrically connected to the junction on the semiconductor substrate, the transmission lines  12  and  22  whose transmission characteristics are variable can be directly formed on the semiconductor substrate in the simple structures. In various functional elements of these structures, specifically in the high frequency element (circuit), the characteristic can be controlled on the frequency axis by controlling the external voltage. This means that functional elements of all bands can be dealt with, and there is a great merit that various applications can be dealt with. 
         [0090]    That these functional elements can be directly formed on the semiconductor substrate means that integration with all types of active elements can be performed simultaneously. As compared with a case where a chip component or the like is formed through a package or the like, the influence of an electrical parasitic component can be avoided. As a result, the characteristic of the functional element can be improved. Further, it is also advantageous in compactness, productivity and cost that the functional element can be formed on the same semiconductor substrate as an active element (circuit). 
         [0091]    Besides, the characteristics of these functional elements can be changed from the outside by changing the widths of the depletion layers formed in the capacitor sections  12  and  22  and the inductor sections  13  and  23  by the external voltages. Further, since the property of the semiconductor junction is used in the reverse bias state, the power consumption is very low. Further, as compared with the related art functional element constructed of only the right handed transmission line, the functional element of the combination of the left handed transmission line and the right handed transmission line is superior in broadband property, low loss property and the like. 
         [0092]    As is apparent from the above, according to the first to the fourth embodiments, in characteristics, power consumption and shape factor, as compared with the related art case where liquid crystal or ferroelectric substance is used, the extremely superior functional element, specifically, the high frequency element (circuit) can be formed on the semiconductor substrate. 
       6. Modified Example 
       [0093]    In the first to the fourth embodiments, although the case where the silicon substrate is used as the semiconductor substrate is used as the example, no limitation is made to the silicon substrate. It is easily understood that any material such as, for example, a semiconductor in which an insulating property is obtained, a IV group semiconductor such as Ge, a III-V group semiconductor such as GaAs or InP, a II-IV group such as ZnS or ZnSe, a ternary compound of these, a quartenary compound or the like may be used. 
         [0094]    Also with respect to the metal of the conductor used as the transmission lines  12  and  22 , it is needless to say that any material, such as Al, Cu, Ag, Pt and Au, may be used as long as the MS junction can be formed in the junction with the semiconductor. 
       7. Application Example 
       [0095]    The semiconductor devices of the first to the fourth embodiments, that is, the functional elements such as the high pass filter, the low pass filter, the band pass filter, and the balun can be used for a communication apparatus, especially a communication apparatus for high-speed transmission of 30 GHz or higher. 
         [0096]    The present application contains subject matter related to that disclosed in Japanese Priority Patent Application JP 2009-208797 filed in the Japan Patent Office on Sep. 10, 2009, the entire contents of which is hereby incorporated by reference. 
         [0097]    It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.