Abstract:
A tuning circuit, as for a television receiver or video recorder, employs switchable tuning circuits including micro-electronic electro-mechanical switches for selecting the ones of an array of capacitors and/or inductors as is useful in tunable circuits. The array of capacitors and/or inductors and micro-electro-mechanical switches of the switched tuning matrix is formed on an integrated circuit or an electronic circuit substrate along with amplifiers and other electronic elements of the tuning circuit for which the switched tuning matrix is employed. The switchable capacitance and inductance matrices are well suited for use in the resonators employed in the pre-selector filters, post-selector filters and oscillators of electronic tuners, such as those employed in television receivers and video recorders. The capacitors and micro-electro-mechanical switches may be connected to select a particular capacitor of the array of capacitors or to select ones of the capacitors of the array of capacitors to establish a particular capacitance value. The capacitors of the array of capacitors may be of like value or may be of different values, such as would advance simplified response to a digital control word, such as a 1-2-4-8 weighting or a 1-2-2-4 weighting. Similarly, the inductors and micro-electro-mechanical switches may be connected to select a particular inductor of the array of inductors or to select ones of the inductors of the array of inductors to establish a particular inductance value. The inductors of the array of inductors may be of like value or may be of different values, such as would advance simplified response to a digital control word, such as a 1-2-4-8 weighting or a 1-2-2-4 weighting.

Description:
This application claims the benefit of U.S. Provisional Application Ser. No. 60/092,178 entitled “MICRO-ELECTRO-MECHANICALLY-SWITCHED CAPACITOR MATRIX” filed Jul. 9, 1998. 
    
    
     The present invention relates to television tuners and, in particular, to television tuners employing micro-electro-mechanically switched tuning matrices, which tuning matrices may include capacitance and/or inductance elements. 
     From the early days of radio, the need for tunable resonant electrical circuits was recognized. Large mechanical tuning elements, such as air-dielectric capacitors and air-core inductors, in time gave way to smaller, more efficient capacitors and inductors. In the continuing evolution from vacuum tubes to transistors to integrated circuits, the trend has been for ever-decreasing size and cost. To this end, micro-electronic circuits and integrated electronic circuits have become the mainstay of modern-day electronics. 
     In the field of television (TV) tuners and other superheterodyne receivers, for example, this evolution has seen the vacuum tubes and multi-gang mechanical switches with discreet capacitors, inductors and resistors soldered thereon yield to transistorized printed-wiring circuit boards, and the transistorized circuit boards yield to micro-electronic and integrated circuits mounted on printed-wiring substrates. But even modem integrated circuit TV tuners still employ discrete components for the capacitive and inductive tuning elements. 
     The electronically-controllable variable tuning elements currently employed are semiconductor varactor diodes which exhibit a capacitance that varies inversely to the magnitude of the DC reverse bias voltage applied thereto. Varactor diodes are coupled to inductors or to a transmission line having inductive reactance to form resonators that are employed in the pre-selector filters, post-selector filters and oscillators of tunable receivers such as modern TV tuners. 
     For example, FIG. 1 shows a conventional tunable circuit of this sort in which the resonant frequency is determined by the value of the capacitance exhibited by varactor diode D 2  and the inductance of inductors L 01  and L 02 . PIN diode D 1  provides band switching under the control of voltage VD 1 . With switching voltage VD 1  at +20 volts, diode D 1  is open (nonconductive) and inductors L 01  and L 02  in series form the inductance of the tunable circuit; and with switching voltage VD 1  at −20 volts, D 1  is conductive substantially shorting inductor L 01 , thereby leaving L 02  as the inductance of the tunable circuit. Varactor diode D 2  exhibits a variable capacitance in response to tuning voltage VD 2  changing between about +1 to +20 volts. Capacitors CD 1  and CD 2  are needed to provide DC isolation for the control voltage VD 1  and the tuning voltage VD 2 , respectively, and have capacitances sufficiently large as not to undesirably affect the resonant frequency of the tunable circuit. Thus, the need for discrete electronic components and for additional components for DC isolation tends to increase the size, assembly difficulty and the cost of these products, all of which are not desirable. 
     Unfortunately, varactor diodes also have undesirable electrical characteristics that limit their usefulness and the performance obtainable. Firstly, the capacitance of a varactor diode is a non-linear function of its reverse bias voltage, thereby being a source of distortion of the signals applied to or passed through the varactor diode. Secondly, varactor diodes are relatively lossy and so will exhibit a relatively low Q. The effect of a low Q on the tuned circuits of a typical TV tuner is to produce greater signal losses, to limit the sharpness, selectivity and narrow bandwidth capability of filters, and to increase the overall noise figure, and thereby increase the signal-to-noise ratio, of the tuner. 
     Accordingly, there is a need for tunable circuits that will have lower distortion, higher Q, and improved filter characteristics, and that will enable tuners having lower distortion, improved image rejection and adjacent channel rejection, and a lower noise figure. 
     To this end, the tuner of present invention comprises a tunable bandpass filter on a substrate having a passband including a resonant frequency responsive to a tuning control signal, a tunable oscillator on the substrate generating a controllable frequency signal responsive to a frequency control signal, and a mixer on the substrate coupled to the tunable bandpass filter for receiving signals in the passband and coupled to the tunable oscillator for receiving the controllable frequency signal. The tunable bandpass filter includes a resonant circuit comprising a plurality of capacitors formed of conductive layers and dielectric layers on the substrate; and a plurality of switches formed of layers of materials on the substrate, wherein the switches are selectively opened and closed by movement of a switch arm in response to the tuning control signal, and wherein ones of the plurality of switches selectively couple respective ones of the plurality of capacitors to a conductive connection on the substrate. A tuning control generates the tuning control signal and the frequency control signal. 
     The present invention also comprises a method for fabricating a matrix of a plurality of capacitors and electro-mechanical switches connected in circuit on a substrate by: 
     depositing a conductive layer on parts of the substrate to form a plurality of capacitor plates, and to form a plurality of switch contacts and a plurality of control conductors associated with respective ones of the plurality of switch contacts; 
     depositing a dielectric layer on each of the plurality of capacitor plates and another conductive layer on each dielectric layer to form the plurality of capacitors on the substrate; 
     forming a removable layer overlaying the plurality of switch contacts and at least portions of the plurality of control conductors associated therewith, the removable layer having a plurality of holes therethrough with one of the holes proximate to each control conductor; 
     depositing a second conductive layer on the removable layer, the second conductive layer forming a plurality of conductive areas, each conductive area overlying a respective one of the control conductors, a respective one of the switch contacts and being attached to the substrate through a respective one of the holes to form a respective switch arm associated with one of the plurality of switch contacts; 
     removing the removable layer to leave the plurality of switch arms spaced apart from the substrate and attached thereto at one end thereof and spaced apart from the respective switch contact associated therewith at its other end; and 
     depositing a plurality of conductive connections between ones of the capacitors, ones of the switch arms and ones of the switch contacts to connect ones of the capacitors and the electro-mechanical switches in circuit on the substrate. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The detailed description of the preferred embodiments of the present invention will be more easily and better understood when read in conjunction with the FIGURES of the Drawing which include: 
     FIG. 1 is a schematic diagram of a prior art tunable circuit; 
     FIG. 2 is a schematic block diagram of a television tuner including an embodiment according to the present invention; 
     FIG. 3 is a simplified schematic diagram of a tunable circuit including an embodiment according to an aspect of the present invention; 
     FIG. 4 is a plan view of a portion of the surface of an integrated circuit embodiment of a portion of the tunable circuit of FIG. 3; 
     FIG. 5 is a plan view showing details of a portion of the integrated circuit embodiment of FIG. 4; 
     FIG. 6 is a sectional view of the portion of the integrated circuit embodiment shown in FIG. 5; 
     FIGS. 7A-7J are a series of cross-sectional views depicting the fabrication sequence of a switch of the sort shown in the exemplary embodiments of FIGS. 4-6; 
     FIGS. 8A and 8B are a plan view and a side cross-sectional view, respectively, of an inductor according to an aspect of the present invention; 
     FIG. 9 is schematic block diagram of an exemplary embodiment of an oscillator circuit according to an aspect of the present invention; and 
     FIG. 10 is a schematic diagram of an alternative embodiment of an oscillator circuit according to an aspect of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In FIG. 2 is shown an exemplary embodiment of a tunable system employing tunable circuits including the present invention. Specifically, a two-band television tuner  10  includes a single-pole-double-throw (SPDT) switch  12  that routes received incoming radio frequency (RF) signals to either a UHF-band tuner or a VHF-band tuner under control of a switch control voltage VS generated by tuning control  42 . The UHF-band tuner includes a pre-selector tuning circuit  20  that includes a tunable bandpass filter circuit having a center frequency tuned to the RF carrier signal frequency f RF  of the UHF channel to be selected and a bandwidth compatible with that of such channel, e.g., about 6 MHz for conventional TV channels. RF amplifier  22  amplifies the pre-selected UHF channel signal and applies it to post-selector tuning circuit  24  which, like pre-selector tuning circuit  20 , includes a tunable bandpass filter circuit having a center frequency tuned to the carrier signal frequency f RF  of the UHF channel to be selected and a bandwidth compatible with that of such channel. Tuning circuits  20  and  24  are tunable by a switched capacitance/inductance array including a plurality of micro-electro-mechanical (MEM) switches operable in response to control signals VC generated by tuning control  42 . UHF mixer  28  receives at one of its inputs the amplified, bandwidth-limited RF signal from tuning circuit  24  and at the other of its inputs a frequency signal f LO  generated by voltage-controlled local oscillator  26 . The frequency f LO  of local oscillator  26  is selected to generate at the output of mixer  28  a beat frequency f IF  at a predetermined fixed intermediate frequency (IF) of the tuner, e.g., about 45 MHz. As is known, f RF −f LO =f IF . IF tuning circuit  40  is a bandpass filter circuit having a center frequency at the predetermined fixed IF frequency f IF  of the tuner and a bandwidth compatible with that of such channel, e.g., about 6 MHz for conventional television channels. 
     Similarly, the VHF-band tuner includes a pre-selector tuning circuit  30  that includes a tunable bandpass filter circuit having a center frequency tuned to the RF carrier signal frequency f RF  of the VHF channel to be selected and a bandwidth compatible with that of such channel, e.g., about 6 MHz. RF amplifier  32  amplifies the pre-selected VHF channel signal and applies it to post-selector tuning circuit  34  which, like pre-selector tuning circuit  30 , includes a tunable bandpass filter circuit having a center frequency tuned to the carrier signal frequency f RF  of the VHF channel to be selected and a bandwidth compatible with that of such channel. Tuning circuits  30  and  34  are tunable by a switched capacitance array including, for example, a plurality of micro-electro-mechanical (MEM) switches operable in response to control signals VC generated by tuning control  42 . VHF mixer  38  receives at one of its inputs the amplified, bandwidth-limited RF signal from tuning circuit  34  and at the other of its inputs a frequency signal f LO  generated by voltage-controlled local oscillator  36 . The frequency f LO  of local oscillator  36  is selected to generate at the output of mixer  38  a beat frequency f IF  at a predetermined fixed intermediate frequency (IF) of the tuner, e.g., about 45 MHz, which is applied to IF tuning circuit  40 . 
     Each of tuning circuits  20 ,  24 ,  30  and  34  includes a switched capacitance array, or switched capacitance and inductance arrays, and micro-electro-mechanical switches formed on a substrate according to the present invention. Because UHF tuning circuits  20  and  24  operate at the same time and are tuned to the same UHF frequency, the same tuning control signals VC may be applied to both, thereby simplifying tuning control signal generator  42 . Similarly, because VHF tuning circuits  30  and  34  operate at the same time and are tuned to the same VHF frequency, the same tuning control signals VC may be applied to both, thereby simplifying tuning control signal generator  42 . Because UHF tuning circuits  20 ,  24  are not operated at the same time as are VHF tuning circuits  30 ,  34 , i.e. either the UHF band or the VHF band is selected by switch  12 , but not both, the same tuning control signals VC may be used for both sets of tuning circuits  20 ,  24 ,  30 ,  34 , thereby further simplifying tuning control signal generator  42 . In addition, local oscillators  26  and  36  may also include a micro-electro-mechanically-switched tuning array, for example, a capacitance array, according to an aspect of the present invention for selecting the frequency f LO  of its output signal. The tuning control signals VO for local oscillators  26  and  36  are also generated by tuning control signal generator  42 , and may be the same tuning control signals VC as are employed to control tuning circuits  20 ,  24 ,  30 ,  34 . Tuning control signal generator  42  generates the aforementioned control signals in response to selection of a channel by a user, e.g., a person pressing buttons on a TV remote control or on a TV receiver. 
     FIG. 3 is a simplified schematic diagram of a tuning circuit including the present invention as may be employed, for example, in tuning circuits  20 ,  24 ,  30  and  34  of the TV tuning system described in relation to FIG. 2 above. In tuning circuit  30 , a switchable inductance matrix  48  including inductors L 1  and L 2  provides the inductance and switchable capacitance matrix  50  provides the capacitance of the tunable resonant tuned circuit. MEM switch SWO is controlled by control signal VLO for selectively not shorting inductor L 1  for selecting the low-frequency (57-85 MHz for VHF channels  2 - 6 ) portion of the TV VHF band or for selectively shorting inductor L 1  for selecting the high-frequency (177-213 MHz for VHF channels  7 - 13 ) portion of the TV VHF band. In addition, a portion of inductor L 1  may be shorted by closing MEM switch SW 1  in response to control signal VL 1  so as to further divide the lower VHF band into two sub-bands and a portion of inductor L 2  may be shorted by closing MEM switch SW 2  in response to control signal VL 2  so as to further divide the upper VHF band into two sub-bands, thereby reducing the range of capacitance values needed to tune tunable circuit  30  over the full range of VHF carrier frequencies. 
     Switchable capacitance matrix  50  of tuning circuit  30  includes an array of capacitors C 1 , C 2 , . . . CN that are formed on a substrate with the MEM switches S 1 , S 2 , . . . SN. C 1 , C 2 , . . . CN may be connected in parallel with the inductance of inductors L 1 , L 2  of switchable inductance matrix  48  by closing MEM switches S 1 , S 2 , . . . SN, respectively. MEM switches S 1 , S 2 , . . . SN are controlled by switch control voltages VC 1 , VC 2 , . . . VCN, respectively, to selectively close and thereby select the ones of capacitors C 1 , C 2 , . . . CN necessary to resonate with the inductance of inductors L 1 , L 2  at the desired center frequency f RF  of the tunable bandpass filter  30 . The aforementioned control voltages are each applied through a respective impedance which may include resistors and/or RF inductors, illustrated by respective wavy lines RL 0 , RL 1 , RL 2 , RS 1  . . . RSN, to isolate the control voltages applied to the MEM switch from the signals coupled through the MEM switch contacts. 
     Exemplary switch control voltage states for MEM switches SW 0 -SW 2  and S 1 , S 2 , . . . SN to select VHF channels  2  through  13  are listed in Table 1 below, wherein “Gnd” indicates that no potential is applied and the MEM switch is open and “+V” indicates that a positive control voltage is applied sufficient to close the MEM switch. 
     
       
         
               
             
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Switch States for VHF Channel Selection 
               
             
          
           
               
                 Channel 
                 Freq. MHz 
                 VL0 
                 VL1 
                 VL2 
                 VC1 
                 VC2 
                 VC3 
                 ... 
                 VCN-1 
                 VCN 
               
               
                   
               
             
          
           
               
                 2 
                 57 
                 Gnd 
                 Gnd 
                 Gnd 
                 +V 
                 +V 
                 +V 
                 ... 
                 Gnd 
                 Gnd 
               
               
                 3 
                 63 
                 Gnd 
                 Gnd 
                 Gnd 
                 +V 
                 Gnd 
                 Gnd 
                 ... 
                 Gnd 
                 Gnd 
               
               
                 4 
                 69 
                 Gnd 
                 +V 
                 Gnd 
                 +V 
                 Gnd 
                 +V 
                 ... 
                 Gnd 
                 Gnd 
               
               
                 5 
                 79 
                 Gnd 
                 +V 
                 Gnd 
                 +V 
                 +V 
                 Gnd 
                 ... 
                 Gnd 
                 Gnd 
               
               
                 6 
                 85 
                 Gnd 
                 +V 
                 Gnd 
                 +V 
                 Gnd 
                 Gnd 
                 ... 
                 Gnd 
                 Gnd 
               
               
                 7 
                 177 
                 +V 
                 Gnd 
                 Gnd 
                 Gnd 
                 Gnd 
                 Gnd 
                 ... 
                 +V 
                 +V 
               
               
                 8 
                 183 
                 +V 
                 Gnd 
                 Gnd 
                 Gnd 
                 Gnd 
                 Gnd 
                 ... 
                 +V 
                 +V 
               
               
                 9 
                 189 
                 +V 
                 Gnd 
                 Gnd 
                 Gnd 
                 Gnd 
                 Gnd 
                 ... 
                 +V 
                 Gnd 
               
               
                 10 
                 195 
                 +V 
                 Gnd 
                 +V 
                 Gnd 
                 Gnd 
                 Gnd 
                 ... 
                 +V 
                 Gnd 
               
               
                 11 
                 201 
                 +V 
                 Gnd 
                 +V 
                 Gnd 
                 Gnd 
                 Gnd 
                 ... 
                 Gnd 
                 Gnd 
               
               
                 12 
                 207 
                 +V 
                 Gnd 
                 +V 
                 Gnd 
                 Gnd 
                 Gnd 
                 ... 
                 Gnd 
                 Gnd 
               
               
                 13 
                 213 
                 +V 
                 Gnd 
                 +V 
                 Gnd 
                 Gnd 
                 Gnd 
                 ... 
                 Gnd 
                 Gnd 
               
               
                   
               
             
          
         
       
     
     FIG. 4 is a plan view of a substrate  100  including exemplary arrangements of the switch  12  and tuning circuit  30  portions of the tuner shown in FIG. 2 above. Received RF signals on conductor  110  are coupled to SPDT MEM switch  12 . Double pole switch arm  114  thereof is supported by torsionally-flexible hinges  113 A,  113 B extending from anchor posts  112 A,  112 B which raise the hinge arm  114  above the substrate  100 . When a positive control voltage +V is applied to UHF select control line  116 , switch arm  114  is electrostatically attracted thereby and rotates about hinges  113 A,  113 B until it contacts conductor  120  to complete an electrical connection from conductor  110  to conductor  120  for coupling the received RF signal to a UHF-band tuner (not shown in FIG.  4 ). In like manner, when a positive control voltage +V is applied to VHF select control line  118 , switch arm  114  is electrostatically attracted thereby and rotates about hinges  113 A,  113 B until it contacts conductor  132  to complete an electrical connection from conductor  110  to conductor  132  for coupling the received RF signal to tunable pre-selector filter  130  of a VHF-band tuner. Filter  130  includes an inductance L 1 , L 2 , L 3  in parallel with a capacitance C 1 , C 2 , C 3 , C 4 , C 5  to form a tunable parallel resonant circuit. 
     Switchable inductance matrix  148  includes inductors L 1 , L 2 , L 3 , shown symbolically because they may be either integrated inductors formed on the substrate  100  or discrete inductors not formed on the substrate  100 , connected in series between conductor  132  and ground  138 ,  140 . Each inductor L 1 , L 2 , L 3  of switchable inductance matrix  148  has a MEM switch  146 ,  144 ,  142 , respectively, connected in parallel therewith. Inductor L 1  is connected between conductors  136  and  138  which are selectively connected together by MEM switch  146  under control of switch control voltage VL 1  applied via control line  147 . When control voltage VL 1  is applied, switch arm AL 1  is electrostatically attracted to control line  147  causing flexible hinge HL 1 , which supports switch arm AL 1  on anchor post AN 1 , to flex until switch arm AL 1  contacts conductor  136 , thereby to short inductor L 1 . Inductor L 2  is connected between conductors  136  and  134  which are selectively connected together by MEM switch  144  under control of switch control voltage VL 2  applied via control line  145 . When control voltage VL 2  is applied, switch arm AL 2  is electrostatically attracted to control line  145  causing flexible hinge HL 2 , which supports switch arm AL 2  on anchor post AN 2 , to flex until switch arm AL 2  contacts conductor  134 , thereby to short inductor L 2 . Similarly, inductor L 3  is connected between conductors  134  and  132  which are selectively connected together by MEM switch  142  under control of switch control voltage VL 3  applied via control line  143 . When control voltage VL 3  is applied, switch arm AL 3  is electrostatically attracted to control line  143  causing flexible hinge HL 3 , which supports switch arm AL 3  on anchor post AN 3 , to flex until switch arm AL 3  contacts conductor  132 , thereby to short inductor L 3 . 
     Switchable capacitance matrix  150  includes an array of capacitors C 1 , C 2 , C 3 , C 4 , C 5  formed on substrate  100 . Each of capacitors C 1 , C 2 , C 3 , C 4 , C 5  is selectively connected between a respective contact area  151 ,  152 ,  153 ,  154 ,  155  of conductor  132  and a respective ground conductor  161 ,  162 ,  163 ,  164 ,  165  by a respective micro-electro-mechanical (MEM) switch S 1 , S 2 , S 3 , S 4 , S 5 . MEM switch S 1  includes a switch arm A 1  cantilevered from anchor post AN 1  by flexible hinge H 1 . Hinge H 1  flexes to allow switch arm A 1  to contact the contact area  151 , thereby completing a conductive connection from the upper plate of capacitor C 1  to contact area  151 , under the influence of the electrostatic force attracting switch arm A 1  to control line  171  when control voltage VC 1  is applied thereto. In like manner, MEM switches S 2 -S 5  include respective switch arms A 2 -A 5  that are respectively cantilevered from anchor posts AN 2 -AN 5  by flexible hinges H 2 -H 5 , respectively. Hinges H 2 -H 5  flex to allow switch arms A 2 -A 5  to respectively contact the respective contact areas  152 - 155 , thereby completing conductive connections from the respective upper plates of capacitors C 2 -C 5  to contact areas  152 - 155 , respectively, under the respective influences of the electrostatic forces attracting switch arms A 2 -A 5  to their respective control lines  172 - 175  when control voltages VC 2 -VC 5  are respectively applied thereto. 
     In FIG. 4, capacitors C 1 -C 5  are proportionately sized in area in a ratio of about 1:2:4:8:12. Because the capacitance of a capacitor is directly proportional to the area of its plates, the capacitances of capacitors C 1 -C 5  are in substantially the same 1:2:4:8:12 proportion. Accordingly, a total capacitance value C T  is in a range between the capacitance C C1  of capacitor C 1  and twenty-seven times that capacitance (i.e. C T =(1+2+4+8+12) C C1 =27 C C1 ) as may be obtained with the various combinations of the open and closed positions of MEM switches S 1 -S 5 . The value of the increment of change of capacitance is the capacitance C C1  of capacitor C 1 . It is advantageous to employ a capacitance ratio based on the number two for facilitating and simplifying the convenient interfacing of a digital control word produced by a digital processor, such as may be included in tuning control  42 , to produce the control voltages, VC 1 , VC 2 , . . . VCN that are applied to the respective MEM switch control lines. Because the value of each of the foregoing control voltages VC 1 , VC 2 , . . . VCN is either zero or a positive voltage, each can be considered a binary bit and the set of control voltages VC 1 , VC 2 , . . . VCN can be considered a binary digital word. Thus, tuning control signal generator  42  generates a digital word control signal including the various individual control voltages VC 1 , VC 2 , . . . VCN applied to tuning circuits  20 ,  24 ,  30 ,  34  and local oscillators  26 ,  36 . 
     Specifically, the structure of the foregoing arrangement can best be appreciated by considering the enlarged plan view of capacitor C 1  and MEM switch S 1  as shown in FIG. 5 in conjunction with the corresponding side and sectional view thereof shown in FIG. 6. A ground conductor  200  deposited on substrate  100  forms the lower plate of capacitor C 1 . Capacitor C 1  is formed of a dielectric layer  202 , such as a silicon nitride or silicon dioxide layer, deposited on conductive lower plate  200  and a conductive upper plate  204  deposited on dielectric layer  202 . Switch S 1  is formed of an elongated thin metal flexible hinge member  220  cantilevered from the top of anchor base  222 , which is deposited on substrate  100 , and hinge member  220  extending to overlie switch contact  151 . A switch arm member  224  is deposited on the end of hinge member  220  that is overlapping switch contact  151 . Switch contact  151  is deposited on substrate  100  and RF transmission line conductor  132  is deposited on substrate  100  to overlie and contact switch contact  151 . The end  228  of conductive control line  171  underlies switch arm  224  forming a capacitor therewith. When control voltage VC 1  is applied to control line  171 , the potential generates an electrostatic attraction force that causes hinge  220  to flex allowing switch arm  222  to move toward substrate  100  until switch arm  224  contacts switch contact  151 , thereby closing the switch S 1 . It is preferred for certain applications that the end  228  of electrostatic control line  171  be enlarged and be overlaid with a dielectric and that switch arm  224  also be enlarged to increase both the size of the respective plates and the capacitance of the capacitor they form, thereby increasing the electrostatic attractive force generated by control potential VC 1  for actuating MEM switch S 1 . 
     Additional conductive material is deposited to form a contact  206  on the upper plate  204  of capacitor C 1 , to form contact  226  on hinge member  220  overlying anchor base  222 , and to form bridging conductors  236  therebetween. The same deposition may also form contact  161  on the remote end of the lower plate  200  of capacitor C 1  and fill a via hole  102  in substrate  100  to form a via  104  by which connection to a point of ground potential is made. 
     FIGS. 7A-7J are cross-sectional views showing the fabrication process sequence of a MEM switch and an associated capacitor of the sort described above in relation to FIGS. 4-6. FIG. 7A shows a substrate  300 , for example, a ceramic substrate, that is metallized on its bottom side with a titanium layer  302  and then with a gold layer  304  which layers of metal will serve as the ground conductor or ground plane for the substrate  300 . The top surface of substrate  300  is metallized with a layer of chromium  306 , then with a layer of copper  308  and then with a further layer of chromium  310  from and upon which layers will be formed electrical conductors on the top surface of substrate  300 , including control lines for the MEM switches and the lower plates of capacitors. In FIG. 7B, a  300  nanometer (nm) thick layer  320  of silicon nitride insulation is deposited on the upper chromium layer  310 , from which layer will be formed various insulating members such as the dielectric layers of capacitors. For example, FIG. 7C shows a patterned photo-resist layer  322  atop that portion of silicon nitride insulator layer  320  that remains after the silicon nitride has been etched away to leave a dielectric layer  320  of a capacitor (on the left) and a dielectric layer on the MEM switch control conductor (on the right). 
     In FIG. 7D the remaining photo-resist  322  has been stripped away and the upper chromium layer  310  has been etched away to expose copper layer  308 . Next, a patterned photo-resist  326  is applied to define the pattern of the electrical conductors as shown in FIG. 7E and a layer  330  of gold is plated onto the exposed portions of copper layer  308  to over-plate the pattern of the electrical conductors and onto the exposed portions of the dielectric layer  320  to form the second or top plate of the capacitors. Then, the photo-resist  326  is stripped away and the exposed portions of the copper layer  308  and the chromium layer  306  are etched away, as shown in FIG.  7 F. At this step in the process, the structures of switch contact  151  and of switch control line  228 , for example, of FIG. 6 have been formed, as have the plates  200 ,  204 ,  206  and the dielectric layer  202  of capacitor C 1 . 
     In FIG. 7G are shown a patterned photo-resist  334  with a metallized plating seed layer  336  of a titanium base and gold formed thereon, the plating seed layer  336  making electrical contact with the gold plated conductors  330  where holes in the pattern of photo-resist  334  exist, such as to the anchor base  222  of the MEM switch and the upper plate  206  of capacitor C 1 . Then, as shown in FIG. 7H, a further patterned layer  338  of photo-resist is applied over plating seed layer  336  and a patterned layer  340  of gold is plated onto the exposed portions of plating seed layer  336 , such as on portions of switch arm A 1 , anchor base  222  and capacitor C 1 . In FIG. 7I, portions of patterned layer  338  of photo-resist is removed (or all of the photo-resist can be removed and a new patterned layer  338  of photo-resist applied) to expose those portions of the plating seed layer  336  that have not been gold plated  340  and are to be removed, and those portions of layer  336  are then etched away. Finally, all of the photo-resist is removed, such as by plasma washing the diced wafers from substrate  300  in oxygen, to leave the completed structure of MEM switch S 1  and an interconnection  236  between the upper plate  206  of capacitor C 1  and the hinge H 1  of MEM switch S 1  at the anchor  222 ,  226  thereof, as shown in FIG.  7 J. 
     Thus, MEM switch S 1  includes a hinge member  220  formed of the thin plating seed layer  336  which is cantilevered from anchor base  222  and which includes an enlarged contact  224  at the end of hinge member  220  remote from anchor base  222 . Control line  228  underlies the movable end of switch S 1  so that potential applied thereto will generate an attractive electrostatic force, enhanced by the presence of dielectric layer  320 , drawing switch contact  224  downward until it contacts switch contact  151 , thereby closing the switch S 1  circuit. Capacitor C 1  including dielectric layer  202  has its lower plate  200  connected to ground and its upper plate  204 ,  206  connected to one contact of switch S 1  by the bridging interconnect  236 . 
     For MEM switches intended to operate to switch signals in the frequency band of 2-40 Ghz, for example, with  50  ohm input and output transmission lines, the FR signal lines are about 4 mils wide. The arm of the MEM switch is about 2 mils wide and about 4-6 mils long, and is spaced about 2.5 μm from the substrate. The MEM switches actuate at a control voltage of about 20-28 volts in about 12 μsec, and release in about 18 μsec, exhibiting a series capacitance of about 0.015 pf (calculated) when open and a contact resistance in the range of about 1-5 ohms (measured) when closed. 
     FIGS. 8A and 8B show an exemplary spiral inductor  400  of a sort that is conveniently formed on a substrate or an integrated circuit along with MEM switches, capacitors and matrices thereof. Spiral inductor  400  includes a spiral conductor  410  formed on a substrate  412  and having two lead conductors  418 ,  420  connected at opposite ends of spiral conductor  410  and formed on substrate  412 . So that lead conductor  418  may be connected to the end of spiral conductor  410  at the center thereof, spiral conductor  410  has gaps therein through which lead conductor  418  passes. Conductive air bridges  414 ,  416  are spaced apart from the substrate  300  to pass over lead conductor  418  to provide conductive continuity of spiral conductor  410  across such gaps. 
     Spiral inductor  400  is fabricated on a substrate  300  simultaneously with the formation of MEM switches and capacitors thereon (substrate  300  is preferably the same substrate  100  on which are formed capacitors C 1 , C 2 , . . . and MEM switches S 1 , S 2 , . . . ), and utilizing the same processing as described above in relation to FIGS. 7A through 7J. In the following description, layer designations corresponding to those employed in describing the processing of substrate  300  according to FIGS. 7A through 7J will be used, and spiral inductor designations corresponding to those employed in describing spiral inductor  400  according to FIG. 8A will be used. Base layers  306 ,  308 ,  310  of chromium, copper and chromium, respectively are deposited and a layer  320  of silicon nitride is deposited thereon, which layers  310 ,  320  are patterned and etched, as is shown in FIGS. 7A through 7D, to define center lead conductor  418 . Then patterned photoresist layer  326  is applied and patterned gold plating layer  330  is deposited on substrate  300  followed by the stripping of the photoresist  326  and the etching away of base layers  306 ,  308 ,  310 , as shown in FIGS. 7E through 7F, to form spiral conductor  410  having gaps therein and lead conductors  418 ,  420 . Next, removable patterned photoresist  334  is applied, in particular to fill in the gaps in spiral conductor  410  and cover over center lead conductor  418 , and a plating seed layer  336  is deposited thereover followed by application of a further patterned photoresist  338  and the deposit of a plated gold conductor  340  thereon, as shown in FIGS. 7G through 7I, to form the conductors of conductive air bridges  414 ,  416 . Finally, the photoresist layers  334 ,  338  and portions of the seed layer  336  are removed leaving the air bridges  414 ,  416  spaced apart from substrate  300  and conductor  418 , thereby providing a conductive connection across the gaps in spiral conductor  410  and over the center lead conductor  418 , all on the same substrate with MEM switches S 1 , S 2 , . . . and capacitors C 1 , C 2 , . . . and other similar MEM switches and capacitors. 
     FIG. 9 is an exemplary variable frequency oscillator  426  of a sort suitable for use as the local oscillators  26 ,  36  of FIG. 2, above. Variable frequency oscillator  426  includes an amplifier  440  having a gain greater than unity over the range of desired oscillation frequencies. Frequency-determining resonant circuit  430  includes switchable capacitance matrix  450 , which is, for example, of like form and operation to capacitance matrix  50  described above, and which is coupled in circuit with inductance L 4  to form resonant circuit  430  therewith. Resonant circuit  430  is coupled to the output and input terminals of amplifier  440  so that amplifier  440  will oscillate at the resonant frequency of resonant circuit  430 , which frequency is determined by the inductance of inductor L 4  and the capacitance of switchable capacitance matrix  450 . Thus, by changing the various control signals VO to the various MEM switches of switchable capacitance matrix  450 , those MEM switches are selectively opened and closed thereby to change the capacitance of switchable capacitance matrix  450  and, therefore, the frequency f LO  at which amplifier  440  oscillates to produce controllable frequency signal f LO . 
     FIG. 10 is another exemplary variable frequency oscillator  426 ′ of a sort also suitable for use as the local oscillators  26 ,  36  of FIG. 2, above. Variable frequency oscillator  426 ′ includes an amplifier  440  having a gain greater than unity so as to oscillate at the desired oscillation frequency which is determined by a crystal  442  to which amplifier  440  is coupled. Frequency-determining circuit  430 ′ includes, for example, a switchable programmable ÷N counter  432  of conventional type that receives the frequency signal generated by oscillating amplifier  440  which is divided by a numerical value N to produce the controllable frequency signal f LO . Programmable counter  432  is controlled by digital words produced from memory  434  in response to being addressed by the control signals VC generated by tuning control  42 . I.e. the oscillator frequency control signal VO and the filter tuning control signal VC are the same. Thus, by tuning control  42  generating the various control signals VC that are employed to control the various MEM switches of switchable reactance matrices included in tuning circuits  20 ,  24 ,  30 ,  34  of tuner  10 , tuning control  42  also causes the numerical divisor N of programmable counter  432  to be selected, thereby to also change the controllable frequency signal f LO . 
     While the present invention has been described in terms of the foregoing exemplary embodiments, variations within the scope and spirit of the present invention as defined by the claims following will be apparent to those skilled in the art. For example, although the array of capacitors C 1 , C 2 , C 3 , C 4 , C 5  of FIG. 4 are shown as five capacitors connected in parallel, any combination of series and parallel connections of any number of capacitors appropriate to provide the desired capacitance values for a particular application is satisfactory. The depositions of the various materials and layers in the formation of a MEM switch capacitor array may be formed of suitable conductive materials, such as copper, aluminum, gold, silver, as metals or as inks to be fired, applied by suitable processes, such as sputtering, vacuum deposition, plating, electroplating, thin-film techniques, and the like, with or without the use of seed layers of titanium, chromium, gold or other suitable material. Similarly, the capacitance matrix, inductance matrix and the MEM switches may be formed on any suitable substrate, such as ceramic, alumina, silicon, silicon-on-sapphire, gallium arsenide and the like. 
     Spiral inductors  400  may be rectangular or helical or elliptical and need not be substantially square in shape as illustrated in FIG.  8 A. Further, it is noted that the conductive air bridges  414 ,  416  of spiral inductor  400  may include plating seed layer  336  and plated gold layer  340  as described above, in which case they are similar to switch arm  224 , or they may include plating seed layer  336  and omit plated gold layer  340 , in which case they are similar to flexible hinge member  220 . 
     In addition, resistors can be formed on substrate  300  along with MEM switches, capacitors, and/or inductors, from the chromium layer  306  which can be patterned and etched to form a straight, serpentine or other shaped resistor. To this end, in relation to FIG. 7F, the exposed copper layer  308  is etched away to expose chromium layer  306 . An additional photomask step is performed to define on chromium layer  306  the pattern of the desired resistors, such as by ion beam milling or chemical etching. These resistors can be formed, for example, in available open areas between the gold-plated conductor segments. Alternatively, a titanium or nichrome layer could replace the base chromium layer  306  in which resistors are to be formed. In addition, resistors could be defined by deposition of cermet resistance material prior to depositing the base layer  306  which cermet resistors are connected in circuit by the gold-plated conductors formed by the process described hereinabove. Any of these alternatives are compatible with the processing described in relation to FIGS. 7A through 7J and require, at most, an additional photomasking step. 
     In addition, the frequencies to which the respective tuning circuits and/or oscillators of a tuner are tuned may be varied to accommodate automatic frequency control, cable TV system carrier offsets and the like by employing MEM switches to switch additional capacitors and/or inductors therein, or alternatively, for example, by a fine-tuning circuit employing a small voltage-variable capacitance, such as a varactor diode. 
     The switchable tuning matrices according to the present invention may find application in tuners of all types, and in the oscillators, signal processors, modulators and demodulators, transmitters and receivers, and the like employed therein.