in the following description , numerous specific details are set forth to clearly describe various specific embodiments disclosed herein . one skilled in the art , however , will understand that the presently claimed invention may be practiced without all of the specific details discussed below . in other instances , well known features have not been described so as not to obscure the invention . in the following rf switches with phase change materials are referred to as rf - pcm switches . referring now to fig1 a and 1b , two different four - terminal rf - pcm switches are shown . the rf - pcm switch shown in fig1 a is designed with a vertical geometry between the rf transmission lines . the rf - pcm switch shown in fig1 b is designed with a parallel geometry between the rf transmission lines . the rf - pcm switch shown in fig1 a has a first rf transmission line 12 , which is electrically connected to a first conductor 22 . the first conductor 22 is also electrically connected to a top electrode 16 , which functions as a switch control , and is electrically connected to the pcm 20 . the pcm is formed on an insulator 26 . a second conductor 24 is connected to the pcm 20 , and separated from the first conductor 22 by the pcm 20 . the second conductor 24 is electrically connected to a bottom electrode 18 , which along with the top electrode 16 functions as the switch control . the second conductor 24 is also electrically connected to a second rf transmission line 14 . the rf - pcm switch may be built on a substrate 34 . the rf transmission lines may be also used to transmit signals other than rf signals . to switch the rf - pcm switch of fig1 a , a current pulse may be applied from the top 16 electrode to the bottom 18 electrode , thereby passing through the pcm 20 . the current pulse may have a pulse width of less than a microsecond . the current pulse changes the pcm 20 from an amorphous high resistance material to a crystalline low resistance state . when in a crystalline low resistance state , the pcm 20 allows an rf signal to be transmitted from the first rf transmission line 12 to conductor 22 , then through the pcm 20 and through the conductor 24 to the second rf transmission line 14 . to prevent the rf signals from transmitting through the top electrode 16 or the bottom electrode 18 , the top electrode 16 is connected to rf blocking inductor 17 , and the bottom electrode 18 is connected to rf blocking inductor 19 to block rf signals . also , because the first rf transmission line 12 and the top electrode 16 are electrically connected , to block any direct current ( dc ) on the top electrode 16 from transmission on the first rf transmission line 12 , the first rf transmission line 12 is connected to dc blocking capacitor 30 . similarly , because the second rf transmission line 14 and the bottom electrode 18 are electrically connected , to block any dc on the bottom electrode 18 from transmission on the second rf transmission line 14 , the second rf transmission line 14 is connected to dc blocking capacitor 32 . the rf - pcm switch may be fabricated on a substrate 34 , which may be silicon ( si ), silicon germanium ( sige ), silicon carbide ( sic ), sapphire , pyrex , gallium arsenide ( gaas ), or iii - v compounds such as gan , inas , insb , and inp . the first and second rf transmission lines 12 and 14 , and the top and bottom electrodes 16 and 18 may be formed from any metal such as aluminum ( al ), cooper ( cu ), or gold ( au ). the insulator 26 is preferably a low - k dielectric insulator , such as silicon dioxide ( sio 2 ), silicon nitride ( si 3 n 4 ), or benzo - cyclo - butene ( bcb ), to reduce any parasitic capacitive coupling between the first and second rf transmission lines 12 and 14 . other appropriate materials for insulator 26 are polyimide , and polymethylglutarimide ( pmgi ). the first and second conductors 22 and 24 can be titanium nitride ( tin ), tungsten ( w ) or any other metal that doesn &# 39 ; t deform at high temperature and that doesn &# 39 ; t form an alloy with the phase - change material ( pcm ). the rf - pcm switch shown in fig1 b is similar to the rf - pcm switch of fig1 a ; however , the rf - pcm switch shown in fig1 a is designed with a vertical geometry between the rf transmission lines , while the rf - pcm switch shown in fig1 b is designed with a parallel geometry between the rf transmission lines . the rf - pcm switch of fig1 b has a first rf transmission line 42 , which is electrically connected to pcm 50 . a second rf transmission line 44 is electrically connected to pcm 50 , but is not electrically connected to the first rf transmission line 42 . a top electrode 46 is connected to conductor 52 , and the conductor 52 is connected to the pcm 50 . the pcm 50 is also electrically connected to conductor 54 to electrically connect the pcm 50 to the bottom electrode 48 . the rf transmission lines 42 and 44 and the pcm 50 may be formed on insulator 56 , which along with bottom electrode 48 may be formed on substrate 64 . to switch the rf - pcm switch of fig1 b , a current pulse may be sent from the top electrode 46 to the bottom electrode 48 electrode thereby passing through the pcm 50 . the current pulse may have a pulse width of less than a microsecond . the current pulse changes the pcm 50 from an amorphous high resistance material to a crystalline low resistance state . when in a crystalline low resistance state , the pcm 50 allows an rf signal to be transmitted from the first rf transmission line 42 to the second rf transmission line 44 . to prevent the rf signals from transmitting via the top electrode 46 or the bottom electrode 48 , the top electrode 46 is connected to an rf blocking inductor 17 . the bottom electrode 48 is also connected to an rf blocking inductor similar , such as rf - blocking inductor 19 shown in fig1 a to block rf signals . to block any dc on the top electrode 46 from being transmitted on the first rf transmission line 42 , the first rf transmission line 42 is connected to dc blocking capacitor 60 . similarly , to block any dc on the bottom electrode 48 from being transmitted on the second rf transmission line 44 , the second rf transmission line 44 is connected to dc blocking capacitor 62 . the rf - pcm switch may be fabricated on a substrate 64 , which may be silicon ( si ), silicon germanium ( sige ), silicon carbide ( sic ), sapphire , pyrex , gallium arsenide ( gaas ), or iii - v compounds such as gan , inas , insb , and inp . the first and second rf transmission lines 42 and 44 , and the top and bottom electrodes 46 and 48 may be formed from any metal such as aluminum ( al ), cooper ( cu ), or gold ( au ). the insulator 56 is preferably a low - k dielectric insulator , such as silicon dioxide ( sio 2 ), silicon nitride ( si 3 n 4 ), or benzo - cyclo - butene ( bcb ), to reduce any parasitic capacitive coupling between the first and second rf transmission lines 42 and 44 . other appropriate materials for insulator 56 are polyimide , and polymethylglutarimide ( pmgi ). the first and second conductors 52 and 54 can be titanium nitride ( tin ), tungsten ( w ) or any other metal that doesn &# 39 ; t deform at high temperature and that doesn &# 39 ; t form an alloy with the phase - change material ( pcm ). the phase - change materials ( pcms ) 20 and 50 may be ge x te 1 - x , ge x sb y te z , or their derivatives . measurements of sheet resistance of ge 0 . 16 sb 0 . 24 te 0 . 6 and ge 0 . 4 te 0 . 6 pcm materials have shown a phase change from an amorphous high resistance state to a crystalline low resistance state with a 106 : 1 resistance ratio between the high resistance and the low resistance . the sheet resistance of the crystalline state of pcm may be 100 ω / sq for 100 nm thick gete and 82 ω / sq for 200 nm thick gesbte . important for switch applications , it has been shown that gesbte digital - pcm cells fabricated with a 190 nm diameter can successfully have 10 million read / write cycles , and be switched with a current pulse 0 . 5 ma . a rf - pcm switch with pcm cells of approximately 40 μm 2 may be designed to deliver a resistance in the r - set state of approximately 1ω . gete - based digital pcm cells with pcm cells having approximately a 0 . 3 μm diameter may have a resistance in the r - set state of 20ω . in this configuration the ratio of the resistance in the r - reset state to the resistance in the r - set state is approximately 105 , which allows rf - pcm switches to be designed with a low on resistance ( ron ), a high off resistance ( roff ), and a high ron / roff ratio . for example , a rf - pcm switch with 2 μm 2 pcm switch may have a resistance in the r - set state of & lt ; 1ω and a reset / set resistance ratio of 105 : 1 . the maximum needed voltage and current for switching the pcm from r - set to r - reset may be 3 volts and ˜ 500 ma , respectively . fig2 a shows a schematic of an equivalent circuit 70 for an rf - pcm switch and its simulated rf insertion loss at the set state and rf isolation at the reset state . an rf - pcm switch may be simulated with a resistor 72 and a capacitor 74 to model parasitic capacitance . the rf insertion loss and isolation was simulated for an rf - pcm switch with a r - set resistance of 10 ω / sq and a contact resistance of 15 ω · μm between the conductors 22 , 24 , or 52 , 54 and the pcm 20 or 50 . an rf insertion loss s21 set of 0 . 1 - 0 . 2 db and an rf isolation s21 reset of 25 db or better can be achieved up to 100 ghz . the rf isolation result is mainly due to the parasitic capacitive coupling though the substrate . the rf insertion loss and isolation may also be traded off , one for the other , in rf - pcm switch designs . fig2 a shows the r - reset for a pcm configuration with 5 × 10 4 ω / sq and for a pcm configuration with 10 5 ω / sq . fig2 b shows the simulated rf s21_set insertion loss of an rf - pcm switch for different configurations of the pcm and a contact resistance of 15 ω · μm . the contact resistance is the resistance between a conductor , such as conductor 22 , 24 , 52 , or 54 , and the pcm . the pcm configurations shown in fig2 b include curves for r - set equal to 1 ω / sq , 5 ω / sq , 10 ω / sq , and 20 ω / sq from 0 to 100 ghz . rf - pcm switches can be integrated with conventional semiconductor rfic and mmic processes , enabling reconfigurable rfics and mmics . the semiconductor materials used for the substrate 34 and 64 for integration into rfics and mmics may include si , sige , and iii - v compounds such as gan , inas , insb , and inp . the device technologies that may be integrated include fets and bipolar transistors . the rf - pcm switches may also be integrated with resistors ( r ), inductors ( l ), and capacitors ( c ). integrating the rf - pcm switches with other circuit elements allows the circuits of passive elements , such as l , r , c elements , and active circuits , such as fets or bipolar transistors or other such elements , to be reconfigurable . for example , fig3 a and 3b show filter schematics with lc lumped elements and rf - pcm switches integrated together . the reconfigurable filter shown in fig3 c may have its passband reconfigured to be 1 ghz or 2 . 4 ghz , as shown in fig3 d , depending on the r - set and the r - reset status , as shown in fig3 c , of the rf - pcm switches 88 . another aspect of the use of rf - pcm switches is shown in fig3 a . the ability to integrate rf - pcm switches with other circuit elements in a rfic or mmic allows very compact structures and even three dimensional ( 3d ) circuitry . as shown in fig3 a , rf - pcm switches 80 and other circuitry , such as capacitors , inductors , resistors , and transistors may be integrated on one circuit plane 82 . the circuit plane 80 may be a substrate , a rfic , a mmic , or a circuit board with the integrated rf - pcm switches 80 and other circuitry . other rf - pcm switches 84 and other circuitry , such as capacitors , inductors , resistors , and transistors may be integrated on another circuit plane 86 , which also may be a substrate , a rfic , a mmic , or a circuit board . the rf - pcm switches allow the circuitry to be reconfigurable . by stacking circuit planes on one another and connecting the circuitry on circuit plane 82 to the circuitry on circuit plane 86 with conductors 85 between the circuit planes , a very compact three dimensional reconfigurable circuit may be realized , as shown in fig3 a . the conductors 85 between the circuit planes 82 and 86 may be metal vias . fig4 a shows a reconfigurable low - noise amplifier consisting of rf - pcm switches 90 , 92 , 94 and 96 and gan field effect transistors ( fets ) in a mmic layout . the two gan lnas , shown in fig4 a may be configured to improve the third order intercept point ( oip3 ) to 51 dbm and the spurious signal performance to less than 98 dbc at a pin of − 10 dbm up to 18 ghz , which enables high dynamic range signal detection immune to jamming signals . fig4 b shows an example layout of a gan mmic amplifier with a reconfigurable output matching network 100 using rf - pcm switches 102 . the fabrication process flow for an rf - pcm switch may be made to be similar to a tantalum nitride ( tan ) mmic resistor process with some modifications . the process for fabricating a rf - pcm switch is the following . 1 . lift - off metal - 1 to form a bottom dc electrode and an rf transmission line , 3 . pattern an opening # 1 in the dielectric layer around to be formed rf - pcm switches , 4 . lift - off an adhesion metal pillar ( tungsten ( w ) or tiw ) on phase change material ( pcm ), 6 . pattern an opening # 2 in the dielectric layer # 2 to the pcm , 8 . lift - off metal - 2 for the top dc electrode and rf transmission line . in summary , the disclosed rf - pcm switches based on pcm materials such as ge x te 1 - x , ge x sb y te z , or their derivatives enable reconfigurable rf functions in rfics , mmics , and passive devices such as single - pole - double - throw ( spdt ) switches , phase shifters , and filters . the disclosed rf - pcm switches are binary ( on or off ). if necessary , the rf - pcm switches can be designed with multi - bit switches , especially for phase - shifter , phase - shift - key ( psk ), and quadrature - amplitude - modulation ( qam ) applications . having now described the invention in accordance with the requirements of the patent statutes , those skilled in this art will understand how to make changes and modifications to the present invention to meet their specific requirements or conditions . such changes and modifications may be made without departing from the scope and spirit of the invention as disclosed herein . the foregoing detailed description of exemplary and preferred embodiments is presented for purposes of illustration and disclosure in accordance with the requirements of the law . it is not intended to be exhaustive nor to limit the invention to the precise form ( s ) described , but only to enable others skilled in the art to understand how the invention may be suited for a particular use or implementation . the possibility of modifications and variations will be apparent to practitioners skilled in the art . no limitation is intended by the description of exemplary embodiments which may have included tolerances , feature dimensions , specific operating conditions , engineering specifications , or the like , and which may vary between implementations or with changes to the state of the art , and no limitation should be implied therefrom . applicant has made this disclosure with respect to the current state of the art , but also contemplates advancements and that adaptations in the future may take into consideration of those advancements , namely in accordance with the then current state of the art . it is intended that the scope of the invention be defined by the claims as written and equivalents as applicable . reference to a claim element in the singular is not intended to mean “ one and only one ” unless explicitly so stated . moreover , no element , component , nor method or process step in this disclosure is intended to be dedicated to the public regardless of whether the element , component , or step is explicitly recited in the claims . no claim element herein is to be construed under the provisions of 35 u . s . c . sec . 112 , sixth paragraph , unless the element is expressly recited using the phrase “ means for . . . ” and no method or process step herein is to be construed under those provisions unless the step , or steps , are expressly recited using the phrase “ comprising the step ( s ) of . . . .”