Ultrananocrystalline Diamond Films With Optimized Dielectric Properties For Advanced RF MEMS Capacitive Switches

Abstract

An efficient deposition process is provided for fabricating reliable RF MEMS capacitive switches with multilayer ultrananocrystalline (UNCD) films for more rapid recovery, charging and discharging that is effective for more than a billion cycles of operation. Significantly, the deposition process is compatible for integration with CMOS electronics and thereby can provide monolithically integrated RF MEMS capacitive switches for use with CMOS electronic devices, such as for insertion into phase array antennas for radars and other RF communication systems.

1 . A process for use in fabricating a radio frequency (RF) microelectromechanical systems (MEMS) capacitive switch, comprising the steps of:
 providing a bottom electrode; and   layering ultrananocrystalline diamond (UNCD) on the bottom electrode to provide a multilayered UNCD dielectric film having electrical leaky characteristics on the bottom electrode for fast dielectric charging and discharging and rapid recovery of the RF MEMS capacitive switch.   
     
     
         2 . A process for use in fabricating a RF MEMS capacitive switch in accordance with  claim 1  wherein the layering comprises depositing layers of UNCD by microwave plasma chemical vapor deposition (CVD) with microwave CVD plasma. 
     
     
         3 . A process for use in fabricating a RF MEMS capacitive switch in accordance with  claim 2  including forming a layer of substantially continuous dielectric film with rapid nucleation of UNCD by decreasing hydrogen (H 2 ) content of the microwave CVD plasma. 
     
     
         4 . A process for use in fabricating a RF MEMS capacitive switch in accordance with  claim 2  including increasing hydrogen (H 2 ) content of the microwave CVD plasma to form a high resistivity layer of film with a hydrogen-enriched grain boundary. 
     
     
         5 . A process for use in fabricating a RF MEMS capacitive switch in accordance with  claim 4  including decreasing hydrogen (H 2 ) content of the microwave CVD plasma for dense renucleation of the UNCD for filing in gaps or pinholes between grains and forming a substantially uniform continuous layer. 
     
     
         6 . A process for use in fabricating a RF MEMS capacitive switch in accordance with  claim 2  wherein said microwave CVD plasma comprises argon (A R ), methane (CH 4 ) and hydrogen (H 2 ). 
     
     
         7 . A process for use in fabricating a RF MEMS capacitive switch in accordance with  claim 1  including reducing stress in the film. 
     
     
         8 . A process for use in fabricating a RF MEMS capacitive switch in accordance with  claim 1  including increasing hydrogen (H 2 ) concentration in a grain boundary of an intermediate layer of the dielectric film. 
     
     
         9 . A process for use in fabricating a RF MEMS capacitive switch in accordance with  claim 1  including:
 placing a membrane above the dielectric film; 
 positioning an upper electrode above the membrane; and 
 positioning the RF MEMS capacitive to operate for at least 45 million cycles when driven by a complementary metal-oxide-semiconductor (CMOS) electronic device. 
 
     
     
         10 - 16 . (canceled) 
     
     
         17 . A radio frequency (RF) microelectromechanical (MEMS) switch, comprising:
 a RF MEMS capacitive switch moveable for a switching time from an off position in an off state to an on position in an on state, comprising;
 a bottom electrode comprising metal providing a RF signal path and having an upwardly facing portion; 
 a top electrode comprising a RF ground and a direct current (DC) ground; 
 a moveable metallic membrane less than 0.4 μm thick, said membrane being spaced from said bottom electrode by an air gap ranging from about 2 microns to about 10 microns resulting in a substantially insignificant capacitance relative to an operating frequency of the switch; 
 a multi-layer dielectric film comprising ultrananocrystalline diamond (UNCD) including:
 a bottom UNCD layer covering a substantial area of the upwardly facing portion of the bottom electrode; 
 an intermediate UNCD layer on said bottom UNCD layer for providing a high resistivity film, said intermediate UNCD layer having a hydrogen enriched grain boundary for enhanced charge conduction; 
 an upper UNCD layer on the intermediate UNCD layer; and 
 the dielectric film comprising a substantially continuous UNCD film substantially without pinholes; 
 
 said membrane contacting said multi-layer dielectric film when a voltage ranging from about 30 volts to about 50 volts is applied across the top and bottom electrodes in the on state; and 
 said multi-layer dielectric film discharging and leaking accumulated charges and said RF MEMS capacitive switch recovering within 80 μsec. 
   
     
     
         18 . An RF MEMS switch in accordance with  claim 17  wherein said RF MEMS switch is designed to operate for over 100 billion cycles. 
     
     
         19 . An RF MEMS switch in accordance with  claim 17  wherein said multi-layer dielectric comprises an ultra thin UNCD dielectric film ranging from 200 nm to 300 nm. 
     
     
         20 . An RF MEMS switch in accordance with  claim 17  wherein:
 the membrane comprises molybdenum (Mo); 
 the bottom electrode selected from the group consisting of bottom electrode comprising tungsten (W) and a stack comprising chromium (chrome) (Cr), tungsten and chromium; 
 the bottom electrode is positioned on a substrate selected from the group consisting of silicon on sapphire (SOS) and a silicon wafer; and 
 the RF MEMS capacitive switch is monolithically integrated with a complementary metal-oxide-semiconductor (CMOS) electronic device.