Ultrananocrystalline Diamond Films with Optimized Dielectric Properties for Advanced RF MEMS Capacitive Switches

A process for fabricating a radio frequency (RF) microelectromechanical switch (MEMS) capacitive switch, comprising the steps of:

• providing a substrate;
• placing a bottom electrode on the substrate;
• depositing layers of ultrananocrystalline diamond (UNCD) thin film on the bottom electrode by microwave chemical vapor deposition (CVD) with a microwave CVD plasma gas comprising argon (Ar), methane (CH4) and hydrogen (H2) to form multilayered UNCD dielectric films including
• depositing a bottom UNCD layer on the bottom electron with H2 flow for rapid nucleation of the UNCD and forming a substantially continuous dielectric film;
• depositing an intermediate UNCD layer on the bottom UNCD layer with a higher H2 flow and forming a higher resistivity film with a hydrogen enriched grain boundary;
• depositing an upper UNCD layer on the intermediate UNCD layer with a lower H2 flow than for the intermediate UNCD layer for dense nucleation of the UNCD to fill in the gaps or pinholes between grains and forming a substantially continuous layer;
• positioning a moveable metallic membrane above the multilayered UNCD dielectric film;
• positioning a top electrode above the membrane;
• and
• forming a long life RF MEMS capacitive switch with the multilayered UNCD dielectric film, membrane, electrodes and substrate so that the RF MEMS capacitive switch is operable for more than 100 billion cycles.

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.