Direct Electrical and Mechanical Characterization of Carbon Nanofibers Turf Using a Probe Card and Nanoindentation

Ver­ti­cal­ly aligned car­bon nanofibers (VAC­N­Fs) turf are char­ac­ter­ized elec­tri­cal­ly and mechan­i­cal­ly for prospec­tive on-chip appli­ca­tions. The CNFs turf of 10 microm­e­ter diam­e­ter and 20 microm­e­ter pitch are fab­ri­cat­ed at high tem­per­a­ture (550 °C) and CMOS com­pat­i­ble tem­per­a­tures (390 °C) direct­ly on sil­i­con sub­strates where the num­ber of CNFs per μm² area are 13 and 38 for the respec­tive growth tem­per­a­ture. The elec­tri­cal char­ac­ter­i­za­tion are accom­plished by using kelvin test struc­tures, and a poly­eth­yl­ene neph­tha­late based trans­par­ent probe card con­tain­ing Tita­ni­um and Gold based probe bumps of size 10 microm­e­ter in diam­e­ter and 20 microm­e­ter pitch. The entire prob­ing sys­tem not only have mea­sure­ment pre­ci­sion but also min­i­mizes the risks of dam­age to turf. The trans­mis­sion line mea­sure­ments (TLM)-based mod­el approach is used for the elec­tri­cal char­ac­ter­i­za­tion to de-embed the con­tact resis­tance con­tri­bu­tion and extract the intrin­sic prop­er­ties of a sin­gle CNF. Apply­ing the mod­el to the TLM mea­sure­ments yields a con­duc­tiv­i­ty of 6530 S/​m and 67000 S/​m for a sin­gle CNF grown at 390 °C and 550 °C, respec­tive­ly. The hard­ness and reduced mod­u­lus of fine pitch turf are mea­sured by using nanoin­den­ta­tion tech­nique. The CNFs grown at 390 °C have high­er elas­tic mod­u­lus (0.84–1 MPa) than 550 °C grown CNFs (0.26–0.84 MPa) due to dense growth.