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.