Carbon nanomaterial-based interconnects, integrated capacitors and supercapacitors

The con­stant mini­atur­iz­a­tion and steady per­form­ance improve­ment of elec­tron­ics devices have gen­er­ated innov­at­ive ideas such as inter­net of thing (IoT), which also includes devices with integ­rated energy sources.

The high per­form­ance is con­ceived by the high dens­ity of the devices on a chip lead­ing to a high dens­ity of inter­con­nects, to con­nect these devices to out­side world. Since the size and the pitch of the inter­con­nects have decreased, the cur­rent dens­ity in inter­con­nect has increased, pos­ing chal­lenges on the exist­ing cop­per pil­lar inter­con­nect tech­no­logy, such as inter­metal­lic com­pound form­a­tion and elec­tro-migra­tion res­ult­ing in open cir­cuit. The chal­lenges are fore­cas­ted to increase on fur­ther down scal­ing due to bridging of the solder between pil­lars. Moreover, the envir­on­ment­al pol­lu­tion and the threat of van­ish­ing of fossil fuel have promp­ted to find cheap and effi­cient altern­at­ing energy sources and energy stor­age systems.

Car­bon nan­o­ma­ter­i­als such as car­bon nan­otubes and car­bon nan­ofibers have unpre­ced­en­ted elec­tric­al, mech­an­ic­al and thermal prop­er­ties, high res­ist­ance to cor­ro­sion and high sur­face area have been pro­posed for the solu­tion of above men­tioned challenges.

In this thes­is, ver­tic­ally aligned car­bon nan­ofibers (VACN­Fs) have been grown by dir­ect cur­rent plasma enhanced chem­ic­al vapor depos­ition (dc-PECVD) at com­ple­ment­ary met­al oxide semi­con­duct­or (CMOS) com­pat­ible tem­per­at­ures for on chip applic­a­tion. In addi­tion, the cata­lyst to grow VACN­Fs is depos­ited using innov­at­ive low-cost polymer–Pd nan­o­hybrid col­loid­al solu­tions by an effect­ive coat­ing method.

Also, due to con­trol­lable DC beha­vi­or and good mech­an­ic­al rein­force­ment prop­er­ties of solder-CNFs, the sol­der­able micro-bumps of VACN­Fs have been shown to poten­tially yield the accept­able elec­tric­al res­ist­ances. Moreover the CNFs bumps can be made in sub­micron size range, which can com­ply with fur­ther down scal­ing of inter­con­nect. In addi­tion, advanced CNF based adhes­ives, pro­duced by coat­ing CNFs with low tem­per­at­ure poly­mers, have been invest­ig­ated as altern­at­ing aniso­trop­ic con­duct­ing film for aniso­trop­ic con­nec­tion, using a thermo-com­pres­sion bond­ing. The shear­ing strength of the bon­ded chip qual­i­fies the MIL-STD-883 stand­ards of bond­ing strength in micro­elec­tron­ics devices.

Fur­ther, super­ca­pa­cit­or are the energy stor­age devices hav­ing high energy dens­ity, and high power dens­ity due to quick intake and release of charges and long cycles life of about 1 mil­lion. On-chip integ­rated sol­id-state par­al­lel-plate capa­cit­or and super­ca­pa­cit­or are demon­strated based on VACN­Fs. The pre­lim­in­ary capa­cit­ance of the par­al­lel-plate capa­cit­or and super­ca­pa­cit­or are 10–15 nF/​mm² and 10 μF/​mm², respect­ively. The pro­file of par­al­lel plate capa­cit­or is below 10 micro­met­ers, which enables integ­ra­tion even in advance 2.5 and 3D het­ero­gen­eous pack­aging. The on-chip capa­cit­or can work as decoup­ling capa­cit­or to resolve the energy fluc­tu­ation related issues and also power up devices on the chip.

Then, along with oth­er prop­er­ties, high aspect ratio and ease of fab­ric­a­tion, the car­bon nan­otubes (CNTs) are con­sidered as poten­tial elec­trode mater­i­al for future high per­form­ance super­ca­pa­cit­or. The CNTs are dir­ectly grown on elec­tro­spun CNFs giv­ing the spe­cif­ic capa­cit­ance of 92 F/​g, i.e. twice the capa­cit­ance of bare CNFs. Finally, a com­plete energy stor­age device coin-cell super­ca­pa­cit­or is made by dir­ectly grow­ing VACN­Fs on the cur­rent col­lect­or and the capa­cit­ance is 15 times high­er than the capa­cit­ance without CNFs. Thus such super­cap­cait­or is suit­able to be com­bined with har­vester to col­lect energy to the level of oper­at­ing power of the devices and can provide dur­able solu­tion to the fre­quent change of bat­tery in the devices moun­ted at sens­it­ive or air­borne locations.