Ultra-Thin Capacitors based on Carbon nanofibers with Ultra-High Capacitance Density

In this paper, we present the cur­rent state-of-the-art tech­nol­o­gy of sol­id-state capac­i­tors based on car­bon nanofibers (CNFs). Tak­ing advan­tage of the large 3D sur­face fea­tured by ver­ti­cal­ly aligned and tight­ly spaced car­bon nanofibers direct­ly grown on the capac­i­tor’s elec­trode, capac­i­tance den­si­ties in excess of 650 nF/​mm² have been achieved at a pro­file height of only 7 μm, when employ­ing medium‑k field dielec­tric mate­ri­als such as HfO₂ and Al₂O₃ , to form the MIM-like capac­i­tors. The inte­grat­ed capac­i­tors were fab­ri­cat­ed on high-resis­tive Si sub­strate, while employ­ing ful­ly CMOS com­pat­i­ble process­es. For the devices with high­est capac­i­tance den­si­ty, the leak­age cur­rents are typ­i­cal­ly below 0.01 nA/​nF at 1V, while sus­tain­ing volt­ages up to 6 V as well as very good tem­per­a­ture and volt­age sta­bil­i­ty. For the largest devices, the equiv­a­lent series resis­tance (ESR) and induc­tance (ESL) are as low as 60 mΩ and 6 pH, respec­tive­ly, as well as very good tem­per­a­ture and volt­age sta­bil­i­ty. The results of the exten­sive DC and RF char­ac­ter­i­za­tions strong­ly sup­port the poten­tial for CNF-based sol­id-state capac­i­tors to com­pete with estab­lished high capac­i­tance den­si­ty tech­nolo­gies and are suit­able both in inte­grat­ed on-chip solu­tions as well as in dis­crete elec­tron­ic appli­ca­tions at a min­i­mal com­po­nent volume.