On-Chip Integrated Solid-State Micro-Supercapacitor

Fol­low­ing the trend of elec­tron­ic device minia­tur­iza­tion, on-chip inte­grat­ed sol­id-state micro-super­cap­caitors (MS) were fab­ri­cat­ed based on ver­ti­cal­ly aligned car­bon nanofibers (VAC­N­Fs) as elec­trode mate­ri­als and poly­mer­ic gel elec­trolyte as the sol­id elec­trolyte. The VAC­N­Fs were grown at 390 °C and 550 °C tem­per­a­ture on inter­dig­i­tat­ed micro-pat­terns, where the dimen­sions of the dig­its were kept the same but the gap between the dig­its var­ied from 10–100 μm. A max­i­mum capac­i­tance of 1 mF/​cm² and 0.53mF/cm² (com­bined foot­print area of dig­its and gaps) were mea­sured for devices with CNFs grown at 390 °C and 20 μm gap, for 550 °C and 10 μm gap, respec­tive­ly. These capac­i­tances are an order of mag­ni­tude high­er than the one for sol­id dielec­tric based sil­i­con trench­es capac­i­tors. The low tem­per­a­ture MS show an inverse capac­i­tance rela­tion with the gap size where­as high tem­per­a­ture shows ran­dom behav­ior. High char­ac­ter­is­tic fre­quen­cies at 45° phase angle are 114 Hz for 100 μm gap and 142 Hz 30 μm gap for 390 °C and 550 °C tem­per­a­tures. A mod­el for the inter­dig­i­tat­ed capac­i­tors was devel­oped and the results showed that by elim­i­nat­ing the cur­rent col­lec­tor resis­tances the char­ac­ter­is­tic fre­quen­cies can be increased to 965 Hz and 866 Hz from 67 Hz and 127 Hz for 10 μm gap pat­terns for 390 °C and 550 °C tem­per­a­tures. The entire fab­ri­ca­tion was done using CMOS com­pat­i­ble process­es thus enabling inte­gra­tion direct­ly on active CMOS chip.