Fig. 3
From: Direct writing of anodic oxides for plastic electronics
Multilayer capacitors fabricated by local anodisation. a Schematic of multilayer structure and corresponding STEM image, highlighting the high precision and reproducibility of the anodisation process down to nm-size. Scale bar: 50 nm b Each layer increases the capacitance linearly until a value of 4.2 µF cm−2 is achieved for six layers. No significant influence of the substrate (50 µm PEN, 1.4 µm PET, and borosilicate glass) is observed. The increase matches well with theoretical predictions (solid blue line) were an oxide thickness of 12 nm and a dielectric constant of εr = 9 is assumed (see SI for details). This leads to an increase of 650 nF cm−2 per layer. c Impedance data show a linear increase in capacitance and the same shape for all number of layers. The dielectric loss tangent is independent on the number of layers. Dotted lines are for samples prepared on glass, solid lines represent flexible devices on PEN. d High and low pass filters from anodically printed resistors and multilayer capacitor structures. Here, a resistor of 933 Ω and a capacitance of 41.9 nF is used. Measurements (black and red points) agree excellently with simulation (solid lines, see SI for details). e Comparison of capacitance per area and leakage current density with literature.51,58-68 Our multilayer capacitors (red symbols) reach record-high capacitance of 4.2 µF cm−2 at sub-10 nA cm−2 leakage current levels
