Thin Film Al‐Al2O3‐Al Capacitors With Dielectric Layer Formed at400℃

A comparative study is made of Al 2 O 3 layers formed at 400℃ in molten KNO 3 and Al 2 O 3 formed at room temperature in a common solution of ammonium pentaborate in ethylene glycol. At 400℃ and constant current (0.5 mA/cm 2 ) the linear anodization range is limited to 2.7 V by scintillation and local oxide breakdowns. Nonporous 200 Å thick (0.4 μ F/cm 2 ) oxide layers were produced at 2.0 V (400℃) and 8 V (20℃). Electron diffraction indicated a γ -Al 2 O 3 structure at an anodization temperature of 400℃ and amorphous structure at room anodization temp. The initial values of tan δ were 100   ·   10 − 4   ±   40   ·   10 − 4and 400   ·   10 − 4   ±   200   ·   10 − 4respectively. Capacitance and tan δ measurements during accelerated life test indicated that the films produced at 400℃ are not superior to those formed at room temperature. In both cases a diffusion of metal at the metal-oxide interface seems to be the main ageing mechanism. The internal electrical field measured by the C-V method was unchanged in γ -Al 2 O 3 layers during the life test.