Intrinsic and extrinsic reliability of a serial connection of capacitors

The on-wafer serial connection of two capacitors (stacked capacitors) is attractive for two reasons: on one hand the intrinsic reliability and especially the immunity against high voltage pulses increases and on the other hand the early fail risk decreases tremendously. The intrinsic and extrinsic reliability of stacked capacitors are demonstrated using the example of a metal insulator metal capacitor (MIMCAP) with Al2O3 dielectric. The intrinsic reliability of a stacked capacitor, where each of the capacitors uses a dielectric of thickness thk, is equal to the intrinsic reliability of a single capacitor with twice the dielectric thickness 2 * thk. The reduction of early fails for a stacked capacitor is a probability effect: if a single capacitor has the probability p to fail early and an early fail of the stacked capacitor is the combination of two single capacitors each of which contains an early fail, then the stacked capacitor fails early with a probability of p2. This basic idea is checked by voltage ramp experiments on single and stacked MIM capacitors, where the single MIM capacitors show besides the intrinsic branch a prominent extrinsic branch.