Breakdown mechanisms in PZT thin film capacitors

Breakdowns of PZT thin film capacitors were demonstrated by applying input signals such as DC bias, square waves, triangular waves, and unipolar pulse. Effects of frequency, capacitor size, and pulse width on breakdown were investigated in order to understand breakdown mechanisms. It was confirmed that impulse breakdown is related to rise time of the input signal in association with charging time of the capacitors and steady-state thermal breakdown, pulse width. Energy stored in the ferroelectric capacitors during hysteretic cycling may be additional thermal breakdown source. Electrode burst was observed which may occur due to thermal breakdown through grain boundaries. In addition to breakdown, a new leakage current test technique for FRAM application was suggested in consideration of transient current of the capacitors. In conclusion, breakdown is more serious and leakage current is less serious in FRAM applications than in DRAM applications. Finally, homogeneous polycrystalline structure or single crystal structure is recommended to minimize electrode burst.