Contribution of electrodes and microstructures to the electrical properties of Pb(Zr 0.53 Ti 0.47 )O 3 thin film capacit
- PDF / 1,827,214 Bytes
- 8 Pages / 576 x 792 pts Page_size
- 86 Downloads / 165 Views
O. Auciello Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695-7907, and MCNC, Electronics Technology Division, Research Triangle Park, North Carolina 27709-2889 (Received 2 May 1994; accepted 26 July 1994)
Pb(Zr0.53Tio.47)03 (PZT) thin film capacitors have been fabricated with four electrode combinations: Pt/PZT/Pt/SiO 2 /Si, RuO 2 /PZT/Pt/Si0 2 /Si, RuO 2 /PZT/RuO 2 /SiO 2 /Si, and Pt/PZT/RuO 2 /SiO 2 /Si. It is shown that polarization fatigue is determined largely by the electrode type (Pt vs RuO 2 ), and microstructure has only a second-order effect on fatigue. If either the top or bottom electrode is platinum, significant polarization fatigue occurs. Fatigue-free capacitors are obtained only when both electrodes are RuO 2 . In contrast, the bottom electrode is found to have a major effect on the leakage characteristics of the PZT capacitors, presumably via microstructural modifications. Capacitors with bottom RuO 2 electrodes show high leakage currents (J = 10~ 3 -10~ 5 A/cm 2 at 1 V) irrespective of the top electrode material. Capacitors with Pt bottom electrodes have much lower leakage currents (J = 10~8 A/cm 2 at 1 V) irrespective of the top electrode material. At low voltage, the I-V curves show ohmic behavior and negligible polarity dependence for all capacitor types. At higher voltages, the leakage current is probably Schottky emission controlled for the capacitors with Pt bottom electrodes.
I. INTRODUCTION Research on the integration of ferroelectric thin films into microelectronic devices has increased dramatically in the past few years. Possible applications include ferroelectric nonvolatile memories (NVFRAM's), dynamic random access memories (DRAM's), and electrooptic devices. The Pb(Zr v Tii-^)O 3 system (referred to as PZT in this paper) has been the subject of intensive investigation for use in nonvolatile memories.1'2 Work on PZT films for nonvolatile memories has progressed significantly, and attention is now focused on the long term properties of PZT thin film capacitors. Such properties include fatigue, retention, imprint, dc leakage, and dielectric breakdown. Several groups have shown that the problem of fatigue can be overcome by using oxide electrodes such as RuO 2 , LSCO (La!- x Sr x CoO 3 ), or SrRuO3.3"8 The electrode type was also shown to have an effect on the leakage and I-V characteristics of the ferroelectric capacitors.9-10 The unique feature of this work is that a set of capacitors with various top and bottom electrode combinations has been tested. By looking at these combinations much can be learned about the role of the electrode material in controlling a particular property. We present hysteresis, fatigue, dc leakage, and I-V results on capacitors with four different 2968
J. Mater. Res., Vol. 9, No. 11, Nov 1994
electrode combinations. The effects of electrode type and film microstructure on each of these properties are discussed. Implications in terms of fatigue and leakage mechanisms are also discussed. II. EXPE
Data Loading...
