Analysis on interface layer between Pt electrode and ferroelectric layer of solution-processed PZT capacitor
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Analysis on interface layer between Pt electrode and ferroelectric layer of solution-processed PZT capacitor Thanh V Pham 1, Trinh N Q Bui 2, Tue T Phan1, Takaaki Miyasako2, Eisuke Tokumitsu2,3, Tatsuya Shimoda1,2 1
Japan Advanced Institute of Science and Technology, 1-1 Asahidai, Nomi, Ishikawa 9231292, Japan. 2 Japan Science and Technology Agency, ERATO, Shimoda Nano-Liquid Process Project, 25-3 Asahidai, Nomi, Ishikawa 923-1211, Japan. 3 Precision and Intelligence Laboratory, Tokyo Institute of Technology, 4259-R2-19 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan. ABSTRACT Pt/Pb(Zr0.4Ti0.6)O3 (PZT)/Pt capacitors were prepared by the sol-gel technique and their electric properties were analyzed. The asymmetry of polarization-electric field (P-E) and capacitor-voltage (C-V) curves exhibits existence of an interface layer (dead-layer) between top Pt electrode and PZT thin film. By conducting temperature dependant measurement, the Pt/PZT/Pt capacitor was confirmed to be Schottky emission conduction. In addition, the Schottky barrier height of Pt/PZT contact was calculated to be 0.67eV. On the basic of a series capacitors model and Schottky contact of Pt/PZT interface, the thickness and the dielectric constant of this dead-layer were estimated to be 6.4 nm and 170, respectively. Moreover, the dielectric constant of 900 was obtained for the real PZT ferroelectric layer. The existence of the dead-layer was also confirmed by the high resolution transmission electron microscopy (HR-TEM) observation and the energy dispersive X-ray (EDX) analysis on PZT ferroelectric layer in the Pt/PZT/Pt structure. Based on EDX analysis result, a 10-nm layer at Pt/PZT contact was suggested to be the deadlayer. INTRODUCTION Ferroelectric thin films (PZT, BST …) have been of great interest for their applications in electronic devices, such as FeRAMs, infrared sensors, etc [1,2]. Some reports showed that an interface layer (dead-layer) exists between electrodes (Pt and SrRuO3) and ferroelectric (PZT, BST…) layers and this dead-layer influences much on electric properties of the ferroelectric capacitors [3-5]. Therefore, this dead-layer forms a parasitic capacitor in series with the real ferroelectric layer. Chen et al estimated thickness and dielectric constant of dead-layer to be 2.8 nm and 42.6 on the Pt/BST/YBa2CuO7 capacitor [3], respectively, based on a series capacitors model, current-voltage (I-V) measurement behavior as the Schottky model and the modified space-charge-limited current model. Larsen et al reported that the ratio of thickness to dielectric constant of dead-layer was from 0.036 to 0.05 nm in the Pt/PZT/Pt capacitors [4]. Moreover, Nguyen et al reported that the thickness of dead-layer was 6.5 nm in the SRO/PZT/SRO capacitor [5]. However, the value of thickness and dielectric constant of dead-layer of a Pt/PZT/Pt capacitor has not been reported yet, although the existence of the dead-layer has been widely suggested.
In this work, PZT thin films were deposited on Pt(111)/Ti/SiO2/Si substrates by the solgel method. The e
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