Preparation of sub-100nm Thickness PZT thin Films with Chemical Solution Deposition Method for low Voltage Operation
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Preparation of sub-100nm thickness PZT thin films with Chemical Solution Deposition method for low voltage operation
Yong Kyun Lee, June Key Lee, Chang Jung Kim, Insook Yi, Ilsub Chung Microelectronics Lab, Material and Device Sector, Samsung Advanced Institute of Technology, P.O. Box 111, Suwon, Korea 440-600 Phone:82-31-280-9336, fax:82-31-280-9349, Email : [email protected]
ABSTRACT PZT thin films with a thickness of 70 nm were successfully fabricated using a modified solution combined with PbTiO3 seed layer. Throughout various approaches, we found that the microstructure of PZT thin film plays an important role in determining the electrical properties such as hysteretic properties and leakage currents, particularly when the thickness is below 100 nm. We modified the precursor system to improve the microstructure in PZT thin film. In addition, we also adopted a thin PbTiO3 seed layer to enhance the initial nucleation density. Finally, we could obtain good electric properties similar to those obtained from 240 nm thick PZT film. The hysteretic properties is excellent enough to operate at a low voltage (2V) for a high density FRAM application. INTRODUCTION PZT is one of the well-known ferroelectric material for the non-volatile memory application due to the high remnant polarization value. A wide variety of preparation techniques have employed to produce PZT thin films. Among these methods, the CSD(chemical solution deposition) process offers several advantages, including low processing temperature, composition control, uniform homogeneity, ease of fabrication over large areas, and low cost.[1-3] Recently, 4Mbit FRAM was successfully fabricated using PZT thin film, in which about 200 nm thick PZT film was applied for 3.3V operation.[4] However, as for the higher density FRAM, it is necessary to reduce the PZT film thickness due to not only the process issue but also the operating voltage. In spite of such requirements, there were only limited efforts addressed to reduce PZT film thickness. Generally, it is hard to fabricate PZT thin film with the thickness below 100nm. Meng et. al. varied thermal annealing route with different single-annealed-layer in thickness from the same precursor solution. They found that the degree of (111) orientation in films increases as the CC1.7.1
thickness of single-annealed-layer decrease. They could make PZT thin film with the thickness of 40 nm, but the hysteretic properties seemed to be very leaky.[5] Soyama et. al. deposited PZT thin films with thickness of 90 nm by increasing the initial nucleation density of PZT precursor gel film using modified sol-gel solutions.[6] Similarly, Wouter et. al. demonstrated a 75 nm thick PZT film using modified CSD solution. In this study, we deposited PZT thin films with the thickness around 100nm, by using three different methods. Firstly, PZT thin films were prepared with a conventional method by just changing the spin-coating parameter and diluting solution concentration.[7] Secondly, we utilized etch-back and wet cleaning technology
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