Mist Deposition of Micron-Thick Lead Zirconate Titanate Films
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Mist Deposition of Micron-Thick Lead Zirconate Titanate Films Mark D. Losego and Susan Trolier-McKinstry Materials Research Institute and Materials Science and Engineering Department The Pennsylvania State University, University Park, PA 16802, U.S.A. ABSTRACT A majority of the work published on liquid source misted chemical deposition (LSMCD) has focused on the fabrication of thin ferroelectric films for random access memory (RAM) applications. However, the ability of LSMCD to combine the characteristically good stoichiometry control of a chemical solution deposition process with good film conformality, makes this a desirable technique for other applications, including microactuators and integrated passive components. For these applications, though, LSMCD is limited by its low throughput. This paper describes the feasibility of depositing micron-thick lead zirconate titanate (PZT) films using the LSMCD tool. PZT films of 52/48 composition were deposited on both platinized silicon and platinized alumina substrates. The chamber temperature and the delivery geometry of the LSMCD tool were identified as limiting factors in the rate at which micron-thick samples can be prepared. By switching to a focused nozzle delivery geometry and increasing the chamber temperature from room temperature to 60oC, the total process time for 1 µm thick films can be reduced from 480 min to 90 min. Polarization hysteresis measurements indicated a 75% higher remanent polarization for PZT films deposited on platinized alumina substrates (35 µC/cm2) compared to those deposed on platinized silicon substrates (20 µC/cm2). The polarization loop for the silicon substrate sample was also tilted. These observations are evidence of higher tensile stresses in the PZT films deposited on silicon substrates due to a larger mismatch in the thermal expansion coefficients of the film and the substrate. INTRODUCTION Since the mid-1980s when Budd et al. [1] first demonstrated the utility of chemical solution deposition (CSD) as a method for depositing ferroelectric thin films, CSD has become a common laboratory technique for preparing complex oxide films. Currently, spin-coating and dip-coating are the most commonly used methods for depositing the CSD liquid precursors [2]. However, over the past decade, a new technique has emerged for depositing sol-gel solutions—liquid source misted chemical deposition (LSMCD) [3-7]. In the LSMCD system, a pressurized gas (commonly argon or nitrogen) is used to inertially separate the liquid precursor into a fine aerosol mist consisting of sub-micron sized droplets [6]. A carrier gas under laminar flow then transports this mist through the enclosed LSMCD system to the deposition chamber. (See diagram of LSMCD system in Figure 1.) The mist commonly enters the chamber through a pattern of holes drilled in a stainless steel plate that resembles a showerhead (see Figure 2). Because the mist generation process results in charged mist droplets, an electric field is commonly applied between the showerhead and substrate
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