AVS 60th International Symposium and Exhibition
    Thin Film Thursday Sessions
       Session TF+EM+NS+SS-ThA

Paper TF+EM+NS+SS-ThA6
Atomic Layer Deposition of Pb(ZrxTi1-x)O3 Thin Films

Thursday, October 31, 2013, 3:40 pm, Room 104 A

Session: Thin Film: Growth and Characterization II
Presenter: D. Chien, UCLA
Authors: D. Chien, UCLA
T. Kim, UCLA
J. Choi, UCLA
J.P. Chang, UCLA
Correspondent: Click to Email
Lead zirconate titanate at its morphotropic phase boundary composition, Pb(Zr0.52Ti0.48)O3, exhibits strong coupling between electrical and mechanical energies, making it a promising material for piezoelectric MEMS. As MEMS continue to scale down to smaller sizes with more complex topography, the ability to deposit high quality PZT thin film conformally over high aspect ratio 3D structures and surfaces that are not in line-of-sight of deposition sources becomes an enabling factor. Atomic layer deposition (ALD) is a promising method because it is a surface-reaction controlled process based on alternating self-limiting reactions which can obtain superior uniformity and conformality over complex surface structures. Another challenge is to deposit (001) oriented PZT because it has a higher piezoelectric constant than (111) oriented PZT.

In this work, a (100) textured ALD PbTiO3 (PT) seed layer was used to attain (100) oriented PZT on platinized silicon substrates. The PT and PZT thin films were synthesized by depositing alternating layers of PbO, ZrO2, and TiO2 using Pb(TMHD)2, Zr(TMHD)4, and Ti(O.i-Pr)2(TMHD)2 as metal precursors and H2O as the oxidant. The growth sequence consisted of a(Pb-O)-b(Ti-O)-c(Pb-O)-d(Zr-O) where a:b:c:d ratio of local cycles and global cycles were regulated to achieve the desired stoichiometry and thickness, respectively. To tailor the composition of PT and PZT by ALD, the incubation time of depositing one constituent oxide on another on KBr crystal disks was quantified by in-situ FTIR. The IR absorption spectrums of one metal oxide layer deposited on another were acquired after each ALD cycle until specific stretching vibration mode of the target metal oxide was observed to indicate the required incubation time to initiate the target oxide growth. These results were used to guide the design and synthesis of PT and PZT with precise composition control. The stoichiometry and crystallinity of PbTiO3 and PZT films were confirmed by XPS and XRD, respectively.

To assess the feasibility of ALD P(Z)T films for piezoMEMS application, ALD PZT thin films were deposited on ALD PbTiO3 seed layer and fabricated into simple capacitors with platinum as the top electrode. The dielectric and ferroelectric properties of ALD PZT thin films were characterized via CV measurements and PE hysteresis loops, which are sensitive to the composition of PZT. The (100) oriented ALD PZT thin film was poled to attain the desired (001) oriented PZT film, for which the effective transverse piezoelectric coefficient, e31,f, was quantified via the wafer flexure method. The conformality of 15nm ALD PZT films were confirmed over 300nmx700nm hollow Si3N4 cylinders.