Lanthanide-Assisted Deposition of Strongly Electro-optic PZT Thin Films on Silicon: Toward Integrated Active Nanophotonic Devices J. P. George,* ,†,‡,∥ P. F. Smet, §,∥ J. Botterman, §,∥ V. Bliznuk, ⊥ W. Woestenborghs, †,∥ D. Van Thourhout, ‡,∥ K. Neyts, †,∥ and J. Beeckman †,∥ † Department of Electronics and Information Systems, Ghent University, Sint-Pietersnieuwstraat 41, 9000 Gent, Belgium ‡ Department of Information Technology, Ghent University, Sint-Pietersnieuwstraat 41, 9000 Gent, Belgium § LumiLab, Department of Solid State Sciences, Ghent University, Krijgslaan 281-S1, 9000 Gent, Belgium ∥ Center for Nano- and Biophotonics (NB-Photonics), Ghent University, 9000 Gent, Belgium ⊥ Department of Materials Science and Engineering, Ghent University, Technologiepark 903, B-9052 Zwijnaarde, Belgium *S Supporting Information ABSTRACT: The electro-optical properties of lead zirconate titanate (PZT) thin films depend strongly on the quality and crystallographic orientation of the thin films. We demonstrate a novel method to grow highly textured PZT thin films on silicon using the chemical solution deposition (CSD) process. We report the use of ultrathin (5−15 nm) lanthanide (La, Pr, Nd, Sm) based intermediate layers for obtaining preferentially (100) oriented PZT thin films. X-ray diffraction measurements indicate preferentially oriented intermediate Ln 2 O 2 CO 3 layers providing an excellent lattice match with the PZT thin films grown on top. The XRD and scanning electron microscopy measurements reveal that the annealed layers are dense, uniform, crack-free and highly oriented (>99.8%) without apparent defects or secondary phases. The EDX and HRTEM characterization confirm that the template layers act as an efficient diffusion barrier and form a sharp interface between the substrate and the PZT. The electrical measurements indicate a dielectric constant of ∼650, low dielectric loss of ∼0.02, coercive field of 70 kV/cm, remnant polarization of 25 μC/cm 2 , and large breakdown electric field of 1000 kV/cm. Finally, the effective electro-optic coefficients of the films are estimated with a spectroscopic ellipsometer measurement, considering the electric field induced variations in the phase reflectance ratio. The electro-optic measurements reveal excellent linear effective pockels coefficients of 110 to 240 pm/V, which makes the CSD deposited PZT thin film an ideal candidate for Si-based active integrated nanophotonic devices. KEYWORDS: chemical solution deposition, electro-optic effect, ellipsometry, dielectric, lead zirconate titanate, modulator, pockels coefficient ■ INTRODUCTION The deposition of high quality ferroelectric thin films has been studied extensively over the past few decades, because of the excellent piezo-electric, 1 pyro-electric, 2 ferro-electric, 3 and electro-optic 4 properties. The presence of functional properties in many ferroelectric materials has motivated the heteroge- neous integration of crystalline thin films directly on silicon for the realization of a variety of novel devices. Among the known ferroelectric thin film oxides, lead zirconate titanate (PZT) exhibits a large dielectric constant, piezo-electric coefficient 5,6 and electro-optic coefficient, 4 which already lead to applications in ferro-electric thin film capacitors, 7 piezo-electric actuators, 8 and electro-optic modulators. 9,10 Recent advancements in the thin film technology show nanograined PZT film 11 with excellent ferroelectric properties. 11,12 Novel devices with PZT nanofiber have been demonstrated for mechanical energy harvesting. 13 Other interesting properties of the films such as the electron emission characteristics are also explored with nanograined PZT structures, and a low turn on electric field is reported. 14 Although the ferroelectric thin films are explored mostly for electronic applications, the ever increasing demand for higher bandwidth meanwhile putting constraints on power consumption, has resulted in an increasing interest toward the use of the films in the optical domain. To realize optical data transmission, for example, for chip-to-chip interconnects, integrated optical devices which are compatible with the electrical systems are indispensable. The well-established ferroelectric oxide based technologies propelled the develop- ment of high-speed electro-optic devices on different material platforms, however the silicon based photonics technologies have not explored the strong linear electro-optic (EO) properties of PZT thin films. 15 The current state of the art Received: February 26, 2015 Accepted: June 4, 2015 Published: June 4, 2015 Research Article www.acsami.org © 2015 American Chemical Society 13350 DOI: 10.1021/acsami.5b01781 ACS Appl. Mater. Interfaces 2015, 7, 13350−13359 Downloaded by UNIV GENT on September 1, 2015 | http://pubs.acs.org Publication Date (Web): June 12, 2015 | doi: 10.1021/acsami.5b01781