Local Hysteresis Behavior of Ferroelectric Thin Films of Si added PbTiO 3
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Local Hysteresis Behavior of Ferroelectric Thin Films of Si added PbTiO3 V.R. Palkar1, M. Higgins2, S.C. Purandare1, R. Pinto1 and S. Bhattacharya1,2 1. Tata Institute of Fundamental Research, Mumbai 400005, India 2. NEC Research Institute, Inc. Princeton, New Jercy 08540, U.S.A ABSTRACT We report ferroelectric properties and local hysteresis behavior of 2 mole percent Si added PbTiO3 thin films grown on Pt/TiO2/SiO2/Si substrate by using pulsed laser deposition technique. The ferroelectric hysteresis loop and scanning piezoresponce images obtained on these films by using AFM with conducting tip demonstrate excellent properties, which are equivalent to any other established ferroelectric material like PZT. Si segregating at the grain boundaries controls grain growth. The grain size and grain boundaries play a crucial role in determining ferroelectric hysteresis properties. The presence of Si in the matrix can be useful in tuning the properties. INTRODUCTION In recent years, the application of ferroelectric thin films as nonvolatile ferroelectric random access memory (NV-FRAM)[1,2] has been widely investigated. In NV-FRAM, the bit value is represented by one of the two remanent polarization states in a parallel-plate capacitor configuration. Ferroelectric materials in the form of thin films have several advantages over bulk samples, the principal one being the requirement of relatively low voltages for device applications. Moreover, the small inertia of thin films allows higher frequency applications. The decrease in amplitude of the remanent polarization state after repeated switching, known as fatigue, can cause bit failure in NV-FRAM. Thus, uniformity in the ferroelctric properties of the thin films at micron level is critical for reliable performance of the devices. It is essential to understand the role of the thickness, grain size, grain boundary composition, domain orientation etc. in order to optimize these properties Currently, extensive experimental characterization of the ferroelectric properties of ferroelectric thin films is being carried out by various groups [3,4,5]. AFM methods have been used to measure the spatial variation of ferroelectric properties of thin films. Measurement of thin film piezoelectric coefficients is challenging due to the unique geometry and small displacements. Zavala et.al. [6] could detect large variations in piezoelectric magnitude when used AFM technique to test the sample as opposed to double beam interferrometry. Christman et.al. [7] have reported spatial variation of ferroelectric properties with sub-micron lateral resolution using an AFM piezoelectric measurement technique. The phase of the piezoelectric response is related to the polarization direction in the ferroelectric material [8]. Phase images represent the polarization direction while variation in amplitude of the response (contrast) shows variation in |d33|. The local piezoelectric loops provide previously unavailable information about the local properties of the sample. This information, obtained usin
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