Gary F. Derbenwick

Influence of Ti-content in the bottom electrodes on the ferroelectric properties of SrBi2Ta2O9 (SBT)

Abstract Stress behavior, results of AES analysis and electrical properties of SBT in dependence of electrode structure and annealing conditions are discussed. Evidence for degradation of the electrical properties of SBT due to diffusion of Ti is presented.

Characterization of self-patterned SrBi2Ta2O9 thin films from photo-sensitive solutions

Abstract Self-patterned SrBi2Ta2O9 thin films were successfully fabricated from photo-sensitive solutions by means of UV irradiation through photo masks. After conventional baking and wet etching the films were annealed. The photo-sensitive SrBi2Ta2O9 solutions give high resolution negative-pattern of the mask image down to 1 μm line width by deep UV irradiation at 900 mJ/cm2. The capacitor characteristics of the 210 nm thick films fabricated on the Pt/Ti/SiO2/Si substrates by this process showed 2Pr values of 17 μC/cm2, 2Ec of 89 kV/cm, and leakage current densities of 5×10−9 A/cm2 at 5 V. The films showed no fatigue after 1×1011 switching cycles.

Conformal LSMCD deposition of SrBi2(Ta1-xNbx)2O9

Abstract This paper presents new results of Liquid Source Misted Chemical Deposition (LSMCD) of SrBi2(Ta1-xNbx)2O9 thin films showing good step coverage of 150 nm thick films into square openings approximately 1 μm deep by 0.6 μm wide. A SAMCO model HDF-6000 LSMCD machine was used for the ferroelectric deposition. Prior to the deposition of the ferroelectric film, a Pt bottom electrode of approximately 200 nm thickness was sputtered into an initial opening 1μm deep by 1μm wide. The LSMCD and new chemistry methodologies by which these results were obtained will be described in this paper. The electrical characteristics of the LSMCD films will also be reported. LSMCD films resulted in higher switched charge (2Pr) than the spin-on films. The coercive fields (2Ec) and maximum leakage currents were comparable for the two deposition methods. These results show that conformal LSMCD thin films can be used for sub-micron circuits containing ferroelectric memory.

Imprint in ferroelectric SrBi2Ta2O9 capacitors for non-volatile memory applications

Abstract Imprint is known as a failure mechanism in ferroelectric capacitors due to a voltage shift in the hysteresis curve. A detailed study to investigate the time, temperature and bias voltage dependence of the voltage shift was performed on MOD SBT thin films. Lifetime extrapolation under operating conditions (125 °C) reveal values for the lifetime of well over ten years.

Role of recovery anneals for chemical solution deposition (CSD) based SrBi2Ta2O9 (SBT) thin films

Abstract Using a recovery anneal after deposition of the Pt top electrode and patterning the Platinum / SrBi2Ta2O9 bilayer has been established to obtain well shaped hysteresis curves with low leakage currents. Electrical properties of SBT test capacitors in dependence of temperature and time for the recovery anneal are discussed. Evidence for degradation of the electrical properties of SBT capacitors after patterning due to the appearance of a new unknown peak in X-ray diffraction (XRD) is presented.

Preparation of Self-Patterned SrBi 2 Ta 2 O 9 Thin Films from Photo-Sensitive Solutions

Photo-sensitive SrBi 2 Ta 2 O 9 (SBT) solutions were evaluated and the patterning process flow for SBT films using the solutions was optimized. By adding a soft-bake process before UVirradiation, self-patterned SBT films were successfully prepared from the solutions and the cross sectional shape of the patterned films was improved. The photo-sensitivity of the solutions was estimated to be 900 mJ/cm 2 . The photo-reaction in the precursor gel film formed from the solution was traced by measuring IR absorption spectra. The obtained films had excellent ferroelectric properties comparable to conventional SBT films.