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Mat. Res. Soc. Symp. Proc. Vol. 459 ©1997 Materials Research Society

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E-• (a)

Platinum Silicon

ITO PzT

(b)

Figure 1: Layout of (a) ITO-PZT-ITO (b) Pt-PZT-Pt capacitors A Radiant Technology RT66A ferroelectric tester was used to collect hysteresis data and perform standard fatigue on capacitors. A Sawyer Tower circuit in conjunction with a Hewlett Packard digitizing oscilloscope, a desktop computer using Keithley "Viewdac" data acquisition software and a Hewlett Packard LCR meter was used in studying photo-induced changes with light. Continuous monitoring of polarization was done using an input voltage signal in the form of a 5 V sine wave signal operating at 50 Hz. This was done for unfatigued capacitors as well as capacitors which had been cycled for 10' cycles. A 150 W tungsten filament white light source and a fiber-optic guide was used to transmit white light to the film. A 75W xenon light source in conjuntion with a monochromator (with a wavelength resolution 1 nm) by Acton Research Corporation and a fiber-optic was used as a monochromatic light source. The output of the light source varied from approximately 190 nm to 750 nm (6.5 eV to 1.65 eV). Long band pass filters were used to eliminate second- and third-order harmonics. A continuous voltage signal fed to the capacitor and the Sawyer Tower circuit recorded the polarization changes. ITO and Pt films of thickness approximately the same as the electrodes were coated on glass slides. A Magna-IR Spectrometer from Nicolet Analytical Instruments was then used to determine film transmittance between the wavelengths 2.5 pm to 5.0 gm. RESULTS AND DISCUSSION Results of the normalized photo-induced recovery of capacitors to white light illumination are shown in Fig. 2. Figure 2 (a) shows an increase of 1.5 RC/cm 2 and 2.9 g C/cm 2 before and after 10' switching cycles, respectively using the Pt-PZT-Pt capacitors. The corresponding increases were 2.05 gC/cm 2 and 2.35 gC/cm2 for ITO-PZT-ITO capacitors as shown in Fig. 2 (b). Results of monochromatic light tests presented in Fig. 3, however, showed a maximum increase in polarization in the range 3.4 to 3.6 eV. The increases before and after 108 switching reversals were 1.6 jiC/cm 2 and 1.9 gC/cm 2 in case of the Pt-PZT-Pt (shown in Fig. 3 (a)) and 1.84 gC/cm 2 and 1.88 gC/cm 2 in case of ITO-PZT-ITO capacitors (shown in Fig. 3 (b)), respectively. The white light source emits light from the ultraviolet region through the visible into the far infrared region. The intensity is low at either end and attains a maximum at a wavelength of about 1.3 gtm 7 .Attenuation and reflection of the incident white light intensity through electrodes at various surfaces was made from values of physical and optical parameters such as extinction coefficients and reflectance of the Pt and the ITO films8' 1 . A similar calculation was carried out to estimate the intensity of the light as a function of wavelength in the case of the monochromatic light source. It was found that a much higher (- 100 times) intensity o