Integrated Thin Film Capacitor Arrays Utilizing Sol-Gel Derived Ferroelectrics
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Mat. Res. Soc. Symp. Proc. Vol. 596 © 2000 Materials Research Society
More complex modules may also be fabricated using this technique with achievable component density of 60-150 components/cm 2 [4,5]. Thin film processing utilizes deposition techniques such as sputtering, vapor deposition, and spin-on-glass to form sub-micron passive layers on a substrate. Compared to LTCC, thin film processing offers much higher component density (>200 components/cm 2 ) and higher device precision [3]. A number of ferroelectric materials with high dielectric constant, such as Pb(Zr1 _Ti,)O3 (PZT), (Ba, Sr)TiO3 (BST), and SrBi 2Ti 2O 6 (SBT), have long been fabricated in thin layers. They have been intensively studied in the device integration of nonvolatile memories and high density dynamic random access memories (DRAMs) [6]. Various processing techniques have been developed for depositing ferroelectric thin layer materials. Each technique has advantages, depending on the application. For nonvolatile and high density DRAM memory applications, only very thin dielectric layers (10V is further evidence that the dominant mechanism is from dielectric-electrode interface instead of bulk dielectric; (iii) the fact that the C(V) curves fit well to both Eq.(2) and Eq. (3) indicates that space charge distribution is not a primary factor in altering the C- V dependence of PNZT capacitors.
Steady-State Current Voltage Dependence The steady-state leakage current-voltage dependence of PNZT capacitors was investigated by measuring the insulating resistance under a given applied voltage. To assure the measurement was steady-state, the resistance was collected until it was nearly time independent. In addition, each data point was an average value of 10 consecutive resistance readings. The measurements were also conducted at elevated temperature (125°C) to avoid long measuring time. Figure 12 shows the leakage current of integrated PNZT capacitors as a function of applied voltage and dielectric thickness. For a given thickness, at least three capacitors were tested to assure measurement consistency. Figure 12 indicates that dielectric breakdown in PNZT capacitors occurs at a specific current density threshold and not at a specific voltage. This observation agrees with a previous report on dielectric breakdown in BST films [16]. The threshold current density J, however, was found to decrease with an increase in the PNZT thickness: J, is 2x 10(A/cm2) for 473 nm PNZT capacitors and is 2.5x 10-8 (A/cm 2) for 1101 nm capacitors. This indicates that the dielectric breakdown in PNZT is thickness dependent. In addition, the leakage characteristics also change with PNZT thickness variations. At low applied fields (up to -100 kV/cm), a near linear relationship between J,
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