Scaled PLZT Thin Film Capacitors with Excellent Endurance and Retention Performance
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Scaled PLZT Thin Film Capacitors with Excellent Endurance and Retention Performance
Fan Chu, Glen Fox and Tom Davenport Ramtron International Corporation, 1850 Ramtron Drive, Colorado Springs, CO 80921, U.S.A. e-mail: [email protected]
ABSTRACT The requirements for future ferroelectric non-volatile memories (FRAM) include lower operating voltages, higher densities and tighter design rules. In order to achieve these requirements the key component of the FRAM device, viz., the PbZrxTi1-xO3 (PZT) thin film capacitor must be scaled dimensionally to obtain reduced film thickness and capacitor area. This paper presents the ferroelectric performance of RF magnetron sputtered PLZT thin films with thickness scaled down to 1000Å. The switching performance of the thickness scaled PLZT thin films meets the requirements of 1.8V FRAM device. Though PLZT ceramic thin films, of which the fatigue is often a concern, are utilized as non-volatile component, excellent fatigue performance was observed. The scaled PLZT thin film capacitors are fatigue free up to 1011 fatigue cycles (E=200kV/cm). The scaled 1000Å PLZT thin films also showed good imprint performance. The opposite-state charge after 10 years baking at 150oC was still above the sensing level. The thickness scaled PZT thin films, showing dramatically improved ferroelectric performance, can be applied to the manufacturing of low voltage FRAM products.
INTRODUCTION Ferroelectric non-volatile memories (FRAM), which possess the merits of a fast write speed and low power consumption, have been mass-produced for approximately a decade. FRAM memory density has increased and the CMOS design rule for FRAM memory has decreased exponentially since 1988. The primary component for data storage in current FRAM products, such as 64kbit and 256kbit memories, is the ferroelectric capacitor. The core of this capacitor consists of doped (Pb,La)(Zr, Ti) O3 (PLZT) deposited by RF magnetron sputtering. PLZT and doped PZT ceramic thin films exhibit properties such as high switchable polarization, crystallographically textured growth, and low processing temperatures, which facilitate scaling for higher densities and lower operating voltages. PLZT and doped PZT thin film materials provide a clear path for the development of future generations of FRAM products. In order to meet the requirements for future ferroelectric non-volatile memories (FRAM), such as lower operating voltages, higher densities and tighter design rules, PLZT thin film capacitors must be scaled down with respect to thickness and area. Scaling in terms of thickness is one of the most interesting topics as the reduction in PLZT thin film thickness can effectively lower the ferroelectric switching voltage. To achieve higher densities and tighter design rules, a reduced capacitor stack height is also necessary in order to facilitate the etching of the PLZT thin film capacitors with smaller lateral dimension. However, scaling requires process modification otherwise degraded ferroelectric performance will be obtained. CC1.2.1
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