Fabrication of ultrathin film capacitors by chemical solution deposition
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A facile solution-based processing route using standard spin-coating deposition techniques has been developed for the production of reliable capacitors based on lead lanthanum zirconate titanate (PLZT) with active areas of 艌1 mm2 and dielectric layer thicknesses down to 50 nm. With careful control of the dielectric phase development through improved processing, ultrathin capacitors exhibited slim ferroelectric hysteresis loops and dielectric constants of >1000, similar to those of much thicker films. Thus, it has been demonstrated that chemical solution deposition is a viable route to the production of capacitor films which are as thin as 50 nm but are still macroscopically addressable with specific capacitance values >160 nF/mm2.
I. INTRODUCTION
As the push toward further miniaturization and increased integration continues in the electronics market, integrated capacitors for energy storage and decoupling are in high demand. Currently, the body of work on thin film ferroelectrics can largely be divided into two general categories according to film thickness and application.1 On one hand there are “standard” thin film capacitors of ∼200–1000 nm thickness. Although fundamental questions about the processing and properties of such films remain, much of the recent work with such films has focused on tailoring film behavior for specific device applications.2,3 Until now, difficulties with reliability and property degradation have prevented such macroscopic devices from taking advantage of increased capacitance that should accompany thinner layers, effectively limiting the thickness of films used in such applications to 艌200 nm. Presently, fabrication of ultrathin (∼5–100 nm) films is typically accomplished by deposition from the vapor phase using methods such as molecular beam epitaxy (MBE), pulsed laser deposition (PLD), or sputtering. Studies on ferroelectric films in this category generally focus on the structural aspects of the films in an indirect probe of “size effects” on ferroelectric behavior.4–7 Electrical characterization of such films is commonly carried out using some version of scanning probe microscope. Whereas considerable fundamental understanding has
come out of such studies, to the authors’ knowledge, there have not yet been any reports of macroscopicallyaddressable ultrathin film capacitors with properties comparable to those of thicker films. This paper reports two significant improvements in the fabrication of lead zirconate titanate (PZT)-based thin film capacitors that help to bridge the gap between the two communities by enabling the fabrication of macroscopically addressable device-ready ultrathin capacitors with excellent dielectric and ferroelectric properties. First, a solution-based processing route has been developed that has enabled the production of ultrathin layers (80% yield for capacitors with areas of 1 mm2 across an entire 3-in. Si wafer using standard chemical solution deposition (CSD) spin coating techniques in a simple laboratory laminar flow hood. Second, careful control of P
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