(Ba,Sr)TiO3 (BST) thin films with thicknesses ranging from 15 to 50 nm are prepared by a rf magnetron sputtering on Pt/SiO2/Si substrates. The dielectric constants of BST thin films increase with increasing deposition temperature and thicknesses. The leakage current increases with increasing deposition temperature and this prevents the deposition temperature of the 20 nm thick BST thin film from being increased to a value more than 640 °C. The leakage current is also critically dependent upon the postannealing temperature and atmosphere after the top electrode fabrication. The dielectric constant increases with increasing postannealing temperature which further reduces the SiO2 equivalent thicknesses of the BST thin films. A 20 nm thick BST thin film deposited at 640 °C and postannealed at 750 °C under N2 atmosphere for 30 min, shows a SiO2 equivalent thickness of 0.24 nm, dielectric dissipation factor less than 1%, and leakage current of about 40 nA/cm2 at ∓1.5 V.
Pt/(Ba, Sr)TiO3/Pt capacitors are fabricated using DC and RF magnetron sputtering processes on thermally oxidized silicon wafers for ultralarge scale integrated dynamic random access memory (ULSI DRAM) applications. (Ba,Sr)TiO3 (BST) thin film deposited at 640°C to 20 nm thickness shows an equivalent SiO2 thickness (t
oxeq) of 0.35 nm and a leakage current density, measured at an applied voltage of 1.5 V, of about 100 nA/cm2. t
oxeq of the BST film and leakage current density are further decreased to 0.24 nm and 40 nA/cm2, respectively, by postannealing at 750°C after fabrication of the top electrode.
In this paper, we demonstrated the machining process of a novel Light Emitting Diodes (LED) beam shaping lens, called TIR Fresnel lens, for GaN-based blue Chip Scale Packaged (CSP) LEDs. Upon achieving a precise alignment of the tool and identifying the best manufacturing condition, we have successfully fabricated a prototype of this lens on poly methyl methacrylate (PMMA) plate. The form error of the central aspheric lens was less than 1 μm deviation, and surface quality of the Fresnel facets were sufficient for Total Internal refraction without any burr or adhesion of the machined chip. Fabricated TIR Fresnel lens reduced the viewing angle of the testing CSP LED from 140° to 17.4° in FWHM. The proposed lens produced extreme compactness as well as high collimation efficiency, thereby applicable to an ultra-thin optical system.
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