BaxSr1 − xTi1.02O3 metal-insulator-metal capacitors on planarized alumina substrates

Nanocrystalline barium strontium titanate (Ba_xSr_1 − xTi_1.02O₃) thin films with a barium content of x = 0.8, 0.9 and 1 have been fabricated in a metal-insulator-metal configuration on glass-planarized alumina substrates. Cost-effective processing measures have been utilized by using poly-crystalline alumina substrates, wet-chemical processing of the dielectric, and by a small physical area of the ferroelectric capacitors (as low as 50 µm² for radio frequencies measurements). Glass-planarization on alumina ceramic substrates enables barium strontium titanate films with high quality and homogeneity. We mainly focus on fine-tuning the electrical performance in the low gigahertz range (< 10 GHz). Extensive micro-structural and electrical characterization has been performed. Micro-structural information is obtained by: Transmission Electron Microscopy, Scanning Electron Microscopy and X-ray diffraction. The dielectric response is investigated as a function of temperature, frequency and electric field for each sample. We measured a relatively constant permittivity for typical operating temperatures of applications. The quality factor Q is between 21 and 27 at 1 GHz at zero DC bias and the tuning ratio η between 1.8 and 2.2 at |E| = 0.4 MV/cm.