Dielectric Properties of (Ba,Sr)TiO₃ Thin Film Capacitors Fabricated on Alumina Substrates

Abstract

Double layer (DL) Ba0.7Sr0.3TiO3 (BST) capacitors with Pt electrodes have been fabricated with similar growth conditions on different substrates. The substrates used in the present study were r-plane sapphire, polycrystalline alumina Al2O3 (99.6% and 96%), and glazed polycrystalline alumina. BST films were grown by metal-organic decomposition (MOD) method. By varying the annealing conditions which affects the formation of the crystalline structure, significant changes in the dielectric properties of the BST films have been observed. BST films were characterized by Field Emission Scanning Electron Microscopy (FE-SEM) and Powder X-ray Diffractometer (PXRD). These observations showed that BST films grown at lower temperatures on alumina substrates exhibited the smallest grain size. BST films of the same thickness prepared under the same thermal processing conditions showed higher capacitance when grown on all types of alumina-based substrates compared to those deposited on control SiO2/Si. The higher capacitance on alumina was always associated with larger dissipation factor, and lower or similar leakage current density. The final tuning, of the dielectric properties of BST DL capacitors on non-silicon substrates, was correlated to the initial film formation temperature and post-annealing conditions of the BST films. The leakage current density, of DL BST capacitors fabricated on glazed alumina, becomes smallest when the BST processing temperature was lowered by 100 °C compared to the control SiO2/Si. The typical achieved leakage current density for 1500×1500 μm2 DL capacitors on glazed alumina was 3.8×10-9 A/cm2 at 250 kV/cm (36.5 fF/μm2), about 3 times lower than on SiO2/Si substrates (1.1×10-8 A/cm2 at 250 kV/cm, 31 fF/μm2).

Processing and dielectric characterization of Ba0.3Sr0.7TiO3 thin films on alumina substrates

“…They found that with increasing annealing temperature and consequently increasing the grain size, the permittivity of the films increases, reaching the values close to those of bulk material. 6 A similar relationship between annealing temperature, the microstructure and the dielectric properties has been reported for (Ba,Sr)TiO 3 thin films on platinized silicon 7 and platinized alumina substrates, 8 namely with increasing the annealing temperature the grain size increases and the dielectric properties are improved.…”

Enhancement of Photon Absorption onBaxSr1-xTiO3Thin-Fi

“…This thin film can be produced with various methods such as metalorganic chemical vapor deposition (MOCVD) [13], sol-gel [14][15][16][17], atomic laser deposition (ALD) [18], hydrothermal synthesis [19], metal organic decomposition (MOD) [20,21], and chemical solution deposition (CSD) [22][23][24][25][26].…”

Thin fim barium strontium titanate capacitors for tunable RF frond-end applications

“…2) higher residual stress caused by thermal strain due to a difference in thermal expansion of the substrate and the ferroelectric during processing [83,88,89]. A CTE mismatch between the substrate and the 3.1.…”

“…These substrates are attractive due to the excellent match of the coefficient of thermal expansion (CTE) with BST (see Table 6.1). A CTE mismatch between the substrate and the film will increase the residual stress caused by thermal strain during heat treatments [83] and can lower the relative permittivity ε r [88,89] and tuning ratio η. Unpolished ceramic substrates are, however, very rough and may result in short circuited capacitors. Therefore, capacitors on top of either polished ceramic substrates or substrates with planarization layers were studied.…”

“…Deposition of BST metal-organic decomposition on alumina substrates with planarization layer is reported by I.P. Koutsaroff et al [88] for integrated multilayer capacitors. Furthermore, alumina substrates have a superb isolation, with an electrical resistivity of > 1 TΩ·cm (even at temperatures as high as 300 • C) [130], resulting in low microwave losses.…”