HIGH-FREQUENCY ELECTRICAL CHARACTERIZATION OF BST CAPACITORS

We have characterized the dielectric properties of barium strontium ti tanate (Ba1-xSrxTiO3, x=0.5; BST) capacitors up to 5 GHz employing a s imple, single port scattering parameter measurement technique. Metal-i nsulator-metal type capacitors with areas ranging from 400 to 10,000 m u m(2) were defined by standard photolithographic and etching techniqu es BST films were rf-magnetron sputter-deposited on metallized (111) s ilicon. The bottom electrode was made by evaporating 100A of Ti for ad hesion followed by 1500A of Pt. The top electrode consisted of 3000A o f gold with a 100A titanium adhesion layer. The test capacitors were s urrounded by a reference capacitor approximately 140 times in area to facilitate high frequency measurements with air coplanar (ACP) probes. The test and the reference capacitors were in series during character ization ensuring that the resulting capacitance was dominated by the s maller test structure. Single port scattering parameters (S11) were ob tained using a HP8510B network analyzer. HP Microwave and RF Design Sy stem (MDS) was used for data analysis. The BST capacitor structures ex hibited a roll-off near 1 GHz where the dielectric constant was reduce d by 10-20% of the value at 50 MHz.