SrTiO_3 Thin Film Varactors on Si for Microwave Applications

摘要

Dielectric properties of SrTiO_3 (STO) thin films in Au/Pt/STO/Pt/TiO_2/SiO_2/Si structure are studied at microwave frequencies. STO films with thickness of 300 nm were grown by laser ablation at different temperatures on templates of Pt/TiO_2/SiO_2 on Si with resistivity of 5 kΩ·cm. XRD measurements reveal highly textured (111)STO films with small amount of (100) and (110) domains. The full with at half maximum of the rocking curve of (111 )STO domains is about 2 degrees. Circular Au/Pt top electrodes with diameters in the range of 10-60 μm were formed by e-beam evaporation and lift-off process. The on chip microwave impedance of devices was measured in the frequency range of 45 MHz-45 GHz as a function of DC electric field in the range of 0-800 kV/cm. The loss tangent is less than 0.06 in the whole frequency range. Application of DC bias results in resonant absorption of microwave power at frequencies of 1.3, 3.0, 4.7, 6.4, and 9.7 GHz. The relative change of the dielectric permittivity under 800 kV/cm DC field is more than 20% in the whole frequency range. The results indicate that the varactors based on these STO films are suitable for tunable microwave applications.