Integration of Coplanar (Ba,Sr)TiO₃ Microwave Phase Shifters onto Si Wafers Using TiO₂ Buffer Layers

ABSTRACT In this paper, a Ba_0.6Sr_0.4TiO₃ (BST) tunable phase shifter with TiO₂ films as microwave buffer layer between BST and silicon (Si) substrates is presented. The TiO₂ buffer layer is grown by atomic layer deposition (ALD) onto Si substrate followed by pulsed laser deposition (PLD) of BST thin films onto the TiO₂ buffer layer. The phase shifter fabricated on BST films grown on TiO₂/Si substrate shows a good figure of merit (FOM) of 75.4°/dB by exhibiting improved tunablity while retaining an appropriate dielectric Q as compared to 55.1°/dB of BST/MgO structure. The TiO₂ buffer layer grown by ALD enables successful integration of BST-based microwave tunable devices with high resistive Si wafer.

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