Integration of coplanar (Ba,Sr)TiO/sub 3/ microwave phase shifters onto Si wafers TiO/sub 2/ buffer layers

In this paper, a Ba/sub 0.6/Sr/sub 0.4/TiO/sub 3/ (BST) tunable phase shifter with TiO/sub 2/ films as microwave buffer layer between BST and silicon (Si) substrates is presented. The TiO/sub 2/ buffer layer is grown by atomic layer deposition (ALD) onto Si substrate followed by pulsed laser deposition (PLD) of BST thin films onto the TiO/sub 2/ buffer layer. The phase shifter fabricated on BST films grown on TiO/sub 2//Si substrate shows a good figure of merit (FOM) of 75.4/spl deg//dB by exhibiting improved tunability while retaining an appropriate dielectric Q as compared to 55.1/spl deg//dB of BST/MgO structure. The TiO/sub 2/ buffer layer grown by ALD enables successful integration of BST-based microwave tunable devices with high resistive Si wafer.