High tunability (Ba,Sr)TiO/sub 3/ thin films on atomic layer deposited buffer layers for Si integration

In this study, we report on Si integration of Ba/sub 0.6/Sr/sub 0.4/TiO/sub 3/ (BST) thin film based microwave tunable devices by use of TiO/sub 2/ films as microwave buffer layer between BST and Si substrates. TiO/sub 2/ buffer layer were grown by atomic layer deposition (ALD) onto Si substrates followed by pulsed laser deposition (PLD) of BST thin films onto the TiO/sub 2/ buffer layer. The interdigital capacitor (IDC) fabricated on BST films grown on TiO/sub 2//high resistivity Si substrates showed much enhanced tunability value of 33.2% while retaining an appropriate Q factor, as compared to 21% value obtained with BST films grown on MgO single crystal substrates. The microwave phase shifters were fabricated on BST thin films to investigate the potential feasibility of integrating BST films as microwave tunable devices. The phase shifter fabricated on BST films grown on TiO/sub 2//Si substrate showed better figure of merit (FOM) of 30.7/spl deg//dB, as compared to 12.1/spl deg//dB of BST/MgO structure. ALD grown TiO/sub 2/ buffer layers enable successful integration of BST based microwave tunable devices onto high resistivity Si wafers.