Abstract
Ba Sr TiO (BST) thin films have large dielectric constants that can be varied by as much as a factor of 3 with an applied field, making them attractive for radio frequency (RF) cir- cuits as small-area ac bypass/dc blocking capacitors, or high-power varactors. However, BST must be deposited at relatively high tem- peratures in an oxidizing environment, presenting significant in- tegration challenges for MMIC applications. This letter describes the successful integration of BST films on AlGaN/GaN high elec- tron-mobility transistor (HEMT) monolithic microwave integrated circuits on sapphire substrates. A sacrificial SiO buffer layer is used to protect the underlying AlGaN during the RF magnetron sputtering of the BST film at an elevated temperature, with a care- fully controlled heater ramp rate to avoid degradation of the ohmic contacts on the HEMT.
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