Buried Tantalate-Niobate Microwave Varactors

Abstract

We present characteristics of microwave variable capacitors (varactors) buried in 2.5 pim thick AgTao.5NbO.503 (ATN) film pulsed laser deposited on sapphire single crystal. 2 ptm gap interdigital capacitors (IDC) were fabricated by photolithographic, dry etching and lift-off processes. For comparison, similar IDCs were also defined on top of ATN film. Capacitance and loss tangent have been deternined using a modified deembedding technique in the microwave range 25 MHz -40 GHz. Buried structures show higher values of capacitance and tunability, keeping the same level of losses compared to standard topped devices and resulting in an increased K-factor = tunability/tan A Experimental results are explained within equivalent circuit model. Besides the increased perfornance, the new design avoids the need of a successive planarization step, which could be required in an integration process.