Investigation of loss mechanisms in thin film barium strontium titanate capacitors

In recent years there has been significant progress in the development of thin film ferroelectrics and related materials for tunable RF/microwave applications. A significant impediment to the widespread deployment of this technology remains. Circuit designers need accurate models for simulations. Understanding the different contributions to device performance is necessary for the development of these models. This requires the separation of intrinsic film properties from total device properties, as well as an understanding the effect of geometric scaling upon the devices.; In this work, the electrical properties of thin film barium strontium titanate (BST) capacitors are studied from the perspectives of film optimization and analysis of loss contributions. Unoptimized films are found to be disordered, as indicated by the presence of unusually long time scale behavior, with leakage current transients persisting past 105 seconds. Reevaluation of growth conditions results in materials with improved properties: tunabilities greater than 90%, loss tangents lower than 0.67%, and transients shorter than 5 seconds. The combination of low and high frequency measurements, along with loss calculations from measured capacitance data, are used to isolate the properties of the electrodes and electrode-film interfaces; microwave frequency losses are shown to be dominated by this grossly frequency dependent extrinsic contribution. Geometric scaling of device properties is shown to be a function of frequency, with larger area devices having lower loss at low frequencies (MHz) and smaller area devices having lower loss at high frequencies (GHz). Parasitic contributions to both low and high frequency equivalent circuit models are discussed, along with measurement considerations.