Barium strontium titanate thin film varactors have been widely investigated for the purpose of creating tunable front-ends for RF and microwave systems. There is an abundance of literature observing the capacitance-voltage behavior and methods on improving tunability. However, there is a lack of thorough investigations on the nonlinear behavior, specifically the third order intermodulation distortion, and the parameters that impact it. There is also a research void that needs to be filled for nanoscale barium strontium titanate varactors as nanotechnology becomes increasingly prevalent in the design of RF and microwave components. This work aims to advance the understanding of nonlinear properties of barium strontium titanate varactors. Temperature and voltage impacts on the third order intermodulation distortion products of BST varactors are observed by two-tone measurements. The material properties of the films are correlated with the nonlinear behavior of the varactors. Additionally, size reduction capabilities are shown by fabricating planar barium strontium titanate interdigital varactors with nanoscale size gaps between the electrodes. Modeling techniques are also investigated.