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In this paper, we report our studies on field effect transistor (FET) THz detectors operating in the non-resonant mode based on the Dyakonov-Shur plasma wave detection theory, where the quantum capacitance dominates. The influence of quantum capacitance in detector response is theoretically developed and numerically simulated at low and high frequencies. Fundamental constraints in the upper frequency limit are also analyzed for FET THz detectors based on various materials, showing advantages of GaN for 8 - 20 THz applications. Experiments at microwave and THz frequencies have been carried out for GaN based devices showing agreement with the theory.

We have studied the effect of some of the possible deviations on the values of the extracted parameters of a specific OTFT model, considering OTFTs designed using P3HT as semiconductor layer, PMMA as insulator, bottom gate, and top gold contacts. Specifically, we have studied the influence of misposition or misalignment of the masks, the effect of imperfections of etching, and the effect of variations on the layer deposition process. These effects have been simulated using the Silvaco Athena software, and they have been modeled as horizontal shifts of the etching windows and variations of the layers thickness. Once the devices were defined, they were simulated using Silvaco Atlas, and parameter extraction was performed using a specifically developed algorithm. We have found a strong correlation among some of the physical parameters and the model parameters that may offer useful insight for process optimization. Moreover, strong correlations have been found also among the model parameters. We have used these results to develop a Monte Carlo model, suitable for statistical circuit simulation.