Characterization and modeling of low-frequency noise in thin-film source-gated transistors for display applications
(2026)
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- (en) With the rapid development of advanced displays, flexible electronics, and sensors, thin-film transistors (TFTs) have become essential building blocks of the information society. Among candidate channel materials, low-temperature polycrystalline silicon (LTPS) and amorphous indium gallium zinc oxide (IGZO) are intensively investigated due to their excellent electrical performance and large-area manufacturing uniformity. However, traditional TFT architectures encounter inherent physical limits such as short-channel effects, finite output impedance, and high saturation voltages, which restrict their intrinsic gain and power efficiency in analog applications. As an alternative, the source-gated transistor (SGT) replaces the ohmic source with a gate-modulated Schottky contact, realizing a transition from "channel potential control" to "contact barrier height control". Although SGTs show great potential for low-power analog circuits, systematic research on their low-frequency noise (LFN) mechanisms and circuit-level performance is still required. This thesis first systematically investigates the LFN of n-type LTPS SGTs in the linear and saturation regimes. Noise measurements demonstrate that the LTPS SGT LFN is dominated by 1/ f noise. The results suggest that conventional TFT noise models based on channel carrier number and mobility fluctuations cannot accurately describe the LFN behavior of SGTs. Based on the mechanism of thermionic emission and drift-diffusion current fluctuations in the reverse-biased Schottky barrier depletion layer, a specific physical SGT LFN model is proposed and established. By incorporating the gate-modulated barrier lowering effect, the model successfully reproduces the measured dependence of noise on drain and gate voltages. The study reveals as well that the Schottky barrier noise increases with barrier height and decreases with both temperature and gate-source overlap length. Subsequently, the characterization and physical modeling of LFN are extended to n-type IGZO SGT devices. DC measurements reveal that the IGZO SGT achieves a saturation current comparable to the its TFT counterpart, indicating a relatively low Schottky barrier. Meanwhile, the IGZO SGT shows relatively low output impedance compared to the LTPS SGT due to the absence of a field-plate structure. Regarding noise characteristics, the IGZO SGT exhibits a similar noise dependence on drain voltage. By applying the physical LFN model derived for the LTPS SGT to the IGZO SGT, the strong agreement validates the universality of the proposed Schottky barrier LFN model across different semiconductor material systems. These findings provide valuable physical insights for optimizing IGZO-based devices in advanced, low-noise analog applications. Finally, this work comprehensively evaluates the analog figures of merit (FoMs) for LTPS and IGZO devices using a display pixel driver circuit (source-follower structure) as a benchmark platform. The results show that the SGT architecture demonstrates significant advantages in power efficiency and output stability. Specifically, SGTs achieve far lower saturation voltages than TFTs, providing great potential for scaling supply voltage (VDD) and reducing power consumption. LTPS SGTs exhibit an excellent off-state current (∼ 10−14 A/µm), which is two orders of magnitude lower than that of the LTPS TFT. Benefiting from an extremely high Early voltage (VEA), LTPS SGTs achieve a peak intrinsic gain up to approximately 1150, outperforming TFTs by two orders of magnitude. The IGZO SGT exhibits a lower intrinsic gain than the LTPS SGT, yet it maintains a slight improvement over the conventional IGZO TFT. Despite certain trade-offs in dynamic response speed (fT), SGTs displays non-negligible advantages for low-power, high-stability next-generation analog driving applications.
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Chen, Q. (2026). Characterization and modeling of low-frequency noise in thin-film source-gated transistors for display applications. https://hdl.handle.net/2078.5/277321