An improved analysis of low frequency trapping noise in a MOS device is proposed. This analysis takes into account the supplementary fluctuations of the mobility induced by those of the interface charge. It enables an adequate description of the gate voltage dependence of the input equivalent gate voltage noise to be obtained in various actual situations. The outputs given by the Hooge mobility fluctuation model are also presented and discussed with respect to those obtained by the carrier number fluctuation model. In particular, the impact of the channel length or channel width, and the model type on the input gate voltage and drain current noise characteristics is studied and compared to typical experimental data. Finally, a procedure for the diagnosis of the low frequency noise sources in a MOS transistor is proposed.
A modified transmission-line method (TLM) for organic transistors contact resistance extraction is proposed. It is shown that the issues of conventional TLM reside in the channel resistance scattering due to parameter variations. These difficulties are overcome in the modified TLM, in which the linear regression slope is directly controlled by the contact resistance rather than by the channel resistance as in conventional TLM. Much smaller transistor-to-transistor dispersion of contact resistance results in a more stable and more reliable extraction method. Moreover, an error study by simulation has been carried out, confirming the greater accuracy of the modified TLM.
Conjugated polymers came to an unprecedented epoch that the charge transport is limited only by small disorder within aggregated domains. Accurate evaluation of transport performance is thus vital to optimizing further molecule design. Yet, the routine method by means of the conventional field-effect transistors may not satisfy such a requirement. Here, it is shown that the extrinsic effects of Schottky barrier, access transport through semiconductor bulk, and concurrent ambipolar conduction seriously influence transport analysis. The planar transistors incorporating ohmic contacts free of access and ambipolar conduction afford an ideal access to charge transport. It is found, however, that only the planar transistors operating in low-field regime are reliable to explore the inherent transport properties due to the energetic disorder lowering by the lateral field induced by high drain voltage. This work opens up a robust approach to comprehend the delicate charge transport in conjugated polymers so as to develop high-performance semiconducting polymers for promising plastic electronics.
The reliability of mobility has come to be a critical issue to the development of new electronics especially for organic electronics, since mobility is typically extracted from field‐effect transistors containing various extrinsic effects and overestimation is popular in the literature. Recently, this issue is emphasized and a reliability factor (r) is proposed by pioneers to gauge the mobility reported. Albeit many factors discussed, how much the extrinsic effects influence r remains unrevealed and a facile solution by using organic transistors is still lacking. Here, it is shown that the widely used extraction method based on the saturation transfer characteristics is sensitive to contact effect and temperature with r dropping to 43%, indeed leading to large mobility overestimation. By contrast, the linear‐regime methods are more reliable particularly the Y‐function method that demonstrates great reliability (r ≈ 100%) even for short‐channel transistors at ultralow temperatures. In addition, operating in saturation regime induces ambipolar conduction further deteriorating reliability if contact doping is absent. High Schottky barriers, on the other side, distort device characteristics making extraction impossible. The results of this study reveal that, aside from device optimizations, selecting a right method is essential for reliable and precise evaluation of the carrier mobility by using organic transistors.
A study of carrier transport in top-gate and bottom-contact TIPS-pentacene organic field-effect transistors (OFETs) based on mobility is presented. Among three mobilities extracted by different methods, the low-field mobility obtained by the Y function exhibits the best reliability and ease for use, whereas the widely applied field-effect mobility is not reliable, particularly in short-channel transistors and at low temperatures. A detailed study of contact transport reveals its strong impact on short-channel transistors, suggesting that a more intrinsic transport analysis is better implemented in relatively longer-channel devices. The observed temperature dependences of mobility are well explained by a transport model with Gaussian-like diffusivity band tails, different from diffusion in localized states band tails. This model explicitly interprets the non-zero constant mobility at low temperatures and clearly demonstrates the effects of disorder and hopping transport on temperature and carrier density dependences of mobility in organic transistors.
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