Charge Distribution and Contact Resistance Model for Coplanar Organic Field-Effect Transistors

Hlaing

Hong

et al. 2014

Adv Materials Inter

Self Cite

In bottom‐contact organic field‐effect transistors (OFETs), the functionalization of source/drain electrodes leads to a tailored surface chemistry for film growth and controlled interface energetics for charge injection. This report describes a comprehensive investigation into separating and correlating the energetic and morphological effects of a self‐assembled monolayers (SAMs) treatment on Au, Ag, and Cu electrodes. Fluorinated 5,11‐bis(triethylsilylethynyl) anthradithiophene (diF‐TES‐ADT) and pentafluorobenzenethiol (PFBT) are employed as a soluble small‐molecule semiconductor and a SAM material, respectively. Upon SAM modification, the Cu electrode devices benefit from a particularly dramatic performance improvement, closely approaching the performance of OFETs with PFBT‐Au and PFBT‐Ag. Ultraviolet photoemission spectroscopy, polarized optical microscopy, grazing‐incidence wide‐angle X‐ray scattering elucidate the metal work function change and templated crystal growth with high crystallinity resulting from SAMs. The transmission‐line method separates the channel and contact properties from the measured OFET current–voltage data, which conclusively describes the impact of the SAMs on charge injection and transport behavior.

Section: −3mentioning

confidence: 99%

Decoupling the Effects of Self‐Assembled Monolayers on Gold, Silver, and Copper Organic Transistor Contacts

Hlaing

Hong

et al. 2014

Adv Materials Inter

Self Cite

“…To achieve carrier density equivalent of the dual-channel, at least V GS < −2 V would be required in the TG devices. Since the mobility was associated with gate-voltage [30], we suggest that higher carrier density of the DG devices would contribute to obtaining the higher mobility than the TG devices.…”

Section: Discussionmentioning

confidence: 94%

Charge Carrier Distribution in Low-Voltage Dual-Gate Organic Thin-Film Transistors

et al. 2018

Dual-gate organic thin-film transistors (DGOTFTs), which exhibit better electrical properties, in terms of on-current and subthreshold slope than those of single-gate organic thin-film transistors (OTFTs) are promising devices for high-performance and robust organic electronics. Electrical behaviors of high-voltage (>10 V) DGOTFTs have been studied: however, the performance analysis in low-voltage DGOTFTs has not been reported because fabrication of low-voltage DGOTFTs is generally challenging. In this study, we successfully fabricated low-voltage (<5 V) DGOTFTs by employing thin parylene film as gate dielectrics and visualized the charge carrier distributions in low-voltage DGOTFTs by a simulation that is based on finite element method (FEM). The simulation results indicated that the dual-gate system produces a dual-channel and has excellent control of charge carrier density in the organic semiconducting layer, which leads to the better switching characteristics than the single-gate devices.

“…[27,28] Figure 2 provides clear evidence that morphology is another key contributor to the difference between the TC and the BC geometries. The atomic force microscopy (AFM) images here show that, despite the nominally identical DNTT deposition, there are striking differences in the final film microstructure.…”

Section: Film Morphologymentioning

confidence: 95%

“…[27] The coplanar OFETs, meanwhile, are sensitively affected by the barrier height, while the semiconductor mobility still is an important factor. [28] Now that we know the accurate values for µ ch and R c , we can further our analysis to gain deeper understanding of R c . As a sharp carrier-density bottleneck region is responsible for R c in coplanar devices, [27] R c in our BC and BC-SAMs OFETs can basically expect twofold influences from V G ; first as the chargedensity modulator (capacitive effect), second as the mobility changer within the same R c zone.…”

Section: Physical Descriptionmentioning

confidence: 99%

Potentiometric Parameterization of Dinaphtho[2,3‐b:2′,3′‐f]thieno[3,2‐b]thiophene Field‐Effect Transistors with a Varying Degree of Nonidealities

Thomas

et al. 2018

Adv Elect Materials

in a fully standardized manner with, for instance, no extra light, heat, or active areas involved. [4] By contrast, widely discussed parameters (i.e., charge-carrier mobility and threshold voltage, V T ) for organic field-effect transistors (OFETs) are model parameters, meaning that the numbers are inherently dependent on the model used as well as the procedure followed to implement this model. [5,6] Therefore, the lack of consensus may lead to discrepancies in parameters extracted even from the same current-voltage curve.In 2004, Horowitz et al. summarized and extended a series of their earlier works to clarify nonidealities, or disagreement with metal-oxide-semiconductor field-effect transistors (MOSFETs) in OFET devices. [7] As illustrated here, gate-voltage (V G ) dependence of mobility and existence of the contact resistances (R c ) are two common and theoretically justifiable sources of deviations from ideal MOSFET characteristics. Until recently, many experimental studies employed techniques such as the transmission-line method (TLM) or gated fourpoint probe measurements (gFPP), which can in principle directly probe these phenomena by separating the channel and contact properties. [8][9][10][11][12][13][14] In our view, the reported data bring strong evidence for the pronounced variability in relative strengths, and voltage-or structure dependence of the contact and channel effects, which makes different theoretical frameworks often necessary to understand different devices. Nonetheless, the MOSFET current-voltage model has been employed quite universally for simple parameter extraction. In 2016, Gundlach and co-workers used impedance spectroscopy to systematically address mobility overestimation in rubrene single-crystal transistors, [15] an issue that in fact originates from neglecting R c and/or noncontextually adopting simplified equations. In this context, it is timely to critically reassess basic assumptions of the device parameters, specific behavioral nonidealities, and associated calculation issues. Ideally, growing efforts into such a process will be transformed into carefully thought-out and broadly accepted practices for OFET research.In this article, we report on the use of scanning Kelvin probe microscopy (SKPM) and correlated analysis aimed at generalizable parameterization. SKPM is a powerful, surface-sensitive technique that can directly probe critical resistive pathways in OFETs to quantify material-and interface-related parameters. Furthermore, SKPM holds some advantages over the TLM or gFPP in that neither averaging Taking full account of the contact effects and including an explicit threshold voltage in calculation are shown to be critical to access the intrinsic carrier mobility, while simple derivative-based extraction may over-or underestimate it. Further analytical developments correlate individual physical parameters, leading to the discovery that pentafluorobenzenethiol self-assembled on gold predominantly affects the carrier mobility rather than the injection barrier.