Critical Impact of Gate Dielectric Interfaces on the Contact Resistance of High-Performance Organic Field-Effect Transistors

Abstract

Extensive research on organic field-effect transistors (OFETs) performed to date investigated separately the electronic contact and the gate dielectric interfaces but rarely probed the relation between the two. In this report, the strong impact of the gate dielectric on the contact resistance (R c ) is revealed. With the same semiconductor dioctylbenzothienobenzothiophene (C8-BTBT) and the same device configuration, the R c value varies greatly from 10 to 66 kΩ•cm depending on the gate dielectric interfaces. Also, the gatevoltage dependency of R c exhibits an unexpectedly large discrepancy when different dielectrics are used. Intuitive comprehension points to the possibility that the gate dielectric interface affects the morphology of semiconductor and thus the charge injection. However, from microstructure study, albeit the semiconductor film exhibits structural defects on certain dielectrics, the impact on the injection is not crucial. Instead, bias-stress test correlates well with the contact resistance on different dielectric interfaces. At a quantitative level, gate-voltage-dependent R c can be described by taking into account the different charge trapping induced by the gate dielectrics. The origin of the varied R c is thus attributed to the trapped charges, which screen the gate field and reduce the carrier mobility simultaneously. A general method is proposed to examine whether the charge injection is significantly influenced by the charge trapping effect due to the gate dielectrics.

Molecular Orientation‐Dependent Bias Stress Stability in Bottom‐Gate Organic Transistors Based on an n‐Type Semiconducting Polymer

“…Although previous research has focused on charge trapping in the channel region, [ 15,16,[34][35][36][37] trapping events in the injection region are also important. [38][39][40][41] First, we tried to control thickness of P(NDI2OD-T2) layers to examine the role of the semiconductor bulk. The normalized I D decay of the devices with P(NDI2OD-T2) layers of varied thickness was investigated.…”

Contact engineering in organic field-effect transistors

“…The group of R tot -L linear-regression lines often converge at a common point, called the convergence point (CP), which can be used to qualify the charge injection and charge transport [29]. When there is considerable scatter in m and V th (e.g., OFETs on bare SiO 2 with significant trapping effect), a modified TLM (M-TLM) is suggested to improve extraction accuracy [30,31]. Furthermore, to extract R c in a saturated regime, power TLM (P-TLM) should be applied by measuring the output characteristics (I d -V d ), which are derived from the dissipated power in the whole device regardless of the linear or saturated source-drain electric field [32].…”

“…Due to (a) and Eqn 7, it has been observed that R c also exhibits a power dependence on V g [31,49] ðR c À R c0 Þ / jV g À V th j g ;…”

“…Hence, for a certain OSC, different morphologies (such as single crystalline, poly-crystalline and amorphous) and trap densities induced by depositions can result in different values and V g -dependence of R c [50]. Even insulating dielectric layers can also affect R c by tuning morphology, defect states and energetic disorder in OSC layer [31]. …”

Reducing contact resistance in ferroelectric organic transistors by buffering the semiconductor/dielectric interface

“…Similar studies also show the strong influence of the gate dielectric interface on the contact resistance. 31,32 In summary, the contact resistance in Fe-OFETs was significantly reduced by using an ultrathin PMMA layer inserted between the ferroelectric polymer and organic semiconductor layers. Our investigations revealed that such an enhanced charge injection was due to the narrowing of the trap distribution in the access region of Fe-OFETs after buffering the interfacial polarization fluctuation.…”