Photo-Fries-based photosensitive polymeric interlayers for patterned organic devices

Fine-Tuning the Performance of Ultraflexible Organic Complementary Circuits on a Single Substrate via a Nanoscale Interfacial Photochemical Reaction

Flexible electronics has paved the way toward the development of next-generation wearable and implantable healthcare devices, including multimodal sensors. Integrating flexible circuits with transducers on a single substrate is desirable for processing vital signals. However, the trade-off between low power consumption and high operating speed is a major bottleneck. Organic thin-film transistors (OTFTs) are suitable for developing flexible circuits owing to their intrinsic flexibility and compatibility with the printing process. We used a photoreactive insulating polymer poly((±)endo,exo-bicyclo[2.2.1]hept-ene-2,3-dicarboxylic acid, diphenylester) (PNDPE) to modulate the power consumption and operating speed of ultraflexible organic circuits fabricated on a single substrate. The turn-on voltage (V _on) of the p- and n-type OTFTs was controlled through a nanoscale interfacial photochemical reaction. The time-of-flight secondary ion mass spectrometry revealed the preferential occurrence of the PNDPE photochemical reaction in the vicinity of the semiconductor-dielectric interface. The power consumption and operating speed of the ultraflexible complementary inverters were tuned by a factor of 6 and 4, respectively. The minimum static power consumption was 30 ± 9 pW at transient and 4 ± 1 pW at standby. Furthermore, within the tuning range of the operating speed and at a supply voltage above 2.5 V, the minimum stage delay time was of the order of hundreds of microseconds. We demonstrated electromyogram measurements to emphasize the advantage of the nanoscale interfacial photochemical reaction. Our study suggests that a nanoscale interfacial photochemical reaction can be employed to develop imperceptible and wearable multimodal sensors with organic signal processing circuits that exhibit low power consumption.

Heterogeneous Functional Dielectric Patterns for Charge-Carrier Modulation in Ultraflexible Organic Integrated Circuits

Flexible electronics have gained considerable attention for application in wearable devices. Organic transistors are potential candidates to develop flexible integrated circuits (ICs). A primary technique for maximizing their reliability, gain, and operation speed is the modulation of charge-carrier behavior in the respective transistors fabricated on the same substrate. In this work, heterogeneous functional dielectric patterns (HFDP) of ultrathin polymer gate dielectrics of poly((±)endo,exo-bicyclo[2.2.1]hept-ene-2,3-dicarboxylic acid, diphenylester) (PNDPE) are introduced. The HFDP that are obtained via the photo-Fries rearrangement by ultraviolet radiation in the homogeneous PNDPE provide a functional area for charge-carrier modulation. This leads to programmable threshold voltage control over a wide range (-1.5 to +0.2 V) in the transistors with a high patterning resolution, at 2 V operational voltage. The transistors also exhibit high operational stability over 140 days and under the bias-stress duration of 1800 s. With the HFDP, the performance metrics of ICs, for example, the noise margin and gain of the zero-V_GS load inverters and the oscillation frequency of ring oscillators are improved to 80%, 1200, and 2.5 kHz, respectively, which are the highest among the previously reported zero-V_GS -based organic circuits. The HFDP can be applied to much complex and ultraflexible ICs.

Ex situ and in situ characterization of patterned photoreactive thin organic surface layers using friction force microscopy

Photolithographic methods allow an easy lateral top-down patterning and tuning of surface properties with photoreactive molecules and polymers. Employing friction force microscopy (FFM), we present here different FFM-based methods that enable the characterization of several photoreactive thin organic surface layers. First, three ex situ methods have been evaluated for the identification of irradiated and non-irradiated zones on the same organosilane sample by irradiation through different types of masks. These approaches are further extended to a time dependent ex situ FFM measurement, which allows to study the irradiation time dependent evolution of the resulting friction forces by sequential irradiation through differently sized masks in crossed geometry. Finally, a newly designed in situ FFM measurement, which uses a commercial bar-shaped cantilever itself as a noncontact shadow mask, enables the determination of time dependent effects on the surface modification during the photoreaction.

High performance p-type organic thin film transistors with an intrinsically photopatternable, ultrathin polymer dielectric layer

A high-performing bottom-gate top-contact pentacene-based oTFT technology with an ultrathin (25-48 nm) and electrically dense photopatternable polymeric gate dielectric layer is reported. The photosensitive polymer poly((±)endo,exo-bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid, diphenylester) (PNDPE) is patterned directly by UV-exposure (λ = 254 nm) at a dose typical for conventionally used negative photoresists without the need for any additional photoinitiator. The polymer itself undergoes a photo-Fries rearrangement reaction under UV illumination, which is accompanied by a selective cross-linking of the macromolecules, leading to a change in solubility in organic solvents. This crosslinking reaction and the negative photoresist behavior are investigated by means of sol-gel analysis. The resulting transistors show a field-effect mobility up to 0.8 cm2 V-1 s-1 at an operation voltage as low as -4.5 V. The ultra-low subthreshold swing in the order of 0.1 V dec-1 as well as the completely hysteresis-free transistor characteristics are indicating a very low interface trap density. It can be shown that the device performance is completely stable upon UV-irradiation and development according to a very robust chemical rearrangement. The excellent interface properties, the high stability and the small thickness make the PNDPE gate dielectric a promising candidate for fast organic electronic circuits.