Solution-Processed Organic Field-Effect Transistors with High Performance and Stability on Paper Substrates

Breaking the mobility-stability dichotomy in organic semiconductors through adaptive surface doping

Organic semiconductors (OSCs) are pivotal for next-generation flexible electronics but are limited by an intrinsic trade-off between mobility and stability. We introduce adaptive surface doping (ASD), an innovative strategy to overcome this dichotomy in OSCs. ASD's adaptive mechanism accommodates a broad range of dopant concentrations, optimally passivating trap states as needed. This approach significantly lowers the trap energy level from 84 meV to 14 meV above the valence band edge, promoting a transition from hopping to band-like transport mechanisms. ASD boosts carrier mobility by over 60%, reaching up to 30.7 cm2 V-1 s-1, while extending the extrapolated operational lifetime of treated devices beyond 57.5 y. This breakthrough sets a standard in organic electronics, positioning ASD as a powerful method for simultaneously enhancing performance and stability in OSC devices.

Versatile Papertronics: Photo-Induced Synapse and Security Applications on Papers

Paper is a readily available material in nature. Its recyclability, eco-friendliness, portability, flexibility, and affordability make it a favored substrate for researchers seeking cost-effective solutions. Electronic devices based on solution process are fabricated on paper and banknotes using PVK and SnO2 nanoparticles. The devices manufactured on paper substrates exhibit photosynaptic behavior under ultraviolet pulse illumination, stemming from numerous interactions on the surface of the SnO2 nanoparticles. A light-modulated artificial synapse device is realized on a paper at a low voltage bias of -0.01 V, with an average recognition rate of 91.7% based on the Yale Face Database. As a security device on a banknote, 400 devices in a 20 × 20 array configuration exhibited random electrical characteristics owing to the local morphology of the SnO2 nanoparticles and differences in the depletion layer width at the SnO2/PVK interface. The security Physically Unclonable Functions (PUF) key based on the current distribution extracted at -1 V show unpredictable reproducibility with 50% uniformity, 48.7% inter-Hamming distance, and 50.1% bit-aliasing rates. Moreover, the device maintained its properties for more than 210 days under a curvature radius of 8.75 mm and bias and UV irradiation stress conditions.

Recent Progress and Challenges of Implantable Biodegradable Biosensors

Implantable biosensors have evolved to the cutting-edge technology of personalized health care and provide promise for future directions in precision medicine. This is the reason why these devices stand to revolutionize our approach to health and disease management and offer insights into our bodily functions in ways that have never been possible before. This review article tries to delve into the important developments, new materials, and multifarious applications of these biosensors, along with a frank discussion on the challenges that the devices will face in their clinical deployment. In addition, techniques that have been employed for the improvement of the sensitivity and specificity of the biosensors alike are focused on in this article, like new biomarkers and advanced computational and data communicational models. A significant challenge of miniaturized in situ implants is that they need to be removed after serving their purpose. Surgical expulsion provokes discomfort to patients, potentially leading to post-operative complications. Therefore, the biodegradability of implants is an alternative method for removal through natural biological processes. This includes biocompatible materials to develop sensors that remain in the body over longer periods with a much-reduced immune response and better device longevity. However, the biodegradability of implantable sensors is still in its infancy compared to conventional non-biodegradable ones. Sensor design, morphology, fabrication, power, electronics, and data transmission all play a pivotal role in developing medically approved implantable biodegradable biosensors. Advanced material science and nanotechnology extended the capacity of different research groups to implement novel courses of action to design implantable and biodegradable sensor components. But the actualization of such potential for the transformative nature of the health sector, in the first place, will have to surmount the challenges related to biofouling, managing power, guaranteeing data security, and meeting today's rules and regulations. Solving these problems will, therefore, not only enhance the performance and reliability of implantable biodegradable biosensors but also facilitate the translation of laboratory development into clinics, serving patients worldwide in their better disease management and personalized therapeutic interventions.

Paper-based facile capacitive touch arrays for wireless mouse cursor control pad

Wireless devices have become extremely inexpensive and popular in recent years. The two most significant advantages of wireless devices over wired ones are convenience and flexibility. Considering this, a wireless mouse pad prototype for access has been developed in this study. A capacitive sensors-based mouse pad with basic operations and conventional features has been developed using sensing arrays on paper. A facile, do-it-yourself fabrication process was utilized to develop a cost-effective, thin, wearable, and cleanroom-free wireless mouse cursor control (MCC) pad. The ablation process was used to cut the traces of conductive tape and paste them onto the paper to develop the MCC pad. The pad was connected with Espressif Systems (ESP)32 to wirelessly control the cursor of mobile and laptop. The capacitive touch sensor array-based pad is easy to reproduce and recycle. This pad can contribute to future advancements in thin human-machine interfaces, soft robotics, and medical and healthcare applications.

Superhydrophobic, stretchable kirigami pencil-on-paper multifunctional device platform

Wearable electronics with applications in healthcare, human-machine interfaces, and robotics often explore complex manufacturing procedures and are not disposable. Although the use of conductive pencil patterns on cellulose paper provides inexpensive, disposable sensors, they have limited stretchability and are easily affected by variations in the ambient environment. This work presents the combination of pencil-on-paper with the hydrophobic fumed SiO2 (Hf-SiO2) coating and stretchable kirigami structures from laser cutting to prepare a superhydrophobic, stretchable pencil-on-paper multifunctional sensing platform. The resulting sensor exhibits a large response to NO2 gas at elevated temperature from self-heating, which is minimally affected by the variations in the ambient temperature and relative humidity, as well as mechanical deformations such as bending and stretching states. The integrated temperature sensor and electrodes with the sensing platform can accurately detect temperature and electrophysiological signals to alert for adverse thermal effects and cardiopulmonary diseases. The thermal therapy and electrical stimulation provided by the platform can also deliver effective means to battle against inflammation/infection and treat chronic wounds. The superhydrophobic pencil-onpaper multifunctional device platform provides a low-cost, disposable solution to disease diagnostic confirmation and early treatment for personal and population health.

Vertically Integrated Electronics: New Opportunities from Emerging Materials and Devices

Vertical three-dimensional (3D) integration is a highly attractive strategy to integrate a large number of transistor devices per unit area. This approach has emerged to accommodate the higher demand of data processing capability and to circumvent the scaling limitation. A huge number of research efforts have been attempted to demonstrate vertically stacked electronics in the last two decades. In this review, we revisit materials and devices for the vertically integrated electronics with an emphasis on the emerging semiconductor materials that can be processable by bottom-up fabrication methods, which are suitable for future flexible and wearable electronics. The vertically stacked integrated circuits are reviewed based on the semiconductor materials: organic semiconductors, carbon nanotubes, metal oxide semiconductors, and atomically thin two-dimensional materials including transition metal dichalcogenides. The features, device performance, and fabrication methods for 3D integration of the transistor based on each semiconductor are discussed. Moreover, we highlight recent advances that can be important milestones in the vertically integrated electronics including advanced integrated circuits, sensors, and display systems. There are remaining challenges to overcome; however, we believe that the vertical 3D integration based on emerging semiconductor materials and devices can be a promising strategy for future electronics.

Ultralow-Power and Radiation-Tolerant Complementary Metal-Oxide-Semiconductor Electronics Utilizing Enhancement-Mode Carbon Nanotube Transistors on Paper Substrates

The development of eco-friendly, ultralow-power and easy-to-process electronics is facing dominant challenges in emerging off-the-grid applications, such as the Internet of Things (IoTs) and extreme environment explorations at the south/north pole, in the deep sea, and in outer space. Eco-friendly, biodegradable, lightweight, and flexible paper-based electronics can provide many new possibilities for next-generation devices and circuits. Here, enhancement-mode (E-mode, remaining off state at zero gate voltages) carbon nanotube (CNT) complementary metal-oxide-semiconductor (CMOS) thin-film transistors (TFTs) are built on paper substrates through a printing-based process. Benefitting from the CMOS circuit style and E-mode transistors, the fabricated CMOS inverters exhibit high voltage gains (more than 11) and noise margins (up to 75% 1/2 V_DD at V_DD of 0.4 V), and rail-to-rail operation down to a V_DD as low as 0.2 V and record low power dissipation as low as 0.0124 pW μm^-1 . Furthermore, the transistors and integrated circuits (ICs) show an excellent radiation tolerance of a total ionizing dose (TID) exceeding 2 Mrad with a high dose rate of 365 rad s^-1 . The record power consumption and outstanding radiation tolerance behavior achieved in paper-based and easy-to-process CNT electronics are attractive for emerging energy-saving and environmentally friendly ICs in harsh environment (such as outer-space) applications.

Flexible organic optoelectronic devices on paper

Paper substrate has many advantages, such as low cost, bendable, foldable, printable, and environmentally friendly recycling. Nowadays, paper has been further extended as a flexible platform to deliver electronic information with the integration of organic optoelectronic devices, such as organic thin-film transistor, organic solar cell, organic electrochromic device, and organic light-emitting device. It has great potential to become the new generation of flexible substrate. Given rough surface and porous of paper, many efforts have been underway in recent years to enable the compatibility between optoelectronics and paper substrate. In this review, we present the development history of paper and its physicochemical properties, and summarize the current development of paper-based organic optoelectronic devices. We also discuss the challenges that need to be addressed before practical uses of paper-based organic optoelectronic devices.

Paper-based field-effect transistor sensors

The present scenario in the world largely demands affordable, fast, recyclable, and flexible electronic devices for bio sensing. Varieties of paper-based devices such as microfluidics paper electrodes, paper diodes, and paper-based transistors etc. have been developed and validated. Most of the fabrication techniques published so far have focused on economic, environment-friendly straightforward methods to develop paper-based field-effect transistors (PFET) sensors, additionally, explored their applications. The synthetic-free, mechanically flexible, biocompatible, and signal amplification capability render PFET based sensors for wearable device makers. Modified organic/inorganic PFETs identify target analytes based on the electrical signal and endow them as perfect transducers. In the field of PFET bio sensing technology, numerous challenges are needed to be discussed to proceed forward in biomedical and other analytical applications. Realizing biologically or chemically modified PFET having an exceptional signal to noise ratio, specificity, with rapid detection ability is challenging. This review recapitulates the fabrication techniques, performances of various PFET sensors, and summarizes the report by concluding remarks including the limitations of the existing PFET based sensors and the future holds in regards to the sustainable nature of PFET.

Paper-Based Sensors for Gas, Humidity, and Strain Detections: A Review

Paper, as a flexible, low-cost, lightweight, tailorable, environmental-friendly, degradable, and renewable material, is emerging in electronic devices. Especially, many kinds of paper-based (PB) sensors have been reported for wearable applications in recent years. Among them, the PB gas, humidity, and strain sensors are widely studied for monitoring gas, humidity, and strain from the human body and the environment. However, gas, humidity, and strain often coexist and interact, and the paper itself is hydrophilic and flexible, resulting in that it is still challenging to develop high-performance PB sensors specialized for gas, humidity, and strain detections. Therefore, it is necessary to summarize and discuss them systematically. In this review, we focus on summarizing the state-of-art studies of the PB gas, humidity, and strain sensors. Specifically, the fabrications (electrodes and sensing materials) and applications of PB gas, humidity, and strain sensors are summarized and discussed. The current challenges and the potential trends of PB sensors for gas, humidity, and strain detections are also outlined. This review not only can help readers to understand the development status of the PB gas, humidity, and strain sensors but also is helpful for readers to find out and solve the problems in this field through comparative reading.

Wettability Control of Interfaces for High-Performance Organic Thin-Film Transistors by Soluble Insulating Polymer Films

Organic small-molecule semiconductors have higher carrier mobility compared to polymer semiconductors, while the actual performances of these materials are susceptible to morphological defects and misalignment of crystalline grains. Here, a new strategy is explored to control the crystallization and morphologies of a solution-processed organic small-molecule semiconductor 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) using soluble polymer films to control the wettability of substrates. Different from the traditional surface modification method, the polymer layer as a modification layer is soluble in the semiconductor solution during the fabrication of organic thin-film transistors (OTFTs). The dissolved polymer alters the state of the semiconductor solution, which in turn, changes the crystallographic morphologies of the semiconductor films. By controlling the solubility and thickness of the polymer modification layers, it is possible to regulate the grain boundary and domain size of C8-BTBT films, which determine the performances of OTFTs. The bottom-gate transistors modified by a thick PS layer exhibit a mobility of >7 cm²/V·s and an on/off ratio of >10⁷. It is expected that this new modification method will be applicable to high-performance OTFTs based on other small molecular semiconductors and dielectrics.