High-kGate Dielectrics for Emerging Flexible and Stretchable Electronics

Abstract

Recent advances in flexible and stretchable electronics (FSE), a technology diverging from the conventional rigid silicon technology, have stimulated fundamental scientific and technological research efforts. FSE aims at enabling disruptive applications such as flexible displays, wearable sensors, printed RFID tags on packaging, electronics on skin/organs, and Internet-of-things as well as possibly reducing the cost of electronic device fabrication. Thus, the key materials components of electronics, the semiconductor, the dielectric, and the conductor as well as the passive (substrate, planarization, passivation, and encapsulation layers) must exhibit electrical performance and mechanical properties compatible with FSE components and products. In this review, we summarize and analyze recent advances in materials concepts as well as in thin-film fabrication techniques for high- k (or high-capacitance) gate dielectrics when integrated with FSE-compatible semiconductors such as organics, metal oxides, quantum dot arrays, carbon nanotubes, graphene, and other 2D semiconductors. Since thin-film transistors (TFTs) are the key enablers of FSE devices, we discuss TFT structures and operation mechanisms after a discussion on the needs and general requirements of gate dielectrics. Also, the advantages of high- k dielectrics over low- k ones in TFT applications were elaborated. Next, after presenting the design and properties of high- k polymers and inorganic, electrolyte, and hybrid dielectric families, we focus on the most important fabrication methodologies for their deposition as TFT gate dielectric thin films. Furthermore, we provide a detailed summary of recent progress in performance of FSE TFTs based on these high- k dielectrics, focusing primarily on emerging semiconductor types. Finally, we conclude with an outlook and challenges section.

Highly Efficient Flexible Organic Light Emitting Transistor Based on High‐k Polymer Gate Dielectric

“…The water contact angle of PVA films (36.6°) shows a hydrophilic characteristic due to a large number of hydroxyl groups ( Figure a). For the OLET and OTFT device based on C‐PVA dielectric layer under a humidity environment, the water molecules gradually adsorb at the C‐PVA and C‐PVA/C8‐BTBT interface gradually, and act as charge trap states . This reduces the output current and increases the leakage current.…”

Accessing MHz Operation at 2 V with Field‐Effect Transistors Based on Printed Polymers on Plastic

“…This promise stemmed from the prospect of utilizing printing tools derived from well-established graphical arts technologies to deposit a variety of functional materials, which exhibit a suitable combination of mechanical and electronic properties. In this respect, ionic gating schemes through electrolyte dielectrics, [40,41] which allow to achieve 1 V, or even lower, operational voltages, are not suitable because of their slow switching speed, in the tens of kHz range for the best reported cases, [42,43] because of the slow movement of ions. [11] (3.7 MHz at a bias of 3 V [38] and 1.5 MHz at 4 V [39] ).…”

Solution‐Processed High‐Performance p‐Type Perovskite NdAlO3 Thin Films for Transparent Electronics

“…Although the TFTs based on NdAlO 3 /SiO 2 exhibit superior electrical performance, an operating voltage as high as 60 V impedes the practical application in portable devices. To reduce the operating voltage, employing the gate dielectrics with high‐permittivity ( k ) and large areal capacitance is one of the most effective ways 42,43. In this study, solution‐processed Al 2 O 3 thin film was annealed at 800 °C and was integrated into the TFTs, due to its relatively large permittivity and low interface trap density 44.…”