Fabrication of air-stable n-type carbon nanotube thin-film transistors on flexible substrates using bilayer dielectrics

Abstract

Single-walled carbon nanotube (SWNT) thin-film transistors hold great potential for flexible electronics. However, fabrication of air-stable n-type devices by methods compatible with standard photolithography on flexible substrates is challenging. Here, we demonstrated that by using a bilayer dielectric structure of MgO and atomic layer deposited (ALD) Al2O3 or HfO2, air-stable n-type devices can be obtained. The mechanism for conduction type conversion was elucidated and attributed to the hole depletion in SWNT, the decrease of the trap state density by MgO assimilating adsorbed water molecules in the vicinity of SWNT, and the energy band bending because of the positive fixed charges in the ALD layer. The key advantage of the method is the relatively low temperature (120 or 90 °C) required here for the ALD process because we need not employ this step to totally remove the absorbates on the SWNTs. This advantage facilitates the integration of both p-type and n-type transistors through a simple lift off process and compact CMOS inverters were demonstrated. We also demonstrated that the doping of SWNTs in the channel plays a more important role than the Schottky barriers at the metal contacts in carbon nanotube thin-film transistors, unlike the situation in individual SWNT-based transistors.

Bendable CMOS Digital and Analog Circuits Monolithically Integrated with a Temperature Sensor

“…For the benchmarking of the flexible CMOS circuits, Table 1 shows the comparison of electrical performance. The electrical performance is comparable to others reported previously . The importance of this study is to demonstrate the J‐K flip‐flop circuit and the differential amplifier monolithically integrated with a printed temperature sensor using CNT‐ and InGaZnO‐TFTs as the first time.…”

“…In order to develop viable platforms for flexible electronics, signal processing and amplifier components must be fabricated on flexible substrates, thereby allowing for integration with sensors. In this regard, there have been reports on many different approaches for fabricating flexible digital and analog circuits using both inorganic and organic materials . In particular, flexible digital flip‐flop circuits and differential amplifiers have been reported, usually employing either p‐type or n‐type thin film transistors (TFTs) .…”

“…In this regard, there have been reports on many different approaches for fabricating flexible digital and analog circuits using both inorganic and organic materials . In particular, flexible digital flip‐flop circuits and differential amplifiers have been reported, usually employing either p‐type or n‐type thin film transistors (TFTs) . Low‐power consumption and high operating speed are highly desired qualities in integrated circuits (ICs), characteristics that are often found in complementary metal‐oxide‐semiconductor (CMOS)‐based circuits: These are usually used in Si‐based ICs, rather than those using only p‐type or n‐type TFTs.…”

Thread‐Like CMOS Logic Circuits Enabled by Reel‐Processed Single‐Walled Carbon Nanotube Transistors via Selective Doping

“…In these regards, single‐walled carbon nanotubes (SWCNTs) can be considered as a good candidate for 1D fiber transistors owing to their high carrier mobility, good structural flexibility, and simple fabrication using a solution process . Moreover, the semiconductor type of SWCNTs can be intentionally controlled from p‐type to n‐type by a simple doping process such as surface chemical doping, alkali metal doping, or metal contact engineering and consequently, complementary metal‐oxide‐semiconductor (CMOS) integrated circuits can be realized solely by using the SWCNT transistors.…”

Printed flexible thin-film transistors based on different types of modified liquid metal with good mobility

“…Compared to long-channel CNT-TFTs (L ch ≫ L CNT , that is, percolation transport), the utilization of n-type channel doping is a common method for preparing n-CNT-TFTs (however, recent reports have shown n-type TFTs where Sc is utilized as the source-drain contacts [55]). Many dielectric films (such as Si 3 N 4 , Al 2 O 3 , and HfO 2 ) and organic molecules have been used as n-type doping sources for CNT TFTs [56][57][58][59]. However, devices based on organic molecules may encounter obstacles regarding compatibility and stability.…”