Energy-Band Engineering by Remote Doping of Self-Assembled Monolayers Leads to High-Performance IGZO/p-Si Heterostructure Photodetectors.

Metal oxide semiconductors are of great interest for enabling advanced photodetectors. However, operational instability and the absence of an appropriate doping technique hinder practical development and commercialization. Here, a strategy is proposed to dramatically increase the conventional photodetection performance, having superior stability in operational and environmental atmospheres. By performing energy-band engineering through an octadecylphosphonic acid (ODPA) self-assembled-monolayer-based doping treatment, the proposed indium-gallium-zinc oxide (IGZO)/p-Si heterointerface devices exhibit greatly enhance the photoresponsive characteristics, including a photoswitching current ratio with a 100-fold increase, and photoresponsivity and detectivity with a 15-fold increase each. The observed ODPA doping effects are investigated through comprehensive analysis with X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and Kelvin probe force microscopy (KPFM). Furthermore, the proposed photodetectors, fabricated at a 4 in. wafer scale, demonstrate its excellent operation robustness with consistent performance over 237 days and 20 000 testing cycles.

Highly stacked 3D organic integrated circuits with via-hole-less multilevel metal interconnects.

Multilevel metal interconnects are crucial for the development of large-scale organic integrated circuits. In particular, three-dimensional integrated circuits require a large number of vertical interconnects between layers. Here, we present a novel multilevel metal interconnect scheme that involves solvent-free patterning of insulator layers to form an interconnecting area that ensures a reliable electrical connection between two metals in different layers. Using a highly reliable interconnect method, the highest stacked organic transistors to date, a three-dimensional organic integrated circuits consisting of 5 transistors and 20 metal layers, is successfully fabricated in a solvent-free manner. All transistors exhibit outstanding device characteristics, including a high on/off current ratio of ~107, no hysteresis behavior, and excellent device-to-device uniformity. We also demonstrate two vertically-stacked complementary inverter circuits that use transistors on 4 different floors. All circuits show superb inverter characteristics with a 100% output voltage swing and gain up to 35 V per V.

Negative Transconductance Heterojunction Organic Transistors and their Application to Full-Swing Ternary Circuits.

Multivalued logic (MVL) computing could provide bit density beyond that of Boolean logic. Unlike conventional transistors, heterojunction transistors (H-TRs) exhibit negative transconductance (NTC) regions. Using the NTC characteristics of H-TRs, ternary inverters have recently been demonstrated. However, they have shown incomplete inverter characteristics; the output voltage (VOUT ) does not fully swing from VDD to GND . A new H-TR device structure that consists of a dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT) layer stacked on a PTCDI-C13 layer is presented. Due to the continuous DNTT layer from source to drain, the proposed device exhibits novel switching behavior: p-type off/p-type subthreshold region /NTC/ p-type on. As a result, it has a very high on/off current ratio (≈105 ) and exhibits NTC behavior. It is also demonstrated that an array of 36 of these H-TRs have 100% yield, a uniform on/off current ratio, and uniform NTC characteristics. Furthermore, the proposed ternary inverter exhibits full VDD -to-GND swing of VOUT with three distinct logic states. The proposed transistors and inverters exhibit hysteresis-free operation due to the use of a hydrophobic gate dielectric and encapsulating layers. Based on this, the transient operation of a ternary inverter circuit is demonstrated for the first time.

Chemical Doping Effects in Multilayer MoS2 and Its Application in Complementary Inverter.

Multilayer MoS2 has been gaining interest as a new semiconducting material for flexible displays, memory devices, chemical/biosensors, and photodetectors. However, conventional multilayer MoS2 devices have exhibited limited performances due to the Schottky barrier and defects. Here, we demonstrate poly(diketopyrrolopyrrole-terthiophene) (PDPP3T) doping effects in multilayer MoS2, which results in improved electrical characteristics (∼4.6× higher on-current compared to the baseline and a high current on/off ratio of 106). Synchrotron-based study using X-ray photoelectron spectroscopy and grazing incidence wide-angle X-ray diffraction provides mechanisms that align the edge-on crystallites (97.5%) of the PDPP3T as well as a larger interaction with MoS2 that leads to dipole and charge transfer effects (at annealing temperature of 300 °C), which support the observed enhancement of the electrical characteristics. Furthermore, we demonstrate a complementary metal-oxide-semiconductor inverter that uses a p-type MoSe2 and a PDPP3T-doped MoS2 as charging and discharging channels, respectively.