Hyeon Jun Ha

Flexible low-voltage pentacene memory thin-film transistors with combustion-processable Al2O3 gate dielectric and Au nanoparticles

A Au nanoparticles (NPs) embedded pentacene thin-film transistor (TFT) with solution-based Al2O3 was fabricated on a polyethersulfone substrate. The TFT for low-voltage operation within −3 V was realized with the Al2O3 dielectric film. By a combustion process for Al2O3, efficient driving of conversion reaction at low annealing temperature of 200 °C can be achieved and the device can be made on a plastic substrate. And, the Au NPs were deposited by the contact printing method using the polydimethylsiloxane stamp. From the electrical characteristics of the devices, a saturation mobility value of 4.25 cm2 V−1 s−1, threshold voltage (Vth) of ~0.5 V, subthreshold swing of 70 mV dec−1 and memory window of 0.21 V at −3 V programming gate bias voltage were obtained.

High-Performance Amorphous Indium Oxide Thin-Film Transistors Fabricated by an Aqueous Solution Process at Low Temperature

This paper presents low temperature solution-processed fabrication techniques for modern thin-film transistors (TFTs). We have investigated the electrical performance of aqueous solution-processed amorphous indium oxide (a-In2O3) TFTs prepared using different annealing temperatures. Even though the a-In2O3 TFTs were annealed at 200 °C, electrical characteristics of aqueous solution-processed a-In2O3 TFTs were obtained. High performance such as a saturation mobility of 8.6 cm2 V-1 s-1 and an on/off current ratio of over 106 was exhibited by a-In2O3 TFTs annealed at 250 °C.

The electrical and photoconductivity characteristics of donor-acceptor alternating copolymer using solution process

The authors report on the electrical and photoconductivity characteristics of donor-acceptor alternating copolymer, poly(dioctyloxinapthalenediketopyrrolopyrrole) (PONDPP) with Al/PONDPP/p-Si/Al hybrid organic/inorganic Schottky diode for optoelectronic applications. The fabricated device shows ideality factor value of 2.6 and barrier height of 0.68 eV obtained from current-voltage characteristics. The high rectification ratio of 1.86 × 104 and photo-responsivity of 55 mA/W at 650 nm is achieved. From results, we found that the fine photo-response and electrical characteristics are attributed to the modified band-gap structure to have Schottky barrier at highest occupied molecular orbital to valence band of silicon and high hole mobility of PONDPP.

Highly flexible titanium dioxide-based resistive switching memory with simple fabrication

We demonstrate a flexible resistive switching random access memory (ReRAM), which is a promising next-generation memory on a flexible substrate. The proposed method enables us to fabricate an Al/TiO2/Al structure on a polyimide substrate, which has highly flexible and durable characteristics, rather than a Si-based substrate by a simple fabrication process. To understand the role of oxygen vacancies in TiO2, our devices was analyzed by X-ray photoelectron spectroscopy (XPS) and XPS depth profile analyses. Moreover, severe bending of the device did not affect the memory performance owing to its small channel length and the high ductility of the electrode. The results presented here can provide a new approach to the fabrication of nonvolatile memories for flexible electronic devices.

Flexible ambipolar organic field-effect transistors with reverse-offset-printed silver electrodes for a complementary inverter

We report ambipolar organic field-effect transistors and complementary inverter circuits with reverse-offset-printed (ROP) Ag electrodes fabricated on a flexible substrate. A diketopyrrolopyrrole-based co-polymer (PDPP-TAT) was used as the semiconductor and poly(methyl methacrylate) was used as the gate insulator. Considerable improvement is observed in the n-channel electrical characteristics by inserting a cesium carbonate (Cs2CO3) as the electron-injection/hole-blocking layer at the interface between the semiconductors and the electrodes. The saturation mobility values are 0.35 cm(2) V(-1) s(-1) for the p-channel and 0.027 cm(2) V(-1) s(-1) for the n-channel. A complementary inverter is demonstrated based on the ROP process, and it is selectively controlled by the insertion of Cs2CO3 onto the n-channel region via thermal evaporation. Moreover, the devices show stable operation during the mechanical bending test using tensile strains ranging from 0.05% to 0.5%. The results confirm that these devices have great potential for use in flexible and inexpensive integrated circuits over a large area.

Localized-surface-plasmon-enhanced multifunction silicon nanomembrane Schottky diodes based on Au nanoparticles

Au nanoparticle (NP)-modified Si nanomembrane (Si NM) Schottky barrier diodes (SBDs) were fabricated by using a transfer-printing method to create pedestals using only one photomask on a flexible substrate. The transfer using the pedestals afforded a yield of >95% with no significant cracks. The plasmonic Au NPs can facilitate the improvement of the incident optical absorption. The Au NP-modified Si NM SBD exhibited enhanced photoresponse characteristics with an external quantum efficiency (η(EQE)) of 34%, a photosensitivity (P) of 27 at a voltage bias of -5 V, a light intensity of 1.2 W cm(-2), and a responsivity (R(ph)) of 0.21 A W(-1). Additionally, the mechanical bending characteristics of the device were observed while a compressive strain up to 0.62% was applied to the diode. The results suggest that the Au NP-modified Si NM SBD has great potential for use in multifunction devices as a strain sensor and photosensor.

Printed silicon broadband membrane reflectors by laser interference lithography

We report on printed silicon photonic crystal broadband membrane reflectors (MRs) based on laser interference lithography (LIL) patterning. Single-layer photonic crystal membrane which was formed by the LIL technique on a silicon-on-insulator (SOI) wafer was transferred by the contact printing method using the polydimethylsiloxane (PDMS) stamp on a glass substrate. These broadband silicon-MRs show high-reflectivity of 95 % around 1200 nm wavelength with bandwidth of about 100 nm. This simplest and easiest method to fabricate broadband MRs has great potential for many types of optoelectronic and photonic devices.

The effect of Au nanoparticle on metal organic semiconductor field effect transistor on plastic substrate by transfer method

We report on organic nonvolatile memory devices, using pentacene as the active semiconductor layer and gold nanoparticles (Au NPs) array as charge storage elements. An effective and facile fabrication by self-assembly of Au NPs at a toluene/water interface with ethanol as the inducer is used for the forming of gold nanoparticles (Au NPs) monolayer. The organic memory devices exhibited good memory effects by hole trapping/detrapping in the gold nanoparticles. And also we design a modification of memory window by transfer times.