In-Kyu You

Remarkable Enhancement of Hole Transport in Top‐Gated N‐Type Polymer Field‐Effect Transistors by a High‐k Dielectric for Ambipolar Electronic Circuits

A remarkable enhancement of p-channel properties is achieved in initially n-channel dominant ambipolar P(NDI2OD-T2) organic field-effect transistors (OFETs) by the use of the fluorinated high-k dielectric P(VDF-TrFE). An almost two orders of magnitude increase in hole mobility (~0.11 cm(2) V(-1) s(-1) ) originates from a strong interface modification at the semiconductor/dielectric interface, which provides high-performance complementary-like inverters and ring oscillator circuits.

Charge Injection Engineering of Ambipolar Field-Effect Transistors for High-Performance Organic Complementary Circuits

Ambipolar π-conjugated polymers may provide inexpensive large-area manufacturing of complementary integrated circuits (CICs) without requiring micro-patterning of the individual p- and n-channel semiconductors. However, current-generation ambipolar semiconductor-based CICs suffer from higher static power consumption, low operation frequencies, and degraded noise margins compared to complementary logics based on unipolar p- and n-channel organic field-effect transistors (OFETs). Here, we demonstrate a simple methodology to control charge injection and transport in ambipolar OFETs via engineering of the electrical contacts. Solution-processed caesium (Cs) salts, as electron-injection and hole-blocking layers at the interface between semiconductors and charge injection electrodes, significantly decrease the gold (Au) work function (∼4.1 eV) compared to that of a pristine Au electrode (∼4.7 eV). By controlling the electrode surface chemistry, excellent p-channel (hole mobility ∼0.1-0.6 cm(2)/(Vs)) and n-channel (electron mobility ∼0.1-0.3 cm(2)/(Vs)) OFET characteristics with the same semiconductor are demonstrated. Most importantly, in these OFETs the counterpart charge carrier currents are highly suppressed for depletion mode operation (I(off) < 70 nA when I(on) > 0.1-0.2 mA). Thus, high-performance, truly complementary inverters (high gain >50 and high noise margin >75% of ideal value) and ring oscillators (oscillation frequency ∼12 kHz) based on a solution-processed ambipolar polymer are demonstrated.

SrTa2O6 Thin Films Deposited by Plasma-Enhanced Atomic Layer Deposition

SrTa2O6 (STO) thin films were prepared by plasma-enhanced atomic layer deposition (PEALD) with an alternating supply of reactant sources, Sr[Ta(C2H5O)5(C4H10NO)]2 {strontium bis-[tantalum penta-ethoxide dimethyllaminoethoxide]; Sr(Ta(OEt)5dmae)2} and O2 plasma. It was observed that the uniform and conformal STO thin films were successfully deposited using PEALD and the film thickness per cycle was saturated at approximately 0.8 A at 300°C. Electrical properties of STO thin films prepared on Pt/SiO2/Si substrates at various annealing temperatures were investigated. While the grain size and dielectric constant of STO films increased with increasing annealing temperature, the leakage current characteristics of STO films slightly deteriorated. The leakage current density of a 40 nm STO film annealed at 600°C was approximately 5×10-8 A/cm2 at 3 V.

Low-voltage-operated top-gate polymer thin-film transistors with high capacitance poly(vinylidene fluoride-trifluoroethylene)/poly(methyl methacrylate) dielectrics

We report on low-voltage-operated polymer transistors with poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)]/poly(methyl methacrylate) (PMMA) blended films as a gate dielectric layer. Top-gate polymer transistors are fabricated by all-solution processes on poly(9,9-dioctylfuorene-co-bithiophene) (F8T2) as an active layer. Both the operating voltage and charge carrier mobility are improved using P(VDF-TrFE)/PMMA blended films as a dielectric layer and by optimization of the ratio of the composite. F8T2 transistors have a high field-effect mobility of 1×10−2 cm2/V s and a low operation gate voltage of less than 10 V. The operation voltage effectively decreases owing to the high permittivity of the P(VDF-TrFE)]/(PMMA) blended film (10.4–8.4). The hysteresis induced by the ferroelectric polymer effectively disappears with the addition of a small amount of amorphous PMMA (5 wt %).

Crystallographic orientations and electrical properties of Bi3.47La0.85Ti3O12 thin films on Pt/Ti/SiO2/Si and Pt/SiO2/Si substrates

We report on the crystallization and electrical properties of Bi3.47La0.85Ti3O12 (BLT) thin films for possible ferroelectric non-volatile memory applications. The film properties were found to be strongly dependent on process conditions especially on the intermediate heat treatment conditions. The crystallographic orientation of the films showed sharp changes at the intermediate rapid thermal annealing (RTA) temperature of 450°C. Below 450°C, BLT thin films have orientation while they have preffered c-axis orientation above 450°C. We found that RTA conditions of the first coating layer play a major role in determining the entire crystallographic orientation of the films. The films also showed of ferroelectric hysterisis behavior strongly dependent on RTA treatment. In fact, the remanent polarization of Bi3.465La0.85Ti3O12 thin films having preferred crystallographic orientation showed much smaller value compared to those having orientation. The BLT films also exhibited good fatigue characteristics under bipolar stress up to 1011 cycles regardless of their intermediate thermal treatments.

New High-k SrTa2O6 Gate Dielectrics Prepared by Plasma-Enhanced Atomic Layer Chemical Vapor Deposition

We report on the electrical characterization of SrTa2O6 (STA) films as alternative gate dielectrics deposited directly on Si by plasma-enhanced atomic layer chemical vapor deposition. The dielectric constant extracted from the accumulation capacitance and the fixed charge of the interface state for STA films annealed in O2 ambient are about 20 and 6.54×10-8 C/cm2, respectively. The interface trap density Dit at the midgap obtained from a quasistatic capacitance-voltage technique is estimated approximately to be in the low 1011 cm-2eV-1 range and the leakage current is approximately 2.98×10-9 A/cm2 at 1 V bias in accumulation. The films annealed in N2 ambient exhibit a relatively larger fixed charge and interface trap density than those annealed in O2 ambient. These electrical properties support the possibility of STA oxide application to a new high-k gate dielectric.

Modeling etch rate and uniformity of oxide via etching in a CHF3/CF4 plasma using neural networks

Abstract An oxide film etched in a magnetically-enhanced CHF 3 /CF 4 plasma has been modeled using neural networks. The etch process was characterized with a 2 4−1 factorial experiment. The experimental factors and ranges include 20–80 sccm CHF 3 flow rate, 10–40 sccm CF 4 flow rate, 300–800 W radio frequency (RF) power, and 50–200 mTorr pressure. Radicals (F, CF 1 , and CF 2 ) measured with optical emission spectroscopy were related to etch responses. In the experiments conducted, increases in etch rate generally corresponded to decreases in nonuniformity. Etch nonuniformity was strongly dependent on RF power. The relative significance of polymer deposition and ion bombardment was separated and explained. The root-mean-squared prediction errors are 174 A/min and 0.425% for etch rate and etch nonuniformity models, respectively.

Fast diffusion supercapacitors via an ultra-high pore volume of crumpled 3D structure reduced graphene oxide activation

In order to obtain a high performance supercapacitor, there are several factors that must be achieved including a high specific surface area (SSA), high electrical conductivity, and a high diffusion rate of the electrolyte due to an appropriate pore volume. Herein, we report a high performance supercapacitor using activated non-stacked reduced graphene oxide (a-NSrGO) that has a high SSA (up to 999.75 m2 g−1) with intrinsic high graphene conductivity (1202 S m−1) and fast diffusion of the electrolyte. Due to a high total pore volume (5.03 cm3 g−1) and a wide pore size distribution from macro- to micropores (main pore width: 0.61 – 0.71 nm) in the a-NSrGO sheets, the as-prepared a-NSrGO electrode shows high specific capacitance (105.26 F g−1) and a short relaxation time (τ0 = 1.5 s) in a propylene carbonate (PC)-based organic electrolyte. A maximum energy density of 91.13 W h kg−1 and a power density of 66 684.73 W kg−1 were estimated in a fully packaged coin cell. The high performance of the a-NSrGO supercapacitors is attributed to their specific appearance and enlarged pore distribution with high SSA.

Transparent and flexible tactile sensor for multi touch screen application with force sensing

In this paper, we propose and demonstrate a transparent and flexible tactile sensor which is designed for multi touch screen application. The sensor module is composed of 2-D array capacitive tactile cells to measure the touch force on multiple positions. The device was fabricated with transparent materials on transparent plastic substrate. The touch input was measured by the capacitance variation resulting from the mechanical deformation of parallel plate capacitor.

Etch characteristics of SrBi2Ta2O9 (SBT) thin films using magnetized inductively coupled plasmas

Abstract In this study, SrBi 2 Ta 2 O 9 (SBT) thin films were etched using a magnetized inductively coupled plasma (MICP) and their etch characteristics were investigated as a function of Cl 2 /Ar gas mixing ratio, inductive power and bias voltage. The SBT etch rate appeared to show the highest value when Cl 2 concentration in the Cl 2 /Ar mixture was 30%, even though the SBT etch rate remained nearly constant when the Cl 2 concentration in the mixture was higher than 10%. SBT etch rates were also strongly influenced by both inductive power and bias voltage. This result implies that the etching of SBT is dependent upon both ion bombardment and chemical reaction. An etch rate of 150 nm/min could be obtained using 30% Cl 2 /70% Ar, 6.7 Pa of operation pressure, 600 W of inductive power, and −300 V of bias voltage. The etch selectivity of SBT over Pt, and photoresist were less than 0.5 and 1.0∼1.2, respectively, when the Cl 2 was more than 10% in Cl 2 /Ar mixtures. An SBT (200 nm)/Pt (100 nm)/Ti (100 nm) heterostructure was etched using the MICP with 30% Cl 2 /70% Ar mixture, which resulted in an anisotropic etch profile without the formation of sidewall residue.