Structural Analysis on Organic Thin-Film Transistor With Device Simulation

A 2-D device simulation for organic thin-film transistors (OTFTs) was carried out to reveal the characteristic difference between staggered and planar structures. Assuming the OTFT with Schottky barrier contact, the staggered-structure TFT has more current flow, bigger field-effect mobility, and lower contact resistance than the planar structure. The simulation results indicate that the source electrode of the staggered structure has better ability to supply the current than that of the planar structure.     

Subjective Listening Experiments on a Front and Rear Array‐Based WFS System

Wave field synthesis (WFS) has been gathering more and more attention recently due to its ability to perfectly reproduce an original sound field. However, to realize theoretically perfect WFS, a four‐sided loudspeaker array that encloses the listener is required. However, it is difficult to build such a system except in large listening spaces, such as a theater or concert hall. In other words, if the listening space is a home, installing a side loudspeaker array is impractical. If the two side walls located to the left and right of the listener can be omitted, a setup using only front and rear loudspeaker arrays may be a solution. In this letter, we present a subjective listening experiment of sound localization/distance based on a WFS using a front and rear loudspeaker array system which is conducted on two listening points and shows average localization errors of 6.1° and 9.18°, while the average distance errors are –27% (0.5 m) and –29% (0.6 m), respectively.     

Thin-film encapsulation of top-emission organic light-emitting devices with polyurea/Al2O3 hybrid multi-layers

We developed a room-temperature encapsulation process based on multi-stack of ultra thin Al₂O₃ and polyurea layers for top-emission organic light-emitting devices (TEOLEDs). Device structure, including a capping layer for refractive-index matching and a thick polyurea buffer layer, was optimized to enhance light extraction without distorting electroluminescence spectrum. The efficiency of a TEOLED encapsulated with 5 pairs of Al₂O₃(50 nm)/polyurea(20 nm) layers was better than that of a glass-encapsulated TEOLED, whereas their color coordinates were almost identical. Moreover, the half-decay lifetime of a TEOLED encapsulated with 5 pairs of Al₂O₃/polyurea layers was 86% of that of a glass-encapsulated TEOLED. Water vapor transition rate of 5 pairs of Al₂O₃(50 nm)/polyurea(20 nm) layers on PET film was measured as low as 5 × 10⁻⁴ g/m² day.     

A gain-clamped SOA with distributed Bragg reflectors fabricated under both ends of active waveguide with different lengths

We demonstrate a gain-clamped semiconductor optical amplifier (GC-SOA) which has gratings under both end regions of an active waveguide. Two gratings of the new GC-SOA are fabricated in different lengths. Their lasing modes and gain characteristics are measured and analyzed with different combinations of grating lengths. It shows different gain and noise characteristics according to the measurement direction in asymmetric grating combinations.     

Mixed-objective optimization of a track-following controller using linear matrix inequalities

This work describes a design method for track-following controllers in data storage drives using mixed-objective optimization. Stability and performance requirements on the track following controller are established using norm conditions, which are converted to linear matrix inequalities (LMIs). The minimization of the position error in the root-mean-square sense is shown to be an H/sub 2/ norm minimization problem, whereas the vibration rejection requirements are expressed as H/sub 2/ or H/sub /spl infin// norm constraints. The robust stability requirement is enforced by an H/sub /spl infin// norm constraint. The mixed-norm problem is converted into a constrained minimization problem in LMIs, which is solved by convex optimization algorithms. The controller is designed directly in the discrete time domain to avoid typical degradation caused by continuous-time to discrete-time conversion. The proposed controller is implemented and tested on production hard disk drives. Experiments show that the proposed controller reduces the position error by 7%-11% while maintaining comparable stability margins and vibration rejection capability compared with the conventional controllers.     

Nanoshuttered OLEDs: Unveiled Invisible Auxiliary Electrode

In this study, organic light‐emitting diodes (OLEDs) with enhanced optical properties are fabricated by inserting a nanosized stripe auxiliary electrode layer (nSAEL) between the substrate and an indium tin oxide (ITO) layer. This design can avoid the shortcomings of conventional microsized layers while maintaining high optical uniformity due to the improved conductivity of the electrode. The primary advantage is that the nSAEL (submicrometer scale) is no longer visible to the naked eye. Moreover, the reflective shuttered (grating) structure of the nSAEL increases the forward‐directed light by the microcavity (MC) effect and minimizes the loss of light by the extracting the surface plasmon polariton (SPP) mode. In this study, the degree of the MC and SPP can be controlled with the parameters of the nSAEL by simply conjugating the conditions of laser interference lithography (LIL). Therefore, the current and power efficiencies of the device with an nSAEL with optimized parameters are 1.17 and 1.23 times higher than the reference device at 1000 cd/m², respectively, and at these parameters, the overall sheet resistance is reduced to less than half (48%). All of the processes are verified by comparing the computational simulation results and the experimental results obtained with the actual fabricated device.     

Double S-Shaped Polarization – Voltage Curve and Negative Capacitance from Al2O3-Hf0.5Zr0.5O2-Al2O3 Triple-Layer Structure

The negative capacitance (NC) effect, recently discovered in a fluorite-based ferroelectric thin film, has attracted great attention as a rescue to overcome the scaling limitations of the conventional memory and logic devices of highly integrated circuits. The NC effect manifesting an S-shaped polarization–voltage (P–V) curve is initially interpreted by a 1-dimensional Landau Ginzburg Devonshire (LGD) model. However, a series of recent studies have found that this effect can also be explained by the inhomogeneous stray field energy (ISE) model. In this study, by extending the ISE model in the ferroelectric (FE)-dielectric (DE) layered structure, an analytical model that considers the influence of the interfacial screening charge distribution is presented. This model showed that the NC effect in the FE-DE heterostructure can be manifested in various forms other than a single S-shaped P–V curve. In particular, a double S-shaped P–V curve is expected from the fully compensated anti-parallel domain structure, confirmed experimentally in the actual Al₂O₃/(Hf_0.5Zr_0.5)O₂/Al₂O₃ triple-layer structure. Furthermore, to reveal the origin of the double S-shaped P–V curve, a multidomain LGD model is presented. It is confirmed that this phenomenon is attributed to the evolution of inhomogeneous stray field energy.     

An Experimental 0.8 V 256‐kbit SRAM Macro with Boosted Cell Array Scheme

This work presents a low‐voltage static random access memory (SRAM) technique based on a dual‐boosted cell array. For each read/write cycle, the wordline and cell power node of selected SRAM cells are boosted into two different voltage levels. This technique enhances the read static noise margin to a sufficient level without an increase in cell size. It also improves the SRAM circuit speed due to an increase in the cell read‐out current. A 0.18 µm CMOS 256‐kbit SRAM macro is fabricated with the proposed technique, which demonstrates 0.8 V operation with 50 MHz while consuming 65 µW/MHz. It also demonstrates an 87% bit error rate reduction while operating with a 43% higher clock frequency compared with that of conventional SRAM.