Mechanical bending of flexible complementary inverters based on organic and oxide thin film transistors

Flexible complementary inverters composed of p-channel pentacene thin-film transistors (TFTs) and n-channel amorphous indium gallium zinc oxide TFTs were fabricated on polymer substrates. The characteristics of the TFTs and inverters were evaluated at different bending radii. Throughout the bending experiments, the relationship between the performances of the inverters and the characteristics of the TFTs under mechanical deformation was analyzed. The mechanically applied strain led to a change in the voltage transfer characteristics of the complementary inverters, as well as the source–drain saturation current, field-effect mobility and threshold voltage of the TFTs. The switching threshold voltage of the fabricated inverters decreased with decreasing bending radius, which was related to changes in the field-effect mobility and the threshold voltage of the TFTs.     

Merocyanine/C60 Planar Heterojunction Solar Cells: Effect of Dye Orientation on Exciton Dissociation and Solar Cell Performance

In this study the charge dissociation at the donor/acceptor heterointerface of thermally evaporated planar heterojunction merocyanine/C₆₀ organic solar cells is investigated. Deposition of the donor material on a heated substrate as well as post‐annealing of the complete devices at temperatures above the glass transition temperature of the donor material results in a twofold increase of the fill factor. An analytical model employing an electric‐field‐dependent exciton dissociation mechanism reveals that geminate recombination is limiting the performance of as‐deposited cells. Fourier‐transform infrared ellipsometry shows that, at temperatures above the glass transition temperature of the donor material, the orientation of the dye molecules in the donor films undergoes changes upon annealing. Based on this finding, the influence of the dye molecules’ orientations on the charge‐transfer state energies is calculated by quantum mechanical/molecular mechanics methods. The results of these detailed studies provide new insight into the exciton dissociation process in organic photovoltaic devices, and thus valuable guidelines for designing new donor materials.     

A Provable Billing Protocol on the Current UMTS

This paper proposes a simple method that equips UMTS-based telecom companies with a mechanism to prove the records on mobile users’ phone bills. In the history of mobile phone communication, we have seen countless unsettled disputes where the mobile user disagrees with the telecom company either on the calling time or on the duration, or even on whether or not a call was actually made. In this paper, a provable billing protocol will be presented that can effectively solve disagreements between the two parties. Equipped with a non-repudiation function, the proposed protocol enables the service provider to hold on to the solid proofs as to exactly when and to which number a mobile phone user made a call so that the mobile user cannot deny; at the same time, the mobile user also gets to have his/her own share of proofs as to when and how the mobile services were accessed, so that the bill can be double checked to make sure nothing goes wrong. And, to make it even better, this new protocol is perfectly compatible with the standard UMTS protocol and is therefore readily applicable to the current mobile phone communication environments.     

Asymmetrical current conduction across a 50 A Thick aluminium gallium nitride polarisation barrier

Rectification by a 50 Aring (5 nm) thick aluminium gallium nitride (AlGaN) polarisation barrier with maximum voltage swing of 27 V is demonstrated. In order to achieve a large voltage swing, the device is constructed with a 3000 Aring (300 nm) thick undoped gallium nitride (GaN) space charge layer adjacent to the barrier to enable a large voltage drop before the advent of impact ionisation breakdown. The spontaneous and piezoelectric polarisation discontinuities at the AlGaN/GaN interfaces determine the band profiles and the thermally assisted tunneling flux of electrons through the barrier. The 3.24 MV cm ^-1 electric field across the 50 Aring thick barrier at low bias enables efficient tunneling of electrons, despite the large effective electron mass of 0.19. The effective barrier seen by electrons changes from triangular to trapezoidal for one direction of bias and enhances the asymmetry effect. The demonstrated device characteristics show that wide band-gap polarisation barriers can potentially be used as the basic components of high-power microwave limiters     

Efficient OVSF code assignment and reassignment strategies in UMTS

This paper presents an integrated solution for code management, assignment, and reassignment problems in UMTS. We propose a new architecture for code management and, based upon this new architecture, a code assignment strategy, referred to as "crowded-group first strategy". Our system architecture and code assignment strategy represent significant improvements both in the time complexity and the maintenance complexity. Moreover, the code blocking probability of the crowded-group first strategy is competitive to that of the other strategies. In this paper, we also propose a new code reassignment strategy, called the "crowded-branch first strategy". The main objective of this reassignment strategy is to reduce reassigned call probability with low computation overhead and extend this strategy for the general case. In order to systematically analyze the performances of the code assignment strategy, we implement a simulator to analyze the code selection behavior and code blocking probability of each strategy. Moreover, we propose some new performance metrics, named "weighted code blocking", "reassigned call probability", and "ratio of actual code reassignments", in order to precisely measure the performance obtained by different strategies. From the simulation results, we show that our proposed strategies efficiently utilize the OVSF codes with low computation overhead.     

High-Performance Al–Sn–Zn–In–O Thin-Film Transistors: Impact of Passivation Layer on Device Stability

We fabricated high-performance thin-film transistors (TFTs) with an amorphous-Al–Sn–Zn–In–O (a-AT-ZIO) channel deposited by cosputtering using a dual Al–Zn–O and In–Sn–O target. The fabricated AT-ZIO TFTs, which feature a bottom-gate and bottom-contact configuration, exhibited a high field-effect mobility of 31.9 $ hbox{cm}^{2}/hbox{V}cdothbox{s}$, an excellent subthreshold gate swing of 0.07 V/decade, and a high $I_{{rm on}/{rm off}}$ ratio of $≫hbox{10}^{9}$, even below the process temperature of 250 $^{circ}hbox{C}$. In addition, we demonstrated that the temperature and bias-induced stability of the bottom-gate TFT structure can significantly be improved by adopting a suitable passivation layer of atomic-layer-deposition-derived $hbox{Al}_{2} hbox{O}_{3}$ thin film.      

Strained CMOS Devices With Shallow-Trench-Isolation Stress Buffer Layers

In this brief, shallow-trench-isolation (STI) stress buffer techniques, including sidewall stress buffer and channel surface buffer layers, are developed to reduce the impact of compressive STI stress on the mobility of advanced n-type MOS (NMOS) devices. Our investigation shows that a 7% driving current gain at an NMOS device has been achieved, whereas no degradation at a p-type MOS (PMOS) device was observed. The same junction leakage at both the NMOS and PMOS devices was maintained. A stress relaxation model with simulation is thus proposed to account for the enhanced transport characteristics.     

Numerical and experimental investigation of radiation caused by the switching noise on the partitioned DC reference planes of high speed digital PCB

Influence of the partitioning and bridging of the power/ground planes on the radiation caused by the switching noise on the dc reference planes is investigated both theoretically and experimentally. Based on the three-dimensional finite-difference time-domain modeling, the electromagnetic interference (EMI) performance of the partitioned power/ground planes is studied. Radiated emission at the 3-m distance from the tested boards is measured in a fully anechoic chamber. The measured and the numerical results agree generally well. The radiation behavior of four kinds of partitioned configuration of the power/ground planes is studied. It is found that completely isolating the noise source by the etched slits, or moats, significantly reduces the radiation level at the frequencies near resonance. However, bridges connecting two sides of the moat not only significantly degrade the ability of the EMI protection of the moat, but also excite a new low-frequency resonant mode. The effect of the geometrical parameters, such as the moat size, moat location, bridge width, and bridge position, on the radiation behavior of the printed circuit board is considered. The radiation mechanism of the EMI behavior of the partitioned dc reference planes is discussed.     

A comprehensive compact-modeling methodology for spiral inductors in silicon-based RFICs

A new comprehensive wide-band compact-modeling methodology for on-chip spiral inductors is presented. The new modeling methodology creates an equivalent-circuit model consisting of frequency-independent circuit elements. A fast automated extraction procedure is developed for determining the circuit element values from two-port S-parameter measurement data. The methodology is extremely flexible in allowing for accurate modeling of general classes of spiral inductors on high- or low-resistivity substrate and for large spirals exhibiting distributed trends. The new modeling methodology is applied to general classes of spirals with various sizes and substrate parameters. The extracted models show excellent agreement with the measured data sets over the frequency range of 0.1-10 GHz.