Wavelength Tuning of Double-Cavity Micromachined Filter with Electrical and Thermal Actuations

We demonstrate double-cavity micromachined tunable filters with electrical actuations for both blue and red wavelength tuning. Electrical actuations for both shifts can be achieved by combining electrostatic and electro-thermal actuations below and above the breakdown voltage of p-n junctions in the micromachined cantilevers. The measured tuning range with the actuation is 8 nm for both tuning sides and the micromachined filter with a cantilever length of 80 μm exhibits a switching time of less than 115 μs for both turn-on and turn-off states. We also present the theoretical and measured temperature dependence of fabricated micromachined filters at various cantilever lengths, which experimentally gives us a temperature dependence of 0.14 nm/K for a cantilever length of 100 μm.     

Multiple air-gap filters and constricted mesa lasers – material processing meets the front of optical device technology

Real three-dimensional material structures enable enormous perspectives in the functionality of advanced electronic and optoelectronic III/V semiconductor devices. We report on the technological implementation of surface-micromachined III/V semiconductor devices for optoelectronic applications. Considering fabrication technology, the general principles can be reduced to three fundamental process steps: deposition of a layered heterostructure on a substrate, vertical structurization and horizontal undercutting by selectively removing sacrificial layers. Very useful quality-control elements for precise process control are presented. The basic principles are applied and illustrated in detail by presenting two selected optoelectronic examples. (i) The fabrication technology of buried mushroom stripe lasers is shown. Bent waveguides on homogeneous grating fields are used to obtain chirped gratings, enabling a high potential to tailor specific performances. Excellent optical properties are obtained. (ii) The fabrication technology of vertical optical cavity based tunable single- or multi-membrane devices including air gaps is shown. Record optical tuning characteristics for vertical cavity Fabry–Pérot filters are presented. Single parametric wavelength tuning over 142 nm with an actuation voltage of only 3.2 V is demonstrated. PACS 85.60.-q; 87.80.Mj; 68.65.Ac     

Room temperature fabrication Oxide TFT with Y2O3 as a gate oxide and Mo contact

In this investigation, an operating voltage as low as 5 V has been achieved for Oxide TFT with Y₂O₃ as a gate oxide and a-IGZO as an active layer. The OTFT has been fabricated at room temperature using RF sputter. The mobility and threshold voltages are 11.3 cm²/V s and 3.4 V for the device with W/L = 0.8, respectively. The annealing at 400 °C in N₂ containing 5% H₂ ambient has been utilized to improve the electrical performance of TFT. The on-off current which is determined by gate dielectric has been observed to be 10⁴. It has also been observed that the dielectric properties of gate oxide deteriorate on annealing. The dielectric constant of Y₂O₃ is observed in the range between 5.1 and 5.4 measured on various devices.     

Leakage current and capacitance characteristics of Si/SiO2/Si single-barrier varactor

We investigate, both experimentally and theoretically, current and capacitance (I–V/C–V) characteristics and the device performance of Si/SiO₂/Si single-barrier varactor diodes (SBVs). Two diodes were fabricated with different SiO₂ layer thicknesses using the state-of-the-art wafer bonding technique. The devices have very low leakage currents (about 5×10^-2 and 1.8×10^-2 mA/mm²) and intrinsic capacitance levels of typically 1.5 and 50 nF/mm² for diodes with 5-nm and 20-nm oxide layers, respectively. With the present device physical parameters (25-mm² device area, 760-μm modulation layer thickness and ≈10¹⁵-cm^-3 doping level), the estimated cut-off frequency is about 5×10⁷ Hz. With the physical parameters of the present existing III–V triplers, the cut-off frequency of our Si-based SBV can be as high as 0.5 THz. Received: 9 February 2001 / Accepted: 9 February 2001 / Published online: 23 March 2001     

Generating power of a thermoelectric generator under periodically alternating temperature gradients

The thermo-emf ΔV and thermoelectric current ΔI generated by imposing a temperature gradient alternating at a period of T on a thermoelectric (TE) generator were measured as a function of t, where t is the lapsed time and 1/T was varied from 0 to 1/30 s^-1. A TE generator was sandwiched between two Peltier modules connected in series. The alternating temperature gradients were produced by imposing an alternating voltage V on two Peltier modules, where V was varied from 1.0 to 3.7 V. Both ΔV and ΔI generated by the TE generator oscillate at a period of T but their amplitudes tend to increase monotonically with an increase of V. The effective thermo-emf ΔV_eff and current ΔI_eff calculated from ΔV and ΔI increase abruptly with an increase of 1/T and have a local maximum at 1/T=1/120 or 1/240 s^-1. The generating power ΔW_eff(=ΔV_effΔI_eff) tends to increase proportionally with an increase of input power W_input, owing to the increase in the temperature difference. The rate of ΔW_eff to W_input at 1/T=1/240 s^-1 reached approximately 3.2 times as large as that obtained for the steady temperature gradient corresponding to 1/T=0 s^-1. It was thus found that the generating power of the TE generator operating under the temperature gradient alternating at an optimum period is remarkably increased compared to that of a TE generator working under a conventional steady temperature gradient. PACS 72.15.Jf; 84.60.Rb; 85.30De     

Ultra‐high long‐term stability of oxide‐TTFTs under current stress

In this letter the stability of transparent thin‐film transistors (TTFTs) based on the ZnO–SnO₂ (ZTO) material system is investigated. Bottom‐gate devices have been subject to electrical stress via a gate–source bias of 10 V and a drain‐source bias of 10 V leading to a drain–source current of 188 µA. In optimized TTFTs with a composition of [Zn]:[Sn] = 36:64 the relative change of the saturated field effect mobility was less than 1% and the threshold voltage shift was about 320 mV after 1000 hours of operation. This extraordinary stability of ZTO TTFTs underlines their suitability as drivers in active matrix OLED displays. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The effect of strong electrical field on the conductivity of proton solid electrolytes NaHSO4 and KHSO4

The influence of passing of high voltage pulse discharges through proton solid electrolytes NaHSO₄ and KHSO₄ and corresponding melts on their conductivities has been investigated. We have discovered the phenomenon of high voltage activation of the investigated electrolytes which is seen by a relative increase of the conductivity. This relative conductivity increase Δσ_rel reaches 754 % (at U=2.8 kV and 181°C) and 218 % (at U=2.0 kV and 200°C) for the solid NaHSO₄ and KHSO₄, respectively. For molten NaHSO₄ and KHSO₄ Δσ_rel is considerably higher and reaches 613% (at U=1.4 kV and 207°C) and 572 % (at U=2.2 kV and 232°C), respectively. We established the “memory” effect which was seen in maintaining of the excess conductivity for a long period of time. The process of relaxation of the excess conductivity of these electrolytes has been studied. The relaxation times of the non-equilibrium charge carriers in these electrolytes varies within the range of (1.9–7.8).10⁴s.     

Quantitative analysis of charge-carrier trapping in organic thin-film transistors from transfer characteristics

A dynamic method for quantifying the amount and mechanism of trapping in organic field effect transistors (OFETs) is proposed. It exploits transfer characteristics acquired upon application of a triangular waveform gate sweep V _G. The analysis of the transfer characteristics at the turning point V _G=−V _max between forward and backward gate sweeps, viz. around the maximum gate voltage V _max applied, provides a differential slope Δm which depends exclusively on trapping. Upon a systematic change of V _max it is possible to extract the initial threshold voltage, equivalent to one of the observables of conventional stress measurements, and assess the mechanism of trapping via the functional dependence on the current. The analysis of the differential logarithmic derivative at the turning point yields the parameters of trapping, as the exponent β and the time scale of trapping τ. In the case of an ultra-thin pentacene OFET we extract β=1 and τ=10²–10³ s, in agreement with an exponential distribution of traps. The analysis of the hysteresis parameter Δm is completely general and explores time scales much shorter than those involved in bias stress measurements, thus avoiding irreversible damage to the device.     

Multiple Devil's staircase in a discontinuous circle map

The multiple Devil's staircase, which describes phase-locking behavior, is observed in a discontinuous nonlinear circle map. Phase-locked steps form many towers with similar structure in winding number(W)-parameter(k) space. Each step belongs to a certain period-adding sequence that exists in a smooth curve. The Collision modes that determine steps and the sequence of mode transformations create a variety of tower structures and their particular characteristics. Numerical results suggest a scaling law for the width of phase-locked steps in the period-adding (W=n/(n+i), n,i∈int) sequences, that is, Δk(n)∝n^-τ (τ>0). And the study indicates that the multiple Devil's staircase may be common in a class of discontinuous circle maps.     

Tuning the contact resistance in organic thin-film transistors with an organic-inorganic hybrid interlayer

We demonstrated the tunable contact resistance in pentacene thin film transistor (TFT) by inserting an organic-inorganic hybrid interlayer between Au electrode and pentacene layer. The contact resistance of pentacene-TFT varies with concentration of pentacene-TFT varies with concentration of MoO_x in organic-inorganic hybrid interlayer. MoO_x in organic-inorganic hybrid interlayer. The contact resistance of the device with 55 wt% MoO_x doped pentacene interlayer is about 7.8 times smaller than that of device without interlayer at the gate voltage of −20 V. Comparing the properties of pentacene-TFT without interlayer, the performance of the pentacene-TFT with 55 wt% MoO_x doped pentacene was significantly improved: saturation mobility increased from 0.39 to 0.87 cm²/V s, threshold voltage reduced from −21.3 to −7.2 V, and threshold swing varied from 3.75 to 1.39 V/dec. Our results indicated that the organic-inorganic hybrid interlayer is an effective way to improve the performance of p-channel OTFTs.     

Numerical Study on a Lateral Double-Gate Tunnelling Field Effect Transistor

A novel lateral double-gate tunnelling field effect transistor （DG-TFET） is studied and its performance is presented by a two-dimensional device simulation with code ISE. The result demonstrates that this new tunnelling transistor allows for the steeper sub-threshold swing below 60mV/dec, the super low supply voltage （operable at VDD 〈 0.3 V） and the rail-to-rail logic （significant on-state current at the drain-source voltage VDS = 50mV） for the aggressive technology assumptions of the availability of high-k/metal stack with equivalent gate oxide thickness EOT =0.24 nm and the work function difference 4.5 eV of materials.     

Continuous tuning of the threshold voltage of organic thin-film transistors by a chemically reactive interfacial layer

For the design and manufacture of complex integrated circuits, control over the threshold voltage of the transistors is essential. In the present contribution, we present a non-invasive method to tune the threshold voltage of organic thin-film transistors after device assembly over a wide range without any significant degradation of the device characteristics. This is realized by incorporating a thin, chemically reactive siloxane layer bonded to the gate oxide. This results in threshold voltages of around 70 V in the as-prepared devices. By exposing a transistor modified in this way to ammonia at different concentrations, the threshold voltage can be tuned in steps of only a few volts. This treatment affects only the charge density at the semiconductor–dielectric interface, leaving the overall shape of the transistor characteristics and the charge-carrier mobility largely unaltered.     

Ground state structure of some double-λ hypernuclei by a three-body model using a simple coordinate space approach

New experimental data on the binding energyB _λλ of_λλ6He, reported very recently, come up with the valuesB _λλ = 725 ±0.14 MeV and ΔB_λλ = 101 ±0.2 MeV which are substantially lower than the old dataB _λλ = 109 ±0.8 MeV and ΔB_λλ = 4.7±10 MeV in use in literature since 1966. In view of the new data we decided to undertake a re-study of the _λλ ⁶ He hypernucleus using the same three-body model (α-λ-λ) with a simple coordinate space variational approach which was employed earlier with the old data on_λλ/6He. After fitting different λ-λ potentials to the new data of _λλ ⁶ He we have applied our method to study some double-λ hypernuclei in light, medium and heavy mass regions and have determined the structural quantities like Bλλ, the r.m.s. values of core-λ (〈r_core-λ〉〉) and λ-λ (〈r_λ-λ〉〉) distances theoretically. The core-λ interaction considered is of Woods-Saxon type. The strength and the range of the core-A potential have been adjusted to reproduce the λ-binding energy(B _λ) . These are in good agreement with the relativistic mean field (RMF) results. Our study shows that the λ-λ bonding energy ΔB_λλ decreases with increasing mass number from _λλ ¹⁰ Be to _λλ ²¹⁰ Pb of a double-A hypernucleus     

Stability of polymer thin-film transistors based on poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene)

Polymer thin-film transistors (PTFTs) based on poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV) semiconductor are fabricated by spin-coating process and characterized. In the experiments, solution preparation, deposition and device measurements are all performed in air for large-area applications. Hysteresis effect and gate-bias stress effect are observed for the devices at room temperature. The saturation current decreases and the threshold voltage shifts toward the negative direction upon gate-bias stress, but carrier mobility hardly changes. By using quasi-static C-V analysis for MOS capacitor structure, it can be deduced that the origin of threshold-voltage shift upon negative gate-bias stress is predominantly associated with hole trapping within the SiO₂ gate dielectric near the SiO₂/MEH-PPV interface due to hot-carrier emission.     

Amorphous IZO TTFTs with saturation mobilities exceeding 100 cm2/Vs

In this paper we demonstrate the use of amorphous binary In₂O₃–ZnO oxides simultaneously as active channel layer and as source/drain regions in transparent thin film transistor (TTFT), processed at room temperature by rf sputtering. The TTFTs operate in the enhancement mode and their performances are thickness dependent. The best TTFTs exhibit saturation mobilities higher than 10² cm²/Vs, threshold voltages lower than 6 V, gate voltage swing of 0.8 V/dec and an on/off current ratio of 10⁷. This mobility is at least two orders of magnitude higher than that of conventional amorphous silicon TFTs and comparable to or even better than other polycrystalline semiconductors. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

H2S Solid oxide fuel cell based on a modified Barium cerate perovskite proton conductor

Urea combustion method was adopted to prepare precursor powder, MCeO₃ doped with Zr (M is alkaline earth element, such as barium, strontium, and calcium). The precursor powder has typically perovskite structure after being calcined at 873 K. In 773 K∼1,273 K, BaCe_0.425Zr_0.475Y_0.1O₃ has the highest conductivity above 10⁻² S cm⁻¹ and good chemical stability, while the phase transition may exist in H₂S atmosphere for the proton conductors. In the single fuel cell composed of MoS₂-BaCe_0.425Zr_0.475Y_0.1O_3-σ-Ag with BaCe_0.425Zr_0.475Y_0.1O_3-σ as electrolyte, the best performance is obtained. The open circuit voltage of fuel cell is all about 0.72 V, the max power density, 1.55 mW cm⁻². The performance drop is attributed to ohmic loss resulting from the separation of electrolyte and electrode, and improvement is required to bring out new anode materials compatible to the proton conductor, BaCe_0.425Zr_0.475Y_0.1O_3-σ, as electrolyte.     

Magnetoelectric effect in laminates of polymer-based pseudo-1–3 (Tb0.3Dy0.7)0.5Pr0.5Fe1.55 composite and?0.3Pb(Mg1/3Nb2/3)O3–0.7PbTiO3 single crystal

We report an extrinsic magnetoelectric effect in composite laminates made by sandwiching one thickness-polarized 0.7Pb(Mg_1/3Nb_2/3)O₃–0.3PbTiO₃ (PMN–PT) piezoelectric single crystal plate between two length-magnetized, polymer-based pseudo-1–3 (Tb_0.3Dy_0.7)_0.5Pr_0.5Fe_1.55 magnetostrictive composite plates. The laminates exhibit large magnetoelectric voltage coefficients (α _V ) of ∼0.17 V/Oe with a flat response for frequencies in excess of 40 kHz and of ∼2.97 V/Oe at the natural resonance frequency of ∼65 kHz. The distinct advantages of the laminates include high magnetic field sensitivity, low Joule heating loss, wide operating bandwidth, and low cost.     

Defect modes tuning of one-dimensional photonic crystals with lithium niobate and silver material defect

In this paper, a novel PCs defect mode is designed by inserting a Ag/LiNbO₃/Ag sandwich structure into periodically stacked TiO₂/MgF₂ dielectric superlattice. The band gap calculation is conducted using transfer matrix method. An emergence of defect mode around 525 nm is demonstrated. By applying an external voltage on this defect mode, remarkable wavelength tuning can be achieved. At normal incidence, a tuning bandwidth up to 70 nm is obtained by moderate change of external voltage from −250 to 250 V. This feature can be employed to fabricate practical tunable filters in visible region.     

Continuous-wave high power laser operation and tunability of Yb:LaSc3(BO3)4 in thin disk configuration

We report power scaling of the Yb³⁺:LaSc₃(BO₃)₄ (Yb:LSB) laser material in thin disk configuration. Employing a 300-μm thick Yb(25 at. %):LSB crystal, the continuous-wave output power around 1.0 μm wavelength reaches 40 W for 95 W of pump power at 974 nm; the overall optical-to-optical efficiency and the slope efficiency are 0.43 and 0.48, respectively. Preliminary experiments show continuous tuning of the laser output between 991 nm and 1085 nm. PACS 42.55.Xi; 42.60.Fc; 42.55.Rz     

Influence of Thomson effect on the resultant local Seebeck coefficient in thermoelectric composite materials

The resultant local Seebeck coefficient α _R (=α _S−α _T) at the interface of a thermoelement has not yet been measured, although it is an important factor governing the thermoelectric efficiency, where α _S is the local Seebeck coefficient and α _T is the one caused by the Thomson effect. It is shown in this paper that α _S, α _T, and α _R of the p- and n-type Cu/Bi–Te/Cu composites are obtained analytically and experimentally on the assumption that the local temperature of the composite on which the temperature difference ΔT is imposed varies linearly with changes in position along the composite. They were indeed estimated as a function of position from the local experimental data of R,ΔI,ΔT, and V generated by applying an additional current of ±I to the composite, where R is the electrical resistance and ΔI is a current generated by the composite. As a result, it was found that the absolute values of α _S at the hot interface of the p- and n-type composites are approximately 1.5 and 1.4 times higher than their lowest values in the middle region of the composite, respectively, while those of α _T are less than 8% of α _S all over the composite and are so small that the relation α _R≈α _S can be held. We thus succeeded in measuring α _R at the interfaces of the composite.