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A novel thin-film transistor test structure is proposed for monitoring the device hot-carrier (HC) degradations. The new test structure consists of several source/drain electrode pairs arranged in the direction perpendicular to the normal (i.e., lateral) channel of the test transistor. This unique feature allows, for the first time, the study of spatial resolution of HC degradations along the channel of the test transistor after stressing. The extent of degradation as well as the major degradation mechanisms along the channel of the test transistor can be clearly identified.

A multi-carrier UHF RFID system provides the required power of a passive tag via multiple carriers. It is proved that the method can effectively extend the tag access range since the tag operating power is almost always satisfied. However, the extension is confined due to waveform distortion of reader command at the tag's demodulator. This work discusses this problem and proposes a solution by adding an additional bandpass filter before the envelope detector. Computer simulation results show that the proposed solution effectively mitigates the demodulation problem.

We use ab initio pseudopotential electronic-structure methods to describe successfully both the detailed static structures and the structural transformation in ${\mathrm{B}}_{2}$${\mathrm{O}}_{3}$ crystals. Employing a reduced cell volume, with full relaxation of all internal coordinates, our calculations model the structural transformation from the polymorph containing the ${\mathrm{BO}}_{3}$ triangular unit into that containing the ${\mathrm{BO}}_{4}$ tetrahedral unit. In order to interpret the mechanism, individual energy contributions to the total energy are analyzed.

We investigate the structure change of semiconducting carbon nanotubes under an external electric field with density functional theory. It is shown that the shape of the nanotube remains cylindrical and the length of the nanotube is also the same, even under a strong electric field. The only change observed is the diameter of the nanotube. It increases along with the increase of the applied electric field.

A passive RFID tag derives its power from RF signal emitted by a RFID reader and responds its modulated backscatter signals to the reader. Because of the large propagation loss, the accessible range of a passive RFID tag is hence limited. In addition, the readability of a passive RFID tag is often influenced by multipath fading problems. In order to mitigate the problems, a multi-carrier UHF passive RFID system utilizes isolated power sources which provide additional power to passive RFID tags via a carrier frequency different with the RFID reader operating frequencies. This approach however affects reader command demodulation circuit of a passive RFID tag. This work proposes a new passive tag demodulation circuit design which is more suitable for multi-carrier RFID systems.

We show, based on systematic first-principles calculations, that the ultraviolet (UV) optical properties of the nonlinear optical crystal ${\text{K}}_{2}{\text{Al}}_{2}{\text{B}}_{2}{\text{O}}_{7}$ can be dramatically improved by eliminating the Fe impurity through the controlling of Fe charge state during crystal growth. Our results reveal that the ${\text{Fe}}^{3+}$ impurity can easily replace the Al site with very low formation energy, resulting in the strong UV absorption which can be quantitatively understood from the formation of in-gap states and corresponding $p\text{\ensuremath{-}}d$ transition. Moreover, it is demonstrated that modification of the Fe charge state greatly increases its formation energy, which prevents it from incorporation into the crystal during the growth process and results in the elimination of these absorption peaks and the improvement of UV optical properties.

We have carried out a band-resolved analysis of the optical absorption spectra of structural disorder in ${\text{SiO}}_{2}$ glass by using a first-principles method, where dominant orbitals involved in the absorption spectra can be analyzed. We provided a strong theoretical support to a model where heavily strained bonds in three-membered ring structures affect the fundamental absorption edge. We found that the main absorption peak induced by an oxygen vacancy can be ascribed to a transition between the occupied and unoccupied defect states consisting of Si-Si and neighboring O orbitals due to the structural disorder. The present scheme is effective for analyzing the relationship between microscopic atomic structures and macroscopic optical properties.

In this work, a new test structure was employed in the analysis of hot-carrier degradation under AC operations. We find that the on-current degrades with reducing falling time and confirm that the damage region is located near the drain. The experiment shows such tester has a high sensitivity in detecting AC degradation and provides unambiguous evidence that the damageoccurs during transient stages. With these unique features, the proposed test structure represents a powerful tool in practical applications for studying the reliability of TFT devices.

The nonlinear optical (NLO) properties in La9Na3B8O27, La2Na3B3O9 and La2CaB10O19 are investigated using a plane-wave pseudopotential method. Based on the first-principles electronic band structures, the birefringence and second harmonic generation (SHG) coefficients for the three crystals are determined. The calculated values match well with the experimental results. In order to elucidate the microscopic origins of the NLO performances in these crystals, a real-space atom-cutting method is adopted to calculate the contribution from the respective ions and groups. It is revealed that the La cations have covalent interactions with the neighbor O ions so as to form the La-O groups. The La-O bond covalency, combined with the distortion of La-O groups, makes the large contribution to the overall SHG coefficients in addition to the B-O groups, as also intuitively demonstrated by a SHG-density analysis.

Birefringence plays a great role in phase matching of the nonlinear optical (NLO) crystals. Small birefringence restricts various crystals from achieving deep-ultraviolet laser output although they exhibit short UV cutoff edges and high second-harmonic generation (SHG) intensities. An access to achieve deeper coherent light output through external pressure on NLO crystal, K3B6O10Cl is proposed and demonstrated through computer experiment based on the first principles theory. The “hot spot” in structure that determine the SHG effects and birefringence were highlighted. The shortest achievable phase-matching wavelengths are predicted based on calculated refractive indices. It is found that the quasi-planar (B6O10)2− group is the dominant contributing unit to optical anisotropy. The pressure-induced increase of polarizability anisotropy of (B6O10)2− group can notably enlarge birefringence which extends the shortest achievable wavelength of K3B6O10Cl frequency conversion. The results show that pressure engineering may be a promising scheme to overcome the drawback of small birefringence of some NLO crystals.

Ab initio calculations show that the band-gap modulation of semiconducting carbon nanotubes with mono-vacancy defect can be easily achieved by applying a transverse electric field. We found that the band structures of the defective carbon nanotubes vary quite differently from that of the perfect nanotube, and strongly depend on the applied direction of the transverse electric field. A mechanism is proposed to explain the variation of the band gap, and potential applications of these phenomena are discussed.

A novel methodology that greatly simplifies the procedure of extracting the effective density-of-states (DOS) in polycrystalline-Si thin-film transistors (poly-Si TFTs) is proposed and demonstrated. The characterization is performed on a Schottky barrier (SB) TFT with electrical source/drain extensions induced by a field-plate. Only one single device and two simple subthreshold I-V measurements at room temperature are needed for full band-gap DOS extraction. Impacts of different process treatments are clearly resolved using this methodology.

The hygroscopic properties of the borate crystals $\mathrm{Li}{\mathrm{B}}_{3}{\mathrm{O}}_{5}$, $\mathrm{Cs}{\mathrm{B}}_{3}{\mathrm{O}}_{5}$, and $\mathrm{Cs}\mathrm{Li}{\mathrm{B}}_{6}{\mathrm{O}}_{10}$ are studied by density-functional theory. It is found that the absorption energy and the diffusion mechanism of water molecules differ significantly for the three crystals. The deliquescent properties of borate crystals are determined mainly by the stress induced by water absorption. Our calculations are in good agreement with experimental observations.

Through three case studies, plane wave pseudopotential density functional theory calculations are performed to investigate the mechanism of second harmonic generation (SHG) of the nonlinear optical materials. We want to know how SHG coefficients are affected by: (1) anion substitution in $\mathrm{AgGa}{({\mathrm{S}}_{x}{\mathrm{Se}}_{1\ensuremath{-}x})}_{2}$; (2) the isomeric effect in push-pull benzenes; and (3) the length of $\ensuremath{\pi}$-conjugate chain in push-pull polyenes. A sum-over-states type formalism is used for the evaluation of static SHG coefficients. Orbital contribution to the $\ensuremath{\beta}$ or ${\ensuremath{\chi}}^{(2)}$ can be decomposed on a (energy) level-by-level basis by partially summing only two out of all three band indices. Through such process that we proposed, the dominant orbitals that give major contribution to a SHG process can then be identified and analyzed. These so-called ``band-resolved'' plots of SHG coefficient are sensitive to the variation of structure and configuration of the materials, and can thus be used to study the detailed mechanism of SHG processes in crystals and molecules.

Determining theoretically the respective contributions of cations and anionic groups in inorganic crystals to their linear and NLO effects is meaningful when searching for new NLO materials. In the past we used a theoretical model called anionic group theory to evaluate the relationship between microstructure of the oxide NLO crystals and their macro-optical properties, and calculate their n/sub i/, /spl Delta/n and d/sub ij/ coefficients. The investigations of the band energy calculation method confirm that anionic group theory is successful for the oxide series NLO crystals. In the case of refractive index and birefringence in particular, the results are consistent with experiments. For calculating d/sub ij/ coefficients, the theory is basically successful. Its major shortcoming is that it is unable to consider the effect of cations on the d/sub ij/ coefficients.

Summary form only given. The investigations of band energy calculation method confirm that anionic group theory is successful for borate series crystals. In the case of refractive-index, birefringence in particular, the results are quite consistant with experiments. For calculating d/sub ii/ coefficients, the theory is basically successfull. Its major shortcoming is that it is unable to consider the effect of cations on the d/sub ii/ coefficients.

Nonlinear optical (NLO) crystals are very important optoelectronic functional materials and their developments have significantly contributed to the progress of laser science and technology for decades. In order to explore new NLO crystals with superior performances, it is greatly desirable to understand the intrinsic relationship between the macroscopic optical properties and microscopic structural features in crystals. In this paper, the applications of density functional theory (DFT) method to the elucidation of the structure-property relationship and to the exploration on novel NLO materials in the ultraviolet and infrared spectrum regions are reviewed. The great success in the linear and NLO property predictions has been achieved using the first-principles computational simulations, and the mechanism understanding obtained by various analysis tools can give substantial guidance to the search and design of new NLO crystals.

With the development of laser technology and related scientific fields, understanding of the structure–property relationships in nonlinear optical (NLO) crystals is becoming more and more important. In this article, first-principles studies based on density functional theory, and their applications to elucidate the microscopic origins of the linear and NLO properties in NLO crystals, are reviewed. The ab initio approaches have the ability to accurately predict the optical properties in NLO crystals, and the developed analysis tools are vital to investigating their intrinsic mechanism. This microscopic understanding has further guided molecular engineering design for NLO crystals with novel structures and properties. It is anticipated that first-principle material approaches will greatly improve the search efficiency and greatly help experiments to save resources in the exploration of new NLO crystals with good performance.

We conduct first-principles total-energy density functional calculations to study the band structures in Ge1−xSnx infrared semiconductor alloys. The norm-conserving optimized pseudopotentials of Ge and Sn have been constructed for electronic structure calculations. The composition-bandgap relationships in Ge1−xSnx lattices are evaluated by a detailed comparison of structural models and their electronic band structures. The critical Sn composition related to the transition from indirect- to direct-gap in Ge1−xSnx alloys is estimated to be as low as x∼ 0.016 determined from the parametric fit. Our results show that the crossover Sn concentration occurs at a lower critical Sn concentration than the values predicted from the absorption measurements. However, early results indicate that the reliability of the critical Sn concentration from such measurements is hard to establish, since the indirect gap absorption is much weaker than the direct gap absorption. We find that the direct band gap decreases exponenti...

The atomic and electronic structure of a tilt grain boundary in rutile ${\mathrm{TiO}}_{2}$ has been calculated in an ab initio manner. The method employs a plane-wave basis set and optimized pseudopotentials and is carried out within the local-density approximation of density-functional theory. The study focuses on the structure and energy of the \ensuremath{\sum}=15 36.9\ifmmode^\circ\else\textdegree\fi{} (210)[001] tilt boundary, which is relaxed to equilibrium using a conjugate gradients iterative minimization technique. The calculations confirm the stability of a proposed atomic model for the boundary and provide some insight into its electronic structure. \textcopyright{} 1996 The American Physical Society.

Eu doped aluminum nitride phosphors were successfully synthesized by a novel gas-reduction-nitridation route with a reaction temperature of 1400 °C and a soaking time of 3 h. The obtained AlN:Eu phosphors were analyzed to elucidate the location of the Eu luminescent center. High-resolution transmission electron microscopy and transmission electron microscopy-energy dispersive spectra proved that Eu was located in the crystal lattice of AlN, then EXAFS revealed that Eu occupied a highly distorted Al site coordinated by four nitrogen at about 2.30–2.40 A, and the second nearest neighbors of Eu were 12 Al. This could be confirmed by the first-principles calculations based on the obtained local structure around the Eu luminescence center, where the theoretical absorption spectrum was similar to the experimental excitation spectrum. X-ray appearance near edge structure showed that Eu existed in terms of both Eu3+ and Eu2+ ions, which could be related to the limited location space of Eu. High temperature treatm...

The relationship between the electric properties and the vacancy density in single-walled carbon nanotubes has been investigated from first principles as well as the dependence of the influencing range of a vacancy in the nanotube on the nanotube chirality. Compared with the long-range interaction of the vacancies in a single-walled carbon nanotube with non-zero chiral angle, a much shorter interaction was found between vacancies in a zigzag single-walled carbon nanotube. In this study, we investigated the bandstructure fluctuations caused by the nanotube strain, which depends on both the vacancy density and the tube chirality. These theoretical results provide new insight to understand the relationship between the local deformation of a defective single-walled carbon nanotube and its measurable electronic properties.

Twist boundaries in the deep-UV nonlinear optical crystal KBe2BO3F2 (KBBF) are studied through first-principles calculations. It was found that the optical qualities and the capability for second-harmonic generation (SHG) in KBBF obtained from the different single-crystal growth methods are very different. These properties are associated with the presence of defects. Our studies demonstrate that the (0001) twist boundaries in KBBF are easily formed due to the quite weak interaction between the in-plane layers. These grain boundaries have very small influences on the modifications of the UV optical absorption edge and the refractive indices in KBBF. However, the SHG conversion efficiency in KBBF can be significantly deteriorated as the (0001) twist boundaries occur, so it is necessary to eliminate these twist boundaries during the single-crystal growth processes. Our theoretical results are consistent with experimental observations.

This article investigates the threshold voltage (V t ) shift induced by a self-heating effect for n-channel low temperature poly-Si thin film transistors (TFTs) and finds that there is a shift of more than 3 V in the negative direction after a self-heating operation of 100 ms. The negative V t shift can be attributed to the charge-trapping effect caused by the holes generated by trap-assisted band-to-band thermionic field emission and trapped in the grain boundary of the poly-Si film substrate. We used lateral body contact structure to verify that this unusual V t shift is related to the holes trapped in the substrate.

We have developed a new AMLCD with multiple ambient light sensors (ALSs) for reducing backlight (BL) power consumption, and false sensing of ambient illuminance. ALSs perform well in showing BL control for power-saving, even though one of the sensors is covered by a finger shadow. Architecture of integrated ALS with a-Si and LTPS technologies are presented. We fabricate the in-cell, and wide-dynamic-sensing ALSs display using new light sensor technology. Photo-electrical characteristics with well linearity and reliability under long-term operation were observed.

Systematic studies based on first-principles calculations of second-order optical susceptibilities as well as the dielectric function of CsGeX3 (X = Cl, Br, and I; CGX) are presented. The relationship between structural properties and optoelectronic responses are examined. The structural factors Δα, and dGe, dX are proposed to describe the degree of distortion from an ideal perovskite structure. Δα and dGe increase when halide anions are changed from Cl to I; while halide anion displacement, dX, decreases. The structural distortion effect on these rhombohedral CGX crystals is analyzed by first-principles calculations. The dielectric function and the second harmonic generation (SHG) response coefficient also increase with increasing Δα and dGe. The direct band gaps (EG) of CsGeX3 all occur at the R-point, ΔER. The experimental band gaps of CGX crystals become smaller, i.e., ECGCG (=3.67 eV) >ECGBG (=2.32 eV) >ECGIG (=1.53 eV), as Δα and dGe increase, i.e., dCGCGe

Characterization of the interaction between vacancy defects in zigzag single-walled carbon nanotubes (SWCNTs) was carried out through geometric and bandstructure analyses with density functional theory (DFT). This interaction depends on the detail orientation between the defects and, in turns, influences the electric properties of the defective zigzag SWCNTs if any two defects are within the defect influencing range. Our results shed some light on the origin of the instability found in the electric properties of SWCNTs.

Results on indium-oxide-based transparent oxide TFTs, which the active layer is prepared by DC sputtering, are presented. The fabricated TOS TFTs show high mobility (37 cm2/V-s), high ON/OFF current ratio and large on-state current. Fabricating oxide TFTs on temperature-sensitive substrates is also attainable owing to the low temperature process of the active layer preparation.

In this work, quantitative information for nonuniform hot-carrier degradation, especially under mild stressing condition, is investigated. A test structure capable of revealing hot-carrier degradations of polycrystalline silicon (poly-Si) thin-film transistors in specific portions of the channel is employed. Effective density-of-states (DOS) distributions at the damaged sites can be extracted using field-effect conductance method, thus providing an effective tool to evaluate the impact of hot-carrier degradations. By measuring along individual sections of the channel, it becomes possible to extract the DOS for the device as a whole. The combination of the proposed test structure and DOS extraction technique also provides a powerful tool for modeling and simulating current-voltage characteristics of thin-film transistors under hot-carrier stressing.

The electro-optical modulation effect of a (10,0) boron nitride nanotube is investigated by first-principles, density functional theory calculations. The optical properties of boron nitride nanotubes can be tuned through perturbation by a transverse electric field. Large optical anisotropy in variations of the absorption spectra and refractive indices in response to external electric field is found. In addition, a method called the band-resolved absorption density analysis technique is developed to investigate the detailed optical absorption transition processes. The result is consistent with the recent experimental observation [M. Ishigami et al., Phys. Rev. Lett. 94, 56804 (2005)] and suggests that the boron nitride nanotubes can be a promising material for electro-optical modulation device applications.

Electronic structure calculations of Na2SbF5, BaMgF4, and BaZnF4 are performed from first principles based on a plane-wave pseudopotential method. The linear optical properties and the static second-harmonic generation coefficients are also calculated. Furthermore, a real-space atom-cutting method is employed to analyze the respective contributions of the anionic groups and cations in Na2SbF5 to the optical response. The results show that the anionic groups (SbF5)2− in the crystal are quite favorable for producing larger microscopic second-order susceptibilities.