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Matching the resonant wavelength of plasmonic nanoparticles (NPs) and the emission band of organic materials is critical for achieving optimal plasmon-enhanced luminescence in organic light-emitting devices (OLEDs). However, the spectral matching is often unsatisfactory because the interior architecture of OLEDs limits the dimensions of the NPs to support the desired wavelength adjustment. In this article, we proposed a design strategy via AuxAg1−x alloy NPs to enable resonance tuning while preserving the size of the NP to suit the OLED design requirements. The bimetallic NPs, especially for x < 0.6, not only add one more degree of freedom to vary the plasmon wavelength but also provide the benefits of higher scattering and more intense and outspread electric fields over a broader spectrum compared to Au monometallic NPs. These features allow smaller NPs, which are more compatible with OLED interiors, to scatter electric fields more efficiently and increase the density of molecules interacting with the NP plasmons. In the presence of a nearby dipole emitter, the bimetallic NPs can simultaneously increase radiative enhancement and suppress non-radiative losses, which are advantageous for increasing the quantum yield and luminescence efficiency of the emitter. These improvements are associated with lower intraband and interband activities resulting from the higher molar fraction of Ag in the alloy NPs. We provided composition mappings to achieve enhanced luminescence for specified wavelengths at fixed NP sizes. Finally, we theoretically demonstrated that the bimetallic NPs could improve the light-extraction efficiency of OLEDs better than Au monometallic NPs. This work provides essential guidance to enable versatile plasmon-enhanced applications with predefined nanostructural geometries and wavelengths to match the device requirements.

In this article, the excitation of dipolar localized surface plasmon resonances (LSPRs) in both the far- and near-field regions is described in terms of the relevant static, dynamic, and radiative ...

A low-profile differentially fed dual-polarized antenna with high gain and isolation is proposed for fifth-generation (5G) microcell communications. By introducing two pairs of symmetrical meandering conductors to connect both ends of the radiating cross slots, a compact-size antenna with wide bandwidth can be achieved. By further adopting an artificial magnetic conductor-backed (AMC) reflector that is arranged below the radiating patches with a distance of 6 mm, the antenna profile can be reduced from $0.25\lambda _{c}$ to $0.13\lambda _{c}$ (where $\lambda _{c}$ is the free-space wavelength at the center frequency), while both the gain and frequency bandwidth are also enhanced. Furthermore, owing to the orthogonal differentially fed structure, the antenna element displays a high port isolation of 37 dB. Finally, by meticulously designing the feeding network, much narrower beamwidth can be yielded, and hence, the unidirectional gain is further improved. The measured results show that a lower-frequency bandwidth of 13.5% (3.26–3.73 GHz) with a gain of 15.7 ± 0.1 dBi and upper-frequency bandwidth of 7.6% (4.68–5.05 GHz) with 15.55 ± 0.05 dBi gain can be obtained by the proposed antenna array. In addition, port isolation better than 28 dB and stable radiation patterns can be achieved. With the aforementioned characteristics, the proposed antenna is a good candidate for future 5G microcell communications.

A dual-wideband dual-polarized antenna using metasurface for the fifth generation (5G) millimeter wave (mm-wave) communications is proposed. It is designed and analyzed based on characteristic mode theory (CMT). The proposed metasurface is mainly composed of a $3\times 3$ square-patch, in which its four corner patches are further sub-divided into a $4\times 4$ sub-patch array, while the size of the other four edge patches is reduced and the center patch is etched with a pair of orthogonal slots. By doing so, the side lobe level can be effectively reduced and the main beam radiation can be enhanced. The metasurface is excited by a pair of orthogonally arranged substrate-integrated-waveguide (SIW) to grounded-coplanar-waveguide (GCPW) dual-polarized feeding networks that help to reduce the insertion loss and expand the frequency bandwidth of the feeding ports. In order to yield higher gain, four proposed metasurfaces are fed by a pair of 1-to-8-way power divider feeding networks including a pair of low-transmission-loss E-plane phase shifter. Measured results show desirable impedance bandwidths of 13.85% (24.2-27.8 GHz) and 14.81% (36.9-42.8 GHz) in the lower and upper frequency bands, respectively, and their corresponding average gains are 13.96 and 15.46 dBi.

A dual-band dual-polarized stacked microstrip antenna with high-isolation and band-notch characteristics is proposed. The proposed antenna is comprised of three layers of substrate. To obtain high isolation between two input ports, a pair of orthogonal differentially driven feeding lines are printed on the top side of the bottom layer. To yield the desired lower- and upper-frequency bandwidths for 5G microcell communications, two sets of $2\times 2$ radiating patch arrays are printed on the second and top layer substrates, respectively. Compared with the conventional microstrip antenna, besides demonstrating a smaller size of $0.48\times 0.48\times 0.085\,\,\lambda _{0}^{3}$ , the proposed antenna has also exhibited higher isolation of better than 40 dB and higher gain of >8 dBi. Finally, a novel technique of arranging four meander lines that connects the four array elements printed on the second layer substrate is proposed to achieve an adjustable band-notch characteristic.

A dual polarized magneto-electric dipole antenna with dual wide beamwidths is proposed and investigated. Dual-layer U-shaped electric dipoles are cooperated with orthogonal η-shaped feeding line to obtain dual polarized and dual wideband features for 5G microcell applications. In addition, modified tetrahedral ground together with dual-layer three-element dipoles that are arranged as a triangle array is used to provide dual wide H-plane radiation characteristics. By doing so, a large coverage area and a reduced number of antennas can be achieved at the same time. In order to satisfy the stringent needs of high capacity and low mutual coupling, a three-dimensional (3D) MIMO system that consists of three proposed antenna elements is also designed. The antenna prototypes were fabricated and measured. Measured results show that an overlapped impedance bandwidth of 22.6% (VSWR -4 and the nearly identical MEG can be achieved by the MIMO system due to the 3D design. Hence, the proposed antenna is a desirable candidate for the future 5G microcell applications.

This paper proposes a leaky-wave antenna implemented on mobile phone side rims for 5G millimeter-wave bands. The proposed leaky-wave antenna is formed by a microstrip line periodically loaded with series metal-insulator-metal capacitors. To cover both the 24.25-29.5 GHz and 37–40 GHz frequency bands, two of the proposed leaky wave antennas are combined by a diplexer. Measured results show that a 10-dB return loss bandwidth from 23.8 GHz to 27.1 GHz and 37.2 GHz to 40 GHz is achieved. The measured realized gains are all greater than 6.5 dBi in the frequency range.

A design for beam-switching antennas is proposed in this study. A cylindrical cavity with a reconfigurable conformal slot array distributed evenly along the middle of its side wall is presented. The reconfigurable feature of the slots is achieved by placing a diode switch across each slot. An integrated bias scheme is introduced for the diode switches to activate and disable the slots. By properly selecting the dimensions for the cavity and the number of activated slots, the optimum values for the gain and front-to-back ratio (FBR) of the antenna can be obtained. The gain value is further increased by adding a skirt-like structure to both the top and bottom of the cavity. A design example is presented with the operating frequency set at 5.8 GHz. The conformal array comprises 24 slots to provide a 15° resolution for main beam switching. The simulation results indicate that the design can offer an antenna gain up to 8.62 dBi and a FBR above 10 dB. These results and the corresponding radiation patterns have gone through experimental verification, from which good agreement is observed.

A high-gain dual-polarization patch antenna array is proposed. This antenna is formed by $\mathbf{8\times 8}$ . rectangular stacked patches and fed by microstrip lines. One polarization is fed directly at the edge of the patch while the other polarization is fed by slot coupling from the other side of the ground plane. The measured results show that the 10-dB bandwidth satisfies the 5 GHz WiFi bands. The realized gains of the two polarizations are about 17 dB and 25 dB at the center frequency, respectively. The isolation between the two ports is larger than 46 dB.

The antenna in package (AiP) designed in millimeter wave (mm wave) bands induces the outsourced semiconductor assembly and test (OSAT) industry as a newcomer to build the capability to test antenna over the air (OTA). According to the features of the mm wave AiP that are small size, highly directional radiation and probe-contacted interface, the OTA environment can be specialized to be a vertical probe station with 85cm distance to keep far field radiation that ensures high dynamic range of system and the wide size of package to be tested. The proposed vertical probe station will be used not only in the early stage of product development, but also in the sampling inspection during high volume mass (HVM) production. In this paper, the mechanical and electrical schematic drawing of the proposed probe station were revealed. And the calibration method of it was also presented. An experimental instance was given to demonstrate the accuracy of the system by comparing the measurements in between it and a standard anechoic chamber. The differences were only 0.3 dB in antenna gain and 0.75 degree in beamwidth.

In an age with rapid development of science and technology, how to cultivate the young generation's scientific literacy becomes extremely important. The study aims to investigate the dynamic process of parent-child co-reading natural science storybooks. Through children's exploring and experimenting daily life science with parents' scaffolding in five reading strategies, including Predictive Strategies, Connective Strategies, Summary Strategies, Summary for Them Strategies, and Note Taking Strategies, the integrated information and analysis results were as follows: First, children with different learning styles had different strategies to read science books. Next, parents need to select appropriately tailor-made reading strategies to enhance children's reading motivation. Thirdly, parent-child co-reading strategies do help improving the children's scientific literacy; children hence had higher interest in absorbing and applying to natural science knowledge, ability as well as more positive attitude towards exploring science.

This research aims to explore how preschool educators understand about raising children's reading motivation through operating classroom aesthetic reading environment. With one year qualitative research, sixteen 4-6 years old young were observed and interviewed. The first stage interviews were undergone with environmental guidance. After the physical class reading environment was adjusted into aesthetic perspective, children's reading motivation and attitudes were triggered. The second stage involved themed reading activities, including the child-centered extended reading activities, arranging parent-child and peers shared reading time, designing borrowing books home activities, promoting peers and parent-child shared reading, and classroom hot-popular reading books selection ballot. Data collection methods included observation, interviews, children's relative documents, drawings, and hands-on works. Based on analysis of research data, main results were extracted as below: young children's reading motivation including interest, perceived control, collaboration, involvement, and efficacy were promoted through classroom aesthetic reading environment and parent-child shared reading promotion activities. Finally, according to conclusion of this research, suggestions for relative teaching application and subsequent research were proposed as reference.

The participation of parents shared reading with children is a topic that has generated a lot of attention among many researchers in the world. For the use of picture story books which have caused positive impact on the child's learning process has also been recommended as the best strategies to develop children's aesthetic ability. The purpose of the study aims to investigate the effectiveness of parent-child shared reading in developing children's learning; and to investigate the key virtues of parent-child shared learning that are critical in development of child's aesthetic abilities. Ten pairs of mother-child shared reading aesthetic wordless storybook in preschool and at home were observed and interviewed. The results show the positive effects of quality accompany time, environment setting up, and skills to scaffold children within parent-child shared reading. Finally, according to conclusion of this research, suggestions for relative practical application were proposed.

For the impact of parent-child reading picture books have on the child's learning process has been recommended at the elementary level as the appropriate strategies to bridge preschool and family education. The purpose of the study is firstly, to investigate the key virtues of the implementation in children's reading in preschool and at home; secondly, in terms of the challenges encountered to propose appropriately efficient solutions; thirdly, to enforce teachers' self-fulfillment and confidence in promoting young children's reading. Qualitative data were collected through observations, interviews, recording of anecdotes, adults' feedback sharing, and reflective journals from four projects, including advocating parent-child reading, inspiring young children's motivations to read, enhancing young children's interactions with picture books, and reading is funny. Data analysis included the sound and video records from teaching process, book list for learners, parents' sharing, teachers' sharing, researchers introspection daily, interviewing kids. According to these qualitative data, researchers adopted triangulation strategy to encode the data collected on the scene one by one. The results revealed four elements contributing in successful reading-extension activity, including environmental settings, appropriately developed activities during parent-child reading, the educators' scaffolding, and the educators' fulfillment in growth and self-professionalism. A last, the practical suggestions and possible directions for young children reading were proposed for the institute, preschool, educators and parents of early childhood education.

Dispersion relation of the surface plasmon polariton (SPP) propagating along a subwavelength gold waveguide deposited on a substrate is studied theoretically. The eigenvalues of a 1D waveguide are calculated using the finite element method combined with the method of moments in the visible-NIR regime. The dispersion curve is obtained directly by calculating the complex wavenumber versus real frequency, rather than the complex frequency versus real wavenumber. This method particularly benefits the problem with frequency-dependent material property. The shape effect (square or rectangle) of a gold nanowire and the refractive index of substrate on the propagation length, phase velocity and group velocity are investigated. Moreover, the mode profile is analyzed to evaluate the local confinement of SPP's evanescent field. In addition, the analytical solution of a circular nanowire is provided for comparison. Our results show that a plasmonic waveguide is a lowpass filter with a cutoff frequency, which decreases as the substrate's refractive index increases.

The pulsed off-time is a crucial parameter in reactive high power impulse magnetron sputtering (HiPIMS). In this work, zirconia thin films were deposited using reactive HiPIMS. The mean ionization distance of zirconium atoms was calculated as a function of electron energy and plasma density. The peak current and power density of the target increased with increasing off-times during the sputtering process. Furthermore, the microstructural, optical, and electrical properties of thin films fabricated using various off-times were investigated. Atomic force microscopy revealed a minimal RMS roughness of less than 1.7 nm was obtained. The transmittances of all films exceeded 89.3%. The energy band gap shifted to high energy as the pulsed off-time was increased. The film prepared with a pulsed off-time of 2500 μs yielded the highest energy band gap (5.93 eV) and the lowest leakage current density (0.7 × 10 −7 A/cm 2 ).

Zirconia films are deposited by reactive high power impulse magnetron sputtering (HiPIMS) technology on glass and indium-tin-oxide (ITO)/glass substrates. Preparation, microstructure and optical characteristics of the films have been studied. During deposition, the influence of the target power and duty cycle on the peak current–voltage and power density has been observed in oxide mode. Transparent thin films under different oxygen proportions are obtained on the two substrates. Atomic force microscopy measurements showed that the surface roughness of the films was lower by reactive HiPIMS than DC sputtering for all oxygen contents. The transmission and reflectance properties of differently grown zirconia films were also investigated using an ultraviolet–visible spectrophotometer. The optical transmittance of films grown on glass substrates by HiPIMS reached maximum values above 90%, which exceeded that by DC sputtering. The band edge near 5.86 eV shifted to a lower wavelength for zirconia films prepared with oxygen flow rates lower than 4.5 sccm. For the films prepared on ITO/glass substrates, the transmittance and the band gap of zirconia films were limited by ITO films; a maximum average transmittance of 84% was obtained at 4.5 sccm O 2 and the energy band gap was in the range of 3.7–3.8 eV for oxygen flow rates ranging from 3.5 to 5.0 sccm. Finally, the electrical properties of zirconia films have also been discussed.

A fully symmetrical six-polarization circular patch antenna is proposed. This antenna is coaxial-fed at center with 12 p-i-n diodes placed across a circular ring slot on the patch. By turning these p-i-n diodes on or off, six linear polarizations at a 30° interval can be produced. Due to the circular symmetry, in theory all these polarizations share the same characteristics. A prototype operating at 2.4 GHz is designed and fabricated. The measured gains of these six polarizations are from 2.64 to 3.52 dBi. Simulated and measured results are in good agreement.

In this letter, a dual-polarized array antenna with wide bandwidth and high gain is presented for Wi-Fi/WiMAX application. The array antenna comprises a single substrate layer, a radiation patch layer, and conical elements. For comparison, an array antenna with two layers of substrates is designed. The reflection coefficient of the antenna with cones is better than -10 dB in the range of 4.9 ~ 5.96 GHz with a relative bandwidth of 19.52%, which is higher than that of the antenna with two substrate layers (14.05%). The maximum gains of the proposed antenna with cones achieve approximately 19.2 and 18.8 dBi at 5.5 GHz for the two orthogonal polarizations, respectively. In addition, high isolation and low cross-polarization levels are observed.

A measurement technique is proposed to conduct S-parameter measurements on symmetrical reciprocal three-port devices using a two-port vector network analyzer. The technique takes the effects of reflection from an unmeasured port terminated with a non-ideal 50-Ω load into consideration. These reflected signals cause errors in S-parameter measurements, especially at higher frequencies where the reflection is too large to be ignored. The errors have been overlooked in the traditional three-port measurement using two-port network analyzers. In this paper, analytic equations are presented for some common symmetrical reciprocal three-port devices to improve the accuracy of their S-parameter measurements. The improvement is justified by comparing the data before/after applying the proposed technique with the measured data from four-port vector network analyzers. In addition, error analysis is conducted to ensure that the errors introduced by vector network analyzers would not be deteriorated by the proposed equations.

The scattering and absorption properties of the monomer (single), dimer (double), trimer (triple), tetramer (quadruple), and pentamer (quintupling) assemblies with gold nanoboxes as building blocks are studied theoretically. Using the finite element method, the far-field and near-field optical responses of 1-D and 2-D assemblies are analyzed numerically to identify the plasmon modes. Our results illustrate that the longitudinal plasmon modes of 1-D array are red-shifted and more higher-order modes appear as the number of nanoboxes increases. Moreover, the 2-D assemblies show their versatile multiple modes. For example, five configurations of the tetramer (tetris structure) exhibit different plasmon modes as illuminated by different-polarized plane waves. Due to the symmetry breaking of the 2-D assemblies, the Fano resonances and dips are observed. These phenomena demonstrate that the plasmon modes of a nanobox-cluster assembly are tunable to manipulate light on demand by tailoring the configuration.

A reconfigurable multi-polarization and multi-band circular patch antenna is proposed. This antenna is coaxial-fed at center with 18 PIN diodes placed across a circular ring slot on the patch. By different diode on-off states, four frequency bands can be produced. Due to the circular symmetry, in theory the polarization can rotate at a 20° interval with the same antenna characteristics. A prototype operating in GSM900, LTE1500, GSM1800 and IEEE802.11b/g bands is designed and fabricated. The measured results shows that the 10-dB bandwidths of the four bands are almost covered.

A new connector for coaxial-to-microstrip transitions is proposed. The structure designed for the transformation of the electromagnetic field distributions of a coaxial line and a microstrip line consists of two blocks split from a metallic ring and two parallel arrays of via holes embedded in the substrate of the microstrip line. Insertion loss caused by a field discontinuity at their transition is reduced, particularly at higher frequencies. Thus, the transmission passband of the transition is extended. A prototype of the new connector is prepared and its transition to a microstrip line with two embedded via arrays is simulated and measured for a design example. The results indicate that the proposed design can improve the 1-dB passband of the transition by more than 60% compared to the conventional design. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:2716–2719, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27165

This paper presents a new type of planar balun implemented by trans-directional (TRD) couplers. The formulation of the proposed balun is derived and the characteristics of the balun are analyzed. This balun requires no via-hole connection to ground. Thus, the phase errors caused by the inductive effect of via-holes are reduced. The configuration of TRD couplers also helps to reduce the complexity of dc biasing of active circuits in the next stage. Two prototypes are designed and built to verify the design concept. The first one, operated from 1.94 to 2.69 GHz, is realized by 3-dB TRD couplers. The second prototype, which is operated from 376 to 458 MHz, is constructed by two 4.8-dB TRD couplers. The dimension of this prototype is only 16.8 mm × 39.4 mm. This small area is achieved by meandering the coupled-line sections because its coupling effect is purely contributed by periodical shunt capacitors on the microstrip lines. Measured results are in good agreement with simulated results.

This paper presents difierential-fed patch antennas with excellent cross-polarization. This paper provides a detailed graphic illustration of factors that lead to deteriorated H-plane cross- polarization by the conventional single-ended feeding probes. A novel difierential rat-race feeding structure was constructed to allow easy impedance matching. An experimental antenna was realized on low- temperature co-flred ceramic (LTCC) at 8GHz. An excellent cross- polarization of less than i22:5dB was achieved. When the operation frequency is high, the parasitic inductance caused by feeding probes may degrade the performance of antennas. This paper further proposes the use of difierential aperture-coupled structures at high frequencies. An aperture-coupled antenna realized at 40GHz with low cross- polarization < i15dB has been achieved.

This article presents a design for wideband bandpass filters using a microstrip cavity coupler. The broadband nature of the cavity-coupled designs is fully exploited for this application. Two additional circuits are introduced to improve the stopband performance of the cavity-coupled bandpass filter. A prototype design example is presented with its center frequency located at 6.28 GHz. The design has the merits of wide bandwith of more than 140%, flat group delay within the passband, good insertion/return loss, and stopband attenuation of nearly 30 dB up to 30 GHz. The validity of the simulation results is verified experimentally. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:2814–2817, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26410

This paper presents a new design to improve the transmission characteristics of coaxial-to-microstrip transitions. A metallic ring is added to a conventional coaxial structure to serve as a buffer between a coaxial line and a microstrip line. The introduction of the metallic ring reduces the insertion loss of the transition caused by the sudden changes of the electromagnetic field distributions from one transmission line to another. This improvement is more prominent at higher frequencies; hence, the 1-dB transmission passband of the transition is increased significantly. A practical design example is implemented and measured. The increase of the 1-dB passband is more than 60%. The new design is also proven to be suitable for transitions between various coaxial cables/connectors and microstrip lines on different substrates or another commonly used planar transmission line, the coplanar waveguides. The robust nature of this design makes its performance not susceptible to the fabrication and assembly errors of the transitions. These characteristics qualify the proposed design as an excellent candidate for coaxial-to-microstrip transitions at higher frequencies.

A dual-port antenna is proposed to operate in the two frequency bands of global positioning system (GPS) and ultrawideband (UWB). First, the shorted ring-slot antenna is etched on the top surface of the FR4 substrate to radiate circularly polarized (CP) waves in the GPS band. Second, a monopole antenna, which is responsible for operation in UWB, is constructed on the bottom surface. In order to reduce the coupling coefficient, the monopole antenna is located in the center region of the bottom surface and the microstip line is placed in the specific region, whose reverse side is grounded. The measured data for impedance and axial ratio (AR) bandwidths in the GPS band are 320 MHz (21.1%) and 80 MHz (5.0%), respectively. As for UWB, experimental results show that the reflection coefficient is below – 10 dB between 2.93 GHz and 10.7 GHz. The antenna gain in GPS is 4.74 dBic and those in UWB are between 4.4 and 5.8 dBi. Moreover, the measured coupling coefficient is below –14 dB between 1.5 GHz and 10 GHz, whi...

This study develops a 28-GHz patch antenna array using LTCC (Low Temperature Co-fired Ceramic) technology, for use in applications of LMDS (Local Multipoint Distribution Service). The design comprises 2 × 2 stacked patch elements and parallel-fed networks, yielding a wide bandwidth and superior gain performance. Broadband performance is achieved by varying the dimensions of the parasitic patch. The arrays are excited through using a novel opposite-side feeding structure to prevent any electrical effect on the parasitic patch. Measurements correlate closely with the simulation results: a gain of 10.35 dBi and a bandwidth of 2.85 GHz (26.75–29.6 GHz) are achieved.

A steerable phased array antenna driven mechanically is realized by utilizing the variation of dumbbell electromagnetic bandgap (EBG) structures. The variation takes place under the feed line of a 4-element array that gives the change in relative phase shift. The phase shift achieved from different shaping combinations of EBGs shifting under the feed lines. The feed lines are connected with four microstrip patches to yield a 4-element phased array antenna. The mechanical controlled pattern shapes of phase array antenna are simulated in electromagnetic (EM) software Zeland IE3D. Finally the design is fabricated with the help of optical lithography. It can be seen that the beam steering angle can be controlled mechanically without phase shifter and PIN switches.

PurposeThe purpose of this paper is to introduce a non‐uniform Chebyshev distributed low‐pass filter (LPF) with dumbbell‐shaped photonic bandgap structure (PBGs), implemented in the 50 Ω microstrip line, with improved defected ground structure.Design/methodology/approachThe non‐uniform distribution of PBGs and dumbbell‐shaped DGS of PBGs have been discussed in open literatures. In this study, the influence of FF of PBGs in dumbbell‐shaped PBG is represented.FindingsBy varying filling factor (FF) of the periodic structure from 0.25 to 0.8 of the dumbbell squares can generate better rejection band than uniform dumbbell LPF. Different FF of each square can produce different band rejection range and then yields the LPF with different cutoff. By using chirp adjustment of distance between PBGs, the band rejection performance can be optimized.Originality/valueIt can be seen that the chirped and non‐uniform dumbbell‐shaped PBGs generate excellent bandgap performances in linearly varying period (chirped devices) than those of structures with constant period (non‐chirped or uniform devices).

This work presents a quadrature voltage-controlled oscillator (QVCO) realized by on-chip trans-directional (TRD) couplers. The TRD coupler is implemented by sections of parallel- coupled lines connected by shunt capacitors periodically. The TRD couplers allow decoupling the DC path between input and output. Thus, it can make connections with active circuits easier, eliminating some ofi-chip biasing circuits. Since the quadrature signals are generated by 90 - hybrid couplers, the oscillator core can be optimized for circuit performance without considering the generation of quadrature signals. A Ka band QVCO fabricated in CMOS 0.18"m technology was designed to verify the efiectiveness of the proposed QVCO structure. The measurement results reveal that the quadrature output signals of QVCO have about i1:52dBm output powers with less than 1dB amplitude imbalance and less than 6 - phase difierence in the frequency range of 31.9 to 32.7GHz. The best measured phase noise of the QVCO is i110:6dBc/Hz at 1MHz ofiset from the center frequency. The flgure-of-merit of the circuit is 187.5dBc/Hz.

Transdirectional coupled-line couplers have the benefit of perfect input/output isolation. However, for a coupled-line coupler to operate in transdirectional mode, both phase- and impedance-coupling are required, which is difficult to meet by traditional coupled lines. To overcome this problem, this paper presents a novel transdirectional coupled-line coupler implemented by periodically loaded coupled lines. Two 3-dB 90° hybrids are designed and built to verify this concept. The first one was built on FR-4 substrates and operated at 3.6 GHz. The second one was built on Roger RT/Duroid 5870 substrates with length reduced and operated at 3.6 GHz. A good agreement with simulated results is reached.

An amorphous Ta-Zr diffusion barrier was studied under the Cu metallization. A stack of Cu/Ta 50 Zr 50 /Si with a 50 nm amorphous film fabricated by co-sputtering was found to fail when annealed up to 650 °C, which is much lower than the crystallization temperature (800 °C) of the amorphous Ta 50 Zr 50 film. Besides, results show that the existence of Cu layer can induce the formation of three metal silicides, namely TaSi 2 . ZrSi 2 and Cu 3 Si almost all at 650 °C. A mechanism for the failure of barrier film is proposed based on the change of activation energy for diffusion by the metallization-induced tensile stresses during annealing.

An amorphous Ta-Zr alloy film was studied as a diffusion barrier in the Cu metallization. On the experimental part, a Cu/Ta 50 Zr 50 /Si stack with thickness of 50 nm amorphous film was first prepared by sputtering and found effectively to suppress the penetration of Cu atoms into the substrate under rapid thermal annealing up to 650 °C. However, by examining the thermal stability of the barrier it revealed that these amorphous Ta 50 Zr 50 films crystallized at 800 °C, much higher than its failure temperature. Moreover, three metal silicides, TaSi 2 , ZrSi 2 and Cu 3 Si were found almost simultaneously when samples annealed at 650 °C. This result indicates that the existence of Cu layer not only promotes the diffusion of Ta and Zr to form metal silicides but also the diffusion of itself to pass through the barrier film to react with Si. A failure mechanism of the diffusion barrier is therefore proposed and verified quantitatively based on the relation between the thermal stress and the activation energy of diffusion.

In this study, wave functions are used to analyze the transmission of micro-scale particles throughout a sequence of one-dimensional potential barriers. This model can be used to simulate the motion of particles through a crystalline or non-crystalline thin film. Our focus is on the configuration of barriers which can be characterized by their heights, widths and lengths, and on their effects on the transmission probability. As a common phenomenon in crystalline structure, the resonant transmission can be found at classical forbidden energy levels and they form some energy bands. We further investigate the effects of voids and impurities on the transmission of particles by introducing variations to barrier heights. Results indicate that transmission can be weakened or reinforced by the presence of impurities or voids. In order to study more realistic structures, a statistical approach is introduced for us to imitate more variations on the barrier heights. This scheme allows us to study the transmission of particles through amorphous-like thin film. The quantitative results show that resonant energy bands can be significantly reduced by the irregular structures inside an amorphous-like film due to the destructive interference among waves.

A mathematical model for reactive sputtering with multiple gases is established. Several non-dimensional parameters were identified with their physical significance and then the governing equations were cast in a non-dimensional form. For an illustration, a two-reactive gas system is used for study. Results show that the stability is characterized by the well-known hysteresis loop in the steady state solutions. Through parameter analysis, we found when the ion fluxes intensified, the range of hysteresis loops were enlarged and shifted to higher inflow rates. Moreover, when the chemical reactions dominate either on target or substrate, the steady state can be totally stable without hysteresis. Pumping speed also controls the process stability. At high pumping speed, excessive reactive gas is less likely to present in the chamber, leading to the extinction of hysteresis loops.

A simple mathematical model based on Berg's original work for reactive sputtering is introduced to study the plasma cleaning process. The governing equations are formulated by overall mass balance for the gases inside the chamber and compounds on the substrate surface. Several non-dimensional parameters were identified along with their physical meanings to non-dimensionalize the governing equations. Solutions were obtained analytically and studied parametrically. Results show that the existence of reactive gas in a chamber could prevent the compound fraction being reduced to zero by ion sputtering. Increasing the reactive gas flux would increase the compound fraction and sputtering rate but lower the reactive gas concentration. At steady state, when the reactive gas flux is dominant, asymptotic values for compound fraction, reactive gas concentration and sputtering rate can be derived. A minimum value for the inflow rate at steady state is also identified as the starting threshold of a cleaning process.

Two designs for broad-band vertical transitions using microstrip-fed cavity couplers are presented in this paper. Both designs feature a cavity in an electrically thick ground plane between two parallel back-to-back microstrip lines terminated by open-circuited stubs. The cavity in the first design can be treated as a section of a waveguide, whereas the second design has the cavity operate in nonresonant modes. The electrically thick ground plane can provide isolation between modules, thermal dissipation for on-board active devices, as well as structural support for thin substrates. The finite-element method is chosen to carry out the required simulations for the proposed designs because of its accuracy. Both rectangular and circular cavity couplers are investigated. More than 100% fractional bandwidth can be achieved. The validity of the simulation results is verified experimentally. For applications at millimeter-wave frequencies, sensitivity study is conducted to demonstrate that the proposed design is robust and not susceptible to potential errors in dimension and misalignment, which may occur during the fabrication process of the vertical transitions

The excitation power of a scattering body is governed, in general, by the forward-scattering theorem. In this paper, the theorem is reconfirmed by simply applying Poynting's theorem to a loaded transmission line. It is shown that the excitation power is determined by the interaction of the incident voltage with the forward-scattered current. For some special cases, the backward-scattering formula can yield the same result. A transmission line with a shunt load is one of the examples where the excitation power can be expressed as the real part of the product of the incident voltage and the conjugate of the backward-scattered current. In this work, an experiment has been performed to verify the above results.

Spontaneous emission characteristics of self-organized InAs/GaAs quantum dots embedded in a photonic-crystal-based microcavity are theoretically investigated. Results are obtained from a three-dimensional quasi-mode analysis of the photonic-crystal microcavity and through calculations of energy levels and eigenstates for electrons and holes in self-organized quantum dots. The spontaneous emission rate from quantum dots is significantly enhanced by up to a factor of 14, compared to that in free space. In addition, the maximum coupling efficiency to the fundamental mode is close to unity.

This letter presents the design and realization of a new compact bandpass filter (BPF) fabricated on multilayered ceramic substrates. This BPF features coupled resonators with negative coupling coefficients. A BPF with center frequency 2.45 GHz is designed and fabricated. Its size is only 2.0 mm/spl times/1.8 mm/spl times/0.67 mm when implemented by a standard low temperature co-fired ceramic technology. The size reduction is due to the higher coupling coefficient between the negatively-coupled resonators than the positively-coupled ones, allowing tighter space between the resonators. The measured insertion losses of the previous BPF were less than 3dB and return losses more than 18dB in the passband. The measured result agrees very well with the electromagnetic (EM) designed response.