R. H. Jansen

Broadband Doherty Power Amplifier via Real Frequency Technique

A comprehensive method of designing a broadband Doherty power amplifier is presented in this paper. The essential limitations of bandwidth extension of a Doherty power amplifier are discussed based on the proposed structure of the Doherty power amplifier, which also takes the output matching networks of both sub-amplifiers into account. The broadband matching is realized by applying the simplified real frequency technique with the desired frequency-dependent optimum impedances. GaN transistors were selected to implement the circuit structure.

Study on quaternary AlInGaN/GaN HFETs grown on sapphire substrates

We report on AlInGaN/GaN heterostructure field effect transistors (HFETs) and the effect of different barrier material compositions. The analytical model for the interface charge in quaternary nitride heterostructures is described in detail and is applied in the calculation of the expected sheet carrier density. Experimental results from different lattice-matched AlInGaN/GaN heterostructures are presented and compared with the analytical predictions. Three heterostructures with AlInGaN barriers grown on sapphire substrates were processed and have been investigated. Each barrier layer was lattice-matched to GaN and the gallium content was 0.1, 0.15 and 0.2 at a barrier thickness of 13.5, 12.8 and 11.3 nm, respectively. Additionally, from these experiments, the basic trends for quaternary nitride Schottky barrier contacts are discussed. Finally, comprehensive dc characterizations have been performed. All devices had a gate length of 1 µm and exhibited a good transconductance of around 260 mS mm−1 at nearly the same current density level. An increase in threshold voltage as well as a decrease in gate leakage current for increasing GaN content has been observed. The nearly constant electron mobility in the range of 1700 cm2 V−1 s−1 at room temperature is within the best reported so far for HFETs with InN-containing barriers.

Fast Accurate Hybrid Mode Computation of Nonsymmetrical Coupled Microstrip Characteristics

A numerically efficient rigorous spectral domain solution of the wave equation is presented for covered and open nonsymmetrical coupled microstrip lines. Dispersion characteristics of the two fundamental quasi-TEM modes existing on this structure are given and found to agree excellently with measurement. In addition, the associated characteristic impedances of the unequal strips to ground and the line losses are computed from the eletromagnetic field. With this set of design data the four-port admittance matrix of a nonsymmetrical coupled line section is calculated taking the different modal phase velocities into account. As an example of application and as a further test for the computed results elementary microstrip bandfilter structures are analyzed.

Design methodology, measurement and application of MMIC transmission line transformers

A design methodology is presented for MMIC transmission line transformers (TLTs) typically having three conductor levels. Several such structures on GaAs have been processed and measured showing good broadband performance. The usefulness of TLTs is demonstrated by an MMIC amplifier design.<<ETX>>

Highly efficient yellow organic light emitting diode based on a layer-cross faded emission layer allowing easy color tuning

An easy way to adjust the color of yellow organic light emitting diodes (OLED) is realized by basing the emission layer on a cross-fading zone of two unipolar-conducting host materials doping parts of it either with a red or green phosphorescent emitter at varying thickness ratios. At color coordinates of 0.47/0.50, a current efficacy of 42.2 cd/A (16.2% external quantum efficiency) and a power efficacy of 32.9 lm/W (1000 cd/m2) are measured without light extraction enhancement. Mixed-host emission layer OLED without cross-fading are processed for comparison. Exciton distributions are studied. The concept is suggested to be useful for white OLED.

Crystal growth and properties of LiAlO2 and nonpolar GaN on LiAlO2 substrate

In this study, the growth and properties of LiAlO2 material and a nonpolar GaN-based light-emitting-diode (LED) structure on LiAlO2 have been investigated. The LiAlO2 material is grown by the Czochralski pulling technique and is used as a substrate for nonpolar nitride growth. An improved surface roughness can be obtained by a four-step polishing process. With subsequent nitridation treatment, a pure M-plane (1010) GaN can be obtained. An electron microscope shows an abundance of cracks that are oriented parallel to the (001) and (100) planes of the LiAlO2 substrate on the rear surface of GaN. The absence of the polarization-induced electric field of a GaN-based LED structure on LiAlO2 was shown by using photoluminescence measurements. Therefore, this approach is promising to further increase the luminescence performance of GaN-based LEDs.

Employing exciton transfer molecules to increase the lifetime of phosphorescent red organic light emitting diodes

The lifetime of phosphorescent red organic light emitting diodes (OLEDs) is investigated employing either N,N′-diphenyl-N,N′-bis(1-naphthylphenyl)-1,1′-biphenyl-4,4′-diamine (NPB), TMM117, or 4,4′,4″-tris(N-carbazolyl)-triphenylamine (TCTA) as hole-conducting host material (mixed with an electron conductor). All OLED (organic vapor phase deposition-processed) show similar efficiencies around 30 lm/W but strongly different lifetimes. Quickly degrading OLED based on TCTA can be stabilized by doping exciton transfer molecules [tris-(phenyl-pyridyl)-Ir (Ir(ppy)3)] to the emission layer. At a current density of 50 mA/cm2 (12 800 cd/m2), a lifetime of 387 h can be achieved. Employing exciton transfer molecules is suggested to prevent the degradation of the red emission layer in phosphorescent white OLED.

Modular Source-Type 3D Analysis of Scattering Parameters for General Discontinuities, Components and Coupling Effects in (M)MICs

A deterministic full-wave solution to the hybrid-mode characterisation of basic and non-elementary structures in (M)MICs is described. It is modular, not restricted to a few specific shapes and involves surface wave excitation and coupling effects. Results up to the full-wave 3d analysis of simple strip filters treating these structures as one field-theoretical block are presented. They demonstrate the potential of the approach for the solution of highly complex (M)MIC design problems.

RF Characterization of Schottky Diodes in 65-nm CMOS

Schottky diodes in 65-nm CMOS have been designed, measured up to 67 GHz, and modeled in the reverse-bias voltage range. An array of 8 × 8 minimum-sized parallel diode junctions is compared with a single-junction diode and to linear arrays of 3, 12, and 64 elements of the same total area. An iterative analysis method and a more detailed equivalent circuit than that used in previous work are developed to extract the junction capacitance, the stray capacitance, and the series resistances separately. Based on the equivalent circuit model, the extrapolation of the diode RF behavior to frequencies beyond the measurement range is discussed. The relevance of the cutoff frequency of the Schottky junction itself for evaluation of the suitability of the diodes in millimeter-wave and terahertz applications is explained.

Novel Green's Function Database Technique for the Efficient Full-Wave Analysis of Complex Irregular (M)MIC-Structures

An efficient analysis of arbitrarily shaped shielded microstrip circuits using a new spatial Greens function database technique is presented. Generation of the associated large moment method matrix equations is reduced to a few simple operations per element. The speed advantage of direct databased solutions is discussed and compared to a spectral domain conjugate gradient solver. The accuracy of computed results is verified by measurements and shown to be superior to conventional CAD simulation. One of the examples of direct importance for design is a 90° coupled bend analysis.