For a development of energy harvesting system, the fact of radio waves and ambient RF (Radio Frequency) sources, including passive devices along with novel circuits, are very closely related to mobile charging devices and energy storage system. The use of schottky diode and voltage multiplier circuits to express on the ambient RF sources surrounding the system is one way that has seen a sudden rise in use for energy harvesting. Practically speaking, the RF and ambient sources can be provided by active and passive devices such as inductors, capacitors, diode, etc. In this paper, we present a schottky based voltage multiplier circuits for mobile charging device which integrate the power generation module with radio wave generation module. We also discuss that multi-stage schematic, e.g., three-stage schottky diode based voltage multiplier circuits, for a continuing effort on energy harvesting system.

This paper presents a novel isolator that employs a varactor that tunes the operating frequency for use in future multi-band mobile handsets. The proposed isolator employs only one varactor for compactness and has a three-fold symmetric structure to reduce the parasitic reactance at each port. Analytical and experimental results clarify the tuning range of the proposed isolator. This paper presents the fundamental characteristics of the proposed isolator such as the insertion loss, isolation, and adjacent channel leakage ratio (ACLR) using a W-CDMA signal. The impact of the proposed isolator on the system performance is described based on experimental evaluation of the ACLR with a multi-band transmission system consisting of a power amplifier and the proposed isolator.

In this letter a circular polarization microstrip antenna with switchable polarization is proposed. The switchable polarization sense characteristic is realized via a shunt connected varactor tuning diode. The appropriate capacitance of the diode at the reverse bias voltage can alter two circular polarizations, as the tuning diode, which is located near the rectangular slot in the circular patch, is utilized in a perturbation element. The switchable polarization is analyzed using the equivalent circuit model representing the resonances of each orthogonal mode. Simulation, calculated, and measured results agree well.

A novel type of millimeter/submillimeter wave sampler based on resonant tunneling diodes (RTDs) was proposed, and its operation was confirmed by circuit simulation. It consists of an RTD pulse generator and an RTD detector. Owing to the fuse-like nonlinear I-V curve, highly sensitive sampling can be obtained. We also found that the effects of non-ideality in the I-V curve of the RTD can be corrected by sweeping the DC bias for the RTD detector.

Reverse-recovery modeling for p-i-n diodes in the high current-density conditions are discussed. With the dynamic carrier-distribution-based modeling approach, the reverse recovery behaviors are explained in the high current-density conditions, where the nonquasi-static (NQS) behavior of carriers in the drift region is considered. In addition, a specific feature under the high current-density condition is discussed. The proposed model is implemented into a commercial circuit simulator in the Verilog-A language and its reverse recovery modeling ability is verified with a two-dimensional (2D) device simulator, in comparison to the conventional lumped-charge modeling technique.

We performed the (NH4)2S surface treatments before Al2O3 deposition to improve the Al2O3/III-Nitride interface quality in Al2O3/AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors (MOSHFETs). Interface state density at the Al2O3/GaN interface was decreased by the (NH4)2S treatment. The hysteresis width in ID-VGS and gm-VGS characteristics of the Al2O3/AlGaN MOSHFETs with the (NH4)2S treatment was smaller than that without the (NH4)2S treatment. In addition, transconductance (gm) decrease at a large gate voltage was relaxed by the (NH4)2S treatment. We also performed ultraviolet (UV) illumination during the (NH4)2S treatment for further improvement of the Al2O3/III-Nitride interface quality. Interface state density of the Al2O3/GaN MOS diodes with the UV illumination was smaller than that without the UV illumination.

Large-signal-based nonlinear models are developed to analyze a variety of dynamic performances in a resonant tunneling diode (RTD) with peripheral circuits such as an integrated broad band bow-tie antenna, a bias circuit and a bias stabilizer circuit. Dynamic modes of the RTD are classified by the time-domain analysis with the model. On the basis of our model, we suggest a possibility to discuss a terahertz order oscillation mode control, and the ASK modulation in several tens Gbit/sec in the RTD with the broad band antenna. Validity of the model and analysis is shown by explaining measured results of modulated oscillation signals in fabricated triple-barrier RTDs.

The design, fabrication and characterization of GaN based varactor diodes are presented. MOCVD was used for layer growth and the DC characteristic of 4 µm diameter diodes showed a turn-on voltage of 0.5 V, a breakdown voltage of 21 V and a modulation ratio of 1.63. High frequency characterization allowed obtaining the diode equivalent circuit and observed the bias dependence of the series resistance. The diode cutoff frequency was 900 GHz. A large-signal model was developed for the diode and the device power performance was evaluated. A power of 7.2 dBm with an efficiency of 16.6% was predicted for 47 GHz to 94 GHz doubling.

We estimated the transit time of GaInAs/AlAs double-barrier resonant tunneling diodes (RTDs) oscillating at 0.6–1 THz. The RTDs have graded emitter structures and thin barriers, and are integrated with planar slot antennas for the oscillation. The transit time across the collector depletion region was estimated from measured results of the dependence of oscillation frequency on RTD mesa area. The estimated transit time was slightly reduced with the introduction of the graded emitter, probably due to reduction of the electron transition between Γ and L bands resulted from the low electric field in the collector depletion region.

A novel type of optically clocked all-optical flip-flop based on a coupled-mode distributed Bragg reflector laser diode is proposed. The device operates as a bistable laser, where the two lasing modes at different wavelength are switched all-optically by injecting a clock pulse together with a set/reset signal. We employ an analytical model based on the two-mode coupled rate equations to verify the basic operation of the device numerically. Optically clocked flip-flop operation is obtained with a set/reset power of 0.60 mW and clock power of 1.8 mW. The device features simple structure, small footprint, and synchronized all-optical flip-flop operation, which should be attractive in the future digital photonic integrated circuits.

We developed advanced techniques for the growth of self-assembled quantum dots (QDs) for fabricating a broadband light source that can be applied to optical coherence tomography (OCT). Four QD ensembles and strain reducing layers (SRLs) were grown in selective areas on a wafer by the use of a 90° rotational metal mask. The SRL thickness was varied to achieve appropriate shifts in the peak wavelength of the QD emission spectrum of up to 120 nm. The four-color QD ensembles were expected to have a broad bandwidth of more than 160 nm due to the combination of excited state emissions when introduced in a current-induced broadband light source such as a superluminescent diode (SLD). Furthermore, a desired shape of the SLD spectrum can be obtained by controlling the injection current applied to each QD ensemble. The broadband and spectrum shape controlled light source is promising for high-resolution and low-noise OCT systems.

Current density-voltage (J-V) and capacitance-voltage (C-V) characteristics of P3HT/n--silicon heterojunction diodes were investigated to clarify the carrier conduction mechanism at the organic/inorganic heterojunction. The J-V characteristics of the P3HT/n--Si junctions can be explained by a Schottky diode model with an interfacial layer. Diode parameters such as Schottky barrier height and ideality factor were estimated to be 0.78 eV and 3.2, respectively. The C-V analysis suggests that the depletion layer appears in the n--Si layer with a thickness of 1.2 µm from the junction with zero bias and the diffusion potential was estimated at 0.40 eV at the open-circuit condition. The present heterojunction allows a photovoltaic operation with power conversion efficiencies up to 0.38% with a simulated solar light exposure of 100 mW/cm2. The forward bias current was enhanced by coating the Si surface with a SiC layer, where the ideality factor was improved to be the level of 1.451.50.

In this study, the design and fabrication of a 110–140-GHz varistor mode frequency tripler made with four Schottky diodes pair are presented. Nonlinear simulations were performed to calculate the optimum diode embedding impedance and the required input power. A compact microstrip resonant cell (CMRC) filter was introduced for the first time in submillimeter multiplier, instead of the traditional low-and-high impedance microstrip filter. The shorter size and the wider stop band of the CMRC filter improved the performance of the tripler. The tripler exhibited the best conversion efficiency of 5.2% at 129 GHz and peak output power of 5.3 mW at 125 GHz. Furthermore, within the output bandwidth from 110 to 140 GHz, the conversion efficiency was greater than 1.5%.

A novel predistortion technique using an automatic average-power bias controlled diode is proposed to compensate the complicated nonlinear characteristics of a microwave class-F power amplifier using an AlGaN/GaN HEMT. The optimum value for diode bias voltage is automatically set according to detected input average RF power level. A high-efficiency 1.9 GHz class-F GaN HEMT power amplifier with the automatic average-power bias control (ABC) diode linearizer achieves an improved third order inter-modulation distortion (IMD3) of better than -45 dBc at a smaller than 6 dB output power back-off from a saturated output power of 27 dBm, without changing drain efficiency. The adjacent channel leakage power ratio (ACPR) for 1.9 GHz W-CDMA signals is below -40 dBc at output power levels of smaller than 20 dBm for the class-F power amplifier.

In order to realize stable n-type characteristics of pentacene for applying to the organic complementary metal-oxide-semiconductor field-effect transistors (CMOS), we have fabricated pentacene based MOS diodes using ultra-thin Yb layer such as 0.5-3 nm between gate insulator and pentacene. From the results of capacitance-voltage (C-V) measurements, excellent n-type C-V characteristics of the devices with 1 and 2 nm-thick Yb were observed even though the devices were measured in air. These results suggested that the n-type semiconductor characteristics of pentacene are able to be improved by the thin Yb interfacial layer. Furthermore, the improved n-type characteristics of pentacene will enable the fabrication of flexible complementary logic circuits utilizing one kind organic semiconductor.

The fabricated 1.55 µm high power superluminescent light emitting diodes (SLEDs) with 115 mW maximum output power and 3 dB bandwidth of 50 nm, using active multi-mode interferometer (MMI), showed high coupling efficiency of 66% into single-mode fiber, which resulted in maximum fiber-coupled power of 77 mW.

This work presents a novel field emission organic light emitting diode (FEOLED), in which an inorganic phosphor thin film is replaced by an organic EL light-emitting layer in the configuration of a field emission display (FED). The field emission electrons emitted from the carbon nanotubes (CNTs) cathode of the proposed FEOLED intensify the electron density in the multi-layer organic materials of the OLED; thus, resulting a higher luminous efficiency than that of a conventional OLED. Additionally, the luminance of the proposed FEOLED can be further increased from 10,820 cd/m2 to 27,393 cd/m2 by raising the current density of OLED through an external electron source. A balanced quantity of electrons and holes in the OLED, which is achieved by the proposed FEOLED increases the number of excitons and attributes the enhancement of luminous efficiency of the OLED. Under the same operating current density, the proposed FEOLED exhibits a higher luminous efficiency than that of a conventional OLED.

High luminance and high speed response with the cut-off frequency of more than 50 MHz in multilayer polyfluorene-based light-emitting diodes with an interlayer were achieved. We realized multilayer polyfluorene-based light-emitting diodes for frequency response up to 100 MHz.

We fabricated a p-i-n photodiode (PD) with an integrated microlens, and demonstrated its high performance capabilities including high speed (35 GHz), high responsivity (0.8 A/W), and large misalignment tolerance (26 µm), and an error-free 25-Gbit/s 10-km single-mode fiber transmission by using a 100-Gbit/s Ethernet quadplexer receiver module with the PDs.

In renewable power generators, because of high initial cost and duty cycle of systems, efficiency parameter has an important place. For this reason, line frequency controlled multilevel inverters are one of most proper choices for renewable power converters. Among these, diode-clamped multilevel inverter structures are one of most important and best efficient inverters. In this paper, a simple diode-clamped equivalent circuit for exploring the efficiency under resistive loads is proposed, and based on this simple circuit, the on-state power dissipation in improved and original diode-clamped multilevel inverter under resistive loads is analyzed. Then, comparative efficiency equations are extracted for inverters that use metal oxide semiconductor field-effect transistors (MOSFETs) and other p-n junction as switches. These equations enable us to have a better idea of conducting power dissipation in diode-clamped and help us to choose appropriate switches for having a lower on-state power dissipation. Some cases are studied and in the end it is proven that the calculated efficiency under resistive load is a boundary for inductive load with the same impedance in diode-clamped inverter with p-n junction switches. This means that calculating the efficiency under resistive loads enables us to approximately predict efficiency under inductive loads.