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Purpose High-speed Indium Phosphide (InP) HBTs have been widely used to design high-speed analog, digital and mixed-signal integrated circuits. The purpose of this study is to propose a new parameter extraction procedure for determining an improved T-topology small-signal equivalent circuit of InP heterojunction bipolar transistors (HBTs). Design/methodology/approach The alternating current crowding effect is considered through adding the intrinsic base capacitance in the small-signal equivalent circuit. All of the circuit parameters are extracted directly without using any approximation. Findings The extraction technique is more easily understood and clearer than other extraction methods, as the equations are derived from the S-parameters by peeling peripheral elements from small-signal models to get reduced ones and extracting each equivalent-circuit parameter using each equation. Originality/value To validate the presented parameter extraction technology, an n-p-n emitter-up InP HBT was analyzed adopting the method. Excellent agreement between measured and modeled S-parameters is obtained up to 40 GHz.

an improved small-signal model for the GaN pseudomorphic high electron mobility transistor (P-HEMT) process is proposed in this paper. Experimental studies have found that a high positive bias voltage usually damages or destroys the Schottky grid. In order to solve this problem, a method of extracting parasitic inductance and parasitic resistance using low gate bias voltage technology is proposed. Experimental research found that the parasitic circuit parameters will change with the bias voltage. New intrinsic resistance (RL) and intrinsic inductance (Lds) are introduced into the intrinsic equivalent circuit to suppress its bias dependence to solve this problem. At the same time, it is found that there is a time delay phenomenon in the parasitic parameter model, so the RC network (Rpds and Cpds, Rpgd and Cpgd) is introduced to represent this phenomenon. It is successfully applied to model a GaN P-HEMT. Excellent agreement between measured and modeled S-parameters is obtained from 0.5 to 20.5 GHz.

Tetrapod zinc oxide (T-ZnO), being a kind of nano-material, has large specific surface area and surface binding energy, which will make it sensitive to the ambient gas condition. So the field emission properties will be influenced by the gas adsorption when being applied as the cathode materials of field emission devices. Carbon monoxide is the main residual gas in T-ZnO field emission devices. In this paper, carbon monoxide was introduced into a field emission device with T-ZnO emitters. The field emission currents of tetrapod ZnO were compared before and after exposure to CO.

Printable carbon nanotubes field emission displays with shadow mask (Shadow Mask CNT-FED) is suggested. A layer of insulator is screen printed on the upper surface of shadow mask, and address electrodes are fabricated on it. MgO film is deposited on shadow mask by electron beam evaporation. Secondary emission electrons escape from MgO film under the bombardment of primary electrons. In the simulation, 93% of the landing electrons are found to be secondary emission electrons. The modulating amplitude of the voltage on the address electrodes is low (∼ 250 V) because of the low-energy secondary emission electrons. The comparable results are also got from the experiments. The modulating amplitude of the voltage is found to increase with the thickness of the insulator. The optimized thickness (40 ∼ 50 μm) and the fabrication process of the insulator are suggested in this research report.

Field emitters of vertical carbon fibers on a silicon substrate are fabricated by catalytic chemical vapor deposition. After an ageing process of 150 min, field emission measurement of the fibers is carried out in a vacuum chamber with a base pressure of 5.0 × 10−4 Pa. The experimental results display that field emission performance of the carbon fibers depends strongly on the vacuum level during the experiments. After the field emission measurement, damage to the carbon fiber field emitters is observed from the scanning electron microscopic images.

In this paper, a fully integrated Ku-band voltage controlled oscillator (VCO) with low phase noise is presented in a GaAs heterojunction bipolar transistor (HBT) technology. A cross-coupled configuration is employed to achieve low phase noise, and to achieve high output power, the largest HBT and higher bias current are adopted. The implemented VCO demonstrates that the oscillation frequency is from 13.77[Formula: see text]GHz to 14.8[Formula: see text]GHz, with a maximum 4.83[Formula: see text]dBm output power at 13.77[Formula: see text]GHz. The phase noise of the VCO is [Formula: see text]100.2[Formula: see text]dBc/Hz at 1[Formula: see text]MHz offset from 14.36[Formula: see text]GHz oscillation frequency. The VCO consumes 61.2[Formula: see text]mW from 6[Formula: see text]V supply and occupies an area of 0.51[Formula: see text]mm[Formula: see text][Formula: see text]mm. Finally, the figure-of-merits (FOMs) for VCOs are discussed.

Zinc oxide is a wide band gap semiconductor (WBGS). Its band bending, which usually favors field emission by lowering surface barrier and bringing more electrons to the bottom of conduction band, can be quite dramatic under high field. In the last few years, different kinds of ZnO nano-materials has been synthesized and applied as the cathode materials for field emission. For better application of ZnO in commercial field emission devices, long-term current stability is one of the most important aspects to be ensured. So in this paper, the field emission behavior of screen printing tetrapod ZnO will be studied by exposing to CO, which is the main residual gas in sealed tetrapod ZnO (T-ZnO) field emission device.

Plasmon coupling of dimers of Ag nanoparticles is studied by the EELS as shown in Fig 1a [1]. The spectroscopic images in the above Fig. 1a are extracted from 2.8eV, 3.4eV and 3.6eV respectively, where one can see the preferable exciting points of the features around the Ag nanoparticles. With the aid of DDA calculation(Fig. 1b), the three features are identified as the in-phase plasmon coupling, non-coupling and anti-phase coupling modes. The in-phase mode is able to conduct the light transportation due to its dipolar nature, which redshifts from the 3.4eV at large spacings to 2.7eV near touching (Fig. 1c). Such behaviour is also observed in the chain of 3 and 4 nanoparticles. The experiment provides clear evidence on the plasmon coupling of Ag nanoparticles. Extracting the dopant states in the Co-doped ZnO nanoparticles [2]. In order to assign the dopant-introduced states in the low-loss EELS, we employ both the core-loss EELS and the valence EELS on the same Co-doped ZnO nanoparticles by spatially mapping the dopant concentration distribution via the core-loss EELS (Fig 2a 2b 2c) and simultaneously by identifying the dopant features in the accumulated valence EELS via the measured dopant richness (Fig 2d). Three Coincidentally-growing Co dopant states are successfully determined in Fig. 2e. The experimental inputs feed the first-principles calculation, which generates full electronic structure of the doped ZnO nanoparticles. The experiment supports the carrier mediated room-temperature magnetism, which is a main confusion with current dilute magnetic semiconductors.

The effects of ion bombardment on the field emission of screen printed tetrapod zinc oxide cathodes are reported. The field emission characteristics of this cathode degrade strongly after Ar ion bombardment for 10min at an energy of 3keV and ion current of 5µA. The emission current density decreases from 1.65 to 0.32mA/cm2 at 4.50V/µm field strength, while the turn-on field increases from 2.16 to 3.11V/µm at a current density of 0.1µA/cm2. This result demonstrates that the field emission of the ZnO emitters severely degrades upon ion bombardment. The emission degradation can be attributed to a lower value of the field enhancement factor β, which is caused by changes of the morphology, and a higher work function ϕ, which is caused by changes of the surface composition of ZnO.

Tetrapod zinc oxide (T-ZnO), being a kind of nano-scale material, has a large specific surface area and high surface binding energy, which will make it sensitive to ambient gases; hence, the field emission (FE) properties of this ZnO nanomaterial will be influenced by gas adsorption. The effect of methane on the field emission of T-ZnO emitters was investigated. It was found that CH 4 enhanced the field emission substantially. By curve fitting we are able to describe the experimental results adequately as a function of the methane pressure. The increase of the field emission is caused by a lower work function of the ZnO-emitters.

The Ba and BaO evaporation rates of a thermionic cathode have been measured at 145K and 170K above the typical operating temperature being about 1033K. According to the measurement result, the relationship between cathode lifetime and operation temperature has been discussed. A comparison life test also be done between a poisoned but reactivated cathode and a normal one under the same condition. We found almost the same emission current at the beginning but different current decrease speed and Ba evaporation rate at the course of the life test.

Evaporation of carbon nanotubes (CNT) cathodes and the degradation of its field emission are reported in this paper. After 100h at 1323K the emission current density decreases from 6.50 to 0.20mA/cm2 at 7.50V/µm field strength, while the turn-on field increases from 1.92 to 2.45V/µm at a current density of 0.1µ/cm2. The C+-ion current in a mass spectrometer has also been measured to compare the CNT evaporation at different cathode temperatures between 1173K and1373K. The results indicate that the CNT evaporation rate increases greatly at temperatures above 1100K. Scanning electron microscopy (SEM) images show that the emission degradation can be mainly attributed to the decreased value of field enhancement factor β, which is caused by CNT evaporation.

The true outgassing from cathodes is often masked by the production of gases released by phosphors in field emission displays (FEDs). The outgassing characteristics of CNT cathode and ZnO cathode for application in FEDs are presented. Quadropole mass spectrometer[QMS] has been used to measure the outgassing characteristics from carefully prepared samples of CNT and ZnO cathodes in ultra-high vacuum(UHV) system. We observe that the outgassing rate of Z n O cathode is much lower than it of CNT cathode due to its solid structure, but they have the similar outgassing. It has been shown that the main components of released gases are water vapor, carbon monoxide, carbon dioxide and oxygen.

This paper reports the development and the operation of field emitters with low turn on electric field based on carbon fibres. Field emitters of vertical carbon fibres on silicon substrate were fabricated by the catalyst chemical vapor deposition. The diameter of the fibres is about 3~4 mum and the height is larger than 1 mm. After one aging process of 150 minutes, field emission measurements of carbon fibres were carried out in a vacuum chamber with pressure of 5.0times10-4 Pa. The experimental results showed the turn on electric field is 1.5V/mum and the emission current density rises to 46.7mA/cm2 under the field of 2.8 V/mum. The field emission performance and stability of carbon fibres depends strongly on the vacuum level during the process of the experiments. Damages on carbon fibres were also observed because of ion bombardment

Field emission characteristic and stability of a carbon nanotubes (CNTs) cathode have been studied by testing the emission current at different levels. By monitoring the emission I-V curves, we can obtain a relative stable maximum current from a CNTs cathode, after reaching the maximum current, the emission current fluctuate seriously and sparking can be seen at the site of emission. From the experimental results, the causes of emission instability and sparking is concluded and the influence of the sparking and ion bombardment on the emission performance of a CNTs cathode is obtained

In this paper, the outgassing of field emission display (FED) was studied using vacuum chamber and FED panel. The gas was measured with a quadrupole mass spectrometer (QMS), and the mean gas outgassed from the FED panel is CO when the device is working at about 1000V

We studied the residual gases inside Field Emission Displays (FEDs) with carbon nanotube(CNTs) emitters, and found that the main residual gases inside sealed CNT-FEDs are Ar and CO, both of which are typical residual gases inside electronic vacuum tubes.

In this paper, a novel gun of RF power amplifier based on always-on cathode was described. Double hopping electron funnels are fabricated into the devices. RF modulated signal is applied on the aluminum electrode. The process of secondary electron emission, potential distribution and trajectories were simulated. In the simulation model, the primary electrons, which are low energy, emit from the ring cathode with proportional spacing

An efficient method is used to improve the emission stability and uniformity of the field emission from a carbon nanotube (CNT) cathode. In this method, a fully sealed device with CNTs cathode is exhausted by a pumping system. At the same time, this device is baking at a temperature about 400degC and maintains for a few minutes, and an overload current is applied. The overload current can burn the nanotubes which are over-outcrop to the surface. Besides this, successive emission cycles process is designed to aging the cathode and get rid of the residual gas stored in the cathode layer. Consequently, the emission stability and uniformity of a CNTs cathode have been improved apparently

A new triode structure for printable carbon nanotube field emission displays is described in this paper. In the structure, silver paste is printed on the surface of a metal mesh and acts as the gate electrode. Between the gate and the metal mesh is a dielectric layer. MgO film and MgF/sub 2/ film are deposited on the surfaces of the mesh and the funnels by evaporation. A voltage applied on the metal mesh, the primary electrons emit from the CNT cathode and bombard on the surface of the metal mesh with initial energy. The secondary electrons and backscatters are generated. Because of the low energy of the secondary electrons, the gate can control the emission current easily. Therefore the range of the modulate voltage can be withdrawn. The dielectric layer on the surface of the metal mesh must be compact, otherwise silver paste will penetrate in after firing and under high voltage, breakdown of the insulator materials will occur by surface flashover. This paper reports the fabrication process of dielectric layer and the preparation of the materials.

The influences of ion bombardment on the field emission performance of tetrapod ZnO nanostructures are reported. As the scanning electron microscopy images and photoluminescence spectrum show, the tips of the field emitters are destroyed and the surface state of the field emitters is also changed after the ion bombardment. The ion bombardment has a considerable effect on the field emission properties of the tetrapod ZnO field emitters. After Ar+ ion bombardment with the energy of 3 keV and the ion current of 0.05 μA for 30 min, the turn-on field increases about 63% and the threshold field increases about 77%, respectively. There are two main reasons for the variation in field-emission property: (1) the decrement of the field enhancement factor β, which is caused by the variation in morphology of field emitter; (2) the increment of work function φ, which is caused by the changed concentration of the surface oxygen vacancy.

The authors measured the residual gas spectrum of a field emission display (FED) with carbon nanotube (CNT) emitters and found that the main residual gases inside a sealed CNT FED, containing an evaporated Ba getter, are H2, CH4, CO, Ar, and CO2, all of which are typical residual gases of electronic vacuum tubes. Additionally they also measured the electron stimulated desorption of gases by operating their field emission devices.

A novel gun double hop gun of rf power amplifier based on an always-on ringed cold cathode is suggested. Double hopping electron funnels, including a metal funnel and a glass funnel, are fabricated in. MgO film is deposited around the walls of the funnels by electron beam evaporation. Secondary electrons or backscatters (elastic and inelastic) escape from the dielectric film (MgO) under the bombardment of accelerated electrons and are driven to the exit window of the glass funnel by a modulated voltage. Among the escaping electrons, the ratios of secondary emission electrons, elastic scatters, and inelastic scatters are 90%, 9%, and 1%, respectively. Most of the escaping electrons at the exit window have low energy (