Design and Experiments of the Sheet Electron Beam Transport with Periodic Cusped Magnetic Focusing for Terahertz Traveling-Wave Tubes

The successful transport of a sheet electron beam under the periodic cusped magnet (PCM) focusing at the terahertz frequencies is reported. The sheet beam with a current density of 285 A/cm2 is intended for the developing G-band sheet-beam traveling-wave tube (TWT) whose operating voltage is nominally 24.5 kV. A beamstick was developed to validate the design of the electron optics system, which is considered as the most challenging part for developing a sheet-beam device. A beam transmission ratio of 81% is achieved over a distance of 37.5 mm at a cathode voltage of −25.0 kV. The total current and the collector current were measured to be 125 and 102 mA, respectively. The experimental results are promising, demonstrating that the PCM scheme is capable of focusing a high-current-density sheet beam and hence can find use in the terahertz TWTs, offering the advantages of compact size and light weight.

A Curvature Compensation Technique for Low-Voltage Bandgap Reference

Based on the standard 40 nm Complementary Metal Oxide Semiconductor (CMOS) process, a curvature compensation technique is proposed. Two low-voltage, low-power, high-precision bandgap voltage reference circuits are designed at a 1.2 V power supply. By adding IPTAT (positive temperature coefficient current) and ICTAT (negative temperature coefficient current) to the output resistance, the first-order compensation bandgap voltages can be obtained. Meanwhile, the third high-order compensation current is also superimposed on the same resistance. We make use of the collector current of the bipolar transistor to compensate for the nonlinear term of VBE. The simulation results show that TC (temperature coefficient) of the first circuit reference could be reduced from 29.1 × 10−6/°C to 5.71 × 10−6/°C over the temperature range of −25 to 125 °C after temperature compensation. The second one could be reduced from 17 × 10−6/°C to 5.22 × 10−6/°C.

Investigation of a cold atmospheric plasma jet generation in single and multichannel planar devices

A plasma source of atmospheric pressure with a planar geometry of the device and an adjustable number of planar discharge channels has been developed. The dependence of the recorded collector current on the amplitude of the applied voltage is investigated. It was found that the current in each of the channels consists of a set of independent current channels whose propagation does not depend on each other.

Research on dynamic current sharing method of parallel connected IGBT modules for NPC three level converters

The parallel connection of IGBTs has been being applied in high power neutral point clamped (NPC) three level converters. This paper investigates the impact of gate parameters (gate resistor and capacitance) on dynamic current imbalance of parallel connected IGBT for NPC three level converter. A gate parameters calculation method is proposed in the paper, and the delay time and collector current difference can be analysed quantitatively. Experimental results have shown the effectiveness of the method.

Investigation of Base Transport Mechanism in Silicon-Germanium Heterojunction Bipolar Transistor Operating over Wide Temperature Range

A high breakdown voltage silicon-germanium heterojunction bipolar transistor operated over a wide temperature range from 300 K to 10 K has been investigated. The measured Gummel characteristics illustrate that the collector current and base current both shift to the higher voltage as the temperature decreases. The fT/fmax are extracted to be 23/40 GHz at 300K, 28/40 GHz at 90 K, and 25/37GHz at 10K, respectively. The effective amplification range becomes narrow as the temperature decreases. And the ideality factor of base current in the low current region is shown to be temperature-dependent and its value is much larger than 2 at cryogenic temperatures. This phenomenon indicates that the base current is not only contributed by drift, diffusion, and Shockley-Read-Hall recombination, but also by trap-assisted tunneling. The Hurkx local trap-assisted tunneling has been used to analyze the non-ideal base transport mechanism. And a calibrated TCAD device model is developed to further verify this non-ideal transport mechanism.

Comparative Study of Si-Ge-Sn Resonant Cavity Enhanced Heterojunction Bipolar Phototransistor (RCE-HPT) under Quantum Confined Stark Effect (QCSE) and Franz Keldysh Effect (FKE) at 1.55 µm

Group-IV and their alloy based Heterojunction Bipolar Phototransistors (HPTs) are of immense interest in recent day optical communication. In this paper first resonant cavity enhanced heterojunction bipolar phototransistor (RCE-HPT) with Ge0.992Sn0.008/Si0.30Ge0.61Sn0.09 Quantum Well/barrier structure under Quantum Confined Stark Effect (QCSE) has been evaluated. Further the bulk GeSn absorption region has been considered instead of QW/barrier structure and estimated the Franz Keldysh Effect (FKE). Finally different RCE-HPT related parameters such as quantum efficiency-bandwidth product, responsivity, collector current and optical gain have been studied and compared under QCSE and FKE.

The influence of uncontrolled technological impurities on the temperature dependence of the gain coefficient of a bipolar n-p-n-transistor

Herein, the temperature dependences of the static current gain (β) of bipolar n-p-n-transistors, formed by similar process flows (series A and B), in the temperature range 20–125 °С was investigated. The content of uncontrolled technological impurities in the A series devices was below the detection limit by the TXRF method (for Fe < 4.0 · 109 at/cm2). In series B devices, the entire surface of the wafers was covered with a layer of Fe with an average concentration of 3.4 ∙ 1011 at/cm2; Cl, K, Ca, Ti, Cr, Cu, Zn spots were also observed. It was found that in B series devices at an average collector current level (1.0 ∙ 10–6 < Ic <1.0 ∙ 10–3 A) the static current gain was greater than the corresponding value in A series devices. This was due to the higher efficiency of the emitter due to the high concentration of the main dopant. This circumstance also determined a stronger temperature dependence of β in series B devices due to a significant contribution to its value from the temperature change in the silicon band gap. At Ic < 1.0 ∙ 10–6 A β for B series devices became significantly less than the corresponding values for A series devices and practically ceases to depend on temperature. In series B devices, the recombination-generation current prevailed over the useful diffusion current of minority charge carriers in the base due to the presence of a high concentration of uncontrolled technological impurities. For A series devices at Ic < 10–6 A, the temperature dependence of β practically did not differ from the analogous dependence for the average injection level.

Effects of Temperature and Stress on the InGaP/GaAs Heterojunction Phototransistor

Although the effects of electrical stress and temperature on the performance of the InGaP/GaAs heterojunction bipolar transistors (HBTs) have been widely studied and reported, little or none was reported for the InGaP/GaAs heterojunction phototransistors (HPTs) in the literature. In this paper, we discuss the temperature-dependent characteristic of InGaP/GaAs HPTs before and after electrical stress and assess the effectiveness of the emitter-ledge passivation, which was found to effectively keep the InGaP/GaAs HBTs from degrading at higher temperature or after an electrical stress. The emitter-ledge passivation is also effective keeping a higher optical gain even at higher temperature. An electrical stress was given to the HPTs by keeping the collector current at 60 mA for 15 min. Since the collector current density as an electrical stress is 24 A/cm2 and much smaller than the stress usually given to smaller HBTs for the stress test, the decreased optical gain was not observed when it was given at room temperature. However, when it was given at 420 K, significant decreases of the current gain and optical gain were observed at any temperature. Nevertheless, the emitter-ledge passivation was found effective in minimizing the decreases of the current gain and optical gain.

An Anti-Interference Online Monitoring Method for IGBT Bond Wire Aging

Due to the constant changes of the environment and load, the insulated-gate bipolar transistor (IGBT) module is subjected to a large amount of junction temperature (Tj) fluctuations, which often leads to damage to the bond wires. The monitoring parameters of IGBTs are often coupled with Tj, which increases the difficulty of monitoring IGBTs’ health status online. In this paper, based on the collector current (Ic) and collector-emitter on-state voltage (Vce_on) online monitoring circuit, an online monitoring method of IGBT bond wire aging against interference is proposed. First, the bond wire aging model is established, and the Vce_on is selected as the monitoring parameter. Secondly, taking a three-phase inverter circuit as an example, the Vce_on and Ic waveforms of the IGBT module are monitored in real time, and the process of online monitoring is introduced accordingly. Finally, the experimental results indicate that the method proposed in this paper can accurately identify the aging state of IGBT bond wires under different conditions.

Development of an Electrothermal Simulation Tool for Integrated Circuits

The goal of this research was to develop a capability for the electrothermal modeling of electronic circuits. The objective of the thermal modeling process was to create a model that represents the thermal behavior of the physical system. The project focuses on electrothermal analysis at devices and chip level. A novel method to perform electrothermal analysis of integrated circuits based on the relaxation approach is proposed in this research. An interface program couples a circuit simulator and a thermal simulator. The developed simulator is capable of performing both steady state and transient analaysis at devices and chip level. The proposed method was applied to perform electrothermal analysis of Silicon Bipolar Junction Transistor (BJT) to predict the temperature distribution and the device performance in a circuit. Thermal nonlinearity due to temperature-dependent material parameters in the context of thermal modeling of the device and circuit has also been considered. The DC characteristics of the device were investigated. The obtained results indicate that the operating point of the device varies while the device reaches its junction temperature. The accuracy of the electrothermal simulator has been evaluated for steady state analysis. The experimental results of a BJT amplifier were compared to the simulator results of the similar circuit. The electrothermal simulation results of BJT amplifier circuit indicate a good agreement with the available experimental results in terms of power dissipation, collector current and base-emitter voltage. The performance of the electrothermal simulator has been evaluated for tansient analysis. A current mirror circuit using Si NPN BJTs was simulated. According to the electrical simulator, the output current follows the reference current immediately. Nonetheless, the electrothermal simulator results depict that the load current has delay to reach a constant value which is not the same as the reference current, due to the influence of thermal coupling and self heating. The obtained results are in agreement with the available results in literature.