Increase In Junction Temperature Research Articles

Influence of Relative Humidity on the Temperature Increase of a Power Converter

As a vital part of renewable energy and electrical traction, power converters are supposed to have high reliability and good performance. However, power semiconductors produce considerable heat when the power converter works, which results in high junction temperatures that lower the reliability and performance of the power semiconductors. Many studies show that ambient humidity has a significant effect on power devices, but the influence of high humidity on junction temperatures has yet to be studied. Therefore, this paper presents a thermal model for power converters in moist air to obtain the junction temperature increase, which is utilized for the power converter used in a Switched Reluctance Motor System. Simulation results show that the law of converter temperature distribution is independent of the relative humidity in the case of fixed ambient temperature, whereas the temperature in the power converter decreases as the ambient relative humidity increases. These simulation results are validated with the experimental results.

Analysis of GaN-based light-emitting diodes degraded by generation of deep-level states

GaN-based light-emitting diodes (LEDs) degraded by the generation of deep-level states were analyzed by means of temperature dependent current–voltage measurements. After accelerated aging test of LEDs, the density of deep-level states was found to increase by a factor of ∼5.0, which resulted in an increase in junction temperature of 7 °C associated with increased nonradiative recombination. The optical microscopy images of LEDs under zero bias (left) and 50 µA (right).

Thermal and luminous investigations of a pcLED based refrigerating liquid prototype

The heat management plays a key role for high performance operation of LEDs. The increase of junction temperature determines the decrease of LEDs' lifetime, the failure of these devices, the shift of color spectrum, and lower operational efficiency. The paper deals with the thermal management and luminous experimental analysis of a new fabricated LED prototype using refrigerating oil as cooling agent. The dielectric cooling liquid represents an effective thermal management solution for high-power LEDs due to their superior heat transfer characteristics compared with air. The new proposed configuration, based on phosphor converted blue LEDs, is investigated by setting up a thermal model and validated through performed experimental tests. A series of experiments were performed on four LED configurations (air/silicon oil as cooling agent, and with/without heat sink) in steady state and heating/cooling transient processes to evaluate the heat dissipation performances. The thermal modeling and experimental results were compared and highlighted, demonstrating good agreement. In addition, the laboratory luminous tests were conducted to analyze if the fabricated guarantees higher luminous efficiency.The experiments indicated that the proposed pcLED based refrigerating liquid prototype efficiently dissipates heat and has good luminous performances.

Characteristics of InGaN-based superluminescent diodes with one-sided oblique cavity facet

We have fabricated InGaN-based superluminescent diodes (SLDs) with one-sided oblique facet. The characteristics of the SLDs and laser diodes with the same cavity length (800 mu m) were compared. The typical peak wavelength and the full width at half maximum of the spectrum in superluminescence regime are 445.3 and 7.7 nm for the SLDs with 800 mu m cavity length. The characteristics of the SLDs with different cavity length were also demonstrated in a comparative way. It is found that the gain of the InGaN multi-quantum wells in blue spectral range is a linear function of the current density below gain saturation region. The lasing threshold current turns out to be higher for the shorter SLD (S-SLD) (400 mu m), but the output light intensity of the longer SLD (800 mu m) is higher than that of the S-SLD under the same current density. The gain saturation phenomenon was observed in S-SLD when it was biased at a current density larger than 27.5 kA/cm(2). The increase of junction temperature was identified as the main reason for gain saturation through spectra analysis.

Investigation of the prediction model of IGBT junction temperature based on the rate of voltage change

Based on semiconductor physics and the essential structure of insulated gate bipolar transistor (IGBT), the model of dV_{CE}/\d t is established through reasonable simplification and theoretical derivation. The influencing factors and temperature characteristics of dV_{CE}/\d t are studied in depth. It is concluded that dV_{CE}/\d t increases linearity with the increase of voltage or current, and decreases with the increase of junction temperature also linearly. On the basis of the model for dV_{CE}/\d t, the prediction model of junction temperature is established. Results of simulations and experiments verify the correctness and accuracy of the models. It is significant in theory and practical application for realizing IGBT junction temperature monitoring on-line and improving the reliability of IGBT module and power electronic equipment.

Saga of efficiency degradation at high injection in InGaN light emitting diodes

Saga of efficiency degradation at high injection in InGaN light emitting diodes

Effect of Different Quantum Well Structures on the Output Power Performance of GaN-Based Light-Emitting Diodes

We investigated the effect of two different quantum well (QW) structures having different indium contents on the optical performance of fully packaged GaN-based light-emitting diodes (LEDs). Dual-spectrum QW LEDs exhibit ∼4% higher external quantum efficiency (at 350 mA) than single-spectrum QW LEDs. However, the two types of LEDs exhibit similar efficiency droop behavior. For both types of LEDs, the output power decreases with increasing junction temperature. When the junction temperature exceeds 70°C, the dual-spectrum QW LEDs exhibit lower output power than the single-spectrum QW LEDs. The wavelength dependence of the output power (at 350 mA) of single-spectrum QW LEDs shows that the LEDs with shorter wavelengths experience more rapid optical degradation than the LEDs with longer wavelengths. Based on the wavelength- and junction-temperature-dependent output power, the droop behavior of the dual-spectrum QW LEDs is described and discussed.

Analysis and Research of the High Power LED Temperature Characteristics

This paper is mainly about the high power LED temperature characteristics. With the integrating sphere, we conduct an experiment to observe and analysis the relationships of temperature and color coordinates, peak wavelength, color temperature, forward voltage, peak bandwidth, color purity, electric power. Finally we get that the temperature is the main factor to affect the color performance of white LED photoelectric, with the white LED apparent temperature rise, forward voltage, the color coordinates and color purity tends to go down. On the contrary with increasing junction temperature, the half-value wavelength and color temperature are increased accordingly.

Investigation of Si IGBT Operation at 200$\,{}^\circ$C for Traction Applications

In order to satisfy the high-density requirement and harsh thermal conditions while reducing cost in future electric and hybrid electric vehicles (HEV), a systematic study of a 1200-V trench-gate field-stop Si insulated gate bipolar transistor (IGBT) operating up to 200°C is performed to determine its feasibility, issues, and application guideline. The device forward conduction characteristics, leakage current, and switching performance are evaluated at various temperatures. Based on the device characterization, the impact of the increased junction temperature on a traction drive converter loss and thermal management is analyzed. It is shown that by extending the device junction temperature to 200°C, the additional 65°C coolant loop can be eliminated without compromising power density and thermal management design. Furthermore, the possible failure mechanisms including latching, short circuit fault, and avalanche capability are tested at elevated temperatures. The criteria considering thermal stability, thermal management, short circuit capability, and avalanche capability are given at 200°C to ensure the safe and reliable operation of Si IGBTs.

High Brightness III - V Light-Emitting Diodes on Diamond/Silicon Composite Substrate

Thermal management of LED is currently an important issue because the increase of junction temperature degrades LED’s performance and reliability. Replace that substrate to high thermal conductivity substrate can improved this problem. Diamond has the highest thermal conductivity (~2000W/mK) in all material but is hard to process and has low reactivity with other material. In this study, high-brightness Ш-Ѵ light-emitting diodes on Si/diamond composite substrate can be fabricate by filled diamond particle into the blind-hole of the silicon substrate, wafer-bonding and lift-off process. In order to confirm that diamond particle provided a direct thermal path for heat dissipation, a simple sandwich structure was also been done.

Effect of junction temperature on the large-signal properties of a 94 GHz silicon based double-drift region impact avalanche transit time device

The authors have developed a large-signal simulation technique extending an in-house small-signal simulation code for analyzing a 94 GHz double-drift region impact avalanche transit time device based on silicon with a non-sinusoidal voltage excitation and studied the effect of junction temperature between 300 and 550 K on the large-signal characteristics of the device for both continuous wave (CW) and pulsed modes of operation. Results show that the large-signal RF power output of the device in both CW and pulsed modes increases with the increase of voltage modulation factor up to 60%, but decreases sharply with further increase of voltage modulation factor for a particular junction temperature; while the same parameter increases with the increase of junction temperature for a particular voltage modulation factor. Heat sinks made of copper and type-IIA diamond are designed to carry out the steady-state and transient thermal analysis of the device operating in CW and pulsed modes respectively. Authors have adopted Olson's method to carry out the transient analysis of the device, which clearly establishes the superiority of type-IIA diamond over copper as the heat sink material of the device from the standpoint of the undesirable effect of frequency chirping due to thermal transients in the pulsed mode.

Channel temperature determination of a multifinger AlGaN/GaN high electron mobility transistor using a micro-Raman technique

Self-heating in a multifinger AlGaN/GaN high electron mobility transistor (HEMT) is investigated by micro-Raman spectroscopy. The device temperature is probed on the die as a function of applied bias. The operating temperature of the AlGaN/GaN HEMT is estimated from the calibration curve of a passively heated AlGaN/GaN structure. A linear increase of junction temperature is observed when direct current dissipated power is increased. When the power dissipation is 12.75 W at a drain voltage of 15 V, a peak temperature of 69.1 °C is observed at the gate edge on the drain side of the central finger. The position of the highest temperature corresponds to the high-field region at the gate edge.

Extreme Thermal Transient Stress Analysis with Pre-Stress in a Metal Matrix Composite Power Package

This paper culminates several years of development of a SiC MOSFET-based solid-state circuit breaker power module designed and fabricated for aluminum-based composite metal-ceramic packaging. The aluminum composite structure was used for high temperature thermal management >350°C and high reliability. Testing of the final module surpassed 750 total cycles. The module was optimized for four dies, 4.1mm × 4.1 mm each for SiC or GaN. The electrically loading per die was 48 A for 5 ms with a di/dt of 2.1 kA/us (23 ns opening time). An internal snubber increased the response to 390 ns. The die absorbed ∼4.6 J causing a transient junction temperature increase of ∼245 °C. Two ambient temperatures were used in testing and set at 25 °C and 105 °C. The maximum junction temperature was conservatively projected to reach 350 °C during the 5 ms pulse. Electrical, thermal and mechanical design and testing results are presented.

Spin transfer torque switching assisted by thermally induced anisotropy reorientation in perpendicular magnetic tunnel junctions

A method to switch the magnetization of the free layer in magnetic tunnel junctions with perpendicular anisotropy is demonstrated. It consists in assisting the spin transfer switching of the magnetization by a thermally induced reorientation of the free layer magnetic anisotropy from out-of-plane to in-plane. The junction temperature increase is due to the Joule dissipation around the tunnel barrier produced by the same pulse of current which generates the spin transfer torque. This magnetic reorientation allows the spin transfer torque efficiency to be maximal since the spin polarization of the current is perpendicular to the magnetization of the free layer. Such a thermally assisted switching allows designing highly down-size scalable magnetoresistive random access memory cells with improved write efficiency.

Thermal reliability of VCO using InGaP/GaAs HBTs

Degradations of InGaP/GaAs heterojunction bipolar transistor (HBT) collector current and base current subjected to cumulative long-term junction temperature stress are examined experimentally. The aged SPICE model parameters as a function of stress time are extracted from the measurement data. The VCO phase noise, tuning range, and output amplitude are studied in circuit simulation. The phase noise increases, tuning range and output amplitude decrease with increasing junction temperature.

Degradation of light emitting diodes: a proposed methodology

Due to their long lifetime and high efficacy, light emitting diodes have the potential to revolutionize the illumination industry. However, self heat and high environmental temperature which will lead to increased junction temperature and degradation due to electrical overstress can shorten the life of the light emitting diode. In this research, a methodology to investigate the degradation of the LED emitter has been proposed. The epoxy lens of the emitter can be modelled using simplified Eyring methods whereas an equation has been proposed for describing the degradation of the LED emitters.

Turn-off Time as a Precursor for Gate Bipolar Transistor Latch-up Faults in Electric Motor Drives

In this paper, effects preceding a latch-up fault in insulated gate bipolar transistors (IGBTs) are studied as they manifest within an electric motor drive system. Primary failure modes associated with IGBT latch-up faults are reviewed. Precursors to latch-up, primarily an increase in turn-off time and junction temperature, are examined for the IGBT. In addition, the relationship between junction temperature and turn-off time is explained by examining the semiconductor properties of an IGBT. To evaluate the effects preceding latch-up, seeded fault testing is conducted using aged transistors induced with a fault located in the die-attach solder layer. Since junction temperature cannot be directly measured, the transistor turn-off time is used as a measured system parameter to correlate between healthy and fault conditions. The experimental results provide statistically significant evidence (within 99% confidence) that an IGBT latchup event, caused by elevated junction temperatures, can be detected by monitoring the transistor turn-off time insitu.

Advanced packaging yields higher performance and reliability in power electronics

Power density of power electronics will continue to grow. It is always supported by progress in power semiconductors. Further significant loss reduction of IGBT and diodes becomes possible if power circuit design improves with respect to electro-dynamic performance. Efforts to improve cooling for better power dissipation out of smaller volumes appear to be disadvantageous in comparison to increase of junction temperature. The direction of increasing junction temperature is most effective for air cooled systems as well as liquid cooled systems with high ambient temperature. To enable long life time of modules under higher operation temperature heavy copper wire bonding and diffusion soldering of chips are presented to fulfill the requirements. New chip technologies with integrated heat buffers ensure transient thermal capability for shrunk power chips.

Thermal Characterization of Junction in Solar Cell Packages

This is the first report on the direct measurement of the junction temperature and on the determination of thermal resistance of a commercial amorphous silicon (a-Si) solar cell package under real operating conditions. Thermal transient method was utilized for the thermal characterization. Irradiation of sunlight to the solar cell package was found to induce significant heat generation inside the solar cell package. It was shown that the driving of the solar cell package with a sun power of 1 sun (100 mW/cm2 and 1.5 AM) resulted in a junction temperature of about 113°C. Surprisingly, the temperature difference between the junction and the case surface of the solar cell package was as high as 43°C. The efficiency drop was observed with the increase of junction temperature in the solar cell package. Thermal resistance was determined under various operating conditions.

α-SiC nanoscale transit-time diodes: performance of the photo-irradiated terahertz sources at elevated temperature

The effects of elevated junction temperature on the terahertz (THz) frequency characteristics of α-(hexagonal, 4H and 6H) silicon carbide (SiC) based double-drift region (DDR, p++ p n n++ type) impact ionization avalanche transit-time (IMPATT) devices are studied and compared for the first time through simulation experiments. This study reveals that at 300 K < T < 600 K, a 4H-SiC IMPATT diode may yield 3.5 W of output power (efficiency (η) ∼ 8.6%) at 1.3 THz, while its 6H-SiC counterpart can deliver 3 W of output power (η = 6.3%) at 1.2 THz. It is interesting to observe that at elevated temperature, the performance of a 6H-SiC IMPATT diode degrades more in comparison with its 4H-SiC counterpart. These comparative analyses reveal the superiority of 4H-SiC diodes over their 6H-SiC counterparts, and thus establish the potential of the former as a high-power THz IMPATT oscillator even in harsh environments. Mobile space charge effects and the effect of positive series resistance on the high-temperature performance of the THz devices are also simulated, and it is found that series resistance reduces the output power level of the diodes by at least 15.0%. Moreover, the effects of increased junction temperature on the photo-sensitivity of top mounted (TM) and flip chip (FC) α-SiC IMPATTs are also investigated using a modified simulation technique. The device operating frequencies, under TM illumination configuration, shifts upward by at least 40.0 GHz, whereas the operating frequency shifts upward by at least 100.0 GHz under FC illumination configuration. The simulation results and the proposed experimental methodology presented here may be used for realizing optically controlled α-SiC transit-time devices for application in THz communication.