Junction Temperature Variation Research Articles

Analysis of junction temperatures in high-power GaN-based LEDs

We presented the analysis of the incomplete conduction in bonding medium in high power GaN-based light-emitting diode (LED) packages. A numerical study was carried out with parametric model to understand the junction temperature variation due to bonding medium defects. Transient thermal measurement was performed to evaluate LED’s junction temperature. Thermal resistance from chip to lead frame was 20 K/W in our sample LED. It was suggested that only 60% of the surface area of the bonding medium was involved in the thermal conduction. This result was also supported by the SEM image. Blocking of thermal path induced by ineffective area of the bonding medium was regarded as a factor of its thermal resistance. Thus, the effective area of the bonding medium should be included in the FEM model and considered as another important factor in high power LED’s thermal management.

Measurement of the thermal characteristics of packaged double-heterostructure light emitting diodes for space applications using spontaneous optical spectrum properties

In this paper, the thermal characteristics of packaged infrared double-heterostructure light emitting diode (DH-LED), used in space applications, are measured under conditions that reproduce space environments. The characterisation uses spontaneous optical spectrum characteristics, current–voltage curves and optical power measured under a primary vacuum (<10 −2 Torr) at temperatures between −30 and 100 °C. The investigations have been specifically oriented toward the extraction of junction temperature in the steady-state regime and junction-to-case thermal resistance. A specific model based on semiconductor theory for electrical transport has been used to calculate the shape of the spontaneous emission spectrum between the band-gap energy and higher energies and its change versus temperature. A linear relation between the junction temperature and the dissipated power has been found for various case temperatures appropriately controlled in a LN 2 cryostat. These results confirm that thermal behavior of DH-LEDs depends on both environment temperature and dissipated power level in the active zone and that the junction-to-case thermal resistance is not constant over a large range of temperatures, diminishing at higher currents as already reported by recent papers on high brightness DH-LED. Finally, this study could represent a practical non-destructive method providing qualitative information about variations of junction temperature and junction-to-case thermal resistance taking into account an industrial qualification framework approach based on electroluminescence analysis, frequently measured by manufacturers or end-users.

Effects of junction temperature and its variations on the performance of GaN‐based high power flip‐chip LEDs

AbstractIn this paper, high power flip‐chip GaN‐based LEDs were fabricated, and then the effects of junction temperature and its variations were investigated. It was found that the optical output decreases seriously with rising temperature. The variations of junction temperature can be achieved to 9 °C at 350 mA in most regions of flip‐chip LED except for some hot regions around some electrodes. The combination of screening of quantum confined Stark effect (QCSE) and thermal effect surprisingly makes the peak wavelength constant from 300 mA to 800 mA in electroluminescence spectra. The full‐width at half‐maximum (FWHM) of emission peak was narrowed by thermal effect in constant current (CC) injection. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Advanced electrothermal Spice modelling of large power IGBTs

A novel IGBT electrothermal model is implemented for the first time in PSpice for the simulation of steady state and transient temperature dependent IGBT operation including self-heating and latchup. A thermal circuit representing the characteristics of the IGBT package is developed and validated against a finite element model and experimental results. A novel electrical IGBT model based on the Kraus model is developed to account for the electrical impact of instantaneous junction temperature variations owing to self-heating. The resulting electrothermal model is validated against experimental DC and transient FBSOA measurements.

Cooling characteristics of diamond-shaped interrupted cooling fin for high-power LSI devices

We propose a diamond-shaped interrupted microgrooved cooling fin to decrease the junction temperature variation across the chip. The analytical result indicates that the junction temperature variation decreses to less than 25% compared with a conventional paralles-plate-shaped cooling fins. This cooling structure is sufficient to cool high-power-consumption silicon chips.

Broad-Band Small-Signal Impedance Characterization of Silicon (Si) P+-N-N+ Impatt Diodes

A method is described that permits a broad-band small-signal characterization of an IMPATT diode mounted in a package. From automatic-network-analyzer measurements on a package-shaped metal dummy, an empty package, and the diode under test biased below and above breakdown, the method allows first determination of a coupling-circuit parameter, bonding-wire inductance, and diode series resistance, and then evaluation of junction admittance above breakdown. Experimental results on silicon (Si) p+-n-n+ diodes over 2.5-15 GHz are shown. Nearly frequency-independent bonding-wire inductance is observed. Avalanche frequency squared (f/sub a//sup 2/) is found to be sublinear with respect to dc current density (I/sub d), possibly due to a variation of junction temperature (T/sub i/). An experimental formIda for (f/sub a//sup 2/) / (I/sub d) is obtained in terms of (T/sub i/).Detailed comparisons of the measured junction admittance with an existing analytical theory indicate a good agreement, if a suitable amount of saturation current is postulated, and also suggest that the estimated amount is in excess of the prebreakdown saturation current.

The effect of junction temperature on the output power of a silicon IMPATT diode

The pronounced sensitivity of output-power/junction-temperature choracteristics for some silicon IMPATT diodes, which has been demonstrated by a number of authors, is shown to be related to the fact that the drift region of the epitaxial layer is not entirely punched through at lower junction temperatures. It is shown that a simple measurement of the static dV b /dT characteristic may be used to select diodes with power output characteristics that are relatively insensitive at a given frequency to junction temperature variations.

AN ANALYSIS FOR THE OPERATION CURRENT RANGE OF INJECTION LASER

本文直接利用阈值电流随温度变化的实验关系,通过解热传导方程,得到了连续及脉冲工作状态下起始工作电流、最大工作电流及临界阈值电流的定量结果,供研制参考。其中全面地考虑了结内及体内发热的贡献,后者可用一归一化等效体内发热电阻r来表征。连续工作状态的分析表明,体内发热的影响不可忽略。对脉冲工作状态的分析,分别考虑了脉冲宽度和重复频率的影响。指出:在兼顾功率和重复频率的情况下,脉冲工作比以取0.03左右为宜。当实际应用中对重复频率要求不高时,为了提高功率,取重复周期比二极管热弛豫时间约大3倍比较合适。如果要求重复频率很高,则器件性能主要由脉冲工作比决定。文中利用所得结果结合实例进行了讨论,并讨论了脉冲工作情况由于结温变化所导致的发射频谱展宽效应。

The periodic variation of junction temperature in a transistor

The instantaneous junction temperature of a transistor used as a class B amplifier is considered from very low frequencies, when the temperature is shown to follow a law similar to that of the instantaneous dissipation at the junction, to high frequencies, when the junction temperature attains a mean value which is constant throughout the cycle. An expression is derived for the instantaneous junction temperature of such a transistor, computed results illustrating the conditions of maximum dissipation in the transistor, and of maximum drive. It is shown that under conditions of maximum dissipation the peak temperature attained by the junction above that of its mount is, at low frequencies, 2.48 times that at high frequencies, while under conditions of maximum drive the ratio reaches 2.97 for a practical transistor; this higher value is due to the lower mean dissipation under these conditions. The instantaneous junction temperature of a transistor type OC22 is measured when operated under conditions of maximum drive, close agreement being obtained with the predicted results.

Transistor Junction Temperature as a Function of Time

An analysis of the heat flow in transistors is presented which enables one to determine the variation of junction temperature with time for a given transistor excitation. A one-dimensional heat flow model is considered which is repsentative of grown-junction and some alloy transistors. The step and impulse temperature responses are obtained from the solution of the heat equation. A comparison made between the step response so obtained and the often assumed simple exponential response indicates that the assumed response can be low by a factor of two or more. Utilizing the impulse temperature response for the transistor, the junction temperature as a function of time is determined for periodic rectangular pulse excitation. Numerical calculations are made and curves presented for the maximum, average, and minimum junction temperatures in terms of the duty cycle, repetition rate, and fundamental thermal time constant. These curves indicate that the maximum junction temperature can be several times the average value at low duty cycles and low repetition rates. Measurements of junction temperatures are presented which essentially substantiate both the step response and the repetitive pulse response which were theoretically obtained. Finally, using simplified approximate expressions, the procedure for calculating the maximum, average, and minimum junction temperatures for repetitive pulse excitation is described. The use of these predicted junction temperatures with relation to the maximum junction temperature ratings, thermal stability, and electrical parameter changes is also discussed.