We review the Raman thermography technique, which has been developed to determine the temperature in and around the active area of semiconductor devices with submicron spatial and nanosecond temporal resolution. This is critical for the qualification of device technology, including for accelerated lifetime reliability testing and device design optimization. Its practical use is illustrated for GaN and GaAs-based high electron mobility transistors and opto-electronic devices. We also discuss how Raman thermography is used to validate device thermal models, as well as determining the thermal conductivity of materials relevant for electronic and opto-electronic devices.

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A Review of Raman Thermography for Electronic and Opto-Electronic Device Measurement With Submicron Spatial and Nanosecond Temporal Resolution

\n Much effort in the area of electronics thermal management has focused on developing cooling solutions that cater to steady-state operation. However, electronic devices are increasingly being used in applications involving time-varying workloads. These include microprocessors (particularly those used in portable devices), power electronic devices such as IGBTs, and high-power semiconductor laser diode arrays. Transient thermal management solutions become essential to ensure the performance and reliability of such devices. In this review, emerging transient thermal management requirements are identified, and cooling solutions reported in the literature for such applications are presented with a focus on time scales of thermal response. Transient cooling techniques employing actively controlled two-phase microchannel heat sinks, phase change materials (PCM), heat pipes/vapor chambers, combined PCM-heat pipes/vapor chambers, and flash boiling systems are examined in detail. They are compared in terms of their thermal response times to ascertain their suitability for the thermal management of pulsed workloads associated with microprocessor chips, IGBTs, and high-power laser diode arrays. Thermal design guidelines for the selection of appropriate package level thermal resistance and capacitance combinations are also recommended.

A Review on Transient Thermal Management of Electronic Devices

Temperature distribution and thermal resistance analysis of high-power laser diode arrays

Experimental study of ultralow flow resistance fractal microchannel heat sinks for electronics cooling

Thermal analysis and improvement of cascode GaN device package for totem-pole bridgeless PFC rectifier

As with any electronic device, the performance and reliability of laser diode arrays (LDAs) is a strong function of the temperature at which the array operates. However, the electrical and optical environment in which the LDA operates makes direct temperature measurements difficult. Wavelength measurements can be used as a means to deduce temperature by exploiting the linear relationship between wavelength and laser diode operating temperature. The process by which wavelength measurements are translated into temperature is discussed and experimental results using this methodology are shown. A wide range of information about both the transient and steady state thermal performance of LDAs can be acquired from such experimental measurements. These experimental results are compared with simulated numerical temperatures as a means to validate the simulation.

Temperature dependence of optical wavelength shift as a validation technique for pulsed laser diode array thermal modeling

For applications where space restrictions limit the feasibility of heat spreading in high-powered electronic devices, integrated direct cooling is a viable but underexplored method for keeping critical devices cool. Direct integrated cooling by putting microchannels of varying designs into common device substrate materials (e.g., SiC) is examined. Laser machined microchannels are shown to be a feasible method for fabricating microchannels into materials where etching is not. The flexibility of laser machining to fabricate more complex microchannel designs is assessed and tree-branch or “fractal-like” microchannels are shown to provide considerable reduction in pressure drop for a given flow rate compared to traditional straight microchannels.

Fabrication and performance of tree-branch microchannels in silicon carbide for direct cooling of high-power electronics applications

Laser diode arrays are a high thermal flux electro-optic application where performance and reliability are a strong function of operating temperature. An understanding of the movement of heat in arrays and the effect of material choices on thermal performance are critical to optimum design of arrays. A modeling tool and accompanying methodology are outlined. Simulated diode array performance under a wide array of conditions and can be used to simulate tests that are difficult or cost-prohibitive. Through the development process, models of full 10-bar arrays were found to be accurate in modeling steady state or quasi-steady state performance but insufficient for microsecond transient responses. Initial efforts to incorporate small-scale laser diode properties into a large scale device model are described.

Transient thermal modeling of high-power pulsed laser diode arrays

Gallium Nitride high-electron mobility transistors (HEMT) devices show great promise in their ability to tolerate the high temperature environments of advanced radar systems. This paper examines how GaN HEMT junction temperature determination can vary, owing to factors such as packaging variability, measurement error, and uncertainty in material property data. To demonstrate the impact of these variables, this paper uses practical examples of infrared thermography, micro-Raman thermography, device transient electro-thermal response analysis on GaN HEMT devices, and finite element analysis (FEA). These variations in temperature are combined into a probability model to estimate how life prediction will change as a function of these various factors.

Thermal factors influencing the reliability of GaN HEMTs

An apparatus was designed and built to explore the effects of transient flow fluctuations on the dynamic behavior of particles in low Reynolds number (LRN) flows. While many experiments have been performed on LRN particle flows, relatively few have investigated periodic oscillations on the flow dynamics. The apparatus was oscillated at a frequency of 10 Hz with peak-to-peak displacements on the order of 10 mm. Particles of varying densities and diameters were placed into the oscillating flow. Video images of the particle dynamics were captured with both a personal video camcorder and high-speed digital camera. In parallel, computations were performed for the particle system in order to validate the experimental method and apparatus.

Jason A. Carter

Papers

Temperature dependence of optical wavelength shift as a validation technique for pulsed laser diode array thermal modeling

Fabrication and performance of tree-branch microchannels in silicon carbide for direct cooling of high-power electronics applications

Transient thermal modeling of high-power pulsed laser diode arrays

Thermal factors influencing the reliability of GaN HEMTs

Design of an oscillating flow apparatus for the study of low Reynolds number particle dynamics