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THERMAL ISSUES IN EMERGING TECHNOLOGIES THEORY AND APPLICATIONS, THETA

Microscale and Nanoscale Thermal Characterization Techniques

[+] Author and Article Information
J. Christofferson, K. Maize, Y. Ezzahri, J. Shabani, X. Wang, A. Shakouri

Baskin School of Engineering, University of California at Santa Cruz, Santa Cruz, CA 95064

J. Electron. Packag 130(4), 041101 (Nov 13, 2008) (6 pages) doi:10.1115/1.2993145 History: Received October 01, 2007; Revised September 08, 2008; Published November 13, 2008

Abstract

Miniaturization of electronic and optoelectronic devices and circuits and increased switching speeds have exasperated localized heating problems. Steady-state and transient characterization of temperature distribution in devices and interconnects is important for performance and reliability analysis. Novel devices based on nanowires, carbon nanotubes, and single molecules have feature sizes in 1–100 nm range, and precise temperature measurement and calibration are particularly challenging. In this paper we review various microscale and nanoscale thermal characterization techniques that could be applied to active and passive devices. Solid-state microrefrigerators on a chip can provide a uniform and localized temperature profile and they are used as a test vehicle in order to compare the resolution limits of various microscale techniques. After a brief introduction to conventional microthermocouples and thermistor sensors, various contact and contactless techniques will be reviewed. Infrared microscopy is based on thermal emission and it is a convenient technique that could be used with features tens of microns in size. Resolution limits due to low emissivity and transparency of various materials and issues related to background radiation will be discussed. Liquid crystals that change color due to phase transition have been widely used for hot spot identification in integrated circuit chips. The main problems are related to calibration and aging of the material. Micro-Raman is an optical method that can be used to measure absolute temperature. Micron spatial resolution with several degrees of temperature resolution has been achieved. Thermoreflectance technique is based on the change of the sample reflection coefficient as a function of temperature. This small change in $10−4–10−5$ range per degree is typically detected using lock-in technique when the temperature of the device is cycled. Use of visible and near IR wavelength allows both top surface and through the substrate measurement. Both single point measurements using a scanning laser and imaging with charge coupled device or specialized lock-in cameras have been demonstrated. For ultrafast thermal decay measurement, pump-probe technique using nanosecond or femtosecond lasers has been demonstrated. This is typically used to measure thin film thermal diffusivity and thermal interface resistance. The spatial resolution of various optical techniques can be improved with the use of tapered fibers and near field scanning microscopy. While subdiffraction limit structures have been detected, strong attenuation of the signal reduces the temperature resolution significantly. Scanning thermal microscopy, which is based on nanoscale thermocouples at the tip of atomic force microscope, has had success in ultrahigh spatial resolution thermal mapping. Issues related to thermal resistance between the tip and the sample and parasitic heat transfer paths will be discussed.

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Figures

Figure 1

IR image of a large microcooler using liquid nitrogen cooled focal plane array (in collaboration with Oak Ridge National Laboratory, Hsin Wang)

Figure 2

Temperature measured on top of microcooler devices using scanning thermal microscopy: (a) thermal and topographical maps and (b) cooling versus current for different device sizes

Figure 3

SiGe microcooling device image, left; 1 s real-time thermal image, center; and scanned and enhanced thermal image, right

Figure 4

Thermoreflectance imaging using an ICCD; microcooler illuminated with blue LED, left; thermal image, center; and phase image, right

Figure 5

Laser single point transient thermoreflectance results; left is the thermal transient measured in the time domain for two different size microcoolers; right shows a similar measurement acquired in the frequency domain with the lock-in amplifier

Figure 6

Experimental PPPT obtained on Si/SiGe superlattice structure covered by the 100 nm Al film

Figure 7

Thermocouple and Raman measurements of the surface temperature as a function of microheater bias current

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