Microscale and Nanoscale Thermal Characterization Techniques

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.

Thermometry at the nanoscale

“…25,26 Furthermore, the precise mapping of the temperature of living cells, especially cancer cells that have higher temperatures than those of normal tissues due to the increased metabolic activity, 6,9,27 strongly improves the perception of their pathology and physiology and, in turn, the optimization of premature diagnosis and therapeutic processes (e.g. in hyperthermal tumour treatment and photodynamic therapy).…”

“…26 Early works on scanning microscopy-based thermometry employing diagnostic techniques 24,59,60 and either electrical or scanning probe microscopy (with a particular emphasis on microelectronics and data storage devices) 25 were available between 1999 and 2005. Three other reviews partially covering the subject and dealing with ceramic phosphors that can withstand extreme temperatures, 61 multiple optical chemical sensors 62 and temperature-stimuli polymers 63 have been published in 2011.…”

High-Precision Nanoscale Temperature Sensing Using Single Defects in Diamond

“…These are scanning thermal microscopes (SThM) [5], dispersed or scanned individual nanoprobes [3,6], direct methods like micro-Raman spectroscopy [7] or near-field optical temperature measurements [8]. SThMs have temperature sensitive elements at a scanning tip (e.g.…”

Characterization of Single Barrier Microrefrigerators at Cryogenic Temperatures

“…The illumination wavelength can be chosen to allow a sub-micron spatial resolution, which is unavailable from diffraction-limited standard infrared (IR) imaging. 6 Multiple-channel lock-in signal processing for each pixel allows fast full field detection without the lengthy time required by a scanning laser method. These advantages make thermoreflectance imaging suitable for cryogenic measurement, since the sample is placed inside a sealed chamber and the ambient temperature is kept stable during the imaging process.…”