Thermoreflectance Imaging of (Ultra)wide Band-Gap Devices with MoS2 Enhancement Coatings

Riley Hanus*, Sonal V. Rangnekar, Shahab Mollah, Kamal Hussain, Nicholas Hines, Eric Heller, Mark C. Hersam, Asif Khan, Samuel Graham

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

6 Scopus citations

Abstract

Measuring the maximum operating temperature within the channel of ultrawide band-gap transistors is critically important since the temperature dependence of the device reliability sets operational limits such as maximum operational power. Thermoreflectance imaging (TTI) is an optimal choice to measure the junction temperature due to its submicrometer spatial resolution and submicrosecond temporal resolution. Since TTI is an imaging technique, data acquisition is orders of magnitude faster than point measurement techniques such as Raman thermometry. Unfortunately, commercially available LED light sources used in thermoreflectance systems are limited to energies less than ∼3.9 eV, which is below the band gap of many ultrawide band-gap semiconductors (>4.0 eV). Therefore, the semiconductors are transparent to the probing light sources, prohibiting the application of TTI. To address this thermal imaging challenge, we utilize an MoS2 coating as a thermoreflectance enhancement coating that allows for the measurement of the surface temperature of (ultra)wide band-gap materials. The coating consists of a network of MoS2 nanoflakes with the c axis aligned normal to the surface and is easily removable via sonication. The method is validated using electrical and thermal characterization of GaN and AlGaN devices. We demonstrate that this coating does not measurably influence the electrical performance or the measured operating temperature. A maximum temperature rise of 49 K at 0.59 W was measured within the channel of the AlGaN device, which is over double the maximum temperature rise obtained by measuring the thermoreflectance of the gate metal. The importance of accurately measuring the peak operational temperature is discussed in the context of accelerated stress testing.

Original languageEnglish (US)
Pages (from-to)42195-42204
Number of pages10
JournalACS Applied Materials and Interfaces
Volume13
Issue number35
DOIs
StatePublished - Sep 8 2021

Keywords

  • AlGaN
  • GaN
  • power electronics
  • radio frequency (RF) electronics
  • thermal imaging
  • thermoreflectance
  • ultrawide band gap
  • wide band gap

ASJC Scopus subject areas

  • General Materials Science

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