BS IEC 62951-5:2019 pdf download.Semiconductor devices - Flexible and stretchable semiconductor devices
1 Scope
This part of IEC 62951 specifies the test method for thermal characteristics of flexible materials. This document includes terms, definitions, symbols, and test methods that can be used to evaluate and determine thermal characteristics of flexible materials for practical use.The measurement method relies on non-contact optical thermometry that is based on temperature dependent optical reflectance. This document is applicable to both substrate and thin-film flexible semiconductor materials that are subjected to bending and stretching.
4.1 General
Thermoreflectance is one of non-contact optical thermal characterization techniques that relies on the change of refractive index of materials as a function of temperature. Depending on their thickness, flexible semiconductor materials can be categorized as either substrate or thin-film. For substrate materials, their optical reflectance values change linearly with temperature. However, optical reflectance values of thin-film materials show highly non-linear behaviours as shown in Figure 1. For thin-films, non-linear optical reflectance is also strongly dependent on the sample thickness as shown in Figure 2. Such a non-linearity requires reflectance measurements at multiple wavelengths. Once optical reflectance values at one or more wavelengths are calibrated at various temperatures, thermal characterization is enabled.
4.2 Test apparatus
In case of substrate materials, thermoreflectance signals at a given wavelength tend to change linearly with increasing temperature. Thin-film materials, however, exhibit highly non-linear thermoreflectance behaviours as tem perature increases. Therefore, single wavelength optical probing is necessary and sufficient for substrate flexible semiconductor materials and at least dual wavelength probing is required for thin-film materials. Thermoreflectance ratio at different wavelengths is still non-linear with temperature but can provide an acceptable match with the theoretical estimation and more precise temperature measurements. Figure 3 and Figure 4 show schematics of thermoreflectance thermometry with one laser source used for calibration and measurement (for example， wavelength, λ = 633 nm herein but other wavelength can be used), respectively. For calibration, heating or cooling blocks with fixed temperature are used. The substrate is joule heated with DC or AC (simple periodic sine) power supplies for actual measurements.
Figure 5 and Figure 6 show schematics of thermoreflectance thermometry with two lasers of different wavelengths that are well suited for thin-film materials but can be generally applicable to substrate materials. Three dimensional design of the dual wavelength thermoreflectance setup is also shown in Annex A. For calibration, heating or cooling blocks with fixed temperature are used. The substrate is joule heated with DC or AC (simple periodic sine) power supplies for actual measurements.BS IEC 62951-5 pdf download.