Collinear Deflection Method for the Measurement of Thermal Conductivity of Transparent Single Layer Anisotropic Material

Abstract

Transparent anisotropic materials have garnered attention along with the growth of the semiconductor and display industries. Transparent anisotropic materials have the characteristic of varying electrical, optical, and thermal properties based on their crystal orientation, and many studies are being conducted on this topic. In order to utilize transparent anisotropic materials properly, thermal properties such as thermal conductivity are essentially required. However, due to the limitations of the existing thermal property measurement methods for transparent anisotropic materials, it is difficult to provide the thermal properties of transparent anisotropic materials. To address this problem, a transparent anisotropic collinear method capable of measuring the effective thermal conductivity of a transparent anisotropic material according to its crystal orientation is proposed in this paper. To this end, the internal temperature distribution of a transparent anisotropic material and the phase delay of the probe beam were theoretically derived through a numerical analysis model that uses a three-dimensional heat conduction equation. This model was applied to anisotropic thermal conductivity with orthorhombic structure. To verify the proposed method of measuring the thermal conductivity of a transparent anisotropic material, the thermal properties of 3 mm-thick A-plane sapphire glass were measured and compared with those of the existing literature. It was confirmed that the absolute errors were less than about 4 W/mk.

Research on Measuring Thermal Conductivity of Quartz and Sapphire Glass Using Rear-Side Photothermal Deflection Method

“…The phase delay of the point of each graph was used the three repeated measurements to the average value, and the standard deviation us represented through an error bar. As mentioned previously, the rear-side mirage deflection method, applying a light absorption thin film, physically prevented mutual interference between the pump and the probe beam, as compared to the collinear deflection method [31], which is one of the existing measurement methods for transparent materials. Thus, the relative position at 0 mm can be accurately measured for the phase delay signal.…”

“…The detailed alignments of the specimen, pump beam, and probe beam are illustrated in Figure 3, and the intensity of the pump beam, the diameter of the pump beam, the height of the probe beam, the relative position between the pump and probe beam, and the modulated frequency of the pump beam were set as shown in Table 6. The thermophysical measurement technique using the photothermal effect cannot use a section between 0 mm and 0.15 mm owing to the interference between the pump and the probe beam [31]. However, because the technique used in this study has no interference owing to the characteristics of the optical alignment, it can use the entire section between 0 mm and 0.6 mm to obtain the phase delay.…”

“…Measurement of thermophysical properties for mono-layer anisotropic materials was conducted by Jeon et al [26,27]. For the photothermal collinear deflection method, research on materials with mono-layer/multi-layer structures was conducted by Salazar [28,29], Spear [16,30], and Kim et al [31]. The photothermal effect is used to measure thermophysical properties by thermoelastically deforming a specimen via periodically modulated heating, changing the refractive index of an air layer or that of the specimen's interior.…”

“…Moreover, in the case of the collinear method, a part of the pump beam can transmit and arrive at the sensor. Although the pump beam is blocked by a bandwidth filter that is equipped in front of the sensor, the pump beam cannot be completely filtered; it causes an error for the phase delay measurement [31]. As stated above, because materials with high optical transmittance generally tend to have low thermal conductivity, it is difficult to secure the necessary change in the refractive index for measurements.…”

Feasibility of Novel Rear-Side Mirage Deflection Method for Thermal Conductivity Measurements

“…For the mirage deflection method, Salazar et al [ 16 ] established a thermal property measurement method for monolayer isotropic materials, and Jeon et al [ 34 , 35 ] studied the measurement of the thermal properties of monolayer anisotropic materials. For the collinear deflection method, Salazar [ 36 , 37 ], Spear [ 17 , 38 ], and Kim [ 39 ] conducted research on materials with transparent single/double layer structures.…”