JPS6110752A - Measurement for diffusitivity of heat by intermittent heating - Google Patents

Abstract

PURPOSE:To enable the determination of thickness-wise heat diffusion rate of a sample plate from a characteristic curve in the logarithm of the amplitude ratio of AC temperature at two points different in the thickness on the back, by intermittently irradiating a wedge-shaped sample plate to be measured with a heat energy of a fixed amplitude. CONSTITUTION:Thermocouples 21 and 22 are mounted at two points on the back of a wedge-shaped sample plate 1 to be measured which is long enough thickness-wise. The surface of the sample plate 1 is irradiated with heat energy of a heat source 3 such as tungsten lamp. Here, the heat energy is interrupted at the frequency set with a chopper 4 to keep the amplitude constant. The energy is amplified with a lockin amplifier 5 through a changeover switch 7 using the output of a sensor 6 as reference signal. With such an arrangement, amplitudes of AC temperatures are determined varying the frequency at two points on the back of the sample plate 1 and then, a characteristics curve in the logarithm of the amplitude ratio of AC temperatures can be plotted at two points with the root of the frequency as variable therefrom to obtain the gradient of the straight line thereof. From the results thereof, the thickness-wise heat diffusion rate of the sample plate 1 is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermal diffusivity measurement method using intermittent heating for determining the thermal diffusivity in the thickness direction of a thin sample plate. 5. Conventionally, various methods have been devised for measuring thermal diffusivity, but it has been impossible to determine the thermal diffusivity in the thickness direction of a thin sample with a thickness of 0.5 W or less. However, in recent years, with advances in electronics technology, semiconductor materials vi-0,5 are being placed on thin electrical insulators, such as ceramic plates.
It has become increasingly necessary to know the thermal properties of thin plate-like materials such as tungsten, etc., as they are often deposited to a film thickness of W or less.

The object of the present invention is to provide a method for measuring the thermal diffusivity in the thickness direction of a thin sample plate that satisfies such requirements. Thermal energy of a constant amplitude is intermittently irradiated, the AC temperature 'rac of two points with different thicknesses on the back surface of the sample plate is measured at various AC frequencies, and the square root of the frequency is used as a variable to calculate the AC temperature 'rac' of the two points. The slope m is obtained from the characteristic line of the logarithm of the amplitude ratio of the AC temperature, and the slope m is obtained by the following formula, where s At is characterized by obtaining the thermal diffusivity Dt in the thickness direction of the sample plate to be measured from the difference in thickness between two points. According to the second invention, the surface of a wedge-shaped sample plate to be measured is irradiated with a constant amplitude of thermal energy intermittently, and the AC temperature Tac'i'' at two points with different thicknesses on the back surface of the sample plate is varied at various AC frequencies. The slope mf is calculated from the characteristic line of the phase difference of the AC temperature at the two points using the square root of the frequency as a variable.

The method is characterized in that the thermal diffusivity Dt in the thickness direction of the sample plate to be measured is obtained.

Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1 and 2 show an example of a measuring device used to determine the thermal diffusivity Dt in the thickness direction of a sample plate to be measured.

In the figure, (1) is a wedge-shaped sample plate to be measured that is sufficiently long relative to its thickness. L.

A thermocouple (21) (2 g) was attached to the location.

(3) is a heat source such as a tungsten lamp placed above the sample plate to be measured (1), and (4) is a chopper that cuts off the thermal energy of the heat source (3) that irradiates the sample plate to be measured (1). , the chopper'? (4) consists of a semi-circular plate rotatably supported at its diametrical center as shown in the figure, and rotated at various rotational speeds by a motor (not shown). (5) is a lock-in amplifier that amplifies the AC output of a thermocouple (22), which is input via a changeover switch (7), using the output of a sensor (6) consisting of, for example, a phototransistor as a reference signal. .

Although not shown in FIGS. 1 and 2, the sample plate (1) to be measured was placed in a heat bath to increase the thermal resistance when heat escapes from the sample plate (1) to the outside.

Next, a first measurement method of the present invention will be described in which the thermal diffusivity Dt in the thickness direction of the sample plate to be measured is measured using the measurement apparatus shown in FIGS. 1 and 2.

As shown in Figure 1, thermal energy with an amplitude q per unit area is applied to the surface of a wedge-shaped sample plate (1).
) to irradiate intermittently at the frequency set.

At this time, the AC temperature Tao at the thickness Lj of the back surface of the sample plate (1) is given by the following equation.

However, 几 is the sample plate (when heat escapes from IJ to the outside, Q thermal resistance St is the thermal conductivity in the thickness direction of the sample plate (1), and k
The reciprocal of t is the thermal diffusion length, ki =, /; 7 votes ... (2) However, f is the AC frequency Dt of thermal energy by the chopper is the sample (1
) Thermal diffusivity in the thickness direction When the thermal resistance R is increased and the AC frequency is increased, Equation 11 becomes as follows.

As is clear from this equation, the amplitude value ITa,l of the alternating current temperature TaG of the sample plate to be measured (1) at the thickness Lt is.

Thus, the thickness of the sample plate (1) to be measured is L(1,l1t2
The amplitude ITao, l of the AC temperature 'rac at the two points
, 1 Tac21 and transforming the equation (5) (where lt=Lj, -Li2) is the slope m of the following equation.

Thus, the amplitude of the AC temperature at various frequencies at two points in the thickness Ltl, Lt of the back surface of the sample plate (1) is
, llTa0. I'm attached to those two points.
It is determined from the output of the lock-in amplifier (5) that amplifies the output of the c thermocouple (2+H22). From this, the thermal diffusivity Dtt'' of the AC temperature in the thickness direction at two points of thickness Lt, Lt2 with the square root η of the frequency as a variable is obtained.

Next, a second measurement method of the present invention for measuring the thermal diffusivity Dtt in the thickness direction of the sample plate to be measured (1) will be explained.

AC temperature T'a at thickness Lt of sample plate to be measured (1)
Since equation (3) holds true as described above, c is the thickness Ltl
* Phase difference ψ of AC temperature 'I'ac at two points at Lt
(Ltx)-ψ(Lt2) can be obtained from equation (3).

Thus, the thickness of the back surface of the sample plate (1) Lt, , Lt,
Thermocouples (21) (22) are attached to the two points to measure the phase difference between AC temperatures at various frequencies at two points in K.
) is determined from the output of the lock-in amplifier (5).

From that, based on equation (7), the AC temperature TllC at two points of thickness Ltl and 1t2 with the square root β of the frequency as a variable.
A characteristic line of the phase difference of l I TaO2 is drawn, and the thermal diffusivity Dt in the thickness direction of the sample plate (1) is obtained from the line.

In the above embodiments of the first and second measurement methods of the present invention,
2 with different thicknesses with the square root of the frequency a as a variable
The characteristic line of the logarithm of the amplitude ratio of the AC temperature at a point and the square of the frequency S
Draw a characteristic line for the phase difference of AC temperature at two points with different thicknesses, which is the t variable.

Although the slope of the straight line was determined to obtain the thermal diffusivity, the slope may be determined by other means without drawing the percentage line on the paper.

As is clear from the above description, the first and second aspects of the present invention
This method has the effect of easily obtaining the thermal diffusivity in the thickness direction of a thin sample plate.

[Brief explanation of the drawing]

Figure 1 is a diagram of the measuring device used to carry out the present invention;
The figure shows a planar view of the first figure with the heat source and lock-in amplifier removed, and FIG. 3 shows a perspective view of the sample to be measured used to implement the present invention. 2ri (2*)...
Thermocouple (3)... Heat source (4)... Chotsunogu (5)
...Lock-in amplifier (6) ...Sensor (7)
...Selector switch

Claims (1)

[Claims] 1. The surface of a wedge-shaped sample plate to be measured is intermittently irradiated with thermal energy of a constant amplitude, and the AC temperature T_a_c at two points with different thicknesses on the back surface of the sample plate is varied at various AC frequencies. The slope m is determined from the characteristic line of the logarithm of the amplitude ratio of the AC temperature at the two points, using the square root of the frequency as a variable, and the slope m is calculated using the following formula: m=√(π/D_f)l_t, where l_t is 2 points. A method for measuring thermal diffusivity by intermittent heating, characterized in that the thermal diffusivity D_t in the thickness direction of the sample plate to be measured is obtained from the difference in thickness. 2. The surface of a wedge-shaped sample plate to be measured is intermittently irradiated with thermal energy of a constant amplitude, and the AC temperature T_a_c at two points with different thicknesses on the back surface of the sample plate is measured at various AC frequencies. The slope m is obtained from the characteristic line of the phase difference of the AC temperature at the two points, using the square root as a variable, and is expressed by the following formula: m=√(π/D_t)l_t. However, l_t is calculated from the difference in thickness between the two points. A method for measuring thermal diffusivity by intermittent heating, characterized by obtaining thermal diffusivity D_t in the thickness direction of a measurement sample plate.