Test methods for power function of electronic matericals

SJ 3195-1989 Test method for work function of electronic materials SJ3195-1989 standard download decompression password: www.bzxz.net

Standard SJ3195--89 of the Ministry of Machinery and Electronics Industry of the People's Republic of China
Test method for work function of electronic materials
Published on February 10, 1989
Implementation on March 1, 1989
Approved by the Ministry of Machinery and Electronics Industry of the People's Republic of China Standard SJ3195--89 of the Ministry of Machinery and Electronics Industry of the People's Republic of China Test method for work function of electronic materials
1 Subject content and scope of application
1.1 This standard specifies the determination of work function of electronic materials by scanning low-energy electron probe method. 1.2 This standard is applicable to solid metals, alloys and electron emitting materials. 2 Summary of method
SJ3195--89
The scanning low-energy electron probe method is to measure the contact potential difference between each point on the target surface (test material) and the cathode of the electron gun in a deceleration field. At the same time, the contact potential difference between the filter tungsten belt and the cathode of the electron gun is also measured. The work function reference value of the tungsten belt, 4.54 eV, is used to determine the absolute value of the work function at each point on the target surface. The working principle is shown in Figure 1A
Figure 1 Schematic diagram of the work function measurement in the deceleration field
K—cathode; A—target; E. Vacuum energy level; qo
E—Fermi level; Φ gun cathode work function; @ target work number,
Take the beam scanning tube as an equivalent diode, add a low voltage Vx between the target and the cathode (electron gun). Whether the electrons from the cathode can reach the target depends on Vx. If Vx is less than the contact potential difference between the target and the cathode, that is, when Vx<（@-Φx）/e, the electrons are repelled and cannot reach the target; when V>（Φk）/e, the Ministry of Machinery and Electronics Industry of the People's Republic of China approved on February 10, 1989 and implemented on March 1, 1989
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all the electrons reach the target. Since the cathode of the electron gun has been aged, its work function is relatively constant. In a short measurement time, it can be considered unchanged, so the change in the value of V can reflect the change in the target work function (Φ). In fact, the initial energy of cathode-emitted electrons is distributed according to Maxwell, so even if V is less than the contact potential difference, a small part of them still reaches the target, and the target current increases with the increase of Vx, following an exponential law; when Vx> (Φ, -)/e. It is in a saturated state and under a rejection potential, and the target current I obeys the following formula: p[e (Va+Vx)
I,loexp
where: Io is the electron beam current emitted by the electron gun; V. (Φ-Φ)/e is the contact potential difference between the cathode and the target; K is the Boltzmann constant;
T is the cathode temperature.
The correct test state is V< (5-)/e, and the target current I is within the exponential range. Generally, I is fixed at
because the electron beam is very thin. @ is just the work function of the electron beam hitting the target point. Adjust V so that the target current is equal to, and record the corresponding V value at each point. The distribution of V values ​​reflects the numerical distribution of the work function on the target surface. The 10
sampling, statistics and conversion are automatically completed by the microcomputer. For a circular end target with a diameter of 3mm and a probe beam with a beam diameter of 15um, 30,000 discernible sample points can be detected. The numerical distribution formed by 30,000 V values ​​reflects the numerical distribution and statistical average of the work function on the sample surface.
3 Test equipment
a. Scanning low-energy electron probe tester;
b. Dynamic vacuum system, the ultimate vacuum degree is better than 1×10~p..c
Function recorder;
d. Oscilloscope:
e. Micro-optical pyrometer.
4 Sample preparation
4.1 Generally, the test material is made into a sheet with a diameter of 3mm and a thickness of 0.5mm. The maximum allowable sample size is 10×10mm and the thickness is 6mm.
4.2 According to the requirements of the electric vacuum device for the internal parts of the tube, the above-mentioned sheets are cleaned, hydrogen burned or vacuum degassing is carried out. The specific cleaning treatment specifications vary depending on the material to be tested. 5 Test steps
5.1 Assemble the cleaned sample into a target assembly. 5.2 Insert the above-mentioned target assembly into the sample rack of the sample analysis chamber of the dynamic vacuum system shown in Figure 2. Adjust the sample 2-
SJ3195-89
stand so that the target reaches the designated position in front of the electron gun. Figure 2 Principle of dynamic vacuum system
1. Mechanical pump 2. Solenoid valve; 3. Adsorption pump; 4. Ultra-high vacuum valve: 5. Thermocouple bubble, ionization bubble: 6. Sublimation pump: 7. Small cooling pump; 8. Release valve; 9 Ultra-high vacuum reading: 10. Fine adjustment valve; 11. Sample analysis chamber 12. B--A bubble; 13.650 Ultra-high vacuum valve; 14. 2501/s cold pump; 15. Electron gun; 16. Target assembly; 17. Adjustable sample holder 5.3 Evacuate, and when the vacuum reaches 5×10-p., bake and degas for 4h. When the pressure in the analysis chamber is less than 1×10-p, connect the scanning low-energy electron probe instrument with the electron gun and target assembly circuit on the dynamic vacuum system. 5.4 Turn on the scanning low-energy electron probe instrument and other electronic instruments, and preheat for 15min. 5.5 Heat the reference tungsten belt and clean it. 5.6 Enter the test program for testing. The function recorder records the work function statistical curve of the material to be tested, and records the work function average value and half-width value representing uniformity displayed on the panel. 6 Precision
The precision of this method is ±0.03eV.
7 Main sources of error
a. Uneven energy scanning separation
b. Nonlinear distortion of micro-current amplifier.
Uncertainty of the work function of the tungsten ribbon.
d. The tungsten ribbon is not cleaned thoroughly.
e The sample surface is contaminated.
8 Precautions
SJ3195--89
8.1 The sample must be thoroughly cleaned before being loaded for testing, and no other substances are allowed to remain on the surface. 8.2 For semiconductor samples with poor conductivity, the sample must be heated during testing (but it must be lower than the temperature at which thermal emission occurs) to prevent surface charging and affect the test accuracy.
Additional instructions:
This standard was drafted by Nanjing Institute of Technology, and the main drafter of this standard was Chen Desen.
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