High and low temperature system in vacuum and radiation environment

There are a large number of high-energy particles in the space radiation environment, which can cause single-particle effects in semiconductor devices (especially memories), which will seriously affect the reliability and lifespan of the spacecraft. The satellites are orbiting and the temperature of the surface facing the sun is as high as several hundred degrees, while the surface facing away from the sun is as low as several hundred degrees below zero. In this harsh environment, the radiation effect of astral semiconductor devices with temperature changes is a subject that needs to be studied.

Since the 252Cf originates from fission and emits heavy ion fragments, its LET value is greater than the LET value of charged particles in the space radiation environment, and can be used to test the single-particle-overlapping saturation cross-section of the device and to evaluate the device's single-particle inversion reinforcement performance. Therefore, it becomes Single particle effect.

The 252Cf source single-particle effect irradiance measurement system establishes a high-low temperature device that is to enable the researcher of the surface temperature of the device under test (DUT, Devices Under Testing) to be the deputy researcher of the Nuclear Technology Research Institute and engage in the research of nuclear electronics.

High-low temperature measurement and control system The cooling system is similar to the heating system except that the temperature changes in the opposite direction. Therefore, the PID algorithm with differential action and integral action is also used in three stages: free cooling, automatic temperature adjustment and balance temperature adjustment. In addition. The cooling system still has the following problems. First, the stepper motor is directly mounted on one end of the spool to control the movement of the spool of the digital control valve. By directly controlling the opening size of the spool displacement control valve, the control method is simple and reliable and easy to implement. However, because the stepper motor works with a large amount of heat, if the spool length is too short, the stepper motor heats liquid nitrogen gas, then the liquid nitrogen is wasted, so a longer spool is selected. Second, the actual operating temperature of the valve is low. When the temperature is around -100*C, the contraction coefficient of the valve body and the valve body are different. The valve body is made of cast iron, and the valve core is steel. The former has a large coefficient of contraction and is easily seized due to shrinkage at low temperatures. After the test, the diameter of the valve core is heated through the heating wire to heat the device on the test platform. The same method is used for closed-loop control. The difference is that the computer controls the on-off of the heating wire current through the controller so that the temperature of the device surface reaches the desired temperature.

Control system block diagram see. The control object for the low temperature part is the stepper motor and the digital control valve; the control object for the high temperature part is the current of the relay and the heating wire. In addition, the system has digital displays and printouts to display and record the temperature and output values ​​during system operation.

Because the change of temperature lags behind the change of liquid nitrogen flow and the on-off of the electric wire current, a control algorithm must be designed to prevent temperature overshoot, resulting in too large temperature fluctuations and reaching the required accuracy.

The heating process is divided into three stages: free heating, automatic temperature regulation and temperature adjustment. What really needs to be controlled by the amount of computation is the next two phases. In order to avoid excessive adjustment, from the initial temperature to the desired temperature of 80% for the free heating phase; 80% 95% of the desired temperature value for the automatic adjustment of the heating phase, the desired temperature value of 95% 105% for the equilibrium temperature adjustment phase . Considering the influence of hysteresis, the control algorithm must add a differentiation factor, ie PD adjustment. With PD regulation, the amount of adjustment depends not only on the size of the temperature difference, but also on the temperature difference, so that the temperature does not appear over-modulated. Also in the cooling process. In addition, the integral action can improve the static accuracy of the temperature control, and if the integral action is properly selected, the accuracy of the temperature control can be improved without affecting the dynamic performance. Therefore, a PID algorithm that has both differential and integral action is selected. At the same time, changes in temperature difference and accuracy of the system are taken into consideration, so that the dynamic and static performance of the system are optimized.

Within a certain range, and can be controlled. When the high-low temperature device raises and lowers the temperature of the device while it is in the radiation environment of 252Cf fissile fragments 104s-1 and neutron 104s-1, the semiconductor refrigeration method originally considered cannot be adopted because the semiconductor refrigerator itself is relatively sensitive to radiation, As time goes by, its performance will degrade. In addition, because the device is in a vacuum environment, heat must be transferred through direct contact, and a dedicated test platform is designed for this to allow the device to be tightly attached to the test platform. In this way, it is necessary to change the manner in which the conventional device is inserted into the circuit board so that the device is inserted upward into the socket, and at the same time, an irradiation window is opened in the center of the socket so that the fission fragments can be injected into the sensitive area of ​​the device without being blocked. The test platform we used was a hollow body made of metallic copper. During cooling, the liquid in the cavity was vaporized liquid nitrogen; when heated, the heating wire was placed inside the cavity. Copper is selected because of its good heat transfer performance, but copper is also a good conductor. When laying out devices and irradiating plates, accidental short circuits must be avoided to burn the device or test system. Because the test platform is in a vacuum environment, its sealing performance must be very good, so as not to damage the vacuum or leakage of liquid nitrogen.

The low temperature is achieved by using vaporized liquid nitrogen as a cooling material. HPGe detectors use liquid nitrogen refrigeration, but its temperature is constant and does not need to change. We need to adjust the temperature of the device surface, we must make liquid nitrogen flow, and can control its flow.

The liquid nitrogen is automatically discharged from the self-pressurizing liquid nitrogen tank and enters the cavity of the test platform via a digital regulator valve to cool the device on the test platform. A platinum resistance resistor was used to sample the temperature of the outer surface of the test platform and the upper surface of the device. The temperature signal is fed back to the computer via the sampling circuit, amplifier, A/D converter and data acquisition card. The computer controls the digital control valve through the controller and drive power to regulate the flow of liquid nitrogen and change the temperature of the device surface to reach the desired temperature.

The work becomes smaller, so that the two do not get stuck because of low temperature cooling.

In addition, because the valve core and the valve body are easily rusted under long-term working conditions, under the working condition of -100*C, the lubricating medium is quickly frozen, resulting in the consolidation of both the valve body and the valve core. movement. Therefore, the valves in the system have no lubrication medium. In addition, when the system is working, when the expected temperature and the actual temperature have a large difference, according to the principle of system operation control, the spool displacement is naturally larger, and the liquid nitrogen flow is relatively large at this time. Liquid nitrogen does not contain air. Under certain pressure, the air in the valve chamber is washed away. At this time, the water vapor contained in the air cannot condense in the valve chamber. However, writing 55* or AA* in them has almost no effect on the relationship of the single-particle cross-section with temperature change. For HM62256, the single-particle cross-section increases with temperature. The temperature was increased from 8C to 120C, and the single-particle cross section was reduced from 3. to 4.6X10 8C to about -100C, and the single-particle cross section was almost unchanged. For HM628128, from 18C to 120C, the single-particle cross section is added from about 6.9X10-8cm2/bit to about 80C. The single-particle cross section is from 5. When the temperature difference is not large, the spool displacement is naturally smaller, and the liquid nitrogen flow is smaller at this time. Also small, the air is easier to enter the valve chamber, the condensation of the water vapor in the case, resulting in the spool can not be fixed to death. In order to prevent this from happening, after many tests and comparisons of the absolute control method without oscillation, the relative control method with oscillation, and the absolute control method with oscillation, the absolute oscillation control method was finally determined. At a certain displacement, the valve core makes a relatively high frequency of back and forth vibrations to eliminate the possibility of ice condensation. In order to prevent the motor from losing its operation for a certain period of time, the program controls the valve spool to return once every time. Through the above measures, the cooling system has better temperature sensing accuracy and temperature control accuracy.

Each input/output channel on the control panel is isolated from the field signal or equipment by an optical coupling device, effectively blocking the ground circulation path between the on-site and the computer system, and greatly improving the system's anti-interference ability. At the same time, it can prevent the accidental input of high voltage on the site and cause damage to the computer system.

6.0 The Windows application program written in the integrated software development environment has the functions of acquiring and displaying data signals, describing the dynamic situation of the system, and the user interface is good.

2 The application of established high and low temperature devices and measurement and control system can control the surface temperature of the semiconductor device changes within -100125C, control accuracy: high temperature ShiC, low temperature * 3C ... For different integration of the device, the change rule is not the same, but Near 0C, the single-particle cross-section is the smallest. In addition, the memory cell bit is added to 1.10-7Cm2/bit. In general, the magnitude of the single-particle cross-section changes with temperature is not large.

The relationship between the single-particle reversal cross-section and the temperature variation of Qi is summarized. 3 Concluding remarks The method of obtaining high and low temperatures in a certain degree of vacuum (about 1 Pa) and irradiation environment (fission fragment 104s-1, neutron 104s-1) is particularly studied. It is a low-temperature (-5520C) implementation technology. Developed a high-low temperature device and measurement control system adapted to a helium source irradiation measurement system, with a temperature range of -100125C, control accuracy: high temperature ±1C, low temperature ±3C. This system was used to carry out heavy-ion single-particle flip-flops of semiconductor memories. Study on the relationship between cross section and temperature change. In the country, the relationship between the cross-section of heavy ion single-particle reversal and temperature is obtained for the first time in the country, and the magnitude of single-particle reversal section with temperature changes is not large.

Less, the measurement data is rough. This work is not limited by the actual measurement environment. Selecting a suitable sampling point distribution can achieve relatively fine measurement results in space. The calculation results in this paper can reflect the detailed shape of the dose distribution curve. And, compared with the point source approximation, the calculation result of the planar source is more valuable for practical work.

From the dose distribution curve under surface source conditions, it can be seen that the detection beam obtained in this paper satisfies the requirements of actual work and has good radiation safety. The dose received by the detection object is calculated at a very low level. In this paper, the ray intensity distribution near the near detection surface is obtained, and the content is the basis for studying the ray imaging physical process. Radiation source devices based on this model have been used in cobalt source radiation imaging systems.

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