JPS61161480A - Method and instrument for monitoring integrated radiation doze - Google Patents

Abstract

PURPOSE:To grasp the state of the original function of a semiconductor by constituting a ring oscillator by a semiconductor element and monitoring the radiation dose of the semiconductor element. CONSTITUTION:The output of the ring oscillator 1 is connected to a frequency divider 2. The frequency divider 2 can be constituted by connecting FFs by n stages in series. Since these FFs are used, the frequency divider 2 can be used for the waveform shaping of a pulse signal in addition to the frequency division. The output of the frequency divider 2 is inputted to a counter 3 to be used as a frequency measuring unit. The counter 3 is automatically reset at a proper time interval. The count value of the counter 3 may be connected to a display unit or a comparator for comparing the count value with a reference value. The reset time of the counter 3 is selected to a proper value <=N.n/f0 when the oscillation frequency of the normal oscillator 1 is f0, a frequency dividing ratio is n and the maximum count value of the counter 3 is N. Thus, the integrated radiation doze can be monitored.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method and device for monitoring the integrated dose of radiation received by semiconductor devices, etc., which can effectively determine the state of deterioration of semiconductor devices due to radiation. Semiconductor devices used in radiation environments, such as in technical spacecraft and nuclear power plants, undergo permanent deterioration due to radiation damage. The amount of this deterioration increases as radiation accumulates,
Eventually, this will lead to malfunction of the semiconductor device.

In the case of ionizing radiation such as gamma rays, X-rays, and electron beams, electron-hole pairs are generated, causing damage to the oxide film. On the other hand, when high-energy particles collide, crystal defects occur, creating recombination centers and causing problems such as an increase in capacity. As described above, the electrons in the electron-hole pairs generated by radiation exposure have high mobility and move toward the positive electrode, but the positive charges are trapped in the recombination center as they move. In MOSFETs, the generation of positive charges and interface trap charges are caused by fluctuations in the flat band voltage of the MOS capacitor, fluctuations in threshold voltage, and deterioration of conductance characteristics, and in bipolar transistors, they are caused by deterioration of hpε and vice versa. This causes an increase in directional leakage current, and ultimately leads to malfunction of the semiconductor device.

Therefore, this problem is important in today's situation where semiconductor devices are widely used due to the microelectronics of various devices in spacecraft and nuclear power plants.

However, although it is not impossible to completely prevent semiconductor devices from being exposed to radiation, it requires significantly larger shielding means compared to semiconductor devices, which not only makes equipment incorporating semiconductor devices extremely large, but also This is not practical for ships and the like because it involves an increase in weight.

Problems to be Solved by the Invention Accordingly, it is more practical to monitor the deterioration of semiconductor elements due to exposure to radiation and replace the deteriorated semiconductor elements. but,
Providing a Geiger tube etc. for radiation detection is
The result is that the benefits of miniaturization of semiconductor devices are completely negated.
It is not realistic and does not reflect the exposure situation of the semiconductor device itself. As described above, heretofore, there has been no effective and practical method for monitoring the deterioration of semiconductor elements due to exposure to radiation.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a method and apparatus that can easily and effectively monitor the exposure status of semiconductor devices without sacrificing the advantages of miniaturization of semiconductor devices.

Means for Solving the Problems In view of the above-mentioned objectives, the inventor of the present invention conducted various studies and found that when a semiconductor element is exposed to radiation, its response speed decreases, that is, the transmission delay time increases, and finally, Focusing on the fact that the semiconductor device becomes inoperable, he came up with the idea of using the semiconductor device itself as a radiation monitor. As a result of research based on this idea, the present invention has been completed.

That is, according to the present invention, there is provided a method for monitoring integrated radiation dose, characterized in that a ring oscillator is configured by a semiconductor element, and the integrated radiation dose of the semiconductor element is monitored based on the oscillation frequency of the ring oscillator.

Further, according to the present invention, the device includes a ring oscillator made of a semiconductor element, a frequency divider connected to the output of the ring oscillator, and a counter connected to the output of the frequency divider. Provided is a radiation integrated dose monitoring device characterized by:

Work J In the radiation integrated dose monitoring method and apparatus according to the present invention as described above, the semiconductor element connected in the form of a ring oscillator oscillates at a frequency corresponding to its response speed, that is, its propagation delay time.

Therefore, by measuring the oscillation frequency of the ring oscillator before exposure, it is possible to measure the oscillation frequency of the ring oscillator in a normal state.

On the other hand, when a semiconductor element is exposed to radiation, its functionality deteriorates as described above, and this appears in the form of an increase in transmission delay time. Therefore, the oscillation frequency of the ring oscillator decreases. The oscillation frequency of the ring oscillator decreases significantly as the integrated radiation dose increases, and eventually the ring oscillator stops oscillating.

Therefore, by observing the decrease in the oscillation frequency of the ring oscillator compared to normal times or the stoppage of oscillation, it is possible to monitor the integrated radiation dose of the semiconductor element.

Furthermore, the oscillation frequency of the ring oscillator can be measured with an oscilloscope, etc., but in the device according to the present invention, the output of the ring oscillator is divided by a frequency divider,
The frequency is measured by counting the divided frequency with a counter. In this way, by dividing the oscillation frequency with a frequency divider, the counting capacity of the counter can be reduced, and by measuring the frequency with a counter, the measuring device can be made into a size comparable to that of a semiconductor device. , without impairing the compactness of the semiconductor element.

Embodiments Hereinafter, embodiments of a method and apparatus for monitoring integrated radiation dose of a semiconductor device according to the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a block diagram of one embodiment of the apparatus of the present invention for carrying out the method of monitoring integrated radiation dose of a semiconductor device according to the present invention.

The ring oscillator 1 is constructed by using semiconductor elements in an inverter format, connecting them in odd number stages, in series, and in columns, and further connecting the output of the final stage to the human power of the first stage.

Furthermore, a gate circuit is provided in one of the odd-numbered series inverters to add an oscillation/stop function.

The semiconductor elements used include silicon MOS semiconductor elements, silicon bipolar semiconductor elements, and GaA
Various devices such as sMES semiconductor devices can be used.

The output of such a ring oscillator 1 is connected to a frequency divider 2 . The frequency divider 2 can be configured, for example, by connecting n stages of flip-flops in series. When such n-stage flip-flops are used, not only frequency division but also waveform shaping into pulse signals can be performed.

The output of the frequency divider 2 is input to a counter 3 which is used as a frequency measuring device. The counter 3 is configured to be automatically reset at appropriate time intervals. The count value of counter 3 at the time of resetting is shown on the display (
(not shown), or may be manually connected to a comparator (not shown) for comparison with a reference value. In addition, counter 3
The reset time T is selected to be an appropriate value smaller than N-n/fo, where the normal oscillation frequency f0 of the ring oscillator 1, the frequency division ratio is n, and the maximum count value of the counter 3 is N.

In the above configuration, a silicon MOS semiconductor element, a silicon bipolar semiconductor element, and a GaAsMES
When the integrated radiation dose was monitored using a semiconductor device, it was found that the silicon MOS semiconductor device had a
The ring oscillator's oscillation frequency fluctuated and decreased until the ring oscillator stopped functioning within the irradiation dose range of 104R and reached the irradiation dose of 104-H.

Also, in the case of silicon bipolar semiconductor devices,! -0'
The ring oscillator's oscillation frequency fluctuated and decreased until the ring oscillator stopped functioning at an irradiation dose of ~10''R and reached an irradiation dose of 10''R. It stops functioning within the dose range and until the irradiation dose reaches 108R,
The ring oscillator's oscillation frequency fluctuated and decreased.

As described above, according to the integrated radiation dose monitoring method according to the present invention, it is possible to monitor the integrated radiation dose received by a semiconductor element.

In addition, if three ring oscillators each made up of the silicon MO5 semiconductor element, silicon bipolar semiconductor element, and GaAs MES semiconductor element described above are prepared and the oscillation state of each is monitored, 104 to 109
Radiation integrated dose up to R can be monitored.

In other words, if the ring oscillator of the silicon MOS semiconductor device stops oscillating, it can be seen that there was an integrated dose in the range of 104 to 104 R, and if the ring oscillator of the silicon bipolar semiconductor device stops oscillating, then the integrated dose is 104 R.
It can be seen that integrated doses in the range ~108R were reached. Further, it can be seen that when the oscillation of the ring oscillator of the GaAs MES semiconductor device stopped, there was an integrated dose of 10'' to 109R.

Furthermore, it is not necessary to keep the ring oscillator in an operating state all the time, and even if it is left unpowered or in a biased state without being oscillated while being powered, its function will deteriorate due to exposure to radiation. Therefore, it is not necessary to monitor all the time, and even if you monitor at appropriate intervals,
The accumulated radiation dose up to that point can be monitored.

In addition, a ring oscillator is configured with various semiconductor elements,
If you record the oscillation frequency while irradiating the ring oscillator with radiation and create a table of the integrated dose and oscillation frequency, you can measure the oscillation frequency of the ring oscillator and compare it with the table to determine the amount of radiation. It is also possible to estimate the integrated dose.

Note that the embodiment of the method for monitoring the integrated radiation dose of a semiconductor device according to the present invention described above uses a counter as a frequency measuring device, but when used on the ground, other measuring means such as an oscilloscope may also be used. be able to.

However, if a counter is used as the frequency measuring means as described above, not only the ring oscillator and the frequency divider but also the frequency measuring means can be made into solid-state devices. Therefore,
The integrated radiation dose monitoring device for semiconductor devices according to the present invention can be realized in a very compact manner. Therefore, for example, if a radiation integrated dose measurement device consisting of the ring oscillator, frequency divider, and counter described above is incorporated into a semiconductor device using a silicon substrate, a GaAs substrate, or the like, it can be configured integrally with the semiconductor device to be measured.

In this way, when it is determined that the semiconductor device has deteriorated in function as a result of monitoring, the semiconductor device can be replaced together with the monitoring device.

Effects of the Invention As is clear from the above explanation, the method for monitoring the integrated radiation dose of a semiconductor device according to the present invention uses a ring oscillator made of a semiconductor device as a radiation integrated dose sensor. , unlike Geiger tubes, etc., it is possible to grasp the functional status of the semiconductor device itself.
Second, the circuit configuration is simple, and by integrating the sensor, the sensor can be miniaturized and can also be incorporated into a semiconductor device to be measured.

Furthermore, by changing the material and structure of the semiconductor element constituting the ring oscillator, it is possible to measure over a wide range of 104 to 109R.

Further, since all the components of the device for monitoring the integrated radiation dose of a semiconductor device according to the present invention can be made solid, the device can be realized in a very small size.

Therefore, it can be used as a maintenance monitor for semiconductor devices in spacecraft, nuclear power plants, and the like.

Particularly, when used as a maintenance monitor for semiconductor devices in a spacecraft, it is particularly effective because there is no substantial increase in weight or space.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a schematic configuration of an embodiment of an apparatus according to the present invention for carrying out a method of monitoring integrated radiation dose of a semiconductor device according to the present invention. [Main reference numbers] 1. Ring oscillator, 2. Frequency divider, 3. Counter

Claims (6)

[Claims] (1) A method for monitoring integrated radiation dose, characterized in that a ring oscillator is configured with a semiconductor element, and the integrated radiation dose of the semiconductor element is monitored based on the oscillation frequency of the ring oscillator. (2) Divide the output of the ring oscillator with a frequency divider,
A method for monitoring integrated radiation dose according to claim (1), characterized in that the frequency division frequency is measured. (3) A radiation source comprising a ring oscillator made of a semiconductor element, a frequency divider connected to the output of the ring oscillator, and a counter connected to the output of the frequency divider. Integrated dose monitoring device. (4) The integrated radiation dose monitor according to claim (3), wherein the semiconductor element is a silicon MOS semiconductor element, and is configured to measure an integrated radiation dose of 10^4 to 10^5R. Device. (5) The integrated radiation dose monitor according to claim (3), wherein the semiconductor element is a silicon bipolar semiconductor element, and is configured to measure an integrated radiation dose of 10^7 to 10^8R. Device. (6) The radiation integrated dose monitoring device according to claim (3), wherein the semiconductor element is a GaAs MES semiconductor element, and is configured to measure an integrated radiation dose of 10^8 to 10^9R. .