Data processing: generic control systems or specific application – Generic control system – apparatus or process – Having protection or reliability feature
Reexamination Certificate
1999-03-17
2002-05-21
Gordon, Paul P. (Department: 2819)
Data processing: generic control systems or specific application
Generic control system, apparatus or process
Having protection or reliability feature
C307S126000
Reexamination Certificate
active
06393330
ABSTRACT:
TECHNICAL FIELD
The present invention concerns a method for managing the functioning under irradiation of at least one electronic component with complementary MOS (metal-oxide-semiconductor) transistors. It also concerns a device powering such an electronic component in systems including one or more such devices.
Within the meaning of the present invention, electronic component with complementary MOS or CMOS transistors means not only individual elementary components such as gates or inverter gates including CMOS transistors, but also assemblies formed by a plurality of individual elementary components, such as circuits, parts of circuits, microprocessors or computers, including CMOS transistors.
The invention finds application in the manufacture of electronic devices, such as control devices, which can be used in a hostile atmosphere of ionising radiations, notably in the civil nuclear industry. The invention also finds application in the production of embedded electronic devices intended to be used in a hostile ionising radiation environment.
STATE OF THE PRIOR ART
The development of electronic systems used in the civil nuclear industry has increased considerably during the 1990s.
For reasons of cost, delivery times and legislation, these specific components designed to resist radiation have, to a great extent, been replaced by very widespread standard components, in particular by components of the CMOS type (components with transistors of the complementary metal-oxide-semiconductor type).
Thus, by selecting in advance components whose resistance to radiation is good and by complying with certain design rules for the architecture of the systems, these systems can be used with ionising radiation doses greater than 1 Mrad.
Studies currently being carried out even show that increasing the quality of the methods of manufacturing, the intrinsic resistance of the components improves very significantly. It nevertheless remains true that the versatility of the new components makes it difficult to control in advance the resistance to radiation. With the majority of embedded applications, it is important to react preventatively to the loss of functionality of an electronic system. A loss of functionality can in fact be the cause of a significant degradation of the components due to the assimilated radiation dose.
It is considered that a component is subject to a loss of functionality either when it has failed or when the execution of the tasks assigned to it are not error-free.
If the architecture of an electronic system is designed with a certain number of redundant elements or parts, it is possible to reconfigure the system in order to connect up new elements which were not powered and to disconnect elements which were powered. In this regard reference can be made, for example, to Rad-hard Embedded Computer for Nuclear Robotics by A. Giraud et al, Conference Proceedings RADECS 1993, pages 43-47.
Such a reconfiguration thus makes it possible to eliminate from the system, in a preventive, temporary or definitive fashion, the components which have failed or are liable to cause a failure.
The reconfiguration of an electronic system subjected to radiation, during which some components are powered down, makes it possible to avoid excessive degradation of the components and even to “regenerate” the latter. It is in fact known that the electronic components of microcontrollers and particularly components of the MOS (metaloxide-semiconductor) type, subjected to ionising radiation, but powered down, may recover, at least partly, their initial characteristics, after having being degraded when they were powered down.
The phenomenon of regeneration of powered-down components, in the presence of radiation, is due to a discharge of the charges caused by the radiation and by an effect of compensation and redistribution of the charges. In particular, in MOS components, the holes migrate towards the oxide-semiconductor interface region in order to compensate for the charges trapped in the oxide layer. In this regard reference can be made to French Patent Applications FR-A-2 721 122 and FR-A-2 633 160.
In order to envisage a reconfiguration of an electronic system and anticipate any failures of the components, it is necessary to establish a relationship between the ionising radiation dose received by the components and the functionality of the system.
In order to determine the radiation dose received by the components, it is known that a shifting of the threshold voltage of the CMOS components can be taken into account.
By way of example, a simple CMOS component, such as an inverter gate of the 7404 type, can be used as a dosimeter. An inverter gate of the 7407 type is composed of a pair of NMOS and PMOS transistors. For a given supply voltage +Vcc for the component, the switching threshold of the inverter gate is around Vcc/2. When the component is subjected to radiation, this threshold decreases. Depending on the biasing conditions during the irradiation (high biasing) the threshold can even become negative.
It appears that, under nil biasing, during the irradiation of the component, the threshold voltage of the inverter gate is a relatively homogeneous function of the dose received.
Associated with an electronic system, an inverter gate of the 7404 type with MOS components can thus serve to measure the radiation dose received. In this regard reference can be made to the document Handbook of Radiation Effects, by Andrew Holmes-Siedle/Lens Adams, Oxford Science Publications, pages 110-113.
Another useful parameter for measuring the irradiation is the consumption current of the complementary MOS (CMOS) components. The consumption current of a CMOS component increases with the radiation dose received. This is a consequence of the threshold voltage of 0 volts of the NMOS (n-type MOS) transistors being exceeded. The leakage current of the transistors increases in fact when the threshold voltage is negative. Thus, in certain devices, the measurement of the quiescent current is used to monitor the ionising radiation dose received. In this regard reference can be made to Total-Dose Issues for Microelectronics in Space Systems, by Ronald L. Pease, IEEE Transactions on Nuclear Science, Vol. 43, No. 2, April 1996, pages 442-450.
It appears, however, that the use of the parameter of the current consumed by a component does not well represent the availability of the component or of the electronic system on which this current is measured. This is because the intensity of the current remains sensitive to the dose rate and does not show the influence of a regeneration of the component. It is normal to observe a rapid increase in the consumed current followed by a slower decrease, without the availability of the component or components being effected thereby. Moreover, the electronic components subjected to radiation are usually able to function beyond the characteristics supplied by the manufacture of these components.
The devices or methods for determining the irradiation doses described above certainly make it possible to indicate that predetermined critical thresholds have been exceeded but do not guarantee the functioning of an electronic system for a given task to be accomplished in a given length of time.
Thus, in order to increase the reliability of the functioning of an electronic system, this system is generally oversized. Such a measure, however, has negative consequences on the cost of the system, its complexity and its bulk.
In addition, the means described above do not take account of the phenomenon of regeneration of the components, already mentioned.
DISCLOSURE OF THE INVENTION
The aim of the invention is to propose a method and device for managing the functioning of electronic components which do not have the limitations set out above.
One aim of the invention is in fact to guarantee the functioning of a component or of a plurality of electronic components for a given length of time, taking account of the ionising radiation received by the components during this time.
Another aim of the invent
Giraud Alain
Joffre Francis
Burns Doane , Swecker, Mathis LLP
Commissariat a l'Energie Atomique
Frank Elliot
Gordon Paul P.
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