Static information storage and retrieval – Read/write circuit – Having fuse element
Patent
1993-08-31
1996-08-06
Popek, Joseph A.
Static information storage and retrieval
Read/write circuit
Having fuse element
365 96, 235380, G11C 1700
Patent
active
055441114
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to processes making it possible to program integrated memories, particularly those provided for smart cards, for recording therein binary data of various types.
2. Description of the Prior Art
Smart cards, also known as chip cards, are cards of the same size as a credit card and in which is inserted at least one integrated circuit having a memory and logic processing circuits which can optionally constitute a microprocessor. At least part of the memory is programmed in order to form a read-only memory (ROM), so as to e.g. be able to personalize the card. For this purpose the memory is programmed and then a fuse is blown, which makes it possible to prevent any writing in the thus programmed area. Thus, said area can be read, but cannot be reprogrammed. In principle, the blowing action of a fuse leads to a very reliable protection, because normally a fuse is not reconstituted. However, in practice, although it is not reconstituted, the blown fuse returns to a relatively conductive state, which can then permit the reprogramming of the normally protected area. The reason for this is not known and it is believed that particles of conductive elements reconstitute over a longer or shorter term the destroyed connection, as a result of the minute dimensions of said connection. As a result of the very small dimensions, for the purpose of blowing the fuses, the breakdown voltage is only applied for a short time of between 5 and 10 ms and the maximum intensity of the breakdown current is limited to approximately 30 mA, so as not to risk damaging the connections adjacent to that which has been blown.
The devices known at present for blowing fuses are very simple and are essentially dedicated to one circuit type. Therefore they do not make it possible to modify the breakdown voltage to be applied to the circuit or the time during which said voltage is applied. Moreover, in order to respect the limits given above, the current supplied is low. Finally, the breakdown is not systematically verified.
SUMMARY OF THE INVENTION
In order to obtain a reliable programming of smart cards, the invention proposes a process for programming an integrated memory of the fuse-protected type, in which for a predetermined time a breakdown voltage is applied to a fuse corresponding to a current limited to a given intensity and which is mainly characterized in that said intensity is at least equal to 1 ampere.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is described in greater detail hereinafter relative to a non-limitative embodiment and with reference to the attached drawings, wherein show:
FIG. 1 a general diagram of the programming and protection means according to the invention.
FIG. 2 a diagram of the breakdown voltage generating device.
DETAILED DESCRIPTION OF THE INVENTION
In FIG. 1, a smart card reader 101 in accordance with ISO Standard 7816-3 is connected to a control member 102, e.g. of the personal computer (PC) type and to a breakdown module 103, which supplies the fuse breakdown voltages. For this purpose, the reader comprises interface circuits, which make it possible to control the module 103 from the PC 102 and apply the voltage obtained to the interface, which is in itself known from the reader with the card. These interface circuits have connections and logic circuits assembled in accordance with standard procedures. They facilitate the connection to the PC and it would be possible to use a direct connection thereto, but this would have the disadvantage of requiring a supplementary output on the PC, which is more expensive than the interface integrated into the reader.
The diagram of the breakdown module is shown in FIG. 2. A transformer 201, supplied from the mains, is connected to a rectifying circuit 202 in order to obtain two d.c. voltages + and -60 V. At present, these are the extreme voltages necessary, according to the invention, for the blowing of the fuses of fuse-protected memories. If in the future it proved necessa
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Recherch, LA, M. Ugon et al:`Les Cartes a puce`, Apr. 1986, pp. 470-479.
Paul Franklin and David Burgess, "Reliability Aspects of Nichrome Fusible Link PROM's", Apr. 2, 1974, pp. 82-86.
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Berthozat Michel
Morgavi Paul
Gemplus Card International
Plottel Roland
Popek Joseph A.
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