Registers – Coded record sensors – Particular sensor structure
Reexamination Certificate
2002-11-15
2004-02-10
Le, Thien M. (Department: 2876)
Registers
Coded record sensors
Particular sensor structure
C235S492000, C235S487000
Reexamination Certificate
active
06688520
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2002-029351, filed on Feb. 6, 2002, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an authentication circuit, a semiconductor device having the authentication circuit, a process for operating the semiconductor device, an IC card having the authentication circuit, and a process for operating the IC card.
2. Description of the Related Art
Semiconductor devices, particularly, semiconductor memories having various properties are known. Among the semiconductor memories, particularly, those which retain data even when a power source is turned off are called nonvolatile memories. Among the nonvolatile memories, a nonvolatile memory which uses a ferroelectric as a material of a capacitor for holding charges and can be accessed at random is called a ferroelectric random access memory (FeRAM).
In the case where the material of a capacitor is not the ferroelectric, that is, a paraelectric, polarization is maintained only when there is a potential difference from an electrode. When the potential difference is eliminated, the polarization is not maintained, so that non-volatility is not exhibited and the memory becomes volatile. On the other hand, in the case where the material of the capacitor is the ferroelectric (in the case of the FeRAM), two residual dielectric polarization properties of different polarities are used and, even when the power source is turned off, polarization is maintained, data is retained and demonstrates non-volatility. In the case of the FeRAM, polarization can be achieved in one of two directions. By distinguishing the polarization direction, information “1” corresponding to polarization in one direction and information “0” corresponding to polarization in the other direction can be stored. The number of rewriting times as a measure of the performance of volatility is as many as 10
10
to 10
12
. The rewriting speed is on the order of tens ns, so that high-speed performance is obtained. Consequently, recently, a system LSI using the ferroelectric is actively being developed.
Since the system LSI is used for a device using money information, personal information, and the like such as an IC card or Smart card, a countermeasure against forgery is indispensable in the system LSI. As a countermeasure against forgery, conventionally, for example, as disclosed in Japanese Patent Application Laid-Open (JP-A) No. 11-240227, a method for writing data into a storage area before scribing and then cutting out a pad being scribed in a data so that the storage area remains unaccessed is proposed. This method has, however, a problem such that since information has to be written into the storage area at the time of manufacturing a chip or mounting the chip onto a card, the method cannot be applied after a card is manufactured.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an authentication circuit from which stored information cannot be decoded without being destructed, to/from which information can be written/erased even after the circuit is manufactured, and which is suitable for various devices from the viewpoint of forgery prevention, a semiconductor device having an excellent forgery preventing function suitable for a system LSI or the like, a process for operating the semiconductor device capable of performing a predetermined function while preventing forgery, an IC card having the excellent forgery preventing function, which is suitable for a Smart card or the like, and a process for operating the IC card, which can perform a predetermined function while preventing forgery.
A first authentication circuit of the present invention comprises at least two types of ferroelectrics comprising a ferroelectric
1
and a ferroelectric
2
having different Curie temperatures. Since the ferroelectrics have properties of retaining charges by residual polarization the ferroelectric functions as a nonvolatile memory. In the ferroelectrics, authentication signals as secret information for making a semiconductor device or the like perform a predetermined function are stored. When the authentication circuit is held at the Curie temperature of ferroelectrics
1
or higher and lower than the Curie temperature of the ferroelectric
2
, an authentication signal stored in the ferroelectrics
1
is erased. When the authentication circuit is held at the Curie temperature of the ferroelectric
2
or higher, the authentication signal stored in the ferroelectric
2
is erased. Consequently, the authentication circuit is held at room temperature and operated, the authentication signal is output from the ferroelectric
1
to the ferroelectric
2
, after that, the information stored in the ferroelectric
1
is erased. Subsequently, the authentication signal is output from the ferroelectric
2
to the semiconductor device or the like to make the semiconductor device or the like to perform a predetermined function. After that, the information stored in the ferroelectric
2
is erased. After conducting these operations, a third person cannot nondestructively re-transmit an output signal of the semiconductor device or the like stored in the authentication circuit. That is, if the third person could not give a predetermined temperature pattern corresponding to the Curie temperatures of the two or more types (n types) of ferroelectrics provided in the authentication circuit to the authentication circuit, a normal authentication signal stored in the authentication circuit cannot be output to the semiconductor device or the like. To output the normal authentication signal to the semiconductor device or the like, the third person has to destroy the authentication circuit to know the Curie temperatures of the two or more types (n types) of ferroelectrics provided in the circuit. Consequently, in the authentication circuit, authentication signals exists in the number equal to the number of the ferroelectrics provided in the circuit, and normal authentication signals are sequentially output only when a predetermined temperature pattern corresponding to the Curie temperatures of the two or more types (n types) of ferroelectrics is given, hence the authentication circuit has a superior forgery preventing ability. Since the property of the ferroelectric itself is utilized in the authentication circuit, even after a semiconductor device, an IC card or the like which includes the authentication circuit is manufactured, information can be written/erased to/from the storage area.
A second authentication circuit of the present invention comprises two or more ferroelectrics. Since the ferroelectrics have properties of retaining charges by residual polarization, the ferroelectric functions as a nonvolatile memory. In the ferroelectrics, authentication signals as secret information for making a semiconductor device or the like perform a predetermined function are stored. When only ferroelectrics
1
in the authentication circuit or the ferroelectric
2
is heated or cooled by means for thermally stimulating the ferroelectrics (such as heat generating device, cooling device, or the like) and held at a predetermined temperature and the ferroelectric
1
or the ferroelectric
2
is held at the Curie temperature of the ferroelectric
1
or the ferroelectric
2
or higher and the authentication circuit is held at a temperature lower than the Curie temperature of the ferroelectric different from the above, an authentication signal stored in the ferroelectric
1
or ferroelectric
2
is erased. Consequently, the authentication circuit is held at a predetermined temperature or less and operated, the authentication signal is output from the ferroelectric
1
or the ferroelectric
2
to the different ferroelectric, after that, the information stored in the ferroelectric
1
or ferroelectric
2
is erased. Subsequently, the authentication signal is outp
Fujitsu Limited
Hess Daniel A
Le Thien M.
Westerman Hattori Daniels & Adrian LLP
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