Static information storage and retrieval – Systems using particular element – Ferroelectric
Reexamination Certificate
2001-02-26
2002-08-13
Nguyen, Tan T. (Department: 2818)
Static information storage and retrieval
Systems using particular element
Ferroelectric
Reexamination Certificate
active
06434038
ABSTRACT:
BACKGROUND OF THE INVENTION
(i) Field of the Invention
The present invention relates to a ferroelectric memory used in, e.g., an IC card to record information thereon.
(ii) Description of the Related Art
FIG. 1
is a block diagram showing an example of a prior art IC card.
This IC card is supplied with required power by electromagnetic coupling with a non-illustrated card read/write unit and provided with an antenna coil
11
for transmitting/receiving data. To the antenna coil
11
are connected a power supply portion
12
for converting power obtained by electromagnetic coupling into a direct-current voltage to be supplied to each part in the IC card and a switching portion
13
for switching between transmission and reception of data.
The receiving side of the switching portion
13
is connected to a central processing unit (which will be referred to as a “CPU” hereinafter)
16
through a demodulating portion
14
and decoding portion
15
. Further, the CPU
16
is connected to the transmitting side of the switching portion
13
via an encoding portion
17
and a modulating portion
18
. The decoding portion
15
and the encoding portion
17
are designed for encoding data to be transmitted/received between the IC card and the card read/write unit. Moreover, the demodulating portion
14
and the modulating portion
18
are used for transmitting/receiving encoded data in the form of a signal suitable for a transmission path.
To the CPU
16
are connected a ROM (Read Only Memory)
19
in which a processing program is stored and a non-volatile memory
20
such as an EEPROM (Electrically Erasable & Programmable Read Only Memory) for storing processed data, and an encrypting portion
21
for encrypting data to be stored in the non-volatile memory
20
.
When such an IC card is set in the card read/write unit, electromotive force induced in the antenna coil
11
is given to the power supply portion
12
, and the power supply portion
12
generates necessary direct-current power to be fed to each part in the IC card. On the other hand, a signal received by the antenna coil
11
is demodulated into reception data by the demodulating portion
14
, and this data is further converted from a cipher text into a plain text by the decoding portion
15
. The reception data outputted from the decoding portion
15
is supplied to the CPU
16
to be processed in accordance with a program in the ROM
19
. A part of the data obtained as a result of processing is fed to the encrypting portion
21
to be encrypted and further saved in the non-volatile memory
20
.
In addition, the data stored in the non-volatile memory
20
is read via the encrypting portion
21
to be processed in the CPU
16
. Transmission data as a result of processing executed by the CPU
16
is encrypted by the encoding portion
17
and then modulated by the modulating portion
18
to be transmitted from the antenna coil
11
.
As described above, in the IC card, data to be transmitted/received to/from the card read/write unit is encrypted by the decoding portion
15
and the encoding portion
17
to improve privacy, and data to be stored in the non-volatile memory
20
is encrypted by the encrypting portion
21
. Consequently, even if the stored content in the non-volatile memory
20
is read by a physical technique such as resin removal or optical analysis, security is protected so as not to decrypt the content of data.
The prior art IC card, however, has the following problem.
That is, the encrypting portion
21
is required in order to encrypt data to be stored in the non-volatile memory
20
. The size of the encrypting portion
21
may differ depending on a number of digits of a cipher key or an arithmetic operation method. For example, in case of a 32-bit key, an encryption processing circuit having a scale of approximately 10,000 gates is required. There is, thus, a problem such that a required area of the encrypting portion
21
occupying in the IC card is increased.
In order to eliminate the above-described drawback in the prior art, an object of the present invention is to provide a non-volatile memory which can reduce its necessary area and protect security and a manufacturing method thereof.
SUMMARY OF THE INVENTION
To achieve this aim, according to a first aspect of the present invention, a non-volatile memory comprises: storing means which uses as a storage device a ferroelectric material whose remaining polarization characteristic changes due to application of a predetermined voltage under a constant temperature condition and sets the storage device to have either a first remaining polarization characteristic or a second remaining polarization characteristic for each address in accordance with a predetermined address pattern; controlling means for outputting based on the address pattern a control signal indicative of distinction of the remaining polarization characteristic of the storage device selected by an address signal; and reading means for reading data in the storing means by determining in accordance with the control signal a remaining polarization value of the storage device selected by the address signal and outputted from the storing means.
According to the first aspect of the present invention, since the non-volatile memory is configured as described above, the following action is performed.
The storage device of the storing means is selected by the address signal, and the remaining polarization value of its ferroelectric material is outputted to the reading means. Further, the controlling means outputs the control signal indicative of distinction of the remaining polarization characteristic of the storage device selected by the address signal. The reading means determines in accordance with the control signal outputted from the controlling means the remaining polarization value outputted from the storing means, thereby reading data in the storage device.
According to a second aspect of the present invention, in a method for manufacturing a non-volatile memory by which a plurality of insulated gate type transistors and a plurality of ferroelectric capacitors are formed on a silicon substrate and the insulated gate type transistors are electrically connected to the ferroelectric capacitors to form a plurality of memory cells selectable by an address signal, there is added processing that a predetermined memory cell in a plurality of the memory cells is sequentially selected by using the address signal and a predetermined voltage is applied to the ferroelectric capacitor of the selected memory cell under a constant temperature condition to change the remaining polarization characteristic.
REFERENCES:
patent: 5159183 (1992-10-01), Yamaguchi
patent: 5525528 (1996-06-01), Perino et al.
patent: 5555219 (1996-09-01), Akiyama et al.
patent: 5905672 (1999-05-01), Seyyedy
patent: 5943256 (1999-08-01), Shimizu et al.
patent: 6078516 (2000-06-01), Hayashi
patent: 6128213 (2000-10-01), Kang
patent: 6201731 (2001-03-01), Kamp et al.
patent: 6246603 (2001-06-01), Brady
patent: 09-232532 (1997-09-01), None
Frank Robert J.
Nguyen Tan T.
Oki Electric Industry Co. Ltd.
Venable
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