Static information storage and retrieval – Systems using particular element – Capacitors
Reexamination Certificate
2002-06-14
2003-10-28
Nguyen, Viet Q. (Department: 2818)
Static information storage and retrieval
Systems using particular element
Capacitors
C365S117000, C365S114000, C365S145000, C365S102000, C365S185010, C365S185200, C365S185030
Reexamination Certificate
active
06639825
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a data memory having a multiplicity of memory cells for storing data represented by a first physical variable, particularly by the conductivity or the charge, for the storing storage elements, particularly in the form of storage capacitors, in the memory cells. A detection device is provided to detect the first physical variable representing the data. The invention also pertains to a method for permanently storing information in memory cells in a data memory for reversibly or permanently storing data.
In semiconductor memories, particularly DRAM semiconductor memories (dynamic RAMs), memories whose storage capacity is lower than that of the memory cell arrays are required for permanently storing the “redundancy information”. These permanent memories are growing in terms of their required capacity and hence in terms of their space requirement on the memory chip as the memory cell arrays for reversibly storing data become larger and larger. In this context, separate drive and evaluation circuits are necessary for the permanent memories, which occupy further valuable space on the semiconductor chips. An alternative to the additional permanent memories would be worthwhile in order to be able to use the space thus gained for the memory cell array, and hence to increase the storage capacity.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a data memory and method, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which provides for a data memory wherein the storage capacity is increased without increasing the number of memory cells.
With the foregoing and other objects in view there is provided, in accordance with the invention, a data memory, comprising:
a multiplicity of memory cells for storing data represented by a first physical variable and for storing a detectable information item represented by a second physical variable;
a first detection device connected to the memory cells and configured to detect the first physical variable representing the data;
a second detection device connected to the memory cells and configured to detect the second physical variable representing the second detectable information item independently of the data represented by the first physical variable;
wherein the first physical variable is a conductivity associated with a respective memory cell, and the second physical variable is a discharging or charging time associated with a respective memory cell.
In accordance with an added feature of the invention, the memory cells each include a storage element and the first physical variable is the conductivity of the storage element and the second physical variable is the discharging or charging time of the storage element. In a preferred embodiment, the second detection device records the second physical variable for the memory cell as a measured value, assesses the measured value with reference to a predetermined threshold value, and delivers a measurement signal as a result thereof.
In other words, according to the invention, a second detection device is provided for detecting a second physical variable for the memory cells or parts thereof, particularly for the storage element, particularly the leakage current of the storage capacitor provided for storing the data, which second variable represents not only the first physical variable representing the data but also, independently thereof, a second detectable information item.
The invention proposes providing a conventionally designed memory, particularly a semiconductor memory of the random access type, with a second detection device which, particularly in the case of semiconductor memories containing storage capacitors in the individual memory cells of the memory cell array, uses a further, otherwise unevaluated physical variable for the storage elements in order to store data, without adversely affecting the storage capabilities for the data in the memory cells. The effect achieved by this is multiple use of the storage capacity of a memory cell; the maximum volume of information which can be stored in the data memory, that is to say information and data together, is significantly increased, at best even multiplied. In DRAM semiconductor memories customary today, it would thus be a simple matter to dispense with the fuse array required for storing the redundancy information, the fuse array being made up from permanently programmable memory cells, in contrast to the reversibly programmable memory cell array. In addition, the proposed further development of data memories is possible without any great technological changes in the layout or in the design of the memory cells, particularly in the case of semiconductor memories of the random access type. This means that it is possible to use existing structures without added technological complexity, and hence to implement the invention in existing concepts quickly and cheaply. Novel data memories for storing a greater maximum possible volume of data or information than previously are now technically possible.
In one advantageous and therefore particularly preferred refinement of the invention, the second detection device records the second physical variable for the memory cell directly or dependently using a signal derived therefrom as a measured value and assesses the measured value in terms of its exceeding or falling short of at least one predetermined threshold value, and delivers a measurement signal as the result of the assessment. The proposed stipulation of a threshold value considerably simplifies determination of the storage state for the information. The adjustability of the detection threshold also permits variable settings, which means that the information can assume a plurality of values or states as a result of the threshold value being staggered.
In one preferred refinement of the invention, the second physical variable is the capacitance, the resistance, the impedance, the discharging or charging time, the charging constant, the leakage current, the direction or strength of magnetization for the memory cell or parts thereof, particularly for the storage element. This means that it is a particularly simple matter to store information in addition to the data in the individual memory cells without restricting the functionality of the memory cells in terms of reversible or permanent storage of the data.
A refinement of the invention which is likewise preferred provides for the first physical variable to be the conductivity, the charge, the direction of magnetization or the strength of magnetization for the memory cell or parts thereof, particularly for the storage element.
Advantageously, the memory cell is formed by an electric or ferroelectric memory cell of a memory of the random access type. Accordingly, the storage element is preferably formed by a storage capacitor. When a storage capacitor is used as storage element, the information can be impressed particularly simply by altering the capacitance of the storage capacitor, without affecting the storage capacitor's storage capability for the data represented by means of the charge.
In addition, the second physical variable is particularly advantageously the retention time or the charging and discharging constant or an associated physical variable, particularly the time-altered charging voltage, which can be tapped off, for the storage capacitor in the memory cell. This means that, in the case of information impressed using the capacitance, this information can be ascertained particularly easily by virtue of the proposed indirect determination of the storage capacitor's capacitance.
In accordance with another advantageous refinement of the invention, the data memory can be operated in two operating modes, where, in the first operating mode (normal mode), the memory cells are operated while detecting the first physical variable, and, in the second operating mode (permanent mode), the second physical varia
Feurle Robert
Schneider Helmut
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