Nondestructive sensing mechanism for polarized materials

#Polarized materials include ferroelectric and magnetic materials. For purposes of this discussion, polarized materials will include any material capable of being polarized, whether they are currently polarized or not. The material has a polarization of one state or the opposite state, such a positive or negative polarity. The polarization state often depends upon the nature of the polarizing force applied. For example, ferroelectric materials will assume a positive or negative polarization with application of an electric field. In some materials, application of a positive electric field will cause the material to assume a positive polarity. In many polarizable materials, the hysteresis loop of the material exhibits a non-linear slope during the application of the forcing function.

#Once a polarized cell has been polarized to a particular state, and that state is correlated to a ‘one’ or a ‘zero,’ that data will be retained for a period of time and in some cases indefinitely. However, current techniques for sensing the state of the cell are ‘destructive’ in that the sensing operation causes the cells to assume one of the two states, nominally the ‘zero’ state. A charge release caused by the forcing of the cell to the ‘zero’ state is the mechanism sensed to determine the state of the cell. For example, if a ‘one’ state is of positive polarity, the cell is switched to negative polarity and the charge released is sensed. However, in the process, the data state changed from ‘one’ to ‘zero.’ For ‘zero’ state cells, the cell does not change states. However, in order to preserve the data in the cells in the one state, the data must be stored and rewritten into the cells after the read cycle. This is time consuming, power consuming and inefficient.

#Therefore, it would be useful to have a robust, non-destructive means for sensing the polarization state of polarized materials.

#The invention may be best understood by reading the disclosure with reference to the drawings, wherein:

#FIG. 1 shows an example of a polarized ferroelectric material memory cell.

#FIG. 2 shows a polarization versus applied voltage hysteresis curve for a polarized material memory cell, in accordance with an embodiment of the invention.

#FIG. 1 shows one example of a cell in a ferroelectric memory array. The cell 10 has an electrode layer 16, a ferroelectric material layer 14 and a second electrode layer 18. The arrangement of FIG. 1 is provided for ease of discussion and many other arrangements of the ferroelectric material may be used, as well as many other arrangements of the electrode or other addressing means. For purposes of discussion, however, the arrangement of FIG. 1 will be used and the region of ferroelectric material located at the cross over point between the two electrode layers will be referred to as a cell. One application of such a region may be a memory cell, and that example will be used here with no intention of limiting the scope of the invention.

#If there were a memory cell, the data value in the cell would be either a one ‘1’ or a zero ‘0’. The value of the cell is determined by the polarization of the material versus the voltage being applied. Referring now to FIG. 2, a polarization versus voltage hysterisis curve demonstrates the nature of the memory cell and how it stores data values of ones or zeros. Control of the voltages applied to the active word line and active bit line may cause the material to experience a polarization shift. The differential voltage seen at the cell is due to a voltage differential between the two electrode layers 16 and 18.

#FIG. 2 has as its horizontal axis this differential voltage. The vertical axis is the polarization of the material at the cell and is represented by the change in current flow from the cell as the voltages are applied across the cell. The origin of the axes corresponds to zero voltage and zero polarization. FIG. 2 shows a typical polarization versus voltage curve. A characteristic of certain types of ferroelectric and magnetic materials is that the hysterisis curve is not square. This characteristic provides an alternative opportunity to sense the state of the polarization, ‘reading’ the cell, other than a destructive read process. One application of this invention will exploit this non-linear behavior to sense the state of polarization of the material. It is helpful to first discuss manipulation of the polarization state.