These above recited features of the present invention will become clear from the following description, taken in conjunction with the accompanying drawings. It is to be noted, however, that the accompanying drawings illustrate only typical embodiments of the present invention and are, therefore, not to be considered limiting of the scope of the invention. The present invention may admit other equally effective embodiments.
In a CBRAM memory circuit, each memory cell 12 may comprise a selection transistor and a resistive storage element. A first terminal of the resistive storage element is connected to a conductive member (usually called plate) providing a plate voltage VPL (all voltages with respect to a predefined reference potential). The other terminal of the resistive storage element is connected to the source drain area of the selection transistor. The resistive storage element provides (at least) two resistance states, a low resistance state and a high resistance state representing respectively either a logical 0 and a logical 1.
Further, the memory circuit 10 comprises a plurality of parallel bit-lines 21, 22, 23, 24, 25, 26, 27, 28 and a plurality of parallel word-lines 31, 32, 33, 34. The memory cells 12 are arranged at cross points of the bit-lines and the word-lines.
Furthermore, the memory circuit 10 comprises a plurality of sense amplifiers 41, 42, 43, 44 each of which is connected to two bit-lines 21, 22, 23, 24, 25, 26, 27, 28. For each sense amplifier 41, 42, 43, 44, one bit-line connected to the sense amplifier is called a true bit-line and the other bit-line connected to the same amplifier is called the complement bit-line. In the following, the bit-lines 21, 23, 25, 27 are called true bit-lines, and the bit-lines 22, 24, 26, 28 are called complement bit-lines. However, the nomenclature could be the other way round as well.
Furthermore, the memory circuit 10 comprises a plurality of switches 51, 52, 53 and 54, each of which is connected to a respective pair of bit-lines 22, 26; 21, 25; 24, 28; 23, 27, for switchably short-circuiting the respective pair of bit-lines. Each of the plurality of switches 51, 52, 53, 54 is either connected to two true bit-lines 21, 23, 25, 27 or connected to two complement bit-lines 22, 24, 26, 28. A controller 61 is connected operatively to the switches 51, 52, 53, 54 via control lines 63, 64.
Before or preferably during any access to a memory cell 12 connected to a true bit-line 21, 23, 25, 27, a reference potential is provided to the corresponding complement bit-line 22, 24, 26, 28 connected to the same sense amplifier. Before or preferably during any access to a memory cell 12 connected to a complement bit-line 22, 24, 26, 28, a reference potential is provided to the corresponding true bit-line 21, 23, 25, 27, connected to the same sense amplifier. The reference potential is usually an arithmetic mean of a read voltage Vread and a plate voltage VPL or of any other first and second predetermined potentials.
For an access to one or several memory cells 12 connected to a true bit-line 21, 23, 25, 27, the first predetermined potential is impressed to the complement bit-lines 22, 24, and the second predetermined potential is impressed to the complement bit-lines 26, 28. Thereafter, the controller 61 closes the switches 51, 53 thereby short-circuiting the pair of complement bit-lines 22, 26 and short-circuiting the pair of complement bit-lines 24, 28. As a result, the complement bit-lines 22, 24, 26, 28 are tuned to an arithmetic mean potential Vmean between the first and second predetermined potentials, i.e. between the plate potential VPL and the read voltage Vread.
During or after the generation of the reference potential, the respective one of the plurality of word-lines 31, 32 is activated in order to connect the resistive storage element of the respective memory cells 12 to the true bit-lines 21, 23, 25, 27, and the read voltage Vread is provided to the true bit-lines 21, 23, 25, 27.
In one embodiment, the read voltage Vread is provided to the true bit-lines 21, 23, 25, 27 for a short period of time. After this short period of time, the voltage at each of the true bit-lines 21, 23, 25, 27 is a sense voltage indicating the resistance state of the respective resistive storage element. The sense voltage rapidly declines to the plate voltage VPL when the respective resistive storage element is in a low resistance state. When the respective resistive storage element is in a high resistance state, the sense voltage slowly declines to the plate voltage VPL.
The data stored in the respective resistive storage element is read by comparing the sense voltage at the respective true bit-line 21, 23, 25, 27 and the mean potential Vmean at a corresponding complement bit-line 22, 24, 26, 28 by means of the respective sense amplifier 41, 42, 43, 44 connected to the respective true bit-line 21, 23, 25, 27 and to the corresponding complement bit-line 22, 24, 26, 28.
For an access to one or several memory cells 12 connected to a complement bit-line 22, 24, 26, 28, the first predetermined potential is impressed to the true bit-lines 21, 25, and the second predetermined potential is impressed to the true bit-lines 23, 27. Thereafter, the controller 61 closes the switches 52, 54 thereby short-circuiting the pair of true bit-lines 21, 25 and short-circuiting the pair of true bit-lines 23, 27. As a result, the true bit-lines 21, 23, 25, 27 are tuned to an arithmetic mean potential Vmean between the first and second predetermined potentials, i.e. between the plate potential VPL and the read voltage Vread.
During or after the generation of the reference potential, the respective one of the plurality of word-lines 33, 34 is activated in order to connect the resistive storage element of the respective memory cells 12 to the complement bit-lines 22, 24, 26, 28, and the read voltage Vread is provided to the complement bit-lines 22, 24, 26, 28.
In one embodiment, the read voltage Vread is provided to the complement bit-lines 22, 24, 26, 28 for a short period of time. After this short period of time, the voltage at each of the complement bit-lines 22, 24, 26, 28 is a sense voltage indicating the resistance state of the respective resistive storage element. The sense voltage rapidly declines to the plate voltage VPL when the respective resistive storage element is in a low resistance state. When the respective resistive storage element is in a high resistance state, the sense voltage slowly declines to the plate voltage VPL.
The data stored in the respective resistive storage element is read by comparing the sense voltage at the respective complement bit-line 22, 24, 26, 28 and the mean potential Vmean at a corresponding true bit-line 21, 23, 25, 27 by means of the respective sense amplifier 41, 42, 43, 44 connected to the respective complement bit-line 22, 24, 26, 28 and to the corresponding true bit-line 21, 23, 25, 27.
As already described above, the read voltage Vread may be provided to the respective bit-line for a first predetermined short period of time. A second predetermined short period of time later, the storage state of the respective resistive storage element is sensed by sensing the voltage or potential difference between the respective bit-line and a corresponding bit-line providing the reference potential. In CBRAM technology, the resistance values of a resistive storage element in the high and low resistance states differ by several orders of magnitude. Therefore, the second predetermined period of time can be set and usually is set to such a value that the sense voltage at the moment it is detected by the sense amplifier either essentially equals the read voltage Vread (when the resistive storage element is in the high resistance state) or essentially equals the plate voltage VPL (when the resistive storage element is in the low resistance state).
As an alternative, the respective bit-line connected to the memory cell to be read is still connected to the read voltage source when the respective sense amplifier reads the stored data by sensing the potential difference. In this case, when a resistive storage element of a memory cell activated by the respective active word-line is in the high resistance state, the read voltage Vread is maintained at the respective bit-line. When a resistive storage element of a memory cell activated by the respective active word-line is in the low resistance state, the potential of the respective bit-line is pulled to the plate voltage VPL. For this alternative reading procedure, the internal resistance should provide an appropriate level between the resistance levels of the resistive storage element in the low and high resistance states.
In one embodiment, the impression of the predetermined potentials to the bit-lines is controlled by the controller 61 via control lines, switches and sources providing the potentials, wherein these lines, switches and sources are not displayed in
The bit-line 22 is arranged between two bit-lines 21, 23, the potential of which is falling from Vread to Vmean. The bit-line 26 is arranged between two bit-lines 25, 27, the potential of which is rising from VPL to Vmean. Thereby, the potential of the bit-line 22 and the potential of the bit-line 26 are affected by capacitive coupling from the neighboring bit-lines 21, 23, 25, 27. This influence is detrimental and will even rise in future memory circuits because of the progressive miniaturization of microelectronic devices.
Similar to the memory circuit described above with reference to
The bit-lines of each respective pair of bit-lines 22, 24; 26, 28; 21, 23; 25, 27 are connected to two different sense amplifiers 341, 342, 343, 344. For example, considering switch 351, the first bit-line 22 connected to the switch 351 is connected to the sense amplifier 341, and the second bit-line 24 connected to the switch 351 is connected to the sense amplifier 343. In contrast to the memory circuit described above with reference to
The operation of the memory circuit 310 shown in
The embodiment described above with reference to
For example, before or while an access to one or several of the memory cells 12 connected to the word-line 31, the first predetermined potential is impressed to the bit-lines 22 and 26 and the second predetermined potential is impressed to the bit-lines 24 and 28. Thereby, the bit-line 23 is arranged between one bit-line (bit-line 22) with the first predetermined potential and one bit-line (bit-line 24) with the second predetermined potential; the bit-line 25 is arranged between one bit-line (bit-line 26) with the first predetermined potential and one bit-line (bit-line 24) with the second predetermined potential; and the bit-line 27 is arranged between one bit-line (bit-line 26) with the first predetermined potential and one bit-line (bit-line 28) with the second predetermined potential.
Similarly, in preparation of an access to one or several of the memory cells connected to one of the word-lines 33, 34, the first predetermined potential is impressed to the bit-lines 21, 25 and the second predetermined potential is impressed to the bit-lines 23 and 27. Thereby, the bit-line 22 is arranged between one bit-line (bit-line 21) with the first predetermined potential and one bit-line (bit-line 23) with the second predetermined potential; the bit-line 24 is arranged between one bit-line (bit-line 25) with the first predetermined potential and one bit-line (bit-line 23) with the second predetermined potential; and the bit-line 26 is arranged between one bit-line (bit-line 25) with the first predetermined potential and one bit-line (bit-line 27) with the second predetermined potential.
If this symmetry, i.e. the arrangement of each bit-line between two neighboring or adjacent bit-lines connected to different predetermined potentials, shall be provided for the outer most bit-lines 21, 28, too, additional dummy bit-lines not displayed in
This symmetry makes sure that the capacitive influences of neighboring bit-lines on any bit-line cancel out each other. The net effect of capacitive coupling between the bit-lines is zero.
A further advantage of the memory circuit 310 described above with reference to
A further advantage of the memory circuit 310 described above with reference to
A plurality of switches 451, 452, 453, 454 are provided switchably connecting respective pairs of bit-lines 21, 22, 23, 24, 25, 26, 27, 28. A controller 461 is operatively connected to the switches 451, 452, 453, 454 via control lines 463, 464 and controls the switches 451, 452, 453, 454. Similar to the memory circuit described above with reference to
The memory circuit 410 described with reference to
As a result of this particular topology and as a further difference from the memory circuit described above with reference to
The operation of the memory circuit 410 displayed in
The memory circuit 410 described with reference to
As a further advantage, there are no cross points of the wires connecting the switches 451, 452, 453, 454 to the bit-lines 21, 22, 23, 24, 25, 26, 27, 28 (confer the above discussion with reference to
As has been already mentioned, the
Although the present invention is particularly advantageous for CBRAM and other memory circuits with resistive storage elements and with sense amplifiers of the voltage sensitive type, the present invention is also advantageous for other types of memory circuits or other storage technologies, respectively. In particular, the present invention is advantageous for CBRAMs with charge sensitive or current sensitive sense amplifiers and for other (non CBRAM) types of memory circuits in which potentials or charges are compared by differential amplifiers during a reading, writing or refreshing procedure and in which an arithmetic mean potential or charge is used as a reference potential or reference charge, respectively.
The microelectronic device 70 may be a processor or microcontroller with cache or other internal memory provided by the memory circuit 510 or any other microelectronic device with one or several memory circuits 510.
In one embodiment, the microelectronic device 70 is a memory device with a plurality of memory circuits 510, each of which comprises an array of memory cells. In this case the other circuits 72 schematically represent input and output amplifiers, registers, address decoders etc.
Alternatively, the microelectronic device 70 is an embedded system formed for an application in a mobile communication system (for example a mobile telephone) or a mobile information technology system (for example a handheld computer, a notebook computer or a laptop computer), for automotive or any other applications.
In a third step 93, a second predetermined potential is applied to a third bit-line connected to a second sense amplifier. When referring to a memory circuit as described above with reference to
In a fourth step 94, the second and the third bit-lines are short-circuited.
In a fifth step 95, the memory state of the memory cell connected to the first bit-line is sensed by activating a respective word-line, thereby connecting the storage element of the memory cell to the first bit-line. Although this step may be conducted after the fourth step 94, the fifth step 95 is preferably conducted simultaneously to the fourth steps 94 or simultaneously to the second through fourth steps 92, 93, 94.
In a sixth step 96, the data stored in the memory cell is read by comparing the voltages or potentials of the first and second bit-lines.
The preceding description only describes advantageous exemplary embodiments of the invention. The features disclosed therein and the claims and the drawings can, therefore, be essential for the realization of the invention in its various embodiments, both individually and in any combination. While the foregoing is directed to embodiments of the present invention, other and further embodiments of this invention may be devised without departing from the basic scope of the invention, the scope of the present invention being determined by the claims that follow.