The present disclosure relates generally to methods and systems for reducing the complexity of electronically programmable nonvolatile memory, and—in particular—the complexity of embedded flash memory such as hot source triple poly (HS3P) flash memory.
Electronically programmable and erasable nonvolatile memories typically need some overhead circuitry to be operated. For instance, charge pumps need to be implemented to provide increased voltages for the operation of the nonvolatile memory cells. Furthermore, at the startup of a nonvolatile memory device, the charge pumps may need some time to power up before being fully functional.
Moreover, to securely read memory cells of the nonvolatile memory device, complex sense amplifiers might be needed to avoid misinterpretation of memory cell contents due to relatively low distances between logical signal levels. Furthermore, due to the operation principles of an electronically programmable nonvolatile memory as a cycled memory, the duration of a read cycle may set undesired lower limits to content access times for certain applications.
Hence, the characteristics of typical electronically programmable nonvolatile memories may lead to a relatively high complexity and performance limits for certain applications. A typical example for such an application may be the fast and reliable access to nonvolatile memory content in the boot or startup procedure of an automotive electronic control unit (ECU) into which the nonvolatile memory has been embedded.
For these or other reasons, there is a need for the present disclosure.
A method and system for reducing the complexity of nonvolatile memory is provided, substantially as shown in and/or described in connection with at least one of the figures, as set forth more completely in the claims.
Further features and advantages of embodiments will become apparent from the following detailed description made with reference to the accompanying drawings.
The accompanying drawings are included to provide a further understanding and are incorporated in and constitute a part of this specification. The drawings relate to examples and embodiments and together with the description serve to explain the principles of the disclosure. Other embodiments and many of the intended advantages of embodiments will be readily appreciated as they become better understood by reference to the following detailed description.
In the following Detailed Description, reference is made to the accompanying drawings, which form a part hereof, and in which are shown by way of illustration specific embodiments. It is to be understood that other embodiments may be utilized and structural or other changes may be made without departing from the scope of the present disclosure. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present disclosure is defined by the appended claims.
In the following, for illustration purposes, the disclosure will be described with reference to flash memory as embedded nonvolatile memory (eNVM) for automotive applications. However, the disclosure is not so limited and may find its application in conjunction with reducing the complexity of any other kind of electronically programmable nonvolatile memory.
Embodiments of the disclosure may reduce the complexity of small integrated circuit products where it is favorable to combine different circuit functions into one module or nonvolatile memory device. In particular, the nonvolatile function of an electronically programmable nonvolatile memory device—that may, for instance, comprise floating gate transistors in nonvolatile memory cells—may be combined with a data persistent Read Only Memory (ROM) functionality. This combination may be implemented by firmly programming at least a portion of the electronically programmable and erasable nonvolatile memory cells through the usage of a processing mask that establishes or omits fixed connections such as by via contacts to predetermined select or floating gate transistors of the electronically programmable and erasable nonvolatile memory cells.
In this regard, in some embodiments, the firm programming may be implemented by a processing mask for via contacts for an integrated nonvolatile memory device. However, the fixed connections for firm programming of electronically programmable and erasable nonvolatile memory cells may also be established or omitted to the electronically programmable and erasable nonvolatile memory cells by any other suitable processing mask such as a processing mask for a specific metal or polysilicon layer.
In embodiments, the mask programmable portion of the electronically programmable and erasable nonvolatile memory device may be read with the same sense amplifiers that are used for the electronically programmable portion of the electronically programmable and erasable nonvolatile memory device. In this regard, the sense amplifiers and other overhead circuitry may be re-used instead of providing dedicated infrastructure circuitry for a conventional ROM portion within the electronically programmable and erasable nonvolatile memory device.
Moreover, in embodiments, the firmly programmed electronically programmable and erasable nonvolatile memory cells may reduce the requirement for charge pumps. In conventional electronically programmed nonvolatile memory cells, such charge pumps may also be necessary to provide elevated read voltages at the control gates of the floating gate transistors of nonvolatile memory cells during read access operations.
However, since in firmly programmed electronically programmable and erasable nonvolatile memory cells the no-current “programmed” mode is typically very distinct due to an omitted connection of the select transistor to the source line or of the floating gate transistor to the bitline, pumped reading voltages are typically not needed to distinguish if a firmly programmed electronically programmable and erasable nonvolatile memory cell represents a logical one state or a logical zero state.
As a result of these firmly established or omitted connections firmly programmed by a processing mask, the data retention of the firmly programmed electronically programmable and erasable nonvolatile memory cells—representing the ROM part of the electronically programmable and erasable nonvolatile memory device—may practically be infinite. As a further result, the information content of such ROM part may be more reliable than the information content of the electronically programmed portion of the nonvolatile memory device. This results from the fact that latter information content may be cycled or altered by write operations. Moreover, the electronically programmed information content may even need periodic refreshments in order to avoid its possible misinterpretation due to gradual loss of charge on the floating gates of floating gate transistors or wear of the gate oxide of the floating gate transistors in an electronically programmed nonvolatile memory cell due to an excessive number of write operations.
As a result of the above explained increased reliability of the information content in the firmly programmed electronically programmable and erasable nonvolatile memory cells, no disturbing effects or disturbs such as information content cycling, supply voltage fluctuations or spikes as well as alpha particle strikes may decisively affect the correct interpretation of the information content of the ROM part of the electronically programmable and erasable nonvolatile memory device.
In certain embodiments, the read access time to a certain bit of information stored in the firmly programmed portion of electronically programmable and erasable nonvolatile memory device may be reduced or minimized by selecting a plurality—in particular two adjacent—firmly programmed nonvolatile memory cells to represent the certain bit of information. In this way, the current delivered by the firmly programmed nonvolatile memory cells is correspondingly increased and serves to change the voltage level of the associated bitline representing the memory cells' logic content in a correspondingly shorter period of time. As a result, the logic content, in other words, the certain bit of information may be accessed faster in the firmly programmed portion of the electronically programmable and erasable nonvolatile memory device.
Hence, in embodiments, the information content of two memory cells associated with two wordlines may be combined to represent one bit of information to ensure good performance margin for reading the corresponding information content during power-up of a system using the firmly programmed electronically programmable and erasable nonvolatile memory. In other words, the increased number of memory cells per bit of information may be used to provide increased read access performance—for instance for boot applications—during power-up of a system with reduced access times to the information content.
In embodiments, during firmware development, the ROM portion of the electronically programmable and erasable nonvolatile memory may be alterable and implemented by a processing mask that may be applied in the manufacturing process of the corresponding memory device after verification of the developed firmware. In particular embodiments, hot source triple poly (HS3P) flash memory may comprise such firmly programmed electronically programmable and erasable nonvolatile memory as a ROM portion wherein the firm programming may be implemented by a contact processing mask.
Moreover, the four select gate lines (SG) 130, 131, 132 and 133 each may connect the select gates of four select gate transistors of a row of four electronically programmable and erasable nonvolatile memory cells. As in this first embodiment, the current that may be drawn by the two uppermost rows of four electronically programmable and erasable nonvolatile memory cells may be collected from the sources of the corresponding two rows of four select gate transistors to the first source line 140 via the three source line contacts 160 in a first row of source line contacts. With respect to the two uppermost electronically programmable and erasable nonvolatile memory cells in the third column of electronically programmable and erasable nonvolatile memory cells connected by bitline 112, however, reference number 161 designates that a contact between the first source line 140 and the sources of the two select gate transistors of the two uppermost electronically programmable and erasable nonvolatile memory cells in the third column of memory cells may be omitted.
As a result, the two uppermost electronically programmable and erasable nonvolatile memory cells in the third column of electronically programmable and erasable nonvolatile memory cells cannot draw current from third bitline 112 such that the sense amplifier assigns the non-conducting cell state to a logical “1”. This is symbolized in
In contrast to that, e.g., the remaining three electronically programmable and erasable nonvolatile memory cells in the uppermost row of memory cells may draw current from first, second and forth bitlines 110, 111 and 113 respectively, in case the uppermost row of memory cells is selected by providing a high voltage at first select gate line 130 such that the sense amplifier assigns the conducting cell state to logical zeros as content of the corresponding memory cells. This is symbolized in
To summarize the above, a first way to firmly program a plurality of electronically programmable and erasable nonvolatile memory cells according to the embodiment in
Now, a further way to firmly program a plurality of electronically programmable and erasable nonvolatile memory cells is shown in the second row of memory cells in
Now in contrast to the first row of bitline contacts 150 at the upper edge of
To summarize the above, a second way to firmly program a plurality of electronically programmable and erasable nonvolatile memory cells according to the embodiment in
Turning now to the next Figure, this
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In other words, letter “C” at the first control gate line 220 or 320 and the first select gate line 230 or 330 expresses that a read operation may be performed by the selection of a single wordline such as wordline 230 or 330. In this way, a low power read operation may be implemented since only one memory cell is used to represent one bit of information. This leads to only one memory cell possibly drawing current per bit of information depending on the definition whether a current drawing memory cell represents a logical zero, as in this example, or a logical one as in possible other examples. Consequently, the four memory cells in the first row of memory cells represent four bits of information.
In contrast to the above, letter “D” at the third and forth control gate lines 222 and 223 (or 322 and 323) as well as at the third and forth select gate lines 232 and 233 (or 332 and 333) expresses that a read operation may be performed by the selection of two adjacent wordlines such as wordlines 232 and 233 (or 332 and 333). In this way, a high speed read operation may be implemented since two memory cells are used to represent one bit of information. This leads to two memory cells with double the cell current in the conducting state. Consequently, the sense amplifier may detect the corresponding logical level faster than in the case of the current driven merely by one memory cell.
At 401 of the method, one word of firmly programmed information may be read by selection of a single wordline associated with a single row of firmly programmed electronically programmable and erasable nonvolatile memory cells in a first predetermined row of memory cells by a sense amplifier.
At 402 of the method, one word of firmly programmed information may be read by selection of two wordlines associated with two rows of firmly programmed electronically programmable and erasable nonvolatile memory cells in second predetermined rows of memory cells by the same sense amplifier.
According to 403 of the method, one word of electronically programmed information is read by selection of a single wordline associated with a single row of electronically programmed nonvolatile memory cells in a third predetermined row of memory cells by the same sense amplifier.
With respect to the above-described embodiments which relate to the Figures, it is emphasized that the embodiments basically served to increase the comprehensibility. In addition to that, the following further embodiments try to illustrate a more general concept. However, also the following embodiments are not to be taken in a limiting sense. Rather—as expressed before—the scope of the present disclosure is defined by the appended claims.
In this regard, one embodiment relates to a nonvolatile memory device comprising a plurality of electronically programmable and erasable nonvolatile memory cells, at least a portion of which configured to be programmed by a processing mask configured to establish or omit connections to predetermined ones of the plurality of nonvolatile memory cells.
In an embodiment of the memory device, the processing mask is configured to be used after a verification in a manufacturing process of the nonvolatile memory device. This may allow an adoption of the firmly programmed portion to the results of the verification by altering the processing mask.
According to an embodiment, the processing mask is a mask configured to establish or omit contacts or vias to predetermined transistors of predetermined ones of the plurality of nonvolatile memory cells.
In embodiments, the processing mask is configured to program predetermined ones of the plurality of nonvolatile memory cells by establishing or omitting contacts or vias of the predetermined ones of the plurality of nonvolatile memory cells to associated bitlines.
In a further embodiment, the processing mask is configured to program predetermined ones of the plurality of nonvolatile memory cells by establishing or omitting contacts or vias of the predetermined ones of the plurality of nonvolatile memory cells to associated source lines.
A further embodiment relates to a nonvolatile memory device comprising electronically programmable and erasable nonvolatile memory cells, at least a portion of which is configured to be firmly programmed in a processing of the nonvolatile memory device.
An embodiment of the nonvolatile memory device further comprises sense amplifiers for reading the nonvolatile memory cells, wherein the sense amplifiers are configured to be re-used for reading the firmly programmed portion of the nonvolatile memory cells.
A further embodiment of the nonvolatile memory device is configured to read the firmly programmed portion of the nonvolatile memory cells without using charge pumps.
A still further embodiment of the nonvolatile memory device is configured to read one bit of firmly programmed information by selection of a single wordline associated with a single firmly programmed nonvolatile memory cell.
According to an embodiment, the memory device is configured to read one bit of firmly programmed information by selection of at least two wordlines associated to at least two firmly programmed nonvolatile memory cells.
A further embodiment relates to a nonvolatile memory device comprising at least one electronically programmable and erasable nonvolatile memory cell being firmly programmed as Read Only Memory (ROM) during manufacturing of the nonvolatile memory device.
In an embodiment, the at least one nonvolatile memory cell is a hot source triple poly (HS3P) flash cell.
According to an embodiment, the at least one nonvolatile memory cell is configured to be firmly programmed by a processing mask to establish or omit connections to the firmly programmed nonvolatile memory cell, wherein the processing mask is alterable during development of firmware stored on the memory device.
In an embodiment, an access time to one bit of information of the firmly programmed ROM is reduced by selecting a plurality of adjacent firmly programmed electronically programmable and erasable nonvolatile memory cells to represent the one bit.
In a further embodiment, at least one sense amplifier is shared between electronically programmable and erasable nonvolatile memory cells—that are writeable and exhibit nonvolatile functionality of electronically programmable and erasable nonvolatile memory—and firmly programmed electronically programmable and erasable nonvolatile memory cells—that are not writable and exhibit data persistent ROM functionality.
A further embodiment relates to a method for programming a nonvolatile memory comprising programming at least a portion of a plurality of electronically programmable and erasable nonvolatile memory cells by a processing mask configured to establish or omit connections to predetermined ones of the plurality of nonvolatile memory cells.
In an embodiment, the programming comprises using the processing mask after a verification in a manufacturing process of the nonvolatile memory device.
In another embodiment, the processing mask is a mask establishing or omitting contacts or vias to predetermined transistors of predetermined ones of the plurality of nonvolatile memory cells.
In a still further embodiment, the processing mask programs predetermined ones of the plurality of nonvolatile memory cells by establishing or omitting contacts or vias of the predetermined ones of the plurality of nonvolatile memory cells to associated bitlines.
According to an embodiment, the processing mask programs predetermined ones of the plurality of nonvolatile memory cells by establishing or omitting contacts or vias of the predetermined ones of the plurality of nonvolatile memory cells to associated source lines.
A further embodiment relates to a method for programming a nonvolatile memory comprising firmly programming at least a portion of a plurality of electronically programmable and erasable nonvolatile memory cells in a processing of the nonvolatile memory device.
A further embodiment of the method comprises sense amplifiers for reading the nonvolatile memory cells. This embodiment of the method further comprises re-using the sense amplifiers for reading the firmly programmed portion of the nonvolatile memory cells.
Another embodiment of the method further comprises reading the firmly programmed portion of the nonvolatile memory cells without using charge pumps.
An embodiment of the method further comprises reading one bit of firmly programmed information by selection of a single wordline associated with a single firmly programmed nonvolatile memory cell.
According to an embodiment, the method further comprises reading one bit of firmly programmed information by selection of at least two wordlines associated with at least two firmly programmed nonvolatile memory cells.
Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this disclosure be limited only by the claims and the equivalents thereof.