Integrated volatile and non-volatile memory

[0002] 1. Field of the Invention

[0003] The present invention relates to memory devices, and more specifically, to memory devices having both volatile and non-volatile memory devices.

[0004] 2. Background of the Invention

[0005] Manufacturers of memory components are often requested by their customers to provide non-volatile information within volatile memory components. The non-volatile information may include serial numbers, device type, lot number, date processed, customer specific information, etc. In some cases, there are a large number of non-volatile memory elements dedicated to storing the non-volatile information.

[0006] Non-volatile memory elements presently are not integrated with volatile memory elements or components. The term “non-volatile memory element” shall be defined herein for the purposes of this invention to mean a one-time programmable memory element. The term “volatile memory element” shall be defined herein for the purposes of this invention to mean a multi-time programmable memory element. The term “integrated” shall be defined herein for the purposes of this invention to mean that the non-volatile memory elements are coupled to the same bit lines that the volatile memory elements are coupled (e.g., a cell of a volatile memory section shares a bit line or bit line pair with a cell of a non-volatile memory section). Because the non-volatile and volatile memory components of conventional memory systems are not integrated, access to each section of memory (i.e., non-volatile and volatile memory) is performed on separate electrical paths that are multiplexed. Because access to each memory section of memory is created by a multiplexing operation, the non-volatile and volatile memory is not considered to be integrated. Multiplexing allows for reading the stored information in either the non-volatile or the volatile memory elements from the same input/output port, but not the same reading device. In general, drivers are utilized to read from the non-volatile memory and a sense amplifier is utilized to read from the volatile memory. Additionally, these non-volatile memory elements can be relatively big and bulky and not interface easily with the volatile memory elements due to the different reading devices.

[0007] To overcome the problems of contemporary memory having non-integrated, non-volatile and volatile memory elements, the two types of memory components are integrated. The term “integrated” shall be defined herein for the purposes of this invention to mean that the non-volatile memory elements are coupled to the same bit lines that the volatile memory elements are coupled. The integration of the two types of memory creates a small, compact solution with a minimum number of elements. The integration of the two memory types further allows for a simple interface that utilizes a single reading device (e.g., a sense amplifier).

[0008] One embodiment according to the principles of the present invention is a memory device having a first and a second memory section. The first and the second memory sections are coupled via bit lines. The first memory section may be static or dynamic random access memory. The second memory section includes current path elements capable of being substantially permanently opened. The second memory section may further include at least one fuse.

[0009] A second embodiment according to the principles of the present invention is an integrated circuit having at least one bit line pair shared by volatile and non-volatile memory elements and at least one word line coupled to each memory element. The memory elements are organized in a matrix configuration, the bit lines forming columns of memory cells and the word lines forming rows of memory cells. A first type and a second type of memory element share at least one bit line pair. The first type of memory element may be a static or dynamic random access memory and the second type of memory element is read only memory. The second type of memory may include at least one fuse.

[0010] Another embodiment according to the principles of the present invention includes a system having a processor and a memory. The memory includes a first memory type and a second memory type. The memory further includes a sense amplifier shared by both the first and second memory type. The first memory type is volatile memory and the second memory type is non-volatile memory. The second memory type may include at least one fuse.

[0011] The present invention further includes a method of pre-laser testing a non-volatile memory element integrated within a volatile memory. At least one logic voltage level is applied to the non-volatile memory element. The non-volatile memory element is selectively accessed and a logic level stored within the non-volatile memory elements is read. Prior to reading, bit lines are precharged.

[0012] A more complete understanding of the method and apparatus of the present invention may be obtained by reference to the following Detailed Description when taken in conjunction with the accompanying Drawings wherein:

[0013] FIG. 1 is a schematic diagram of a random access memory device having integrated volatile and non-volatile memory sections;

[0014] FIG. 2 is a schematic diagram of a single static random access memory cell and one embodiment of a non-volatile memory cell according to the configuration of FIG. 1;

[0015] FIG. 3ais a schematic diagram of a single static random access memory cell and a second embodiment of a non-volatile memory cell according to the configuration of FIG. 1;

[0016] FIG. 3bis another schematic diagram according to the configuration of FIG. 3ahaving multiple control circuits;

[0017] FIG. 4 is a representative flow diagram of a pre-laser testing operation of a non-volatile memory element integrated within a volatile memory according to FIGS. 1-3b;

[0018] FIGS. 5a-5care exemplary memory layouts for integrated volatile and non-volatile memory cells according to FIGS. 1-3b;

[0019] FIG. 6 is a schematic of a chip package that houses an integrated circuit having the integrated volatile and non-volatile memory of FIGS. 1-3b; and

[0020] FIG. 7 is an exemplary system that utilizes the integrated volatile and non-volatile memory of FIGS. 1-3baccording to the principles of the present invention.

[0021] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0022] Non-volatile memory elements are integrated within volatile memory to reduce space and eliminate circuitry for accessing previously non-integrated, non-volatile memory elements. The term “integrated” shall be defined herein for the purposes of this invention to mean that the non-volatile memory elements are coupled to the same bit lines that the volatile memory elements are coupled. The non-volatile memory elements, which generally comprise fuses, are utilized for storing manufacturing and customer information, such as lot number, date processed, serial number, etc. By integrating the non-volatile memory elements within the volatile memory, both the volatile and non-volatile memory may be read via substantially the same circuitry (e.g., sense amplifier, row and column decoders) and the timing for reading either the volatile or non-volatile memory is substantially similar. Additionally, because the non-volatile memory elements are integrated within the volatile memory, pre-laser testing can be performed on the non-volatile memory elements.

[0023] FIG. 1 is a schematic diagram of a random access memory (RAM) device 100. The RAM device may be a static random access memory (SRAM) device or a dynamic random access memory (DRAM) device. The RAM device 100 includes a memory 105, a sense amplifier 110, a row decoder 115, an output section 120, and a controller 125. The memory 105 comprises a volatile memory section 130 and a non-volatile 135 memory section. The volatile 130 and non-volatile 135 memory sections may be considered to reside in distinct regions, however, the volatile 130 and non-volatile 135 memory sections are integrated. The non-volatile memory section 135 is coupled to distinct word lines 160 from the volatile memory section 130. Note that both sets of word lines 160 are coupled to the same row decoder 115. Both the volatile 130 and non-volatile 135 memory sections are coupled to or share the same bit line pairs 165. The word lines 160 and the bit line pairs 165 form a grid or matrix of memory cells. The output section 120 includes a column decoder 140 and an output buffer/driver 145.

[0024] In operation, to access (e.g., read, write, refresh) a particular memory cell, an external address is transmitted on an address bus 150 to the row 115 and column 140 decoders. The particular access mode is enabled by control inputs on a control bus 155 and asserted by the controller 125 to the memory 105 and the sense amplifier 110. Because the volatile 130 and the non-volatile 135 memory sections are integrated, access to a particular memory cell within either the volatile 130 or non-volatile 135 memory section is performed by providing an external address to the controller 125 and accessing the particular memory cell using the sense amplifier 110. It should be understood that access to the volatile 130 and non-volatile 135 memory sections is performed utilizing the same bit lines and in the traditional manner that the volatile memory section 130 is accessed.

[0025] FIG. 2 is an exemplary circuit 105acomprising one volatile 130aand one non-volatile 135amemory cell. The volatile memory cell 130ais a static random access memory (SRAM) cell 130ahaving a six transistor (6T) configuration as is known in the art. Alternatively, a dynamic random access memory cell or some other volatile memory cell could be the volatile memory cell. The static random access memory cell 130ais coupled to a bit line pair 165aand 165b(hereinafter 165) for reading and writing data to and from the SRAM cell 130a. A word line WL 160ais coupled to the SRAM cell 130afor providing access to the SRAM cell 130aduring read and write operations.

[0026] The non-volatile memory cell 135a, which may be read only memory (ROM), comprises a pair of transistors 215a, 215band a pair of fuses F1 and F2. The pair of transistors 215a, 215bare each coupled to a word line (WL) 160bvia a gate terminal for providing access to the stored logic level (i.e., datum) within the non-volatile memory cell 135a. Each transistor 215a, 215bis an N-type transistor having a drain terminal connected to a bit line 165a, 165b, respectively, and a source terminal connected to a fuse F1 and F2, respectively. Alternatively, an electrical component capable of being temporarily or substantially permanently opened could be utilized instead of the fuses F1 and F2. Notably, the non-volatile memory cell 135aand the volatile memory cell 130ashare the same pair of bit lines 165.

[0027] The non-volatile memory cell 135ais programmed by blowing either fuse F1 or F2 using a laser as is well understood in the art. To program the non-volatile memory cell 135a, for example, fuse F1 is blown, so that bit line BL 165ahas no discharge path upon word line 160bbeing set to a high logic voltage level. As fuse F2 is not blown, a discharge path through transistor 215bfor bit line 165bexists, thereby allowing the bit line 165bto discharge by 100 milli-volts (mV) upon transistor 215bbeing enabled by the word line 160b, for example. Therefore, a high logic voltage level is stored in the non-volatile memory cell associated with the transistor 215aand a low logic voltage level is stored in the non-volatile memory cell associated with the transistor 215b.

[0028] To read the non-volatile memory cell 135a, a similar process to reading the volatile memory cell 130ais performed. The reading process includes: precharging the bit line pair 165 to the same voltage level (e.g., VCC), applying a high logic voltage level to the word line 160b, and sensing by the sense amplifier that one of the bit lines 165a, 165bof the bit line pair 165 discharges. Because the non-volatile memory cell 135ais integrated within the volatile memory (i.e., along the same shared bit lines), the timing and the circuitry for reading the non-volatile memory cell 135aare substantially the same as for reading the volatile memory cell 130a. In other words, the same sense amplifier 110 and row 115 and column 140 decoders are utilized for reading the non-volatile 135 and volatile 130 memory cells. During the read process, in general, the sense amplifier 110 senses a discharge of 100 mV, for example, on a bit line to measure a differential across the bit line pair 165, which is true for reading either the volatile 130aor non-volatile 135amemory cell.

[0029] Non-volatile memory cells may replace existing volatile memory cells to maintain an existing volatile memory device design (i.e., having the same number of memory elements) In other words, a 64K memory device may remain a 64K memory device having integrated non-volatile and volatile memory cells. For example, one kilobyte (1K) of non-volatile memory cells can replace 1K of volatile memory cells so that the memory device includes 63K of volatile memory cells and 1K of non-volatile memory cells. Alternatively the non-volatile memory cells may be added to an existing volatile memory device design, but additional circuitry, such as additional word lines and sense amplifier components, may be necessary. While the fuses F1 and F2 are shown connecting Vss to respective transistors 215aand 215b, a different voltage level could be connected, such as Vcc. However, to read from the non-volatile memory cell, the bit lines 165a, 165bwould be precharged to a voltage level other than Vcc so that a voltage differential across the bit line pair 165 could be sensed by the sense amplifier.

[0030] FIG. 3ais another embodiment of a circuit 105bcomprising the volatile 130aand a non-volatile memory cell 135baccording to the principles of the present invention. The non-volatile memory cell 135bcomprises two fuses F3 and F4. Fuse F4 is connected to an output line 305aof a control circuit 310aand fuse F3 is connected to Vss. In another embodiment, fuse F3 could be connected to the output of the control circuit 310aand the fuse F4 could be connected to Vss. In yet another embodiment, two control circuits could be included, where a first control circuit 310ais connected to fuse F3 and a second control circuit (not shown) is connected to fuse F4 (see, FIG. 3b). It should be understood that the control circuit 310ais used for pre-laser testing and not as part of the read operation (i.e., the read operation for FIGS. 2 and 3 operate identical and that the control circuit 310ais not utilized during normal operations).

[0031] The control circuit 310aincludes a fuse F5, a pair of series-connected inverter gates 315aand 315b, and a parallel-connected N-type CMOS transistors 320aand 320b. The fuse F5 is connected to Vcc and the input of the inverter gate 315a. The output of the inverter gate 315bis connected to the output line 305aof the control circuit 310a. Alternatively, the fuse F5 can be connected to circuitry that provides a logic high voltage level during test mode and a logic low voltage level during normal operating mode. In another embodiment, a test pad can utilized to control the output line 305aduring test mode, where the control circuit 310amay or may not includes a fuse and/or other logic components. It should be understood that the other circuit configurations are possible, and the principles of the present invention are meant to cover the functionality to provide for prelaser testing.

[0032] In operation, the control circuit 310aallows for prelaser testing of the non-volatile memory cell 135b. To test the non-volatile memory cell 135b, the word line 160bis selected (i.e., set to a logic high voltage level) to turn on the N-type transistors 215aand 215b. Because both fuses F3 and F4 are still intact during prelaser testing, when fuse F3 is connected to Vss (i.e., logic low voltage level) and fuse F4 is connected to a logic high voltage level from the control circuit 310a, a differential voltage between the bit lines 165a, 165bof the bit line pair 165 is created when the bit lines 165aand 165bare precharged at a logic high voltage level (i.e., bit line 165ais discharged and bit line 165bremains at a logic high voltage level). Because fuse F5 is connected to Vcc having a logic high voltage level, the output line 305aof the control circuit 310ais a logic high voltage level. It should be understood that in the other embodiments described above (e.g., fuse F3 connected to the control circuitry 310aand two different control circuits connected to the fuses F3 and F4), a differential voltage is also created on each bit line 165a, 165bof the bit line pair 165 to test the non-volatile memory cell 135b.

[0033] After testing the non-volatile memory cell 135b, the fuse F5 is blown using a laser. Although the laser blows the fuse F5, the fuse F5 sometimes has slight residue remaining to provide a weak conductor. The parallel-connected N-type transistors 320a, 320bprovide for pulling the input terminal of the inverter gate 315ato a logic low voltage level. Because the blown fuse F5 may remain a weak connection to Vcc, a logic low voltage level (i.e., Vss) being applied to the input terminal of the inverter gate 315aas a result of a logic high pulse signal on a pulse line 325 ensures that the output line 305aof the control circuit 310aremains low during normal operating mode. In other words, the configuration of the non-volatile memory cell 135bis guaranteed to be identical to the non-volatile memory cell 135a(see FIG. 2) upon the fuse F5 being blown, which causes output line 305ato be at a logic low voltage level.

[0034] FIG. 3bis another embodiment according to FIG. 3a. A second control circuit 310bcontrols a voltage level being applied to fuse F3 via output line 305b. Fuses F3 and F4 are independently controllable using control circuits 310band 310a, respectively, so that the non-volatile memory cell 135bcan have each of the transistors 215aand 215btested prior to setting the non-volatile memory cell 135bby blowing either fuse F3 and F4. By utilizing two control circuits 310aand 310b, a logic high voltage level can be applied to fuse F3 and a logic low voltage level can be applied to fuse F4 or vice versa so that both transistors 215aand 215bcan be fully tested.

[0035] FIG. 4 is a representative flow diagram 400 of a pre-laser test operation to determine the fidelity of the non-volatile memory cell 135b(see FIG. 3a). The pre-laser testing operation starts at step 405. At step 410, the non-volatile memory element 135bintegrated within the volatile memory 130abeing tested is applied a logic high voltage level to the fuse F4 from the control circuit 310a. The logic high voltage level simulates a logic low voltage level being stored in the non-volatile memory cell 135bas measured along the bit line 165a.

[0036] At step 415, the non-volatile memory cell 135bis selectively accessed (i.e., the bit line pair 165 and the word line 160bare selected). At step 420, the logic level applied to the non-volatile memory element 135bis read by the sense amplifier. At step 425, the logic level applied to the non-volatile memory element 135bis verified to determine if the non-volatile memory element 135bwas properly manufactured. The pre-laser test is completed at step 430. It should be understood that the pre-laser test would be performed differently upon a different configuration of the non-volatile memory cell 135band control circuit 310aas previously discussed with regard to FIGS. 3aand 3b. For example, at step 435, a logic low voltage level may be applied to the non-volatile memory cell 135busing the control circuits 310aand 310baccording to FIG. 3b. Thus, the non-volatile cells can be fully exercised with a stored logic low voltage level and a logic high voltage level prior to blowing any fuses. This can provide detection of defects within non-volatile memory cells and allow for replacement of the inoperative non-volatile memory cells by using redundancy techniques or simply scrapping the dye.

[0037] FIGS. 5a-5care exemplary memory layouts including integrated volatile and non-volatile memory cells according to FIG. 2. As previously discussed, to reduce conventional memory re-design efforts, it is preferable to integrate the two memory types.

[0038] FIG. 5a isa first embodiment of a non-volatile memory cell or fuse cell integrated within a volatile memory. The non-volatile memory cell 135ain this embodiment is sized to fit within the bit line pair 165 and above the word line 160band is capable of residing directly above the 6T cell or volatile memory cell 130a. It should be understood that the volatile memory cell 130acould be a poly resistive (polyR) cell as is commonly known in the art. FIG. 5bshows a fuse cell or non-volatile memory cell 135athat is taller than a normal volatile memory cell 130adue to the use of larger components, such as fuses. By configuring the non-volatile memory cell 135ato be taller, the non-volatile memory cell 135ais capable of fitting within the bit line pair 165.

[0039] FIG. 5cshows a non-volatile memory cell 135athat is wider than the bit line pair 165. Because the non-volatile memory cell 135ais wider than the bit line pair 165, the non-volatile memory cell 135ais staggered above the columns of volatile memory cells 130aso that access to the bit line pair 165 and word line 160bis possible and that redesign of volatile memory devices to include the non-volatile memory elements is reduced. Also, the non-volatile memory cells 135amay share the same word line as the volatile memory cells 130a.

[0040] FIG. 6 is a schematic of a chip package 600 housing an integrated circuit 610. The integrated circuit 610 may be an application specific integrated circuit (ASIC), having circuitry 620 that may or may not be customized and a memory 630 that includes the integrated volatile and non-volatile memory 105 according to the principles of the present invention. The circuitry 620 may be discrete logic, a general processor, a signal processor, a programmable gate array (PGA), a programmable logic array (PLA), or any other circuitry that utilizes the integrated memory 105.

[0041] FIG. 7 is an exemplary system 700 (e.g., processing device, such as a personal computer) that utilizes a processor 710 the integrated volatile and non-volatile memory 105 according to the principles of the present invention.

[0042] It should be understood that the exemplary system 700 could be other types of communication systems (e.g., two-way radio), computing systems (e.g., desktop computers, laptop computers, handheld computers), or display devices (e.g., computer monitor, television), or any other electronic device with or without a processor (e.g., smart card) that utilizes the integrated memory 105.

[0043] The previous description is of a preferred embodiment for implementing the invention, and the scope of the invention should not necessarily be limited by this description. The scope of the present invention is instead defined by the following claims.